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SME

My living room "make over" (aka the "surrounded by bass" project)

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SME    211

The Room

 

Here is a picture of the front stage in my living room as of August 2016:

 

post-1549-0-89937900-1471452520_thumb.jpg

 

And here it is with the TV moved off the wall and the new center channel installed:

 

post-1549-0-92873400-1474405503_thumb.jpg

 

Here are some pictures of the rear of the room as of September 2016:

 

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post-1549-0-94485800-1474405542_thumb.jpg

 

Regrettably, I did not take a picture of the front before I replaced my old cabinet with the racks or the front left/right speakers Hsus with my SEOS-15 TD12M prototypes.

 

In case anyone is wondering, yes, this space is very acoustically challenging, but it has its upsides.

 

 

Speaker / Room Calibration

 

Through the years I have experimented with a variety of methods of speaker and room EQ.  In my current approach, I mostly ignore the room, except for the subs, and I attempt to primarily correct the first arrival of sound.  I aim to make the first arrival *mostly* flat.   To analyze only the first arrival, I use the frequency dependent window feature REW with a crude 1/3rd octave resolution.  This is roughly consistent with the bandwidths of the ear/brains filters.  It's long enough to allow for delays at the crossovers but not so long as to allow inclusion of room reflections that the ear/brain could theoretically isolate.  Note that this particular FDW length may not work well with other speakers or other rooms.  YMMV.

 

I say I aim for "mostly flat" because I use a bit of sub bass boost (boost of the bass in the first arrival, actually) and because I use configurable high frequency adjustments to optimize playback for different content.  Because the HF adjustments are configurable, I leave them disabled (flat in the treble) in the measurements below, but these measurements *do* include the sub bass boost.  A flat-ish first arrival in a listening room that's not acoustically dead tends to result in a frequency response that is sloped up toward the bottom end.  Below is my frequency response for left, right, and center with 1/3rd octave-smoothing:

 

post-1549-0-61073800-1485426295_thumb.png

 

Note that the responses look rather messy and exhibit about 8 dB difference between bass and treble.  Note that with high frequency adjustments, the difference tends to come in closer to -10 dB @ 10 kHz vs. 20 Hz.  Note also that the center channel response appears very hot in the mid/upper bass.  This is because because of speaker/room interface issues that I currently have.  The speaker is very close to the bare wall behind it, and this causes most of the sound of those frequencies to disperse diagonally and to the sides instead of forward.  As such, the first arrival is relative lean.  Now look at the first arrival responses, using FDW in REW with 1/3rd octave resolution:

 

post-1549-0-94632100-1485426290_thumb.png

 

These responses appear rolled-off at the ends because these frequencies are somewhat delayed (ends of the bandwidth) and escape the influence of the filter.  Apart from this, they are very smooth and flat, except for the aforementioned sub bass bump.  The center is a bit messier in the mid/upper bass again.  I could have made it ruler flat at the MLP here, but I opt instead to compromise a bit for off-center seats.  Indeed, think this may sound more balanced, to the extent that the brain uses information from early reflections to ascertain the content of these lower frequencies.  I'm not exactly sure at this point.

 

The configurable high frequency adjustments are of three different kinds: distance compensation, upper mid-range tilt, and X curve.  The measurements below depict the effects on the high frequency response of my center channel from using -0.75 dB of upper-mid tilt (blue line) and several degrees of distance compensation (red lines) on the high frequency response of my center channel:

 

post-1549-0-27912200-1485427974_thumb.png

 

Distance compensation mostly affects frequencies above 8 kHz or so.  Almost all recordings need this compensation, in part because high frequency sound naturally rolls off with distance.  I chose to model this roll-off on actual physical data of distance roll-off, and it seems to be working out quite well.  There is no standardized distance for monitoring music or theatrical recordings, and furthermore, a lot of music is monitored on near-field monitors that implement some kind of roll-off of their own.  The consequence is that the optimal roll-off varies substantially by content.

 

For mid range tilt, I currently use a Q 0.5 @ 2 kHz high shelf filter with variable gain.  I'm not sure this is really optimal, but it works pretty well for me.  Most stuff sounds good either flat or with a tiny bit of treble reduction.  Rarely do I need more than -1 dB.  I'm not sure why this is necessary other than perhaps precedence.  Monitors in days past likely had just a bit of tilt, and the precedent stuck.  A lot of monitors include a HF trim switch that engages a tilt like this.  Of course, every design is slightly different, and many include additional > 8 kHz roll-off here as well.

 

 

Lastly, I have X curve correction, which is used only rarely for movies that need it.  Movies mixed on a dub-stage tend to use speakers behind an acoustically transparent screen, and this almost always introduces high frequency roll-off of some kind.  Instead of compensating by making adjustments to the monitoring system, tended to boost treble in the mix to compensate.  The X curve was intended to standardize the high frequency roll-off in the playback system so that mixes would translate, and it was based on the roll-off that was commonly observed at the time.  (IMO, it largely failed because it measured pink noise energy response instead of first arrival SPL.)  AIUI, dub stages largely ignore the X curve these days opting instead to simply accept the faults of the screen but also avoid hyping the high frequencies too much with the understanding that doing so may make the mix way too bright in some settings.  In any case many movies, particularly stuff from the 90s and older, do benefit from some additional high frequency reduction, and the X curve shape is probably the most generically useful.

 

 

The Speakers

 

post-1549-0-31478900-1464316982_thumb.jpgpost-1549-0-15197700-1453871877_thumb.jpgpost-1549-0-67959800-1454221299_thumb.jpgpost-1549-0-59949900-1454221303_thumb.jpg

 

Click this image.  It is an animation of the box assembly sequence:

 

post-1549-0-36736800-1469920118_thumb.gif

 

The cabinets are separate, and I'm building a left and right pair.  The other bass box is visible in the background, surrounded by a bunch of clamps.

 

On the bottom is an AE TD12M-4A in a 1.5ish cuft box with an aggressively flared 4 inch port.  The cabinet is 1/2" B/BB plywood with double thick front baffle and pairs of shelf style braces running horizontally and vertically (4 braces total).  The design is somewhat noteworthy for being under 9" deep.  On the top is an SEOS-15 horn with a Denovo DNA-360 mounted on it.  The horn cabinet is 1/2" B/BB and is not braced.  It is slightly wider and deeper than the bass cabinet, partly because I started them before I started the bass cabinets and changed my mind and opted to make the bass cabinets smaller.

 

These are currently up and running with fully active crossovers and EQ provided by a prototype version of my custom DSP software, running on a Linux PC with a Motu A16 interface connected via USB.  Each mains driver is powered by a channel from an Emotiva XPA-5.  The amp is rated for 200W/300W into 8/4 ohm with all channels driven, but I expect to "effectively" get 500-700W peaks for the 60-120 Hz range due to the resonance above the tuning frequency, the very low DC resistance of 3.2 ohm, and the amp's beefy power supply that'll be hardly tapped to run the horns.

 

So far, I am very pleased with the performance of these speakers and active crossover.  Here is the a recent measurement of the response (no gate, 1/6th octave smoothing) of each driver playing separately and in unison along with the subs.

 

post-1549-0-90172000-1474438062_thumb.png

 

(Note that I'm tweaking the response all the time.  I'll try to keep this image current, but it probably won't work out that way.)

 

This measurement was taken with a -30 dBFS RMS sine sweep and a calibrated mic.  The pink noise calibration signal (-30 dBFS RMS pink noise band-limited to 500-2000 Hz) reads at about 73.75 dB.  I zoomed in on the data a lot, which makes the response look ugly, but in reality I'm +/-4 dB or so with 1/6th octave smoothing everywhere except for the big dip at 165 Hz.  Even though my room has some treatments, I still have some significant acoustical problems involving the floor and ceiling, which accounts for the unevenness.  I could have EQed much of that out, but for the time being, I'm concentrating on EQing the speaker response and avoiding acoustics, and I have purposely slanted the response through the mid-range to obtain a flatter power response.

 

The crossover filters, 2nd order HPF for the horns and 4th order LPF for the woofers, are centered at 950 Hz.  Note that the woofer and horn aren't completely in-phase here.  This is an experiment, in which I have purposely mis-aligned the drivers in time to try to steer the lobe above or below the MLP, putting the MLP closer to the edge of the lobe.  Then, the response must be boosted to avoid a dip, and this increases power response too.  That's a good thing because directivity typically goes through a maximum where two drivers are crossing over.  The idea here is to avoid that directivity peak to achieve both smooth direct response and smooth power response through the crossover region.  My measurements suggests that the strategy works, but it's not clear how this affects the sound at off-axis locations that may be at a slightly different vertical angle.

 

The cross to the subs is at 110 Hz for now because that works best with the filters on the subs as they are now.  In the long run, they will be blended with the subs over a wide frequency range to optimize multi-seat response.  This means, I am also planning to build subs that can player higher than the traditional 80-100 Hz as well.

 

This is the first part of a larger project to upgrade all the speakers and DSP in my system to fully DIY-built solutions.  I have started building a center channel of identical design, and I have drivers for new subs and surrounds drivers on order as well.

 

Edit: Added details about speaker/room EQ configuration and in-room response.

Edited by SME

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SME    211

Horn / CD measurements are posted here.

 

DNA-360 + SEOS-15 Impedance

 

post-1549-0-68791800-1464238018_thumb.png

 

This measurement is without capacitors inline.  All others that follow use capacitance in series for protection.  There is diaphragm break-up at 17 kHz, and this feature appears in the other measurements.

 


 

 

DNA-360 + SEOS-15 Passive Circuit

 

Even though this system is a fully active design, the compression drivers use passive circuits to flatten the response and cut back the sensitivity a lot to reduce background hiss.  They look like this:

 

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Here is the response before and after the crossover:

 

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Horizontal Polar Response

 

Below are horizontal polar response plots in 7.5 degree increments (un-smoothed with 3 ms window) of the DNA-360 CD inside the SEOS-15 horn, taken at 0 degrees elevation and 1 meter.  SPL figures are only correct in a relative sense.

 

(Note: This plot has been corrected, but note that I messed up the measurement at 75 degrees, so that trace is missing.  Looking at the data, I don't think that leaves a big gap.)

 

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I was surprised to see that the horizontal pattern is a bit wider than I expected from looking at others' measurements.  To my eyes, this is a 120 degree horn rather than a 90 degree horn.  An interesting feature here is that the pattern is actually tightest in the 2-3 kHz range and is also a bit tighter in the 3-5 kHz range.  Otherwise, the response is very smooth, beginning to drop off at between 30 and 37.5 degrees.  Note also the big peak at 17 kHz, which is due to diaphragm break-up and is also visible in the impedance response.

 

Here is a normalized 2D colormap plot of the horizontal polar response, generated with tools provided by 3ll3d00d:

 

post-1549-0-93396900-1462435792_thumb.png

 

I chose a normalization angle of 30.0 degrees.  This involves a toe-in of about 52.5 degrees in my room, but because the seating is spread out so widely, I'm leaning toward this configuration to get the best seat-to-seat coverage.  Note that the 17 kHz break-up is largely gone at 30.0 degrees, which is why the middle is very dark there.  (Edit: The dark area is actually clipped with respect to the color scheme.  See the plotted polar responses.  The 17 kHz response is actually over 10 dB higher at 0 degrees vs. 30 degrees.)  In practice, I would probably EQ most of that break-up peak out to keep the speakers from "glaring" at people sitting on axis of them.  Otherwise, the ripples in the middle aren't as bad as they look.  The normalization makes the response ruler flat at the normalization angle.  A much better approach in practice is to consider frequency response at multiple angles so that EQ effort is put into correcting defects that are consistent from seat-to-seat to reduce these ripples.

 


 

 

Vertical Polar Response

 

Below are vertical polar response plots (un-smoothed with 3 ms window) of the DNA-360 CD inside the SEOS-15 horn, taken at 0 degree azimuth and 1 meter.  SPL figures are only correct in a relative sense.  Note: The increments vary here because I wanted more data for the region that people are actually likely to be listening.  From 0-30 degrees, the increments are 5 degrees.  Beyond there, I measured at 45, 60, and 90 degrees.

 

post-1549-0-33107800-1460348840_thumb.png

 

Looking closely, we can see a portion from 15-17 kHz where the SPL at +/-10 degrees or so is higher (a lot higher, actually) than it is on-axis.  Similar features are visible in other measurements I've seen.  These are also visible in the vertical polar, this time normalized to 0 degrees:

 

post-1549-0-56522500-1460440699_thumb.png

 

It's interesting that the vertical pattern stops expanding at around 1500 Hz and remains consistent for about another octave.  I imagine again that this is a feature of the box as much as the horn on its own.  These measurements were done with an extended baffle above and below the horn.  (Update: measuring the horn with baffle extension below but not above the horn causes the vertical polar response to widen a lot less from 2.5 kHz to 1.5 kHz and to widen more gradually in general down to 500 Hz where it again matches the polar response in the measurements shown here.)

 

The features starting around 13 kHz are also interesting.  There is a null in the response from 13-20 kHz, except in the vicinity of the break-up at 17 kHz, which beams heavily on-axis.  There is plenty of good cause to roll-off the response pretty aggressively from 15 kHz on up, and this more or less defines the maximum frequency at which the horn + CD combo behave as desired.  Above there, EQing flat on-axis will lead to an over-abundance of room energy at those frequencies, which can make the sound seem glaring and bright throughout the room.  Perhaps not coincidentally, 15 kHz is also where I start rolling off in my current EQ setup.  (This was chosen by ear rather than by looking at measurements.  No big surprise here.  Power response matters a lot for these high frequencies, in my experience.)

 


 

 

DNA-360 Linearity of Response vs. output

 

Here are sweeps to show the response linearity the DNA-360 CD in the SEOS-15 horn.  The plot consists of multiple sweeps at successively higher levels.  Each sweep is labelled with its norminal level (e.g. -20 dBFS).  I did these sweeps with my current crossover and EQ filters so I could assess its performance relative to WCS of actual content play at reference level.  Note that my current calibration has the high frequencies collectively attenuated by -5 dB from the "85 dBC theatrical standard".  So, "-20 dBFS" is actually approximately 80 dB in the listening area.  (The SPL scale shown in the plot is not correct in an absolute sense.)  These sweeps are windows at 10 ms and smoothed to 1/48th octave

 

post-1549-0-51166300-1460350253_thumb.png

 

Break up's are a bitch.  Having discovered non-linearity of the break-up in the cheap Ti CD in one my Hsu speakers, part of what I wanted to see in this test is how the break-up at 17 kHz would behave has SPL got pushed higher.  Here we see that this nasty break-up exhibits non-linearity, starting with the -8 dBFS sweep.  At first glance, it appears that the output begins to compress, starting with that sweep.  However, what actually happens is more complicated (and far nastier!) than that.  Note that the sweeps at and above 8 dBFS actually show ripples that weren't there in the earlier sweeps.  Time-frequency spectrograms (5 ms window) for -14 dBFS vs. -8 dBFS reveal just how nasty this transition is:

 

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Note all the ringing that shows up for the -8 dBFS sweeps.  This ringing actually increases the audibility of the problem even though the SPL appears to drop, and each louder sweep increased the ringing visible in the spectrogram substantially.  As a point of note, I wore over-ear hearing protection for the sweeps at -14 dBFS and above.  However, in the -8 dBFS and higher sweeps, I could clearly hear the driver producing lower frequencies (!) when it hit that break-up region.  The sound had a weird kind of "boing" sound to it.

 

Because this break-up is non-linear, it will resist treatment with EQ.  There is at least a chance that, using some EQ to knock down the break-up in the first place will stabilize the driver for those frequencies and allow it to play a lot louder without behaving erratically.  I will have to try it and remeasure.  OTOH, I'm thinking this kind of thing is common to almost all high frequency drivers and may substantially account for perceived differences in sound when things are otherwise EQed to the same response.  Some drivers  (made of Be?) may only exhibit this kind of break-up above 20 kHz.  Larger drivers may exhibit problems at significantly lower frequencies.

 

Something that's unclear to me is how the break-up will respond to actual content vs. sine sweeps.  I can play sine waves cleanly to 86 dB at the MLP.  I surely ought to be able to play transients cleanly to that level as well.  Somewhere between 86 dB and 92 dB, sine waves at 17 kHz will make the driver badly distort.  But does that mean that transients at 92 dB will distort badly?  (This is a totally reasonable SPL for a HF transient.)  I have no idea.

 

At the same time, I wouldn't be surprised if this driver is actually better behaved, on average, than other drivers on the market.  Being that I'm not aware of any other measurements like I've done here, it's hard to say for certain.  In any case, this issue at 17 kHz is definitely the "weak point" of this driver.  It's the problem that's most likely to make it sound other than reference, and the SPL at which this may happen is way below the max SPL that the driver is capable of.

 


 

 

DNA-360 Distortion with "High Level" Output

 

Here is a plot of the distortion harmonics and THD versus frequency for a "-2 dBFS sweep" performed in the same manner as the linearity tests above but as part of a separate measurement.  In other words, this is playing at about 98 dB at the MLP, about 10 feet away from the horns.  This measurement was done with a different set of filters engaged than for the linearity tests because they were done later and reflect updates to my DSP settings.

 

post-1549-0-36546800-1464242848_thumb.png

 

There is a high pass filter at 950 Hz and 40 uF capacitance in series for another 6 dB/octave starting at around 500 Hz.  THD is dominated by 2nd order distortion throughout the pass-band.  The peak THD in the pass-band is around 4% at around 1.5 kHz.  THD remains below that figure all the way down to 600 Hz.  This driver appears to handle the low crossover point and gentle slope very well, and this is despite the fact that the driver response falls off quite slowly in the 700-1000 Hz range.

Edited by SME

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SME    211

TD12M woofer and in-box measurements are posted here.

 

 

TD12M Woofer Impedance

 

post-1549-0-72220600-1464241355_thumb.png

 

Caveats: This woofer was not yet broken in.  The measurement taken with the woofer firing up instead of forward, which is known to some error.

 


 

 

TD12M Woofer In-Box Impedance

 

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This is in a ported box of about 1.5 cubic feet internal volume.

 


 

 

TD12M Woofer In-Box Response (close mic)

 

I aimed for a tuning frequency somewhere in the 40-70 Hz range.  I was pleasantly surprised to see the tune came in right around 45 Hz with the port tube at its minimum length with a response that has a very nice over-damped roll-off.  I'm glad I opted to make the bass box a bit smaller than I originally planned!  In fact, I'm very pleased with the end result:

 

post-1549-0-97902000-1467349022_thumb.jpg

 

Note, these are un-smoothed close-mic measurements, so these shouldn't be interpret as absolute but merely illustrative.  The one on the bottom is before I added acoustic foam to the box.  That 240 Hz resonance was particularly nasty and contributed an impedance spike as well (not shown).  The foam totally nuked it.  I installed a pretty generous amount of foam (more than would be typically recommended) into a box that was already somewhat cramped.  The port exit is not really one port-diameter away from some of the internal surfaces, including the rear, but I did my best to give it as much clearance as possible.  Nevertheless, I really wanted to kill those resonances and wanted to stop as much mid-range sound from coming out of the port as possible.  Thankfully, I don't see much evidence of output loss due to the heavy stuffing.  Here's a comparison of ported versus sealed close-mic responses after stuffing:

 

post-1549-0-42948800-1467349074_thumb.jpg

 

These were done even further off-axis from the woofer and were closer to the port.

 

The ported box gains 2-3 dB over something like two octaves, and I believe that excursion should be better controlled in the ported version in the 40-80 Hz range.  The port does cause a bit of cancellation in the mid-range, but the losses are under 1 dB for the most part and diminish before the port resonance a tad above 1 kHz.  I've also confirmed sufficient attenuation of sound in the port using inside port measurements.

 

It's possible that the tuning frequency was lower than expected because the lack of space around the port inside the box effectively increased the port length.  Unfortunately, this probably also increases turbulence and may cause problems with chuffing and/or compression at high levels.  I may need to do some compression sweeps to verify that these things can breathe at higher levels of output.  The results may impact how low I choose to cross them over in the long term.

 


 

 

Horizontal Polar Response (in-box)

 

Here is a normalized 2D colormap plot of the horizontal polar response windowed to 4 ms and normalized to 30 degrees, generated with tools provided by 3ll3d00d:

 

post-1549-0-41693300-1462434835_thumb.png

 

These measurements were done indoors but were only slightly contaminated by reflections within the window period.

 

Edit: Note that the data is clipped at "+3 dB".  A better picture of the polar response pattern emerges if we normalize at 0 degrees:

 

post-1549-0-07525100-1464240051_thumb.png

 

That looks much better.  Whatever cone break-up exists in the TD12M doesn't seem to perturb the polar response much at all.  Nothing like the break-up in the DNA-360.

 


 

 

Vertical Polar Response

 

Here is a normalized 2D colormap plot of the vertical polar response windowed to 4 ms normalized to 0 degrees:

 

post-1549-0-93032000-1464240128_thumb.png

 

Edit: I updated this image to better use the available color range.

 

These measurements exhibit more contamination from reflections than the horizontal polars.  This effects the measurements taken far off-axis in particular because I could not properly absorb the ceiling reflection.

Edited by SME

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3ll3d00d    72

Are you going to make a polar plot for the horn on its own? It would be interesting to see those results if you do. I got my dual td12/seos10 tested at the weekend and the seos looks quite dinky next to the rest of it (hence wondering if I can squeeze a bigger horn in there if it is really worth it).

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SME    211

It'll probably be at least two weeks before I do any polars.  I expect I'll need to block at least one weekend day for the effort including time for setup.  I also have to figure out exactly how I'm going to set up the measurements.  It'll probably just be in my living room at about one meter distance and a short impulse response window.  That's not really ideal, but it's way less hassle than trying to rig something up outside.  I may be able to use some spare acoustic foam to my advantage too.  We'll see.

 

This weekend, I hope to finish the woodwork on the other cabinets and get them wired up with capacitors for protection during preliminary testing.  Then I can see what kind of sensitivity I get across all frequencies and decide how much resistance I want to add.  After that, I have no idea.  One of my XPA-5 amps is with Emotiva to fix a bad XLR input.  Worse still, it appears that all the odd numbered (top row) outputs on my Motu A16 have electrical issues, and I am still working through tech support who will likely have me send the unit in for service for what may be a crappy soldering job or maybe even just a loose cable.

 

I do still have a fair bit of work to do still on the DSP software, but I'm almost to the point where it would be frustrating to not have the A16 around for testing.  Worst case, I'll find other stuff to hack on.  It's just going to drive me crazy to have two finished speakers but no crossover.  They are really too big to be permanently placed in my room anywhere except where the old front left and right speakers reside.  I'm even half tempted to try to work out an interim passive crossover but I want to see where the thing with Motu goes.

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3ll3d00d    72

I find I can get to 50-60 degrees in room before the data quality degrades too much, til that point the data is consistent with that achieved outside (with a longer gate). I think the horn being in a separate box should make it a fair bit easier for you too.

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SME    211

I just finished sanding the last box.  Tomorrow I'll hopefully finish the other woofer.  Then Sunday, I can work on getting the horns ready for preliminary testing, if I don't lose too much of the day to listening to the woofers in stereo.  If there's time, I'll make changes to the protection circuit as needed.  I doubt I'll find the horns as nice to listen alone as compared to the woofers.  Then I just have a lot of work to do with code while I wait for my electronics to be fixed.  The waiting is going to make me crazy.

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SME    211

So I did get the listen to the horns on Sunday as well as listen to the woofers in stereo.  I listened to the horns mostly in mono (one at a time) with 40 uF capacitance in series and the channel crossed over to the subs at 250 Hz, the max supported by the AVR.  Having some bass definitely improved the experience.  In fact, I thought they sounded fantastic despite the hole in the mid-range response.  There was enough mid-range, for the most part, to hear what was going on, and the 1 kHz+ sound was very smooth.  I had to pull myself away from just listening in order to take a few measurements before I ran out of time for the night.  I'm not posting the data because I'm not too happy with it.  I will need to plan better to get some better measurements.  At the same time, my preliminary sensitivity measurements suggest my measurement gear may be reading at least 2 dB, perhaps even 3 or 4 dB too low.  I guess that's not unreasonable given that my reference is a Rat Shack meter.  Perhaps it's time to splurge and get a calibrated SPL meter or get a new mic with calibrated sensitivity, in addition to calibrated frequency/phase response curves.

 

I was planning to move forward with adding resistance in series until I did a bit more careful study of the problem and realized that series resistance alone is probably not the answer.  The background hiss from the horns was very audible due to noise in my signal chain and their very high sensitivity.  In fact, my wife complained it made her feel uncomfortable and that it remained audible at moderate listening levels.  My best guess is that the MiniDSP OpenDRC-AN units are the culprit.  I noticed a significant bump in background hiss from my current speakers (enough to *just* hear at the listening area) when I added those units to my signal chain.  I was disappointed because I had been getting by fine with only RCA, but the balanced connection between it and the amp didn't seemed to help at all.  I think those units may be somehow flawed in their design.  Once I have custom DSP with my Motu A16, I'll be very glad to part with those things.

 

On Monday, I finally got the RMA finalized and shipped my Motu A16 back.  It looks like I can anticipate at least a two week wait due to shipping alone.  In the meantime, I have a fair bit of code to write so that I'm ready to rock when that unit comes back.  My freshly re-soldered Emotiva XPA-5 amp is arriving tomorrow.  I've gotta say, I thought the hard part about this whole DIY thing was going to be in the shop, but instead, it's the incredible pain involved in finding and acquiring the parts that are needed for the task.  I believe this project has so far led to a total of product re-orders and/or RMAs due to errors or quality issues.  I have a new respect for those who go through the trouble of manufacturing things to sell and persevere despite the constant hassles of having to deal with vendors.  The more infuriating issues were with totally trivial things that were too cheap to bother returning.  Amazon.com sent me a router bit package without the router bit, but I had to wait 13 days to receive the shipment before I realized I would have to re-order it.

 

I'm done ranting.  I have a couple weeks to get as much done as possible with my DSP code so that I can dial-in a useable crossover and integrate the new speakers into my system.  I'll also dive into more measurements so I can work on optimizing their responses.

 

Then I will experiment with different combinations of baffles and/or absorbers to try to clean up the low-end response and directivity.  I am tentatively planning on placing them toed-in at 45 degrees as close to the front wall as possible.  With the woofer centers located about 14 inches from the rear wall, I'm anticipating a fair bit of 250 Hz suck-out, which I expect I can partly mitigate using some appropriately placed OC703.  On the other hand, if I can use a reflective baffle surface to smooth the transition between the face of the speaker and the wall, then I can maybe get a flatter response without having to give up as much efficiency.  Note that the absorber essentially dissipates much of the rearward wave coming from the speaker, and that's a lot of energy to lose.  I know that a very large continuous baffle is ideal, but I want to see what kind of compromises are possible as well as seeing whether I can use baffle design to help increase forward axis directivity at frequencies further below the crossover.

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SME    211

Just a quick update.  I got my amp back and will hopefully get a fully working replacement Motu A16.  Without that, my system is basically dead because I don't want to mess with the mess of cables that hold together my current "signal chain from hell".

 

I did some thought experiments for surround designs.  I looked at a few options involving coaxials, but I'm not sold on them.  No one is showing measurements of what happens when the woofer is moving a few mm back and forth.  As far as those designs go, I think the Eminence CX-10 looks decent, and the wife would certainly appreciate seeing less speaker.  However, given my room layout, I think my best option is to use a SEOS-15 horn turned on its side and matched with a pair of 6.5" woofers such as the AE TD6H, oriented vertically and to one side of the horn.

 

I'll have to double check, but I believe I have enough gain from corner loading to get 80 Hz extension from a sealed box with a much higher resonance.  The AE TD6H in particular look like that can deliver a nice low Q roll-off in a very small box.  The sensitivity of 97 dB/2.83V (4 ohm speaker) is only a little less than my fronts, and the bass gain would in principle make up for the reduced displacement.  I'd love to go with 8", but I think they will be too big and won't integrate as well with even an SEOS-15.

 

Edit: And I forgot to add that after looking over my data more carefully, I believe that my woofer enclosures are tuned closer to 45 Hz with the stuffing added.  Both impedance and inside port measurements point to a tune of 45 Hz with the phase zero-crossing hitting 45 Hz on the mark.  I'm a bit surprised my design ended up tuned so low with such a short fat pipe, but I suspect that the tight dimensions inside the box may be contributing to a longer effective port length.  In any case, I'm still quite happy with the responses.  Once I get them up and running, I can push them a bit more to see if any issues arise.  Oh, and as a point of minor fascination to me, I've never seen anyone post measurements of inside their ports.  I was surprised at how easy it was to clip the mic at 120 or so dB with it stuck in the port.  So of course, I had to put my fist in it and enjoy a free "wrist" massage.  ;)

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3ll3d00d    72

I take it you have seen http://www.diysoundgroup.com/forum/index.php?topic=228.0and the corresponding thread on avs http://www.avsforum.com/forum/155-diy-speakers-subs/1470958-td15m-seos12-bms4550-theater-progress-dual-td6m-seos12-bms4550-build-d.html . AIUI that guy was never happy with the dual TD6 for reasons he couldn't get to the bottom on.

How far away will you be sitting?

I have a radian 5208 waiting to be built, have done the crossover but i am v slow at woodwork :) I have a thread on avs with the details and there is some discussion on diyaudio too (link to diya at the end - http://www.avsforum.com/forum/155-diy-speakers-subs/2104738-surround-options-small-room.html ).

 

I know the 5210 is highly rated as well, I believe beastaudio uses them so plenty of people here must have heard them given the gtg.

If you want some particular measurement then I could probably do that at some point.

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Ricci    652

We did spend time listening to the Radian's when I was at Beast's GTG but they were run for surround duties only. From what I heard they are quite good. I never heard them struggle and they didn't otherwise draw attention to themselves which is a good thing in my book.

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SME    211

I take it you have seen http://www.diysoundgroup.com/forum/index.php?topic=228.0and the corresponding thread on avs http://www.avsforum.com/forum/155-diy-speakers-subs/1470958-td15m-seos12-bms4550-theater-progress-dual-td6m-seos12-bms4550-build-d.html . AIUI that guy was never happy with the dual TD6 for reasons he couldn't get to the bottom on.

 

How far away will you be sitting?

 

I hadn't read those threads yet.  Thanks!  I get the impression that bass addict wasn't so much dissatisfied with the 2 X TD6  speakers he built for "heights" as he was dissatisfied with the overall result, particularly the TD-15M + SEOS-12 + BMS-4550 builds he did.  I can try to guess at what he might of done wrong, but it's largely speculation without some good measurement data.

 

Another important point is that the design uses TD6M drivers.  I don't know why anyone would try to use TD6Ms as woofer because they really are mid-range drivers.  Notes from mtg90 on the DIYSG forum indicated that the mid-range was brought way down to deal with the bass roll-off resulting in a sensitivity around 92 dB/2.83V and 4 ohm impedance.  That's worse than what I have now.  For my design, I planned to use TD6Hs instead.  They have a lot more excursion capability as well as more mass and motor strength for use as actual woofers.

 

I sit about 3 m away.  You would be correct to say that my build is a bit overkill for reference level playback.  But that hardly puts me in strange company around here.  :)  I want something that'll keep up with my mains and deliver excellent sound quality.  The TD6H pair with help from the corner can probably do about 3 dB less than my TD12M mains.  I know it's typically argued that surrounds need not be as big, but I do want a lot of headroom.  For one thing, I'll be sticking to 5 mains channels in this room, so the surrounds will have to handle sides and rears on 7.1 tracks.  For another, Atmos tracks and tracks originating from Atmos theatrical mixes have a lot more bass in the surrounds because of the surround bass management that theatrical playback systems added for Atmos.  Third, I want to use the surrounds to help with room EQ, even for sounds that originate in the mains speakers.  As such, I really wish I could make a pair of 8s work, but that causes too many other issues in the design.

 

I have the same 5210 surrounds and I really like them.

 

Thanks a lot to you, Ricci, and 3ll3d00d for your suggestion.  If I decide to go with a coax, I'll definitely lean heavily in that direction.  I do wish they made a 4 ohm version so I could get a bit more power into them.  Both this and the Eminence have sensitivity of 95 dBish.  I expect a TD6H pair to yield 97 dB.  Of course, the Radian probably has a bit more bass if I end up needing it, but I can't find an Xmax number for it.  Can anyone help?  The other reservation I have is that I'm pretty sure I want the tighter horizontal dispersion of the SEOS-15 horn turn on its side.  I'm fairly certain it will help a lot with front wall reflections I have.  I know because I've done a lot of acoustic measurements already with speakers that are already installed in the planned location.

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3ll3d00d    72

There is a spec for the radian on their site (http://www.radianaudio.com/download/5210-2/) which gives it as 4.65mm

 

There's a some discussion & klippel measurements of the TD6H in http://www.diymobileaudio.com/forum/klippel-reviews-driver-specs/115207-acoustic-elegance-td6h-8-a.htmlif you haven't seen it, you have to register to get the download.

 

I exchanged a few PMs with bassaddict and it was definitely the dual TD he wasn't happy with, he commented on them having a "harsh gritty edge to voices" that he couldn't get rid of despite trying a variety of things to solve it (I don't know what things specifically, it was a few brief PMs). I imagine the thinking is something like ported gives decent output to ~200Hz and that's enough for surrounds/heights. 

 

Won't turning the SEOS on its side blast a whole lot of output vertically? This doesn't seem desirable (though I don't know what your room layout is so can't be sure on that). Do you know how you intend to control directivity "horizontally" (vertical in a normal orientation) given the driver layout?

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SME    211

There is a spec for the radian on their site (http://www.radianaudio.com/download/5210-2/) which gives it as 4.65mm

 

There's a some discussion & klippel measurements of the TD6H in http://www.diymobileaudio.com/forum/klippel-reviews-driver-specs/115207-acoustic-elegance-td6h-8-a.htmlif you haven't seen it, you have to register to get the download.

 

I exchanged a few PMs with bassaddict and it was definitely the dual TD he wasn't happy with, he commented on them having a "harsh gritty edge to voices" that he couldn't get rid of despite trying a variety of things to solve it (I don't know what things specifically, it was a few brief PMs). I imagine the thinking is something like ported gives decent output to ~200Hz and that's enough for surrounds/heights. 

 

Won't turning the SEOS on its side blast a whole lot of output vertically? This doesn't seem desirable (though I don't know what your room layout is so can't be sure on that). Do you know how you intend to control directivity "horizontally" (vertical in a normal orientation) given the driver layout?

Thanks for the additional info on the Radian.

 

I wish we could learn more about what was adversely affecting the sound of his heights.  How often to heights get used for voices anyway?  The "harsh gritty edge" imparted to voices must have been pretty bad.  I wonder if there was a box resonance problem or something.  Or maybe the crossover had serious issues.  We are all left to guess.

 

Turning the SEOS on its side does "blast a whole of output vertically", but it's no different from using a coaxial because both have about 90 degree dispersion in that direction.  The difference is that the side-ways SEOS will hold that pattern to a lower frequency and will provide a tighter horizontal pattern.  Either way, I can take advantage of all that energy being directed to the ceiling by putting diffusers up there to scatter it around the room.

 

Note that my setup is unique, and I believe it is unusually well-suited to use of a side-ways SEOS horn configuration.  My room is set up with the MLP about 10 feet from the front wall and with the surrounds placed at 90 degrees from center, about 9 feet away.  My sofa is a odd-shaped sectional with a very gently curve.  The end seats are about 1.5 feet forward and about 5 feet to each side of the MLP.  This places all the listeners roughly in line with each surround speaker, and my initial estimates suggest I can achieve a remarkably good level balance between the two surrounds at all of the seats by using a 90 degree dispersion pattern.  (The sofa design also makes for a comfortable viewing angle to the TV from each seat).  Both the coaxials and side-ways SEOS horns provide a 90 degree dispersion pattern across the listener seats, but as I said, the SEOS will control the front wall early reflections better.

 

What I see as the downside to using the SEOS versus the coaxial in my application is that the SEOS has more direcitivity and so will provide less overall energy for the same SPL.  For home theater, it is often argued that surrounds should have a more diffuse sound compared to the fronts, and less directivity definitely helps with that, but I don't think it's likely to make that big of a difference here.

 

Edit: I forgot to add that most of the TD6H Klippel results are posted here: http://aespeakers.com/forums/topic/td6h-klippel-results-from-diymobileaudio-com/. It looks like the 6mm Xmax figure is legit.  It also looks like its excursion is probably usable out to more like 8 mm, especially if used in a box that's smaller than Vas, at which point the air spring is more important than the suspension for determining the overall compliance of the system.

Edited by SME

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3ll3d00d    72

It's not obvious how this is better than a big coax.

 

The SEOS 15 starts to lose control vertically at ~3.5kHz as the -6dB point widens from ~50 degrees at 3.5kHz to ~110 degrees at 1kHz (based on http://attitube.com/wp-content/uploads/2013/02/SEOS15Vert.png which comes from Bill Waslo's measurements). It has also narrowed further to ~40 degrees at 10-15kHz. Meanwhile a vertical pair of 6" woofers will be pretty much omni up to this point won't they? This basically means you're omni at ~500Hz down to 120 degrees at 1kHz, 50-60degrees at 4kHz and ~40 degrees at 16kHz

 

Compare to something like http://www.bcspeakers.com/products/coaxial/15-0/8/15cxn76 which gives you ~80 degrees from ~500Hz to ~20kHz (probably marginally narrower at the top end, maybe 60 degrees). 

 

Basically the coax looks like it controls directivity to a much lower frequency while also holding up a wider pattern at the top end. OTOH the upper end of the SEOS will undoubtedly be cleaner than a big coax which seem to get a bit ragged to say the least. 

 

The other wildcard is whether you can maintain that vertical directivity once a crossover is in place, the coax should be much easier to work with in that regard.

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SME    211

The crossover is no wildcard.  In my view, it must be considered as part of the overall design.  In my calculations I found to my surprise that a driver playing even -24 dB from another driver influences its dispersion.  Below 24 dB, it might not matter much, but for a crossover with 24 dB/octave electric+acoustic roll-off on each side, the crossover region where the drivers interactions are significant is full two octaves.

 

The pair of 6.5" woofers in a vertical stack should yield pattern control in the vertical dimension to a much lower frequency than in the horizontal dimension.  Indeed, the acoustic width of the woofer pair in the vertical dimension is very similar to the acoustic width of the side-ways horn, and in the crossover region, the woofer pair and horn exhibit similar vertical dispersion over a fairly wide range.  Furthermore, the difference in distance between the woofer pair and the horn doesn't change much with vertical angle, so after time-aligning the drivers, the combined vertical directivity pattern should be essentially the same as for either source (the woofer pair or the horn) alone.  That's good because both the horn and driver hold vertical pattern very well down to 800 Hz and exhibit some residual vertical pattern control to beyond 500 Hz.

 

In the horizontal dimension, the crossover has a much more dramatic effect.  Both the horn and woofer pair have widening dispersion that begins well above the crossover point.  However, when you measure from different horizontal angles, the difference in distance between the woofer pair and horn changes a lot.  At the most extreme angles, the two are about 8 inches apart, essentially the center-to-center spacing.  This means that the sources interfere completely destructively (180 degrees out of phase) at a horizontal angle of 90 degrees (assuming an infinite baffle) and a frequency of 850 Hz.  (This is because 8" is half the length of an 850 Hz wave.)  At +/- 45 degrees and 850 Hz, the sources are .707 times as far away as at 90 degrees.  This gives a phase difference of 120 degrees between the sources, and the SPL will be -6 dB down from on-axis.  This means that if the crossover is at 850 Hz, the system will have 90 degrees horizontal dispersion at 850 Hz.  That the horizontal directivity can be controlled to so low a frequency is not obvious.  Meanwhile, the vertical dispersion is only just starting to widen there so is not much more than 90 degrees.  Below that point, the dispersion will widen back out as the influence of the horn diminishes.  As such, there is an advantage to being able to use shallow slopes below the crossover.  Above the crossover point, dispersion will eventually narrow even more, but it may widen a bit before narrowing, again depending on what the crossover slopes look like.  If the slopes are fairly shallow, then the loss of directivity as the woofer's influence diminishes will be counteracted by the gain in directivity as the dispersions of each source alone are also narrowing.  I can also play a trick in which I use a slight offset in time-alignment between woofers and horn to steer the main lobe more toward the rear of the room than the front.  I can't do that at all with a coaxial.

 

I do like the looks of the woofer in that coax, but it wants a bigger box than I can give it.  Another concern I have is that the woofer response starts looking ragged before it even hits 1 kHz, and it's designed to cross at 1.2 kHz.  I'm not sure what makes you think it has 80 degrees dispersion from 500Hz-20kHz.  On the low end, a piston radiator hits -6 dB @ 90 degrees when the wavelength equals the diameter.  Assuming that 15" woofer has 12.5" of radiating surface, that frequency is 908 Hz.  However, woofers with a concave cone tend to behave acoustically like they are smaller than they really are, so the real 90 degree point for this woofer may be closer to the recommended crossover point @ 1.2 kHz.  If we model the concave 15" as an 11.25" piston instead (which gives 90 degrees dispersion @ 1.2 kHz), we see the dispersion widens to 120 degrees at 985 Hz, and 150 degrees at 875 Hz.  It's practically omni at 500 Hz.  In contrast, my design can keep the vertical dispersion inside of 90 degrees all the way down to 875 Hz and is able to hold some residual pattern lower still.  My calculations suggest my woofers are 90 degrees out of phase at +/- 60 degrees vertical and 500 Hz, which is -3 dB from on-axis.  The 11.25" piston is only -1.4 dB at +/- 60 degrees and 500 Hz.  (Or -1.7 dB for a 12.5" piston, in case that mattered.)

 

Of course, these calculations aren't perfect because the pair of woofers is treated as a pair of infinitely small point sources, but they probably still have a bit more acoustic width, vertically speaking, than the 15".  In the 500-1 kHz range, the combined effects of diffraction and reflections from the wall and ceiling whose corner the speaker is installed into are of similar if not greater importance to the dispersion pattern than the woofer and horn directivity.  In my view, the baffle and box design is the hard part and is where I need to focus more of my attention.  It's job will be to essentially provide a clean transition between the SEOS-15 horn and the "horn" formed by the wall-ceiling junction itself while keeping the construction sane.  That is no easy task!

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3ll3d00d    72

when I said the crossover was a wildcard, I meant in relation to my commentary which just talked about individual drivers and how they might combine. I just meant that adding a crossover is going to have a major impact (stating the obvious but still). On that note, it sounds like you have a well thought through plan so it will be interesting to see the execution. I take it it is an active crossover? Will be interesting to see if the crossover & physical offset of the drivers is able to maintain control in the horizontal dimension for long enough to allow a smooth transition to the horn alone.

 

The coax figures just came from their website btw, it has some directivity plots on there which show ~80 degrees down to 500Hz. I have no idea how reliable that data is.

 

Any idea if the TD6 is readily available? I enquired about that driver last year & he commented that it's not a regular offering (hence not on the website) but he does have the ability to make them on order. I don't think I'd be particularly confident about receiving such an order in any reasonable timeframe though.

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SME    211

Yeah,  I'm planning an active crossover as I already have the extra amp channels.  And yes, we'll see how the execution works out.  However, I won't be committing to this design until I've had a lot more experience with my new front speakers.  Hopefully (*fingers crossed*) my replacement Motu A16 will arrive today in full working order.  Then I can get back to work on the more immediate project.

 

Now I see the directivity plots for the B&C.  I didn't arrow through the measurement plots far enough to get there.  I'm not sure how to read their plots.  The contours are done in solid colors, each of which are 6 dB apart, according to the colorbar.  That makes for a lot of uncertainty, too much to ascertain what's really going on.  If we assume the on-axis response is "0 dB" and the first color change (brown to red) is "-6 dB", then it does indeed look like the -6 dB is at +/- 40 degrees for both parts.  Diffraction effects may be playing a role in making the woofer appear to hold pattern a bit lower, not that those should be discounted, but of course, the results there will depend on the baffle design.

 

As for the the availability of the TD6H, I haven't yet enquired about it, but I take it as a given that anything ordered from Acoustic Elegance will have a long wait period.  At least my TD12Ms were shipped approximately within the quoted lead time (i.e. 8 weeks), which actually surprised me!

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SME    211

Today, UPS delivered my replacement Motu A16.  I got it plugged in and turned it on to something like this:

 

post-1549-0-64172000-1455599554_thumb.jpg

 

That was actually snapped while I tried to update the firmware in hopes that it would fix the problem.  Nope.  It looks like the front display is bad on this one.  On the upside, all the inputs and outputs at least appear to work.  Still, receiving a replacement unit with a defect that any casual QC would have revealed does not inspire confidence.  What really burns is that I can use this thing with the display broken, but it's a major nice-to-have because it has level meters for all 16 inputs and outputs.  And of course, there's the principle of holding the company responsible for delivering a fully working product to me.  I just hope they'll *at least* cover my side of the shipping this time around.

 

On another note, I forgot to mention a few other things about the surround design.

 

First, I modelled a ported version of the two TD6Hs, but I didn't like what I saw.  These woofers seem to want a big box with a low tuning frequency, despite their small size.  Otherwise the result is way too resonant and/or the ports can't be made to fit without unacceptable port velocities.  Even in the large/low alignments, there's still some roll-off in the 100-300 Hz range due to the extreme over-damped nature of the driver.  Where these woofers seem to excel is in providing a good balance of sensitivity and bass response in a very tiny box that's intended to be used in a car or other environment in which room gain makes up the difference.

 

The other thing I worked out is that the acoustic interaction of the surround speaker with the ceiling is actually fairly simple to model by treating the ceiling as a mirror plane.  Instead of thinking about reflections, I can instead consider the ceiling to be transparent and that a mirror image of the speaker exists above the plane of the ceiling.  In other words, our modelled speaker is actually two horns high and four woofers tall.  The mirror image is inverted, as would be expected for a mirror.  In other words, the bottom of the real speaker is actually the top of the mirrored speaker.  Using this analogy, I can understand how the ceiling reflections are heard by the listener by simply looking at how all the different sources (real and mirror) interfere with one another.

 

Right away, I can say that I don't want two horns at different locations playing together.  That creates a lot of nasty comb filtering.  Hence, I'll want to "block out" the sound from the horn above the plane of the ceiling.  I can do this by acoustically treating the part of the ceiling through which the sound from the mirrored horns would travel to the listeners.  I want either good high frequency absorption or diffusion.  The up-side to using diffusion to to preserve high frequency room energy and improve spaciousness of the sound.  The down-side to using diffusion is that some sound still gets reflected to the listener, which blurs the otherwise sharp images produced by the images.  For surrounds, the diffusion should work fine.  I'm thinking 2D grid-style diffusers would look super cool and would be totally called for as a lot of HF energy hits that area of the ceiling.

 

It gets even more interesting when I consider the four vertically-stacked woofers (two real and two mirror images).  The presence of four woofers means we get double the bass output for free, which is of course what we expect with wall-ceiling corner loading.  However, those four vertically-oriented woofers also have a pattern that extends to a much lower frequency, and indeed, the pattern at higher frequencies is both too narrow and full of lobes in the listening area.  So we also need acoustic treatment to selectively absorb or scatter the mid-range, roughly down to a frequency at which the pattern is not so yucky.  I haven't done the calculations, but my rough estimate suggests the center lobe will be -6 dB @ 90 degrees at a frequency at least as low as 500 Hz.  Unfortunately, low frequency directivity like that isn't really desirable if the pattern widened somewhere between there and the crossover.  I may have to want to absorb or break-up frequencies even lower than 500 Hz.  That's kind of a bummer, because I'm not sure I can adequately scatter sound much lower than 1000 Hz or so.  Instead, I may need to use absorption to get the best 250-1000 Hz response at the seats.  Some 4" OC703 right on the ceiling would probably work great and would not absorb too much bass.

 

One more thought is that if I could somehow take an SEOS horn and cut it perfectly down the middle, then I could mount the cut edge perfectly flush with the ceiling.  The inverted mirror image would complete the half horn into a full horn again.  If I could do this and opted for a different woofer layout (horizontal MTM?), I wouldn't have to treat the ceiling at all.  I'd also benefit from a doubling of output across the entire spectrum.  Not bad ehh?  Of course, it's just a bit impractical due to what you'd have to do with the compression driver.  You can't exactly cut it in half.  I won't say it's impossible, but I'll leave that for someone else to experiment with.

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Ricci    652

Damn...Sorry to hear that. I'd be pissed off at receiving another defective unit. Doesn't give me a warm fuzzy about Motu.

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SME    211

To Motu's credit, the display issue is intermittent, which means it could have been missed by their QC.  When I tried it this morning, the display worked fine for a while before reverting back to broken again.  I got in touch with them and we are doing a cross-ship this time.  My second replacement unit will be sent via expedited shipping and will include a return shipping label.  So hopefully this mess will be resolved once and for all very soon.

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maxmercy    331

Well, at least they are trying to make it right....While my Epson projector is not first rate and has died twice already, Espon sent a refurb unit 2-day to replace it both times.  Thankfully my current one has only needed a new bulb after 1300 hours on the first.

 

The more customized you try to make anything, the more QC issues and unexpected problems you end up dealing with, IME.

 

JSS

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