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


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#41 SME

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Posted 06 March 2016 - 07:46 PM

No progress on DSP yesterday.  Instead, I discovered that I have a problem with electrostatic discharge (ESD).  It looks like only one of my three racks is actually conductive to earth ground, and it conducts to ground via my amps through my line-level audio cable shields into the Motu, which has a 3 prong plug.  The other racks, including the one with the Motu in it are floating.  (The anodized coating on the Motu rack ears is non-conductive.)  Making matters more frustrating, the racks themselves don't even conduct between the panels because of the paint.

 

I will probably have to wire the racks and their panels together and to a good earth ground.  Until then, I'll need to walk over to a light switch or outlet in another part of the room to discharge myself before doing anything in the racks.  That's a big inconvenience, and it makes doing measurements an even bigger pain because I always need to make sure I'm earthed before touching the mic (or even the stand) to avoid zapping it and everything else connected.  This is only a problem now because got I solid metal racks.  Before I was using a wooden A/V shelf, and I could easily reach in a discharge on a computer chassis.  Now I have to touch one of the racks to even to get to a computer chassis, and discharging into one of these un-grounded racks is enough to cause a significant audio pop.  Not good.



#42 SME

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Posted 10 March 2016 - 08:37 AM

I got bi-quads working and adequately tested late Sunday evening.  I've hacked together some filters to get a response that looks pretty damn good but is still a long way to achieving my ambitions.  To do this job right, I need to do a ton of measurements at my different locations, and I'm currently lacking the ability to do sine-sweep measurements using the outputs on the Motu directly.  Fortunately, the code to do this is mostly already done.   mostly exists already. 

 

I've got a 2nd order high pass on the horns and a 4th order low pass on the woofers at 1100 Hz.  I also have a healthy dose of BSC on the woofers and a fair bit of shaping on the horns.  After shaping, the crossovers are closer to 1300-1400 Hz or something like that.  Last night, I worked on bass response and sub integration.  Even with the overdamped response that starts rolling off > 100 Hz, the room gain goes crazy down there, and the woofer interferes with the subs down to 40 Hz, even with a 12 dB/octave crossover engaged.  A bad room mode at 62 Hz or so causes the mains to interfere there even with a 24 dB/octave crossover at 100 Hz!  BTW, I expected all of this based on experience with the speakers these are replacing.

 

Anyway, my response now looks half-decent, but I'll probably still tweak it a bit more.  Otherwise, I'd post some pictures.  I'm actually seeing some acoustic stuff in my measurements that I'd like to understand better.  It's apparent that the larger baffle helps a lot with holding directivity down all the way through the midrange.    My impulse response looks very nice from about 200 Hz on up, and I believe the suck-out I see at 150 Hz will mostly disappear with ceiling bass traps.  I've installed these toed-in about 50 degrees as close to the back wall as possible.  There is a 4" OC703 panel on the wall on the inner side of each.  The OC703 absorbs pretty well down to to the mid 100s or so.  Below there, we actually want to let the bass to pass through so it can benefit from the nearby boundary gain.

 

With my latest EQ iteration, these are sounding absolutely fantastic!  The imaging in the sweet spot is in full 3D.  Visually, the speakers form an imaginary box, and the sound seems to emanate from that shape as if it were a window.  The phantom surround is also superb.  I can very clearly hear sounds pan across the sides and rear of my head with the right content.  It would be easy to convince just about anyone that they were listening with the center and surrounds turned on.  Of course, the magic falls away when leaving the sweet spot, but the sound stage never collapses completely, and some of the phantom surround effects can be heard in locations well off axis.  That's just damn cool, and I know I'm not the only one here running with an SEOS or something comparable to it.  :)  And the bass?  Nothing short of amazing.  The speakers cross at 110 Hz until I get around to re-doing all the sub EQ, but there is definitely a lot more slam than there use to, even at lower playback levels.  The difference is apparent even when listening in the kitchen.  Kick drum just bumps a bit harder and faster.



#43 SME

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Posted 15 March 2016 - 04:41 AM

Just a quick update here.  I have been spending more time enjoying the sound of these speakers instead of working on them.  Over the weekend, I worked on integrating them with my existing center and surrounds.  Listening revealed holes in the sound-stage between left, center, and right, and measurements with both the center and left (or right) speaker playing showed a big dip in the 1-4 kHz range.  Sounds like a timbre matching problem, right?

 

Using a short time window (like 2 ms), I compared the phase response of each type of speaker and noticed that the center went through a 180 degree rotation at right around 4 kHz.  My left and right speaker went through a 180 degree rotation near 1200 Hz or so.  This accounted for the nasty 1-4 kHz dip and the front stage hole.  What to do?  I added 2nd order all-pass filters centered at 4 kHz to the left and right so they would have the same phase rotation as the center.  Then I added a 2nd order all-pass filter centered at 1200 Hz to the center and surround channels.  The all-pass filters did the job nicely, and the sound stage is actually quite cohesive in the sweet spot.

 

Of course, this quick fix doesn't address the fact that the speakers have different dispersion characteristics and thus, different power responses.  Nor does it address the fact that the speakers I just built sound a lot better, overall.  But at least I can continue to enjoy multichannel content until I have a center channel built and installed.

 

My other issue is that the bass is no longer integrated as well as it was.  To fix this, I need to get a lot of measurements at multiple seats, but I don't want to use my old code to do this because it won't work with the Motu directly.  I need to write code for a significant prerequisite component, and then I can port my existing sine-sweep measurement code to use the Motu directly.  Once that's done, I can move my subs off of the MiniDSP 2x4 and OpenDRC units and ping each of them separately during a single measurement run.  This last point is a huge deal as it takes me a long time to measure 10-12 or more listening locations and having to cycle the power switches on the plate amps for each location to get individual measurements from each of the four subs.

 

I also need to finish converting the code I wrote to calculate room EQ filters into a generic program.  That's where I simulate the filters applied to the measured room responses and iterate on the filters and filter generation algorithms until I like what I see.  Better still, by having a more direct interface to my DSP than I did through the MiniDSP systems, I'll be able to listen to the results of each iteration with great ease.  I'll also be able to do A/B switches nearly instantly as well as manage an unlimited number of pre-sets.

 

This weekend, I will try to get measurements of the horns themselves so I can settle on their design.  As much promise as the code holds, I want a center channel real bad now that I've heard what these things do for movies.  :)



#44 SME

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Posted 04 April 2016 - 04:29 AM

Sorry for the lack of posts.  I've unfortunately been occupied with "other" stuff and haven't had much time to work on this project.  Work in particular has been a real bother.

 

I have spent some time thinking about subs again.  Even though I'm probably months away from working on them, I'd like to get the sub drivers ordered well in advance.  I think I'm almost there.



#45 NWCgrad

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Posted 04 April 2016 - 04:36 PM

I hate it when work gets in the way of life.

#46 SME

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Posted 11 April 2016 - 05:37 AM

I just posted some CD + horn measurements I took over the weekend.  I was excited to try 3ll3d00d's idea of using a compass app on my phone for the horizontals.  That turned out to not work as well as I hoped.  The magnetic field from the horn overwhelmed the earth magnetic field out to like 24" vertically.  I imagine I'd needed even more clearance if I were not placing the phone directly above the magnet.  I ended up having to stack a bunch of stuff on top of the horn box to make a place for the phone to lie far enough away from the magnet.

 

In any case, I'm quite happy with the data I got, but I wish I had time to do horizontal polars at different elevations.  My horns will be installed above ear level, so I need to optimize both toe-in and vertical angle to get the best seat coverage.


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#47 3ll3d00d

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Posted 11 April 2016 - 08:03 AM

fwiw (and I might have posted this before but I don't recall off the top of my head) I wrote a v dirty script to turn REW measurements (or rather, a set of frd files) into various directivity sonagrams -> https://github.com/3...rectivity-utils

 

it just needs cygwin, gnuplot and awk (or just run it on linux)

 

perhaps you'll find it useful for visualising & comparing directivity (I find it makes anomalies jump out at you more so than viewing all the raw measurements as FR charts)


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#48 SME

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Posted 12 April 2016 - 05:43 AM

Cool, thanks!  I like the 2D color map plots for a quick glance of the overall pattern, but I find the polar plots to be more useful when I'm studying things more closely.  It does help to be running REW and able to zoom in cleanly to see detail where I need to.

 

I just ran the tool, and it didn't generate the polar graph right, but I did get a good 2D color-map filled-contour plot.  I added it to the post.  Feel free to give me shit about normalizing to 37.5 degrees, but that's about where I think it'll land in my space.  As such, I expect the middle region to run a bit hotter because the listeners who will hear that sound will be sitting farther away.

 

BTW, this thing holds pattern to like 600 Hz.  That's a bit wider than advertised isn't it?  Perhaps it's the box that's doing the job?  Even though the box is only about 1" wider at the ends than the horn?  Now I think I will want to get horizontal and polar measurements of the woofer unit as well.

 

Edit: OK.  I just added a 2D color-map for the vertical polar measurements as well.  This time, the tool choked on generating the regular "sonogram" but the "normalized sonogram" turned out ok.


Edited by SME, 12 April 2016 - 06:11 AM.


#49 3ll3d00d

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Posted 13 April 2016 - 07:49 AM

one thing to bear in mind with indoor measurements that have such a short gate is that the low end of the CD response is impacted by a small but appreciable amount. Here's a comparison of mine indoor vs outdoor, same driver (bms4550/seos10) horn combo in each instance

 

indoor_outdoor_fr.png

 

indoor_outdoor_ir.png

 

I suspect you'll find this impacts your reading of directivity on the low end which might be important for considering where to cross.



#50 SME

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Posted 13 April 2016 - 06:48 PM

Yep.  As the CD rolls off, it exhibits increasing phase delay, so even though the 3 ms should in principle be long enough to assess response down to 333 Hz, the data is probably only accurate to 600 Hz or so because of the added phase delay.  For my own purposes, I can increase the window time quite a bit and accept some minor error/ripple in exchange for better insight into performance below 600 Hz.  Just now, I did exactly this to confirm that the response from 600 Hz and above doesn't change much at all.  The reflections that do occur at 3 ms and later are very weak, even for bass frequencies.  But I opted to stick with a 3 ms window for data posted here because the IR is 100% reflection free up to that point.

 

IMO, the bigger issue with the low frequency parts of the measurements are the baffle effects.  The baffle effects likely have a significant effect on the horizontal polars starting around 1 kHz and on the vertical polars starting around 3-4 kHz.  I believe baffle effects explain the apparent constant vertical pattern at +/- 50 degrees or so all the way from 1500 kHz down to 600 Hz or so as other measurements indicate the vertical pattern continuing to widen from 1500 Hz on down.

 

BTW, I'm not sure what you are trying to demonstrate with your picture.  It looks like your indoor response is about 2 dB lower than outdoor from 500 Hz on up.  This doesn't make any sense.  I would expect the responses to be near equal.  If you used a long time window for the indoor measurement and had very long room decay times, I could see the indoor response being a bit higher than the outdoor response, but not the other way around.  In my room, the response above 3 kHz or so looks almost exactly the same with a 1 ms window or a 100 ms window and a very modest amount of smoothing (say 1/24th octave).  I can't think of any good reason that outdoor measurements should show a 2 dB bump in output like that.  If you were to adjust the green curve down by 2 dB, would it not overlap the pink curve very closely down to 600 Hz?



#51 3ll3d00d

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Posted 13 April 2016 - 07:19 PM

I offset them a bit to separate them, the measurements were taken at different times and at different levels so were not comparable in absolute spl terms at all. My point was just that the resolution available from 3ms tends to have an effect a fair way beyond 2x the resolution so IME it is worth getting outside. If you look closely then you'll see the knee is sharper on the outdoor one and the 1-2kHz (if not 1-6k) range is generally flatter/smoother. Of course it does ultimately depend on the size of the room (and the magnitude of the reflections after that 1st reflection), perhaps your room is just more amenable to measurement than mine.

 

I've also seen the baffle impact directivity as you'd expect, in my case it was centred on 800Hz or so but obviously that depends on the size of the baffle.



#52 SME

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Posted 14 April 2016 - 05:24 AM

OK, that makes way more sense!

 

The impulse responses are very interesting to me.  I'm not talking about the part after 2.5 ms or so, where I expect to see some reflections.  The significant difference in impulse response, from roughly 0.5 to 1.0 ms is interesting to me.  Sound moves roughly 1 foot in a millisecond (ms), so whatever is causing the indoor measurement to differ from the outdoor one is very near the horn or the mic.  Any thoughts as to the difference here?



#53 3ll3d00d

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Posted 14 April 2016 - 08:27 AM

The significant difference in impulse response, from roughly 0.5 to 1.0 ms is interesting to me. Sound moves roughly 1 foot in a millisecond (ms), so whatever is causing the indoor measurement to differ from the outdoor one is very near the horn or the mic. Any thoughts as to the difference here?

It is odd and I can't explain it. The mic stand, speaker and speaker stand are the same in each measurement so the differences are all in the surrounding environment. Clearly I am missing something but I don't know what.

#54 SME

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Posted 27 April 2016 - 03:29 PM

Just a quick update.  Progress has been slow due to lots of other real life stuff getting in the way.  I have been doing some more pre-design work on the subwoofer subsystem.  I hope to be able to order subwoofer drivers very soon.

 

Last weekend, I attempted to do polars of the SEOS-15 with the alternate compression driver, but I couldn't pull it off using the compass method at all.  The magnet was just too strong even with the phone something like 3 feet away.  Worse still, the magnetic field seemed to cause the phone's magnetic directional sensor to progressively lose accuracy as the phone was rotated.  It was only after I got to about 45 degrees that I realized the compass was off.  As such, I'm very suspicious that this problem may have fouled up the horizontal polars I posted for the DNA-360 + SEOS-15.  As such, I am going to re-measure it using a different method that I hope will be much more precise.  Hopefully I will be able to do that this weekend.



#55 3ll3d00d

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Posted 03 May 2016 - 05:31 PM

FWIW I picked up some SEOS12 recently and measured outside with a 8.5ms window, graphs (0-90 degrees at 7.5 degree intervals) are in http://www.avsforum....l#post43753986 

 

I think you can see the sharper knee I was talking about before if you compare them



#56 SME

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Posted 05 May 2016 - 08:17 AM

Excellent, thanks for the update!

 

Edit: It looks like your BMS driver may be exhibiting diaphragm break-up around 17 kHz just like the DNA-360 as evidenced by the considerable beaming there.  I used to think this kind of feature was due to a mismatch between the CD exit and horn throat, but better measurements indicate this is break-up, at least for the DNA-360.  I'm curious about how much output you can get before that break-up goes non-linear.  If you are up to it, you might try doing the sine-sweep tests I did.  Obviously, care should be taken when doing the higher level sweeps.  I looked for evidence of power compression or excessive distortion after each sweep before going forward, just so I didn't damage anything.

 

I finally got a bunch more measurements done including a full redo of my DNA-360 / SEOS-15 measurements.  My hunch was correct in that the compass app on the phone did not give me the most accurate angles.  As the horn was rotated, the error in the reported angle from the compass app accumulated.

 

Here's before:

 

DNA-360-horizontal-2D-map-norm-30.0.bad.png

 

Here's after:

 

DNA-360-horizontal-2D-map-norm-30.0.png

 

Both of these are normalized to 30 degrees instead of 37.5 degrees (as was in my original post) because 30 degrees looks better for the MLP now that I have good data.  ;)  Note that the horn horizontal dispersion appears to be 90 degrees instead of 120 degrees, as it should be.

 

After doing the new measurements, I discovered an unwanted filter in-line, so I'm only updating the normalized maps until I have time to apply the inverse filter to all the data I just collected.  Whoops.

 

I also did some measurements of the woofer in its box, which are posted here.  While I was at it, I also did a set of polars at 10 degrees elevation.  I am hoping that I can assume that the response is approximately separable, i.e.:  P(theta, phi) = P(theta)*P(phi) for pressure P and azimuth and elevation angles theta and phi.  In terms of SPL, that can be written as SPL(theta,phi) = SPL(theta) + SPL(phi) + C. where C is some constant.  If the response is separable, then I can estimate the polar response anywhere on the unit-sphere using only the data along each axis.  I'll use the elevation 10 degrees data to try to verify this assumption.  If this works out, I can use the data I have to model the response at each listening location with any particular crossover as well as to calculate the power response and true directivity with that crossover.


Edited by SME, 05 May 2016 - 08:35 AM.


#57 3ll3d00d

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Posted 05 May 2016 - 02:34 PM

 

 

Edit: It looks like your BMS driver may be exhibiting diaphragm break-up around 17 kHz just like the DNA-360 as evidenced by the considerable beaming there.  I used to think this kind of feature was due to a mismatch between the CD exit and horn throat, but better measurements indicate this is break-up, at least for the DNA-360.  I'm curious about how much output you can get before that break-up goes non-linear.  If you are up to it, you might try doing the sine-sweep tests I did.  Obviously, care should be taken when doing the higher level sweeps.  I looked for evidence of power compression or excessive distortion after each sweep before going forward, just so I didn't damage anything.

 

 

that was some compression sweeps going from 80dB right? I'll give it a go next time I measure in room, I think that sweeping at that level gets me an ASBO if it do it in my garden :)



#58 SME

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Posted 06 May 2016 - 08:17 AM

Yeah, I think you'll definitely want to do them indoors and with hearing protection.  :)  I also suggest doing it with the crossover in place, if possible.  You want to see how the driver handles the highest frequencies when the typical top end roll-off is compensated for, and you don't want your sweeps to be limited by excursion on the low end.  Definitely do some sanity checks after each sweep to ensure there are no visible signs of power compression and that THD remains reasonable for the lower frequencies.  The "80 dB" refers to the SPL at the MLP (at 9 feet or so from the speaker) that my speakers reproduce for the "-20 dBFS" sweep in those measurements, if that makes sense.  My "-2 dBFS" sweep was ~98 dB at the MLP, just as a -2 dBFS treble signal in a soundtrack played at MV "0" would be 98 dB at the MLP.  The horns are toed in, so I'd expect the MLP response is maybe 1.5-2 dB below the on-axis response.

 

Today, I captured the filter response so I can correct the data I have and post non-normalized results once I get around to doing this work.  The changes have no impact on the normalized plots.

 

I also attempted to assess IMD distortion with two-tone stimuli.  One of the two CDs (not the DNA-360) has a shorting ring and notably lower inductance, so I thought I could reveal an advantage for it by doing these tests.  I put on hearing protection, locked the cats in the bedroom (why they think they needed to be in the room for this is another question) and ran dual-tones at levels exceeding 100 dB at the MLP.  For the lower tone, I chose a frequency at the low end of the range of each driver.  The DNA-360 got 800 Hz, which is slightly below its recommended crossover point.  The other driver, which doesn't play as low, got tested with 1100 Hz.  Casual inspection suggests that the lower inductance CD with the shorting ring does indeed have lower IMD when the higher tone is > 10 kHz or so but it's very hard to quantify the differences using the capabilities that REW provides.  Even with the overall response being dominated by direct response energy, there is always the chance that one or both chosen tones will fall in a narrow peak or null, which completely throws off the numbers.  I think to do this "right" requires a series of sine-sweeps simultaneous to a low frequency stimulus.  The stimulus would be increased in level, but not necessarily the sine sweep as most of the IMD seems to be caused by the low frequency tone, even though it only manifests with high frequency tones playing simultaneously.  I'm not sure of how the results should be analyzed either.  So, this will require software tools that I don't have right now, and since I'm rather eager to settle on my choice of driver, I'm thinking I probably won't worry about it, even if it is potentially significant.

 

I'd like to do some more simulations with the data I just got before making a final decision, but right now the DNA-360 is my favorite because of its excellent low frequency performance.  The DNA-360 has a recommended XO of 950 Hz vs. 1.2 kHz for the other driver but after my distortion measurements (not posted), I'd be comfortable using the DNA-360 even lower, whereas 1.2 kHz looks a bit too low for the other CD without a very steep slope.  Likewise, seeing how much the TD12M woofer starts to beam above 1.4 kHz or so suggests that the DNA-360 will work much better in a crossover with a wider transition region, which is something I'm shooting for.  The SEOS-15 itself appears to hold its horizontal pattern all the way down to 600 Hz in its box, and I'd love to be able to take advantage of that control given that I am designing for multiple listeners.

 

My polar response measurements indicate that the change of driver has a negligible impact on polar response, except in the break-up region, which is likely to get EQed way down anyway.  Even then, the differences are fairly minor.  Both of the drivers I'm testing break-up at around 17 kHz, and your measurements suggest that the BMS (4550?) driver has a break-up right around that point as well.  I would guess the particular frequency involved has mainly to do with diaphragm size and material choice.  Incidentally, both the drivers I have use polyimide diaphragms vs. polyester for the BMS 4550.  In any case, the advantage to having "extended response to 20 kHz" is mostly ruined by the presence of break-up, IMO.  If you toe-in to 22.5 degrees or more and EQ the response including the top end to be smooth, listeners sitting outside the MLP and directly in front of a speaker will get a peak there.  Furthermore, the power response will likely be uneven and possibly accentuated in that region.

 

IMO, not nearly enough attention is given to top end response in a typical speaker.  Many people test their hearing with sine waves and conclude things like "I can't hear above 15 kHz" or some such.  For starters, hearing sensitivity drops off quickly above there, so you may be able to hear it if you used a higher playback SPL.  More importantly, sine waves may not be nearly as audible as broadband content there, including transients.  Too much output above 15 kHz adds an ear-pinching sensation and makes the sound brittle and inexplicably loud.  I've used the adjective "glaring" before.  Like it's irritating to your ears even though it doesn't sound loud.  Another analogy is finger nails on a chalk board, which probably does involve a lot of top octave sound in real life.  Any problems in response here tend to be very dependent on source material.  A lot of content has nothing above 15 kHz, but some stuff has a huge amount of energy up there.  I'm fairly certain I can hear the 17 kHz peaks in my current CDs at times.  With most stuff, it adds just a bit of crispness and sparkle to the sound, which while not necessarily accurate, is at least pleasing.  However, I do have some stuff that's not so pleasing to listen to.  Some of the worst offenders IME are a few hi-res remasters where the 15 kHz+ stuff seems to have been pumped way up, presumably to satisfy the customer who expects to hear very high frequencies in digital content mastered with a higher sampling rate.  I have a remaster of "Miles Davis - Sketches of Spain" with muted trumpet that is practically un-listenable in my current setup.  Even standing in the kitchen (outside direct line of sight from the speakers), the trumpets are irritating at even fairly moderate levels.  Thankfully, this is the exception more than the rule.  Otherwise, differences in speakers used in mastering probably account for a lot of variability here.  I suspect the ears are concerned with power response at least as much as direct response in this region, so it wouldn't be surprising if content mastered on domes that beam in a relatively dry room tends to sound very bright on a system with horns and a lot of high frequency ambiance.

 

The next thing I want to do is try to see if I can EQ down the break-up peak in the DNA-360 using a fairly high Q notch filter and if the new response is more or less forgiving with high SPL sweeps.  If it works out, then I can hopefully retain some output above the peak.  Otherwise, I'll probably just have to roll things off a bit more aggressively starting at 15 kHz or so, which kind of defeats the point of having a CD that can extend all the way to 20 kHz in the first place.  Doing this is hardly unprecedented of course.  In fact, I believe most examples I've seen of speaker response voicing involve top-end roll-off that starts well below 15 kHz and becomes quite substantial (6-9 dB or more) above that point.

 

Maybe some day, I can try out a Be diaphragm driver I can actually afford, like a Radian, to see if it's better behaved, but knowing that the Radian's don't have the best reputation for low frequency performance kind of dampens my interest in them for this design.  For now, I want to wrap up this design so I can start building a center channel speaker.  Voices sound so amazingly good with these speakers, and I can't wait to be able to use one for dialog in movies.



#59 SME

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Posted 09 May 2016 - 05:15 AM

Today, I iterated on some PEQ filters to squelch the 17 kHz break-up peaks on each CD.  I ended up using 3 PEQs on each as I couldn't suppress the peaks with a single filter without doing harm to the adjacent regions, and I wanted the roll-off to be a bit lower Q to avoid ringing.  My long term fix will probably use FIRs to a nice low Q target curve.

 

Although the improvement was subtle, the sound is definitely better, most notably on transients, which sound more natural now.  The on-axis IR (measured with sine-sweep) looks way better as the break-ups contributed quite a bit of ringing within the first 1 ms or so.  I think my cat appreciates the change too, and knowing that her hearing is a lot better up there, I trust her judgement.   ;)  The sound also seemed a bit less bright overall, so I added another 1 dB to the high frequency shelf.  I'll have to listen to a variety of content before I decide whether to leave it there, but I think that makes the treble dead flat out to 15 kHz or so.  The hi-res "Miles Davis - Sketches of Spain" album is still un-listenable.  I also have a copy in 128 kbps MP3 format, presumably ripped from the CD, which sounds way better (in more than one way, in fact) despite the MP3 artifacts, so it must be the master that's just royally screwed up.  In comparison even the woodwinds sound alien in the remastered version due to way too much top-end energy.  I'm guessing they hyped it up to appease all the audiophools who obsess about inaudible frequencies to make them think they were getting something "better".  Yeesh, "hi-res" sound is such a racket.  I just wish I could get my money back.

 

I did the linearity measurements on the DNA-360 again, and everything looks great up to -5 dBFS @ MLP.  At -2 dBFS, there is misbehavior, but only above 18.5 kHz.  A slight increase in roll-off should help with that, but I'm not sure it's important right now.  The only caveat here (to repeat what I wrote in an earlier post) is that the misbehavior is non-linear, so it's possible it may manifest more readily with transients than with sine sweeps.  However, I'm leaning toward the opposite being true; i.e., that transients will be less susceptible to trouble than slow sine sweeps.

 

I won't know for sure without more sophisticated measurement tools, but at this point, I'm confident enough that I am committed to going with the DNA-360 drivers.  They are superb drivers, especially with regard to low frequency performance.  My measurements suggest they should work great with a gentle crossover (2nd order electrical < 1000 Hz) and will let me take full advantage of the SEOS-15 horn.  I'm looking to orient them at 7.5 degrees vertical from the MLP as that seems to be a sweet spot, outside the on-axis null > 13 kHz (excepting the break-up peak), where the directivity in the top octave is most smooth.  It's also a good compromise for good response for the other seated positions and for standing listeners.



#60 SME

SME

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Posted 11 May 2016 - 06:02 AM

Been listening a good bit after the changes to suppress the break-up peaks, and there is definite improvement even if it's fairly subtle.  For lack of better description, it sounds more refined.  As

already mentioned, the difference is most apparent on transients.

 

I went ahead and placed an order for more SEOS-15 horns and DNA-360 drivers so I can finish these speakers and have parts I need for the center and surrounds.

 

I did some more research on enclosure damping. 

 

When it comes to speaker enclosure damping, it's very hard to find good information.  It's even harder to find products suited to the purpose, IMO.  I can probably find at least 20 different products of various kinds which claim to damp vibrations in speaker enclosures but have no engineering data to support their claims.  I can also find products intended to damp sheet metal; however, these products are not likely to work well with speaker enclosures which have a lot more flexural rigidity to begin with.  Based on my current theoretical understanding of the engineering problem, the best candidate material I'm aware of right now to glue between sheets of 1/2" BB plywood is 1/8" thick 70 durometer Sorbothane sheet, which can be bought at a reasonable price through McMaster Carr.  They also offer the stuff in thinner sheets, which I believe would damp better, but is not cost effective in the sizes available.  What'd be really nice is to be able to buy 40 durometer in 0.5 mm thick sheets in a size of 12x24" or bigger.  Maybe I can find something better if I look hard enough.

 

With that said, the enclosures I built out of braced 0.5" plywood are a lot more dead than the Hsu speakers made with 3/4" MDF and no bracing.  However, there's still some vibration that finds its way into the floor.  I can isolate the speakers as I did with the Hsu's, but that only solves part of the problem as the enclosures themselves may still radiate unwanted sound.  However, I can't readily quantify the problem with the tools I have, and there is the risk that any attempt to improve things with damping could make things worse by adding more mass than stiffness.  Subjectively, I don't notice any ill-effect on the sound (vs. the Hsus which made a nasty buzzing sound when trying to reproduce enough sound at around 260 Hz or so), so I think I'll continue to ignore the issue for now.  I can always revisit it later.

 

Depending on what I decide, I may start working on a center channel enclosure tomorrow and maybe also do some experiments with angled cuts and joints, which I'll need for the new horn boxes to angle the front face down and for the surrounds.






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