SME

(4) Sealed 21": Funk Audio UH-21v1

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In room treatments are optimal for "fixing" issues from 50-200hz in most rooms.

 

SBIR is usually the reason that region is "messy" in a lot of rooms.

 

Imho, nearfield MBM's are not a "fix".

 

Wow. I used a lot of quotes. :P

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SME, are you DSPing with IIR or FIR?  I was imagining lin. phase crossovers if you're doing complicated mains/subs blending, but at the low frequency end like that you're talking huge numbers of taps and possible major pre-ringing.

 

I'm now very curious what you mean by each crossing mains to each sub differently.  Can you elaborate?

 

Sorry for the lack of update.  I'm knee deep in developing the next gen tools for speaker and room EQ.  These tools will allow me to take full advantage of my custom DSP solution including the ability to do sophisticated crossovers in which each mains channel gets rendered to each of the subs differently.  This is taking longer than I expected, for various reasons, but I'm getting close.  I'm real eager to get this done so I can hear these subs at closer to their full potential.

...

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SME, are you DSPing with IIR or FIR?  I was imagining lin. phase crossovers if you're doing complicated mains/subs blending, but at the low frequency end like that you're talking huge numbers of taps and possible major pre-ringing.

 

I'm now very curious what you mean by each crossing mains to each sub differently.  Can you elaborate?

 

I'm using both IIR and FIR but mostly FIR now.  FIR filters are just so much easier to work with if one has the DSP capability and horsepower.  The filters are mostly minimum phase right now, but I am finding use for some excess phase delay in a few places.  The pre-ringing is very minor in those examples.  And anyway, I don't have a "video delay" capability, so I can't tolerate much extra latency anyway.

 

Linear phase crossovers are kind of a fantasy when it comes to mains/sub blending in small rooms.  My room response suffers from substantial acoustic problems right in the range of frequencies that the typical main/sub XO (e.g. 60-120 Hz) falls in.  I'd bet it's not just my room that does this but almost *every* small listening room.  A lot probably has to do with ceiling heights tending to fall in the 7-10 foot range.

 

In any case, this fact makes crossover between mains and subs a total crap-shoot.  The best tool most people have to optimize this blend is adjusting the sub delay.  However, even if the sub impulse response is perfectly time aligned to the other mains, the blend is often very poor.  Better results are often achieved by "optimizing" the delay to achieve the smoothest response with one channel, but this frequently involves compromising smooth response of the other mains channels, to the particular detriment of 2 channel music.  Finally, this kind of optimization rarely takes into consideration multiple listening locations.

 

I aim to do much better.  What I mean by crossing each main to the subs separately is the the signals that go to each of the subs are different depending on which mains channel the sound came from.  For example, if I play a sound in the left mains channel, the subs will see different signals than if I play the same sound in the right mains channel or the center or one of the surrounds.  I may even go a step further and process bass for the left+right phantom center differently, but that's a ways into the future.

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I'm using both IIR and FIR but mostly FIR now.  FIR filters are just so much easier to work with if one has the DSP capability and horsepower.  The filters are mostly minimum phase right now, but I am finding use for some excess phase delay in a few places.  The pre-ringing is very minor in those examples.  And anyway, I don't have a "video delay" capability, so I can't tolerate much extra latency anyway.

...

 

Cool.  Re: horsepower, yeah I found that was the easy part.  I have an aging intel i7 for the HTPC, and I found that 64k taps x 7 channels took a few % of cpu.  No big deal.  The much bigger pain is the video delay, or lack thereof.  I went down to 16k taps and am doing everything I can to speed up the audio chain and slow down the video one, but it's still never enough.  Jriver, which I love/hate but mostly hate, handles movies fine, but I find I watch a lot more youtube in practice.  Adding to that, shrinking buffers too much gives me popping and crackles, and I hate that even more than bad lipsync.  First world problems...

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Cool.  Re: horsepower, yeah I found that was the easy part.  I have an aging intel i7 for the HTPC, and I found that 64k taps x 7 channels took a few % of cpu.  No big deal.  The much bigger pain is the video delay, or lack thereof.  I went down to 16k taps and am doing everything I can to speed up the audio chain and slow down the video one, but it's still never enough.  Jriver, which I love/hate but mostly hate, handles movies fine, but I find I watch a lot more youtube in practice.  Adding to that, shrinking buffers too much gives me popping and crackles, and I hate that even more than bad lipsync.  First world problems...

 

Well, I managed to overload a single core i5 (the original Neleham) 2.4 GHz DSP in the past few days using something like 24 FIRs with 165887 taps each.  That's in addition to several other processing elements, so the FIRs alone may not be to blame.  I had to bump my block size up from 256 to 1024 to get it to run stable.  :(  With three periods, that's 64 ms latency out of the gate.  Thankfully, my Denon AVR supports a max distance of 60 feet, and it looks like it actually does buffer and delay the video.  That helps *a lot*.  I'll still probably try to reduce the size of the filters, but I kind of wanted to see what I could get away with.

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Sorry for not updating, but I've been super busy working on my next gen software tool and then using it to create an optimized DSP config.

 

Unfortunately, the new software tool proved to be cumbersome in its first iteration.  The plotting library I used proved to be slow and buggy, so I will have to re-write a lot of the code.  However, I was very eager to get *something* in place to improve my sub responses, so I muddled through with what I had.

 

The second part took a while.  Having a lot more capability at my finger-tips, I wanted to experiment to see what I could achieve.  Needless to say, the deep bass cleaned up beautifully.  I fixed the tendency of the bass to concentrate on one side of the room and achieved very even coverage between 20-40 Hz, and for all practical purposes, the decay is essentially instantaneous.  Wall shaking seems to be considerably improved.  I think the ULF is better too, but I had to sacrifice more headroom for it than I'd like to admit.

 

The mid-bass is where things proved to be painful.  The region from about 70-120 Hz is where I spent most of my effort, and I'm not at all satisfied with the result.  Pretty much everything sucks there.  My mains, subs and MBMs all struggle to cover that range well due to their placements and the properties of the room.  The MBMs cover it better than the other sources, but they still need a lot of boost to get there, and the seat-to-seat variation is still uneven.  I will soon revisit it to improve on it.  I think it has the potential to be lot better.  However, I'm thinking I'm going to want the 4 independent MBMs for the sofa as opposed to 2 MBMs behind and two up front stacked between the subs and the mains.  I'll probably also want more bass traps in the right places.

 

Anyway, I'll try to very soon get the pictures fixed and post some nice measurements to show what I've been up to.

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Oh yeah, I forgot to mention that I watched Star Wars: The Force Awakens with BEQ and flat response to 5 Hz, with bass played back more or less at reference.  That proved to be an excellent work-out for the system.  The amp got pushed to near its limit repeatedly but never clipped to my knowledge.  The subs never made any untoward sounds.  In fact, the sound remained subjectively very clean, even with violent levels of ULF going on.

 

I also did some testing with the famous "How to Train Your Dragon" crash scene.  With my current EQ config, I can't go beyond "-9 dB" or so without seeing "the orange (clip) lights" on the amp.  I didn't go much beyond there at all, but I didn't hear any unpleasant sounds when this was going on.  I think the amp lights up orange a bit before it actually clips when its getting a lot of ULF, but I don't know.

 

One thing I can't readily explain is that I seem to prefer these calibrated a few dB hotter than the old subs for the subjective quantity of bass.  Is it because their distortion is so low?  I don't know, but I do know that these sound and feel incredibly clean and powerful once they get above the masking thresholds.  Indeed, I'm surprised to be experiencing what I would describes as slam sensations rooted at deep bass frequencies.  I've generally thought of slam as being a 50 Hz+ sort of thing, but these seem to deliver the feeling a lot lower.  It also feels like a lot more tactile sensation comes from the air instead of the furniture.

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I finally fixed all the pictures on the front page.

 

Here's a picture of my "baseline" sub-bass frequency response shown with crossover from the front left channel, and measured at the inside 5 of 7 seats of my extra wide sofa.  The x-axis resolution is 1/24th octave.  Note the very fine resolution on the y-axis to understand just how tight this is:

 

front-left-sub-bass-only-2017-07-04.png

 

I think I can do a lot better on the mid-bass, but the plotting functionality in the last iteration of the software tool I used is way too much of a pain.  I am going to re-write it to be much better, but that will take time.

 

I additionally use some biquad filters for "house curve" shaping, arrived at by ear for this config:

 

  LowShelf @ around 70-90 Hz or so with gain +4.4 dB and Q 0.707

  LowShelf(s) @ 27.5 Hz and 20.0 Hz +0.375 dB and Q 0.707

 

These filters are applied to the responses of each channel before bass management rather than going to just the subs.

 

Below are the raw, un-shaped responses of each front sub, measured at each of the 7 sofa seats:

Left sub (closer to end of house):

sub-front-left-raw-2017-07-07.png

Right sub (farther from end of house):
sub-front-right-raw-2017-07-07.png

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That looks pretty good. Do you have a response with no signal shaping at all? How much are you using to get the responses shown above?

 

Are you on a suspended floor? I forget.

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Above 60hz or so you're seeing the effects of the position of the speakers/subs and the MLP.

 

You can try moving your speakers out into the room and see the effects. Or try putting one of these subs behind you and time aligning them. Worked for me.

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That looks pretty good. Do you have a response with no signal shaping at all? How much are you using to get the responses shown above?

 

Are you on a suspended floor? I forget.

 

I edited the post above to show the unshaped responses of each front sub at each seat.  I'm not sure what the sums would look like.  I'd need to run my program for that, and I don't want to try to mess with it right now.  I can revisit this once I'm done with the next iteration.

 

Note that I also have two MBMs behind the sofa and in my current configuration, they start to contribute above 60-70 Hz or so.  From about 80-100 Hz, I'm letting the MBMs do more than more than the front subs, which unfortunately struggle a lot to cover the listening area in that range.  This is caused by a combination of side-wall and ceiling reflections and is not a fault of the subs themselves at all.  The left and right mains sit on top of the subs and also suffer from side-wall reflection interference.  Above 100 Hz, the MBMs are rapidly shelved out and the front subs handle the rest of the crossover region with the mains.

 

Yes, my floor is suspended, but it seems to be pretty boring under 10 Hz.  At 11 Hz, where you see the dip in all the measurements, my floor and the rest of the house shake like crazy.  I believe there are many mechanical resonances of the floor and ceiling around that frequency that cause both the shaking and the considerable loss of SPL there.

 

Above 60hz or so you're seeing the effects of the position of the speakers/subs and the MLP.

 

You can try moving your speakers out into the room and see the effects. Or try putting one of these subs behind you and time aligning them. Worked for me.

 

My speaker and sub locations are non-negotiable.  Pulling them away from the wall will only make things worse.   It is the side-wall reflections, and in the case of the subs, the ceiling reflections that are causing problems in the mid-bass.

 

I may be able to improve performance by moving the MBMs, keeping them behind the sofa but moving them further out toward the edges.  I will do a lot more experiments along those lines once my software is working better.  I'm still planning to replace these whimpy Hsu MBMs with up to four ported D.O. AE TD10X units.  I have the drivers to do all four of them, but I'm leaning towards building only two and using the rest of the drivers up front.

 

If I use the TD10X up front instead, then I'll set them up in vertically aligned pairs, one on each side on top of the subs.  I'll put the mains on top of them, at approximately the same height as my center channel, which is on a shelf over the TV.   With all the DSP capability I have, this will effectively turn my mains into "2.5.5-ways" (3.25-ways?), or something like that.  Basically, the horns would cross to the TD12M at 900-1400 Hz (roughly).  Then the TD10Xs would kick in around 300-500 Hz to try to better shadow the seats that are physically much closer to the speaker.  Then the subs would join in somewhere around 150-250 Hz, to fill out the quasi-line source and reduce ceiling and floor reflections as much as possible.  The two MBMs behind the sofa would remain there to try to counteract the effects of the side-wall reflections.

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Have you tried out Vibsensor app yet, SME?

 

Tactile response is a thing now. :D

 

Not yet.  And I kind of doubt that measuring the couch tells us what we want to know.  In fact, I think my couch shakes and vibrates quite a bit less than it did with the old subs, and that's a good thing.  Now I feel much more tactile sensation from the sound itself.  It feels cleaner, faster, more precise, and more powerful.  Couch shaking seems kind of gimmicky by comparison.

 

My other big issue with measuring tactile sensation is my recent findings that the overall perceived quantity and quality of bass depends *enormously* on the coarse response shape (i.e. house curve or target curve) and balance, not just with the sub area but with the mains too.  As of yet, I'm not aware of a formula for figuring out the optimal shape in any given room, system, or even multi-sub EQ config.  My above plot shows that I have superbly smooth, nearly anechoic bass under 70 Hz, over a wide area.  Yet the results sounded and felt pretty blah without the last bit of tuning by ear (and feel).

 

So what I'm saying here is that psychoacoustic masking is a big deal, and it affects tactile sensation as well as hearing sensation.  Anything out of balance will tend to dominate perception causing an apparent weakening of the sound.  But when things are balanced, the brain perceives the entire bandwidth of big broadband transients, and they have maximum impact.  Indeed, when doing my tuning by ear, I'm paying attention to the tactile sensation as well as the sound.  I'm adjusting the relative balance of infra sound, deep bass, mid bass, and upper bass until I can clearly perceive their simultaneous contribution to the feel of kick drum and other impulse sounds.  I also have music with doubled or even tripled electronic basslines, and if things are just right, I can distinguish the bass playing at three separate octaves at the same time.  In classical music, the string bass often doubles the cello an octave below, and I can clearly hear that as well.

 

I guess if I were to want any improvement in tactile sensation, I wouldn't rule out supplementing the ULF a bit with Crowsons, but that would be very expensive and awkward with this couch.  I seriously don't think I'm missing much though.  The sound quality is unarguably the best I've heard anywhere.  Though, I haven't toured the AVSForum circuit yet.  :)

 

BTW, if any of you find yourself in Denver, feel free to send a private message.  I could probably set up time for a demo if it's not too late.  Don't expect me to run the subs 20 dB hot or anything.  This is a system focused on quality, first and foremost.

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I would be curious to see what your findings are for house curves at different listening levels for good impact.....My crowsons give me all the infrasound 'shake' (but none of the 'pressure/underwater' sensation) I lost from my last room, but I am missing some of the impact from my last room's final iteration, that had quite a good impulse response.  Much of that is due to the new room and utter lack of ceiling treatment.

 

JSS

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I would be curious to see what your findings are for house curves at different listening levels for good impact.....My crowsons give me all the infrasound 'shake' (but none of the 'pressure/underwater' sensation) I lost from my last room, but I am missing some of the impact from my last room's final iteration, that had quite a good impulse response.  Much of that is due to the new room and utter lack of ceiling treatment.

 

JSS

 

I wouldn't say the house curve is for different listening levels.  The house curve is for natural sounding bass at a reference listening level, where reference level should be assess by dialog loudness and not pink noise measurements.  And it probably shouldn't be called a house curve, but it effectively is when we have no idea why it sounds better than other options.

 

I think I have a method of systematically calibrating response of a well-behaved speaker above 120 Hz or so.  At least, it seems to work very satisfactorily for me, my speakers, and my room.  But I'm still at a loss as to what to do down below.  I may not be able to figure anything out until I can experiment in a wide variety of rooms, which could take a very long time.  As it is, I'm not entirely confident that I'm as balanced as I could be.  Content variation is likely a big confounding factor here, just like it is for ultra high frequencies.

 

An alternative option may be adjustable controls that are tailored to the problem.  With the help of software, perhaps an untrained listener could be guided through the process of optimizing the controls by listening to various test samples.  It'd be kind of the audio equivalent of a video test pattern used to calibrate video.

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Not yet.  And I kind of doubt that measuring the couch tells us what we want to know.  In fact, I think my couch shakes and vibrates quite a bit less than it did with the old subs, and that's a good thing.  Now I feel much more tactile sensation from the sound itself.  It feels cleaner, faster, more precise, and more powerful.  Couch shaking seems kind of gimmicky by comparison.

 

My other big issue with measuring tactile sensation is my recent findings that the overall perceived quantity and quality of bass depends *enormously* on the coarse response shape (i.e. house curve or target curve) and balance, not just with the sub area but with the mains too.  As of yet, I'm not aware of a formula for figuring out the optimal shape in any given room, system, or even multi-sub EQ config.  My above plot shows that I have superbly smooth, nearly anechoic bass under 70 Hz, over a wide area.  Yet the results sounded and felt pretty blah without the last bit of tuning by ear (and feel).

 

So what I'm saying here is that psychoacoustic masking is a big deal, and it affects tactile sensation as well as hearing sensation.  Anything out of balance will tend to dominate perception causing an apparent weakening of the sound.  But when things are balanced, the brain perceives the entire bandwidth of big broadband transients, and they have maximum impact.  Indeed, when doing my tuning by ear, I'm paying attention to the tactile sensation as well as the sound.  I'm adjusting the relative balance of infra sound, deep bass, mid bass, and upper bass until I can clearly perceive their simultaneous contribution to the feel of kick drum and other impulse sounds.  I also have music with doubled or even tripled electronic basslines, and if things are just right, I can distinguish the bass playing at three separate octaves at the same time.  In classical music, the string bass often doubles the cello an octave below, and I can clearly hear that as well.

 

I guess if I were to want any improvement in tactile sensation, I wouldn't rule out supplementing the ULF a bit with Crowsons, but that would be very expensive and awkward with this couch.  I seriously don't think I'm missing much though.  The sound quality is unarguably the best I've heard anywhere.  Though, I haven't toured the AVSForum circuit yet.  :)

 

BTW, if any of you find yourself in Denver, feel free to send a private message.  I could probably set up time for a demo if it's not too late.  Don't expect me to run the subs 20 dB hot or anything.  This is a system focused on quality, first and foremost.

 

"Not yet.  And I kind of doubt that measuring the couch tells us what we want to know.  In fact, I think my couch shakes and vibrates quite a bit less than it did with the old subs, and that's a good thing.  Now I feel much more tactile sensation from the sound itself.  It feels cleaner, faster, more precise, and more powerful.  Couch shaking seems kind of gimmicky by comparison."

 

More "couch shaking" isn't the point of suggesting the App to you, it was to see the shape of the tactile sensation. You say it feels "cleaner, faster, more precise and more powerful". Okay. That will show up on the app. Comparing it to what you had before would be useful data.

 

"I guess if I were to want any improvement in tactile sensation, I wouldn't rule out supplementing the ULF a bit with Crowsons, but that would be very expensive and awkward with this couch.  I seriously don't think I'm missing much though.  The sound quality is unarguably the best I've heard anywhere.  Though, I haven't toured the AVSForum circuit yet."

 

All power to you. I wasn't suggesting you improve it. Just measure it. No difference from frequency response. Maybe it might sound perfect but it's still good to measure.

 

"BTW, if any of you find yourself in Denver, feel free to send a private message.  I could probably set up time for a demo if it's not too late.  Don't expect me to run the subs 20 dB hot or anything.  This is a system focused on quality, first and foremost."

 

That's okay because I don't run my subs 20dB or... hot at all, afaik. People think of me as some sort of nutty basshead cartoon character or something but I like balance just like most people. I just like to retain a linear, clean, dynamic sound at spirited levels and I'm prepared to put the appropriate firepower in a room to do it. ;)

 

Thanks for the invite! I would love to! One day I'll have to make a road trip out that way.

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Oh yeah, I forgot to mention that I watched Star Wars: The Force Awakens with BEQ and flat response to 5 Hz, with bass played back more or less at reference.  That proved to be an excellent work-out for the system.  The amp got pushed to near its limit repeatedly but never clipped to my knowledge.  The subs never made any untoward sounds.  In fact, the sound remained subjectively very clean, even with violent levels of ULF going on.

 

I also did some testing with the famous "How to Train Your Dragon" crash scene.  With my current EQ config, I can't go beyond "-9 dB" or so without seeing "the orange (clip) lights" on the amp.  I didn't go much beyond there at all, but I didn't hear any unpleasant sounds when this was going on.  I think the amp lights up orange a bit before it actually clips when its getting a lot of ULF, but I don't know.

 

One thing I can't readily explain is that I seem to prefer these calibrated a few dB hotter than the old subs for the subjective quantity of bass.  Is it because their distortion is so low?  I don't know, but I do know that these sound and feel incredibly clean and powerful once they get above the masking thresholds.  Indeed, I'm surprised to be experiencing what I would describes as slam sensations rooted at deep bass frequencies.  I've generally thought of slam as being a 50 Hz+ sort of thing, but these seem to deliver the feeling a lot lower.  It also feels like a lot more tactile sensation comes from the air instead of the furniture.

 

Promising and impressive results after all the work put into the project.  I couldn't quickly find and answer, but are you currently running the SP2-12k off 120V or 240V power?

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Not yet.  And I kind of doubt that measuring the couch tells us what we want to know.  In fact, I think my couch shakes and vibrates quite a bit less than it did with the old subs, and that's a good thing.  Now I feel much more tactile sensation from the sound itself.  It feels cleaner, faster, more precise, and more powerful.  Couch shaking seems kind of gimmicky by comparison.

 

More "couch shaking" isn't the point of suggesting the App to you, it was to see the shape of the tactile sensation. You say it feels "cleaner, faster, more precise and more powerful". Okay. That will show up on the app. Comparing it to what you had before would be useful data.

 

I guess if I were to want any improvement in tactile sensation, I wouldn't rule out supplementing the ULF a bit with Crowsons, but that would be very expensive and awkward with this couch.  I seriously don't think I'm missing much though.  The sound quality is unarguably the best I've heard anywhere.  Though, I haven't toured the AVSForum circuit yet.

 

All power to you. I wasn't suggesting you improve it. Just measure it. No difference from frequency response. Maybe it might sound perfect but it's still good to measure.

 

BTW, if any of you find yourself in Denver, feel free to send a private message.  I could probably set up time for a demo if it's not too late.  Don't expect me to run the subs 20 dB hot or anything.  This is a system focused on quality, first and foremost.

 

That's okay because I don't run my subs 20dB or... hot at all, afaik. People think of me as some sort of nutty basshead cartoon character or something but I like balance just like most people. I just like to retain a linear, clean, dynamic sound at spirited levels and I'm prepared to put the appropriate firepower in a room to do it. ;)

 

Thanks for the invite! I would love to! One day I'll have to make a road trip out that way.

 

Hmm.  Too bad I didn't measure before.  Though like I said, there's a lot more going on with tactile sensation than couch vibration, so the vibsensor measurement is only going to tell part of the story.

 

You do inspire curiosity though.  I downloaded the app and will try to get a good measurement soon.  Hopefully the "full-band" pink noise in REW isn't filtered at 10 Hz, but I might have to do a bit more research on AVSForum or whatever.  Maybe I'll see some signs of life under 5 Hz?  My UMIK-1 is not calibrated below that point and may be lying when it shows my response dropping rapidly below there.

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Recent versions of REW (as in, the last year or so) have unfiltered noise. If you have an rpi lying around, I recommend using the app I wrote with an offboard sensor for greater accuracy.

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Promising and impressive results after all the work put into the project.  I couldn't quickly find and answer, but are you currently running the SP2-12k off 120V or 240V power?

 

Right now, I'm merely running with 120V power.  I do plan to upgrade to 240V, but at this point, I don't expect a big improvement.  Almost all the power gets used for ULF as it is, and I'm not sure I have any more clean excursion to work with here.  Too bad I don't have room for two more pairs.  :)

 

Out of curiosity, why do you ask?

Edited by SME

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sub-front-left-raw-2017-07-07.png

 

 

 

 

That is a lot of boost going in from 7-14Hz. That is definitely where your demands on the drivers and amps is going to be heaviest. Looks like a boundary related loss over that range for sure. At least it should cause a big tactile shake though. I'd bet that a vibration test picks up strong signals in that range.

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Recent versions of REW (as in, the last year or so) have unfiltered noise. If you have an rpi lying around, I recommend using the app I wrote with an offboard sensor for greater accuracy.

 

No RPI here, but obviously they aren't hard to come by.  I'll definitely consider your app if/when the time comes to optimize "couch vibration" response, like if I installed Crownsons.  But I have no particular plans to do so right now.

 

Here's what I captured using -15 dBFS full-band pink noise played on the front left and right channels together at reference level with the left and right speakers muted so only the subs play.  This is measured "as-calibrated" but without the "house curve" shelves:

 

sub-vib-psd-mlp-2017-07-10.png

 

It *looks* like it's filtered below 10 Hz, but I verified that the test signal extends below there.  As I said before, my suspended floor is pretty much a no-show in the single digits.  The PSD doesn't even show any activity at 5.5 Hz.  Though I've verified the existence of a very high Q floor-wobble resonance there.  The low teens response peaks at 12 Hz, but that's because my cal leaves the worst of the resonance at 11 Hz notched out.

 

Edit: The result here should be disregarded until I can re-do the measurement correctly.

Edited by SME
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That is a lot of boost going in from 7-14Hz. That is definitely where your demands on the drivers and amps is going to be heaviest. Looks like a boundary related loss over that range for sure. At least it should cause a big tactile shake though. I'd bet that a vibration test picks up strong signals in that range.

 

That's why I'm suggesting Vibsensor.

 

It might look awful in the frequency domain but at the seat you wouldn't know it.

 

D'youknowwhatImean? [/Jason Statham voice]

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