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post #3151 of 3170 Old 04-11-2015, 08:35 AM - Thread Starter
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Quote:
Originally Posted by coolrda View Post
I'm wrong on the 1/4 wave. The correct answer is 1/2 or less then half a wavelength. Heres a post explaining it by LTD02 on one of my builds from three years back.



"My rooms dimensions are 18ft x 19ft x 8ft."

"I measured room gain by comparing the Winisd graph against actual in room via the OmniMic and RG starts at +1db@20hz and increases at 10db per octave. It's +11db@10hz and +21db@5hz. Room gain is more than I expected, but I wish it started an octave higher."

pressure vessel gain kicks in when the long dimension of the room is less than 1/2 the wavelength at the critical frequency.

long dimension of the room = (H^2 + W^2 + D^2)^0.5 = (8^2 + 19^2 + 18^2)^0.5 = (64+361+324)^0.5 = 749^0.5 = 27.37 ft.

27.37 is the half wavelength, for the full wavelength multiply by 2 = 54.74 ft.

1130(ft./s) / 54.74 ft. = 20.64 (1/s) = 20.64 hz

the theoretical gain is 12db per octave, but that is if you are losing nothing to wall flexing, etc.

so your room is performing pretty much exactly according to theory.


Using a frequency/wavelength calculator my PVG with a long dimension of 15'4"X11'x9' starts around 22hz, I think which shows on the graph. This is where room gain begins and where phasing's effect ends. I have about the same PVG as room 1(19x18x8) in my current room, room 3{15'4"x11'x9'). I believe room 2 measured the same as well. So while TA/phase/distance can have a drastic effect above PVG it has none below. An average rooms PVG start point is around where ULF starts as well. I've seen this for years looking at the graphs but just never thought of the correlation of ULF and Phase. I think this is why Bossobass, years ago, always recommended sealed sub systems in sealed rooms. The subs 12db an octave rolloff matches perfectly with PVG's 12db gains per octave theoretically giving one a flat in room response to 5hz or lower. You still have to eq someway those freqs above PVG's start point. Your 16db loss from time misalignment above your PVG start point has zero db loss below, hence no change to your vibrometer reading. Then when you compensate by raising the sub level +16db, ULF or below PVG start point will be thunderous. Sound waves are phase dependent only above PVG start point. That how I interpret the graphs. I may be way off base here.
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Originally Posted by coolrda View Post
Time alignment should have zero effect from the 1/2 wavelength of the long dimension and rise to to have max effect at frequency of full wavelength of long dimension and all freqs above, in effect, a zero null to max null at an octave above it. Those dimensions make up the room nodes that wreak havoc with our rooms. See above posts last sentence for disclaimer if i"m
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Heres another post by Mark Seaton about a decade back on another forum.

"There are changes below where a 1/2 wavelength won't "fit" in the room, usually defined by the longest dimension, top-to-bottom of opposite corners. Below this point you no longer see modal behavior, problems, or variations. What you do see is a gain in LF output for a given subwoofer output. So in fact the result is the opposite: More output, less distortion. In simplest terms you transition to a mode of pressure modulation, where you are basically modulating the pressure in the entire room. Remember that our ears react to air pressure modulations and it doesn't matter what causes the level of modulation, since the observer (us in this case) is exposed to the same changes in pressure as if they were outdoors."
Here is an example of how changing phase impacts SPL significantly less below a certain frequency in my room.


In this example, I'm adjusting the phase of my FTW21s from 0 to 180 degrees, and then back.

You can see that above 20hz, the phase significantly impacts SPL. From 10hz to 20hz, the change is a max of 2-3db. Below 10hz, there is no change.

Port tune of the FV15HP is ~12hz, but believe there is a hpf at 14hz. As you can see, not a whole lot of variance in SPL at or below tune. Given @coolrda sources above, in my room it does appear that the common "phase issues" because of mixing ported and sealed is not really an impact at all.
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post #3152 of 3170 Old 04-11-2015, 11:32 AM
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I have been mixing sealed and ported for 3-4 years now in different room with good results. I brought an Omnimic in Dec. to prove it to myself, lol.
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post #3153 of 3170 Old 04-11-2015, 11:43 AM - Thread Starter
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I have been mixing sealed and ported for 3-4 years now in different room with good results. I brought an Omnimic in Dec. to prove it to myself, lol.
I believe you mentioned that your room behaves similarly in that below a certain freq, adjusting phase has little impact on the response?
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post #3154 of 3170 Old 04-11-2015, 11:59 AM
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Can the vibration app be calibrated somehow, I doubt anyone has the instrument to do this though, as not all phones accelerometer will have had the same tolerances coming out of the shop?
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post #3155 of 3170 Old 04-11-2015, 05:09 PM
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Originally Posted by dominguez1 View Post
I believe you mentioned that your room behaves similarly in that below a certain freq, adjusting phase has little impact on the response?
True, three of the subs have a 0 phase setting and the fourth on is at 180. It is a little odd that one rear is 0 and one 180 but, this gives the most even listening level in the room.
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post #3156 of 3170 Old 04-11-2015, 07:31 PM
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Originally Posted by dominguez1 View Post
@coolrda , can you post the PSD graphs (2x) of just the rear subs inverted vs not inverted?

When inverted, you mentioned that it sucked the SPL out of the room. Did you see that on the omnimic as well?

My point is, that if there was a reduction in SPL, but the PSDs look similar, then PVL must be increasing the sound intensity to produce similar levels.
Heres the graphs.





I pretty much observed the same thing as you did in your video. I'll do some more testing tonight and tomorrow.
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post #3157 of 3170 Old 04-11-2015, 07:51 PM
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Looking at those graphs while reading the DB Forum thread on the same topic leads me to believe that the relationship of SPL and PVL changes at the point where room gain starts. The graph shows the drop in vibration intensity when the rears are inverted. That would also explains why velocity follows the FR then they go their separate way at the long dimension. I want to start testing with all subs straight up with no delay and test that out more. And also work on the main/front sub integration which I haven't dealt with as well as using the miniDSP eq.
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post #3158 of 3170 Old 04-12-2015, 02:05 PM - Thread Starter
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As the image above illustrates, when you had your rear subs in phase, there was more vibration at 30hz. However, when you inverted them, there was a drop in vibration; likely because SPL decreased as a result of the phase shift.

However, at 25hz, you can see that the Vibration increased on the Z axis (blue), but also pretty significantly at the Y axis (red). My hypothesis is that SPL either stayed the same or reduced at 25hz, but the out of phase condition increased PVL and thus Sound Intensity. It didn't behave this way at 30hz because the 1/2 wavelength 'fit' in the room. Whereas at 25hz, the 1/2 wavelength did not; thus reducing the SPL impact that running out of phase would normally have.

@coolrda , do you know what SPL was doing at these frequencies comparatively?
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post #3159 of 3170 Old 04-12-2015, 10:53 PM
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Quote:
Originally Posted by dominguez1 View Post


As the image above illustrates, when you had your rear subs in phase, there was more vibration at 30hz. However, when you inverted them, there was a drop in vibration; likely because SPL decreased as a result of the phase shift.

However, at 25hz, you can see that the Vibration increased on the Z axis (blue), but also pretty significantly at the Y axis (red). My hypothesis is that SPL either stayed the same or reduced at 25hz, but the out of phase condition increased PVL and thus Sound Intensity. It didn't behave this way at 30hz because the 1/2 wavelength 'fit' in the room. Whereas at 25hz, the 1/2 wavelength did not; thus reducing the SPL impact that running out of phase would normally have.

@coolrda , do you know what SPL was doing at these frequencies comparatively?
Very interesting observation Dom. I think your on to something there. I'll look for the Omnimic graphs. Actually I'll rerun those test and document it better. After reading yours and OKV's comments about increasing PVL, I'm going to explore the out of phase properties and how it all measures out. For instance running all subs without time alignment and then comparing Frequency and Tactile responses without EQing. I didn't get a chance to do any testing today like I had hoped. I'm intrigued by this. If inverting the rear subs not only isn't detrimental to frequencies below the transfer function but actually increases tactile response, my interest is piqued.
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post #3160 of 3170 Old 04-13-2015, 10:14 AM
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Originally Posted by DotJun View Post
Can the vibration app be calibrated somehow, I doubt anyone has the instrument to do this though, as not all phones accelerometer will have had the same tolerances coming out of the shop?
Not that I know of. I have an iPhone 5s, 6, 6+ and several generations of iPads so I was going to try them for comparison. I'm not sure that matters with this type of testing. While that is important in component testing, we are testing tactile/vibrational response of different media/substrate, as well as, how your LF and ULF response coincides with your LF and ULF tactile response. We have a hypothesis that we are trying to prove and one way to go about it is testing and documenting and more testing and documenting. If its repeatable then we may be on to something even if we don't know what that is or understand it right now. Thats why I try to put as much info as possible on these sample. Even if my accelerometer isn't perfectly calibrated ts the same unit used in all my test runs. So any variation that shows up is nullified. Now I may not be able to compare my data numbers with Dom's or anyone else posting theirs, but I bet the patterns will match. So IOW, in said room with front only or front and rear sub arrays or on concrete or riser or suspended floor we will have some idea, some definitive answers of how to tune for a smooth flat frequency AND tactile response, or if thats even possible.
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post #3161 of 3170 Old 04-16-2015, 04:26 PM
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Just a quick update. Took a couple runs on Monday, then spent a great deal of time then and last night trying different phase and eq options. I like how Omnimic Can auto EQ then upload file as REW and implement the biquads into the minidsp. It's easy once you get the hang of it. I think I still prefer Audyssey over the minidsp for EQ. Though I didn't spend much time taking tactile measurements I did take 3 runs each of the subs time aligned and without. As Dom demonstrated at the beginning of this thread there was no real difference in the test runs. They were repeatable and tested the same. You can see ever so slight the advantage to time aligning the subs as far as tactile response of sine waves goes. Tones used were 16-17-18-19-20-25-30-35-40hz.







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post #3162 of 3170 Old 04-16-2015, 07:18 PM
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Dom, time for an update on the next go round. I added two Dayton Ultimax 18 in. sealed subs in 4 ft. cubic boxes and room size 4300 cu ft. The sub will be stacked so, I will have the basically three dual cab subs. These subs will be paired with my 2 vented 18 in. subs and 8 Aura pro shakers. Six Ultimax in sealed boxes and two in vented boxes Thanks!
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post #3163 of 3170 Old 04-17-2015, 07:13 PM
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Dom, time for an update on the next go round. I added two Dayton Ultimax 18 in. sealed subs in 4 ft. cubic boxes and room size 4300 cu ft. The sub will be stacked so, I will have the basically three dual cab subs. These subs will be paired with my 2 vented 18 in. subs and 8 Aura pro shakers. Six Ultimax in sealed boxes and two in vented boxes Thanks!

I would love to come over to your house and watch a IMAX movie of the shuttle launch.


SOUND: Marantz AV-7702 Pre/Pro, McIntosh MC1706 Amp,
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post #3164 of 3170 Old 04-17-2015, 07:35 PM
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Thanks!
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post #3165 of 3170 Old Yesterday, 09:12 AM - Thread Starter
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Just a quick update. Took a couple runs on Monday, then spent a great deal of time then and last night trying different phase and eq options. I like how Omnimic Can auto EQ then upload file as REW and implement the biquads into the minidsp. It's easy once you get the hang of it. I think I still prefer Audyssey over the minidsp for EQ. Though I didn't spend much time taking tactile measurements I did take 3 runs each of the subs time aligned and without. As Dom demonstrated at the beginning of this thread there was no real difference in the test runs. They were repeatable and tested the same. You can see ever so slight the advantage to time aligning the subs as far as tactile response of sine waves goes. Tones used were 16-17-18-19-20-25-30-35-40hz.







@coolrda , this is a great test!

So, at least for sine waves, Time Alignment wasn't that significant of an impact, but nonetheless, it did improve! With complex content, I'm sure TA would have a bigger overall impact than what is showing on the vibration meter...perhaps 'tighter' and more dynamic feeling?

What were your subjective observations for TA vs non-TA? It would also be interesting to see how much difference it would be based upon how 'un-aligned' you are (e.g. how the tactile response varies based on the sub distance in your AVR/EQ relative to the actual physical distance. How much weaker is the impact the further off you are?)
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post #3166 of 3170 Old Yesterday, 09:13 AM - Thread Starter
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Dom, time for an update on the next go round. I added two Dayton Ultimax 18 in. sealed subs in 4 ft. cubic boxes and room size 4300 cu ft. The sub will be stacked so, I will have the basically three dual cab subs. These subs will be paired with my 2 vented 18 in. subs and 8 Aura pro shakers. Six Ultimax in sealed boxes and two in vented boxes Thanks!
Nice! You're addicted my friend!

How much did that improve your ULF card? What are you using for power? inuke6k?
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post #3167 of 3170 Old Today, 10:49 AM
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These will be stacked and I will use an I Nuke 3000 DSP rated at 3000 watts bridge at 4 ohoms. I already have this amp but, most likely get another 6000 DSP. The DYI subs have been painted and will go into the system tomorrow.

The new score should be 6.6 @ 10 & 12 Hz. I have not figured it for the other frequencies but, I was already at a 5 star rating. The room is also smaller and need to be factored into the score.
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post #3168 of 3170 Old Today, 02:33 PM
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Originally Posted by dominguez1 View Post
@coolrda , this is a great test!

So, at least for sine waves, Time Alignment wasn't that significant of an impact, but nonetheless, it did improve! With complex content, I'm sure TA would have a bigger overall impact than what is showing on the vibration meter...perhaps 'tighter' and more dynamic feeling?

What were your subjective observations for TA vs non-TA? It would also be interesting to see how much difference it would be based upon how 'un-aligned' you are (e.g. how the tactile response varies based on the sub distance in your AVR/EQ relative to the actual physical distance. How much weaker is the impact the further off you are?)
Yes, With multiple subs TA gives you a tighter, quicker and more dynamic tactile feel. Having front and rear sub arrays TA has much less effect though. For instance my front outside subs are set at 0.0ms and fronts inside subs have a delay of 0.58ms. So theres very little difference. Likewise the rear bottom subs are 6.5ms and the top rear subs are 7.5ms delay. So while a minidsp, or like controller, with control over each sub/subs individually is nice its not a big deal. But you must have separate control over front and rear arrays as far as TA goes. Any receiver or preamp with dual sub out should handle this fine. I'll test some more with different distance settings and post.
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post #3169 of 3170 Old Today, 06:49 PM - Thread Starter
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But you must have separate control over front and rear arrays as far as TA goes.
Hmmm...I do not. I currently only have the capability to change distance with my AVR (only 1 sub out). I use the distance on the AVR to help smooth the crossover frequencies with my center channel.

I'm guessing my time alignment can certainly be optimized. I have analog EQs (2x eD eQ.2) between the AVR and both front and rear subs, but it only has a phase dial and no distance setting.

Guess I won't be able to TA the front and rears separately without getting a new AVR or minidsp?
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Hmmm...I do not. I currently only have the capability to change distance with my AVR (only 1 sub out). I use the distance on the AVR to help smooth the crossover frequencies with my center channel.

I'm guessing my time alignment can certainly be optimized. I have analog EQs (2x eD eQ.2) between the AVR and both front and rear subs, but it only has a phase dial and no distance setting.

Guess I won't be able to TA the front and rears separately without getting a new AVR or minidsp?
My dilemma as well. My almost 8 year old Onkyo preamp is way beyond its expiration date which has necessitated several work arounds. While it decodes all the 7.1 formats it doesn't pass 3D or 4K so I had to buy an external switcher. That was an ordeal as I had to go thru several different models to find one that worked ok. Then I replaced an old BFD with a MiniDSP which I knew about the 0.9V input and output issue when running prosound amps but never thought about it with consumer grade gear. After hearing some chatter the last couple days about the minidsp clipping the inputs on Interstellar I did some additional testing. I never thought that it would be an issue driving the Emotiva amps that I'm using presently due to the EP4000/minidsp incompatibility issues. However the first gen XPA5 needs 1.25v to reach max wattage. I assume the minidsp is a hard cap at .9v which means you would have to throw a voltage meter on the sub outs to make sure you stayed inbounds. If the input doesn't get you by clipping, the outputs will run out before reaching max wattage, sometimes by a substantial amount. Who wants to leave even 1db on the table, let alone 10 or 20. So I loaded up Interstellar and set my Fluke 17 DMM to rec max voltage. Using the clip at the 2:18 mark which seems to be the loudest part of the movie, I made a dozen test runs to see what the voltage output of the Onkyo looked like. On all runs the peak voltage hit was at 2:19:26. I believe this is the high peak in the movie. Its also where my back subs tapped the back plate rather severely right before I was about to tapout myself, while watching with a MV of -8db. This scene is ruthless. My subs are set at -7.5db which is the auto setup setting. So while I knew I couldn't reach max performance with the minidsp in the chain, I needed to know how far I could go, how many DB's was I forfeiting with the minidsp in the loop.

Heres the what the tests revealed.



I was obvious severely clipping the inputs at a MV of -8db. How much am I losing because of the .9v output cap?



This is the volume needed to use the amp to its full potential. A 3db loss is unacceptable. The unbalanced minidsp should be avoided at all costs. If you can't drive an Emotive with its high gain stage, its an unusable product. Maybe a commercial sub would work, I don't know. I'll work around this issue by running the front array straight off the preamp then the rears thru the dsp for the purpose of TAing. that'll help a little while I wait on the DTS:X preamps to come to market. I may even go back to a receiver.
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