Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 481 - AVS | Home Theater Discussions And Reviews
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post #14401 of 14644 Old 04-02-2015, 07:51 PM
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Quote:
Originally Posted by lovingdvd View Post




This whole use CH1 vs CH2 vs HDMI 1 vs HDMI2 thing etc confuses me. I haven't used REW yet with HDMI (in the past always used an RCA output to one channel) so maybe it'll take some playing with it to get the hang of it. Earlier it was said in this thread that for multi-channel audio its best to use the C+Sub. I'm still confused why it's not best to use L+C+R+Sub since in my mind when watching a movie all those speakers are engaged at the same time, not just the center...? Also its confusing how we are supposed to get REW to output to all those speakers at the same time.
What is confusing? An HDMI audio connection from the PC to the AVR supports eight channels. HDMI1=left channel, HDMI2=right channel, HDMI3=center channel, HDMI4=LFE channel, etc.

REW can output to at most two channels at a time. So, in REW, select any two HDMI channels to send a signal to. If your speakers are set to small, any channel receiving a REW signal will also output the audio signal to the subwoofer channel below the speaker's crossover frequency. So, if you choose HDMI1 for REW output, you will really be sending a signal to left+sub, and HDMI2 will be right+sub, etc.

You cannot output to L+R+C+sub because that would require REW to output to three channels, which it cannot do.

And finally, it is your choice whether you output to L+R+sub, or C+sub. However, as explained a number of times before, mono bass is more likely to appear in the center channel, that's why it is important. That is not to say that measuring L+R+sub is not also important. Feel free to take as many measurements as you want, as long as you analyze them in the proper perspective.

Has this made it any clearer for you?
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post #14402 of 14644 Old 04-02-2015, 08:15 PM
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I am a little confused by the thought of using distance settings to compensate for FR issues.

I thought the process would be:

Set up speaker configuration in the processor. How many speakers, positions, maybe even size and crossover.

Measure distance to MLP. Put that into the AVR.

Adjust levels in the AVR. My processor has a self generated signal that is meant to be 75 dB at the MLP. So us and SPLIT meter to measure and adjust the Level control in the AVR.

Then at that point run some REW sweeps. And figure out what to do. As best I can figure this is either room treatments, EQ tweaks or maybe modifying crossovers.

It seems at this point that going back and adjusting distances to make a flatter FR could have unintended consequences in phase or waterfall or etc. All things I don't really understand.

Really just looking to understand why the distance tweak is the right first option for flattening out an FR...



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Originally Posted by Alan P View Post
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Originally Posted by MiniBones View Post
Gotcha. So given my situation that has no auto EQ...Just me, my limited intellect and experience, some equipment and this website.

I don't think I need to go the distance tweak route to end run the non-existent auto-EQ.


I think I first need to level everything and then measure FL, FR and C on their own with no XO. Just to see how they perform.

Then maybe a sub only measurement. Not really sure how to do that without using CH4 and the 10dB hot signal from REW. Any Advice? Or is this just a waste of time?

I think that will let me figure out a decent spot to cross over the FL, FR and C.

Then given a selected XO I can run CH1, 2 and 3 crossed over and see how the FR looks for the combined speaker + subs.

Once I have that data I don't really know what to do about corrections. I think I might rely on REW to do a room correction EQ calc and give me the right EQ information to enter into my CT-SSP. But perhaps there are some things I should do first.

Happy to hear all comments.

You will still benefit from the sub distance tweak...it's doubtful that you and a tape measure got it right either.

To measure sub only (and not use the LFE channel), you can output to a speaker and unplug that speaker from your AVR. I find it easier to just use the LFE channel and reduce the MV by 10db. However, with the LFE channel, you don't see what the crossover is doing to your sub's FR.
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post #14403 of 14644 Old 04-02-2015, 08:32 PM
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Quote:
Originally Posted by MiniBones View Post
I am a little confused by the thought of using distance settings to compensate for FR issues.

Really just looking to understand why the distance tweak is the right first option for flattening out an FR...
The sub distance tweak is only used to improve the crossover region. This is because of the special relationship between the mains and sub in this region (i.e. Both are playing the same frequency). The order of operations has been posted several times in the thread already:

1. Optimize speaker placement
2. Add room treatments
3. Apply EQ
4. Sub distance tweak (with or without EQ)

Don't overthink it...if you're worried about negative consequences of the tweak then just do a simple before/after measurement. There will always be tradeoffs for each step. You'll have to decide which ones you can personally live with in your room.

Last edited by jkasanic; 04-02-2015 at 08:35 PM.
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post #14404 of 14644 Old 04-02-2015, 08:43 PM
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Quote:
Originally Posted by MiniBones View Post
I am a little confused by the thought of using distance settings to compensate for FR issues.

I thought the process would be:

Set up speaker configuration in the processor. How many speakers, positions, maybe even size and crossover.

Measure distance to MLP. Put that into the AVR.

Adjust levels in the AVR. My processor has aY self generated signal that is meant to be 75 dB at the MLP. So us and SPLIT meter to measure and adjust the Level control in the AVR.

Then at that point run some REW sweeps. And figure out what to do. As best I can figure this is either room treatments, EQ tweaks or maybe modifying crossovers.

It seems at this point that going back and adjusting distances to make a flatter FR could have unintended consequences in phase or waterfall or etc. All things I don't really understand.

Really just looking to understand why the distance tweak is the right first option for flattening out an FR...
As Joe has said, the only changes to distances that have been recommended in this thread, AFAIK, is the sub tweak. Otherwise, speaker distances should be actual physical distances, and levels should be set to produce the same SPL from each speaker when measured at the MLP.

Of course, many of us use automated room correction technologies to set speaker distances and levels, and these technologies are amazingly accurate in this area. Are you doing this by hand?
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post #14405 of 14644 Old 04-02-2015, 08:54 PM
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Originally Posted by AustinJerry View Post
What is confusing? An HDMI audio connection from the PC to the AVR supports eight channels. HDMI1=left channel, HDMI2=right channel, HDMI3=center channel, HDMI4=LFE channel, etc...Has this made it any clearer for you?
Yes, thank you! I was getting confused because when I was reading HDMI1 vs HDMI2 etc here I was getting that confused with HDMI outputs to two different HDMI inputs on the prepro.
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post #14406 of 14644 Old 04-03-2015, 01:37 AM
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Originally Posted by toofast68 View Post
Ok here we go....
What's causing this?

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post #14407 of 14644 Old 04-03-2015, 05:44 AM
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Originally Posted by markus767 View Post
What's causing this?



So I honestly am not sure...but I am just learning all this stuff...could it be a bounce from the seats ? But I had them fairly well covered in blankets...
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post #14408 of 14644 Old 04-03-2015, 05:55 AM
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Originally Posted by lovingdvd View Post

Please tell me more about your bass traps? Floor to ceiling you already mentioned. How about their width? Are they sitting diagonal in the corners or are they a "rectangle" fit snug into the corners? Judging by your textbook waterfall I just may have to follow your lead!

Wow what can I saw. I'm no expert by far, but from what I've gathered your waterfall is textbook, or at least what could be the most reasonably expected output without a perfect room and lots of special treatments. Congrats! With your results so good, its a shame to use 450ms since it hides the excellent low decay times. Can you post another view of this using 250ms? It looks to me like all frequencies are decayed by 250 except 20 Hz which from what I've ready is not audible.

What are your plans for EQ? I think if you can take out the peak at 60 Hz (and perhaps at 25 Hz) and ease the dip at 75 Hz up a little you may be pretty darn close to perfect.
Bass traps are pink fluffy loosely stacked with "wires" in between layers to keep them non-compressed. They are rectangular, but not "stuffed" into the corner...I have columns on both sides of the screen that is roughly 30" deep by 20" wide. They are faced with GOM 701, there are a few inches around all corners to help a bit.


But honestly, it was only once I put the ceiling cloud and the rear traps that it all came together.


As for EQ, well for the moment I am on basic Audyssey XT (nearly the most basic one) - it really does not do well with the sub regions...but I am not sure moving up to XT32 is worth it until the new AVR wars get finalized...or I could go mini DSP for $100, but not sure how much I will get out of it.


Anyways....here is my 250 ms waterfall.


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post #14409 of 14644 Old 04-03-2015, 06:35 AM
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Originally Posted by toofast68 View Post
So I honestly am not sure...but I am just learning all this stuff...could it be a bounce from the seats ? But I had them fairly well covered in blankets...
Not likely due to seats...is this with the center channel as shown in your pic or did you already pull it forward to avoid the issue with the box it's sitting on (a more likely culprit)?
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post #14410 of 14644 Old 04-03-2015, 06:43 AM
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Originally Posted by jkasanic View Post
Not likely due to seats...is this with the center channel as shown in your pic or did you already pull it forward to avoid the issue with the box it's sitting on (a more likely culprit)?

So I have not been back in town to do that, won't be till next week. I was planning on building a center stand (to match my wides) - I think I will tackle that first and then rerun.


Below is the before cloud and after (this is when I think the Center was up further, and it slipped down and I did not realize it)


However, I just realized something else...the no cloud sweep, was with the SUBS turned OFF, the post cloud sweep is with the SUBS back on...I am not a pro of ETC by all means...could that be it, and if so is that normal, or should I only be ETCing with the SUBS off ?





Then of course, post cloud.


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post #14411 of 14644 Old 04-03-2015, 06:51 AM
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Just thank. No system on this one. I have a denon with audessy upstairs and get how it works. Downstairs in the theatre is the classe receiver and no software. Doing it the old fashioned way!


Quote:
Originally Posted by AustinJerry View Post
Quote:
Originally Posted by MiniBones View Post
I am a little confused by the thought of using distance settings to compensate for FR issues.

I thought the process would be:

Set up speaker configuration in the processor. How many speakers, positions, maybe even size and crossover.

Measure distance to MLP. Put that into the AVR.

Adjust levels in the AVR. My processor has aY self generated signal that is meant to be 75 dB at the MLP. So us and SPLIT meter to measure and adjust the Level control in the AVR.

Then at that point run some REW sweeps. And figure out what to do. As best I can figure this is either room treatments, EQ tweaks or maybe modifying crossovers.

It seems at this point that going back and adjusting distances to make a flatter FR could have unintended consequences in phase or waterfall or etc. All things I don't really understand.

Really just looking to understand why the distance tweak is the right first option for flattening out an FR...
As Joe has said, the only changes to distances that have been recommended in this thread, AFAIK, is the sub tweak. Otherwise, speaker distances should be actual physical distances, and levels should be set to produce the same SPL from each speaker when measured at the MLP.

Of course, many of us use automated room correction technologies to set speaker distances and levels, and these technologies are amazingly accurate in this area. Are you doing this by hand?
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post #14412 of 14644 Old 04-03-2015, 07:18 AM
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Originally Posted by toofast68 View Post
...or I could go mini DSP for $100, but not sure how much I will get out of it
I used to use of the these (and paid much less for it):
http://www.musicgoroundgreenfield.co...FVQ2gQodKzwAOQ

Did you really need to quote that entire post in your reply?
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post #14413 of 14644 Old 04-03-2015, 07:24 AM
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Does that sub distance tweak process work by changing the phase slightly of the sub in order to mix better with the mains? Or is it the amount of delay only? Or is that the same thing?
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post #14414 of 14644 Old 04-03-2015, 07:24 AM
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Originally Posted by LastButNotLeast View Post
I used to use of the these (and paid much less for it):
http://www.musicgoroundgreenfield.co...FVQ2gQodKzwAOQ
Man, I have so much to learn....thanks now you are going to make my in laws mad as I research over the holiday vs. doing son in law type things.


However it is only $25 less after you factor in freight...decisions...decisions...
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post #14415 of 14644 Old 04-03-2015, 07:25 AM
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Does that sub distance tweak process work by changing the phase slightly of the sub in order to mix better with the mains? Or is it the amount of delay only? Or is that the same thing?
Crude....I think it is delay, but others will chime in...as my sub is still at 0 phase.
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post #14416 of 14644 Old 04-03-2015, 07:28 AM
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Crude....I think it is delay, but others will chime in...as my sub is still at 0 phase.
I was thinking along the lines of phase of the sub sound as related to the phase of the sound from the mains as they both arrive at the MLP.
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post #14417 of 14644 Old 04-03-2015, 07:46 AM
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Originally Posted by toofast68 View Post
As for EQ, well for the moment I am on basic Audyssey XT (nearly the most basic one) - it really does not do well with the sub regions...but I am not sure moving up to XT32 is worth it until the new AVR wars get finalized...or I could go mini DSP for $100, but not sure how much I will get out of it.
I have XT too, which did a terrible job in bass eq. You can go the minidsp route and tweak everything yourself, else you can get dspeaker antimode and let it auto-eq it flat for you. Audyssey is a gamble. Sometimes it work, sometimes it doesn't. (HTS XT32 measurement)
I have the antimode and it did an awesome job. You can check out my graph here.

Last edited by Skylinestar; 04-03-2015 at 07:52 AM.
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post #14418 of 14644 Old 04-03-2015, 08:00 AM
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Originally Posted by toofast68 View Post
Bass traps are pink fluffy loosely stacked with "wires" in between layers to keep them non-compressed. They are rectangular, but not "stuffed" into the corner...I have columns on both sides of the screen that is roughly 30" deep by 20" wide. They are faced with GOM 701, there are a few inches around all corners to help a bit.
I can't quite picture what you are saying about the bass traps? Are they sitting caddy-corner like a giant rectangle angled at the corner? Or are the more like a 18"x18" square sitting flush in the corners totally filling it? Maybe you can post a picture? And can you elaborate more on how you build them, what insulation you used exactly, etc?

Quote:
But honestly, it was only once I put the ceiling cloud and the rear traps that it all came together.
Can you remind us what you did for your ceiling cloud exactly? I am sure it is helping a lot, but unlikely to be the reason your waterfall is so excellent - unless your ceiling cloud is several inches thick it would not be helping much with decay time in these frequencies below 100 Hz or so.

If a sweep sounds clean and smooth it may not be worth the time and expense at this point to get set up with EQ. There's not a lot to do and the difference may not be noticeable or enough to make it worth it, until a latter time when it makes sense to upgrade your AVR/components for other reasons (Atmos etc).

Regarding Markus' question on what is causing that reflection shown on the ETC - have you tried the string test? Its explained in Jerry's REW guide in his sig. That should help you narrow down the possible locations. Let us know what you find.
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post #14419 of 14644 Old 04-03-2015, 08:29 AM
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Originally Posted by lovingdvd View Post

Regarding Markus' question on what is causing that reflection shown on the ETC - have you tried the string test? Its explained in Jerry's REW guide in his sig. That should help you narrow down the possible locations. Let us know what you find.
With a reflection that close to either the mic or the speaker, the "blocking method" is likely to be more useful than the string technique.
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post #14420 of 14644 Old 04-03-2015, 09:12 AM
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Originally Posted by lovingdvd View Post
I can't quite picture what you are saying about the bass traps? Are they sitting caddy-corner like a giant rectangle angled at the corner? Or are the more like a 18"x18" square sitting flush in the corners totally filling it? Maybe you can post a picture? And can you elaborate more on how you build them, what insulation you used exactly, etc?

Can you remind us what you did for your ceiling cloud exactly? I am sure it is helping a lot, but unlikely to be the reason your waterfall is so excellent - unless your ceiling cloud is several inches thick it would not be helping much with decay time in these frequencies below 100 Hz or so.

Regarding Markus' question on what is causing that reflection shown on the ETC - have you tried the string test? Its explained in Jerry's REW guide in his sig. That should help you narrow down the possible locations. Let us know what you find.
Traps - construction photo and then after photo with same area circled in red. The traps run floor to ceiling, filled with Pink Fluffy R19 - stacked all the way up. 2 sides or drywall. The back (inside of trap) has some air space, then 4" of Rockwool, then 3" of air gap.










Ceiling Cloud:


I have no pictures, but it is 10' x 2.5' of 3.5" thick Roxul Wool, with a 6" or so air gap to the ceiling...so I think the Waterfall is really benefiting from that. The back traps are 3.5" same material with about a 2.5" air space behind.


As for the ETC, when I get back I will dig into the string and blocking tests....


Hope this helps!
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post #14421 of 14644 Old 04-03-2015, 11:31 AM
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Quote:
Originally Posted by lovingdvd View Post

Regarding Markus' question on what is causing that reflection shown on the ETC - have you tried the string test? Its explained in Jerry's REW guide in his sig. That should help you narrow down the possible locations. Let us know what you find.
With a reflection that close to either the mic or the speaker, the "blocking method" is likely to be more useful than the string technique.
What's the distance of the reflection? I wasn't able to see it.
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post #14422 of 14644 Old 04-03-2015, 11:34 AM
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What's the distance of the reflection? I wasn't able to see it.
There is a method in REW that allows you to show the distance. It is described in the Guide, and is key to the string technique.
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post #14423 of 14644 Old 04-03-2015, 12:23 PM
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Headroom

Hello Jerry,
My UMIK-1 has a 18dB gain structure. When I take sweeps at your reco'd 90dB level I'm really close to running out of headroom and on some occasions clipping has occured. Is there a work around for this, lowering the 90dB (MV of AVR). I used the REW SPL meter and pink noise generator to get the 90dB on the SPL meter to take my sweeps, but I am really close to clipping with most sweeps, especially at 15-300Hz? Thanks, any help would be appreciated. I'm finally taking measurements because of your guide.
Sincerely, Jeffrey
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Hello Jerry,
My UMIK-1 has a 18dB gain structure. When I take sweeps at your reco'd 90dB level I'm really close to running out of headroom and on some occasions clipping has occured. Is there a work around for this, lowering the 90dB (MV of AVR). I used the REW SPL meter and pink noise generator to get the 90dB on the SPL meter to take my sweeps, but I am really close to clipping with most sweeps, especially at 15-300Hz? Thanks, any help would be appreciated. I'm finally taking measurements because of your guide.
Sincerely, Jeffrey
I would simply run the sweeps at a level that doesn't clip, Jeffrey. Give it a try.
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post #14425 of 14644 Old 04-03-2015, 01:27 PM
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Does that sub distance tweak process work by changing the phase slightly of the sub in order to mix better with the mains? Or is it the amount of delay only? Or is that the same thing?
There's a discussion in this very thread about the relationship between phase and delay.

hth
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post #14426 of 14644 Old 04-03-2015, 01:52 PM
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There's a discussion in this very thread about the relationship between phase and delay.

hth
Thank you for that link - that is pretty much how I was thinking that they had to somehow related.


So correct me if I am still misunderstanding - in the sub distance tweak you are adjusting the delay, but the effect it can have on smoothing the FR at the XO (and around it) has to do with the relationship between delay and phase (ie. sub cone moving sooner or later) with respect to the signal from the main speakers.


If the sub is exactly in phase with the mains at the MLP there may be a peak in the FR at some particular frequency because everything is pushing and pulling together, and if the sub is 180 out of phase with the mains that may cause a dip? You would likely want it somewhere in between?


Bill
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post #14427 of 14644 Old 04-03-2015, 01:54 PM
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I guess I need to read the whole thread! I read the first 80 or so pages, then skipped to page 300. I am to 318 now


Just started following the end of the thread a few weeks ago as I am still catching up.
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post #14428 of 14644 Old 04-03-2015, 03:51 PM
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Those of you who know me recognize that I am always tweaking my configuration, looking for the last ounce of performance. The purpose of this post is to explore a sub configuration option, and get feedback from the experts here.

I have four subs. Two are on the front wall, positioned left and right, equidistant from the MLP at 12ft. The other two subs are on the back wall behind the MLP, positioned next to each other at 3ft from the MLP. All four subs are on the same MiniDSP 2x4 sub channel, documented in the procedure linked in my sig.

Here is the question on which I need feedback. Currently, the four subs are gain-matched, with the gain setting adjusted to produce a combined output at the MLP optimized for the input channel on the DDRC-88A (approximately 75dB). If I measure the front sub pair from the MLP, they measure 67dB. The rear sub pair measures 72dB. So, one way to look at it is the rear sub pair is "contributing" more to the combined output than the from two subs.

An alternate approach would be to adjust the gain on the subs so that each sub pair measures the same at the MLP. This would mean the gain on the rear subs would be lower than the gain on the front subs. But the combined output would still be the same, i.e. 75dB. Some would call this "level matching", although each sub pair would be gain-matched.

Here is the question. Should the four subs be gain-matched like they are currently configured, or should they be level-matched as in the alternate configuration, or will either configuration provide similar results, i.e. who cares?
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post #14429 of 14644 Old 04-03-2015, 06:11 PM
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Quote:
Originally Posted by AustinJerry View Post
I would simply run the sweeps at a level that doesn't clip, Jeffrey. Give it a try.
Thanks Jerry, I kind of figured that but wanted to clarify with you prior to doing so. Great question you asked above about the configuration of your four subs, very interesting and looking forward to the other's replies. I would go out on a limb and say option two and don't think either way would really matter. Where did that come from???? Thanks again.
Cheers Jeffrey
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post #14430 of 14644 Old 04-03-2015, 06:23 PM
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Not interested in stacking them all behind you?

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Did you really need to quote that entire post in your reply?
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