Two Subs...Gain Matching vs Level Matching - Page 8 - AVS Forum
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post #211 of 222 Old 08-03-2014, 05:31 PM
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Originally Posted by caloyzki View Post
Hi Craig. What about if i have two mismatched sub? Can i stil do like what you said above?thanks.
You can really only "gain-match" subs that have identical gain structures. IOW, only identical subs can realistically be gain-matched.

If you have non-identical subs, you're probably better off using some variation of the Geddes technique of subwoofer integration:
https://mehlau.net/audio/multisub_geddes/

Good luck.

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post #212 of 222 Old 08-03-2014, 05:39 PM
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Originally Posted by ahblaza View Post
Thank you Craig for the detailed and informative reply, I feel a little better now and not so intimidated by all of this, I can't convey my appreciation for all that you have done, again many thanks my friend.
Sincerely, Jeffrey
You're welcome of course. It's what this forum is all about!

Good luck with your subwoofer integration efforts!!!

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post #213 of 222 Old 08-03-2014, 05:53 PM
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Originally Posted by craig john View Post
You're welcome of course. It's what this forum is all about!

Good luck with your subwoofer integration efforts!!!

Craig

Thank you of course, I will let you know how things turned out, I decided to unstack the four subs, two in each front L&R corners and spread them out as you said, maybe two near field behind PLP and two up front in each corner after gain matching with sub's on their sides and mic 2' from center of driver. It's going to be time consuming and a little work but I believe it will be well worth it. Thanks again Craig. Not all forums are equal my friend, AVS is unique because of people like your self willing to help the uninformed.

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post #214 of 222 Old 08-03-2014, 07:20 PM
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Originally Posted by ahblaza View Post
Thank you of course, I will let you know how things turned out, I decided to unstack the four subs, two in each front L&R corners and spread them out as you said, maybe two near field behind PLP and two up front in each corner after gain matching with sub's on their sides and mic 2' from center of driver. It's going to be time consuming and a little work but I believe it will be well worth it. Thanks again Craig. Not all forums are equal my friend, AVS is unique because of people like your self willing to help the uninformed.
Distributed subs will virtually always result in better FR across a wider listening area than co-located subs. They will give up some max output/headroom, but IMO, that is a worthwhile sacrifice for better "sound quality" across more listening positions. This is especially true if you have more than enough output for your listening preferences. When one has 4 subs, MOST people will have all the output capability they'll ever need. At that point, better FR becomes the more important priority.

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post #215 of 222 Old 08-05-2014, 01:55 PM
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Originally Posted by craig john View Post
That tone should work. It's generally a 40 to 80 Hz "noise" tone. As long as you use the same tone, at the same level, for all the subs, it'll be fine.


If you have 4 identical subs, you want to use a level for *each* sub that results in a *combined* level of 72 to 78 dB when all the subs are placed back in their in-room positions. This will allow the combined subwoofer system to be properly calibrated with the speakers within the range of most receivers and pre/pro's. More below...


In my room, I find that a nearfield setting, (with the mic 2" from the middle of the driver), of 88 dB results in a combined level of 76 dB when each of the subs is placed back in its' in-room position. However, I have 3 dual opposed subs, (6, 15" drivers in 3 cabinets), distributed unevenly around my room. That same 88 dB setting may, or may not, work for you with 4 downfiring subs, and without knowing their in-room placements.

My suggestion for you is to start by having all the subs in their in-room positions, set them all to the same gain setting, and then measure their combined output at the Primary Listening Position, (PLP). If they're higher than 78 dB, lower them all the same amount until the combined SPL reads 72 - 78 dB. If they're lower than 78 dB, raise them all the same amount until the combined SPL reads 72 - 78 dB. If they are all set to the same gain setting, and you're confident that the identical gain setting results in them being gain-matched, you're done. However, some subs will have variations in the gain at identical gain settings on the amps. In that case, if you want to be more precise about it, you can proceed to the next step.

Start by moving one sub to the middle of the room. Lay it on its' side and place the mic/SPL meter 2" from the driver. Play the subwoofer test tone and measure the SPL. Mark the exact location of that sub on the floor with masking or painters tape. Without moving the mic, move that sub out and the next sub into the exact same position and adjust the gain until it reads the same SPL as the 1st sub. Then repeat that process with the other 2 subs. Then move each sub back into it's in-room position and measure the combined output at the PLP. It should be within the 72-78 dB range. If not, adjust each sub by the exact same amount until their combined response is within that range.

From that point, you can continue with your Audyssey XT calibration. It's not terribly important to have a -5 to -8 trim setting in the receiver after running Audyssey, but I personally prefer it. It allows for the ability to add some input signal to the subs to run the system a little "hot" without exceeding the "0" trim setting. Some sub amps can be overdriven with an excessively high input signal. Staying below "0" ensures you won't overdrive the input of virtually any subwoofer amp.

However, you may not be done yet. With 4 subs, if they end up being different physical distances from the PLP, you most likely need to do the Audyssey subwoofer "Distance" tweak, as written by Keith Barnes here:
https://dl.dropboxusercontent.com/u/...Oct%202013.pdf

Good luck!

Craig

Craig, since talking with you last I have acquired Two dual opposed (15") driver subs, so I will try the gain matching with these, do you do both drivers of each individual sub at 88dB with mic at a distance of 2" and repeat with the second sub and then run Audy. One question as well, what about phase, you don't mention anything about this as my subs do have phase control, maybe yours doesn't. I had a PSA Triax that didn't have phase control. TIA my friend, any help is really appreciated.
Cheers Jeff

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post #216 of 222 Old 08-05-2014, 02:04 PM
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Quote:
Originally Posted by ahblaza View Post
Craig, since talking with you last I have acquired Two dual opposed (15") driver subs, so I will try the gain matching with these, do you do both drivers of each individual sub at 88dB with mic at a distance of 2" and repeat with the second sub and then run Audy. One question as well, what about phase, you don't mention anything about this as my subs do have phase control, maybe yours doesn't. I had a PSA Triax that didn't have phase control. TIA my friend, any help is really appreciated.
Cheers Jeff
Just do one driver.

Set the Phase Controls to 0 or +. Set them both the same. Then do your gain-matching. Afterwards use the Subwoofer Distance Tweak in the document I linked above to time align the subs with the speakers and get them in phase.

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post #217 of 222 Old 08-05-2014, 05:48 PM
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Originally Posted by craig john View Post
Just do one driver.

Set the Phase Controls to 0 or +. Set them both the same. Then do your gain-matching. Afterwards use the Subwoofer Distance Tweak in the document I linked above to time align the subs with the speakers and get them in phase.

Craig
Thanks Craig again, helpful as always. I'll try and give you a break here as I have a lot of work to do and you have given me the tools to do so.
Respectfully, Jeffrey

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post #218 of 222 Old 08-08-2014, 04:22 PM
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Orientation drivers

Craig, I know the best spot for my two dual 15" opposed subs is the front two corners (L&R), my question is how important is it which way the drivers are firing, I was thinking right driver into side wall and left into front wall. Is it OK to have one driver firing into front wall and other into room or doesn't it really matter? Thanks again my friend and sorry for all the questions.
Cheers Jeff

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Last edited by ahblaza; 08-08-2014 at 04:58 PM.
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post #219 of 222 Old 08-08-2014, 04:38 PM
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i am not sure, if what i did is right, with my 2 mismatched sub. first sub connected, second sub is off, measure the first sub with my SPL at my MLP until SPL reads 75db. disconnected the first sub, connect the second sub, measure again with my SPL at my MLP until SPL reads at 75db. then run the full audyssey? thanks.
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post #220 of 222 Old 08-08-2014, 07:39 PM
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Quote:
Originally Posted by ahblaza View Post
Craig, I know the best spot for my two dual 15" opposed subs is the front two corners (L&R), my question is how important is it which way the drivers are firing, I was thinking right driver into side wall and left into front wall. Is it OK to have one driver firing into front wall and other into room or doesn't it really matter? Thanks again my friend and sorry for all the questions.
Cheers Jeff
How much space is between the wall and the driver? If it's at least a few inches, it shouldn't matter which way they are firing.

Quote:
Originally Posted by caloyzki View Post
i am not sure, if what i did is right, with my 2 mismatched sub. first sub connected, second sub is off, measure the first sub with my SPL at my MLP until SPL reads 75db. disconnected the first sub, connect the second sub, measure again with my SPL at my MLP until SPL reads at 75db. then run the full audyssey? thanks.
As long as your sub trim (as set by Audyssey) ends up in the acceptable range (-8db to -5db) you should be good to go. If you're not in the acceptable range, adjust each sub by a couple db and re-run Audyssey (first mic position only, then calculate) until you are. Once you got the trim in range, run the full Audyssey calibration and bump the sub trim up 3db to 6db (to your preference).
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post #221 of 222 Old 08-08-2014, 08:53 PM
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Alan, I'm going to try both methods with one driver about 12" from front wall and the other firing into room. Also I will place them sort of catty corner with each driver firing into a wall about 8-12" away from each front and side wall. Thanks
Cheers Jeff

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post #222 of 222 Old 08-08-2014, 10:08 PM
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Originally Posted by ahblaza View Post
Alan, I'm going to try both methods with one driver about 12" from front wall and the other firing into room. Also I will place them sort of catty corner with each driver firing into a wall about 8-12" away from each front and side wall. Thanks
Cheers Jeff
My dual oppose subs worked better catty corner.
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