Two Subs...Gain Matching vs Level Matching - AVS Forum
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post #1 of 222 Old 10-08-2010, 10:13 AM - Thread Starter
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So I just added a second sub (Dual Outlaw LFM-1 EX). This is my first time with dual subs. I have been doing some reading and searching on the concept of level matching vs gain matching. Both really seem to have strong points. I think I like the concept of gain matching better, as to not have one sub run out of steam before the other.

Here is my situation. My room is sealed and pretty small. All of my seating is in the back half of the room (as is most people). Last night I gain matched each sub, and the sub in the room is 3.5 dB louder at the listening position than the one in the front of the room. I didn't have the proper splitter, so that is as far as I got. I am going to spend a ton of time this weekend trying all kinds of positions and measuring and listening.

Is 3.5 dB difference at the listening position too much of a disparity to effectively gain match? Would it be better, if I am going to gain match to put both subs in the front of the room to get a closer match at the listening position between the two subs? In my situation, might it be better to level match each sub at the listening position, since the room is so small, and I "think" I wouldn't push either sub into clipping anyway?

Thanks!
Greg
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post #2 of 222 Old 10-08-2010, 10:32 AM
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I have never gain matched my sub's, but I dont think 3.5 db is anything to worry about. Someone who knows more may chime in. I only level match my subs and If one poops out sooner I just turn it down a notch
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post #3 of 222 Old 10-08-2010, 12:06 PM
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Greg, as Haskin has said, I don't think the 3.5db is that noticeable. Personally, I am a fan of level matching identical dual subs, especially if you are using a calibration tool (such as Audyssey, Anti-mode) and have one LFE out signal Y-split to each sub. If you find that one sub is reaching its max with level matching, I would than use gain matching.

OTOH, with non-identical subs, GAIN matching the subs may help prevent the lesser sub from potentially maxing out (which would limit your sub set-up).
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post #4 of 222 Old 10-09-2010, 05:46 AM
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If you are crossing 80hz or below. It should be nearly impossible to notice one sub is 3dbs lower than the other.
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post #5 of 222 Old 10-09-2010, 12:15 PM
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I am a proponent of gain-matching. I have 3 Submersives, asymmetrically placed around my room. I want them all to drive the room with same energy, no matter what the relative SPL's are at any one listening position. This ensures they all have the same headroom, and they are all contributing equally to the sound. I don't hear any directionality from any of the subs anywhere in the room, even if I stand or sit very close to one of them.

To gain-match identical subs, the most rigorous method is to move each sub to the middle of the room, place a mic very close to the driver, and measure the SPL. Then move each of the other subs to the exact same position with the mic exactly the same distance away, and set the level to the same SPL as the first one. I place tape on the floor around the first sub, so I can ensure the subsequent subs are located in the exact same place. I don't move the mic between measurements. This works for identical subs, and the level knobs should be at the exact same point, assuming the amps are consistent from unit to unit. It also works for different subs, but then you should expect different settings on the amps.

Mark Seaton was the one who suggested this method to me, and if it's good enough for him, it's good enough for me.

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post #6 of 222 Old 10-09-2010, 09:26 PM - Thread Starter
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Thanks for all of the advice. I was really bought into gain matching. I spent a lot of time today trying everything. What I found in my room, is level matching worked better. In my room one sub in the front, and one in the back really sounds the best. When level matching I got a flat response down to 15hz. When I gain matching, the best I could do was flat to 20 Hz and a slight rolloff from there. I get that every room is different, but this is what worked in my room. I am not too worried about overdriving the sub further away, because my room is small enough that even a single sub in that position was probably enough. When I added the second, I added in 4.5 DB of headroom.
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post #7 of 222 Old 10-13-2010, 03:38 PM
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post #8 of 222 Old 10-14-2010, 08:43 PM
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I was at a friends house tonight and he has 2 small, 12" sealed subs subs. One was placed in the left corner, and one was placed on the right but in the middle of the front wall. (The front wall is much wider than the area were the AV system is, so the the right of the right speaker is mid-front wall.) The two subs were obviously receiving significantly different room reinforcement. We initially tried level-matching. We set both subs so their levels matched at the primary LP. This yield about an 8 dB higher gain setting for the mid-wall sub. We watched the Star Wars opening scene. Immediately we realized the mid-wall sub was distorting badly and we had to turn down the overall level to compensate.

Next, we tried gain-matching. This allowed about a 3 to 4 dB increase in *system* level over the level-matched system, while retaining excellent sound quality for the entire system. This, yet again, reconfirmed my belief in the gain-matching technique.

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post #9 of 222 Old 10-14-2010, 09:05 PM
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Please ignore my ignorance but what is gain matching?
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post #10 of 222 Old 10-14-2010, 09:08 PM
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Quote:
Originally Posted by Kimwyn View Post

Please ignore my ignorance but what is gain matching?

See Post #5 above.

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post #11 of 222 Old 10-14-2010, 11:24 PM
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Craig,

I gain matched (using the Anti Mode) my quad Empires a couple of days ago. I have two under the TV firing to the front (10 ft to the seat) and two to the rear of the seat (6 ft from the seat), firing forward. Big improvement over level matching with bass clairity and mid bass slam sounding the best that I have ever heard in my room. Audio thru the system has improved greatly also with gain matching of subs. So much detail that I am watching clips all over again just to see what I have been missing. Finally, just want to say . . . gain match your sub(s) and don't worry about the spl at the seat as the bass will be there.

Bill
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post #12 of 222 Old 10-15-2010, 10:17 PM - Thread Starter
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So as with most things audio, I can't leave well enough alone...and I am glad I can't. I spent tonight moving around my subs and gave gain matching another try. With my subs in their new spots, gain matching measured better and sounds a heck of a lot better.
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post #13 of 222 Old 10-18-2010, 08:35 PM
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I have a quick question and there are several people in this thread that I respect when it comes to subwoofer info. I've changed from having my dual Epik Sentinels on opposite sides of the room, which sounded great, to stacking them in a corner due to wife's request.

I'm splitting with a Y to both, so I don't have to run dual sub cables, and have a question regarding calibration. I'm using the Audyssey on my Onkyo 707 and I'm wondering if I should just hook them both up and calibrate like normal or if I need to do something different? At this point in time I don't have an SPL meter and am relying on the receiver.
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post #14 of 222 Old 10-19-2010, 07:21 AM
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Quote:
Originally Posted by irishluck73 View Post

I have a quick question and there are several people in this thread that I respect when it comes to subwoofer info. I've changed from having my dual Epik Sentinels on opposite sides of the room, which sounded great, to stacking them in a corner due to wife's request.

I'm splitting with a Y to both, so I don't have to run dual sub cables, and have a question regarding calibration. I'm using the Audyssey on my Onkyo 707 and I'm wondering if I should just hook them both up and calibrate like normal or if I need to do something different? At this point in time I don't have an SPL meter and am relying on the receiver.

If they're co-located, (stacked), they should be gain-matched. If you don't have an SPL meter, your only option is to set the amplifiers to the same volume/level setting. Assuming the amps have the same gain structure, this *should* be gain-matched. However, you will now have at least 6 dB more output from the corner-loaded, co-located subs, so you'll need to use the receiver's auto-calibrate to calibrate the combined levels. If Audyssey sets them to the negative limit of it's range, you'll need to turn each sub down by the same amount and re-run Audyssey until you get the levels within the trim range of the sub channel.

Craig

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post #15 of 222 Old 10-19-2010, 09:46 AM
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Quote:
Originally Posted by craig john View Post

If they're co-located, (stacked), they should be gain-matched. If you don't have an SPL meter, your only option is to set the amplifiers to the same volume/level setting. Assuming the amps have the same gain structure, this *should* be gain-matched. However, you will now have at least 6 dB more output from the corner-loaded, co-located subs, so you'll need to use the receiver's auto-calibrate to calibrate the combined levels. If Audyssey sets them to the negative limit of it's range, you'll need to turn each sub down by the same amount and re-run Audyssey until you get the levels within the trim range of the sub channel.

Craig

Craig,
What if you have dis-similar subs....at unequal distances to lp? When I gain matched in this scenario, one sub was over powering the other.
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post #16 of 222 Old 10-19-2010, 09:54 AM
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Quote:
Originally Posted by craig john View Post

If they're co-located, (stacked), they should be gain-matched. If you don't have an SPL meter, your only option is to set the amplifiers to the same volume/level setting. Assuming the amps have the same gain structure, this *should* be gain-matched. However, you will now have at least 6 dB more output from the corner-loaded, co-located subs, so you'll need to use the receiver's auto-calibrate to calibrate the combined levels. If Audyssey sets them to the negative limit of it's range, you'll need to turn each sub down by the same amount and re-run Audyssey until you get the levels within the trim range of the sub channel.

Craig

Thank you very much! Pardon my ignorance but I thought co-locating and corner loading was to achieve the 6db increase? If you match the volume settings on the subs, auto-calibrate afterwards and bring the 2 subs in line with Audyssey's parameters than wouldn't having just 1 sub corner loaded suffice or be the same thing? Or is this simply for gaining more headroom?

I'll be trying this later today. I'm also getting an SPL meter in the very near future.
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post #17 of 222 Old 10-19-2010, 12:02 PM - Thread Starter
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Quote:
Originally Posted by irishluck73 View Post

Thank you very much! Pardon my ignorance but I thought co-locating and corner loading was to achieve the 6db increase? If you match the volume settings on the subs, auto-calibrate afterwards and bring the 2 subs in line with Audyssey's parameters than wouldn't having just 1 sub corner loaded suffice or be the same thing? Or is this simply for gaining more headroom?

I'll be trying this later today. I'm also getting an SPL meter in the very near future.

The purpose is not to increase the sub by 6dB. It is to gain 6dB of headroom and make your sub/subs 6dB more capable than they were before. If you choose to run your subs hotter than calibrated, that is your choice, and the second sub will help in those efforts, but your calibration philosophy should be the same whether you have one sub or four subs.

I chose to seperate my subs rather than co-locating, but my goals were different than adding 6dB of output.

I hope that helps.
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post #18 of 222 Old 10-19-2010, 12:04 PM
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I hope that helps.

That helped a lot! Prior to this week I had my subs separate but the wifey wants to utilize more space in the living room now. Between my job and a 9 month pregnant wife I don't have as much time as I'd like to research and learn about everything I'm interested in. Great explanation and it's appreciated!

The only thing that looks odd is going from BJC subwoofer cable to the Radio Shack splitter, much thicker cable from BJC.
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post #19 of 222 Old 10-19-2010, 12:37 PM
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I dialed both Sentinels down to 3 o'clock on their gain setting and ran Audyssey. It came back with -3.5 so I bumped it up 4db to get some heavy hitting bass. Thanks a bunch for the help!
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post #20 of 222 Old 10-19-2010, 03:01 PM
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Quote:
Originally Posted by irishluck73 View Post

I dialed both Sentinels down to 3 o'clock on their gain setting and ran Audyssey. It came back with -3.5 so I bumped it up 4db to get some heavy hitting bass. Thanks a bunch for the help!

Gain setting dialed in on a sub at 3 o'clock is pretty high. You mean 9 don't you?
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post #21 of 222 Old 10-19-2010, 03:03 PM
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Gain setting dialed in on a sub at 3 o'clock is pretty high. You mean 9 don't you?

Yep I was leaning over the top of them at the time, whoops! I used to have them both at about 11 when they were on opposite sides of my couch but co-located makes a huge difference. Gonna fire up a good bass movie here shortly to test out the new set up.
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post #22 of 222 Old 10-19-2010, 05:24 PM
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Quote:
Originally Posted by irishluck73 View Post

Thank you very much! Pardon my ignorance but I thought co-locating and corner loading was to achieve the 6db increase?

Yes, and that was what I was trying to say. Re-reading what I wrote, I guess you thought I was saying the gain-matching was what gave the 6 dB increase? Sorry if I wasn't clear. Co-locating the 2 subs will provide a roughly 3 dB increase. Corner loading will provide an additional 3 to 6 dB. This additional reinforcement will allow you to turn the levels of each sub down. The benefit is that each sub will be playing back at a lower level with lower distortion and in a more linear range of driver excursion. The downside of co-locating and corner loading is that you lose the FR flattening of the separated, midwall locations. You'll be giving Audyssey a more ragged FR to work with. Audyssey has a limited capability to flatten the FR. The flatter it is to start with, the better job it can do achieving it's "target curve".

Quote:
Originally Posted by irishluck73 View Post

If you match the volume settings on the subs, auto-calibrate afterwards and bring the 2 subs in line with Audyssey's parameters than wouldn't having just 1 sub corner loaded suffice or be the same thing?

Not sure I understand this question, but what do you mean by: "...bring the 2 subs in line with Audyssey's parameters..."? Audyssey will "see" the dual, co-located subs as one sub and it will provide one EQ filter set for the combined response of both subs. It will also set the Distance for the combined subs as well as the levels. I don't know what else one would "bring in line".

Quote:
Originally Posted by irishluck73 View Post

Or is this simply for gaining more headroom?

Yes, that is the primary benefit of co-locating/corner-loading.

Quote:
Originally Posted by irishluck73 View Post

I'll be trying this later today. I'm also getting an SPL meter in the very near future.

Good. An SPL meter is the most basic tool for an HT enthusiast. It's like a hammer for a carpenter.

Craig

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post #23 of 222 Old 10-19-2010, 07:00 PM
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Quote:
Originally Posted by LF911 View Post

Craig,
What if you have dis-similar subs....at unequal distances to lp? When I gain matched in this scenario, one sub was over powering the other.

Hi Larry,

Bass below about 80 Hz is non-directional. Most humans can't hear the direction of origin of bass sounds, (below about 80 Hz.) Therefore, if you hear directionality from one of the subs, (which is what I presume you mean by one sub "overpowering" the other), then there might be some higher frequencies being played back by the closer sub. This could be caused by a crossover higher than 80 Hz, or by harmonic distortion.

Let me ask you this: If you playback using just the closer sub, can you tell the direction of origin of the sounds coming from that sub? Can you hear it as a localizable source of sound? If not, I would be surprised if you can find it as a localizable sound source with two subs running. If so, there is something going on with your sub(s) that is causing the directionality. I would spend some time figuring that piece out first. What crossover frequency are you using? Can you look at the response above 80 Hz for just the subs?

Craig

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post #24 of 222 Old 10-20-2010, 09:33 AM - Thread Starter
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Quote:
Originally Posted by craig john View Post

Hi Larry,

Bass below about 80 Hz is non-directional. Most humans can't hear the direction of origin of bass sounds, (below about 80 Hz.) Therefore, if you hear directionality from one of the subs, (which is what I presume you mean by one sub "overpowering" the other), then there might be some higher frequencies being played back by the closer sub. This could be caused by a crossover higher than 80 Hz, or by harmonic distortion.

Let me ask you this: If you playback using just the closer sub, can you tell the direction of origin of the sounds coming from that sub? Can you hear it as a localizable source of sound? If not, I would be surprised if you can find it as a localizable sound source with two subs running. If so, there is something going on with your sub(s) that is causing the directionality. I would spend some time figuring that piece out first. What crossover frequency are you using? Can you look at the response above 80 Hz for just the subs?

Craig

I can attest to this! If you look at my first post, I had some reservations about having one sub closer than the other, and thus doing gain matching with subs at different spl's at the listening position. It sounds awesome, with no indication that the rear/closer sub is reading more spl's at the listening position.

After doing a ton of research, I implemented a couple of ideas I got from AVS from some experts that worked out beautifully.
1) I went with two subs to get a more even response throughout my room
2) I put one sub in the front of the room, dead center along the front wall from left to right, under my screen and put the rear sub dead center from left to right along the back wall.
3) I gain matched the two subs
4) I positioned my couch using the 38% rule, which says that a good starting point is to have your couch either 38% into the room from the front wall or the back wall (mine is 38% from the back wall)

Of course each room is different, and some of these are more of guidelines and won't work in every room, but I figured, what the heck, why not try some of them.

What I got was amazing. From a measurement standpoint (without any equalization), my bass response is +-3 to 4 dB from 100hz down to 15hz. What was even more amazing is that when I use REW to measure every seat across the entire couch, each bass curve is EXACTLY identical. We are talking about a full size couch and in every seat, there is no variance. I have two chairs that make up my back row, and those are not quite as flat, but pretty darn close. The best part is that it sounds better than it ever has in my room and I was able to sell my sub equalizer.
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post #25 of 222 Old 10-20-2010, 09:47 AM
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Great job, and great summary Redskin!! May I ask if your receiver applied any calibrations to the subs...and if so, which receiver?
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post #26 of 222 Old 10-20-2010, 04:30 PM - Thread Starter
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Originally Posted by deepstang View Post

Great job, and great summary Redskin!! May I ask if your receiver applied any calibrations to the subs...and if so, which receiver?

I have a Pioneer Elite 94 TXH, which does eq to the speakers, but not the sub. It does work a little bit on the distance and phase of the sub/speaker crossover, but no eq to the sub.
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post #27 of 222 Old 10-20-2010, 05:28 PM
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Quote:
Originally Posted by Redskin View Post

I have a Pioneer Elite 94 TXH, which does eq to the speakers, but not the sub. It does work a little bit on the distance and phase of the sub/speaker crossover, but no eq to the sub.

It does set standing wave and sub trim for the reciever.
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post #28 of 222 Old 10-21-2010, 06:41 AM
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Quote:
Originally Posted by Redskin View Post

I can attest to this! If you look at my first post, I had some reservations about having one sub closer than the other, and thus doing gain matching with subs at different spl's at the listening position. It sounds awesome, with no indication that the rear/closer sub is reading more spl's at the listening position.

After doing a ton of research, I implemented a couple of ideas I got from AVS from some experts that worked out beautifully.
1) I went with two subs to get a more even response throughout my room
2) I put one sub in the front of the room, dead center along the front wall from left to right, under my screen and put the rear sub dead center from left to right along the back wall.
3) I gain matched the two subs
4) I positioned my couch using the 38% rule, which says that a good starting point is to have your couch either 38% into the room from the front wall or the back wall (mine is 38% from the back wall)

Of course each room is different, and some of these are more of guidelines and won't work in every room, but I figured, what the heck, why not try some of them.

What I got was amazing. From a measurement standpoint (without any equalization), my bass response is +-3 to 4 dB from 100hz down to 15hz. What was even more amazing is that when I use REW to measure every seat across the entire couch, each bass curve is EXACTLY identical. We are talking about a full size couch and in every seat, there is no variance. I have two chairs that make up my back row, and those are not quite as flat, but pretty darn close. The best part is that it sounds better than it ever has in my room and I was able to sell my sub equalizer.

I have such an unbelievabley bad room...only one true corner and over 6500^ft. I don't care where the xover is..40, 60, or 80....or what sub I use, I can tell where the sub is in the room..you can almost point to it. I've had the same problem with 3 different subs, the 2 I have now, and the 1 sealed I had before these. I dont' think it's because I have super human ears either. It's the floor. . It's a 60 year old wood floor. It's great when you are watching canyon walls coming down, or an A6 fly-over, but I can always tell where the low end is eminating from. Doesn't matter if it's low volume or high....
The FLATEST response I can achive in my room (this is after moving 550 lbs of subs around the room) is when one sub is in the front right corner and the other sub is in the rear right corner. Nice flat graph via sms-1.
I HATED IT. It felt like the room was lopsided. It was like I had a cotton in my left ear...everything was coming from the right side of the room. When I gain matched the problem became worse.
What I ended up doing was moving the right rear sub to the left rear corner (if you can all it a corner with that damm opening) and that balanced the room. I can't tell where low stuff is coming. I also think the extra bracing in the corners of the room help. NATURALLY, it caused a 4-6 db suck out from 60 to 80 hz. I don't care....to these ears it sounds and feels pretty good.
I don't remember if I gain matched with the subs in current position. I'll try it.
Never mind moving the subs around the room...I've changed everything in this room 4 times. I'm done with it. I'm tired of fighting with it. Like I wrote above, it sounds pretty good to me..but what do I know. It's not like I am at Craig's or Bosso's level.
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post #29 of 222 Old 10-21-2010, 08:50 AM
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I've got two Epik Sentinels, one mid wall left, front firing, the second corner right, firing into the side wall. They are "Y" connected and level matched, with the corner sub set much lower than the left. Audyssey sets them at -3.5. If I want to gain match, where do I place my SPL meter? Or do I just move the right sub out into the room and meter it at one meter?

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post #30 of 222 Old 10-21-2010, 09:02 AM
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from a very knowledgeable person

Quote:


Place one subwoofer on the floor in the middle of the room. Place your SPL meter about 2 feet away. Play the test tone in the AVR out of the left speaker and turn up the master volume until the SPL meter reads 75 dB. Then switch to the subwoofer pink noise output on the AVR. Adjust the gain (volume knob) on the subwoofer until it also reads 75 dB on the SPL meter.
Now turn off that subwoofer and move the second one into the exact same place as the first one and repeat the process. You will notice that there will be a slight variation on the volume knob on the sub. One might end up at 11:00 and the other one might be 10:30. They are now gained matched.

Now this is where it will get tricky. Once you place the gained match subwoofers back in your room and run Audyssey their combined output mght be too high and Audyssey will show the trim level for the combined subs at -10 which is too low in my opinion. Then you will have to carefully adjust the subs volume knob down without losing to much of the gain matching you performed early. This only happens in some rare cases.

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