Dual Opposed AV15H Subwoofer Build - Page 7 - AVS Forum
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post #181 of 802 Old 04-23-2010, 06:45 AM - Thread Starter
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I'm going to try all the x-overs available in my 876, and pick the one that gives me the best SQ and frequency response.

Yeah, I couldn't help but crack up as he was litterally lifting his leg and shaking out the pee on my sub and looking awfully "innocent" while doing it. Quite humorous.

 

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post #182 of 802 Old 04-23-2010, 06:51 AM
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Too funny....

Yes def let your room decide on what measures the best - and that should sound the best.... If you cross higher you will get much better impact for movies and better mid bass slam from your sub then the S2's will give you... Right now I'm crossing over my S8's at 120hz, but even Mike Hurd suggested I could easily go up to like 160hz with the LMS's... We crossed over the sub closest to my mains at 120hz, and the side subs at 80hz and the rear sub around 60hz with the DCX, the sound field and impact are fantastic.... but I don't have a symmetrical layout like you do...


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post #183 of 802 Old 04-23-2010, 09:06 AM
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Quote:
Originally Posted by pbc View Post

BTW, I was reading Ricci's write up on how to set the level of identical dual subs (mainly the point about putting htem in the middle of the room to level set each to the same level then putting them in their spots and using the AVR to set final levels to reference).

Curious, given one will be in a corner (with a back and side wall boundary helping it) while the other will only have a back wall (as it will be next to an open doorway), wouldn't it necessitate that the amp puts out more gain to that woofer vs the one in the corner? Have never setup duals before, so go easy on me!!

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Originally Posted by bossobass View Post

I disagree with the method. I see no reason to pull the subs to a different distance from the mic and in-room response for calibration. I would set the levels from the LP to where they'll sit (your placement is virtually equidistant) and set the AVR/amp levels for best stab at unity gain.

Bosso

I need to comment here.

That gain setting post wasn't intended to be a "write up' and has been taken a little out of context. It was in a thread that was originally about how to set disimilar subs and similar subs when they are placed asymmetrically. This was in the commercial subwoofers forum too so most of their subs have plate amps with a variable input on them, which were what I was talking about. There was a lot of bad advice going around in that thread. Namely with people trying to advocate adjusting the subs to have the same output level at the listening position regardless of whether one was 20ft away and the other was 4ft away. This would cause the sub 20ft away to kill itself on demanding material and would be limiting the rest of the system.

PBC,
The comment bolded in your quote above was in relation to identical commercial subs with a typical plate amp and was only to match their relative outputs to each other. It does not relate to your system in any way. You have identical subs that will be run from the same amp which has detented channel controls. No need for all that. Wire the subs into the amp and set the 2 channel trims the same and you should be close enough for gov't work.


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post #184 of 802 Old 04-23-2010, 10:24 AM
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Originally Posted by LTD02 View Post

john j. (aka stryke) mentions av15h has f3 of 67hz or so in another guys small sealed build. the confusion here is just the point of measurement. when i mentioned 60hz, i was talking about without a low pass filter. with an 80hz low pass filter, the peak is at 60hz or so and the -3db point moves down to around 36hz. also, the 12db per octave is a pretty good guess for a small sealed enclosure, until pressure vessel gain kicks in (and remember that is just the shape of the contour, not how much you have to apply, you may only need a few db, if any in a small room, which is why i hedged my comment the way that i did.)

http://www.aespeakers.com/phpbb2/vie...php?f=1&t=1749

bosso, what does a bassis do that a dcx cannot?

from an old post on htguide:
"The LT can be replicated as the sum of 3 filters - two band (bell shaped) filters and one 12dB/octave shelving filter. The first band filter changes the Q of the box/driver to 0.7 at it's Fb. The shelving filter changes the response to Q=0.7 at the new desired Fb. The second band filter sets the Q to whatever you want it to be, e.g. Q=0.5, at the new Fb.
In practice, you may not even need the band filters. Just use a shelving filter to boost the lows. If the final response curve looks the way you want it to, it doesn't matter how you get there or what kind of fancy name you give it. It's all just EQing the bass response to be the way you want it."
http://www.htguide.com/forum/archive...p4/t-9744.html

Let's take a look at the graphs in some detail. I took my REW graph of a close mic measurement and subsequent EQ'd traces and resized the BB model trace and JJ's posted measurement (again, I don't know the particulars of JJ's measurement) and overlaid them for discussion.

Just because sealed subs are 2nd order does not mean that the L/T should be set at 12dB of boost. 12dB is X 16 and anyone employing such a boost should be acutely aware of what he is doing across the entire system.

If the BB model were correct, it shows a near 1st order roll off from 60Hz to 15Hz. If you apply a 2nd order shelf boost, you'll have an anechoic bump which will bloat the response when the sub is corner loaded in 2500 cubes.



My measurement shows a dip at 150Hz. That dip rises back up at 300Hz, but of course, is not shown on the posted graph. JJ's measurement also shows the dip, although less pronounced as rises back at 200Hz, the point is that the model shows a peak in response at 200Hz, but in reality there is a dip there and the peak is much higher. This skews the real F3 point vs the model.

Both JJ's and my measurements show the wide knee I mentioned and 2nd order roll off doesn't occur until below 20Hz.

You may choose to continue to advise people that all sealed subs require a 2nd order shelf boost and that Qtc can be reconciled with 2 parametric filters in every case but please understand that this is simply not the case. Every sub I've built required a much different combination of L/T settings to achieve best performance in-room.

IMHO, 12dB of boost is not in keeping with a properly designed sealed sub utilizing the AV15H driver(s). IOW, it's way too much boost.

I used the Bassis to neutralize the dip by setting the Qb to a higher setting than reality and setting Fb higher as well. The boost setting is ideal at +8dB in my room but with less headroom than I actually have, it would be better set at +6dB to balance for optimum performance and life.

OTOH, one who is in a much larger room and has multiples of subs and plenty of power and who prefers a lower listening level may choose to exceed 12dB of boost and adjust the Qs to a much lower value and have excellent results.

Bosso
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post #185 of 802 Old 04-23-2010, 11:01 AM
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You guys probably already know this but I just wanted to say that the DCX has both a 2nd order shelf and a 1st order one, which adjusts the rate at which the shelf is rolled in. The amount of boost you apply to the shelf is variable between +15 and -15db in 0.1db increments and is separate. Not as flexible as a Bassis but it should be enough for most cases with a bit of trial and error. I'm running a mild 5db 2nd order shelf at 20hz and used another band of parametric to knock down the hump that resulted at 16-23hz in my case.


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post #186 of 802 Old 04-23-2010, 11:58 AM
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the f3 point is the point where the frequency response is down 3db as you are heading *down* the frequency response. the usable topend is typically limited by the point where you get some big resonant peak (and some other debatable things, such as intermodulation distortion of midrange). as you can see, using the av15h up to 120-150hz should present no major problems that exceed the benefit in headroom given your relatively small mains.

i'm not sure of the measurement conditions, but here is one sweep of the av15h-4 in action:


LL

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post #187 of 802 Old 04-23-2010, 12:05 PM
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Originally Posted by LTD02 View Post

the f3 point is the point where the frequency response is down 3db as you are heading *down* the frequency response. the usable topend is typically limited by the point where you get some big resonant peak (and some other debatable things, such as intermodulation distortion of midrange). as you can see, using the av15h up to 120-150hz should present no major problems that exceed the benefit in headroom given your relatively small mains.



Maybe you didn't see my post before you posted this ^^^

The graph you posted is pasted on my posted graph. The Orange trace is that measurement resized to fit my graph and pasted to my graph for reference.

Bosso
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post #188 of 802 Old 04-23-2010, 12:08 PM
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Originally Posted by Ricci View Post

You guys probably already know this but I just wanted to say that the DCX has both a 2nd order shelf and a 1st order one, which adjusts the rate at which the shelf is rolled in. The amount of boost you apply to the shelf is variable between +15 and -15db in 0.1db increments and is separate. Not as flexible as a Bassis but it should be enough for most cases with a bit of trial and error. I'm running a mild 5db 2nd order shelf at 20hz and used another band of parametric to knock down the hump that resulted at 16-23hz in my case.

No, I didn't know that. Good info. Next time you have your measurement rig up, any chance you could apply the 2nd order shelf and show traces with boost settings changed in increments? That would help me see the affect.

I may just get one. It seems to be a versatile piece from what I've been able to piece together, and this post helped a lot.

Bosso
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post #189 of 802 Old 04-23-2010, 12:50 PM
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"Maybe you didn't see my post before you posted this ^^^"

no i didn't; such is the nature of asynchronous communication. :-)

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post #190 of 802 Old 04-23-2010, 01:03 PM
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"You may choose to continue to advise people that all sealed subs require a 2nd order shelf boost and that Qtc can be reconciled with 2 parametric filters in every case but please understand that this is simply not the case. Every sub I've built required a much different combination of L/T settings to achieve best performance in-room.

IMHO, 12dB of boost is not in keeping with a properly designed sealed sub utilizing the AV15H driver(s). IOW, it's way too much boost."

maybe you didn't read my post #178 before you posted this ^^^ ;-)

i didn't say it needs 12db of boost. i said that is the filter in the dcx2496 that he could use to bring up the low end should he need it.

also, what qtc cannot be recreated by 2 peq's and a 12db/octave shelving filter???

"You guys probably already know this but I just wanted to say that the DCX has both a 2nd order shelf and a 1st order one, which adjusts the rate at which the shelf is rolled in. The amount of boost you apply to the shelf is variable between +15 and -15db in 0.1db increments and is separate. Not as flexible as a Bassis but it should be enough for most cases with a bit of trial and error."

i still don't understand what the bassis can do that the dcx2496 cannot. with 2 peqs and a 12db per octave shelf filter any q linkwitz transform can be created. also, if for some reason 15db is insufficient, you can add up to another 15 in a second shelf, and so on.

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post #191 of 802 Old 04-23-2010, 01:08 PM
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just a heads up bosso, you can download the remote software for free (bottom of page) and run it in stand alone mode to see how all the filters work.
http://www.behringer.com/EN/Products/DCX2496.aspx

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post #192 of 802 Old 04-23-2010, 05:17 PM - Thread Starter
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Quote:
Originally Posted by Ricci View Post

I need to comment here.

That gain setting post wasn't intended to be a "write up' and has been taken a little out of context. It was in a thread that was originally about how to set disimilar subs and similar subs when they are placed asymmetrically. This was in the commercial subwoofers forum too so most of their subs have plate amps with a variable input on them, which were what I was talking about. There was a lot of bad advice going around in that thread. Namely with people trying to advocate adjusting the subs to have the same output level at the listening position regardless of whether one was 20ft away and the other was 4ft away. This would cause the sub 20ft away to kill itself on demanding material and would be limiting the rest of the system.

PBC,
The comment bolded in your quote above was in relation to identical commercial subs with a typical plate amp and was only to match their relative outputs to each other. It does not relate to your system in any way. You have identical subs that will be run from the same amp which has detented channel controls. No need for all that. Wire the subs into the amp and set the 2 channel trims the same and you should be close enough for gov't work.

Ah, thanks Ricci, def took the post out of context as it wasn't making sense to me for my application. Sorry about that!

 

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post #193 of 802 Old 04-23-2010, 05:34 PM
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Ricci,

What part of that section of your reply, for setting up two identical subswoofers I copied here earlier was taken out of context, as he is trying to do I have done with my single AV15H's?

Just looking to find so if there is something wrong with this method I do not recommend it to other people or use myself. Thanks.

James
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post #194 of 802 Old 04-24-2010, 08:21 AM - Thread Starter
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Somethings not right. Hooked up the subs to the amp, with the amp in parrallel mode and no high pass filters selected.

I would have thought the one near the corner would require much less gain from the amp than the one near the doorway. But it's quite the opposite. The one near the doorway (no side wall) has the gain set to 2.2 (or about 9pm), whereas the one in the corner requires 3.0 (or say 1 am on a clock).

The fan sounds like a friggin tank and will HAVE to be replaced for sure, my SPL meter hits 60 to 64db with it!!

 

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post #195 of 802 Old 04-24-2010, 08:31 AM - Thread Starter
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Oh, and just playing some Eagles Hell Freezes over DVD, getting a pronounced yellow/orange light from the "weak" channel (i.e., when the drum kicks in that yellow/orange light flutters much brigher than the other channels light)?

Finally, when I do a level check on the speakers and exit the setup routine, the same sub (the one on the ch that requires much more gain) seems to make a low chirp when I exit the 876's speaker level routine, whereas the other one is silent.

Thoughts?

 

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post #196 of 802 Old 04-24-2010, 08:44 AM - Thread Starter
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Looks like it has something to do with the sub itself. Switched the channels up to see if maybe one of the amps channels was messed up, same thing happens with the other channel.

Checked the resistance again, both subs read 3.2OHM on the meter, so I think the hook up is fine?

Thoughts?

 

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post #197 of 802 Old 04-24-2010, 08:48 AM
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Play some 60Hz test tones at somewhat sane volumes and check the voltage across each speaker with the gains for each channel set the same. Check the SPL at say 6" and then the voltage. If they're the same SPL and voltage I wouldn't worry about the lights on the amp.
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post #198 of 802 Old 04-24-2010, 08:55 AM - Thread Starter
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How do I check the voltage?

I guess what I'm more concerned about is why the speaker in the corner requires a much higher gain setting on the amp (more than halfway vs. about 1/4 of the way for the other side), doesn't feel right.

 

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post #199 of 802 Old 04-24-2010, 09:17 AM
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you should try the "white snake dvd". That will definitely let you know how your bass are.
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post #200 of 802 Old 04-24-2010, 09:29 AM - Thread Starter
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Will have to get back to it later. But looking at my old PB13 response graphs (one on the right and one on the left), there is quite the difference at 50hz on upwards with the sub near the doorway having quite the advantage. Wonder if the amp is simply trying to compensate for this (i.e., I crossed it at 120hz, so maybe this difference is even more pronounced).

PB 13 on Left side (doorway opening)


PB 13 on Right side (corner)

 

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post #201 of 802 Old 04-24-2010, 10:42 AM
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Originally Posted by pbc View Post

How do I check the voltage?

Set your multimeter to AC voltage.
Quote:


I guess what I'm more concerned about is why the speaker in the corner requires a much higher gain setting on the amp (more than halfway vs. about 1/4 of the way for the other side), doesn't feel right.

More gain for what? To get an equivalent SPL? equivalent voltage?
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post #202 of 802 Old 04-24-2010, 10:51 AM - Thread Starter
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Originally Posted by Stereodude View Post

Set your multimeter to AC voltage.
More gain for what? To get an equivalent SPL? equivalent voltage?

Equivalent SPL, but that's at the LP so you're right, I need to measure close to the cone to at least factor out as much of the room as possible.

As for checking voltage, I assume I just set the meter to the AC voltage setting (guess 200V given the options are 750 and 200 on the multimeter),

http://www.canadiantire.ca/AST/brows....jsp?locale=en

then just hold them up against the red/black terminal posts while the test tone is running?

 

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post #203 of 802 Old 04-24-2010, 12:37 PM - Thread Starter
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Well, I'll have to set aside some time another day to run more tests.

In the mean time, back to my fan saga. No idea what I'm looking for with fans, other than to say the stock fan is 119mm square by 38mm deep 24v variable speed fan, and sounds like a hair dryer from the moment it is turned on.

I know this fan was popularized by the Crown fan mod thread ...

http://search.digikey.com/scripts/Dk...&name=P9739-ND

But the size is too small at 80mm. I figured I could go with a fan that isn't as deep, and came up with these ...

http://search.digikey.com/scripts/Dk...name=P13449-ND

RPMs seem quite low at 1600 though, however, maybe it's lower because the fan is larger? If I go with a higher RPM the dbs hit the low 40's.

Thoughts?

 

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post #204 of 802 Old 04-24-2010, 02:16 PM
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Quote:
Originally Posted by pbc View Post

As for checking voltage, I assume I just set the meter to the AC voltage setting (guess 200V given the options are 750 and 200 on the multimeter),

http://www.canadiantire.ca/AST/brows....jsp?locale=en

then just hold them up against the red/black terminal posts while the test tone is running?

Yep, play a 60Hz tone, and use the procedure you listed above.
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post #205 of 802 Old 04-24-2010, 02:35 PM - Thread Starter
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Quote:
Originally Posted by Stereodude View Post

Yep, play a 60Hz tone, and use the procedure you listed above.

Done.

Both subs are reading 0.3 on the multimeter (set at 200).

However, the sub on the right side reads 97 to 98db vs 100 to 101db on the left side, same gain applied on the amp.

 

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post #206 of 802 Old 04-24-2010, 03:41 PM
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Quote:
Originally Posted by pbc View Post

Done.

Both subs are reading 0.3 on the multimeter (set at 200).

However, the sub on the right side reads 97 to 98db vs 100 to 101db on the left side, same gain applied on the amp.

You need to turn the volume up a bit more and try again. A reading of .3 is down in the noise on a 200V scale, so I'm not sure you can draw any conclusions from it.

Are the results the same if you swap the channels? What if you swap the channels on the input side of the amp?
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post #207 of 802 Old 04-25-2010, 06:24 AM - Thread Starter
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Hmmm ... haven't tried swapping the CH on the input side of the amp. But the results are the same if I swap channels on the output side.

Will also try swapping sub positions, though given I'm measuring within a few inches of the cone I can't imagine that will make a difference.

 

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post #208 of 802 Old 04-25-2010, 08:29 AM
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I really don't see a problem with the differences in response for the differences in placement. Here are the 2 Ultra traces overlaid for scrutiny:



First, there are differences in mic-to-sub in the 2 placements.

Second, one is in a corner and the other is not and in immediate proximity to an open door.

Third, unless conditions are very closely monitored, there is no certainty that the levels were identical between the 2 measurements.

Finally, as I've said before, the FF Ultra has a problem when corner loaded of driver distance to the 3 reflective surfaces of the corner. There is bound to be an erratic response through the crossover and so, is best placed against a wall and not in a corner.

So, the differences of a few dB and a big difference in response at cross are normal phenomena in such a comparison, IMO.

As far as using the amp in 2 channel mode to power each cabinet separately, it would help if you posted the specifics of the signal chain. I imagine that you're using a Y cable to get the input signal to the 2 channels of the amp and that you're subs are wired to 4 ohms each. I also assume that the cabling is of same lengths from the 876 to the amp and the speaker wire from amp to subs.

Q: Doesn't the 876 have 2 sub outputs? Are you using 1 and not the other or using both, 1 for each channel.

I would suggest to wire your subs to have a switchable input terminal from 4 ohms to 8 ohms. I would personally prefer to run the system at 4 ohms bridged to avoid the gain matching problem.

Of course, checking the voltage from each channel is the proper way to make sure each sub gets the same input, but is a PITA, IMO.

Ricci, LTD; does the DCX allow for level adjustment of its outputs from a single input? If so, it's looking more like the way to go with this system.

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post #209 of 802 Old 04-25-2010, 08:45 AM - Thread Starter
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Originally Posted by bossobass View Post


As far as using the amp in 2 channel mode to power each cabinet separately, it would help if you posted the specifics of the signal chain. I imagine that you're using a Y cable to get the input signal to the 2 channels of the amp and that you're subs are wired to 4 ohms each. I also assume that the cabling is of same lengths from the 876 to the amp and the speaker wire from amp to subs.

Q: Doesn't the 876 have 2 sub outputs? Are you using 1 and not the other or using both, 1 for each channel.

I would suggest to wire your subs to have a switchable input terminal from 4 ohms to 8 ohms. I would personally prefer to run the system at 4 ohms bridged to avoid the gain matching problem.

Of course, checking the voltage from each channel is the proper way to make sure each sub gets the same input, but is a PITA, IMO.

The 876 has 1 sub output, and I'm using a single RCA to XLR cable into the 5050's XLR in for CH1.

I have the amp set to "parrallel mode", which I understand takes a single incoming signal and sends it to each channel equally, but may try splitting the output into a Y Adaptor with two XLR to RCA cables.

The impedence of the subs from the factory was 4ohm. Coils are wired in series for 8ohm, then the drivers in parrallel for 4ohm to the terminal, and is measuring 3.2ohm on my cheapo multimeter from CDN Tire at the terminal.

Not sure what you mean by "running them bridged", do you mean a separate power amp for each sub (which isn't an option due to space unfortunatey!).

 

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post #210 of 802 Old 04-25-2010, 08:50 AM - Thread Starter
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Oh, and I measured the two new dual AV15H subs from about 2 to 3" from the centre of the cone with a tripod so same distance/height when I measured the 3db or so difference at the same gain levels on the amp.

Also, I swapped channels and redid the measurement with the exact same difference, hence why I'm wondering if it has something to do with the sub vs the amp?

Is it possible one sub is "leakier" than the other and causing a 3db difference (seems like a bit drop, but don't know how much of an issue any tiny leaks would make, or how to check for them for that matter!).

 

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