Dual Opposed AV15H Subwoofer Build - Page 7

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...

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.

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

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.

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:

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

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

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

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

"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.

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

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

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.

you should try the "white snake dvd". That will definitely let you know how your bass are.

Set your multimeter to AC voltage.

More gain for what? To get an equivalent SPL? equivalent voltage?

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

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?

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.

Bosso