Dual Tumult in room resp and BFD set-up

Rich X · 09-14-2003, 10:22 AM

I've been busy trying to set-up my BFD this weekend for my Tumults. I have two Tumults in 18" sealed enclosures with a QSC PLX3402 amp and LT.

Measurements at the listening position using Stryke CD and Radio Shack SPL meter w/ corr. values are below. Seems like a very flat response other than a few nasty nulls. I've attempted some corrections with the BFD. Any additional advice would be appreciated. I have not attempted any real room corrections yet (Bass Traps, etc.)

Freq RAW BFD
10hz 76.0 76.0
12.5 78.5 80.5
15hz 82.9 82.9
17.5hz 83.0 84.0
20hz 84.0 85.0
22hz 84.5 87.5
25hz 73.0 83.0
28hz 75.1 82.1
32hz 74.0 83.0
36hz 84.7 87.7
40hz 86.5 88.5
45hz 85.0 86.0
50hz 84.5 84.5
56hz 85.5 85.5
63hz 72.5 73.5
71hz 61.5 62.5
80hz 75.5 76.0
89hz 73.8 73.8
100hz 70.0 71.0
112hz 69.0 70.0
126hz 73.5 74.5

Wayne A. Pflughaupt · 09-14-2003, 04:53 PM

Rich,

Based on these readings, it doesn’t look like things are going well here at all. You did a good job of raising the depressed area between 22 and 36Hz, but you also raised 36-56Hz area. This was not needed and indeed negated most of the ground gained by raising the depressed 22-36Hz area.

Specifically, before equalizing there was a 12dB differential between the two areas. After equalizing the differential is 8dB - only 4dB improved. Thus equalized response is only marginally better than unequalized.

Actually, unequalized response going in is pretty poor, which suggests to me that we can probably make some improvements by experimenting with placement.

A few basics: With an exception being rectangular rooms, typically only one location will give the best unequalized response. Ideally, what you are looking for is the place where:

Average SPL remains the highest.
Response is the smoothest – the fewest peaks and dips.
The smallest differential between the lowest dip and highest peak.

Of course, no position will deliver all three of these in spades, or else you wouldn’t need to equalize. But one location should deliver these goals, or at least two out of three, better than others.

If you haven’t already tried it, a good corner location – one with the longest uninterrupted wall length on both directions - should be one of the locations you take measurements from. I haven’t come across too many rooms where another location gave the best starting point for equalization.

If there is only one prime location in the room, then it stands to reason that if you have two subs, they should both be located there. Placing the second sub in an inferior location obviously means you have one sub performing more poorly than the other. In addition, it is extremely difficult to equalize subs that are in separate locations, delivering significantly different response curves. (Again, the exception here would be a rectangular room, were there is more than one ideal corner).

With two subs it is often to use separate placement, asymmetrical placement, etc. With experimentation, many report that they can achieve smoother response this way, (although it hasn’t worked for me). But IMO this is only an exercise for installations where equalization is not used. I don’t expect an arrangement like this will often – if ever -outperform dual equalized subs that are both located at the room’s prime position.

In addition, your reading should be taken with both the subs and mains on. This will allow equalization to address any phase problems introduced by the crossover.

Since you’re using the BFD, there is no reason to use bass traps, too. The EQ is much more effective, IMO.

So – why don’t you try finding a better location and post some new numbers for us. The BFD is capable of delivering much better response than we’re getting here.

Regards,
Wayne A. Pflughaupt

Brian Bunge · 09-14-2003, 05:15 PM

Wayne,

That's not going to happen. Rich has his Tumults inside a cabinet to the L/R sides of the screen. So playing with placement isn't an option.

Rich X · 09-14-2003, 09:37 PM

Wayne,
Thanks for your detailed feedback. As Brian points out, when it comes to placement I may be screwed, as the subs are in a custom cabinet. My only placement option may be to add a THIRD sub...

But before I go there I'd like to make the best of what I have. As you point out, I was able to improve the null that I have somewhat, however in doing that I also increased the level at the 36-56hz area. I did not make any adjustments to that range--it just happened when I boosted the 22-36hz range. I even added a cut filter to the 36-50hz range but it had no effect.

To be clear these are the BFD adjustments that I have made thus far. This is the first time I've ever experimented with an eq like this so I may be way off from what I really should do.

Freq= 25 BW=6 Gain=8
Freq= 30.9 BW=8 Gain=8
Freq=40 BW=8 Gain=-6
Freq=63 BW=10 Gain=12

Also, I took these measurements without my mains. The reason I did it that way is that I am most interested in their perfomance for the LFE channel. My mains may really help as they are full range. For the music listening that I've done with my mains only I have been very pleased with the low end. I'll have to take some measurements with them engadged with the subs.

Given the limitations that I have, what should I try next?

Thanks

Rich

RichardHOS · 09-14-2003, 11:01 PM

I'm not sure why you have a filter set at 30.9Hz and another at 40Hz (is that 30+9/60 ?), one with a gain +8, the other -6.

Looks like the filter at 40Hz needs more negative gain, unless that is actually another close filter at 30.9 ??

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Wayne A. Pflughaupt · 09-14-2003, 11:21 PM

Rich,

Try taking main/sub readings with the mains set to small, if you haven’t already. Often if there are too many low frequency sources it can mess up response. Not to mention, if the room tends to cause a certain frequency range to peak, it will probably be exhibited in both the mains and subs – and you can’t equalize the mains.

Naturally, after everything is EQ’d properly, if you feel that music sounds better with just the mains running at full, you can always switch over.

Regards,
Wayne A. Pflughaupt

RichardHOS · 09-15-2003, 12:56 AM

Hmm, not sure I really understand that reasoning. I would certainly agree that to begin with it would be best to disconnect the mains and set the sub crossover as high as possible, thus getting a good picture of the room's resonances.

But when setting filters, I would think you first would set filters just for the sub, and then adjust the filters after adding mains back to the mix. No, you can't EQ mains, but if the mains are producing a peak you can sure lower the sub output in that frequency range to compensate.

Rich X · 09-15-2003, 10:09 AM

Quote:

I'm not sure why you have a filter set at 30.9Hz and another at 40Hz (is that 30+9/60 ?), one with a gain +8, the other -6.

Richard,
I originally set the filters at 25hz and 30.9hz to boost the null. After taking measurments with just these filters I notice that the level in the 36-45 hz range had increased so I added the cut at 40hz to try to offset--it did not work.

Quote:

Try taking main/sub readings with the mains set to small

Quote:

I would certainly agree that to begin with it would be best to disconnect the mains and set the sub crossover as high as possible, thus getting a good picture of the room's resonances.

For these measurements, I set the mains to small and raised the x-over to 160hz. This way the signal was entirely going to the subs.

My pre/pro (AVM-20 v1.12) has a couple different sub options. The "yes" setting is the tradtional set-up where LFE and bass from small speakers is routed to the subs. It also has a "super" setting where bass from small speakers and LFE is routed to both the subs AND to Large speakers. Normally I use the yes setting with mains as Large. I don't think I want to send the LFE to the mains and I do not want to x-over the mains at the high x-over that is needed for the center and surrounds. (Center and Surrounds roll-off at 50-55hz. I usually set the x-over at 70hz).

The upgraded DSP board for the AVM-20 (I have one on order with my local dealer) allows you to have two completely different set-ups for music and movies. It also allows you to set individual x-overs for each speaker and to bypass the x-over for the LFE signal (some movies have LFE up to around 120hz)

Once I have the upgraded board, I'm likely to set up the mains as follows:

Music: Small w/ x-over at 30hz (mains begin to roll-off at 35hz)
Movies: Small w/ x-over at 50 or 60hz, sub set to yes so LFE only goes to subs, LFE bypass on so that LFE above the x-over still goes to subs.

With those options, how should I set-up the system to take new measurements with the mains engaged? My thinking is that I should set them to small w/ a cross-over at 50hz and see what it looks like.

Thanks for your help.

Rich

Wayne A. Pflughaupt · 09-15-2003, 10:38 AM

Rich,

Quote:

Music: Small w/ x-over at 30hz (mains begin to roll-off at 35hz)
Movies: Small w/ x-over at 50 or 60hz, sub set to yes so LFE only goes to subs, LFE bypass on so that LFE above the x-over still goes to subs.
Give those options, how should I set-up the system to take new measurements with the mains engaged? My thinking is that I should set them to small w/ a cross-over at 50hz and see what it looks like.

I believe the BFD has memory functions, so you can take readings and equalize for each scenario.

However, since you keep the subs low-passed no higher than 60Hz, your biggest problem with either scenario is the 22-36Hz region. So one EQ setting may work well for both situations.

Quote:

I originally set the filters at 25hz and 30.9hz to boost the null. After taking measurements with just these filters I notice that the level in the 36-45 hz range had increased.

This is a side effect of filters set with the bandwidth too wide.

Once you take some readings with everything set the way you intend to use it for each scenario – small/large settings, crossover frequencies selected, etc. – I’ll see if I can recommend some filter settings.

Regards,
Wayne A. Pflughaupt