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Podcast HomeTheaterUnited Podcast Episode 15 - Dave Upton on room correction and calibration with REW and Audyssey (2 Viewers)

JohnRice

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One of the main reasons for dual subs is to combat room modes and nulls. By colocating the subs, you are giving up that advantage for any axial modes.

So for that reason, I strongly recommend placing them in different spots in the room. Dr. Toole did some great research on this and found the best locations for multiple subs were as follows:

View attachment 92690

I generally tell most folks to go with one of the top 2 on the right, in the corners or on opposing corners. If you want to read the whole presentation, check out the attached PDF.
Thanks Dave. I could do opposing corners like top #3, just with the corners reversed. My option for top #4 would have the left one about 1/3 into the room. It can't go in both front corners.
 

DaveF

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All very interesting. I could do dual subs, separated by 4-6’ behind the back row. But I can’t do opposite corners.

I could maybe do front of room if I really want to, but aesthetically I don’t like it. And the wiring isn’t setup for that at all.

Ideally, I’d get my in-wall sub corrected / fixed. But practically, it’s likely cheaper to toss in a new sealed sub than to have the installer out to investigate the in-wall sub at $120/hr plus possible replacement cost.

I’ve finessed things into working well enough for my normal use. But with fixing the sub situation is in my planning for when I do 4K projector.
 

John Dirk

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I could maybe do front of room if I really want to, but aesthetically I don’t like it. And the wiring isn’t setup for that at all.

Don't forget, there are wireless options such as SVS's "Soundpath" solution. I think support for it is built into pretty much all of their products now.
 

DaveF

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At $120 for a cheap wireless relay, it's good to know about this as an option. And good to look for alternatives. I suspect there are $12 variants that work as well.

But if I'm willing to go this route, and sacrifice aesthetics, I can use most any sub ported or sealed. More importantly, I could put the subs below screen facing front row rather than behind the second row which is probably less good overall.

I don't know. Will continue to noodle on this for a while. :)
 

JohnRice

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OK, I've been diving into REW and optimizing incorporation of my subwoofers. I started in my living room, and achieved some nice improvements. I ended up with the SB-2000 in the front right corner, based on placement tests, then I checked adjusting the phase for best integration with the front speakers. I originally had the speaker distances set for their physical distance in the setup of the Marantz SR7012 receiver. The crossover area was a little bumpy and I wanted to see how I could easily smooth it. The subwoofer is physically 12' from the viewing spot, but I adjusted it in 1 ft. increments down to 8 ft. and found that at 10 ft. it smoothed the crossover area by about 4dB. When I went to 8 and 9 ft. it further smoothed the initial low spot, but created a new one about 1/2 octave higher. 10 ft. gave maximum smoothing of the initial peak, with virtually no increase in the second one.

The smoothness of low frequencies is significantly improved. As with most systems, it had some significant peaks and valleys, but fortunately no nulls. Those are substantially improved.

Today I started in on the HT. In there I have a setup where I can play "Pure" music. No surround electronics, digital crossovers or distance settings. So, in that system, I need to configure everything for that part of the system first, then I can move on to surround once its done. That system has an SVS PB12 Plus/2 subwoofer, which is a dual 12", downward firing, ported model. It has three ports and I plug two of them.

One thing REW allowed me to do is clearly determine the best way to configure the sub. The original instructions for it stated that when using two plugs, to get its infrasonic filter to 16Hz. A few years ago Tom Vodhanel (the "V" in SVS) had suggested that I set it to 25Hz instead. That tamed some wildness the subwoofer always had, but I'd always been bothered that it might be limiting its range. Finally I was able to test it and found that this subwoofer in fact does kind of "lose it" with two plugs and the 16Hz setting. Setting it to 25Hz in fact provided the smoothest playback, because the 16Hz setting resulted in a significant peak around 20Hz.

I tried a few different placements. It had been diagonally behind the front Right speaker, with the ports facing right. I tried closer to the right corner with the ports facing both left and right. Then settled on having it close to the original location, but with the ports facing left rather than right.

The next step was to experiment with the crossovers in the Emotiva XSP-1 preamp I use for music. The crossovers in this unit are very basic analog dials, and there is no way to actually know where they are crossing over without room analysis. Not ideal, but the low price of the XSP-1 relative to its exceptional sound quality is worth the compromise. As I analyzed things, running the main speakers (Thiel CS 3.6) and sub independently, I found there was a peak from the Thiels at around 70Hz. They are big and heavy, and I simply don't want to experiment with their placement. So, I raised the crossovers until it was slightly above that frequency, which made it possible to smooth it out. It wasn't a huge peak, but I wanted to find out what I could do and see how flat I could get things using the very limited options with this setup. I also found that setting the sub's phase to 90 degree made a small improvement in the crossover area.

I spent maybe three hours on this, and haven't actually listened to anything yet. One thing is for certain, the sweeps look a lot better. We'll see how I feel about the sound. Fortunately the room doesn't appear to present any significant problems, since the sweeps look quite good as they are.

Now I need to move on to the surround settings, but since the core performance is corrected, that should be fairly minor.
 
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