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Podcast HomeTheaterUnited Podcast Episode 15 - Dave Upton on room correction and calibration with REW and Audyssey (1 Viewer)

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.
 

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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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gregw78

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Looking for advice from Dave Upton and any other forum members with experience in room correction. His episode with Sam and Brian on the podcast motivated me to get into REW. I was able to even out the repsponse of my single SVS SB1000 PRO quite a bit but only so much that could be done and still have 15 dB peak to valley in the response in the MLP down from a 28 dB peak to valley before activating parametric filters on the SVS app. Would like to add a 2nd subwoofer but realized my receiver does not allow for individual delay adjustment which would be essential for two subs. I could get a minidsp 2x4, but I think I prefer to upgrade my receiver first.

Onkyo has some new receivers coming out shortly that will have Dirac Live. I would be most interested in the onkyo tx-rz50. Yamaha has built in a new low frequency management into YPAO for their 2021 Aventage receivers that allows all parametric filters for YPAO to be applied to the bass region. The Yamaha RX-A6A has the channel processing and channel number that I would need but seems like a lot more coin and their tech has not been proven yet. Any thoughts on these two receivers coming out this month (yamaha a6a) and October ( Onkyo)? The Onkyo seems like it will be the lowest cost entry point into Dirac which you touted so much on the podcast. Thanks!
 

JohnRice

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Would like to add a 2nd subwoofer but realized my receiver does not allow for individual delay adjustment which would be essential for two subs. I could get a minidsp 2x4, but I think I prefer to upgrade my receiver first.
Dave can certainly contribute a lot more than I can, however, your subs have independent phase adjustments, which along with REW should permit you to deal with that particular issue. A MiniDSP will do it much better, while eliminating any need for dual sub outputs, since it can do its thing using a single output.

Sometime soon I will be posting my review of the dual SVS SB-16 Ultras I got a while back, and one thing I delved into is getting them both into phase, as well as using REW along with their internal EQ to get the best results possible without a MiniDSP.

The other problem is probably room interaction. The first thing to do about that is test other placement options. Corners are the best to avoid peaks and nulls. You always want to improve that with placement first, which can do miracles, then room treatments, then EQ.
 
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gregw78

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I had a 7.1 setup before and just added some front height speakers for Atmos and DTS:X so I need a new receiver anyways to have at least 9 amp connections and 11 channels of processing in case I decide to add rear heights. So trying to decide which receiver to get. I was thinking of the Denon x3700H but then I heard Dave's opinion of Audyssey and I had heard about the new Onkyos and Pioneers implementing Dirac Live.
Definitely with you on placement but my setup is in my living room in my apartment with only really one place where the sub can go on the front which is between the center and left main speaker. So I was thinking add the 2nd in the back of the room where I have a little floor space and have a close to front and rear middle as suggested as a placement in Welti's paper.


Learning a ton from you guys, the home theater guru guy on youtube that Dave recommended and from these online webinars that Anthony Grimani gave on bass



John, I will look forward to reading your review of using the internal EQ on the SVS subs with REW. One thing that I found is that removing a peak with the internal EQ worked amazingly well but trying to boost a dip did not work at all. So I have the EQ just removing the two largest peaks at this time. It was amazing what just doing that did in terms of allowing the sub to equally emphasize low bass in the 20-30 Hz range. Started feeling rumbling and thumps a lot more. I had a huge peak at 47 hz that I think was overwhelming the rest of the frequencies but would never have known without doing the EQ.

Much appreciation to everyone. I was a biomedical engineering major in college and would have loved to take a class on room acoustics in college had I known of my future interest. I feel like home theater setup would be a very popular engineering course...
 

JohnRice

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I had a 7.1 setup before and just added some front height speakers for Atmos and DTS:X so I need a new receiver anyways to have at least 9 amp connections and 11 channels of processing in case I decide to add rear heights. So trying to decide which receiver to get. I was thinking of the Denon x3700H but then I heard Dave's opinion of Audyssey and I had heard about the new Onkyos and Pioneers implementing Dirac Live.
Definitely with you on placement but my setup is in my living room in my apartment with only really one place where the sub can go on the front which is between the center and left main speaker. So I was thinking add the 2nd in the back of the room where I have a little floor space and have a close to front and rear middle as suggested as a placement in Welti's paper.


Learning a ton from you guys, the home theater guru guy on youtube that Dave recommended and from these online webinars that Anthony Grimani gave on bass



John, I will look forward to reading your review of using the internal EQ on the SVS subs with REW. One thing that I found is that removing a peak with the internal EQ worked amazingly well but trying to boost a dip did not work at all. So I have the EQ just removing the two largest peaks at this time. It was amazing what just doing that did in terms of allowing the sub to equally emphasize low bass in the 20-30 Hz range. Started feeling rumbling and thumps a lot more. I had a huge peak at 47 hz that I think was overwhelming the rest of the frequencies but would never have known without doing the EQ.

Much appreciation to everyone. I was a biomedical engineering major in college and would have loved to take a class on room acoustics in college had I known of my future interest. I feel like home theater setup would be a very popular engineering course...

The dip you can’t EQ out is a null. Placement and room treatments are the main way to fix that, but a second sub can also do a lot.
 

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I relistened to this podcast with Dave again and picked up on a major game changer (which to be granted he said it was very important). Dave had said that Audyssey could be off by 10-12 ft in the subwoofer distance. I had played around with fixing the crossover region but had only changed by at most 2 feet not really seeing much improvement. So I redid analysis in REW with sweeps again but this time made changes to sub distance in 5 foot increments. Amazingly this time I found a perfect flat crossover region about 5 ft farther than what YPAO had decided. Trying at 10 and 15 feet did not improve things. Making a more dramatic change in sub distance was a great tip!

I am curious now if I added a 2nd sub how would I time align both of them if my receiver could have independent distances for each subwoofer. Do you turn off the 2nd sub, time align the first sub with mains by changing its distance, then add the second sub and time align it by changing its distance? Or do you time align the subs to each other first by altering their distances independently, then time align both of them to the mains by changing their distances by equal amounts? and do you do this time alignment bof subs with mains before or after audyssey? I know some people get a minidsp 2x4 to handle this but if I get a receiver with independent distances and get a 2nd SVS sub with the built in parametric equalizer, I don't see that there would be a need for the minidsp.

I also have a question about leveling the subwoofer with the SPL meter. Is it ok to use pink noise within the receiver for checking the YPAO levels or is it important to use an external pink noise generator for the sub channel like in ASIO4ALL? I am getting dramatically different results. If I use the pink noise in the receiver to match, the end result is that ths sub sounds much louder and ASIO4ALL method measures the sub as 6dB higher than the mains. very confusing

Last is it ok to use the UMIK-1 as an SPL meter in REW? Somewhere I read that it is inaccurate but it seems just as accurate as an app on my phone.
 
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JohnRice

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I relistened to this podcast with Dave again and picked up on a major game changer (which to be granted he said it was very important). Dave had said that Audyssey could be off by 10-12 ft in the subwoofer distance. I had played around with fixing the crossover region but had only changed by at most 2 feet not really seeing much improvement. So I redid analysis in REW with sweeps again but this time made changes to sub distance in 5 foot increments. Amazingly this time I found a perfect flat crossover region about 5 ft farther than what YPAO had decided. Trying at 10 and 15 feet did not improve things. Making a more dramatic change in sub distance was a great tip!

I am curious now if I added a 2nd sub how would I time align both of them if my receiver could have independent distances for each subwoofer. Do you turn off the 2nd sub, time align the first sub with mains by changing its distance, then add the second sub and time align it by changing its distance? Or do you time align the subs to each other first by altering their distances independently, then time align both of them to the mains by changing their distances by equal amounts? and do you do this time alignment bof subs with mains before or after audyssey? I know some people get a minidsp 2x4 to handle this but if I get a receiver with independent distances and get a 2nd SVS sub with the built in parametric equalizer, I don't see that there would be a need for the minidsp.

I also have a question about leveling the subwoofer with the SPL meter. Is it ok to use pink noise within the receiver for checking the YPAO levels or is it important to use an external pink noise generator for the sub channel like in ASIO4ALL? I am getting dramatically different results. If I use the pink noise in the receiver to match, the end result is that ths sub sounds much louder and ASIO4ALL method measures the sub as 6dB higher than the mains. very confusing

Last is it ok to use the UMIK-1 as an SPL meter in REW? Somewhere I read that it is inaccurate but it seems just as accurate as an app on my phone.
Keep in mind that the distance setting in your rec and the phase setting in your subs are essentially doing the same thing. So you have options on how you do that.
 

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I dont understand that. Do you have a reference that explains that better or can you explain why that is? And if you were to use phase changes you would change it in increments of 15 degrees or so to see if there was a flattening of the crossover? I did try changing the phase on the SVS app in increments of 30 degrees but I was seeing no improvement at any phase change.

And I guess using the phase changes would be a way to time align a 2nd sub if your receiver does not have independent sub preouts?
 

JohnRice

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I dont understand that. Do you have a reference that explains that better or can you explain why that is? And if you were to use phase changes you would change it in increments of 15 degrees or so to see if there was a flattening of the crossover? I did try changing the phase on the SVS app in increments of 30 degrees but I was seeing no improvement at any phase change.

And I guess using the phase changes would be a way to time align a 2nd sub if your receiver does not have independent sub preouts?
The phase adjustment on the sub and the distance adjustment in the receiver are both intended to accomplish the same thing. To smooth the transition area between the main speakers and the sub(s). Whenever there are two adjustments that accomplish the same thing, it opens up potential problems and confusion. Just like having volume controls in both the receiver and the sub for the sub's volume level. There are multiple ways to accomplish the same thing and more opportunity to screw things up.

I would pick one method or the other. In other words, adjust at the sub or the receiver, but not both. My system is a little unusual and I have to use a single sub output for dual subs, and it has no distance adjustment, so I use the phase setting on the subs. You should be able to get them integrated that way. If your receiver has dual outputs with individual distance settings, I'd probably leave both subs at 0 degree phase and use the distance setting to adjust them. Again, to avoid confusion, I'd use one or the other, but not both. You can run your REW sweeps with just one sub turned on, find the distance that produces the smoothest transition for that sub, then switch to just the other sub and do it again. Check it with both subs active to confirm the final results.

Regarding level matching, I wouldn't use a test tone. Once everything has been calibrated to your satisfaction, what I would do is run a full sweep in REW with only one sub turned on measured at your main viewing position, then the other one, and look at the two sweeps on the same graph. Adjust the levels on the subs until they visually have the same average level across the entire spectrum. Get them as close as you can. That will make them balanced with each other. A good idea is to set the trim levels for them on your receiver to "0" and match them to the rest of the system using the individual subs' volume. After that, you want to always keep them balanced, so if you decide to raise or lower their levels, you change them in the receiver the same amount. Meaning, if you want to increase them 1dB, you turn them both up to +1, so they stay in balance. I hope that makes sense.
 

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So my current receiver has 2 subwoofer outputs but they are not adjustable independently for distance. Good to know if I do add a 2nd one, I could use the phase adjustment to try to align without having to buy a minidsp or new receiver. Thanks for the explanation. I'm curious though why I didnt see much improvement in the crossover region of my measurements while changing the phase. I picked lots of different angles and saw nothing. Do you go in 10 degree increments?

To all those out there looking to get into REW, I know Dave had suggested Home Theater Gurus and I watched many of his episodes but this guy Home Theater Gamer (who gives credit to Home Theater Gurus for help) does a much better job of showing the adjustments and measurements in real time in REW. He makes it very simple to understand. I have no financial relationship with this person - he just makes good videos explaining and wanted to share.





I did try out the Alignment tool in the beta version of REW but manual stepwise adjustment by a few feet at a time worked better.

Thanks for the level matching rec too. I was thinking that if things look good on full range sweeps then that would be good enough. Not sure why ASIO4ALL was giving me trouble.

I do have to say that in the podcast Dave grossly underestimated the time involved to figure all this out. Once you get used to it, yeah if I was doing it again, I could do everything in a few hours (best sub placement with REW, then EQing the sbs in REW, then room correction, then aligning the subs and mains with a crossover in REW). But to reach this level has been a learning process that's taken many hours. I do agree with him that it's a worthwhile investment. Just having the ability to measure what things look like with room correction on is worth while. I think anyone in this forum who has invested so much into their home theater should definitely become proficient in measuring since it's $100 for the umik1, free REW, and then spending time learning about your hobby.
 

JohnRice

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So my current receiver has 2 subwoofer outputs but they are not adjustable independently for distance. Good to know if I do add a 2nd one, I could use the phase adjustment to try to align without having to buy a minidsp or new receiver. Thanks for the explanation. I'm curious though why I didnt see much improvement in the crossover region of my measurements while changing the phase. I picked lots of different angles and saw nothing. Do you go in 10 degree increments?
The problem could be something other than a phase problem. If it's a big dip that doesn't change with phase, it's probably standing waves or something that can only be fixed with physical solutions like placement and/or sound treatments.

Here are some examples of what the phase/distance adjustment will do. It's really just a matter if fine tuning. It won't fix massive problems.

This is my living room system which has a single SVS SB-2000. The sweep is far from smooth, but doesn't have severe problems. This shows the effect of changing the subwoofer distance in the receiver's setup. Notice again, it's just fine tuning, once major problems have been addressed.

LR Sub 4:11:21.png


I chose the 10' setting, even though the sub is actually about 13' away.

This is the dual sub setup in my HT, which is actually optimized for music and doesn't have any distance adjustment, so I have to use the phase to integrate the dual SVS SB-16 Ultra subs.

Both Phase 5:8:21.png


To explain the legend, the blue line is both subs (Opposing corners, front right, back left) at 0 Degree. The brown (worse) one is the front at 90 degree and the green (best) is the back at 90 degree. Little changes of 10 degree probably won't do much, so I'd start at 90. As you can see, it can't fix major problems. It's just the last little bit of fine tuning once you get other things right.
 

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