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Subwoofer / Speakers Aligment in Time Domain


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#1 of 9 OFFLINE   BraveHeart123

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Posted May 18 2012 - 11:26 PM

I've been trying to seemlessly blend my all 5 speakers with sub, by simply adjusting the distance of subwoofer wrt all my other speakers keeping distance of all other speakers to what audyssey suggested. Which was ok, but I always thought something was lacking. I have a BFD 1124p also in the sub chain and there were huge dips and peaks in my room which I was never able to remove. Reading here, I came across people who suggested that NULLS in the room cannot be corrected no matter what type of equalisation is employed. So, only option was to move the sub to some other position. But I kept thinking on other lines. Yesterday it just occured to me why not keep subwoofer distance constant and play around with distances of each individual speaker. Coz I though what if I get married to 5 women at the same time? I am only one person.....how would I be able to keep all the 5 women happy? It is not possible. So, I thought why not all the 5 women do their own tiny bit and keep me happy? So, I came up with the idea of adjusting the distance of each individual speaker, One At A Time, and match the phase with the sub at my reference volume in my 5.1 setup. This is what I did;
  • Disconnected all the speakers except one.
  • Set the SPL meter on tripod at the main listening position (Slow response/c-weighted).
  • Set the crossover on avr at 80hz, played an 80hz tone, and measured the SPL.
  • Then I adjusted the distance of that particular speaker where I got the max SPL.
  • Repeated the above steps for all the 5 speakers independently. All the distances were now way off the actual physical distances.
RESULTS
  • The NULL at 71Hz, which measured -17dB below my reference SPL now gave me -3dB below reference SPL. Which means that by time aligning my speakers with sub, I automatically removed a NULL from my room. Also, the post measured FR showed other dips and peaks far less pronounced.
  • At the corssover region, my new spl is 4dB hotter than before.
  • The overall sub response is smoother than ever after setting the filters on BFD. I didn't have to do much.
  • The bass in music is very loud, snappy, and fast with no hint of boom at all. Same goes for movies and I get a very loud and smooth response down to 23hz without straining the amp on sub. Also, it is very seemless blending.
  • In a nutshell I am completely blown away with how my system is performing now. I never thought how important time alignment was in a system.
Going by the book, I wasn't getting anywhere by keeping the actual physical distances of speakers in AVR. Coz that distance setting was from the speaker to the main listening position, whereas the speakers have to be in sync with sub from their own actual location against the location of the sub. Going by the book was causing misalignment in time domain causing huge peaks and dips in sub response. Any comments on calibrating the system this way??? Coz I did not do it the old orthodox way

#2 of 9 OFFLINE   Robert_J

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Posted May 19 2012 - 03:07 AM

I'm not familiar with Audyssey so I can't speak on it's time alignment/distance but Pioneer's MCACC is dead on. I used my wife as the "listener" and measured the distance from her head to each speaker and the auto calibration settings were the same. The sub was different though. It actually calibrates it closer than it actually is. The BFD puts a slight delay in the sub chain as it digitally samples, EQs and converts back to analog. It's not much but as you found out, a little change can make a huge difference. Since every room, system and listener is different there is no hard and fast rule for anything we do here but your new method of calibration makes perfect sense to me. Nulls are created by cancelling out frequencies either from the room or from other speakers. So how far away are the settings from the actual distances? What type of signal did you use? Pink noise?

#3 of 9 OFFLINE   BraveHeart123

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Posted May 19 2012 - 04:00 AM

Actual Distances Calculated by Audyssey FR / Center / FL: 10 Feet ........I tape measured it. It was dead on. SR: 6 Feet ....... Tape measured and it was dead on. SL: 7.5 Feet ...... Tape measured and it was also dead on. Sub: 22.5 Feet .... Physical distance is different, but audyssey set it so for obvious reasons. I first changed the sub distance to 21 feet by playing 80hz test tone coz it gave me max SPL at 21 feet keeping distances of all speakers constant and keeping all the speakers hooked on coz that's how it is in the real world. As nobody listens to only subwoofer. Then I reverse engineered using 80hz test tone created using NCH software and setting the crossover at 80 hz on avr. Then I followed the procedure in my earlier post Distances figured out by me of each speaker where I got max SPL FR: 7.5 Feet Center: 8 Feet FR: 13.5 Feet SR: 4 feet SL: 13.5 Feet. Also, I set the BFD filters after running audyssey coz it gave me a starting point. The end result is nothing less than FANTASTIC both in movies and music. btw I am using 256-312kb lossy mp3 format for music. For movies, I am using mkv files. So i can well imagine how SACD and actual blu ray movies would sound. I figured out the rule of thumb ...... You cannot keep 5 wives happy at the same time; let it be the other way round!

#4 of 9 OFFLINE   BraveHeart123

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Posted May 19 2012 - 08:28 PM

Now this also raises the question if at all one needs seperate amplifiers for mains or all channels. I think certainly NOT, at least in a given room. Coz logically speaking, if we are running all speakers small and routing anything below 80-100 hz to the POWERED sub, there is no need throwing money into seperate amplifiers for speakers. Anyone trying to pull the trigger on seperate amplifiers, should first check if their speakers and sub are in phase in time domain or not. The first step is to time align the system. It opens up the compressed soundstage coz subwoofer is now complementing the speakers seemlessly, and most importantly, ACURATELY with tons of low end and LFE. Internal avr amps are enough to drive the speakers. And all these effects have been achieved in my bedroom, which is extremely challanged acoustically making it the last option for any HT freak to install their system in.

#5 of 9 OFFLINE   Robert_J

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Posted May 20 2012 - 09:57 AM

there is no need throwing money into seperate amplifiers for speakers.

As I said, there are no hard and fast rules. With my 4 ohm center channel, my receiver will shut down on gun shots. I'm upgrading my left and right to 4 ohm speakers soon so it really may not have the juice to power them during strenuous passages. You have found what works for you. I admire the effort you put into this as well. Most people would have given up but you stuck with it like a man on a mission.

#6 of 9 OFFLINE   BraveHeart123

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Posted May 20 2012 - 04:17 PM

Most people would have given up but you stuck with it like a man on a mission.

Yeah, coz money is hard to come by

#7 of 9 OFFLINE   amirm

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Posted May 24 2012 - 06:33 PM

If my read is right that you have changed the delay for your 5 channels, I don't think that is a good idea. You no longer have time sync between them and the picture. Yes, changing the phase between them and the sub can help smooth the response as they all act like mini-subs in the crossover region. But it is not the right trade off. I also don't think you have achieved "time alignment." The best solution for low frequency optimization is to have more than one sub and place them optimally. That lets you get rid of some of the nulls, leaving you with just the peaks which can shave off with the DSP. Here is an article I wrote on low frequency optimization which explains this: http://www.madronadi...imization.html. As you see in that article, you also achieve excellent seat to seat variation which is important in home theater applications. All of this said, the results of good optimization is what you are describing. So if sync is not an issue, then I say may already be there :).

#8 of 9 OFFLINE   Robert_J

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Posted May 25 2012 - 05:54 AM

I don't think that is a good idea. You no longer have time sync between them and the picture.

These changes are in milliseconds. Every receiver on the market does this when you set the distance.

The best solution for low frequency optimization is to have more than one sub and place them optimally.

Faisal is in Pakistan. It's not like there is a Best Buy down the street from him. From this and our other discussions, stereo equipment isn't as easy to acquire or as cheap as it is here. He did what he had to do to make his system work. My guess is that Faisal has reflection issues from walls near his speakers. The auto calibration system is doing it's best to work with this but it doesn't satisfy his ears. He used his SPL meter and his ears to make changes that sound good to him. If he attacked the reflection issue (if there really is one) then he may have to make distance changes again.

#9 of 9 OFFLINE   amirm

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Posted May 25 2012 - 02:12 PM

These changes are in milliseconds. Every receiver on the market does this when you set the distance.

I know that. The distance is set to align the speakers to be at the acoustic center. If you mess with the timing for the purpose of equalizing the frequency response then you lose that. And change them enough and you lose sync with the video. Every frame in 24 fps movie is 40 milliseconds. It goes down to 16 msec for 60i video.

Faisal is in Pakistan. It's not like there is a Best Buy down the street from him. From this and our other discussions, stereo equipment isn't as easy to acquire or as cheap as it is here. He did what he had to do to make his system work.

I read him asking for feedback on his method and I provided some. I read that he has a DSP so he is not living in the desert with a rabbit ear and black and white TV :). But sure, if he can't afford some of the solutions, it is not for him. For others who also read these threads, it may provide some additional solution.

My guess is that Faisal has reflection issues from walls near his speakers. The auto calibration system is doing it's best to work with this but it doesn't satisfy his ears. He used his SPL meter and his ears to make changes that sound good to him. If he attacked the reflection issue (if there really is one) then he may have to make distance changes again.

Reflections are an issue above transition frequency and not in the modal region. This graph from my article shows this clearly: Posted Image In the frequencies below transition, sound is modeled using wave acoustics so we do not talk about reflections (other than the fact that they are responsible for room resonances). Best solution for this region is as I have described in the article which follows the teachings of Dr. Toole. Optimal placement of two or more subs is the key together with a DSP. If OP has one sub, he may be able to get a second. If he can't, he can use his DSP to pull down the peaks. As I noted, if he wants to do nothing and he is happy, that is fine too :).




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