REW Noob - is this a good response? - Page 2

Dear God,

Please explain what the subwoofer Distance setting does. How does setting the subwoofer Distance to the physical "tape measured" distance improve the response?

Thank you God.

Craig

What do I care why something works. One doesn't need to know anything about the chemical reaction of gasoline to know how to get it into a gas tank. When it works, it works and one doesn't have to know why for it to work? And if it doesn't work, change the distance setting back to Audyssey's recommendation and be happy.

When I changed the subwoofer distance setting to the tape measured distance setting, the subwoofers came alive and that's all I care about. In my case, Audyssey got it wrong. Every setting had to be changed from subwoofer distance, to size of speakers, to speaker calibration due to our asymmetrical speaker setup, to crossover frequency. And with the addition of an Anti-Mode, even this was an improvement over Audyssey. Since changing the Audyssey settings by calibrating the speaker output and the main listening position, the center channel is no longer in our face. Yep, Audyssey even got the center channel setting wrong. But I'm sure it does a bang up job in the EQ department.

"Toccata and Fugue in D minor for organ" is a pleasure to listen to. All the air space, depth and room reverberation is there. Close your eyes and you're transported to another place. And I'm suppose to know why? No. I'm suppose to enjoy.

We now listen to background music at -60 to -55 as opposed to -40 to -35 and movie volume is -20 as opposed to -15 to -10. The proof is in the pudding and what the pudding tastes like is all that matters. In my book, those are huge improvements.

When I reset up and take new measurements, I'll be better able to see what's what with what.

In another week, when done mulling over the new insight gained from the last measuring session, I'll reset up, strip everything out and play some more to see what can be seen. Don't cost nothing with nothing but more insight to be gained and it all gets to be done with a newly purchased sound meter that's now a newly calibrated sound meter. Now I have two properly calibrated sound meters; the little rabbits.



As to how it improves the response? Resetting the distance to the tape measured distance, fixed the mid-bass hole that Audyssey created by recommending to the AVR to have the subwoofer distance be double the physical distance as there's not a measurement in the room (including adjoining spaces) equal to Audyssey's recommended distance setting.

Anything more than my above and you'll have to ask God himself.



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Edited by BeeMan458 - 2/1/13 at 10:46pm

Or you can ask somebody like craig john who understands how something works.

Audyssey sets its distances based on the arrival of sound at the microphone. So lets say you have a device in between the receiver and the subwoofer (such as an antimode) that is causing delay of the signal, it will give a longer distance to compensate for this electronic delay. It doesn't however measure the interaction with the mains and subwoofers. So it is of benefit to measure post audyssey and play with the subwoofer distance setting to see if its optimized. When utilizing an 80hz crossover I would say ~+/- 4 feet from the audyssey setting as 14 feet is the 80hz wavelength so 7 feet would be 180 degree phase change. Take measurements in MLP every two feet and choose best frequency response and fine tune distance in smaller increments from there. Mark Seaton does this with center channel and I agree as its the most important for HT and then finds best compromise with R and L after.

If you started your own thread documenting your goals and what you have been doing in your room backed up by measurements, you could get a lot of help in optimizing your system such as the OP has done here. I find it is much easier to ask others who have some understanding, or do the research myself and learn how things work before giving advice to others.
Edited by Luke Kamp - 2/2/13 at 12:36am

One builds off what others have to share; education. But one's education does not end with what others have to share. I'm not having any troubles. My efforts are being rewarded. I am succeeding in improving the sound quality of both speaker and subwoofer output by working outside the box. When recommendations and advice fail to provide gain, one is best served by moving on to the new ideas they won't find, until stepping outside the box. Your point is in conflict with my results. Why would anybody want to harm or denigrate the success of another? That behavior permanently escapes me. It hurts nothing to try something new. Change the many settings to personal tastes and if doing so fails to create an improvement, hit reset and go back to what one finds does work. Nothing is set in stone nor are there barriers to sharing.

Currently, our crossovers are set to 40Hz.

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Edited by BeeMan458 - 2/2/13 at 7:21am

Dispense with that and just knock a hole in the wall.

It would be much simpler and could improve one's REW measurement graph.

Well, since you asked...
Phase, time and distance are interwoven. Ideally the phase of two sources in the zone where their outputs overlap will be very close to each other, so that those outputs constructively sum, rather than destructively cancel each other. To align two sources in phase they're also aligned in time, and time is distance. More or less. The problem here is that each individual source will have its own phase characteristics, so perfect time/distance alignment is no guarantee of perfect phase matching. It could even result in the worst possible phase alignment, with the two sources 180 degrees out of phase at the LP. And, to further complicate matters, move over a couple of seats and everything changes. So while time/distance alignment has its benefits, it's by no means either a panacea nor a necessity.

I eliminated the phase/time difference introduced via Anti-Mode by disabling it when dialing in the system. I have continuous phase control on each of the subs and use REW to flag me in on the best subwoofer phase setting and frequency settings. From placement to settings, everything is asymmetrical. After which, I bring in Anti-Mode, then Audyssey and according to taste, fine tune Audyssey's recommended settings with REW being the final arbiter.

How can you, in good conscience, offer advice when you don't even understand the advice you're giving?

That's fine for you. But when you start to tell others to do something, it would be beneficial if you could explain why it will work.


Well, you're absolutely correct that Audyssey often gets the subwoofer Distance setting wrong, especially in systems with multiple subs. However, setting the Distance to the tape-measured, physical distance is usually not the correct or optimal setting. It may have improved your response, but I would bet it can be better still. You need to understand what the Distance setting does in order to know how to properly set the subwoofer Distance.

Since I know you won't read or try to understand what I'm going to say, the following is not intended for you. It is intended for others reading along to help them understand how to set all the Distances properly.

The Distance settings for all the speakers and sub(s) are actually delay settings intended to cause all the wavefronts from all the speakers to arrive at the listening/measuring position at the same time and in-phase with each other. Why is this important? For the speakers, this is important so that the imaging is correct. For example, in the front soundstage, if there is a sound that is produced by both the L and C speakers, and it is intended to "image" between those 2 speakers, if the wavefront from the C arrives before the wavefront from the L, the "image" will seem to come from the C and not between the two speakers. This is known as the Haas effect or the "precedence effect" and it is related to how humans detect the direction a sound is coming from. More can be read about that here: http://en.wikipedia.org/wiki/Haas_effect If the C is physically closer than the L, it's signal can be delayed a few milliseconds so they both arrive at the listening position together. This is what the Distance settings are for; to align all the wavefronts in time so they all arrive together and provide the sonic "image" that the sound engineer intended.

Audyssey measures the arrival time of the wavefronts from each speaker. It's measurements calculate the time it takes for the receiver to generate the signal, have it be processed by the DSP, amplified by the amplifier, transmitted to the speaker, cause the speaker drivers to move and push and pull on the air in front of the drivers, and then have the air push and pull on all the other air molecules across the room until the wavefront arrives at the microphone. This is the "acoustic distance" and it may well be different than the actual, physical difference due to the cumulative latencies in the system. Audyssey does an excellent job of getting these speaker measurements correct, (assuming Audyssey has been run correctly, (see the Guide: http://www.avsforum.com/t/795421/official-audyssey-thread-faq-in-post-1/5700#post_14456895 ), and it is not advised that the speaker Distance settings be changed afterwards, (unless you have some way of measuring the acoustic distance and optimizing it better than Audyssey has.)

The subwoofer Distance is an entirely different beast. It is used to time the subwoofer with the speakers. This is especially important around the crossover frequency due to the way crossovers work. Crossovers are a combination of a High Pass Filter, (HPF), and a Low Pass Filter, (LPF). The HPF filters the low frequencies and allows the highs to pass the the speakers, and the LPF filters the high frequencies and allows the lows to pass to the subwoofer(s). However, these filters are not "brick walls" that completely cut the frequencies they're supposed to cut. They are "sloped" filters that taper off the signal they are intended to filter at a predetermined rate. Here is a diagram of different slopes of crossovers:



The point here is that, around the crossover frequency, both the speakers and the subs are producing the same content. You want the wavefronts from all the speakers and the subwoofer(s) to arrive at the listening position at the same time because, if they don't, they'll arrive out-of-phase and cause destructive interference. The negative wave from one will cancel the positive wave from the other and you won't HEAR anything at the crossover. Here is an example of that:



In the light blue trace, the subwoofer is out of phase with the CC and the frequencies around the 80 Hz crossover point are being cancelled. In the green trace, this has been corrected and the cancellation is removed. This was done by altering the delay of the subwoofer relative to the speakers, i.e., changing the subwoofer Distance setting.

How does this work? Well, Audyssey measures the arrival times of the sub(s) the same way it does for the speakers, measuring all the latencies in the subwoofer signal chain, including any in the subwoofer itself. It then sets their Distance(s) accordingly. But it never goes back and checks whether the blend at the crossover is optimal. In single subwoofer systems, it's usually pretty good and no adjustment is necessary. However, in multi-subs systems, the arrival from the closest sub, (which is what Audyssey sees and uses to set the Distance), may not be the optimal setting when all the subs are played together. It's not unusual to be able to gain some output, (reduce the cancellation) by adjusting the subwoofer Distance setting.

This is what the BeeMan has unwittingly done in his system. However, it is not likely that he has completely optimized his result. Audyssey measured his sub Distance at 26' when the subs are at 12' and 13'. Audyssey clearly found some latency in his system that is causing a delay in the subwoofer signal propagation. When he shortened the Distance to the physical distance he changed the relative timing of the subs and speakers. He likely aligned the wavefronts better, but he probably has his sub firing a whole cycle before the speakers. This may sound "better" but it's not optimal.

The *correct* way to do this is to ensure that Audyssey is exposed to everything in the subwoofer chain that causes latency, (in the BeeMan's system that means having the AnitMode in the chain while running Audyssey.) Then, using his measurement system, check the response around the crossover. If there is a dip in that range, modify the Audyssey set Distance by a few feet and check for improvement. Then, by trial and error, in smaller increments, check other Distance settings until the dip is completely eliminated, as I did in the graph I posted above. This process will account for the latency in the system as well as optimize the response.

Craig

It never hurts to read what I post; "...and according to taste, fine tune Audyssey's recommended settings with REW being the final arbiter."

You posted that while I was typing. Nonetheless, I thought you said you were on a self-imposed sabbatical from REW. Therefore, you made this change *without* REW being the final arbiter.

Craig

I am. Yes as to the timing of the change but that doesn't mean I won't once again be setting up the microphone to do room sweep based measurements. And when I do,the first thing to be done will be to take a baseline reading to compared to the last measurement taken so I can physically see the change that took place. It was startlingly dramatic. And yes, in the end, REW will be the final arbiter.

I try to do my level headed best to accurately convey my sojourn and yes, I freely acknowledge the ongoing nature of the pursuit. Yes, the distance measurement change was made after the room was broken down. The wife likes it when I throw breaks into the process and the side benefit is, it allows my brain time to pass into the subconscious, what it's learned at a conscience level. And I know you know about how powerful the subconscious mind is regarding complex 4-D problem solving issues.

And yes, I understand the need for all the created sounds to come together at the same time and point but since one is dealing with more than one seating position, multiple speaker locations which are bouncing sound around in non-standardized rooms with varying measurements (everybody's listening venue is different then the one the sound engineer used), one needs to create a balance between the ideal and reality.

Personally, it's quite entertaining to watch nulls come and dips go as parametric settings are changed. Whoa, check that out! Okay, that didn't work.

Well your trolling efforts are being rewarded as I am actually replying again. Like Craig John said you are probably a full cycle off changing distance so much. I agree you are outside the box but am uncertain if its helping much of anything but your post count. No need to reinvent the wheel, squares still don't roll well. What results? But please post them in your own thread instead of jumping around in others talking about your system and how it is setup incorrectly. I just don't like people giving incorrect advice on a regular basis, this behavior permanently escapes me.

Crossovers at 40hz Have you measured speakers individually? Do you know compression characteristics? Do you understand modal smoothing below the transition frequency and the purpose of using multiple subwoofers? You do a lot of things "outside the box" and then recommend others to do them. There are a lot more factors to setting up crossovers than a stereo frequency response at 80db IMO. But I am sure you understand all of this with all of your experience and education.

You made changes without measuring. You tell people to set distance setting to physical distance without understanding how or why that works or even what it did because you haven't measured. You say knock a hole in the wall as it might help. Probably had to sleep on that to let the subconscious get a grip on that. You take sabbaticals from measuring, and play God when you override audyssey... and the list goes on and on. I am not trying to knock your success. Rock on with your bad ole self, just be ready for replies on bad advice.

Some of the advice and made up vocabulary pertaining to audio reminds me of the quote from the movie Catfish.

Vince Pierce:
They used to tank cod from Alaska all the way to China. They'd keep them in vats in the ship. By the time the codfish reached China, the flesh was mush and tasteless. So this guy came up with the idea that if you put these cods in these big vats, put some catfish in with them and the catfish will keep the cod agile. And there are those people who are catfish in life. And they keep you on your toes. They keep you guessing, they keep you thinking, they keep you fresh. And I thank god for the catfish because we would be droll, boring and dull if we didn't have somebody nipping at our fin.

Sometimes its the off the wall comments on here that bring about some of the best posts. Another well put together post by Craig John, thanks again.

It is completely impossible to optimize the speaker Distances for more than one location at a time. Have fun trying though. I suggest you write down the Audyssey settings before you start changing them. At least that way you can go back to them after you've screwed everything up.

BTW, if you suggest to someone else that it can and should be done, you can expect some push-back on that.

Craig

I set the 40Hz crossover based on measurements, not the other way around and yes, changes are made first and then measurements are taken. Yes, measurements were taken on individual speakers as necessary. I have quick disconnects on the mains and on/off switches on each of the subs. And I do individual calibrations on each individual speakers. When it comes to measurements, it's quid pro quo baby. None of this is set in stone/

Knowing that you read what I posted, I know you read that yes, I freely acknowledge the changes being made and followup measurements have not been taken. Don't know why this fact would cause you such emotional upset. It sure doesn't bother me. And I guess I could say the same regarding your trolling efforts as here I am responding to you. Responding to each other is what a forum is all about.

Yes, I recommend (encourage) folks challenge the veracity of Audyssey's recommendations and I also recommend they use a room analyzing program to measure what changes take place and since you're reading what I post, you know this is what I recommend. And if someone doesn't like what the changes show when measurements are taken, they can easily change things back but if someone doesn't try, they'll never know, will they?

It don't cost nothing to play with what one has and that's why it's called a hobby; entertainment.


I'm able to keep the settings in my head so I can go back to them. Saves on paper. And if I ever lose my way, I simply hit the reset button and start over, which so far hasn't been necessary.


Shame on me for suggesting someone think outside the box. Nobody's gear is going be hurt, they'll get an education regarding room analyzing programs and in the end, better understand their room's acoustics for the effort and we both know that's a good thing.

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Edited by BeeMan458 - 2/2/13 at 3:50pm

Thanks, Luke!

Multiple subs. The more you have the more jumbled up are all the time, phase and response issues, so that none of them dominate the end result.

There one unmentioned arrow in your quiver that's not much discussed and that's asymmetrical settings of your subwoofer's continuous phase setting beyond that of 0 and 180 degrees.

Another parametric setting I don't see discussed is asymmetrically setting the frequency limiter potentiometer in the subs. Limiting the response of one of our subs has make dramatic differences in nulls. It's interesting to see the quid pro quo nature of parametric setting changes as one gets rid of a null in the mid-bass, a dip shows up in the low end and when the low end is boosted, the mid-bass response is lowered as one begins to see a sonic "axis" develop, based on their room's acoustics.

And what do we do about the crying spouse? ......................(j/k)

(Don't worry honey, you'll get use to it.)

She's so much happier with the subs that just so happen to be in a happier place when hidden. In fact this has brought about purchasing choice changes as I'm now looking to a SVS column sub, coupled with a dual driver sub by PSA as opposed to a pair of Funk Audio subs with a high WAF. Or maybe a pair of Rythmik F12SE's coupled to a E15 as looks are becoming less and less a consideration due to REW inspired placement changes.

The point, if the subs have similar sonic characteristics, asymmetrical purchasing and placement is also also a potential solution.

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Edited by BeeMan458 - 2/4/13 at 10:18am

For the speakers, there is no "best compromise." You should optimize the speakers Distances for the primary LP and take what you get elsewhere. Whenever you move off-center-axis, the imaging will move with it. There is no way around it.

For the sub, Bill nailed it... multiple subs.

Craig