Originally Posted by BeeMan458
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.
How can you, in good conscience, offer advice when you don't even understand the advice you're giving?
Originally Posted by BeeMan458
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.
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.
Originally Posted by BeeMan458
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.
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.