Subwoofer distance

[Buckle-meister]

Dear all,

The following is a quote from the Audioholics paper Subwoofer Calibration Using Rives Audio Test CD 2: "...Also, I had to increase the amount of delay to 20 feet even though the subwoofer is only 13 feet away."

The incorrect subwoofer distance had been deliberately input to reduce a 63Hz spike SPL reading in order to try to achieve as flat a response as possible for the sub.

1. Doesn't this mean that the timing of the LFE information would be wrong? Or does this not matter due to the non-directional nature of the sub coupled with the speed of sound and the 20-13=7 feet distance?

I ask because, the other day I checked on the OSD, the distances Yamahas YPAO automatic calibration had set for my own 5.1 setup. All the speakers bar the sub seemed ok, but the sub was stated as being approximately 5m away from the listening position, whereas in fact it was more like 3m. I then manually overwrote YPAO's setting, believing that the automatic calibration had simply struggled to accurately place the sub. However, I now wonder whether YPAO was doing the same thing as described in the paper, and whether or not I should change the distance setting back again.

2. Whats the consensus?

Regards

Robbie

 

[jeffsg4mac]

Hmmmm, good question. Mabe Gene or Pat could shed some light on the subject. I do know that when I looped the tone and played with the delay I could watch the peak rise and fall. I now have two different subs than when I first wrote that review and my distance setting is at 0 now. Two Velodyne 12's placed in opposite corners. Two subs solved a lot of problems.

 

[rumble]

Dear all,

The following is a quote from the Audioholics paper Subwoofer Calibration Using Rives Audio Test CD 2: "...Also, I had to increase the amount of delay to 20 feet even though the subwoofer is only 13 feet away."

The incorrect subwoofer distance had been deliberately input to reduce a 63Hz spike SPL reading in order to try to achieve as flat a response as possible for the sub.

1. Doesn't this mean that the timing of the LFE information would be wrong? Or does this not matter due to the non-directional nature of the sub coupled with the speed of sound and the 20-13=7 feet distance?

I ask because, the other day I checked on the OSD, the distances Yamahas YPAO automatic calibration had set for my own 5.1 setup. All the speakers bar the sub seemed ok, but the sub was stated as being approximately 5m away from the listening position, whereas in fact it was more like 3m. I then manually overwrote YPAO's setting, believing that the automatic calibration had simply struggled to accurately place the sub. However, I now wonder whether YPAO was doing the same thing as described in the paper, and whether or not I should change the distance setting back again.

2. Whats the consensus?

Regards

Robbie

I don't have any experience with YPAO but the system my Pioneer uses is similar I believe. My system sets the sonic distance of the speakers from the calibration microphone. It also set my subwoofer to a distance greater than my main speakers even though the physical distance is about the same. The speaker distance calculated by the auto calibration system is such that sound from each speaker reaches the listening position(calibration microphone) at the same time. Your subwoofer is probably slower generating the test signals than your other speakers so YPAO sets the distance greater to compensate.

 

[Tom351]

Is it possible that there were other Low Frequency (63hz) sources in the room such as full-range speakers? I ask this because the sub could have been summing (time aligned at the listening position) with another loudspeaker and the extra delay could have been used to get them slightly out of phase with each other thus attenuating that frequency at the listening position.

 

[Buckle-meister]

I don't have any experience with YPAO but the system my Pioneer uses is similar I believe. My system sets the sonic distance of the speakers from the calibration microphone. It also set my subwoofer to a distance greater than my main speakers even though the physical distance is about the same. The speaker distance calculated by the auto calibration system is such that sound from each speaker reaches the listening position(calibration microphone) at the same time. Your subwoofer is probably slower generating the test signals than your other speakers so YPAO sets the distance greater to compensate.

Eh? Isnt it the other way around?

If the sub is slower, then the distance would have to be less to achieve all sound reaching the listening position at the same time.

Is it possible that there were other Low Frequency (63hz) sources in the room such as full-range speakers? I ask this because the sub could have been summing (time aligned at the listening position) with another loudspeaker and the extra delay could have been used to get them slightly out of phase with each other thus attenuating that frequency at the listening position.

My front towers are from 48Hz to 30kHz. The centre and sourrounds are from 80Hz to 30kHz.

Regards

 

[rumble]

Eh? Isnt it the other way around?

If the sub is slower, then the distance would have to be less to achieve all sound reaching the listening position at the same time.


Regards

No. The system sets the distance by calculating how long it takes the test signal to reach the microphone. For example the test signal from one of the main speakers takes .32 seconds to reach the microphone. The system calculates the distance for that speaker to be 15 feet. The signal sent to the subwoofer takes .45 seconds to reach the microphone. The system sets the distance for the sub at 22 feet, it must be "further" away since the sound took longer to arrive at the microphone. Once all of the speaker distances are calculated the receiver can adjust the delay for each speaker so that sound arrives at the calibration area at the same time.

 

[Tom351]

Rumble is correct, I also mistakenly referred to "more delay" but the increased distance setting would decrease the electronic delay to compensate for a later arrival from this greater distance.

 

[Buckle-meister]

No. The system sets the distance by calculating how long it takes the test signal to reach the microphone. For example the test signal from one of the main speakers takes .32 seconds to reach the microphone. The system calculates the distance for that speaker to be 15 feet. The signal sent to the subwoofer takes .45 seconds to reach the microphone. The system sets the distance for the sub at 22 feet, it must be "further" away since the sound took longer to arrive at the microphone. Once all of the speaker distances are calculated the receiver can adjust the delay for each speaker so that sound arrives at the calibration area at the same time.

Ah, OK. However;

1. Doesn't this mean in principal that it doesn't matter if a speakers distance is incorrect (in reality) so long as the corressponding delay ensures that the sound delived from it arrives at the listening position at the correct moment in time?

2. I could leave the (incorrect) distance as it is at present because the delay (as set by YPAO) brings it back 'into line', whereas if I correct the distance from say 5m to 3m, I would also have to increase the delay?

Regards

 

[Tom351]

1. Yes, in principal, because the distance setting's goal is to time align everything and "feet" is easier than "milliseconds" for the average user to measure\input. The electronics just convert feet to milliseconds for the user.

2. You have the right idea, but my theory is that in this case the larger than measured distance setting for the sub (resulting in less electronic delay relative to the rest of the system) is to deliberatly take the sub slightly out of time alignment with the rest of the system (specifically the towers that go down to 48hz) and prevent the summation between all three sources from 48hz up to the top of the subs output range. (This is assuming the the frequency response was measured with all of the speakers activated)

 

[Buckle-meister]

You have the right idea, but my theory is that in this case the larger than measured distance setting for the sub (resulting in less electronic delay relative to the rest of the system) is to deliberatly take the sub slightly out of time alignment with the rest of the system (specifically the towers that go down to 48hz) and prevent the summation between all three sources from 48hz up to the top of the subs output range. (This is assuming the the frequency response was measured with all of the speakers activated)

I understand what you are saying, but how could summing occur since the speakers are all 'small' and the parameter 'Bass Out' is set to sub-only?

The crossover frequency (80Hz in this instance) may not be a brick-wall filter, but assuming for the moment that it was, the lower extension capability of my towers (80-48=32Hz) should, in this case, be irrelevant shouldn't it?

In an ideal world, a tone which dropped from say 100Hz to 40Hz would play through the towers until, at 80Hz, the towers would go silent and the sub would take over. Where is the overlap in frequencies causing the summing?

Regards

 

[Tom351]

With those specs, you are correct that it should not sum at 63hz. But if the sub is the only speaker outputting 63hz, then I do not see how changing a delay setting would affect the level at all. The delay would not affect interactions with the room. Since delay is only really relative to other speakers I would almost say that there would have to be some interaction with other sources for delay to change the frequency response.

 

[Buckle-meister]

With those specs, you are correct that it should not sum at 63hz. But if the sub is the only speaker outputting 63hz, then I do not see how changing a delay setting would affect the level at all. The delay would not affect interactions with the room. Since delay is only really relative to other speakers I would almost say that there would have to be some interaction with other sources for delay to change the frequency response.

So...altering the Distance setting for the sub will not actually change anything after all. Correct?

 

[Tom351]

Yes, it will only change the subs time alignment with the other frequencies, but it should not affect levels at all since it is the only low frequency source.

 

[mtrycrafts]

If the sub is slower, then the distance would have to be less to achieve all sound reaching the listening position at the same time.Regards

The speed of sound is the same whether it is 50Hz or 10kHz. It is about 1140ft per seconds at sea level, standard day.

 

[Buckle-meister]

Thanks folks , but hold on a minute ; this still does not explain why, if the sub is the only source of low frequency information in the room, YPAO incorrectly set the subs distance. After all, if the summing theory has been ruled out, then why not just set the subs distance correct in the first place ?

Regards

 

[rumble]

The speed of sound is the same whether it is 50Hz or 10kHz. It is about 1140ft per seconds at sea level, standard day.

YPAO is measuring the time between test tone signal generation to the speaker and sound wave reception at the microphone. By the time the sound wave leaves the speaker the delay has already occurred. Your big giant slow subwoofer driver does not generate the test tone quite as fast as your other speakers.

The Pioneer MCACC system on my receiver did an unbelievably good job at integrating my sub with the rest of my speakers. I don't think I could do a better job armed with a tape measure and spl meter or just about anything else. It sets the sonic distance, volume level and does a 5 band eq on the speakers in ten minutes. And you can eat nachos and cheese while its running. How can you beat that?

 

[WmAx]

Your big giant slow subwoofer driver does not generate the test tone quite as fast as your other speakers.

If you have an electronic delay circuit activated somewhere, in line with the subwoofer, then of course, this is true. If, however, you do not, then this is not true. The only way a speaker is faster than another, is when it can respond to higher frequencies. Obviously, a subwoofer is not going to respond to 20kHz, so when compared to a tweeter, it would be slow. But when you have two speakers(for example, an 8" woofer vs. a 15" woofer) that can respond to the same tone, then one will not be slower than the other. The only delay(s) that will occur relative to another speaker will be due to physical distance difference and/or electronic delay(s) and/or group delay characteristics due to the frequency response curve(s) of the transducer(s).

-Chris

 

[Buckle-meister]

If you have an electronic delay circuit activated somewhere, in line with the subwoofer, then of coure, this is true. If, however, you do not, then this is not true. The only way a speaker is faster than another, is when it can respond to higher frequencies. Obviously, a subwoofer is not going to respond to 20kHz, so when compared to a tweeter, it would be slow. But when you have two speakers(for example, an 8" woofer vs. a 15" woofer) that can respond to the same tone, then one will not be slower than the other. The only delay(s) that will occur relative to another speaker will be due to physical distance difference and/or electronic delay(s).

-Chris

Im fairly certain that there is not an electronic delay circuit in the loop anywhere, and my towers can go fairly deep in terms of comparable frequencys with the sub.

I should note that my subs 'line of sight' with the listening position is currently blocked by the end of my couch (its an L-shape). Could the sound from the test tone have taken longer because the microphone picked up sound bounced off of an adjacent wall? Could the explanation be as simple as this?

Regards

 

[WmAx]

I should note that my subs 'line of sight' with the listening position is currently blocked by the end of my couch (its an L-shape). Could the sound from the test tone have taken longer because the microphone picked up sound bounced off of an adjacent wall? Could the explanation be as simple as this?

Regards

The couch is not going to have any effect of significance in this circumstance. As for what is causing the seemingly erroneous calculations on the reciever, I can't answer this. To have any degree of certainty of the actual issue, I would need to personally inspect the connections and measure the system via independant hardware/software.

-Chris

 

[mtrycrafts]

By the time the sound wave leaves the speaker the delay has already occurred. Your big giant slow subwoofer driver does not generate the test tone quite as fast as your other speakers.

Would you clarify this, both sentences? My head is spinning.