Sub 'Distance' setting

[Highlander]

Hey all,

At the weekend I was setting up my two subs and after taking a lot of measurements in trialled positions, settled on a low frequency response I was fairly happy with...until I realised that when trialling the positions, I'd not been updating the Distance setting in the receiver with the result that the actual distance of the subs from the listening position was as much as 2m to 3m out. When I corrected the receiver's settings to reflect the actual distances, my frequency response was out.

If I return the distance values to those that are strictly incorrect but which result in a good frequency response, will it matter? True, the timing of the subs will be out, but given the speed of sound as 343m/s, will an error of 2m to 3m be detectable?

Cheers,

 

[peerlesser]

Hey all,

At the weekend I was setting up my two subs and after taking a lot of measurements in trialled positions, settled on a low frequency response I was fairly happy with...until I realised that when trialling the positions, I'd not been updating the Distance setting in the receiver with the result that the actual distance of the subs from the listening position was as much as 2m to 3m out. When I corrected the receiver's settings to reflect the actual distances, my frequency response was out.

If I return the distance values to those that are strictly incorrect but which result in a good frequency response, will it matter? True, the timing of the subs will be out, but given the speed of sound as 343m/s, will an error of 2m to 3m be detectable?

Cheers,

With 2m-3m distance error, you get about 6-9 ms timing error. It's barely noticeable at such low frequencies and probably the flatter response will outweight it. The distance setting is simply linear phase shift relative to other speakers, and sometimes fine-tuning the phase works well in fighting the room interaction. If the system sounds better with slight phase shift between the speakers and sub, then it is adviceable to simply keep it that way. Theres no right or wrong setting for the distance, although usually receivers try to calibrate phase coherency as it's a good initial value. The fact is, that almost none of the receivers are even able to "see" the response at lower frequencies, so it's not a factor in their check list when they calibrate.

 

[bpape]

What you're effectively doing is adjusting the phase and avoid cancellations. If you've got it relatively flat, leave it. The phase police won't come get you

Now, if you don't like where the subs ended up physically, try the exercise again but remember to adjust things as you go. You MAY find a more physically acceptable location. Or you may not. In any case, I'd certainly lay down some tape and write everything down where it is now.

Bryan

 

[Highlander]

Thanks Bryan (and Peerlesser )

What you're effectively doing is adjusting the phase and avoid cancellations. If you've got it relatively flat, leave it. The phase police won't come get you

Yeah, I know, but...but it really bugs me that the setting is incorrect. If I'm honest, I have to admit that I'm seriously considering going through the whole excersise again just to obtain settings that are correct.

...I'd certainly lay down some tape and write everything down where it is now.

I cannot tell you how annoyed with myself I was when Yamaha's YPAO wiped out the (incorrect) distance setting that I'd unknowingly been using to arrive at an optimal speaker placement. I'd known YPAO would overwrite the levels and distances etc, but it hadn't 'clicked' that I needed to take a note of the current (incorrect) distance settings prior to running YPAO (I wasn't bothered about the levels since after YPAO was finished I planned on manually resetting those to the values I'd recorded).

In the end I was, after leaving the subs in-situ and incrementing the distance setting, able (virtually) to return to the frequency response I'd originally obtained manually and in doing so note the (incorrect) distances that must have existed prior to being overwritten by YPAO, but me being me, it doesn't sit well that the setting is wrong, even though the sound is fabulous at present.

What you're effectively doing is adjusting the phase and avoid cancellations.

After things had gone haywire, I figured this out. I've a question for you though; is it theoretically possible that re-trialling positions with the correct distance setting may not lead to as good a (low) frequequency response as the existing positions with an incorrect distance setting?

 

[Johnd]

Yeah, I know, but...but it really bugs me that the setting is incorrect. If I'm honest, I have to admit that I'm seriously considering going through the whole excersise again just to obtain settings that are correct.

Come on Robbie: you know better than that. Do you know how anguished I would be if I wanted all the settings in my projector to be "correct?" I want the picture to be correct, not the settings, and so it goes with your audio. Imho, if it sounds right and good, in fact, if you have the sub optimized, you're there...leave the settings alone and forget about them...just listen to your optimized bass. Much as I watch my optimized HD. Cheers, John

 

[peerlesser]

I've a question for you though; is it theoretically possible that re-trialling positions with the correct distance setting may not lead to as good a (low) frequequency response as the existing positions with an incorrect distance setting?

Depending on your room, yes it is possible. I'm not saying you couldn't get better response, but sometimes the best possible response is achieved with small deviation from coherent phase. This is also due to the fact that some placement options are not very convenient for the subwoofer (such as hanging from the middle of the roof). So with limited placement (and more or less fixed listening position), you are gonna have to use the means that are implementable, such as tweaking the linear phase difference.

 

[Highlander]

Come on Robbie: [you] want the [results] to be correct, not the settings...

On the contrary; I want both to be correct. This attitude, almost bordering on obsessive compulsive disorder, is me to a tee. The fact that achieving both may not - even knowing it wont - lead to an audible difference does not change things.

Depending on your room, yes it is possible.

Hmm. Figured it might be.

 

[bpape]

The thing is that with the 'correct' settings, you may end up with a better response but with sub placements that just aren't practical. What if you could get it but it left the sub right in front of your seat so you couldn't get the footrest up? Or, you may just restrict yourself as to where you can have it and not ever get it as good. One also has to look at it from the stand point of the best response for ALL of the seats. What's great at one might be horrid at another. I'd rather have OK to good at all of them.

Would it make you feel any better if the distance was right but you had a fully adjustable phase adjustment instead of 0 and 180 so you could accomplish the same thing? Not being smart - being serious here. You're doing the same thing in the end.

Bryan

 

[gene]

This is a great discussion and an important one. What matters most is the integration between the sub(s) and the satellite speakers. Its good to start with the correct sub distance but always wise to experiment.

In my system I am using Audyssey Pro MultEQ stand alone processor for the sub channels only which adds 20msec of uniform group delay because of the processing. Thus I had to tell my processor the incorrect distances of my subs to get the subs and actually add delay to two of them to properly align with my speakers. Some subs also have built in DSP processing which could account for why setting the proper distance isn't always correct and why some auto room correction systems result in different than real distance settings.

 

[Highlander]

The thing is that with the 'correct' settings, you may end up with a better response but with sub placements that just aren't practical.

Yes, I do concede that there may well be sub positions that result in a better frequency response at the listening position but which are impractical. My fault for not being more clear that I meant 'correct' with regard to the positions I trialled.

Would it make you feel any better if the distance was right but you had a fully adjustable phase adjustment instead of 0 and 180 so you could accomplish the same thing?...You're doing the same thing in the end.

When I read this this morning, I thought: "Ha! So I am!" Now I'm not so sure.

A phase shift of 180º must translate into a finite duration of time and thus in turn distance. If the sub was positioned from the listening position any multiple of twice the distance represented by 180º, i.e. a distance equal to a phase shift of 360º, plus the original distance that resulted in a desireable frequency response at the listening position, then that response would appear identical to the original even though the timing of the sub with the main speakers would increasingly be out as the integer multiple rose.

Is this not correct?

 

[bpape]

I had to read that a couple of times to make sure I understood what you're saying. From a pure TIME perspective, I believe so. However, that change in distance puts you then farther away from the source so it's also a FULL 360 out plus the 180 or 540 out.

In addition, it will put the sub in a different place with regard to the boundaries so the frequency response, boost, cancellations, etc. will all be quite different.

If it's good, enjoy it. Sit back and listen. Play a bit here and there if you want but be able to recreate what you have.

Bryan

 

[Highlander]

...had to read that a couple of times to make sure I understood what you're saying.

Ha! You should have tried writing it!

Play a bit here and there if you want but be able to recreate what you have.

I saved all the trialled positions, phase and volume settings so returning to what I have at present should be easy. Thanks for all your help.

 

[Highlander]

The power of perseverance

All,

Well, in the end I did go back and re-trial the positions of my two subs and have improved upon the results I obtained previously (then with incorrect distance settings). After settling on their positions I fine tuned the phase by permitting myself up to ±1m distance if a better frequency response at the listening position was returned. Ultimately it was not and so the actual sub distances have been adopted. This of course suits me just fine.

I thought it'd be interesting to show the influence upon frequency response that adding room treatment, subs and finally equalization has, beginning with my untreated room as a datum. The order the frequency response was successively corrected was:

1. Bare room;
2. Treated room;
3. Sub 1 (corner placement) added;
4. Sub 2 (mid side wall placement) added;
5. Equalized room;

Finally, an overlay showing the finished frequency response, i.e. with room treatment, both subs and Equalization all applied is shown overlaid upon the basic case of the bare room. Whilst it is clear that a null still exists at 111Hz, it spans only 8Hz and I can live with it. Put it another way; I aint changin' anythin' no more!

Cheers,