Speaker Positioning: Bass or Imaging?

[DonH50]

Don

Wouldnt you agree that if one can, with eyes closed, localize the postion of a sub in the room it is due to it being crossed over too high thus adding some mid range. IOW IMO a well placed and set up sub should be essentially invisible in the room if crossed over correctly

Yes indeed, with the caveat that "too high" is a variable having different values for different people. Another kicker is that smaller speakers may not have the range to go low enough to get below that threshold of localization, so you end up having to cross over higher than you'd or lose a section of the audio spectrum (or get it highly distorted). Finally, there's that pesky crossover slope to deal with, since brick wall filters are hard to come by, espeically ones that don't absolutely trash the group delay (and thus phase response) for an octave or so above and below the crossover point (digital filters have about solved that problem -- hurray for technology and the engineers that made it! ). I do heartily agree the best sub is one that is "invisible".

In my case, I freely admit that my sub placement is driven partially by aesthetics and a gut feel that may not be valid, especially since I am crossing over an octave below what I know to be my personal localization point. However, I have moved the subs around quite a bit (durn heavy things, not good for an old back!), and not found significant differences in measured response, though some locations sounded/felt better or worse to me. I am not sure I could truly localize the sub in any of those cases, though of course if it's very close I could feel the pressure wave and it didn't always seem to line up well with the sound from the mains. Sometimes, it did! Depends how careful I was dialing everything in.

Does that help? - Don

 

[DonH50]

No reason why you can't but then the best way to do it is to choose sub crossover and slope to match the low frequency extension and roll off of the main speakers. That way you don't them playing over each other. I have done just this for a client who didn't want to introduce a line level XO, and it seems that you may be doing this with your setup as well.

If you have pretty full range mains and then you are just running a sub over them then it is unlikely you will get good outcome

What he said! That's a very good description of my feelings, and in fact is what I implemented in my system. Great minds...

 

[Steve williams]

So where do you cross your subs that you say it is an octave below what you want

 

[DWR]

I believe he stated in his earlier post that he crosses his sub at 40Hz, which goes right along with 1 octave below what most people can start localizing the sub(s) 80 Hz. 40Hz is exactly one octave below 80Hz. It does make a lot of sense to match the slope of your main speakers and sub slopes. Myself I like to overlap the crossover points of the mains and the sub(s) so they blend nicely. And Steve many people get excellent results using quality subs like you have along with full range speakers.

 

[audioguy]

I am using an Audyssey SubEQ for integrating my 4 HT subs (along with Audyssey Pro). The distance to the front two subs is longer than the distance to the rear two subs so the SubEQ first pings the 2 sets of subs and then sets the distance/delay so that the sound of all four subs arrives at the LP at the same time. Then you can measure as many different spots around the LP as you like. I have just set up my TacT (for two channel) to operate in the 2.1 mode which says 2 mains and 1 sub (versus 2.2 which says 2 mains and two subs). Since I am crossing over at about 60 hz to 65hz, I am unable to localize any of the 4 subs. The jury is still out but first impressions are very positive. Certainly the best bass I have ever had in my room.

I continue to experiment which I guess if all part of the hobby.

 

[Steve williams]

Chuck

Why dont you use your TacT for integration of your subs

 

[DWR]

I do the same audioguy my rear sub is closer than my front two so you set the delay to get the sound to the LP at the same time. I started my subs crossed at 80 but am now at 65Hz and can not localize any of the subs either. My speakers roll off pretty quick below 50Hz and 65Hz on crossing the subs has sounded the best so far, but like you say experimenting is all part of the hobby. I too am now getting the best bass I have had in my room.

 

[RUR]

Impulse response (measured) was somewhat trashed because it's hard to really line up the wavefronts with the sub and mains when they are physically separated, imo.

Even if the preamp adjusts latency based on measurements at the listening seat, Don? FWIW I do believe the TacT uses impulse response measurements to determine the filtering.

As regards crossover frequency... Because I'm also imposing filtering, it's best if I choose a crossover frequency at a point where the measured response of sub and both mains coincides - otherwise I get some rather unwieldy filter shelving. Typically, there are several points in the frequency band where such coincidence occurs, and I've tried them all only to settle on 77Hz as the best-sounding in my system. Some of that may be reduced distortion in the upper bass due to the lighter load on the mains woofers.

I have a ton of flexibility in crossovers - staggered or overlapped if I wish, and order selectable anywhere between 2nd and 24th. No matter what I choose, the FR will be essentially flat within a couple of dB, so again, it all boils down to what sounds best. In my case, I use 24th order (144dB/octave). Neither I, nor the folks who've heard my system, can localize the sub at all, though it isn't far from the mains - front wall, somewhat off center.

All very gear/room dependent, I know, so all the usual caveats apply.

 

[audioguy]

Chuck

Why dont you use your TacT for integration of your subs

I do use the TacT. The Audyssey SubEQ just serves the purpose of integrating the 4 subs to each other (as well as providiing some room correction on the subs ) and then I use the TacT with a desired target curve and to set the crossover points and slopes to integrate the mains to the now integrated four subs (which to the TacT, looks like one sub --- that happens to have eight (8) 15 inch drivers !!

As I said, I am just experimenting. Prior to last night, I had the two subs on the left of the room attached to the left channel of the TacT directly (no SubEQ) and the two subs on the right attached to the right channel. My crossover was (and still is) at 65hz so I thought I would just try it with the SubEQ integrating all four subs together.

I'm sure by next week, I'll be working on Plan C

 

[Steve williams]

Chuck

I guess i dont understand why you cant use TacT to do what Audyssey is doing

 

[RUR]

I'm not Chuck, but the TacT will only manage 2 subs, unless they're slaved in some fashion. What I'm trying to sort out is, if Audyssey Sub flattens the response and then one uses a non-flat curve in the TacT (i.e. one with some LFtilt-up, as is common), the TacT is correcting the Audyssey corrections!

What say ye, Chuck?

 

[Steve williams]

Ken

you can slave the Gotham subs so would that be a solution if you have 4 of them

 

[DonH50]

So where do you cross your subs that you say it is an octave below what you want

Hey Steve: What DWR said is correct. I cross over at 40 Hz, an octave below 80 Hz, which in previous tests was about where I could localize a sub. Thus making them invisible. The black grill cloth and dark lighting helps, too.

DWR: We agree on needing to match sub crossover to mains carefully; as I said, I feel that not only getting the actual crossover frequency and level correct is required, but also the sub's phase so the mains and subs meld seamlessly. I think the latter is where a lot of people fall down. The amount of overlap for good sound is very speaker, room, and person dependent, imo. Too much overlap and you'll get a "hump"; too overlap and you'll have a hole. Assuming the crossover doesn't line up on some room mode. - Don

 

[Phelonious Ponk]

I personally find placement of mains for imaging much more critical than sub placement. The most important thing regarding subs, to my ear, is crossover. Subs need to roll up as the mains roll off, with as little duplication as possible. Doubling of mid bass is the enemy of midrange clarity and tight bass response. I'd much rather have a system that rolls off below 60hz than one that muddies up the mids. And right now, I do.

P

 

[FrantzM]

No reason why you can't but then the best way to do it is to choose sub crossover and slope to match the low frequency extension and roll off of the main speakers. That way you don't them playing over each other. I have done just this for a client who didn't want to introduce a line level XO, and it seems that you may be doing this with your setup as well.

If you have pretty full range mains and then you are just running a sub over them then it is unlikely you will get good outcome

Nyal

It seems counter-intuitive. I do however believe that running the mains full range AND adding subwoofers provide the smoothest response possible... I have seen the response in my own case getting better by adding a third subwoofer.. This system is not more nor am I able to retrieve the graphs ... I can however point to some other people who have performed similar experiences ... or to the papers of Floyd Toole and Sean Olive. I would have liked Earl Geddes to chime in since the protocol I used was his , a variation on the multi subwoofers from Olive and Toole for producing better bass response in a room ...
My point is anecdotal. I have gotten the best bass with speakers that could hit 25 Hz in my room with autority .. the addition of 3 subwoofers, one corner placed and not EQ, strangely produced the best bass I have had in my system, actually in most systems. Steve here use EQ'd Gotham to supplement his full range running X-2 and believe me both aurally and measurable his bass is excellent .. I actually believe he would have gotten even better results by using a higher crossover point; something that in I would found to be anathema to high End reproduction only a few years ago ... 43 Hz is Ok but higher might produce better results ..
it's not simply a matter of the bass absorption in the room ... more subs result in better bass, smoother , more extended more integrated ...
The trick become : Place the mains wherever they image best , then add subs to bring the bass smooth and integrated ...

I will PM Earl Geddes and see if he's willing to explain his method here ...he's done it somewhere in this forum but very succinctly ...


P.S. Steve please, leave your system alone .. It took you months to get to that level of bass integration .. Don't listen to me ... .... .... .... ...
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....... but slightly higher(50?, 60?) ... might even be better

 

[DWR]

I am sure Earl would chime in here but he is on vacation right now. I too am using his protocol for sub set-up.

 

[Steve williams]

Frantz i was crossing over initially at 65 hz but it did not sound good

 

[RBFC]

In my current room, I am using a JL F113 to supplement the B&W 801Ds. Because of the shape of the room and limited speaker positioning options, I've found that crossing over the 801Ds to the sub at 80 Hz provides the best integration so far. I'm not sure that's as good as it can get, just that it's difficult to have more bass sources in this room, with the position of the 801s somewhat set. So, using the ARO on the JL gives the best results right now.

Lee

 

[FrantzM]

Frantz i was crossing over initially at 65 hz but it did not sound good

50 ? ...55?

 

[Steve williams]

I went down slowly til I reached 45-50 and then hosted Marty for a weekend and when all was said and done I am now at 43 hz