Why Are Woofer Towers Positioned Behind Midrange/Tweeter Towers?

[Ron Resnick]

In four tower "statement" speaker systems we often see the woofer towers positioned just behind the midrange/tweeter towers (e.g., Genesis 1.2, 2.3; Analysis Audio Orion; MartinLogan Statement E2; Nola Grand Reference Gold, Evolution Acoustics MM7, Wilson XLF/Thor).

Some designers think that speaker drivers should be time-aligned. I think physical time-alignment would dictate that the woofer towers should be a bit in front of the midrange/tweeter towers.

Some designers want to position the woofer towers wherever necessary to achieve the smoothest bass response in the listening room. This could explain the common positioning of woofer towers behind the midrange/tweeter towers.

Or is there some other reason we often see woofer towers located behind the midrange/tweeter towers?

 

[bonzo75]

Marty does that as well, his JL Gothams behind his Pipedreams, and he delays the front tower.

Trios have their subs in the middle or at the sides, but same horizontal plane.

 

[kach22i]

Could it be just to photograph them for promotional reasons?

Real listening room photos would be a more practical guide.

 

[KeithR]

paging Gary K, paging Gary K?

 

[amirm]

Bass frequencies are omnidirectional so the higher frequency enclosures are not "seen" by those waves. The high-frequencies on the other hand are directional and if you put the bass enclosure in front of them, they will reflect back and forth and can cause colorations/comb filtering.

Phase (time) delay is not an audible problem at mid to high frequencies. Time alignment as such in loudspeakers is more of a belief than a real issue in my opinion .

 

[Steve Williams]

paging Gary K, paging Gary K?

I believe that Gary has a time attenuator on the rear of his speakers that take into consideration the time delay. I spoke to Gary about this when I was in Seattle in April at his Dragon launch party

 

[FrantzM]

If the woofers are behind the mains then they are delayed; no control can have them advance their wave launch. Delaying the mains to have them time align with the subwoofer in a non-digital system is not too far from impossible (Oh yes you can but analog delay line have more than a sound of their own ). Woofers are always delayed with respect to the mains if you place them in the back. fortunately it takes us a while to perceive bass ... 50 ms I believe for a 50 Hz wave .. So the bass is in the room and (is processed and so often mangled and distorted by the room) way before we perceive them ... It is one reason why the bass "towers" can sound so integrated.
The Ultimate IMHO is an all digital system where the mains can be completely aligned in time with the bass transducers. Marty hybrid approach is very interesting and from all accounts successful. Using DRC with otherwise Tube Pre and SS amp system. With a digital DRC in the front end You can time aligned the mains and the woofer towers to any extent needed and correct them on top of that.
I am also in favour of separated subs controlled by DSP even for mains with substantial bass output ...

 

[bonzo75]

Hi I agree, I haven't seen a full range speaker with bass as good as an external sub. Which is why I like Marty's bass and that of the bass horns.

I didn't understand your point about bass towers though - are you saying towers are better than normal subs (like JL) or are you using that term for all external subs.

 

[andromedaaudio]

Quote : Hi I agree, I haven't seen a full range speaker with bass as good as an external sub

You havent listened to mine its all about appropriate volume and woofers with a low enough resonance freq ,in which for example the focal audiom woofers used in the big Wilsons dont exxcel

 

[dallasjustice]

Time alignment as such in loudspeakers is more of a belief than a real issue in my opinion .

Does phase matter at low frequencies?

 

[NorthStar]

Does phase matter at low frequencies?

More at shorter distance than farther.

 

[Bruce B]

Does phase matter at low frequencies?

At a wavelength of 56' for 20Hz, or even 37' for 30Hz (18' for half wavelength), phase will only be correct for 1 freq....

 

[dallasjustice]

At a wavelength of 56' for 20Hz, or even 37' for 30Hz (18' for half wavelength), phase will only be correct for 1 freq....

I think you know where I am going with this. In the digital domain, phase/time can be rotated at many points throughout the crossover area. It's not perfect, but compared with using a bass tower with no digital controls, I don't get it. I think it's correct to call the bass tower systems a "statement." I'm not sure what the statement is.

 

[andromedaaudio]

" The statement" is just simple physics , more stiff bass membrane surface , more ambience/ bassinformation.
It can also work as an eff. correction , having a bass tower which is substantially higher in eff. than the main towers , it might be just wise to place them at a considerable distance behind the main towers

 

[amirm]

Does phase matter at low frequencies?

It does and it doesn't. In your case with subs, and in general with two loudspeakers playing a mono bass, then changing timing can significantly modify the standing waves in the room and hence quite audible.

However, if we are talking in the context of a single loudspeaker, being used in a rather reverberant room, studies show that phase distortion is generally not audible. Or if audible, it is very subtle. With headphones, we can hear phase distortions much more clearly but in a room, reflections help mask such changes quite effectively.

A very good read on this is the AES paper, On the Audibility of Midrange Phase Distortion in Audio Systems, by professors STANLEY LIPSHITZ, MARK POCOCK, AND JOHN VANDERKOOY

The bulk of the paper sets out to state what I just said is wrong . But it ends the way I mentioned it:

This is yet another case of measurements being misleading with respect to what we hear in acoustic environments in mid to high frequencies.

 

[Mike Lavigne]

Hi I agree, I haven't seen a full range speaker with bass as good as an external sub. Which is why I like Marty's bass and that of the bass horns.

I didn't understand your point about bass towers though - are you saying towers are better than normal subs (like JL) or are you using that term for all external subs.

not sure your precise meaning. my MM7's have separate integrated (the main towers are not usable as stand alone speakers) bass towers and they are seamless in the bass.

however; their towers ideally are located on the same radius from the listening position as the main towers (which use a 1st order crossover), so they are phase and time aligned for a (close to) perfect wave launch.

my speaker designer says that the bass towers can be located behind the main towers and are still very good; but not as ideal as it can be. every room is different and not every room allows for both towers to be on the same radius.

 

[dallasjustice]

It does and it doesn't. In your case with subs, and in general with two loudspeakers playing a mono bass, then changing timing can significantly modify the standing waves in the room and hence quite audible.

However, if we are talking in the context of a single loudspeaker, being used in a rather reverberant room, studies show that phase distortion is generally not audible. Or if audible, it is very subtle. With headphones, we can hear phase distortions much more clearly but in a room, reflections help mask such changes quite effectively.

A very good read on this is the AES paper, On the Audibility of Midrange Phase Distortion in Audio Systems, by professors STANLEY LIPSHITZ, MARK POCOCK, AND JOHN VANDERKOOY

The bulk of the paper sets out to state what I just said is wrong . But it ends the way I mentioned it:

This is yet another case of measurements being misleading with respect to what we hear in acoustic environments in mid to high frequencies.

I totally agree. But in this case, speaker manufacturers are attempting to integrate bass frequencies at different locations throughout the room. Phase and frequency response are two sides of the same coin. This is why Toole doesn't worry himself too much with phase, because he argues that frequency response will usually tell you whether the phase is a problem. I agree with that.

I think it would be very interesting to see some mic measurements at the seated position; eg. one low frequency sweep with the bass tower and one without the bass tower. I bet the bass isn't very much smoother with the tower over the crossover region.