will a SUB help

[psykostx]

Originally Posted by Paul Spencer

If you buy a car and expect the manufacturer to drive it for you as well, good luck! If you include a sub in a system, then you need to worry about integration, crossovers and phase. The question I'd ask is if you aren't "worrying about the tech crap" how do you know if you have problems or not? I use both measurements and my ears to tell me when I've got a result I'm happy with. My argument is that you need both to know you have a good result.

I don't disagree... but driving a car is hardly designing it's harmonic damper, or positioning the counterweights on the crankshaft. My point is, I buy components I know were designed and manufactured by competent and experienced individuals, thus saving me the hassles of trying to factor every variable into the equation. It's best to do simple measurements based on competent specs and then adjust angles and distances by ear... but with experience and quality components, really all you need is your ear to set up a system... I mean, anyone with some experience knows you could measure a system to death and it can still sound like crap... then you just tweak something by ear using your experience as a guide and bam, it sounds right. So hear hear, use your ears is my main point. It has to sound good despite how it measures... there isn't a system in the world that doesn't have at least one flaw... it's the avoidable flaws you have to get rid of, and usually you can hear those quite clearly.

[SörenHjalmarsson]

Originally Posted by Paul Spencer

Are you saying:
a) multi subs don't smooth out room modes
or
b) other methods are more appropriate in the studio.

b)

If b) then could you perhaps elaborate a little more?

Elaboration in progress...

Originally Posted by DanDan

I am pretty convinced of the value of two subs based on this.
http://www.harman.com/EN-US/OurCompa...s/multsubs.pdf

(Based on Toole's work)

I haven't read the article Dan, but i'll assume that we are discussing the Toole approach. There have been simular topologies presented by Geddes, Welti, Holman, Greer, Moulton, HAA, THX, etc., which were aimed mainly at the audiophile community (the listening experience in home theater set-ups and re-production environments).

Originally Posted by DanDan

Hi Soren, you must have found something interesting in contrast to the well accepted Harman White Paper instigated by Toole, in my earlier post.
You quoted SAC as 'explaining'.
That would be an oxymoron, but I did skim your first link and found nothing addressing our point here.
May I ask your own reasoning

I'm not so sure it is a well accepted approach in critical listening environments (i'm always ready to be wrong however...) and if you skim through my links a bit more you'll see that both Mr Vare, Mr Brandt and SAC agree that subwoofers aren't the way to reduce modal activity - and that the only difference after (properly) integrating subwoofers, is in the frequency extension offered by them. The article by Charlie Hughes also explaines the importance of signal alignment, which is hard to achieve over a wide area with a Toole type set-up (more on that in a minute).

Here is how i am reasoning Dan:

The first thing to recognize is that the Toole approach is aimed at re-production (i.e. not necessarily accuracy) and if we consider the entirety of the Toole topology, we'll find that there's much that do not correspond to what is usually recommended for a critical listening room. Here is what Mr Toole says regarding subwoofer integration in his book "Sound reproduction: loudspeakers and rooms":

"The evaluation of the reproduced sound should be a matter of judging the extent to which the elements are accurately or attractively reproduced"

In a critical listening room however, we do not integrate the subwoofer(s) by a subjectively attractive improvement (not without it being accurate first)


Different Goals and Means

The goal in this kind of home theater set-up is to achieve the smallest amount of difference possible, in the response, between the different seating positions (this is true for the CR aswell). The sweet-spot is aimed at the center of the room, around which, all the seats should be placed as close as possible (to avoid a big seat-to-seat variation).

When using four subwoofers (or more than one) diagonal symmetry across the room is preferred, and therefore, a square room (with same dimensions) is recommended in order to attain acoustic symmetry (in a control room we usually reach for Bolt's golden ratio, in order to achieve good modal distribution). The recommendation for a rectangular room is to face the LONG wall, this is to avoid the big sound variation between seats when you move along the length of the room (we usually recommend the opposite in a CR). Mr Toole also states that, all that will be improved is the modes that create LARGE variations in the designated seating area (and that you also need substantial EQ to achieve this) and if you move outside of this area, everything will change...

The optimum spots for two subs turns out to be centre of walls at the floor wall corner.
Pretty much no SBIR issue there.

The BIG problem with this sort of approach in a critical listening environmnet is that, as soon as you start to place LF transducers all around you, the signal alignment gets a bit tricky.

The irony is that the whole point of multiple subs, at different locations in the room, is to 'broaden your modal sweet spot' (achieve a good response over a larger area/several seating positions), but by doing so, you also minimize the accurate sweet spot (the area in which there is signal alignment between all sound sources).

Let's use your example DD, as a very simple explanation:

The reason for using multiple subs in a CR would then be to attain a good modal response over several listening positions (i.e. mix chair and client couch). We therefore implement TWO subs (one on each short wall) and let's say that we succed in getting a better modal response, GREAT! but WAIT! As soon as we role our mix chair back (or sit ourselves in the client couch) the path length between the rear wall sub and the rest of the speakers are not the same anymore (signal alignment is broken) i.e. you've got a very small accurate sweet spot. Ad more subwoofers and it gets even worse...

If you on the other hand, place your subs in the front half of your room (close to, and aligned with, your main speakers) the signal alignment will hold throughout the room (or at least a big part of it) just like with regular full range speakers.

THIS is why i say that the main purpose of subs is to deliver extended and accurate bandwidth (not to remediate modes for the benefit of polar lobing )


MVH
Sören

[boggy]

Originally Posted by SörenHjalmarsson

...................

The reason for using multiple subs in a CR would be to attain a good modal response over several listening positions (i.e. mix chair and client couch). We therefore implement TWO subs (one on each short wall) and let's say that we succed in getting a better modal response GREAT! but WAIT! As soon as we role our mix chair back (or sit ourselves in the client couch) the path length difference between the rear wall sub and the rest of the speakers are not the same anymore (signal alignment is broken) i.e. you've got a very small accurate sweet spot. Ad more subwoofers and it gets even worse...

If you on the other hand, place your subs in the front half of your room (close to, and aligned with, your main speakers) the signal alignment will hold throughout the room (or you at least get a big sweet spot).

THIS is why i say that the main purpose of subs is to deliver extened and accurate bandwidth (not to remediate modes for the benefit of polar lobing )
.........

+1.


EDIT: Also, some room that is good for sound reproduction not usually meant that it's may be good for sound production, or control room for mixing. It's not that easy to build similarities between rooms good for listening music and rooms good for music production. If someone can't hear bass frequencies accurately, then he can't accurately produce this frequencies... etc.

Cheers.

Boggy

[PaulRain]

the modal response is more or less the same regardless where you put the source....it's more influenced by where you actually sit...am I right?
Then the response is a mix of several facts and this is clear......
I agree that a sub should be used to be able to get really down in Frequencies....but in case, as I was asking at the beginning, the problem is caused by the relationship between the speaker position and the listening position could it be possible that a SUB helps?
I also understand that probably the best position for a sub not to add other problems is between the two monitors, and this will probably not help the LBIR problem because it's coming from the back wall and the distance will be more or less the same.

[boggy]

Originally Posted by PaulRain

the modal response is more or less the same regardless where you put the source....it's more influenced by where you actually sit...am I right?....

No. Both positions, in all three axis, for speakers (source) and for listener, influence, in some degree, modal response in room. Finding best combination with measurement microphone is usually named "loudspeaker placement".

Cheers.

Boggy

[Paul Spencer]

Obviously there are differences in a HT or 2 channel system vs a studio control room. In particular, the location and number of seats and this would suggest a greater demand for multi subs in a HT room where seating is spread over a larger area. There is also a greater tendency in the home to place more emphasis on entertainment and accuracy for some might not be as important. With respect to accuracy rather than preference, this would actually bias choices towards multi subs rather than the other way around. The key issue here is the presence of dips in the response that even in one position may not be solved through any other means.

I don't mean to suggest a "one size fits all" approach that says every room must have a certain number. However, there is a strong argument for adding more subs strategically placed when after using all other options it turns out there are significant dips. Careful placement, phase alignment and acoustic treatment should all be done first. But what if you are still left with dips? With measurements you can easily determine the potential to place additional subwoofers so that they will fill in those dips. It is in the home that this aspect is less critical, because dips may be seen as a more benign problem than peaks which can cause room boom. We might not be concerned in the home because those dips might not take the fun out of a movie, but I would think in a studio this is a bigger concern.

The phase alignment issue related to using multi subs is one easily solved.

Multi subs is a good strategy when all else fails. And I would suspect that if you are aiming for a high standard in terms of an accurate frequency response that most rooms would fail through no fault of the room designer or the one who sets up and calibrates the system. My suspicion is that physics and practicality dictate that more than one subwoofer is normally needed even to get an accurate smooth and flat response even in one position. But we are "speaking" in generalities here. When measurements of an actual room are shown, we then have a better answer. If you get an accurate result with no subwoofer, or just one then there may be no need for one.

How do you define an accurate frequency response? When is it flat enough?

My answer is this. I first aim for a target curve where the bass is set at a higher level when measured from the listening position ungated. I then apply third octave smoothing and aim for +/- 3 db relative to that target curve. I don't generally look at smoothed measurements, but I think of it as a check. That's my take on "accurate enough."

Reproduction vs Production
Surely, if the goal in either case is accuracy, then there will be many things in common. In this case, the need for multiple bass sources is related to the need for a smooth frequency response in the bass region, which is needed in either case.

the modal response is more or less the same regardless where you put the source

The modes within a room are determined by the geometry and physical properties of the boundaries. However, shift either the listening position or the source location and you will see a change in response. The interaction of these three things with the speakers results in the measured response.

[DanDan]

Thanks for the reply Soren. Since neither of us are really reading the links provided by others why don't we just discuss our own thoughts here.
So the following is MHO.

Multiple is a bit academic. It suggests many, Who does that?
Two subs is very usefully better than one. My opinion, based on that White Paper which has predictions and tests.
Consider rectangular room subs in the middle of the long walls.
Lowest axial mode, the biggest and longest in most cases, is not stimulated.
Raise the subs to half height, that mode is not stimulated.
It is possible that the second modes could be 'not stimulated' instead by placing subs at the quarter spots.
The reverse of all of this is also true. Particular spots can be stimulated to fill a hole in the response. Getting racy here.....
Let's not forget the 38% spots, phase reverse, and deliberate cancellation effects. A plethora of tools which we do not have with full range speakers.
Then add all the SBIR benefits. Subs are typically place at the boundary and have a PZM like performance. i.e. No SBIR.

I am not at all convinced about the significance of time alignment.
I never hear my kick drum's transient until 4-5mS after it happens. The LF tone takes much longer to develop. The first 50 Hz wave takes maybe 20mS to reveal itself.
But more to point, the speakers and subs do not put out the same frequency except at the crossover region, which can be made small.


DD