Measured monopole and dipole room responses

[gedlee]

Originally Posted by Omholt

There are very few benefits in a small room with directional bass IMO. In concert arenas however cardioid subs have been used for many years with success.

I completely agree. The whole concept of directionality fails when there are dominate modes because then the sound waves can only travel along very precise prescribed directions. Arbitrary directions are not possible so the whole concept of "source directivity" fails.

[gedlee]

Originally Posted by StigErik

I have proven it to myself on several occasions, that is good enough for me.

The classic audiophile catch-all response. "I don;t care about facts, I know what I believe!"

[gedlee]

Originally Posted by Omholt

When it comes to decay and resonances I would say the monopoles performs overall better. They are noticeable better between 70-200 Hz. The frequency response is clearly improved with the dipoles. Would be interesting to see what change of placements of both subs and sitting postion would do.

And this is a single monopole (I hope nobody believes that is the way to go anymore) without any EQ. The Dipole is obviously EQ'd. Hardly a conclusive test result.

[soundaatma]

Originally Posted by markus76

And this graph is the "key evidence" for what?
Double Bass Array (DBA) - The modern bass concept!

The DBA is essentially absorbing all the bass energy after the wave has travelled the length of the room once. This is similar to extreme room treatment for bass absorption....and no doubt is equally expensive and/or cumbersome.

However the idea is the same: reduce the bass energy in the indirect sound field...which is what the dipole is also doing to a certain degree, without the added expense and effort. Delayed out of phase cancellation of the low frequency sound waves.... is the central theme of both the DBA and damped U-Frames....with a slightly different implementation.

[gedlee]

Originally Posted by lolo

has actually anyone gone from dipole to monopole? the opposite does happen..

I have significant experince with both and my opinion is that both sound comparable when both are done correctly. Why is that so hard to accept?

I do find monopoles much easier to impliment however.

[markus76]

Originally Posted by soundaatma

and no doubt is equally expensive and/or cumbersome.

Huh? A DBA doesn't work in each and every room but have you calculated what it costs to get equal absorption from a passive solution?

[gedlee]

Originally Posted by StigErik

Take a look at my decay measurements again. The monopole has got one long decay, while the dipole has got at "knee" where the room decay really starts.

As a physicist this bothers me since the physics says that this should not happen. Once the source is turned off the decay rate is room dependent ONLY, and if the room is unchanged then the decay rate cannot change.

The only way that you could get two different decay rates is if there are two different systems decaying. If the one is EQ'd and the other isn't then you caould be looking at the decay of the EQ.

At any rate those results are not comparable and no conclusions can be drawn from them. But of course these are just facts so they can easily be ignored but any competent audiophile.

[soundaatma]

Originally Posted by gedlee

I completely agree. The whole concept of directionality fails when there are dominate modes because then the sound waves can only travel along very precise prescribed directions. Arbitrary directions are not possible so the whole concept of "source directivity" fails.

It would be helpful to know the the approximate dimensions of what you call a "small room". What if a small room had multiple openings/doors/windows and the walls are not brick but the usual drywall. Will such a small room acoustically behave like a large one ?

What has been the reason(s) of success of cardioids in concert settings...is it just to prevent feedback to the mics on the stage behind the speaker...or is it actually better bass reproduction than monopoles ??
My guess as stated in a previous post, is that even in an open arena, a dipole/cardioid will sound cleaner with better transients due to minimal stored energy issues.

[badman]

Originally Posted by soundaatma

It would be helpful to know the the approximate dimensions of what you call a "small room". What if a small room had multiple openings/doors/windows and the walls are not brick but the usual drywall. Will such a small room acoustically behave like a large one ?

I am fortunate to have just such a room- my floorplan has largely connected (no doors) kitchen, living room, dining room, and main hallway.

Distributed bass is still very helpful but I've definitely not had the challenges with bass I've had in other rooms.

[gedlee]

Originally Posted by soundaatma

This observation from the graphs by StigErik is the key evidence for the better transient response in a room from a dipole.

The room decay is a function of room acoustics and will be the same independent of the source. However if less sound waves reach the room boundaries, the SPL of the reverberant field is lower to start with for a bidirectional dipole as opposed to a monopole that is omnidirectional. So logically, the ratio of the direct to indirect soundfield higher for a dipole than a monopole. Higher direct sound equals to reduced room coloration...this is true for any speaker. That is why some listeners who prefer uncoloured sound in their rooms go for narrow directivity speakers like horn loaded ones. The only other way to reduce room colourations is to increase wall absorption. While room treatments work well and inexpensively for mid-high frequencies, it is not so for bass frequencies. So the only way to reduce the room colourations in the bass region is to get narrow directivity in the bass region....using a dipole bass unit !

Following the above line of thought, a monopole and a dipole should sound the same in open air or anechoic conditions. Unfortunately even that might not be true...as the backwave from a sealed monopole can never be completely absorbed (unless it is a rare long stuffed sealed TL) the unaccounted and un-simulatable stored energy from a monopole eventually comes out, smearing the sound envelope. In contrast, in a dipole all the energy is accounted for to a greater extent.

There are a lot of mistakes here:
1)"However if less sound waves reach the room boundaries"- except that in the steady state, which is true of all small rooms at LFs, this is just not true. Both sources "see" all boundaries.

2)"The only other way to reduce room colourations is to increase wall absorption."- If you mean this exclusively for LFs it is partially true, but above the modal region it is not. There are many ways to do this and IMO large HF wall absorption is exactly the wrong way to do it.

3)"the only way to reduce the room colourations in the bass region is to get narrow directivity in the bass region"- LF directivity in a small room is a falicy.

4)"as the backwave from a sealed monopole can never be completely absorbed (unless it is a rare long stuffed sealed TL) the unaccounted and un-simulatable stored energy from a monopole eventually comes out" This is not true on several accounts. The back wave IS accounted for, it is the load impedance that is presented to the driver. It does not "come back out", it simply stiffens the cone. We are talking here about wavelengths that are an order of magnitude greater than the source dimensions. These are not short wavelengths that "travel" and "reflect" as sound rays. This is the modal region and "sound rays" are not applicable.