Measured monopole and dipole room responses

[sendler]

Very nice test. I would also be interested in seeing the difference between dipole and sealed mids at 1k.
Can box effects explain some of what you are seeing?

[brianpowers27]

Does it seem reasonable to assume that room pressurization is causing a different phenomenon other than the excitation of room modes? I would assume that monopole pressurization causes more structural borne resonance. (EG: Drywall resonating.)

[gedlee]

Originally posted by badman
Can you define "Dipole Moment" for me w.r.t. acoustics? I've seen references occasionally but not ever in such a way that I have it in-mind beyond a relationship to the size of the side cancellation node(s).

I think that we are off topic and should go elsewhere, but dipole moment is simply the distance between the front and the back sources. The greater this disatnce the lower the cancellation of the two and the greater the "power" output. The pattern remains the same however.

[gtforme00]

Originally posted by brianpowers27
Does it seem reasonable to assume that room pressurization is causing a different phenomenon other than the excitation of room modes? I would assume that monopole pressurization causes more structural borne resonance. (EG: Drywall resonating.)

This is an interesting theory, and as someone who had done alot! of drywall work recently the resonant frequency of 5/8" drywall on 16" centers is right in the upper bass range.

Dr. Geddes has some extensive knowledge in this area, maybe he can address this concern?

-David

[ScottG]

Originally posted by gedlee

Small numbers of monopoles, like one, is pretty much a disaster.

That's the odd thing though, I've heard it with a pair of monopoles where it not only is NOT a disaster, it's actually *very* similar.

I've also heard and "cobbled together" both very good AND bad multi-subs configurations, where both results (good and bad) were *irrespective* of how much or little the freq. uniformity was ("flat") at lower freq.s.

On the best monopoles be it, single "subs", "non-uniform" multiple "subs", or a stereo pair, I often come away with this impression:

"I notice modal problems, especially when entering/exiting a high/low amplitude deviation area, and yet despite this the sound is fantastic." (..or something like that.)

Of course a *good* multi-sub setup can give you both uniformity AND excellent sound (that is not specifically accredited to uniformity).

The one thing that I've found where a Dipole can be superior is with respect to apparent channel separation at lower freq.s. Those side-nulls between sources seem to make a difference in the mid-bass region, providing a marginal yet distinct enhancement in clarity with respect to lateral image placement.

[john k...]

I'll present this link for those interested. http://www.musicanddesign.com/Dipole_modesA.html
We have been through all this before so i don't care to enter the discussion again. However, I will say, as shown in the analysis, that the major difference between dipoles, monopoles and cardioids are that dipoles will not excite the 0,0,0 mode (not room pressurization). Monopoles and cardioids will. With regard to excitation of modes, dipoles may excite fewer, depending on position, but dipoles are also the most sensitive to placement and orientation in that regard. Cardioids are least sensitive to position. Lastly, cardioids and dipoles radiate less power into the room assuming they have the same on axis free field response.

At this time I find that the major differences between the sound of different woofer systems is due the radiated power and the the room pressurization effects, and room pressurization may be the biggest issue, positive or negative, as the case may be.

Also consider: http://www.musicanddesign.com/DP_woofer_room.html

[gedlee]

Hi John

No disagreement, I don't think, but I am confused with what you mean by "room pressurization" - especially when you say that the 0,0,0 mode is NOT room pressurization. Then, when we clear up that deffinition, what do you mean by "room pressurization effects"?

[john k...]

"(not room pressurization)." was a typo. No "not". Room pressurization is the same old same old. Monopoles and cardioids have a finite volume displacement. Dipoles have a net volume displacement of zero. I know, rooms leak, but put a dipole in a small room and the bass will not be over loaded below the room's first non-zero mode, or room fundamental, what every you want to call it.

Frankly I think this is one of the basic reasons people find dipole bass so "different". I have been in a lot of rooms where the woofers are just overloading the room below the fundamental and the bass is mud. Put a dipole woofer in there with the same free field on axis response and things sound immediately better, cleaner, better defined. But correct the overloading with a monopole and there isn't a lot of difference. That's why I said room pressurization can be a plus or minus.

[cuibono]

Thanks to the OP for the measurements - I think they are very telling of typical low frequency driver implementations. I recently been doing in room measurements, and have been pretty shocked to see what happens in the bass. I'm going to do a little write up soon, but my opinion now is that in room measurements are very necessary.

Originally posted by john k...
... but dipoles are also the most sensitive to placement and orientation in that regard...

Thanks John for this series of articles - reading them was my impetus for doing measurements - one of the things I found was that, measured at my listening position of about 3m, my h-frame woofers response changed little with substantial rotation about its center (+/- 30deg), and I had to move things many feet to get largely different interference patterns at the listening position (I might add my 'room' is not rectangular and relatively large). But more to follow later...

[Rudolf]

Originally posted by cuibono
- one of the things I found was that, measured at my listening position of about 3m, my h-frame woofers response changed little with substantial rotation about its center (+/- 30deg) ...

Did you measure one h-frame at a time, or both together? WRT rotation in some situations the interaction of both h-frames results in much greater difference than the plain action of one speaker.