Passive sub for Magnepan 3.6r?

Hi Martykl,

Thanks for your comments.

A dipole can be modelled as two monopoles separated by a path length (the wrap-around distance) with the polarity reversed on one of them. In fact, that's what a dipole is! Take a Maggie and build it into a wall, and on either side of that wall you'll have a monopole source.

It's true that a dipole does not have the same in-room behavior as two asymmetrically-placed monopoles, but both of them more closely approach the same desirable end result: Greater in-room bass smoothness. This is backed up by several AES papers, and I can dig up citations if you really want but frankly would rather not go to the trouble. My point is, their effect is similar enough to make them easily compatible in the crossover region.

Regarding equalization, if it's addressing a global problem then it will be an improvement throughout the room. If it's addressing a local problem, then it will improve the response in one location but may well make it worse in another. How big that "location" is depends on the specifics, but I agree it's not a head-in-a-vice thing.

Suppose in one location you have a +3 dB peak at 50 Hz, and elsewhere you have a -6 dB dip at the same frequency (this is not at all far-fetched with a single-sub system). That's a 9 dB difference. Equalization cannot fix the 50 Hz region at both locations simulaneously; it can fix one, but at the expense of making the other even worse.

Note that one worthwhile advantage of a distrubuted multisub system is that the variation in bass response from one location to another throughout the room is greatly reduced. So any remaining significant problems are more likely to be global, and therefore EQing them is more likely to be beneficial throughout the room.

What I've been talking about in my posts here is only one aspect of getting good in-room bass from a subwoofer system, but it's the one most relevant to integrating well with dipole main speakers.

Duke

Duke,

Thanks for the reply.
My comment re: a dipole = 2 monopoles was intended to illustrate my actual
experience measuring such designs in my room. I assume (as you allude to
in your post) that the problem with the analogy is that it's frequency
dependent. The bass region, where we're lurking, finds monopole speakers
delivering omnipolar response, so perhaps the analogy is least applicable
here.

As to dipoles being "easily matched" in the x-over region, I've had
the opposite experience. I get pretty smooth reponse from my Maggies down
to app 80hz (I use bass busters which help in the octave or so above this
frequency), but it gets pretty ragged below there. IME, the smoothest
"handoff" occurs when the subs and mains are precisely level
matched through a region that is both free of "humps/divots" and
appropriate in level for good overall octave to octave balance - no mean feat.
The Maggies have proved tougher than either omnis or monopoles for me. I
eventually got good results - with a fair bit of EQ - but it was WORK.

The point about local vs global EQ is simply that - if you look at the virtual
systems links - almost all of these set-ups limit the listening area sufficiently
to allow effective EQ while ignoring any "global" room issues.

BTW, I use 2 subs and this helps reduce the need for EQ. However, fine
tuning with EQ, particularly right around the x-over point, is still - IME -
extremely beneficial, particularly for dipoles.

These points are only based on my own (reasonably extensive) in-room
experience and measurements. It's always possible that my specific
experience is idiosynchratic.

Marty

Hi Marty,

Well I can't discount your experience, especially since you were taking actual measurements, nor can I explain it.

In an AES paper entitled "Dipole Loudspeaker Response in Listening Rooms", researcher James M. Kates compares the response of monopole and a dipole at various listening positions and toe-in angles, and he finds the dipole to be usually (but not always) smoother in the bass region.

In an unprinted supplement to his review of the dipole-bass Gradient Revolution, Robert E. Greene records its in-room frequency response, which he finds to be remarkably smooth in the bass region. You can see this supplement at his website:

http://www.regonaudio.com/Gradient%20Revolution%20Loudspeaker.html

Again, I cannot explain your experience. Perhaps the Maggies do not start out "flat" in the bass region; I recall seeing a Stereophile measurement that did not look flat, but it may have been their measurement technique.

Best wishes,

Duke

Duke,

I checked that link. If you can get that kind of in-room response (app +/- 4db down to 25hz!) without EQ, my hat's off to you. I've never gotten close in any of my rooms with monopoles, omnis, di-poles, or even bi-poles (Sunfire CRM) until I added EQ. Pretty impressive.

Marty

ML Depth with my 3.6 maggies has worked well for me.

http://www.integracoustics.com/MUG/MUG/pix/HTFer/