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Panel speakers with moving coil woofers

irb

pfm Member
The recent threat started by davidismynaim about digital crossovers raised an issue I've often thought about: whether panels can be mated successfully with dynamic woofers.

I own, or have owned in the past, several speakers of this type: the Innersound Isis, the Martin Logan Vista (both electrostatic hybrids), and the Apogee Centaur (a ribbon hybrid). All were/are capable of superb results, but in all three cases there was, to my ears, a discontinuity between the woofer and the panel/ribbon. The Centaur, which I still own, is by far the worst. But the ribbon is superb!

I've read many comments about this issue over the years. Usually these have focused on the 'speed' and lightness of the ribbon/electrostatic panel, as opposed to the slowness and weight of the woofer.

Surely this is the wrong way to look at the problem, though.

Conventional moving coil drivers can move their cones plenty fast enough to cover the required range. If they couldn't, it would show as limited frequency response. There is, I accept, an issue about the differing resonant signatures of the woofer cone material and the panel/ribbon. However there's another issue, which I suspect is much more important, but which often gets neglected: dispersion.

If you combine a large electrostatic panel (or a long ribbon) with a moving coil woofer in a box, there are two reasons why they radiate sound into space differently. First, the ribbon/panel is a dipole radiator, generating a figure of eight pattern, where the woofer is monopolar, and therefore essentially omni-directional. Second, the dipole is operating as a line source, while the woofer is a point source: a line source limits dispersion in the vertical axis, as well as altering the way sound falls off with distance.

There's been wide recognition, in recent years, of the importance of loudspeaker dispersion/directivity. Large, sudden shifts in dispersion are generally agreed to be a bad thing. The implication for hybrid speakers is obvious: if you really want to combine moving coil woofers with long ribbons or panels, you should use your woofers in a dipolar, line source configuration, to match the ribbon/panel dispersion pattern.

I have owned one speaker which combined a long ribbon with a dipole mid and woofer: the Dali Skyline 2000. They were probably the best speakers I've owned, all round. But they still didn't address the line source/point source problem.The only speakers range I'm aware of that have gone the whole way and combined a long dipole ribbon-type driver with a line of dipole woofers, was the old Carver Amazing range. I've never heard them, though. (Hardly any made it to the UK, I guess.)

I'm tempted to try a diy project: Apogee ribbon (from the Centaurs), combined with a line of dipole woofers. Maybe even line of dipole mid-woofers, and a line of dipole subs.

It makes perfect sense. Or does it? What do people think?
 
Martin Logan have done a lot of work on phase control around the crossover point, and my Summits don't, to my ears display any discontinuity between panel and woofer, but the crossover frequency is around 400Hz where our ears are not really that sensitive. However, I do like the idea of a completely dipole system, as I like dipole speakers and then modern world of cheap amplification, and digital crossovers dipoles become a lot easier to implement.
 
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I've never had a proper listen to Summits, but they do have the reputation of handling the transition well.

I do like dipole bass, though - the best bass I've managed to get from my system has always been dipolar: the Skylines, Linkwitz Orions, and DIY dipole subs.
 
I never listened to the innsersound isis in passive crossover mode. I went straight to digital crossover which moved the crossover point significantly down to 233Hz. I can’t hear any discontinuity between the panel and bass. Very happy with the sound. I did also radically move things around in my listening room which is a typical uk 1930s living room through to dinning room with a arch. I had always only used half of the space with the listening position up against the back wall and the speakers either side of the fireplace. Now I have moved the listening position in the space where the arch is, so have no back wall. Gone for a classics 6’ equilateral arrangement with the speakers about 3’ away from the side and back walls. So much change. Inc a little dsp room correction from the dbx360. No bass boom and all sounds very integrated. Talking to John westlake he is a fan of dipole bass to go with panels. Not many commercials available as far as I can tell. Celestine did a pair 6000’s to pair with their little bookshelf back in the day. But they are rare as hens teeth I think. Always been tempted to have a good with Linkwitz designs. Maybe one day. I do like the use of transmission line design in the inner sound speaker too.
 
MiniDSP plate amp to power your sub, fully configurable from the comfort of your listening position.
Home built 12" dipole sub.
Quad 989 ESL's with the above works fine for me.

https://www.minidsp.com/products/plate-amplifiers

Measure the room with REW and import the results.
Set the cut off frequency where you want in real time.
3x different configuration settings.
Use the 250 Watt amp to power 2 subs, each separately configurable.
Apply different filters for roll off and control the output volume.
Alter the phase and apply time correction.
All from the comfort of your laptop, though ethernet connection only.
 
Infinity Reference Standard from long time ago when they were Infinity... IIRC line array of 6 or 8 x 12" polypropylene woofers per channel with built in 3KW active power amps... and those were just the bass cabinets..
 


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