[pittsburgh Joe]

I'm looking at REL and JL Audio powered subwoofers for my QUAD 63s. These two companies have very different philosophies regarding connections. JL Audio recommends high-pass filter of the main speakers, while REL doesn't believe in the use of high-pass filters. "The cure is far worse than the desease." What have you found to be the best way to integrate subs with the Quads?  (I have Janis W-1 15" ported subs).

[Jazzman53]

Before commenting, I must stipulate that I've never heard an ESL 63 (only the 57).  Most ESLs have characteristic traits, and I do have some experience with ESLs.  And what I suggest may or may not be an option for your setup, or budget:

For a couple of reasons, I would go high-pass on the mains. 

First; there is the issue of the ESL diaphragm's fundamental resonance (a.k.a the drum head resonance). This resonance is, by definition uncontrolled motion, and it's quite loud and undesirable.  Some ESLs (Acoustats) use an acoustic dampening matt behind the rear stator to mitigate this resonance.  Whereas; some manufacturers opt for no dampening and actually use the drum head resonance to enhance the low bass -- to poor effect IMO.  Example: The bottom octave on a Quad ESL 57 is pretty sloppy because it incorporates the the drum head resonance to play that low. 

Using a high pass that occurs above the drum head resonance can help mitigate it by not actively driving the diaphragm at the resonant frequency.  I don't know where the drum head resonance occurs in and ESL 63, but design principles would dictate it's somewhere around 50Hz in the two bass panels (I believe the 63 uses two LF panels with a HF panel in the middle).  To mitigate the diaphragm resonance; a 24db/octave filter slope and crossover at least one octave above the resonance would be effective. 

Secondly; depending on the diaphragm-to-stator spacing (d/s) of the ESL, unloading the bass to a sub may allow the ESL to play significantly louder (the ultimate limit for an ESL is when the diaphragm is driven into a stator).   

Most powered subs have a built in passive crossover, but passive filter slopes are typically limited to 6 or 12db/octave, which could help only a little.  Whereas; if you can bypass the passive crossover and use an outboard active crossover with a a steeper filter slope of 24db/octave or higher, this would more effectively mitigate the diaphragm resonance.  A DSP crossover, preferably with parametric EQ's, is optimal for this.  A DBX Driverack PA2 is an excellent choice

I use a pair of outboard powered Ripole subs and a DSP crossover with my homebuilt ESLs.  The bass is exceptionally tight and clean. 

If you opt for the passive crossover in the sub(s), I would still go high-pass.

 

[dB Cooper]

Question for Jazzman53: I remember Frank van Alstine saying in his old Audio Basics newsletter that planars resonated bass frequencies in the room and suggested removing them when evaluating conventional speakers in the same room for this reason. (This advice dated from when there were audio shops.) Sounds like the effect you describe. I once saw in the Systems photos here a pair of ESLs placed close to room corners with a pair of big subs directly behind them fully in the room corners, firing directly into the back of the ESLs from what looked like a distance of 2 feet or so. I assume you would agree this is not a 'best practice'?

[Jazzman53]

Yes, I do agree.  A sub located anywhere in the room will excite the ESL diaphragm, but the effect is much worse if the sub is placed directly behind the ESL.  I use a pair of dipole (Ripol) subs located beside my ESLs because their figure-8 radiation pattern nulls the off-axis output, which mitigates the resonant interaction with the ESL's.   

[pittsburgh Joe]

Thank you for your input. The Interphase units that I purchased with the subs had an 18db crossover at 100Hz. I currently have an Emotiva XMC-1 processor that will provide a 24db crossover at multiple frequencies. I will try using the Emotiva at 80 or 100 Hz to see if that provides a better solution for the Janis Subs. Otherwise I'll keep looking at self-powered subs, preferably with high pass filtering.

[Mr. Big]

I owned the ESL 63 and they were totally rebuilt by Electrostatic Solutions from the connectors to the power supply, panels, and screens and never had any bass issues with the panels.