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General speaker questions for audio and home theater.

More thoughts on this

That particular Focal looks like a VERY nice driver, but perhaps not the best suited for your intended purpose. The on-axis response peak right below rolloff definitely needs to be addressed, or it will sound "shouty" in the midrange. I would just notch it out with an LRC trap filter, but that's a no-go if you want to avoid any reactive components in series with the driver. Since it looks real good 30 degrees off axis, it could be mounted in a box with a "bicycle headlight" type tweeter (HiVi, Morel, and others make such tweeters) swivel-mounted on top of the , so you could have the woofers firing straignt ahead and the tweeters tilted in toward the listening position.

In the past, Peerless, Vifa, and others have offered polypropylene cone drivers that don't have that response spike before rolloff -- just ruler flat up to 6kHz or so, and then a smooth second order rolloff. Check current offerings from Madisound. Something like that could be the ticket.

Too many of the "fullrange" drivers out there have low efficiency, low power handling, and awful frequency response. Some of the Fostex models, and possibly the new 6" and 8" Dayton fullrangers from Parts express, are less compromised in this regard. Madisound offers several kit designs with the Fostex models that use back horn (or TL) loading to fill out the bass response, and a supertweeter mounted up top for air and sparkle.

HF beaming is as much a function of baffle width as driver design. Figure that with ANY driver mounted on a baffle of finite width, away from room boundaries, it will be radiating omnidirectionally where wavelength equals or exceeds 8 baffle widths, and its on-axis response will be down -6dB from its "rated" sensitivity. Where wavelength equals 3 baffle widths, on-axis response will be down =3dB from rated sensitivity, and where wavelength equals 1/2 baffle width or less, it will be beaming straight ahead at full rated sensitivity. This is the "baffle step" pehenomenon, which must be addressed unless the speaker is in or right against a room wall. To compensate for it, you will always be throwing away 6dB of sensitivity relative to the rated sensitivity of the driver. A 2.5 way design ADDS 6dB down low, where it is being lost off-axis, so the "upper" midbass driver can operate at full rated sensitivity up to where it meets the tweeter.

You'll probably get lots more good advice over at the PE Tech Talk forum than here, since it's ALL about DIY. Folks there are knowledgeable, friendly, and helpful. Check it out.






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  • More thoughts on this - caspian@peak.org 08:39:21 11/29/10 (0)

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