In Reply to: scooter's idea posted by Mats Gunnars on April 29, 2012 at 14:47:25:
A 10" diameter speaker generates a 90 degree polar reponse(early beaming) at 1Khz to 1.2Khz, based upon the cone profile, surround, and optional phase plug. A horn/waveguide loaded tweeter like the Beyma TPL 150H has a matched 90 degree polar reponse for a seamless controlled directivity transistion crossover. A 90 degree horn can generate a wide soundstage in a normal depth livingroom. Doppler IMD distortion is "acceptable" over 80 to 1.2Khz midbass, and "excellent" over 100-1.2Hkz.
For controlled directivity, a 12" midbass would require a 20Khz tweeter with EITHER an impossible low crossover frequency with 90 degree polars, OR a horn/waveguide that has a less than 90 degree polar reponse. Most 12" speakers generate a 60 degree polar response at 1.6Khz. A 60 degree horn can generate a normal soundstage in a short/narrow man-cave. Expect a nasty 12" cone break-up near 1.6Khz. Doppler IMD distortion is "poor" over 80 to 1.6Khz midbass. B&C has 0.5" and 0.75" compression drivers worth review.
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Physics gives speaker designers a few challenges.
Physics requires that any source which is Constant Directivity cannot also have a flat on-axis frequency response. Some Constant Directivity designs require a toe-in of the speakers plus a narrow polar response (horns/waveguide) to generate a relatively flat frequency response.
Controlled directivity attempts a flat on axis frequency response and a wide listening area by accepting a polar response that narrows as frequency increases: x360 degree bass; x180 at the baffle step; x90 midrange frequencies; <90 for 5K-20K.
A 20Hz wavelength is so long that it generates a 360 degree polar response in the room, and hence will excite physical resonant room modes. The width of the baffle will determine the frequency where the polar response transistions from a 360=4PI to a 180=2PI. A baffle step compensation equalization is necessary to "smoothly taper" the 360-180 degree transistion and corresponding power response changes. As the audio wavelengths get shorter than the diameter of the speaker, a beaming polar response starts to develop.
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Follow Ups
- 10" midbass at limit of Doppler IMD and smooth 90 degree polars - scooter 14:43:02 04/30/12 (1)
- RE: 10" midbass at limit of Doppler IMD and smooth 90 degree polars - acuvox 21:57:56 04/30/12 (0)