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IMHO, the 25Hz number does not add up

Posted by John Marks on January 21, 2024 at 06:36:02

In Reply to: Crystal Cable Minissimo Forte Loudspeaker posted by mark.korda@myfairpoint.net on January 20, 2024 at 20:05:53:

If we are talking about an off-the-shelf driver, it is likely the Scan-Speak Illuminator 15WU/8741T-00 5.5" Woofer. The 8-Ohm version of that 5.5-inch driver has a claimed resonant frequency (Fs) of 35Hz. (Madisound price $381.20/ea.)

However, Madisound's lowest-going cabinet recommendation is:

0.3 cubic feet with 1.5" diameter vent by 6" long for F3 of 56Hz

which strikes me as making sense. To my preferred way of looking at things, that means that that design is -3dB at the note "A" one octave above a full-sized keyboard's lowest "A" (55Hz), so it might be flat at "D" = 74Hz or "E" = 82Hz.

To put this in context, my current prototype project uses Purifi's 5.25-inch woofer-mid, which is more expensive than the Scan-Speak, and which has an Fs of 32Hz. My chosen implementation is a sealed box with two Purifi 5.25-inch passive radiators, one each on each side panel. (The cabinet front panel is Richlite Bamboo Stratum; the cabinet shell is solid .5-inch thick Richlite. $$$) The passive radiators have an Fs of 20Hz. Here's a photo:

I don't expect my design to be flat at 55Hz, much less 27.5Hz. It would be nice if my design turned out to be -2dB or even -1dB at 55Hz, but... please remember that the wavelength of "A" = 55Hz is TWENTY AND A HALF FEET.

So, bottom line, the maker's claim of -3dB at 48Hz might be possible, but perhaps at the cost of "over-porting" the design, which brings on Group Delay. A claim of 25 Hz makes me question the test equipment, frankly.

I have taken a lot of FLAK for my approach to loudspeaker design (sip Campari while the professionals implement my whims), but I have no intention of changing.

Indeed, I used to joke to record retailers, "At John Marks Records, we have 'upped' our game; so now, UP YOURS!"

So, I have upped my own game again, by enlisting Dennis Murphy of Philharmonic Audio, to design this crossover.

I'll let everyone know when that is done.

john

PS: Yes, you are right, I would expect Doppler Distortion, especially of the crossover point is 2400Hz or above. The wavelength of 48Hz is exactly FIFTY TIMES longer than the wavelength of 2400Hz. The total linear travel of that Scan woofer is one inch, which is about 20% of the wavelength (5.65 in.) of 2400Hz.

IMHO, for the $24,000 price tier, there are probably better choices out there, such as Peak Consult's Sonora 2-ways, at $29,000 the pair.

• Philharmonic Audio's BMR Monitor   (Open in New Window)

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Kimber Kable

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