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In the Forum: Horn-Loaded Speakers
In the Thread: It's might be another project...
Post Subject: The silly rebel thoughtsPosted by a.anagnost on: 11/10/2024
My experience with cheap/chip amps:
Around y2k, bored with the bass of those loudspeakers with <=8" bass drivers that my fiends where so proud about, I decided to experiment with a BR box using a 15" driver (irrelevant: a Beyma 15K200). Immediately, I discovered that my 300B amp was unsatisfactory, and decided to test the LM3886 chip amp. I used inverting feedback topology just 2 resistors without any caps in the signal & feedback path: a simple DC amp. I thought that it will fail miserably, but I was smiling for months...
The pic with the FR Melquiades:
My first sentiment was envy. The second thought was: It will fail. Fine... but why? Maybe the load is too low. But the 605A is not a 4ohm driver. In fact it is more like a 16ohm driver! Yes, the output transformer has amorphous core as opposed to the heavy iron core+inductance of the bass channel of the multichannel Melq. Are we done?
Freqs of interest:
I will arbitrary assume that the observed phenomena are involving freqs <=60Hz (wavelength >=19ft/6m)
The silly rebel thoughts:
The Rebel is a two cell horn where the 2 cell's mouths are not close to each other (as opposed to all multicell horns I know of). Physics ensures that at low frequencies/high wavelengths this distance is irrelevant. Fine, but the listening spot distance may be quite less than the 60Hz wavelength. At 30Hz (605A fs) the wavelengths are x2.
How many wavelengths are needed to ensure summation of the 2 cells + the driver? I don't know, by I suspect >= 1x wavelength...
This means that at listening position, one is exposed to much lower freqs than those predicted by the summation (a typical 4th order high-pass).
But, can the amps support this? For sure the FR Melq can not. A DC amp with feedback and high OpenLoop gain (chip amp) on the other hand can!
Measurements:
I wish I knew the anechoic response of the Rebel's mouths and the anechoic response of driver (with the mic at less 1 inch distance).
The same at listening position (the supposed summed response).
Using for sure the Denon, and, whatever other amp.
BR, Antonis
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