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low-mid horn speaker compression ratio
low-mid horn speaker compression ratio
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Old 16th March 2020, 04:55 PM   #1
Cracky is offline Cracky
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Join Date: Mar 2020
Default low-mid horn speaker compression ratio

me and my friends are trying to construct a horn speaker, with a bandwidth of 90-500 Hz. We chose to base our design on the B&C 12FW76 driver. We were surprised, that our calculations gave a compression ratio of about 1:4.88.

I used the following equations to calculate the throat area:

efficiency = Fs / (Fch * Qes)
St = efficiency * Re * density_of_air * c * Sd^2 / ((1 - efficiency) * Bl^2)

St := throat area
Fch := upper cutoff frequency (500 Hz)
The other parameters are the Thiele-Small-Parameters of the driver and physical constants.

Are my equations wrong or do you think this is a reasonable compression ratio?
Can a high compression ratio damage the driver?

Thanks and have a nice day everyone.
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Old 16th March 2020, 11:07 PM   #2
kipman725 is offline kipman725  United Kingdom
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In my notes I have St = (P0)*C*R*Sd^2 / (Bl)^2

P0 = 1.21 kg/m^3
C = 343 m/s

I designed a very similar horn using a 15" driver and got a compression ratio of 1:2.523:
Mega midbass straight horn 139dB
I think your aiming for a specific upper cut off frequency though while I was aiming for the widest possible bandwidth. If you want to cut the horn off at 500 Hz you could add in the a throat chamber.

I recommend simulating in Hornresp, you will quickly see if your sums are correct!
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