Verify my reverse engineering

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presscot

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Joined 2010
#1
I’m attempting to reverse engineer T/S parameters of the woofer of loudspeakers; Braun LS200. I know for accuracy and precision, it should be done by measurement. Nevertheless, I did the calculation because I’m just curious whether the formulas on the textbook would work.

Well, here are all of the parameters I found in the spec sheet and speaker reviews.

Woofer diameter = 10”
Cabinet type = sealed
Cabinet volume = 47 litres (per single woofer)
Cabinet resonance = 36 Hz
Cut-off frequency = 28 Hz

The target is to find Fs, Qts, and Vas of the driver.

Step 1: Starting by finding Qtc from the relationship of F3/Fc = 28/36 = 0.78 or approximately 0.80, then looking at the table 1.12 in Dickason’s cookbook we obtain Qtc = 1.0.

Step 2: Assume the possible Qts are 0.3, 0.4, and 0.5. Looking at table 1.8, we obtain alphas of 10.11, 5.25, and 3, respectively.

Step 3: Verify usable Qts by the formula; Qts = Qtc/(sqrt(alpha + 1)), then, the usable Qts are only 0.3 and 0.5.

Step 4: From the relationship; Fc/Fs = Qtc/Qts, or Fs = Fc x (Qts/Qtc). We obtain Fs = 10.8 and 18 Hz. But, only 18 Hz should be valid because 10.8 Hz is too strangely low, IMHO.

Step 5: Therefore, the valid Qts should only be 0.5. And alpha should also only be 3.

Step 6: Vas is founded by Vas = alpha x cabinet volume, thus, Vas = 3 x 47 = 141 liters or about 5 cu.ft.

In conclusion, the results are as follows:

Given parameters:
F3 = 28 Hz
Fc = 36 Hz
Qtc = 1.0
Alpha = 3

Driver’s parameters:
Fs = 18 Hz
Qts = 0.5
Vas = 141 litres, or 5 cu.ft.

Basically, I’ve tried verifying by myself by putting these values in online calculators. And the results were given as predicted. However, I’m still unsure if I did it correctly. Anyone please verify my calculation.
 

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#8
Looks good using your specs in his well proven online calculator. 👍

That said, 18 Hz Fs means a ref. eff. of only ~73.95 dB using Qts for Qes, but speaker eff. is listed at 91 dB, so with two drivers it's ~88 dB/ea., so seems like you need to work backwards from here........ :headbash: :cuss::sigh:
 
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#10
Interesting one presscot
Is this sealed enclosure?
Looks like large volume achieved with floor standing tower.
From observation of frequency response
Almost what to assume. They may be High Qts speakers
designed for sealed. So suitable replacement would be similar.
Could almost assume Qts around .6 to .8
and Fs might be closer to 28 or 38 Hz

1704965876909.png
 
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#11
 
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