Fostex T/S Paraemeters - Comparison with Fonken - diyAudio
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Old 24th May 2008, 09:09 PM   #1
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Default Fostex T/S Paraemeters - Comparison with Fonken

This discussion has stemmed off from FE126E in a TL or TQWT cabinet

Attached is the measured T/S Parameters for the FE127E as measured by Planet10. These are the average of 120(!) drivers.

My measurements of the Fostex FE127E driver (n=4) are fairly close.

In both cases, the measurements are quite different from what Fostex has published.
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Old 24th May 2008, 09:10 PM   #2
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Attached is the measured impedance for the Fonken.
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Old 24th May 2008, 09:14 PM   #3
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This is the impedance sim of the Fonken.

The orange line is the simulation using the Fostex T/S numbers.

The yellow line is the simulation using the measured T/S numbers.

As you can see, the measured T/S are much closer to the impedance curve in post #2. The small differences are likely the result of the damping material. The simulation does not account for damping.
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Old 24th May 2008, 09:19 PM   #4
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Here is the simulated frequency response. Note that the simulation does not take into account the room.

Again, orange is using the Fostex parameters and yellow are the measured parameters.

Despite the fact that the T/S parameters are very different, you can see that the response is within about 2 dB. A change of 3 dB is generally considered the threshold of hearing and 2 dB is a far cry from what a room will do to the sub 150 Hz response.

edit=typo
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Old 24th May 2008, 10:39 PM   #5
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Default Re: Fostex T/S Paraemeters - Comparison with Fonken

Quote:
Originally posted by gmilitano

In both cases, the measurements are quite different from what Fostex has published.
Depends on your viewpoint. If their calc'd efficiencies are reasonably close, then a cab designed around its published specs should perform well regardless of the disparity between Fs, Vas, Qes. I calc 89.98 dB/W/m published Vs Dave's 90.18 dB/W/m and 90.72 dB/W/m for your one with a Vas spec, an insignificant ~0.22% and 0.82% error respectively, either of which any speaker manufacturer's QA dept. would be proud of.

Note that this line of reasoning doesn't apply to drivers for use in compression horns where the motor's strength (Qes) is key to good performance and of course if you have measured specs might as well use them.

GM
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Old 25th May 2008, 09:10 PM   #6
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Default Re: Re: Fostex T/S Paraemeters - Comparison with Fonken

Quote:
Originally posted by GM
Depends on your viewpoint. If their calc'd efficiencies are reasonably close, then a cab designed around its published specs should perform well regardless of the disparity between Fs, Vas, Qes. I calc 89.98 dB/W/m published Vs Dave's 90.18 dB/W/m and 90.72 dB/W/m for your one with a Vas spec, an insignificant ~0.22% and 0.82% error respectively, either of which any speaker manufacturer's QA dept. would be proud of.
GM,

Could you post some background information on what you have done above. Is that the same as comparing at the ratio of Fs/Qts?
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Old 26th May 2008, 12:04 AM   #7
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Load these formulas into Excel/whatever to calc a reference efficiency for comparing drivers:

n0 = (K*Fs^3*Vas)/Qes

where:

n0 = reference efficiency in percent
K = 9.6352e-10 (Vas in liters)
K = 9.6352e-7 (Vas in cc)
K = 2.723e-8 (Vas in ft^3)

then:

sens = 112.018+10*(log10(n0))

No.

GM
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Old 27th May 2008, 05:13 AM   #8
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Thank you.

The K you noted, for what temperature and humidity is that?
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Old 27th May 2008, 05:33 AM   #9
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You're welcome!

Don't recall, whatever yields a 344.424 m/sec SoS and 1.20997 kg/m^3 air density.

GM
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Old 28th May 2008, 01:24 AM   #10
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Default Re: Re: Fostex T/S Paraemeters - Comparison with Fonken

Quote:
Originally posted by GM


Depends on your viewpoint. If their calc'd efficiencies are reasonably close, then a cab designed around its published specs should perform well regardless of the disparity between Fs, Vas, Qes. I calc 89.98 dB/W/m published Vs Dave's 90.18 dB/W/m and 90.72 dB/W/m for your one with a Vas spec, an insignificant ~0.22% and 0.82% error respectively, either of which any speaker manufacturer's QA dept. would be proud of.

Note that this line of reasoning doesn't apply to drivers for use in compression horns where the motor's strength (Qes) is key to good performance and of course if you have measured specs might as well use them.

GM
Given that drivers with a wide range of TS parameters would all perform 'well' in the same cabinet, provided that their calculated efficiencies were close, is there any advantage in using the actual TS parameters. Put another way, if a person were to design resonant, non-horn enclosures for the FE127E, one optimized for the Fostex TS numbers and the other for the actual TS numbers, would the enclosure designe using the actual numbers perform better?

Regards,

Bob
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