the cheapest way to determine the box resonant frequency of a subwoofer in terms of how much the equipment i would need costs?
Drive it with an amp and a series resistor of around 100 Ohms. See at what frequency the output voltage peaks.
when looking at multimeters they have frequency ranges for ac. does this range need to cover the frequencies tested?
Just use one designed and calibrated for use at 50-60 Hz line frequency. A $9.99 special will do. Any errors you get at subwoofer frequencies (20-40 Hz) will be small. Mids and highs it will be off but who cares?
If you have a true RMS meter that also measures frequency, that will be ok. Otherwise, use your scope for both the amplitude
and frequency measurement. If you don't have a scope, only a cheap DVM, you can use it for adjusting to the peaking frequency,
and then read it off the signal generator.
The cheapest way (assuming your eyes work) to determine Fb is to mark the cone with a dot of contrasting color, run a sine wave sweep, the excursion (cone movement) will be at minimum at Fb (box resonant frequency).
Hi,
No that is wrong. It won't indicate Fb for sealed.
It will indicate Fport for vented which is not Fb.
rgds, sreten.
Sealed impedance will peak at Fb. Vented has twin peaks
and Fport is the minimum impedance between the peaks.
Fb is pretty meaningless for vented, as a parameter.
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Sreten,
In a sealed cabinet maximum excursion occurs at the resonant frequency of the enclosure (Fc).
In a ported enclosure the minimum excursion occurs at the Helmholtz frequency of the enclosure, Fb (Box Frequency).
The Fb is the same frequency regardless of driver.
The Fc of a sealed cabinet is driver dependent.
Never heard of Fport, unless that is the port resonant frequency, which typically would be well above "sub" frequencies, in the 200+ Hz range.
Art
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[SIZE=+1]Finding the Basic Thiele/Small Parametershttp://www.bcae1.com/spboxad3.htm[SIZE=+1]
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Originally Posted by weltersys
In a sealed cabinet maximum excursion occurs at the resonant frequency of the enclosure (Fc).
Nonsense. Depends on Qbox.
In a ported enclosure the minimum excursion occurs at the Helmholtz frequency of the enclosure, Fb (Box Frequency).
No its Fport not Fbox.
The Fb is the same frequency regardless of driver.
Nonsense.
The Fc of a sealed cabinet is driver dependent.
Fc? But true, Fbox depends on the driver.
Never heard of Fport, unless that is the port resonant frequency, which typically would be well above "sub" frequencies, in the 200+ Hz range.
Clueless comment, Fport is the tuning frequency of the port/vent.
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Sreten,
Evidently your definitions of Fb, Fc, Fport are all different than what I grew up with here in the USA.
As far as Fb (Frequency of Box Helmholtz resonant frequency) it does remain the same regardless of driver, as can easily be determined with any online Fb calculator, none ask for any TS parameters to determine Fb.
Programs like Hornresp can also determine the "pipe resonance" of the port duct, though that is not typical of simple ported box programs which just give the response in the low end and a smooth curve above.
As far as my observations being "clueless" and "nonsense", perhaps if you drove on the right hand of the road like the rest of the 65% of the world, your opinions also might be different 😉.
Cheers,
Art
In a sealed cabinet maximum excursion occurs at the resonant frequency of the enclosure (Fc).
Nonsense. Depends on Qbox.
In a ported enclosure the minimum excursion occurs at the Helmholtz frequency of the enclosure, Fb (Box Frequency).
No its Fport not Fbox.
The Fb is the same frequency regardless of driver.
Nonsense.
The Fc of a sealed cabinet is driver dependent.
Fc? But true, Fbox depends on the driver.
Never heard of Fport, unless that is the port resonant frequency, which typically would be well above "sub" frequencies, in the 200+ Hz range.
Clueless comment, Fport is the tuning frequency of the port/vent.
_____________________________________________________________________________
Sreten,
Evidently your definitions of Fb, Fc, Fport are all different than what I grew up with here in the USA.
As far as Fb (Frequency of Box Helmholtz resonant frequency) it does remain the same regardless of driver, as can easily be determined with any online Fb calculator, none ask for any TS parameters to determine Fb.
Programs like Hornresp can also determine the "pipe resonance" of the port duct, though that is not typical of simple ported box programs which just give the response in the low end and a smooth curve above.
As far as my observations being "clueless" and "nonsense", perhaps if you drove on the right hand of the road like the rest of the 65% of the world, your opinions also might be different 😉.
Cheers,
Art
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