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Old 25th October 2015, 04:14 AM   #1
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the cheapest way to determine the box resonant frequency of a subwoofer in terms of how much the equipment i would need costs?
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Old 25th October 2015, 04:21 AM   #2
rayma is offline rayma  United States
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Originally Posted by OpenglCG View Post
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.
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Old 25th October 2015, 04:39 AM   #3
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when looking at multimeters they have frequency ranges for ac. does this range need to cover the frequencies tested?
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Old 25th October 2015, 03:03 PM   #4
wg_ski is offline wg_ski  United States
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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?
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Old 25th October 2015, 03:42 PM   #5
rayma is offline rayma  United States
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Originally Posted by OpenglCG View Post
when looking at multimeters they have frequency ranges for ac. does this range need to cover the frequencies tested?
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.
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Old 25th October 2015, 07:26 PM   #6
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Originally Posted by OpenglCG View Post
the cheapest way to determine the box resonant frequency of a subwoofer in terms of how much the equipment i would need costs?
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).
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Old 25th October 2015, 09:31 PM   #7
sreten is offline sreten  United Kingdom
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Originally Posted by weltersys View Post
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.

Last edited by sreten; 25th October 2015 at 09:34 PM.
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Old 26th October 2015, 01:09 AM   #8
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Originally Posted by sreten View Post
No that is wrong. It won't indicate Fb for sealed.
It will indicate Fport for vented which is not Fb.
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

Last edited by weltersys; 26th October 2015 at 01:12 AM.
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Old 26th October 2015, 02:28 AM   #9
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Finding the Basic Thiele/Small Parameters
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Old 26th October 2015, 10:24 PM   #10
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by weltersys View Post
Sreten,

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.

Art

Last edited by sreten; 26th October 2015 at 10:29 PM.
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