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Old 17th October 2008, 02:12 AM   #1
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Default ideal driver qts for aperiodic IB tuning

I was running some alignments the other day in Win ISB and I thought that since we are able to approximate an IB loading with an aperiodic enclosure. What would be the ideal driver parameters for low bass extension and good transient response for this type of enclosure. I modeled a few drivers with high qts. One that had a qts of around .80 had amazing extension. But I can't remember the driver model off hand. Even better than an ideal driver in a BR alignment.

Normally a driver like this would require an OB mounting or a huge sealed or BR cabinet. But what about a cabinet of average size with a large enough resistive vent to approximate an IB size of enclosure.
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Old 17th October 2008, 02:21 AM   #2
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Can we also approximate an OB model in WinISD?
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Old 17th October 2008, 02:28 AM   #3
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I don't know. The way that I approximated the response was to define a closed box with a huge cabinet. One that would actually be too big to realistically build. Cabinets with 30-50 cubic feet of space or more. If you had a large enough baffle I suppose you could approximate the driver loading with a huge sealed alignment but I think that baffles of realistic widths would nullify the approximation since cancellation at lower frequencies would not be considered.
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Old 17th October 2008, 10:30 AM   #4
sreten is offline sreten  United Kingdom
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Default Re: ideal driver qts for aperiodic IB tuning

Quote:
Originally posted by Hezz

But what about a cabinet of average size with a large enough resistive vent to approximate an IB size of enclosure ......
Hi,

It does not work like that, you end with a small open baffle with no bass.

A resistive opening can increase apparent box volume therefore
reducing box Q, but the output of the resistive vent is out of
phase with the main driver cancelling some of its output.

It works for marginally too high Q sealed boxes -> aperoidic.
THe Q is lowered and some of the peak bass output is reduced.

Overdoing it, it simply stops working.

/sreten.
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Old 17th October 2008, 04:07 PM   #5
GM is offline GM  United States
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Default Re: ideal driver qts for aperiodic IB tuning

Quote:
Originally posted by Hezz
I was running some alignments the other day in Win ISB and I thought that since we are able to approximate an IB loading with an aperiodic enclosure. What would be the ideal driver parameters for low bass extension and good transient response for this type of enclosure.
My take on it is to use a driver with an Fs an octave below the desired Fc with a Qts = 0.5 to make it critically damped in its pass band with a high enough Vas/low Re to offset the otherwise ultra low sensitivity.

Designing a maximally flat impedance TL with an Fc that blends well with room gain seems a simple way to do and has the advantage of a ~flat phase response, something the IB can't do. For example, a theoretical 13 Hz Fs driver with a 0.5 Qts and 20 ft^3 Vas yields a reasonable 10 ft^2 cab.

L = 127"
CSA = 136"^3

Sim assumes 0.708 lbs/ft^3 stuffing density of polyfil.

GM
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Old 17th October 2008, 04:10 PM   #6
GM is offline GM  United States
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Impedance and phase:
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