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Old 26th April 2009, 12:35 AM   #1
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Default Woofer protection for small monitor

I'm building a small speaker using a Vifa TC18 and a Morel MDT20. Sealed box of 9l looks best.

Now, these Vifas have only 4mm of xmax so I'm keen to build in some protection for them at the low end, say sub 50hz.

What's the best way to this passively, in the crossover itself? I could just put some good-sized caps in series, but are there better ways to effective a low freq roll off for this purpose?

All suggestions appreciated.
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Old 26th April 2009, 12:59 AM   #2
Ron E is offline Ron E  United States
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I have some TC18 in ~24 liter boxes and I have never heard a peep of complaint. Unless you are going to really pound on them I wouldn't worry about it. Your situation or music tastes may differ, so...
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Old 26th April 2009, 01:27 AM   #3
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Thanks, Ron.

Being a small design I'm not going to hammer them.

Using Unibox I calculated that in 9l I could throw 15 watts into them before they got to xmax.

But I'd still like to implement some low end protection if it's not too involved.

BTW, what was your alignment? Ported, sealed? Any other details?
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Old 26th April 2009, 02:56 PM   #4
Ron E is offline Ron E  United States
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First, Mine are infinity buyouts, just like yours. The alignment is 24L sealed to get a Qtc of ~0.7, IIRC. I kind of wish I had gone with a smaller box for a bit more oomph/punch in the low end. I don't really notice that they roll off at ~60 - they seem quite extended other than the polite representation.

T/S measured
Fs 43.4
Qts 0.546
Qes 0.653
Qms 3.34
Vas 0.967 cuft = 27.4 Liters
Re 5.5 ohms

Measured frequency response a bit of a dip at 2k and a peak at 4k ~3db each.

You have to realize that 15W broadband is probably not 15W at the exact excursion limited frequency. For this reason power ratings based on Xmax are rather conservative for most fullrange music systems. In fact 15W broadband into these is probably going to be relatively loud. Measured/calculated sensitivity is more like 88-89 than 86. It's about 86 in my finished design, though.

This driver has a high enough Q that you might try a 3rd order sealed alignment, but these actually usually reduce power handling at low frequencies.
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Old 26th April 2009, 09:39 PM   #5
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Thanks for the info, Ron.
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