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Old 27th December 2011, 03:23 AM   #1
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Default Low Q sealed with lots of EQ

I'm thinking about taking an 8" MCM 55-2421 and sticking it in an existing 36 liter sealed enclosure. Qtc will end up around 0.30, which is too low, but that's the box I've already got and I'm so lazy. Then I'm going to bolster the bottom end with about 12 dB of EQ centered at 34 Hz or so. Is this going to be a horrible mistake? I've got about 300 watts to spend at the amplifier end.

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Old 27th December 2011, 05:51 AM   #2
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Download WinISD and model it. If the box is too big maybe try wrapping some polyester stuffing around a couple of bricks and stick them in the box to remove cabinet volume :-)
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Old 27th December 2011, 09:12 AM   #3
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I once put 14dB of gain at 28Hz on a pair of 8" drivers, 44L sealed.

Sounded reasonable until turned up - excursion got very silly very quickly. IMO, the rule of thumb about an 8" driver going to 40Hz is about right. Even then, you're limited on how loud you can have it.

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Old 27th December 2011, 03:37 PM   #4
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Quote:
Originally Posted by col View Post
Download WinISD and model it.
Already did that. It suggested a box about one tenth the size. But, the box I have is already built and happens to have the proper sized cutout for the driver. Guess I'll just try it for a while and see how I like it.
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Old 27th December 2011, 04:38 PM   #5
col is offline col  Australia
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you might find this project interesting:

P48 Sub-Woofer Controller (Rev-A)

I run a pair of 10" car subs in very small enclosures with a ESP P48A with the peak set at 33 Hz in a apartment, works well.
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Old 27th December 2011, 05:20 PM   #6
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The lower qtc (+ EQ), the better for a sealed system. This will reduce distorsion below the system resonance frequency where the mass control is lost.
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Old 28th December 2011, 02:00 AM   #7
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I've never been a fan of peaking response by storing energy in the transducer system. Low Q sealed is about the only way to get a low output impedance into the room. Raising Q just stores energy in the transducer, yuk! I also find building cabinets for large, such as an 18", much more difficult than building four top quality 10" cabinets. Easy to make a small cabinet solid and light weight. But that 18" cabinet was over 400 pounds!
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Old 28th December 2011, 09:22 PM   #8
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Sounded reasonable until turned up - excursion got very silly very quickly.
I did a quick and dirty test using a Tripath amp and a DSP crossover. It actually sounded rather nice, up to the limits of the amp. Boy, when that thing clips there is no mistaking it. As you approach 30 Hz there is a lot of excursion, even with the measly six watts or so coming out the Tripath amp. My daughter was impressed with it, however. My wife wondered what was causing the gentle rumble in the floor.

Overall, it seemed good enough to pursue further. I think I might clean up the boxes a bit, connect it to a real amp, and experiment a bit more with the equalization. If I can find my good mic, I might try to take some measurements and see if I can achieve a somewhat flat response.
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Old 28th December 2011, 10:32 PM   #9
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Cal thinks col's idea about adding some filler to the box is a great place to start. Done it many times to determine the "right" size box. reusing some older, larger ones to experiment with instead of building anew.
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Old 29th December 2011, 08:28 AM   #10
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Just had a look at which driver you're using.

Mine had a mere 3mm one-way Xmax, so I think yours will handle the boost better. I would still consider putting a low cut filter somewhere low down (25Hz?) in case it ever comes into contact with movies - here lieth the monsters.

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