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Old 11th February 2015, 09:08 PM   #1
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Default Low cut/limiting a THAM12

I'm putting the final touches to a THAM12 loaded with a PD.12SB30 which is rated for 400W AES with an xmax of 7mm (no info on xmech/xdamage).

I'm trying to figure out how to get the most from of the sub whilst also protecting it from a redlining DJ. I'm using a DCX2496 which only has 'zero attack' limiters - I appreciate that if I set them to the equivalent of 400W they will prevent any peaks of higher than 400W even though the driver is rated for 1.6kW for 6dB crests, but at the moment my concern is safely limiting it so a DJ that slams into the limiters all night doesn't fry the voice coil with too much average power.

I'm not the most knowledgeable at Hornresp so let me know if anything seems immediately wrong. I started with a lowcut of 45Hz, which I think is sensible for the THAM12, which limits me to about 300W before going through xmax too much;

Click the image to open in full size.

If I raise the lowcut to 50Hz & drop the crossover point to 110Hz I can feed the driver its full 400W with what looks like a 1 to 1.5dB boost at the lower peak;

Click the image to open in full size.

But if I low cut it much lot lower at 38Hz & cross it much higher at 140Hz (after a recommendation from a Speakerplans forum member), even though I can only feed it 250W before it reaches xmax it's actually louder than the 45-125Hz 300W option & barely different to the 50-110Hz 400W option?

Click the image to open in full size.

So what should I do? Unless I've done something wrong in Hornresp, it looks like the 38-140Hz option is best, as it's the same acoustical power as the 400W option (actually more above 100Hz) but without wasting the extra power into power compression?

Last edited by lost eden; 11th February 2015 at 09:13 PM.
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Old 12th February 2015, 10:05 PM   #2
djk is offline djk
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Use a 50hz Q=1 high-pass filter for protection.

Looks like you could run it up to 150hz without a problem.
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Old 13th February 2015, 10:45 AM   #3
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The DCX has dynamic EQ. I'm not entirely sure how it works, but if you tell it to reduce power at the LF tuning frequency when cranked right up, your driver should be fairly safe.

To DJ-proof, I'd recommend running a slightly-low highpass filter, and limit early to avoid over-excursion. That way, you get a little excursion below tuning, which will help cool the driver.

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