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Paper vs. actual

 

Silver Member
Username: Lord_huggington

Ontario Canada

Post Number: 404
Registered: Oct-10
Was it just me who'se sub fell off hard below its tune? I had an 05 RE XXX 12 in 2.2 @ 36 and a 1500W amp (@ 1 ohm), and there was a huge loss below 36 Hz, it sucked for low response, and I thought I'd have gotten the opposite. I had an APX 12 and an Eclipse SW8200 in the same box and the Atomic was the loudest below tune, it also had the stiffest cone, it would barely move on 1500W, and although it was acoustically dead it was a nice sub (it was stolen though). The SW8200 was about the same as the XXX, it just didn't sound as neutral & crisp. Even when I used the SW8200 @ 2 ohm (750W) I couldn't even tell a difference between the halved power.

I also tried 2 Eclipse SW8200's sealed in 1.25 NET each, 375W each, QTC 1.2 / FC 44 Hz, and the lows were so fking nuts, it was like 20-30 Hz was louder than 30-40 Hz. It wasn't head-smacking loud like the XXX around 36-42 Hz, but they held their own.

Where did I go wrong with both boxes? I have the XXX and I don't know what to do with it, I was going to re-cone it to an 18" for 9 NET @ 32.8 Hz, foreward-fire and sealed off. AQ 1200 or 2200 with a battery for power, stock alt cuz I'm mad broke .

--Questions--

I can fit 2 15's ported / foreward fire with port in the middle (~4.3 NET each @ 34.9 Hz with 14.5" of port per cube, port ratio 1:3), or I can do 2 18's sealed in 5.25 NET each & foreward fire. Each setup would be sealed off from the trunk. Keeping an ability to upgrade, I'd like to do either of these, with the most popular cut-outs being (outside) 15.625" with a (inside) 14.125" cut-out, 18's that are (outside) 18.5" and (inside) 16.75".

LMS motors - they have low sensitivity, but do they make up for it in actual out put?

Does Sd * Xmax on paper calculate into a real-world result?

For instance - not that I can afford these - but I probably one day will ;) - 2 LMS Ultra 18's sealed in 10.5 NET and 2 SS XXX 15's in 8.75 NET @ 35 Hz - the 18's have Sd (1200) * Xmax (38mm) * 2 subs = 91200, the 15's have Sd (756.77268) * Xmax (39.88mm) * 2 subs = 60360. Say both are powered by a Soundigital 16k.

The 18's move 1/3rd more air, and in 5.25 NET sealed it yields about QTC .5 / FC @ 30-32 Hz, probably the best response ever.

Sensitivity on LMSU - 89.7 dB (+3 dB for 2 subs) = 92.7 dB
Sensitivity on XXX - 90.8 dB (+3 dB for 2 subs) = 93.8 dB.

The XXX's being ported, there's a +3 dB gain at 35 Hz = 93.8 + 3 - 92.7 dB = theorhetical 4.1 dB gain over 2 sealed 18's.

I'd like to know if they'd equal out - is 4.1 dB @ 35 Hz equal to +30000 square centimeters of cone area with a sealed box? That's equal to something like 3 10's that each have a 30mm Xmax. The pair of 18's would be moving about as much air as 9 10's that each have a 30mm Xmax, quite shocking.
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