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Old 20th November 2014, 06:34 AM   #1
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Default Questions about an 18" BR

Hey everyone,

Talked to my friend about putting together a party system for his house and did a quick experiment with the Dayton PA460 18" woofer. Looks like a steal with 98.5 dB sensitivity and low Qts (.27) but EEK only 6mm Xmax??

*WinISD Experiment*

WHOA. 150 liter box tuned to 40Hz and the sim (although probably slightly optimistic) says ~122 dB from 50 - 100! and thats just tapping 6mm Xmax at 325 Watts! Now If only I can experiment with high-passing and boosting EQ at Fb and get it FLAT to 40

Now for $200 plus a sheet and a half of some 3/4 Arauco, that seems like some SERIOUS low end! Throw in an iNUKE 3000DSP and some Jbell HS12's (PA310 & Selenium D220 loaded) and it sounds like a party (Don't you love spending other people's money!)

Back to reality for a moment, heres the question. With a single 8" port, WinISD gave me a length of 10". Does that nearly square (l x d) port dimension cause response problems? Would I be better off with the 4 x 4" by 13" long ports as an alternative? Either way port velocity maxes at 14 m/s.

Thanks guys. Just looking for a maximum simplicity build so if I can get away with a single 8" port, LET THE CANNON LIVE!
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Old 20th November 2014, 04:19 PM   #2
sine143 is offline sine143  United States
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slot ports are almost always better (the provide bracing to the box).

the dayton pa465 is worth considering as well.
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Old 20th November 2014, 06:38 PM   #3
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The only reason I wanted to stay away from a slot port was because with a slot width of at least 18-20 inches I would need at least a 3 inch height to stay away from that a unfavorable aspect ratio and at that point I was so low on port velocity it seemed like it was eating up box volume that I didn't have to.

How much sound comes from the driver cone opposed to the port? If planning on wall/corner loading is it favorable to have both driver and port on the same side of the box?


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Old 20th November 2014, 06:51 PM   #4
sine143 is offline sine143  United States
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Put them on the same side of the box. 3x21" is not overkill for port size, though the weak xmax of 6mm does aid in keeping velocity low
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Old 20th November 2014, 07:57 PM   #5
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Alright you got me sine, going with the slot haha. Have you ever played with boosting EQ to lower the cutoff?


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Old 20th November 2014, 08:44 PM   #6
sine143 is offline sine143  United States
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Eq does nothing to max output. You will still be limited by exvursion, thermal, and amp output
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Old 20th November 2014, 09:13 PM   #7
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True, though if you usually run out of Xmax, but still have plenty of thermal and amplifier headroom, you'd get away with boosting at Fb. Just make sure your highpass filter is still excursion-safe with the boost in place.

Chris
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Old 20th November 2014, 09:17 PM   #8
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I wasn't looking for extra output overall, just had see other builds and read about using a HP filter to protect from over excursion and a parametric boost at excursion minima to drop the low corner.

However now that I think about it, if I were to limit the sub channel to 41.5 volts (325W Xmax) wouldn't that make this boosting impossible? If excursion is down to ~1-2mm at Fb at 41.5 volts and I wanted to get more output there with EQ, the limiter would stop anything over 41.5 volts correct?


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Old 20th November 2014, 09:18 PM   #9
sine143 is offline sine143  United States
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yes, you will be stopped by your peak limiter meaning, max output has not changed (you just hit it with less lights on the mixer).

If you select a good driver, and tune accordingly for your program content, you will not need a boost at excursion minima.
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Old 20th November 2014, 09:29 PM   #10
sreten is offline sreten  United Kingdom
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Hi,

If your going for max SPL a peaking 2nd (or 3rd) order
high pass is one way to get some boost and prevent
overexcursion of the driver below port frequencies.
It must be done to approach maximum SPL levels.

rgds, sreten.
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