18" Sub box for Mobile DJ help!!! - diyAudio
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Old 11th June 2009, 05:45 PM   #1
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Default 18" Sub box for Mobile DJ help!!!

Hey Guys,

Newbie here, I want to build a box similar to this:

http://pro-audio.musiciansfriend.com...fer?sku=601207

I have already purchased all the hardware necessary and the woofers. I have some car audio box building experience. The problem is I only know how to make sealed boxes. I never learned vented or ported. I have all the specs for the woofer. Now I just need direction on planning for the box. Any help would be greatly appreciated. Oh I am building two and using a QSC RMX 1850HD amplifier running at 4 ohms stereo.

Chuck

Peavey 1808-4 BWX 18"
Impedance: 4 Ohms
Power capacity: 2000 W Peak 1000 W Program 500 W Continuous
Sensitivity: 97.5 dB / 1 W 1 m
Usable freq. range: 35 Hz ~ 1 kHz
Cone: Kevlar® impregnated cellulose
Voice coil diameter: 4.0" / 100 mm
Voice coil material: Aluminum ribbon wire Polyimide-impregnated fiberglass former Nomex® stiffener Solderless diffusion welded OFHC copper leads
Net weight lb. / kg: 18 lbs. / 8.2 kg
Znom (ohms) 4
Revc (ohms) 3.47
Sd (Square Meters) 0.1237
BL (T/M) 13.94
Fo (Hz) 38.9
Vas (liters) 311.7
Cms (uM/N) 143.4
Mms (gm) 116.6
Qms 10.215
Qes 0.509
Qts 0.485
Xmax (mm) 2.0
Le (mH) 0.16
SPL (1W 1m) 97.5
No (%) 3.50%
Vd (cu. in. / ml) 29.5 / 483
Pmax (Watts pgm.) 1000
Disp (cu. in. / ml) 228 / 3737
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Old 11th June 2009, 09:31 PM   #2
GM is offline GM  United States
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Default Re: 18" Sub box for Mobile DJ help!!!

Greets!

OK, then build a 'sealed' box that's ~222.64 L net (i.e. after factoring in the volume loss due to the driver, vent and any bracing) and vent it with a 20.32 cm diameter pipe (or some other duct shape of equivalent area) by 20.32 cm long to get a ~Fs tuning with a ~30 Hz F10 sitting on a solid, non 'floating' floor. Line one side, top and back panel with ~2.54 cm acoustic fiberglass insulation or similar to smooth out its vent induced HF 'hash' (resonances) above ~500 Hz.

BTW, for my records, are these published or measured specs?

GM
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Old 11th June 2009, 09:33 PM   #3
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Specs:
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Old 15th June 2009, 02:52 PM   #4
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Yes those are published specs. Thank you for the input. I cannot wait to see how it turns out. Will post pix when finished.
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Old 15th June 2009, 03:04 PM   #5
GM is offline GM  United States
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You're welcome! Looking forward to your thoughts on its performance.

GM
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Old 15th June 2009, 04:38 PM   #6
jbell is offline jbell  United States
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Xmax (mm) 2.0

You didn't buy low riders.... Those peavey's (1804-4 black widow's) aren't made for big sub use.

You'll exceed xmax at less than 50 watts of power in the proposed vented cabinet.

Can you exchange those for the low riders?
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Old 15th June 2009, 04:50 PM   #7
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True, but at ~115 dB/m, ~120 dB/m on a 100 W minimal overdrive and +6 dB for a pair, just how much is required for a mobile DJ app?

GM
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Old 16th June 2009, 09:50 AM   #8
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Depends on the DJ/room size and other parameters but ussually a lot and preferably even more than that.

Even 4,0 mm would be considered little. Hopefully Xmech is considerably larger.

Best regards Johan
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Old 16th June 2009, 01:45 PM   #9
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Sheesh! That's too loud for banquet, etc. rooms, school auditoriums, etc.. Back when I helped with such apps, the SPL was based on the drum kit regardless of room size, so 115-120 dB was plenty for the <100 Hz BW. Big outdoor events requires more of course, but these aren't 'mobile DJ' events.

And to think I use to take a lot of verbal abuse for waste of money/space 'overkill' designs that I did to keep distortion low and now it seems they would be drowned out with SPLs high enough to permanently damage/distort the ears. Oh well, I know how to do 'loud' for a given driver and the BMX in a band-pass should peak on the far side of 130 dB in the ~50-100 Hz BW even with some thermal power compression.

GM
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Old 16th June 2009, 02:39 PM   #10
jbell is offline jbell  United States
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Quote:
Originally posted by GM
Sheesh! .... and the BMX in a band-pass should peak on the far side of 130 dB in the ~50-100 Hz BW even with some thermal power compression.
GM
now that sounds more like the dj's I know... post that one up for the OP, I'm sure he'd appreciate it.
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