Martin Poulin
September 2019
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Started 2 new enclosures for my rear channel​s.
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Rear channels won't be taxed much so I opted for recycling my Precision Device PD154 woofers.
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90 liters net internal volume.
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24x24x13 inch external
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Baltic Birch plywood used (I don’t typically recommend using BB ply, but used it in this case, it was at 30% sale at my local store).
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Bracing used on all 3 axis.
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Roxul Safe n Sound used inside.
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Will house a single PD154 15" woofer, sealed or aperiodic.
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Nothing progressing during winter, my garage isn't heated.
May 2020,​
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added 1/4" thick metal plate to the back of each cabinet
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Each plate measure 23" x 23" and weight 38 pounds
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Drilled and glued with PL Adhesive
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Rear metal plate are painted flat black with rust proof paint (pic after 1st coat)
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Metal back plate help with rigidity and the extra weight reduce enclosure vibration
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Enclosure are painted with the roller brush and quality Acrylic paint.
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Small defect can be hidden with drywall putty :)
PD154 measured in free air. PD154 measured inside the 90l enclosure.
PD154 simulated in a 90 liters sealed enclosure
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0.42 Qtc of DATS impedance tester perfectly match the simulation model!
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I know that a falling frequency response like that look useless with a -6dB point at around 85Hz.
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This is what you get with a woofer having a Qts of 0.26...
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A bit of DSP equalization and the resulting frequency response will be flat as a ruler.
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My initial target range for this enclosure is 60-750 Hz.
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I intend to mate with the Radian 760PB on a 350Hz Tractrix horn.
Would like a lower crossover point but the 3" dome of the 760PB doesn't like going much below 750Hz...
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Finished enclosure ready for testing.
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Weight in at 108 pounds a piece.
I should have tested it prior to painting it...
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Despite being 108 pounds and all solid Baltic Birch Plywood construction, it vibrate too much for my like on the top and front baffle.
At 400Hz, you can really feel some strong vibration going on, I do not like that at all, I have to fix it.
-What I mean here is that the enclosure walls vibrate to the extent that they will audibly color the speaker output.
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I may add a metal "top plate" and/or double the front baffle thickness from either one extra layer of MDF or another layer of plywood.
Not sure what I'll do first, this box was one of the rare one I constructed without a double thickness front baffle and IT WAS A MISTAKE!
Stuffing inside the box can't do much here, even if I add extra stuffing, the vibration mode will remain.
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Quick test outside:
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2 meters distance, ground plane method.
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Speaker tilted forward to aim the middle of the woofer to the microphone.
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Windy condition, not ideal measurement (high noise floor from measurement)
Those side handle vibrated at 220Hz
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On the distortion plot, you can clearly see the peak at 220Hz created by the handle...
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Will correct that on next measurement but since the wind was getting stronger, the measurement I have does show the handle anomaly...
measurement below 100 Hz aren't very accurate because of the wind. You can see the noise floor raising quickly below 100Hz on the distortion plot.
Spectrogram is the same, you can't consider it accurate at all.
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While comparing the sealed cabinet to my Quarter Pie mid-bass horn, I've experimented with a slot.
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The Q-pie has a 13" wide slot and I've compared the results as a direct radiator.
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At 30 centimetres distance, one gain 2dB (see graph above)
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At 1 meter away, effect is mostly gone in the band that interest me (50-600 Hz)
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Subjective sound is pretty much the same while using a crossover point of 450 Hz in my tests.
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Slot may be beneficial, the BBC LS5/5 used a slot for their woofers and midrange.
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My 450 HZ and below pass band had shown no benefit.
New double thickness of Baltic Birch Plywood on the top of the enclosure
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-Not shown, I added a double thickness front baffle as well.
March 2020
MKII done
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110 pound each!