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PostPosted: December 4th, 2016, 12:00 pm 
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Joined: July 25th, 2015, 12:47 pm
Posts: 60
I am doing a box for JL Audio12w7-3 driver. I prefer sealed box but I thought of making a ported box and seal the port for a sealed box effect. This driver is flexible enough for that as well as do a quarter wave tube. Here are the details. Any help would be appreciated.

Regards,
Jay Bala

JL audio suggests for a sealed box as below (car audio):
Qtc = 0.79
Vb (net) = 39L, 1.375 cu.ft
Fc = 44.7 Hz
F3 = 40.4 Hz

I like a Qtc=0.5 but the box size comes out to be near 30 cu.ft. Thats kinda big.
Qtc=0.79 gives 1.4 cu.ft
Qtc=0.67 gives 2.5 cu.ft
Qtc=0.64 gives 3.0 cu.ft
Qtc=0.57 gives 5.8 cu.ft
Qtc=0.50 gives 29 cu.ft
———

JL audio suggests for a ported box as below (car audio):
(This doesn't look to be for a SBB4 alignment.)
Vb (net) = 50L, 1.75 cu.ft
Fb = 36.7 Hz
F3 = 31.5 Hz
Slot height: 1.75 in
Slot width: 14 in
Slot length: 24 in
Slot volume from above: 0.34 cu.ft (much largewr than ported volume)
Total internal volume:
suggested net+drvier+slot = 1.75+0.14+0.34 = 2.25 cu.ft

Different box calculators on the internet gives different box volumes, one of them gives:
For SBB4 alignment,
Vb = 2.5 cu.ft
f3 = 25.5 Hz
fb = 27.2 Hz
Port diameter = 3 1/16"
Port length = 8.3"

TS:
Free Air Resonance (Fs) = 27.2 Hz
Electrical “Q” (Qes) = 0.514
Mechanical “Q” (Qms) = 7.807
Total Speaker “Q” (Qts) = 0.482
Equivalent Compliance (Vas) = 2.33 cu ft / 66.0 L
One-Way Linear Excursion (Xmax) = 1.15 in / 29 mm
Reference Efficiency (no) = 0.25%
Efficiency (1 W / 1 m) = 86.2 dB SPL
Effective Piston Area (Sd) = 84 sq in / 0.0542 sq m
From Sd, driver diameter = 10.342 in, 26.27 cm
DC Resistance (Re) = 2.7 Ω (measured)
Driver Displacement = 0.14 cu ft / 4.0 L
Nominal imp = 3 ohms
minimum mounting depth = 10.5”
frequency response = 18-200 Hz
Amp power: 400W at 2 ohms
peak power handling = 2,000 watts

http://www.jlaudio.com/12w7-3-car-audio ... vers-92112


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PostPosted: December 5th, 2016, 11:19 am 
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Joined: February 28th, 2013, 1:19 pm
Posts: 914
Jay,

Not clear if you are using this for car audio or home audio. If the latter, I would be inclined to go with the 3 cu ft enclosure, sealed. This gives you an optimally damped enclosure (bessel alignment, as I recall), and is compatable with alot of 12" woofers should you later want to try a different driver. I am not sure about the quality of the bass in any of the vented box alignments.

David


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PostPosted: December 5th, 2016, 4:17 pm 
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Joined: July 25th, 2015, 12:47 pm
Posts: 60
For music at home. Sealed is better.
For best transient, Qtc=0,5 its almost 29 cu.ft. Thats a bit smaller than 2x3x5 ft box.

Also, at 3 cu.ft. Qtc of 0.64 isn't all that bad and I could do a Tapered pipe with slot loading. For a sealed, I could bolt the slot shut.


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PostPosted: December 6th, 2016, 12:44 pm 
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Jay,

3 cu ft may not be enough volume for a proper tapered pipe or transmission line with a 12" woofer, unless you have good plans. If you do, then never mind. A solid, well constructed, thickwalled and internally braced sealed box will give great results. My subs are exactly that, with 1-1/2" thick walls (1-1/4" MDF + 1/4" oak plywood for cosmetics). I actually run them with a 6dB/octave bass lift electronically to provide more extension.

David


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PostPosted: December 6th, 2016, 1:05 pm 
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I was thinking 29 cu.ft :-)
A bit smaller than 2x3x5 ft


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PostPosted: December 6th, 2016, 1:26 pm 
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Joined: July 24th, 2015, 4:17 pm
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Location: Parkville, Maryland
Edgar Villchur invented the acoustic suspension speaker system. His trick was to use a driver with a free-air resonance below 10-Hz. A driver with a free-air resonance of about 27-Hz. in a sealed box just won't get the job done. That said -- referencing the photo of the box with a tapered path -- that could be fiddled with in terms of fiberglass and/or wool fill to create a really cool transmission-line speaker that can get the job done. A word of advice -- do not use foam or polydacron for fill -- both are much too reactive and will create more problems.

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PostPosted: December 6th, 2016, 1:53 pm 
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I dont know of too many drivers with Fs less than 10 Hz.
He said that you would need Fs less than 10 Hz for the acoustic suspension to work best?


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PostPosted: December 6th, 2016, 2:51 pm 
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Villchur had three goals when he designed the acoustic suspension speaker. The primary goal was to reduce the distortions caused by the very non-linear suspensions used in drivers of the time. He also wanted to flatten the frequency response and use a small box. Basically he designed a driver where the suspension was very compliant to the point that the real "spring" in the mass/compliance system was the air in a sealed box. Within reason, the air acted as a more linear spring.

Since the Fs is the result of the moving mass and the compliance of the driver, with a very compliant suspension, and any reasonable moving mass, the Fs is quite low. However, the VAS or equivalent volume of the driver is quite high. As a result, when put in a small sealed box, the Fb and Qb of his drivers went up dramatically. I have heard that the Q in his speakers was around 1 which would give a substantial bump at resonance. However, most amplifiers of the time started rolling off at frequencies that were definitely not subterranean. As a result, to some degree that bump helped offset falling amplifier response. High Q was not uncommon in speakers of that time for exactly that reason.

I have always felt as David just said that sealed boxes give much better transient response than ported, passive radiator, etc. designs. The search for "perfect" Q in my opinion does not make sense with the ability to have electronic control of the frequency response for very little money. Transient response in a sealed box design to a large degree is a function of the mechanical damping of the driver plus the ability of the driving amp to absorb the energy created by the driver acting as a generator after drive signal is removed. Even when those factors are not optimum you are still way ahead of any ported design where by necessity the port output must always lag the cone output by a significant amount. The mass of air in the port must be excited in order to resonate and create output. It is behind at the both the beginning and end of the signal. It will always smear the signal.

Tom


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PostPosted: December 6th, 2016, 3:22 pm 
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Location: Parkville, Maryland
Then why do I have tight detailed bass down to 31-Hz. using a half-ass transmission line in my Altecs? :confusion-confused:

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PostPosted: December 6th, 2016, 4:02 pm 
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Tight compared to what?


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