Sub enclosure suggestions

[Alex2507]

A friend of mine has two JBL GTx subs. I know that they are 4 ohm, have 4.5 lb magnets and are rated for 30-450 watts rms. Oh, and they are 10". On the back it also says sealed, ported and band pass.

I know enough to ask here for suggestions on where to find plans suited to that paticular sub. I also need to pick (plate)? amps. Thanks in advance for suggestions.

Alex

 

[Buckeyefan 1]

Give Parts Express a call at 800 538 0531 8-8pm est m-f, 9-5 sat. They'll tell you the optimum box to build based on the driver, your needs, and size restrictions.

Ported is the most efficient, but the design is sometimes complicated with long ports, large sizes, etc... Sealed is the easiest and most compact, but least efficient. I would advise against bandpass unless all you are out for is a car box that booms. Bandpass is not a very tuneable sub, but they hit extremely hard.

Read up here. It gives a wealth of info on the different types of boxes:
http://mobile.jlaudio.com/support_pages.php?page_id=146

 

[billnchristy]

That is not exactly true on the bandpass. A well designed bandpass can sound as good as a ported design and it eliminates the need for a crossover.

The problem with bandpasses is, by their nature, you cannot hear driver distortion and breakup so people tend to overdrive them and destroy the woofer.

You need to know the Thiel Small parameters of the subs to accurately design and build a box.

 

[Alex2507]

I just figured out that those were for cars. Duh.... Thanks for the PE contact info. I wasn't aware that they offered that type of service. Very cool.

 

[Alex2507]

That is not exactly true on the bandpass. A well designed bandpass can sound as good as a ported design and it eliminates the need for a crossover.

The problem with bandpasses is, by their nature, you cannot hear driver distortion and breakup so people tend to overdrive them and destroy the woofer.

You need to know the Thiel Small parameters of the subs to accurately design and build a box.

Bandpass is probably a bit beyond the amount of effort I'm willing to put into this and it's bulky too if I understand this right.

 

[Alex2507]

About a year has gone by since I posted this. I found the T/S parameters for these subs. I already suspect that these are low quality car subs that really have no place in home A/V. I'm really posting this here to have my suspicions confirmed. Here's the T/S parameters:

Freq response: 30Hz-500Hz
Amp. Power Range: 20W-500W
Continious Power Handling: 250W
Peak Power Handling: 450W
Voice Coil dia: 2,0" (51mm)
Nominal Impedance: 4 Ohms
Sensitivity@2.83V RMS@1M: 87dB
Driver Displacement: 0,09 cu.ft. (2,55l)

Thiele-Small Parameters:
Fs = 31Hz
Vas = 1,85 ft² (52,4l)
Qts = 0,43
Qes = 0,45
Qms = 7,55
Re = 3,3Ohms
Le = 0,6mH
Xmax = 0,480 in. (12,2mm)
Xpk = 0,866 in. (22mm)
Sd = 0,3724 Sq. Ft. (0,0346 Sq.M.)
Vd-linear = 0,000422 Cu. M.
Vd-peak = 0,000761 Cu. M.

 

[TLS Guy]

That is not exactly true on the bandpass. A well designed bandpass can sound as good as a ported design and it eliminates the need for a crossover.

The problem with bandpasses is, by their nature, you cannot hear driver distortion and breakup so people tend to overdrive them and destroy the woofer.

You need to know the Thiel Small parameters of the subs to accurately design and build a box.

Well there are bandpass subs of different orders. The second order band pass (one chamber sealed and one chamber ported) can do a reasonable job, however there are significant distortion and time delay issues. The higher order arrangements, a la Bose, have for too much distortion, time delay and Phase response issues to be considered accurate reproducers in my view.

One advantage of the second order bandpass is that roll off is second order r on the top and bottom end. This means you get a more extended bottom end for a given F3, compared to a standard B4 ported enclosure. The top second order roll off makes for a nice acoustic crossover to a sealed bass mis enclosure if you design both enclosures for a nice seamless transition.

You still need an electronic crossover above the upper F3 though, as otherwise there will be too much mid and HF radiation from the port. I have designed and built 3 band pass designs, and I'm still using them, so I guess they have their uses.