Help me choosing enclosure for GT5 12" Subwoofer

[venki7744]

Hi Gurus,

Last week I got a GT5 12". I am planning to fit this into my new car (yet to arrive) Stile D. Last weekend I measured the T/S specs (as nothing is mentioned on the JBL site). The results was not as I expected (I was under the assumption that the specs would be similar to the GT4 12" series except for the technology). Following are the T/S specs (measured).

* f(s)= 30.95 Hz
* R(e)= 3.75 Ohms
* Q(ms)= 7.413
* Q(es)= 0.864
* Q(ts)= 0.773
* V(as)= 56.000 liters (1.978 cubic feet)
* M(ms)= 223.20 grams
* C(ms)= 0.12 mm/N

The user manual mentions that the sub can either be placed in a sealed or ported box. But from the above specs the only enclosure I can think of is a sealed (EBP ~ 40) and that too with a Q around 1. Now I don't know how to proceed. Gurus, can anyone help me with the following questions.

* Is it normal to have this high Qts/Qes for GT5 12" or is it something else (may be I am doing something wrong or the driver is damaged).

* If the specs are not normal, can somebody share the specs for the sub.

Thanks,
Venki.

[navin]

Originally Posted by venki7744

* f(s)= 30.95 Hz
* R(e)= 3.75 Ohms
* Q(ms)= 7.413
* Q(es)= 0.864
* Q(ts)= 0.773
* V(as)= 56.000 liters (1.978 cubic feet)
* M(ms)= 223.20 grams
* C(ms)= 0.12 mm/N


But from the above specs the only enclosure I can think of is a sealed (EBP ~ 40) and that too with a Q around 1.

the specs do not look like typcial sealed box subs specs. but in a lossy box it can work. on the other hand the OB guy inside me just got excited! :-) just wish the Mms was less.

[venki7744]

Do you think the specs are correct? I will try re-measuring in someone elses PC over the week end and see how things go.

Also pardon me for my ignorance, what is OB (sounds like IB ) and what has Mms to do with that?

Venki.

[abhibh]

Well even i need GT5-12 Specs for Sealed BOX. Maybe Sam can throw some light on this issue.

[amit_mechengg]

hey guys,
i have put my GT5-12" in bass reflex box. the dimensions and make is similar to JBL bass reflex box. this is an amazing match for the GT5 sub.

[DerAlte]

Originally Posted by venki7744

Do you think the specs are correct? I will try re-measuring in someone elses PC over the week end and see how things go.

Also pardon me for my ignorance, what is OB (sounds like IB ) and what has Mms to do with that?

Venki.

How are you measuring the T-S parameters of this sub?

Navin is referring to the HT term - OB = Open Baffle; not exactly IB. Low Mms means that the OB physics will get knocked out of kilter by this sub's moving mass being a bit too heavy.

Sam, this is really strange: none of the products have the "Boxes and Parameters" link enabled under the Product Support pages on the JBL website.

[navin]

Originally Posted by venki7744

Do you think the specs are correct?

Also pardon me for my ignorance, what is OB (sounds like IB ) and what has Mms to do with that?

ref: specs: I am not sure if they are correct. i have never measured a GT5 series JBL sub. However I am not sure if just a change in PC will correct this.

OB = Open baffle.

When a driver is in open baffle the front wanve is not protected from the back wave (no box) and hence there is cancellation once the wavelength of the baffle is exceeded. To compensate for this drivers with a high Qts (rising respnse) are used; the rising response compesates for the cancellation.

However given that the driver has no support from the box (as there is no box) drivers with low Mms (cone mass with air) are preferred.

[venki7744]

Originally Posted by DerAlte

How are you measuring the T-S parameters of this sub?

Using the WT3 (woofer tester 3). The manual mentions its dependancy on the sound card volume. So my guess the accuracy might vary depending on the hardware. Also forgot to mention one think, the first mesaurement I made recorded a Qts of .699. Later on I re-measured the driver till the specs became consistant over multiple measurements.

Originally Posted by DerAlte

Navin is referring to the HT term - OB = Open Baffle; not exactly IB.

I forgot . I think my memory is also becoming "Lossy"

Originally Posted by DerAlte

Sam, this is really strange: none of the products have the "Boxes and Parameters" link enabled under the Product Support pages on the JBL website.

The JBL india site has specs for the GT4 sub though