Smallish cabinet for Jbl GT3-12

[TroelsM]

Hi

I got a GT3-12 for free. Its a pretty common driver and clearly its build for car-fi. BUT, i want to use it for small "PA" from 50Hz to 180Hz. I want to keep it below 55L internal.

Any ideas for cabinets? Closed looks to be best, but it is to booooring ;-).

Data: Parametri di Thiele-Small per gli altoparlanti Car Stereo JBL

I played around with HR and got the attached. Its not pretty and I have no idea how close it getsto reality. I would want to use the volume circled in red to house the driver and classD amp. Hoping for some small cooling effect.

Kind regards TroelsM

 

[BP1Fanatic]

You have to make sure the speaker can fit inside the BP6 enclosure.
I used this link to get the 155mm mounting depth (6 1/8").
I made the 2 internal volumes 13"H x 13"W x 8" D to fit the speaker in either section.

*HELP* JBL GT3-12" Sub box size? - ICE, Electrical and Lighting - Club Polo

 

[Brian Steele]

Qts looks a bit too high for a 6th order BP alignment.

I'd try a 4th order BP system with it instead.

 

[BP1Fanatic]

I agree!

 

[TroelsM]

Qts looks a bit too high for a 6th order BP alignment.

I'd try a 4th order BP system with it instead.

As far as I understand, it would be difficult to cover the whole 50-180Hz with a 4th order BP?

kind regards TroelsM

 

[TroelsM]

You have to make sure the speaker can fit inside the BP6 enclosure.
I used this link to get the 155mm mounting depth (6 1/8").
I made the 2 internal volumes 13"H x 13"W x 8" D to fit the speaker in either section.

*HELP* JBL GT3-12" Sub box size? - ICE, Electrical and Lighting - Club Polo

Thanks for the interesting idea. A little active filtering is OK, as the system is fully active anyways.
I'm a bit worried that the lower knee at 60-70Hz is too high.
(yes, yes, we cant have it all, but we can try ;-) )

Kind regards TroelsM

 

[TroelsM]

I tried a simple 6th order BP and it does work , but it does not sound very good to me (with little to compare with, but still). I still need a better filter to flatten the peak around 160Hz.

I havnt measured the response as I really dont know how to get a descent reading that low. I measured impedance and the lower peak is around 18Hz as predicted, but the high peak is around 65Hz and not 57Hz as predicted. I'm not sure what that means, but its clear that some tuning is off ;-)

Maybe I'm just used to my usual BR sub that goes pretty flat to 50Hz ...

Apart from listening ( with all the pittfalls and bias), how would you verify a design like this? i can measure impedance and it should be pretty simple to find the port resonances. can I measure the output from each port and sum the results ( how?)

HR sim and measured impedance for complete cab included.

Kind regards TroelsM

 

[BP1Fanatic]

Well, I see you used bigger ports which is a good thing! Your modeled response has a dip between the peaks that could be contributing to the bad sound. What low pass frequency did you use? Try a 120hz lowpass and a -3-5db @ 60hz on the EQ.

 

[TroelsM]

Well, I see you used bigger ports which is a good thing! Your modeled response has a dip between the peaks that could be contributing to the bad sound. What low pass frequency did you use? Try a 120hz lowpass and a -3-5db @ 60hz on the EQ.

Yes, the ports appears to big enough to avoid turbulence.

I need the sub to reach around 180Hz,- thats one of the challenges of this design.

TroelsM

 

[BP1Fanatic]

In my model, I still reached 180hz with a 130hz lowpass in Filter Wizard.

 

[GM]

As far as I understand, it would be difficult to cover the whole 50-180Hz with a 4th order BP?

kind regards TroelsM

Your < two octaves is doable, just not with this driver, especially at high SQ in the allotted bulk as you've found out. You want a lower Qt driver with a 50 EBP.

The attached ~177 L sim looks fabulously flat, so probably won't perform well in a typical HIFI/HT app, but the high Qt requires a high compression ratio [CR] to control its relatively weak motor, so might 'grenade' if given much power and why one should avoid high Qt drivers in BP4 alignments.

GM

 

[TroelsM]

In my model, I still reached 180hz with a 130hz lowpass in Filter Wizard.

Yes, the output did reach that high. Sorry. I was thinking about something else.

Kind regards TroelsM