Looking for LF driver upgrade ideas

[doyall]

Is it wishful thinking to hope that there is an 8” JBL driver that will produce anything below 40 Hz at around 90 dB SPL in a ~ .7 (point 7) ft³ ported box, based on interior dimensions not deducting for the driver, port or built-in amp? It looks like the JBL GTO 804 automotive woofer will just about almost nearly get there but then fall off rather steeply. I am fairly well limited by space and aesthetics to a box that size for a rear “sub” woofer to give LFE support to a JBL E250P 12” main sub.

Speaking of the E250P, what would be a better driver to go into one than the cheapie JBL put in?

[4313B]

Is it wishful thinking to hope that there is an 8” JBL driver that will produce anything below 40 Hz at around 90 dB SPL in a ~ .7 (point 7) ft³ ported box, based on interior dimensions not deducting for the driver, port or built-in amp? It looks like the JBL GTO 804 automotive woofer will just about almost nearly get there but then fall off rather steeply.No. Use that GTO 804 in a 0.6 cu ft box tuned to 20 Hz and apply a 20 Hz 6 dB bump filter. Use a PR to get that small of a box tuned that low.

[spkrman57]

I thought I read somewhere that PR's were used when smaller cabinet size was required.

It should also be noted that the PR should be of proper compliance and weight to properly load the active woofer.;)

Ron

[doyall]

Unfortunately this box is not big enough for a PR. Will a bump filter help by itself? Where would one find this item?

[GordonW]

If it's not big enough for a passive radiator, then it's not going to be big enough for a port of ADEQUATE DIMENSIONS to avoid port noise either.

And no, the bump filter will not help, without the low frequency (20 Hz or so, as Giskard mentioned) cabinet tuning. So, either a hugely-long port, or a passive.

Sounds like you need to rethink the cabinet design, and try to get a passive radiator in there...

Regards,
Gordon.

[doyall]

Will a down-facing PR that is mounted at a 90 degree angle to the active driver be acceptable? Will a non-functioning 8" speaker suffice as a PR or should a purpose-made unit be used? If purpose-made is necessary, any ideas on an acceptable 8" unit?

[duaneage]

Your starting to get into several variables that make the design difficult or impossible. Looking for that kind of performance with .6 cu ft is a stretch, 8's are not known for deep bass. PR's are a tricky design because they depend on the PR TS parameters a great deal. I would compromise on the box response a bit and see if you can make it up in room placement, EQ, or a compination of both.

There are some non-JBL drivers that might work, a few peerless drivers come to mind, and there are also some 10's in a sealed arrangement that might work.

Welcome to speaker design....