New loudspeaker from the old JBL TLX2, some question for the experts

[washburn_it]

Hi,

this is my first thread here, first of all I want to briefly introduce me.
I'm a little experienced with cab designing but anyway I don't consider myself an expert.
I've built (with success) a 2x10"+6" bass cab (I'm a bassist) equipped with two Eminence Legend BP102 crossed with a midrange 18Sound 6ND410, a 2.1 loudspeakers system for my pc (using an old car amp and a PSU from a pc) and my 3-ways car hi-fi.

Now what I would like to do...since my good old Technics SU-Z200 "passed away" after 25 years, I decided to renew my home hifi taking advantage of my two JBL TLX2 loudspeakers.
I'm currently building an amp ("Project P101" by Rod Elliott) where each channell will be equipped with 2 modules.
One module will drive one JBL TLX2 and the other (of the same channell) will drive a new "bass unit" (not strictly a sub but a cab to strongly reinforce the bass frequencies).
An active crossover (2-ways 24 dB/octave, "Project P09" by Rod Elliott) will separate the "bass unit" from the JBL TLX2 (it has it's own internal passive crossover with cut freq. at 3500 Hz) around at 250 Hz.
For the "bass unit", I would like to build 2 double 12" using the Dayton DC-300-8 (I know it's not probably the best speaker of the world but I don't want to spend a fortune, for now) rated for 80 Watt RMS, 8 ohm and 90 dB 1W/1m.
Using two of them wired in parallel I can gain +3 dB of sensitivity, doubling the (thermal) power.
Making some simulation with Bass Box Pro, considering a compromise between max power and excursion, I obtained these results (reflex box):

- Vb= 130 liters (max power limited to 130 Watt to keep the XMax within limits)
- Fb= 27 Hz
- F3= 37 Hz
- reflex port= 110 mm (diameter), 203 mm (length)

Now there would be two options:

1) building the cab only for the woofers and put the JBL cab simply on the top
2) building the cab with woofers and JBL's speakers into just one cab

The question is:

what are the advantages/disadvantages (if any) if I put the JBL's midwoofer above the tweeter? (the current "configuration" it's the "standard" config. with tweeter above the midwoofer).
Thanks, best regards.

Roberto


PS: I apologize for the long post but I wanted to clarify what I want to do.

[Inductor]

Originally Posted by washburn_it

Hi,
...
For the "bass unit", I would like to build 2 double 12" using the Dayton DC-300-8 (I know it's not probably the best speaker of the world but I don't want to spend a fortune, for now) rated for 80 Watt RMS, 8 ohm and 90 dB 1W/1m.
...
Now there would be two options:

1) building the cab only for the woofers and put the JBL cab simply on the top
2) building the cab with woofers and JBL's speakers into just one cab

The question is:

what are the advantages/disadvantages (if any) if I put the JBL's midwoofer above the tweeter? (the current "configuration" it's the "standard" config. with tweeter above the midwoofer).
...

If they aren't definitive I would not build them together (one cab).
(Use)Tweeter on top, if nothing else (you don't find any other reasons) like being more compact (tweeter in the middle), maybe less BSC or interference of the size of the baffle (mid on top). For me is like where you have the voices/mouth, so a compromise in frequencies and driver before the technical specs come in place.

[washburn_it]

As for the active crossover cut frequency, is it reliant on the distance from the woofers and the midrange+tweeter?
I mean, what's the criterion to choose the cut frequency with an active crossover?
Thanks, regards.

Roberto