JBL 4331 rebuild using 2445J and JBL woofer - would this be a good idea? Help pls!

[Mazza]

Thanks for sharing your thoughts engineerjoe! Much appreciated.

[sebackman]

Hi Mazza,

I did see the measurement and the scale make it seem like rather ok but in reality you are about 10-15 db down above 10k. Typical for a 2" driver with that phasing plug/exit. That is a lot to even out in a passive filter.

Typically I would recommend a 1,5" driver with an SL diaphragm with a modern waveguide or to add a UHF unit as mentioned. There are very few passive JBL 2-way systems with 2" drivers for HiFi use and with 1,5 drivers being better suited and priced the same that may prove an easier way to go.

I also agree with Mike that 60x40 is a bit on the narrow side for home use.

Sometimes we spend more money trying to use what we have rather than sell and start over. Getting new diaphragms for the 075's is expensive end up taking more money compared to the 1,5" route . It is always better with fewer drivers.

I find that the best drivers for HiFi use are the 2447 (heavy), 2450SL, 2451SL, 2452SL and of course the 476 in various forms.

2453 (SL) as mentioned by engineerjoe is good little driver but it does not fit all horns. They have a short phasing plug that creates a dramatic dip around 10k on some horns. i had to make a spacer to fit them on some waveguides. There is a thread here on LH if you search. Member "nyt" did some good work there.
2453H-SL on STX825 waveguide over 2265g-1 center channel (audioheritage.org).

Kind regards
//Rob

[engineerjoe]

Hi Mazza,



2453 (SL) as mentioned by engineerjoe is good little driver but it does not fit all horns. They have a short phasing plug that creates a dramatic dip around 10k on some horns. i had to make a spacer to fit them on some waveguides. There is a thread here on LH if you search. Member "nyt" did some good work there.
2453H-SL on STX825 waveguide over 2265g-1 center channel (audioheritage.org).

Kind regards
//Rob

My main PA uses all JBL with 2258s for lows, 2262 for mid, and now 2453 for highs. I have mainly 2 models of JBL waveguides on the 2453 being the 60x40 model and the 120x60? model. 2 cabs are JBL AM7212/64s (replaced hf drivers).
All other cabs are home made by me for light weight (I'm disabled).
I play with the active crossovers in my Crown amps and put them at 200hz and 1250hz for now. I made a mistake and set one rack at 1500hz mid to highs for the last show!
The low cabs seem to have a hollow tone somewhere in the 240hz range. I was going to add bracing and still haven't.
Anyways, I was wondering if you had any thoughts about the crossover point choices? I read a lot about using the 18"s for sub duty only and crossing over somewhere at or just over 100hz. I wanted maximum clarity out of the mids and didn't wish to push them lower.
I have acquired some used JBL 2251s for possible use down the road in a all in one flyable cab to still be built. I considered using all the same crossover points universally in a combined system.
I apologize to OP if this takes this post off course now. I am very happy with the performance of those light 2453s against the older 2445/6 and 2450s so far.

[Mazza]

G'day gents, thanks for your inputs.

My build is for a home setting so I'm not chasing max spl. These parts will be coasting in my setup, I rarely listen above 90db.

Regarding the roll off or mass break point for the compression driver and horn - this is a feature of CD mounted to a constant directivity horn and the filtering of this in a passive network is quite straight forward. Its also called top-octave compensation.

Wayne Parham has written a series of terrific white papers about this here.

With regards to crossover points, the most important for me in a home setting is ensuring a smooth transition between woofer and tweeter (or whatever) throughout the passband of the system.

Dr Geddes has a great white paper on this and how to interpret polar maps here.

We want to hand off the narrowing off axis response of the woofer seamlessly to the horn CD combination so that we achieve a smooth on and off axis response like this. ..







Here you can see the crossover is around 1.6khz. This is the measured response of a previous build of mine using modern parts. It turned out sounding very sweet indeed (confirmation bias?? )....







Cheers.