New Equivalent 3145 crossover Network

[Ian Mackenzie]

New Equivalent 3145 Crossover
I will have at last completed the new equivalent crossover boards tonight.

The intention will be to first run some JBL test jig measurements and then post some voltage drives and driver response graphs.

Below are images of the crossover boards and spinning of the wooden coil formers to exact dimensions on a Lathe. This was necessary to arrive at the precise inductance and dc resistance required for this design courtesy of "Giskard".

The resistors are a temporary item until I can arrange some Mills resisters which are not available locally. Perhaps a member can offer to help out here..no doubt they are superior to sand cast types.

The capacitors used in this instance are Claritycaps , film and foil 630 volt 5% tolerance. The boards are polypropolyne and were actually cut from domestic breadboards. The terminations are all 1 mm 100% pure Aust copper.

Ian

[Ian Mackenzie]

I measured all the filters using the JBL test Jig. The results where within 5 % or the tolerance of the components. The horn filter was perhaps a tad sharper with the -17 db point at 8500 (9000 spec).

I then measured the individual response of each driver at a nearfield distance of 1 foot to completely remove room effects and focus on the bandpassfilter actions.

The L pads were adjusted for 0 db and the analyser scale set for 0db. By adjusting the scale I was able to determine the average of the horn was within primarily a 4 db window (+-2 db). Not bad for a 30 year old horn design.

The 2405 was also measured for the L Pad at 0 db on axis as was the 2122H midrange driver. .

The overall full response was then measured in the listening room at about 6 feet on axis with the 2307/2308 horn lense assembly.

Given the room is completely un treated and I had equipment scattered everywhere it is remarkably flat and free from significant peaks and dips (with the exception of the comb effects around 8,000-10,000 hertz which as we know are unavoidable and in my view not audible).

If anyone is interested in the technical aspects of making these crossovers or would like some construction assistance please send me a pm.

Ian

[Ian Mackenzie]

These next two graphs are off axis at approximately 30 degrees taken at 0.5 metre and 1.5 metres off axis with the microphone on the vertical axis of the 2307/2308 horn lense assembly.

There is some tappering off of the horn but the response is still remarkably smooth in both cases. With some careful use of equalisation it would be hard to argue a case for a CD horn and even without any equalisation the results are excellent given many modern systems can't hold a candle to these results.The combined left and right channel off axis would be interesting but I do not have this facility at the present time.

Ian

[Ian Mackenzie]

For those interested the system is pictured below, the JBL Professional Series 4345. This is in fact a clone I build about 18 months ago.

Ian

[Ian Mackenzie]

Hi Earl,

Thats a fair question. My understanding from the data I have and from audible results is that they are. By virtue of their size and the construction I can't imagine why they would not be film foil. Metalised foil types are by design significantly smaller..The Auricaps are case in point but thye are also lower voltage. I am not proposing to destroy one to satisfy curiosity. I would point out however the generic description has nothing to do with is it good or bad..there are good and bad example of both. The Auricaps are regarded as some of the best capacitors available and I think they are ahead of the Claritycaps in some areas but they are more expensive, the Mundorfs Gold line is possibly better again but the are 4x more expensive again.

The Claritycaps have a clean, detailed and perhaps slightly warm sound.

You really have to take the plunge and try some out and this have been beaten to death countless times before on the forums.

The subject here is about this particular crossover and its application in the JBL 4345 and 4344 monitors.

Ian

[johnaec]

Hi Earl,

Thats a fair question.

(I'm assuming a message was deleted here, since I see nothing from Earl before this reply).

Please don't delete messages after they're posted - it just totally breaks the continuity.

If you must, *edit* them - at least a marker will be in place...

John

[yggdrasil]

Very nice Ian.


The coils seem to have the formers in place even after mounting. Is this so? And if so - are you using the formulas for air coils?