Need Help With A Crossover

[bamadawg]

Evening all...

I am wanting to replace the original tweeters in a pair of older Jensen cabinets - it is a Model 20 2-way speaker with a 8" woofer and paper-cone tweeter. It has a simple 2.7uf cap on the tweeter originally.

I want to replace the tweeters with a spare pair of JBL/Altec LE20-1 tweeters I have. I am not a speaker builder, so I need some help with the capacitor size needed for crossover in the Model 20 cabinet.

The only thing I can find on the original 8" woofer are these markings.
J1050
31285
2208015

Any help is greatly accepted!

Nate

[PeteMcK]

To do this accurately, you need to find freq response plot of the woofer, freq response & impedance plot of the new tweeters, and their relative sensitivites.

If you don't have these, just try it with the existing caps (at low volume) and see how they sound.
There are two issues: getting the xover freq right (=choosing correct cap value, you can try different values, but don't go too big - stay under 4.7uF), and matching driver sensitivities - the new tweeters may need to be padded down with resistors if they have higher output than the old ones.

[mjf]

hallo.
i agree with peter.look at the impedance of the tweeter(is it 4 or 8 ohms) and try it with the 2,7uf cap.and look at the polarity.if it sounds generally too loud,build in resistors.are the high tones o.k.,but the mid to weak(some kind of loudness) you can alter the cap(or for an experiment the polarity of the tweeter).
regards...............

[BlueWizard]

My first thought was to make some fair estimation of the tweeter impedance, then work backwards to get some sense of what the crossover frequency was. There are several crossover calculators on the Internet, so it shouldn't be too much of a problem.

Next, determine if your new tweeter can crossover at that frequency. If the existing crossover is in the 1.5khz range, it doesn't do any good if you buy a tweeter that needs a 3khz crossover.

Since the entire crossover consists of one capacitor, it is likely counting on the natural roll-off of the woofer. If you crossover too high, you're going to have a gap in the midrange. If you crossover too low, you're like going to have a peak in the midrange.

So, make some effort to determine where the system is currently crossing over, and try to reproduce that.

A quick glance at a crossover chart in the Parts Express catalog indicates the crossover is vaguely in the 6khz range for an 8 ohm tweeter, which is pretty high but not unrealistic.

If this is true, then any similar tweeter should be workable. If you need to dial it back a bit, a simple two resistor L-Pad will work.

Here is a link to a website that calculates crossovers and resistor L-Pads.

http://www.apicsllc.com/apics/Misc/filter2.html

Steve/bluewizard