Richard Allan crossover query.

I have a pair of Tapco Thump PA speakers which I got with blown internal amp and tweeters. I've replaced the tweeters with Pyle HF drivers and now need to turn them into passive speakers for a band practice room.
I have a pair of Richard Allan crossovers in my "junk" box - actualy they are in the form of separate filters and have the following info on them:
CN 3.5/18....18db/octave low pass filter.......and
CN 3.5/ 24....24db/octave High Pass Filter
I've no idea what speaker they came from.
Any comments on their suitability for this 60 watt project would be welcomed.
Also, Although I've drawn out the circuit diagram there is space on the LF board for a resistor which has been removed. If anyone is familiar with these can you say what value it should be..
And anyone care to hazard a gues on how much to attenuate the hf driver to match the bass..a starting point will do !
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both drivers and the XO are 8 ohms..and I'm working on attaching an image ;-)

Finally suceeded..circuit attached...thanks for you patience


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I see, you originally has 3.5 on one and 3.4 on the other and that confused me - I'm easily confused!

Now, we need some details of the drivers.

There may not be a perfect match, but it may be close enough for band practice purposes.

Sorry about that ..I've edited it back to be correct..This is the resurection of an old unfinished project and I've forgotten the model of Pyle hf driver..I'll have to get a cab open....but it'll have to wait until tomorrow..Thanks for help so far..


2018-04-17 6:50 pm
Thanks for photos.

The black ELCAP, non-polar electrolytic capacitors don't age well and should always be replaced.

If the caps need replaced, we might as well look to simplifying the crossover design, which, anyway, is uniquely tailored for completely different drivers.

The most important information required to proceed is the exact model of your Pyle HF driver. You would probably get away with running the main driver near to full range and just employing a suitable high pass filter for the tweeter.

Have you got an inductance meter with which to measure the inductance, in mH, of the inductors on the boards to see if they are suitable for the above purposes?

P.S. It would be less confusing if you should edit forwards rather than backwards, if you know what I mean. :)
Hi Good point about editing..I'll take note...And about the old capacitors.
I've found the old Grills in the garage belonging to the 1970's speakers from which those XO's came from...Cambridge Audio R40's
I've no way of measuring the inductances of the L's. I was hoping some learned old repair type woul;d pop up with some info like that..especially the Value of R1.
The drivers I put in are Pyle PDS521 Titanium Horn Screw On Type Compression Driver Tweeter 8 Ohm 600w They appear to be discontinued and I can't find any data online.
Originally, when Istarted on this resurected project I also bought a pair of QTX 200W 8 ohm 12dB/oct, XO 3Khz cheaper and simpler Xo's and have tried them as a lash up.(type X8R3KH-200W) But got far too much HF. Perhaps these would actually be a better bet with some fixed attenuation ? These are still sold and plenty of online info.
The bass drivers are Pyle 15" in one case and Eminence 15" in the other..but I'm assuming that's not important in this case as they are both of the stiff paper cone type..

EDIT.. I think I'm wrong about those old XO's coming from R40's having seen an image of one on eBay (sold items) after all....they are marked Richard Allan !
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Paid Member
2008-10-18 11:31 am
Attenuation of the tweeters is probably the least you could do, and certainly important enough to be worth it. For horn drivers, try an L-pad configuration.

About the different woofers. For simple listening needs it could be done, but is one much louder than the other?


2018-04-17 6:50 pm
The Pyle drivers have a frequency response extending down to 500Hz.

Thompsons Ltd | Pyle PDS521 Titanium Horn Screw On Type Compression Driver Tweeter 8 Ohm 600w

I would use them with your QTX crossovers.

Place a 100W, 8 ohm variable L-Pad between crossover and Pyle driver to allow adjustment of treble level.

8 Ohm L-Pad Attenuator - 100 Watts - Willys-Hifi Ltd

Let the woofers run direct - we're not talking about a Hi-Fi application here - it's just for band practice!

Thanks for that..soory I didn't see your reply b4 replying to AllenB - my screen had not refreshed..I'll go and look at the L pad you suggested with a view to purchase...And yes HIFI is not required here....just 1/2 decent reproduction..
Thanks to you both..


Paid Member
2008-10-18 11:31 am
I think Galu's suggestion of variable L-pad for your tweeters is an acceptable option if you can get some.

Worry about the woofers after. I'd be lying if I said I hadn't done the same, set each L-pad to the different woofer level, fixed the difference with the amp balance control. Unfortunately the magnet size does not help. this is a cheapskate job I'be made a start...I've found I already have a 50watt wirewound 10ohm pot which should be near enough (I could put 33ohm in parrallel to bring it to 8) and will do one at a time..I'll decide on a reasonable balance by listening and then replace with two fixed R's of appropriate value.
Right now I'm reclaiming the big space at the back where the amp was to get a little more cabinet capacity. Thank you both for your help..R


2018-04-17 6:50 pm
I've found I already have a 50watt wirewound 10ohm pot which should be near enough (I could put 33ohm in parrallel to bring it to 8) and will do one at a time..I'll decide on a reasonable balance by listening and then replace with two fixed R's of appropriate value.
A 10 ohm pot is not the same thing as a variable L-Pad control which varies two resistances simultaneously, one in series with the tweeter and one in parallel with the tweeter.

Details of L-pads are available here: L-PADS

If you do not wish to go to the expense of L-Pads, then go straight to fixed resistors - see attachment. The above link contains a calculator for determining the values of the required series, R1, and shunt (parallel), R2, resistors.

Ignore the power figures in the calculator, 20W ceramic (wirewound) resistors will be more than adequate.

The problem is deciding how much attenuation in dB to go for.

The Pyle drivers have a very high sensitivity of 107dB so, depending on the sensitivity of your bass drivers, you may have to go for an attenuation in the order of 10dB.

The nearest standard resistor values required to achieve -10dB would be R1 = 5.6 ohm and R2 = 3.9 ohm.

A variable L-Pad is by far the easier option in my opinion, and can be set exactly to your attenuation requirements.

EDIT: If you supply the model numbers of your Eminence and Pyle 15" woofers, I can make a more exact calculation of the tweeter attenuation resistors required in each case.


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Hi Galu..Had to leave speaker building earlier today and just got back...Thanks for putting me right about the way L pads wprk, as opposed to pots..A lesson I won't forget in a hurry..
Firstly the cabs are now open and I've found that the Pyle 15 has a rubber roll surround so will have different characteristics to the Eminence..So I'm replacing it with an original Thump 15" which has the conventional surround. First off I'm going to try the 10db pad with the figures you've given. I will report back in a few days and perhaps take you up on your offer.....BTW..I shied away from the variable ones because of the cost..More cabinet work to do now...Thanks again.R