Designing my first crossover

[Bchiu2000]

Hey guys,

I got an ION PA speaker which doesn't work. So I bought a amplifier board from AliExpress.
The speaker has a 15 inch woofer and a tweeter. I would like to learn how to make a crossover for this pair. Here's some photos.
I would hope some of the electronics from the original board can be reused to build a new crossover.

 

[PRR]

Looks like a mono amp. So there must have been a crossover. Did you save it?

 

[Bchiu2000]

The crossover is integrated into that board in my photo but it's not working. I hope to savage the cap, the inductor and the resistor to build a crossover with it.

 

[Bchiu2000]

I made an assumption that those bigger components on the board are the crossover components. On the top left there's a 5 ohm R, then a 2.2uF C on the bottom right and a coil of unknown value at the bottom left.

My goal is to build a cheap or free crossover so that the tweeter won't blows up. I assume feeding high frequency to the 15" woofer won't damage it? Sound quality is not a concern here.

 

[AllenB]

A capacitor and a resistor sounds like the minimum. Why not reuse them with a different amp.

 

[Mark Tillotson]

The inductor is for stability I think, not a crossover component, too low an inductance.


I suspect the original just used R+C attenuation for the tweeter.

 

[Bchiu2000]

Thanks for the advice. So I assume I don't need to connect anything to the woofer?

Just a high pass RC filter to the tweeter is sufficient?

 

[Galu]

A high pass filter to the tweeter using just the 2.2uF capacitor in series would be a start.

If the tweeter is too loud, then try the 5 ohm resistor in series with the above combination.

The woofer can be run direct without a series component. Do not use the coil on the old board.

 

[PRR]

> Sound quality is not a concern here.

So why haven't you tried it? Put the 2uFd in line with the tweeter and run it softly.

Yes, 2u with 8r looks like 9kHz, and no Fifteen is smooth to 9kHz. But I have seen a similar rig before (now-old E-V). A horn and driver naturally has a falling response above ~~1kHz, but can be far-far more efficient than a cone over much of this range. A hot horn with a small cap "can" make a smooth response and low stress in the horn. This is not a trick you find in books, journals, or hi-fi forums. However it would have been known to ION, and they had incentive to make it work good. Use their work.

 

[Bchiu2000]

Yes, 2u with 8r looks like 9kHz, and no Fifteen is smooth to 9kHz. But I have seen a similar rig before (now-old E-V).

Thanks all for the inputs. What does no fifteen is smooth to 9kHz means?

I traced the circuit with a multimeter and it seems the woofer connected Directly to the amp and the horn was connected in series, from the amp to the 2.2uF cap then to the 3ohm R then to a resettable fuse (the one in my photo) then to the horn. I am wondering should I include the fuse in my circuit or only the cap and the resistor?

Another thing is why the crossover frequency is so high? I have read in most case the xover Freq is around 1k to 3k.

Interesting Enough that setting it at 9KHz does sound good tho.

 

[Bchiu2000]

One more question, since this is a mono amp, I need to bridge my left and right channel together before feeding it to the amp. How should I go about that? Right now the output is from a 3.5mm headphone jack. I assume using a resistor?

 

[PRR]

A horn can be designed "flat", or with a midband peak and long smooth roll-off in the highs. A 9kHz low-cut can be complementary so the result is flat.