Understanding the Zaph Waveguide TMM crossover diagram

[mikan]

I'm building Zaph's Waveguide TMM, and cut the first pieces of wood today .

The crossover I've chosen is the perfectionist crossover, but I don't understand how to connect the actual components, probably due to my near complete ignorance of all things electrical . The schematic shows a point labelled "IN" - is that the positive or negative connection from the amp? The "+" after the tweeter suggests to me that it's the negative connection. What do the earth connections on the schematic represent? The opposite connection to "IN" from the amp?

Finally I have some general crossover questions:

1) If an inductor's DCR does not match that specified in the schematic, should a resistor be added in the circuit after the inductor to bring the DCR up to that specified?
2) Are non-inductive wire-wound ceramic resistors suitable for crossovers?

Thanks for any advice you might give

[daatkins]

IN is the + (red) connection from the amplifier and all the earths connect together to the – (black) from the amplifier. The tweeter is in reverse phase so its + terminal is connected to earth. The woofer is normal phase so – connects to earth.

Adding a small resistor to an inductor is okay, but you’d be better off buying an inductor with the correct resistance (or close, say within 30%). Besides, the thicker gauge wire of a more expensive inductor would be wasted if you add a resistor in series, so save your money!

Non-inductive resistors are ideal for crossover work.

Good luck with your project!

Nice one,
David.

[mikan]

Thanks David, that answered all my questions in one . The DCR of one of the inductors is only 0.1ohm from that specified - 0.3ohm measured vs 0.41ohm on the schematic.

[owdi]

Originally posted by mikan
Thanks David, that answered all my questions in one . The DCR of one of the inductors is only 0.1ohm from that specified - 0.3ohm measured vs 0.41ohm on the schematic.

Using a bigger inductor (in the right place) means your speakers will be more efficient. In your case, the difference is minimal, so you should be fine.

Dan

[lndm]

Adding the extra series resistance will help to ensure that your results are consistent with Zaph's. Naturally this is a good thing, however, it might be true that the lower DCR will sound better as this is often the case where the circuit location permits it.

Ideally I feel, it would be best if Zaph tweaked the crossover to suit your low DCR inductor. Practically speaking, I think you should try both and see which one you prefer.

[mikan]

Originally posted by lndm
Practically speaking, I think you should try both and see which one you prefer. [/B]

That's not a bad idea. The enclosures are mostly assembled now - only the bracing remains, then I'm up to making ports and adding the driver cutouts. I've changed the enclosures slightly so that the actual speakers sit on two stands which are the continuation of the sides (see the attached image) and the crossover is mounted in the base.

I've routed a 1/2" wide channel between the two panels of one of the legs on each enclosure using an R1/4" cove bit for passing the wires through. After gluing everything together, I realised that this channel will be too small to take 6x decent gauge wires and I should have routed at least two channels .

As a workaround, would it be OK to use 4x wires for the drivers all stuffed up this channel (3 for the "+" inputs, 1 for the "-" ground), or is it best if each driver has its own "-" wire? Will having so many wires crammed into such a small channel cause interference issues?

[lndm]

Originally posted by mikan
would it be OK to use 4x wires for the drivers all stuffed up this channel (3 for the "+" inputs, 1 for the "-" ground)

I think this will be fine. If you are looking to take it further, you might consider bringing the three grounds down to one at a single point.

Will having so many wires crammed into such a small channel cause interference issues?

In a crossover? I would think probably not.

[mikan]

Originally posted by lndm

I think this will be fine. If you are looking to take it further, you might consider bringing the three grounds down to one at a single point.


In a crossover? I would think probably not.

Sorry, I didn't explain that very well. The crossover is in the base, so the driver wires need to be passed up through the middle of one of the legs. The channel I've routed for this is only 1/2" wide, so the 4 driver wires (If i use a common driver ground wire) will be very close together. Will interference between the driver wires in this channel be a problem?

[lndm]

I think I understood you but I'll put it another way

Short answer: no.

There will be a small amount of mutual inductance and a small amount of capacitance between the cables. However, considering the frequencies involved, typical crossover impedances, and the lengths you mentioned, I would be very surprised if they caused any problems for your speaker.

[mikan]

Thanks Indm. What gauge wire would you suggest for the driver wires? 6x 1.7mm diameter core/3mm diameter jacket wires will fit up the channel, although they seem a bit thin. Would perhaps 4x heavier core wire be better? Single core or multi strand?