Active speaker DIY

[HoneyBadger]

I am building an active 3 way mono speaker (ultimately intended as a mobile speaker utilizing an Intel WiDi adapter) with a Dayton tweeter (4ohm) and two Klipsch replacement woofers (6ohm ea.) run in parallel. I have a few questions so bare with me.
1.
As I understand it the parallel resistance is calculated as: R=1/{(1/4)+(1/6)+(1/6) which comes to a total resistance of ~1.714ohm - does this mean I will not need to use a high powered amp? (ie. an amp rated at 100W @ 8ohm would be around 400W @ 2ohm) I'm shooting for around 100W RMS.
2.
Should I use resistors in the crossover network to bring the total resistance to a more stable level?
3.
Does anyone know where I can find a good internal mono amp for this configuration? It seems that the best amps for this kind of project can be found at 41hz.com but they need to be bridged (I think this raises the THD)
4.
I was looking to use a 1st order crossover but the 8" woofer's optimal range is 44hz - 1400hz ... should I filter out <44hz ?

[HoneyBadger]

I see a ton of views but no replies. Not a problem if you don't have all the answers. I'd appreciate any help/opinions

[Pano]

Welcome to the forum. Great user name, it's bad-a**.

You don't add the tweeter and woofer together for the impedance as they are both behind a crossover. So basically you'll end up with either a 12 ohm speaker or a 3 ohm speaker depending on how you wire the woofers. Wiring them in parallel for 3 ohms is probably the way to go.

You don't need to filter out <44Hz. A 2nd or 3rd order crossover may be called for here, not first.

Is this "mobile" as in battery powered, or something else? Your amp choice will depend on that.

[CCU]

1:
the total resistance of the speaker i not calculated with all of the drivers.
The total resistance of the speaker is calculated with the drivers playing in the different frequencies.

fx. if you make your crossover at 2500hz.
the resistance from 0-2500hz will be 3ohm(R=1/((1/6)+(1/6)))
The resistance from 2500-higher will be 4 ohm.

But even that is not really true!
because the resistance of the driver varies depending on what frequency it is play.

Notice the blue curve in the bottom.


It might be a good idea to get the specifications on your woofers and tweeter.

2:
that depends on the amp.

3:
A ton of amps like that can be found on ebay at the same price or cheaper pre assembled. Fx look for sure electronics.

4:
that depends on where you want to use the speakers and how high you want to play.
FX. if you want to use them outside. Then you might as well do it because you are never going to hear it. (perhaps even cut of higher)

FX. if you want to play very loud. Then it will be a good idea because of the woofers Xmax(how much the woofers can move before being damage) the lower frequency a sound has at the same sound level. the further the woofers has to move to produce that sound.(again consider cutting of even higher than 44hz)

[HoneyBadger]

You guys are the best. I had to idea that the resistances were calculated that way. When I say "mobile" I mean wall powered but small cabinet design (for a system with an 8" woofer, 5 1/2" woofer, and 4" diameter tweeter. I can't use sure electronics unfortunately.. unbridgeable stereo output I'll check ebay but I think after being enlightened about resistances I will stick to 41hz. Also, I am considering not bridging if I can split a mono line level input to each channel. Then I would dedicate one channel to the 8" and the other to the mid and tweeter. Will this work?

[Pano]

Yes, that will work. It can help you balance the levels between the sections, too.

[HoneyBadger]

OK I think I have a good handle on this... Lastly, any recommendations for capacitors/inductors (brand/material) and amp enclosures? I will try to follow up with a specific amp but it will need ventilation since it will be integrated in the speaker. Also, I have no idea exactly what specs the Klipsch woofers are so it will be hit or miss... I am basing the figures on their 2 way reference bookshelves with the same woofers.

[Pano]

You should be able to pick up whatever you need at P.E. or Madisound. Ventilation may not be needed if you use a metal plate that has one side to the free air. That's common in powered speakers.

[HoneyBadger]

How do we feel about Mauro Penasa amplifiers? vs. Tripath, Gainclone, premades from Hypex? Does it include circuit protection?

[HoneyBadger]

... I'm on a roll... should prob start new threads... Other than load considerations, does impedence matching affect other aspects? ie. THD