W3-871S + Reinforcements...

[CrisTUFR]

I finally got my W3-871's in the mail and they work perfectly for 100Hz+. I am able to move forward in creating a reasonably-priced, decently-performing 2-way system (hopefully).

One thing is sitting in my way of moving forward right now -- the crossover.

I want to use the W3-871S with my Audioyin no-name woofer as a bass Reinforcement. The A6100 woofer (the Audioyin) sounds pretty decent from 100Hz down, but I haven't been able to cut off the higher frequencies to know for sure.

What I want to do is throw together a quick passive crossover that would just act as a lowpass filter at 100Hz for now with the sub, so I can hear how the two speakers sound together in a makeshift box. I am not living at my own place right now (The New Home Blues...) so I would like to just buy a handful. Currently, the A6100 sounds like garbage when you feed it a full-range signal (in the Woofer Cooker, mainly) but when I manually turn off all the high-range frequencies on the Mac, it sounds a lot more controlled.

Anyone have any ideas about what I should pick up (as cheap as possible would be good) in order to play around with crossing this all over? Could a variable resistor and a handful of capacitors make a good makeshift lowpass filter (for RC filtering) or am I stuck with doing something with coils at this stage?

Does anyone know of a small setup I can rig together to play with different values and tweak a filter "by ear"?

Any help would be greatly appreciated. I will try to post progress here as I continue.

Thanks,
Chris

[CrisTUFR]

Okay. Now I'm really confused (or in a bind)...

I'm trying to figure out what type of coil I'd need to do a first-order low-pass filter at 110Hz to test my woofer. All the calculators are saying I need a 12.74 mH coil, which would be absolutely huge!!

How do I get around that if I wanted to roll my own coil? I want to have as few turns as possible (to save my sanity!) but everything's saying I'm going to have this half-pound monster on my hands!

Help!

Thanks,
Chris

[joensd]

1st order crossover-frequencies with a L in series with the woofer and with a C in series with the tweeter are calculated by:

f(3dB)=R/(2*PI*L) for the woofer
f(3dB)=1/(2*PI*R*C) for the tweeter

Solving for L and C you´ll get for example 5,787mH for the coil and 361,716uF for the cap if the impedances of the tweeter and woofer are 4Ohm.

Which impedances did you put in the calculator?
WinISD for example calculates 1st and 2nd order passive filters.

[Timn8ter]

For an 8 ohm driver at 100Hz ~12mH is going to be close. Yep, it's large but typical for this application. You may want to consider moving to 150Hz and put a cap on the 871 to roll it off sooner.

[CrisTUFR]

Hmm. So this is good and bad news.

The good news is that I'm not far off from what I need.

The bad news is that I'm going to have a lot of trouble finding such a large coil, and it certainly won't be cheap to acquire, either. I guess I can just wire a few smaller ones in series (or parallel, or however you do it to add the inductances).

I also have a dome tweeter I could pair with these two speakers for a three-way, but I am unsure about if it's worth it since the 871's are SO good at reproducing the high frequencies. Also, it's a 4-ohm tweeter and I'm not really looking to add more complexity to this box.

Blah. What's the lowest you can get a 871 to -3db at if the cabinet wasn't a concern? Perhaps I can prepare to take the woofer down even lower than 110Hz...

Any help is appreciated, as usual.

Thanks,
Chris

[joensd]

Blah. What's the lowest you can get a 871 to -3db at if the cabinet wasn't a concern? Perhaps I can prepare to take the woofer down even lower than 110Hz...

Then you´d obviously need an even bigger coil.
Why don´t you cross over a bit higher to improve power handling of the Tangband?
Haven´t tried it but seen recommendations for around 200Hz.
Coil would be around 6mH.

[CrisTUFR]

Originally posted by joensd

Then you´d obviously need an even bigger coil.
Why don´t you cross over a bit higher to improve power handling of the Tangband?
Haven´t tried it but seen recommendations for around 200Hz.
Coil would be around 6mH.

Yeah, you're right. Silly me.

I think I may do that, since a 6mH would probably be easier to find, and maybe half the cost.

I just hope that the A6100 is up to the task of handling that much frequency content. We'll soon see. :P

And now I'm thinking of open-baffle possibilities as well due to the high Qts of the woofer (0.97). Oh, the humanity!

Thanks,

Chris

[joensd]

There it was

[navin]

do you have 2 amps. if you do you could use line level XO. BTW I wound a 4mH air core inductor of 14SWG. 2" dia core. i think the inductore weighed 2-3kgs (4.5-6.6 lbs) ! so if you are winding a 6mh monster use iron core.

[CrisTUFR]

Originally posted by navin
do you have 2 amps. if you do you could use line level XO. BTW I wound a 4mH air core inductor of 14SWG. 2" dia core. i think the inductore weighed 2-3kgs (4.5-6.6 lbs) ! so if you are winding a 6mh monster use iron core.

I don't think I could afford to go the route of an active XO, as I have already built my gainclone for these speakers I am building, and it's strictly 2-channel (for my computer).

What I will do tonight is swing by my electronics store again. I bought two spools of 12AWG magnet wire that looks like it won't be enough for what I need, and there's no sense starting to pick up YET ANOTHER hobby of turning my own coils.

At the store, I found a "subwoofer crossover" board that had an iron-core coil on it. It is not marked at all, and I have no clue about the value of the coil, or where it crosses over.

Since those pre-made crossovers are cheaper than the spools of magnet wire, it's probably worth it to try them out and see how well they work. I would assume they probably cross over around 100hz, which would likely be just fine. I can test the response pretty easily with the equipment I have. Also, they're 2nd order, so there's a slightly better chance of figuring out the XO when I have a cap value.

If I use that with a 1st order filter "higher up" on the frequency range for the 871, it'll probably roll off smooth enough so that there may only be a slight "dip" around the mid range.

Obviously, this is all assumptions at this point, and I can't say/do much more until I take those XO's home.