[avalon65]

I posted this in "The Lab", but have only had 30 views (five of which were mine) and zero responses. Maybe it's not juicy enough for them. I think this forum has a lot more action, so I'm hoping someone here can help me solve a basic diy dilemma.

I have a pair of old, no-name, garage speakers and the 8" woofer is blown in one of them after extensive, loud use during a Fourth of July party. I was surprised when I disassembled the blown speaker to see the two drivers were wired directly together with only a small capacitor residing between the tweeter and the woofer located on the negative wire. I guess I was expecting some kind of cross over, but then again these are cheap, cheap, cheap speakers. At first I thought the cap was blown, but after a quick trip to Ratshack the replacement cap didn't do the trick. The woofer doesn't indicate the ohms, but the tweeter indicates it's 8 ohms, should I assume the replacement woofer should be eight as well? Also, if I replace the woofer in both speakers does it matter what ohm they are? Thoughts and any other suggestions are much appreciated.

Thanx!!!

[MaxCast]

My guess is that it was 8 ohm.  Can you check the other woofer to see if its ohms are stamped?  Where are you looking for a replacement?

Do you have a multi-meter?
To anyone:  what does an ohm reading tell you when connected to a driver?

[avalon65]

My guess is that it was 8 ohm.  Can you check the other woofer to see if its ohms are stamped?  Where are you looking for a replacement?

Do you have a multi-meter?
To anyone:  what does an ohm reading tell you when connected to a driver?

I'll check the other woofer for stamping. The only numbers present on the blown one are "116708". Maybe the last digit is indicating the ohms?
My replacement shopping has taken me to e-Bay and mail order (Parts Express and MCM Electronics).
My neighbor has a multimeter that I can borrow.

Thanks.

[mgalusha]

The cap between the woofer and the tweeter is the crossover. It's just acting as a 1st order high pass filter.

If you are going to replace one of them, I'd replace them both. It's doubtful the replacement woofer will be the same as the old one. If you replace both, you don't need to worry much about what the old one's impedance was. I'd buy something cheap from Parts Express. These are only $10.36 each and would probably be OK given that you said they are "cheap, cheap, cheap".

Max - measuring the voice coil resistance can indicate the impedance. The Re (VC resistance) is usually lower than the impedance. In the example above the 8 ohm driver has a listed Re of 7.3 ohms and the 4 ohm version has an Re of 3.5 ohms. What's measured isn't the impeadance but it's usually somewhere near it.

Mike

[markC]

What is the value of the cap? With this info. we can take a stab at estimating the x-o frequency, and that'll help determine the replacement woofer in terms of it's frequency response. I'm betting that the tweet is crossed pretty high if it's cheap, cheap, cheap.

[avalon65]

What is the value of the cap? With this info. we can take a stab at estimating the x-o frequency, and that'll help determine the replacement woofer in terms of it's frequency response. I'm betting that the tweet is crossed pretty high if it's cheap, cheap, cheap.

Cap value is 2.2 uF, 50 volts

[markC]

That's a pretty low value cap that is intended to protect the tweet. You'll want to find a cheap woofer with as high a fr as possible. With that value cap, the woofer is running full range and then some.

[avalon65]

That's a pretty low value cap that is intended to protect the tweet. You'll want to find a cheap woofer with as high a fr as possible. With that value cap, the woofer is running full range and then some.

Mark - Thanks for the valuable input. Any suggestions on what range I should be looking for?

[MaxCast]

Thanks Mike.
I'd replace both woofs with 2 new caps at a value the woofs and tweeters can handle.  Of which, I have no clue.

[JLM]

Another option is to replace both drivers and cap with an extended range driver, anything from a car speaker to something like this from Parts Express for $24.50 each:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-045

I've heard this driver and it's not too bad for the price (extended range drivers tend to get expensive).  As implied it can use a bit of help on the high end, but perfect without for garage speakers.

Parts Express has a speaker selection wizard from their inventory for a given cabinet.  Other helps exist that you can use to "reverse design" (normally you start with a woofer in mind).

Keep in mind that any replacement driver may not be a drop-in replacement (holes may not line up exactly).

This may be getting into more work/cost than it's worth. 

[markC]

Avalon65

I would just check the frequency response of all the low cost woofers and pick the one with the highest. For example, if model x has a fr of 55hz to 2600hz and model y has a fr of 65 to 3500hz, then model y would be the one to go with.
If you start changing cap values to lower the fr for the woofer, your likely to bring the same end to the tweets as the woofer that no longer wiggles. You could get into a 3rd order x-over @ a lower frequency, which will also protect the tweeter, but as stated earlier, cost and effort will soon cath up to you. Another option may be to just drop a hundred bucks and get some new cheap speakers.

[avalon65]

Again thank you for all your suggestions and input. Please keep it coming. I'm fond of learning more on this subject. Yes I could probably go out and buy new speakers, but the DIY aspect of this is exciting me. E-Bay seems to be a very economical way to find used drivers and crossovers. If I fry something in the process I won't be out too much jack.

Since it's already been explained that the current crossover is first order, I was thinking of updating it. I found an interesting pair of Klipsch crossovers that also include better binding post than my current, flimsy screw design. However, it appears like this crossover is for 4 ohm drivers. What affect will it have if connected to an 8 ohm, woofer and tweeter? Also, I'm being careful to find the correct size and shape driver so it fit into my cabinet.

http://www.audiocircle.com/index.php?action=gallery&pos=1

Am I playing with fire by trying to piece together drivers and crossovers without knowing their exact specs? Again, it's being done rather inexpensively and I'm a little geeked by the experimentation.

Thanks.

[markC]

That looks like a 3rd order x-o. BUT, you can't just throw any x-o at a pair of drivers-it just won't work. But, if your just starting into the encompassing realm of DIY, experiment. It's fun if your into it, and if you wreck it-oh well your not out much and hopefully you can come away with some more insight into your hobby/quest. Try a google search for x-o design and play with that before you spend any money. One can usually design a x-o that will function for a given pair/set of drivers, but there's a real art to making one that sounds good. Unfortunately, I am not an artist in this capacity.