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Mirage SM-.5 Woofer Impedance

I would like to find the actual crossover point of the tweeter.... without changing it's portion of the crossover around. Soooo.....

Should where should I put my leads to determine how much the resistor is actually resisting the tweeter?

I tried placing them on the end of the resistor furthest from the tweeter like this

____ tweeter
|
|
|__resistor = 6-2 ohm 10%
|
|------------------------------red lead here
|___capacitor = 6.8 uf

And then I placed the black lead on the ground on the inside of the speakers terminal

(This is all shown in the pictures so you can visualize it)

This got me 14 ohms.

Does that seem right?

So in the calculator I put

High Freq. Impedance 14 ohms
Low Freq Impedance 7.6 ohms
Crossover Freq 1673 hertz (trial and error till I got the cap value at 6.8microfarads)

So from my line of thinking my crossover frequency is 1,673 hz.
Does that sound right at all?
 
If the resistor is 6 ohm, this sound OK. 14 ohm with a 6.8 uF gives you that low crossover point. Some tweeters can be crossed as low as 1800Hz, so this could be 1 of of them.

But what you are measuring is the Voice Coil Resistance + 6ohm resistance, not impedance. Impedance varies with frequency as in the graph I posted before. But the VC resistance usually gives you an idea of the driver impedance.

If you want to be sure of the resistance value, you need to unsolder 1 of its leads and measure it disconnected from the circuit. If it's a 6ohm resistance, I'd connect it before the capacitor, to shift the crossover point to the 3000-3500Hz range, what is the freq we were guessing... You can undo this later if you don't like it.

Think that you are designing a whole new speaker, so you can choose:
-to keep the original tweeter crossover, and modify the woofer xover until match the tweeter.
-To modify also the tweeter to a new crossover point, guessing both crossovers, woofer and tweeter.
 
Totally seems reasonable because when I ran that freq generator through it it sounded pretty solid down to those levels...

Gotcha.

I will probably do that tomorrow so I am sure of the crossover point of the tweeter.

I think I will keep the original tweeter crossover as I think it sounds absolutely terrific the way it is. I plan on buying 2 of these woofers:
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=292-428&scqty=2
From the reviews I have read they seem to do well in a sealed enclosure. The suspension of the clear coned MCM woofers I have is VERY stiff with them out of the enclosure. Which I think is also contributing to the lack of bass... and since this is a learning project and the woofers are cheap what the hell right? but anyway I think that's what I'm going to do...

The resistor's resistance i measured at 7.6 ohms and the tweeter is 7.4 giving these a total resistance of 15 ohms correct?

So I would need to calculate at 15ohms

with the low freq at 7.58 that gives me a cap value of 6.8 which gives me a crossover frequency of 1,560hz :)

Sooo i think i would like to set up the woofer with a 2nd order that will cross over at 2,000hz?

Does that seem like ample overlap or what?
 
the crossover point should be the same for woofer and tweeter. I think you sould try just a 1st order at 1600-1800 Hz and see what happens... But for that lower crossover, you need a larger inductor....(you could try the 2 inductors you have, in series, inductance add in series)

I'd try the change in the tweeter xover with the inductor in the woofer... You can undo it later... It's easier to move the tweeter crossover, changing a capacitor, than the woofer buying larger inductors.

Anyway, remember that the resistance you are measuring is not the impedance, so your calculations are just approx. so you don't need to match 1560Hz exactly.

Remember this is not an exact science, and I've never seen a tweeter crossed that low, the lowest I've seen is 1800Hz, but I'm not an expert.

Regarding the woofer you are thinking to get, I don't think it will be better of what you have. The woofer you've linked has a QTS of 1.11, what is very high, much higher than the one you have now, which means it will work better in very large enclosures. Theorically, in the same cabinet, it will be worst than the one you have now. And is quite less efficient (85dB vs 91dB of your actual woofer), so it will sound at lower volume..

I don't know how stiff that suspension should be. I assume it's the woofer you linked at the beginning, in a good working order. For sure, if some part has hardened, it will affect the ability of the motor to move the cone.

Find some box calculator on line, and input the woofer data, it will show you the size of the optimal box.

Have you tried your signal generator in the woofer, with the inductor, to check when it starts to roll-off?
 
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As i'm in the neighborhood of experimentation I have decided to order a 1.2mh inductor to try a 2,000hz crossover and I did order the woofers... I won't have any problem using up an of these woofers as I have had lots of projects in the pass. I just finally got the courage to delve into crossovers.

When I tried the single 1.5mh inductor I felt the crossover point was too low and i was missing some of that midrange which is why i'm going to try the 1.2mh inductor and then try the 1.2mh inductor with a 5.6uf cap which should give me a crossover of about 2,000hz

The suspension of the clear woofer is VERY stiff.... Typically sealed cabinets have woofers with a little bit looser suspension as the sealed box gives some rigidity back.

I would even say that these clear woofers would work in a car or infinite baffle setup because of how stiff the suspension is. So in total I will have 3 pairs of woofers to mess with in these cabinets.

I did the box calculator on the 2nd page I believe

No i didn't use the signal gen with the woofer but I could plainly tell that there was a hole in the midrange so i decided not to.

I will let you know of my results probably.... this weekend when my parts get here.

Thanks again for all your help... I still need to find some 3D glasses to check out your avatar!
 
I've been following this thread a bit and I'm sorry but I must make a few observations. I will preface these observations by saying this....I know there are a lot helpful and understanding guys here. Also it is a free world and anyone can do whatever they want to. But there is no way I would go this far trying to restore a pair of speakers that if I understand right...don't have the original woofers...don't have the original tweeters....The estimates for matching drivers to the box are just that, estimates. The woofers that were in the boxes when they were found were not original so why buy another pair that aren't original? And, while we're at it change the crossover with costly components that we aren't sure will work well. All this for a speaker that if you found an original pair or a comparable pair of another brand you could get for $50!

I think sometimes the best advice you can give someone is that it is not financially sensible to do certain things. Then give an explanation of why you think that is. And maybe in some cases just let things go where they will and maybe they will die a slow death.

I have a couple of Frankenstein speakers myself but they were put together with spare pieces that really had no other home. I've got a pair of JBL 26 cabinets and crossovers with zenith Allegro woofers and Boston tweeters in them and they really do sound good.

I think the tinkering bug hits us all sometimes. I know it gets me! I've restored speakers that I know won't be worth what I put into them in parts and labor but I just have to try to save them if I can. I do this and try to keep things as original and cheap as possible. I also try to be a realist and know when the end doesn't justify the effort. I suppose it really doesn't matter if you have fun and learn a lot along the way. Then if you keep the piece you've worked on and enjoy it whats the harm? I guess it just boils down to different strokes for different folks doesn't it? Good Luck on your project! Franksta
 
I agree with not spending too much in parts without a guaranteed result... but I see this project turned to a learning experience....

JRosen: If you want to get new woofers, take a look at this, they are good woofers, are on sale, and I'm sure there are crossovers already designed for them:
http://www.madisoundspeakerstore.co...aurasound-ns6-255-8a-paper-cone-woofer-8-ohm/
(NO AFFILIATION). take a look at the values, QTS is 0.55, what to me means a much better woofer.

Here is a crossover for taht woofer:
http://www.madisoundspeakerstore.com/store/images/Image/NS6-255-8A_DQ25SC16-xover.png
 
Well thanks for looking out Franksta I do appreciate that but as elnaldo said this has turned into a learning experience and BOY have I learned.

Technically these are not the actually tweeters that came in the speakers BUT they are the exact model that came in them originally... The only difference is that they don't have the plastic deflector piece on the front. No the woofers are not the originals but that's ok with me. These will probably end up as a present to a friend anyway. If they sound good and I learn something that means much more to me than $50.

My real project is a pair of HPM-150's... but that's for another thread
 
Well I put in the inductor and the cap... (I also just learned how to solder :D)
and put the clear woofer in one and the grs parts express in the other and I actually liked the sound of the clear woofer so I put them back in! The other woofers I can sell to a friend who will need them for his Advent Heritage speakers anyway. This definitely improved the bass and the midrange A LOT. Sweet!!!
 
:D I told you, reading the specs of the woofer... :D Now you can learn how to choose a woofer ;)

You could try your signal generator with each driver, to check the woofer and tweeter crossover point...
 
Yes I will do that and post the results when I get a chance... I just put a coat of tung oil on the speakers and they still need a few more... So they are in the garage for now but I will let you know of the results.
 
I wanted to add after restumbling across this thread that I really appreciate all the help and these speakers are still being enjoyed by a girl I know.
 
No sorry I can't help you directly there ... the woofers were made by Cambridge Speakers of Ontario (long gone) . Just about all the Global / API products were. The tweeters are Philips (you'll find the model number identified elsewhere in this thread).

I can only offer a bit of history. It's nice to see the mention of Inception Audio a couple pages back in this thread, and the mention of SM-1 speakers. One of the 1st pair of speakers I picked up at an Estate sale when I got back into audio ... would have been about 2008. So Inception Audio was the Canadian importer for Tangent Acoustics out of England (http://www.thunders.ca/tangent/tangent.php) Tangent basically went belly-up mostly as a result of KEF's decision to stop providing OEM drivers. Inception Audio turned to Kevin Voeks (yes that Kevin Voeks later of Snell) who designed the initial Mirage lineup for them. My set of SM-1s had Peerless woofers in them (they were original) ... and later versions I have had used Cambridge woofers. Some of the early SM-1s had wood veneer instead of vinyl as well ... I doubt the SM.5 did though. Inception had their speakers manufactured for them by API. API later bought the Mirage name. Ian Paisley was brought on at API and Kevin left for Snell. Course API also made Ian's early line of Paisley Research speakers.
 
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