Building an ultra cheap speaker, help me please...

[kanan]

Hello everyone,

I'm thinking about building a pair of ultra cheap speaker(<$100) with acceptable performance. I'll use some chinese drivers and tweeters to build these 2ways speakers. I bought a pair of tweeter for $7.5 and am going to buy a pair of 6" driver for $19. I'm a newbie but have a little skill about electronic and audio. Where should i start? I've been playing with speaker workshop for a while. I did an imperdance measurement of my tweeters, here is the result....

I know this graph telling me the impedance of the tweeter, its resonance frequency........can this graph tell me anything else such as its performance??

please don't complain me about the components quality , i have very limited budget.. and this project is mainly for educational purpose..

any suggestion would be great

Thank you

[BobEllis]

First, let me commend you for starting with a learning project and not going straight for the ultimate reference system. It will be a good learning experience.

A measurement mike and preamp would be a good next step - you'll need it to really do anything with the drivers. You can usually find supplies at a retail electronics shop for around $20 for a 9V battery powered preamp. It won't be perfect, but at least will give you an idea what is going on.

Besides the primary resonance, there are lots of higher frequency resonances. This is most likely cone breakup modes. When you measure its frequency response, you ought to see ripples in response that correspond to the impedance ripples.

This is probably not a smooth sounding tweeter, but taming the response will be a good exercise. Early on the learning curve, shoot for a XO frequency of 2K or better second order or higher. First order won't attenuate the tweeter enough at low frequency unless you cross much higher.

Have fun

EDIT - here is a mic preamp circuit suitable for use with an electret capsule http://sound.westhost.com/project112.htm

[Nemophyle]

do you have any other information concerning your drivers ? TS parameters, frequency response etc

[kanan]

Thank you for your reply Bob,

Well, I noticed the resonance at the high freq. Is there any way i can eliminate this resonance?

I'm thinking about using a cheap electret capsule ($0.5). How can i test the capsule's freq. response?? I saw this page that show a generic capsule with quite good freq. response...

http://sound.westhost.com/project93.htm

This result is very interesting.....

[Crazy-Stereo]

Hey,

Anyone know which type of mic is cheap and suitable for driver's measurements?

Thanks.

[kanan]

Nemophyle,

unfortunately, as it is a very cheap driver, the manufacturer doesn't give me any details about this tweeter.... But i'll figure out myself...

Tomorrow, i'm gonna build an eletret for testing...

But not sure if that cheap capsule can perform any good....

[BobEllis]

The capsule shown there is the Panasonic WM-61A - $1.83 at Digikey. Short of sending your mike and preamp to a calibration lab, there is no DIY way to measure their combined response. But reports are these capsules come very close to published (almost perfectly flat) specs when built into a wand as Rod suggests. good enough for hobby use until you go really high end.

I suggested the dual opamp preamp as a probably easier/cheaper to build first time preamp. The project 93 preamp probably performs better.

Eliminate the upper end resonances? Oh boy! what is the tweeter? maybe add some ferrofluid or a light coating on the dome surface to damp it. Something rubbery that will dry would be good. But now you are getting into esoterica before working through the basics. If you have a published frequency response curve for both drivers it would be helpful.

For a little more money and a whole lot less aggravation than modifying inexpensive tweeters, the ~$30 Seas 27TDFC and 27TBFC/G are the tweeter value leaders.

[kanan]

Well, I think that is too far from my philosophy......

So, i'm gonna stick with what i have here...
tomorrow, i'll build a preamp and buy a cheap electret capsule.

I'll post the result here.......

Please give me further advice...

Thanks all....

[megajocke]

Something's wrong with that measurment. Those ripples look out of place. Are you sure you are not clipping the soundcard input? I have never seen a wavy impedance plot, even on the crappiest drivers.

[ShinOBIWAN]

Originally posted by BobEllis
...measurement mike....

Is he the guy that does all the measurements?