What Sort Of Crossover Is This?

[Meld]

Ok I was trying to salvage parts from my old speakers to make some DIY surround speakers. I opened an old Sony HTIAB satellite to get its tweeter but I was surprised to find that there was in fact no tweeter at all. There was just the one woofer/midrange. What looked like a tweeter through the grill cloth was actually just a port hole.

There was a 47uF cap with both legs soldered to the + terminal of the woofer. I've never seen one connected like this before. I'm used to seeing a cap wired in series with a tweeter which is connected in parallel to the woofer, as a very cheap hi-pass. But what does the 47uF cap connected to the + terminals do when there is only the one driver?

I'm afraid I can't remember much about LCR circuits anymore. :'(

[geoff888]

Ok I was trying to salvage parts from my old speakers to make some DIY surround speakers. I opened an old Sony HTIAB satellite to get its tweeter but I was surprised to find that there was in fact no tweeter at all. There was just the one woofer/midrange. What looked like a tweeter through the grill cloth was actually just a port hole.

There was a 47uF cap with both legs soldered to the + terminal of the woofer. I've never seen one connected like this before. I'm used to seeing a cap wired in series with a tweeter which is connected in parallel to the woofer, as a very cheap hi-pass. But what does the 47uF cap connected to the + terminals do when there is only the one driver?

I'm afraid I can't remember much about LCR circuits anymore. :'(

If it's a small driver, they are sometimes used for "full range" (but obviously won't reach the very highs or lows as deidcated woofer + tweeter). Can get full range drivers from 3" all the way to 6" eg Fostex. Or it could be a cone tweeter.

If both ends of the cap is connected to the + terminal of the woofer only, it will not do anything as the cap is shorted in the circuit. The cap needs to be connected to 2 different points in the circuit to do "something".

[norpus]

Hehe, if its only one driver no crossover is needed. If the cap is soldered to itself, that is hilarious

'Its a Sony!'

[Meld]

Here is a photo of the speaker in question: http://www.dtvforum.info/index.php?act=att...ost&id=5144

Do you think then it is what you can call a convenience capacitor? So that if you ever wanted to integrate a tweeter with the speaker system, you don't have to supply your own cap?

I used to wonder why these speakers sounded congested when playing back violins and strings. Now I know it was because there was no tweeter. The speakers were part of a $499 HTIAB I bought from Grace Bros 10 years ago.

I'm making Toblerone-shaped speakers to use as surrounds and painting it the same colour as the walls. I wonder if I should just go without a tweeter. If it's good enough for Sony...

I opened up some PC-type speakers as well and found only one driver. I didn't get lucky till I pried open some ghetto-blaster speakers but I found only piezo type tweeters (they look like large watch batteries), and the woofers in these looked nice.

[geoff888]

Hehe, if its only one driver no crossover is needed. If the cap is soldered to itself, that is hilarious

'Its a Sony!'

yeah that's true...

Here is a photo of the speaker in question: http://www.dtvforum.info/index.php?act=att...ost&id=5144

Do you think then it is what you can call a convenience capacitor? So that if you ever wanted to integrate a tweeter with the speaker system, you don't have to supply your own cap?

I used to wonder why these speakers sounded congested when playing back violins and strings. Now I know it was because there was no tweeter. The speakers were part of a $499 HTIAB I bought from Grace Bros 10 years ago.

I'm making Toblerone-shaped speakers to use as surrounds and painting it the same colour as the walls. I wonder if I should just go without a tweeter. If it's good enough for Sony...

I opened up some PC-type speakers as well and found only one driver. I didn't get lucky till I pried open some ghetto-blaster speakers but I found only piezo type tweeters (they look like large watch batteries), and the woofers in these looked nice.

Shot is a little dark, hard to make out.

The only other thing I can think of is that it's a coaxial speaker with the tweeter in the middle of the woofer where the dust cap normally is and the cap is for that. Anyways, there are alot better new drivers on the market that will no doubt sound better, unless you want to keep it on the cheap.

[Meld]

I wanted to keep it free by recycling old junk. It'll be for the AV system mainly used to play Wii using an old Pro Logic amp.

Here's a clearer shot of the cap: http://www.dtvforum.info/index.php?act=att...ost&id=5145

As you can see the legs are soldered to the + terminals of the driver.

I might not use the Sony driver and use the Daewoo pictured here instead removed from an old ghetto-blaster. http://www.dtvforum.info/index.php?act=att...ost&id=5146

Although the Daewoo is rated 10 watts MAX and impedance is 4 ohms, versus 70 watts and 8 ohms Sony. But it has a nice white cone and will blend more with the walls. Or I could use both drivers in series so it'll look more serious, lol.

[geoff888]

I wanted to keep it free by recycling old junk. It'll be for the AV system mainly used to play Wii using an old Pro Logic amp.

Here's a clearer shot of the cap: http://www.dtvforum.info/index.php?act=att...ost&id=5145

As you can see the legs are soldered to the + terminals of the driver.

I might not use the Sony driver and use the Daewoo pictured here instead removed from an old ghetto-blaster. http://www.dtvforum.info/index.php?act=att...ost&id=5146

Although the Daewoo is rated 10 watts MAX and impedance is 4 ohms, versus 70 watts and 8 ohms Sony. But it has a nice white cone and will blend more with the walls. Or I could use both drivers in series so it'll look more serious, lol.

That's a better shot. Ok, the cap is not connect to the "+" on both ends, the other end is connected to something else that is next to the "+" terminal. It' is starting to look like a coaxial speaker esp the Daewoo one and that would make sense as to the 4 ohm load. I would just use one woofer.

[geoff888]

BTW, you can check if the big dome in the middle of the woofer is a tweeter by checking if it's attached to the woofer cone or not. If it is, it's just a dust cap, if not it's a tweeter.

[Meld]

None of them are co-axial drivers. The Sony is a full range speaker and the Daewoo had a separate tweeter. The dust cap of the Daewoo is just metallic looking so it ends up looking like a alum. dome.

I opened up the center speaker of the Sony HTIAB kit and found 2 similar drivers wired in parallel but I think they are 16 ohms each and there is no capacitor this time. The center speaker did sound more full-bodied than the other satellites.

Upon closer inspection of the crossover in question, I think the 47uF cap is just wired in series with the woofer driver. Must be a high-pass filter then. Is my math correct that the cut-off freq. is 423 Hz?

1/(2 * 3.14 * 8 * 47u) = 423 Hz

Isn't that too high a frequency? Granted they are only 3.25" cones. I could perhaps make dipolar speakers with these Sony drivers, or tripolar even.

Edited June 6, 2008 by Meld

[geoff888]

None of them are co-axial drivers. The Sony is a full range speaker and the Daewoo had a separate tweeter. The dust cap of the Daewoo is just metallic looking so it ends up looking like a alum. dome.

I opened up the center speaker of the Sony HTIAB kit and found 2 similar drivers wired in parallel but I think they are 16 ohms each and there is no capacitor this time. The center speaker did sound more full-bodied than the other satellites.

Upon closer inspection of the crossover in question, I think the 47uF cap is just wired in series with the woofer driver. Must be a high-pass filter then. Is my math correct that the cut-off freq. is 423 Hz?

1/(2 * 3.14 * 8 * 47u) = 423 Hz

Isn't that too high a frequency? Granted they are only 3.25" cones. I could perhaps make dipolar speakers with these Sony drivers, or tripolar even.

Sound like a high pass for the cone woofer. I was thinking 47uF is very high for a high pass for a tweeter but make sense for 3.25" cone to stop overexcusion on the low frequencies where it can't handle it. So, 423Hz sounds right or even too low. I guess the "sub" will take care of the frequencies below that.