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Small Computer Speakers as Headphone Drivers?

post #1 of 4
Thread Starter 

I raided a thrift store today and got some Logitech speakers for $1.50. They quickly met with my hammer and I harvested the drivers.

 

Quick measurements reveal that the drivers have 3.2 ohms of series resistance and about 18.5 uH of inductance. There are four of them. I thought they would be interesting headphone drivers despite their weight, size, and impedance.

 

Most headphone amplifiers would have an issue driving what are essentially 4-ohm drivers. In the speakers, two were in series and one had a 33u capacitor across it, making it a "bass" driver. The drivers are 46mm wide and have 33x17 mm magnets on the rear. For prospective headphone drivers, they are HUGE.

 

If I were to do this, I wouldn't want to hook them to any headphone amplifier; doing so would probably overload the current capabilities and cause the final output amplifiers to fail. An idea would be place a 2-watt 150 ohm resistor in series with each driver, in essence making a 150 ohm headphone with a decent amount of damping. There's no telling where that would get me because most of the power would be eaten up in the resistor, meaning I'd need a higher-power amplifier than what one normally has. I'm thinking orthodynamic power, although I don't have any and have never listened to them.

 

If I were to do this, I'd make open-backed cups like the higher-end Grado cans. I am getting a lathe shortly and will be able to turn cups out of any given wood.

 

There's also a possibility that this is a dumb idea and I should go back to the drawing board. Maybe it is. What are the thoughts of the people?

 

The drivers look like the ones in this picture...

 

http://static.productreview.com.au/pr.products/102954_logitech_x230.jpg

 

Ed

post #2 of 4

I think these are quite highly regarded as desktop speakers, but it's a bit late for that now...

 

Most production headphone amps will balk at driving one of these drivers, but some of the high end ones will cope, and many DIY amps will drive 4 ohms, if you look for ones with overbuilt output stages, or you could build something with intent, most opamps used as voltage gain stages have loads of drive capacity and would easily drive, say, 4 unity-gain buffers such as the LME49600. 4 would probably be sufficient. 8 * LME49600's (for 2 channels) wouldn't be cheap though, you'd probably find some big discretes a lot cheaper, but you'd forego the guaranteed low distortion you get with the LME's. Guaranteed if your implementation is up to scratch, that is.

 

Then there's the question of how much power to put into the drivers, but a few volts would probably be enough to make your ears bleed.

 

For myself, I have numerous amplifiers lying around unused that will drive 4 ohms, perhaps you have too, if you look around. Or you can buy one on ebay for peanuts.

 

Interesting, I have a lathe, it never occurred to me to turn some cups. Until now, that is.

 

w

 

In English, we categorically disagree. We say, "Still waters run deep". Which is usually an observation on a person's character. 

post #3 of 4
Thread Starter 
Quote:
Most production headphone amps will balk at driving one of these drivers, but some of the high end ones will cope, and many DIY amps will drive 4 ohms, if you look for ones with overbuilt output stages, or you could build something with intent, most opamps used as voltage gain stages have loads of drive capacity and would easily drive, say, 4 unity-gain buffers such as the LME49600. 4 would probably be sufficient. 8 * LME49600's (for 2 channels) wouldn't be cheap though, you'd probably find some big discretes a lot cheaper, but you'd forego the guaranteed low distortion you get with the LME's. Guaranteed if your implementation is up to scratch, that is.

 

I don't intend on using them bare...rather, I'd put a small value resistor in series with it (say, three 10-ohm resistors). This would get the value of the driver somewhere near 32 ohms. I measured the resistance at 3.2 ohms each and the inductance at 18 uH. At 20 Hz, the inductance adds 0.0022 ohms and at 20 KHz, the inductance adds 2.2 ohms. They don't simply add, so I think it would round out to about 4 ohms although not precise. To get precise drivers I'd likely need to go to Parts Express and spend about $25 per piece, then another $25 for shipping.

 

I think the best bet for me to DIY some headphones would be to find someone who has a decent pair with a broken headband or cable. This would be someone who has really high end cans, then something like Grado SR60s (the broken pair) that they can sell for parts for $10-20. I'm not sure what I would do with these drivers. In all reality, they are way too heavy to be serious contenders for headphones...

 

 

Quote:

For myself, I have numerous amplifiers lying around unused that will drive 4 ohms, perhaps you have too, if you look around. Or you can buy one on ebay for peanuts.

 

Interesting, I have a lathe, it never occurred to me to turn some cups. Until now, that is.

I have a couple myself, including one made with 6V6s. The idea to use these as headphones is probably not a very good one. The head amp I'm using now is not suited to drive low impedance loads such as this.

 

Here's something I found funny about these drivers. There were four identical drivers in two speakers. They come out to about 4 ohms each. Both sets were wired in series, meaning I had a set of 8 ohm speakers. However...one driver per side was bypassed by a 22 uF bipolar electro cap. This means that, above 2260 Hz, that driver is effectively out of circuit. So...for bass frequency we have 8 ohms and for mids/treble we have 4. Somehow that doesn't seem like a good idea.

 

 

Quote:
In English, we categorically disagree. We say, "Still waters run deep". Which is usually an observation on a person's character.

I see. My quote comes from a song about a girl taking advantage of a boy. In that context, it means you have to spend much time and effort into finding someone worthwhile. In my dating experience, I totally agree.

 

My current headphones are iFrogz CS40s. They're a solid gloss white and I think they sound pretty good. What little Head-Fi data I've seen on them points to them being a crappy can. I don't agree. Then again, I haven't heard the likes of Grados and the high-dollar Sennheisers and other bits of audio purity I'll never be able to afford. I don't think I'm willing to put that much into audio.

 

Ed

post #4 of 4
Quote:
Originally Posted by wakibaki View Post

I think these are quite highly regarded as desktop speakers, but it's a bit late for that now...

Most production headphone amps will balk at driving one of these drivers, but some of the high end ones will cope, and many DIY amps will drive 4 ohms, if you look for ones with overbuilt output stages, or you could build something with intent, most opamps used as voltage gain stages have loads of drive capacity and would easily drive, say, 4 unity-gain buffers such as the LME49600. 4 would probably be sufficient. 8 * LME49600's (for 2 channels) wouldn't be cheap though, you'd probably find some big discretes a lot cheaper, but you'd forego the guaranteed low distortion you get with the LME's. Guaranteed if your implementation is up to scratch, that is.

Then there's the question of how much power to put into the drivers, but a few volts would probably be enough to make your ears bleed.

For myself, I have numerous amplifiers lying around unused that will drive 4 ohms, perhaps you have too, if you look around. Or you can buy one on ebay for peanuts.

Interesting, I have a lathe, it never occurred to me to turn some cups. Until now, that is.

w

In English, we categorically disagree. We say, "Still waters run deep". Which is usually an observation on a person's character. 
Not directly for the quote but hopefully...
So I had that smashbox from iLuv and the drivers fell off. They're still WORKING though these ones http://www.amazon.com/gp/aw/d/B002QPQNLC
So I took them apart and simply connected to a earphone wire and it looked like this http://imgur.com/V8Dspzg.jpg
And you know what, it worked just fine but the bass was a little lacking you know why. So I want to make my own headphones from this and please notice I'm only a beginner and I'm 15 so I have no idea what I'm about to try although I did some research. Maybe you know how to help me or know anyone who can?
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