Strange Technics Woofer/Mid-bass driver

[jackand08]

Hi everyone.

I recently dismantled a set of Technics SB-EH60 multi-way loudspeakers that I got from a car boot say for £3! The tweeter and midrange were the usual sealed enclosure, crappy quality units used on speakers sold with micro-systems but the woofer/mid-bass driver had me intrigued. The crossover point for the woofer to mid was around 1-2kHz but it was only a simple R/C x-over so it didn't have a very steep rolloff.

The driver is about 5-6ins in diameter (excluding metal mounting that the surround is attached to) and at a guess has a voicecoil diameter of around 1.5-2ins. When still in the (ported) box, the speakers were rated at 60W (DIN) and 160W (music) power so I'd assume that this driver is rated at around [email protected]

Then things start to get slightly unusual. The dust cap is made from metal, which I know is not a brand new concept but is strange to see it on such a cheap set of speakers. Also, the shape of the dust cap is not exactly conventional either, as it is stepped inwards and is glues to the voicecoil on the other side. My guess for the cap being metal is to act in a similar way as a whizzer on other speakers, to allow it to reproduce higher frequencies more accurately (it did have to go up to 1.5kHz though!). Also, on the underside of the cone, there is a small cutout in the cone, hidden from sight by the dust cap (pic 3). I'm assuming that this is some kind of cooling system, but again not conventional (vented voice coils often have a hole drilled through the magnet assembly instead).

When tested, the driver seems to be ok to around 30-40Hz, but when in free air, bottoms out very easily. I was thinking of using two of these drivers in sealed boxes (to provide some damping) as subwoofers in my main system, driven by a 60W amp (LM3886 probably). The main amp in this system is based on the LM1875 (2x 25W).

I just posted here for people's opinions and to see what they thought about this.

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[rrrremus]

I own a pair of Technics speakers with two of these drivers each.
I remember they sounded very good at their time with rich and natural bass.
Unfortunately the suspension rubber aged and started to develop cracks a few years ago. They are still working today, but i only use them for Tv

 

[jackand08]

When these speakers, were in the boxes, they were quite bass heavy and had very harsh treble and a rather confused mid range. I figured that taking them to bits and using the bass drivers would get more out of them. When I received them, the foam was very dirty and dusty but had not started to rot. Hopefully, if I keep these in good enough conditions, this shouldn't happen.

 

[richie00boy]

I very much doubt the dust cap is a whizzer, most likely it is to aid heat disipation.

 

[jackand08]

I thought this but when you consider that the turns of the coil are not wrapped around the metal part of the cap. Instead they are wrapped round a paper former and the top is attached to the metal cap.

If it is as you suggested, maybe that is the only way that they get their quite high power rating, just by using an underrated voicecoil and lots of cooling.

 

[jackand08]

Bump.

Has anyone else got any opinions about this driver (or maybe two) being used in a sealed box with a bit of EQ'ing to get things down low??

 

[Jonathan Bright]

Is that a second smaller magnet on the back? It's not some form of servo feedback surely?

Interesting.

 

[djk]

"Is that a second smaller magnet on the back?"

Magnetic shielding.

 

[ampimp]

Junk

That driver looks nasty.

 

[rrrremus]

@ jackand08. Did you throw the tweeter away ? I just googled the part number of your speakers and realised i could use a pair of such tweeters. Are you interested in selling them to me ?

Regarding the woofer, i owned the SB-T400 speakers that sounded really good, but i doubt you can use this speaker as a subwoofer as you wish. It's response under 40 hz is weak and you will only end up destroying the speaker with the low freq Eq.

 

[jackand08]

The magnet on the back is not for shielding, as when placed on a metal surface, the driver sticks pretty firmly to it. Definitely not a form of servo feedback, these speakers were not that complicated!!

I wasn't surprised to see that some had labelled the driver as junk and tbh I'm not too bothered as I was kind of half expecting this anyway!

@rrrremus, unfortunately I did not keep the tweeter drivers, sorry about that.

I think I've gone away from the idea of using it as a sub now due to the peoples opinions presented. I might still have a play round with it though because it is quite an interesting driver.

 

[djk]

"The magnet on the back is not for shielding, as when placed on a metal surface, the driver sticks pretty firmly to it."

Never the less, that's what a shielded driver looks like. The second magnet bucks the field of the first magnet, and is generally a bit smaller.

 

[jackand08]

After I posted that about the shielding, I forgot to say that the back of the magnet would stick to the metal surface. I'm guessing then, the this second magnet stops magnetic fields being radiated sideways and outwards instead (would make more sense if they were placed next to a TV for example).

 

[picowallspeaker]

So...are you going to put a tweeter to match woofer's emission ?

 

[jackand08]

@Picowallspeaker: sorry, I didn't quite get what you meant?

 

[picowallspeaker]

I meant : were you in desperate need of some speakers to listen to music or are those just spare parts that don't need to occupy space in some cabinets ?

 

[jackand08]

Yes they are just spare that may or may not get used. If I was to use them, I would probably see how they performed with subwoofer duty however, I wouldn't expect much out of them. I already have a pair of TEAC LS100U's that sound quite good. I am just in need of a subwoofer because, as with all bookshelf speakers, the bottom end is always lacking.