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Old 6th October 2012, 06:20 PM   #1
tomst is offline tomst  United Kingdom
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Default LF driver test

Hi
I acquired 2 sets of speakers today.
however they are very old and totally original.
both tweeters work fine.
however the LF driver on one set moves but does not much. Unless the volume is pushed up. When pressed by hand it moves slowly and is slow to return

Second set the is the same drivers move slowly and slow to return and is slightly one is scratchy. Also the LF is distorted. The more you push up the volume the less distorted it is, up to a point.
i think the scratch ness is due the the fact the the driver is quite heavy and has started to sag, I will try rotating the driver through 180 degrees to sort this. The cabinets are sealed cabinets so will see if the drivers move any better wen removed.

Is it possible that it is just the old cross over caps or are the drivers dead and how can i test the drivers?
thanks
Tom
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Old 6th October 2012, 07:48 PM   #2
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Location: Utrecht, Netherlands
Quote:
Originally Posted by tomst View Post
When pressed by hand it moves slowly and is slow to return
Do you have any complaints about the sound?

If the driver sits in a sealed enclosure that's normal, it means no leak.
I 'test' drivers with a 1.5V battery. You should see the cone move a few millimeters and you should not only hear 'tak' but some bassy sound as well.

A more thorough test is measuring TS parameters with ARTA LIMP (free).
If the rubber surround has dried you will find a rediqulously low Qms. And high Fs.

Last edited by Agent327; 6th October 2012 at 08:02 PM.
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Old 6th October 2012, 09:28 PM   #3
tomst is offline tomst  United Kingdom
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Thanks.
The second set (leak sandwich) that was scratchy and distorted is now working fine the bass driver has a bolt on magnet I took it off and cleaned it out then reset the postion so it moves free. I think a recap might do some good though, the caps must be 40 year old bipolar electrolytic.

Back to the first set Leak mini sandwich 15 Ohm elliptical driver The rubber surrounds are stiff (compared to modern) but i think they are suppose to be they are coated cloth by the looks of it (both sets have the same driver surround). The drivers are set in a seled cabinet. The problem with these is total lack of bass i was not expecting a lot but there is virtually non. The tweeter works fine.

"A more thorough test is measuring TS parameters with ARTA LIMP (free)".
I don't know what that means.

The driver resistances look fine all the connections look good. the drivers move in and out with out a problem. so to test the driver i desolder it and put a 1.5v battery aver the connections. +ve to +ve and -ve to -ve
thanks
tom
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Old 6th October 2012, 10:19 PM   #4
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Location: Utrecht, Netherlands
"Thiele/Small" commonly refers to a set of electromechanical parameters that define the specified low frequency performance of a loudspeaker driver.

LIMP - program for the loudspeaker impedance measurement and loudspeaker parameters estimation.

You need a pc with soudcard, an amplifier, a few connecting wires and a resistor. Everything is explained in the LIMP manual.

You can also measure the resonance frequency and Quality factor of the driver in the box so you have an idea how much/low bass to expect

It is fun to do. If you post your results here i am sure a lot of people on this forum can tell you if your bass drivers are damaged or not

ARTA Home

Cheers
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Old 6th October 2012, 10:32 PM   #5
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Quote:
Originally Posted by Agent327 View Post
it means no leak.
Sorry about that, I didn't know they were LEAK's
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Old 6th October 2012, 11:07 PM   #6
tomst is offline tomst  United Kingdom
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Just been playing some various different types of music through the leak sandwich (not the mini sandwich) using a Rotel RCD-965 and a Leak Stereo 30 plus both restored and modified/upgraded with the help and advice from people on this forum. Thank you. The combination is stunning.
I wonder what effect porting the cabinet would have. Interestingly these speakers have the tweeter attached to the speaker grill. I remember reading somewhere that the Spendor BC1's benefited from detaching the super tweeter or tweeter (cant remember which) from the baffle. Now i'll get back on subject

I'll have a look at that website and have a go see what I get from the driver on the mini sandwich, It'll be a while before i can get round to it. It's odd that both the drivers on the minisandwich seem to have the same problem? Total lack of bass. Makes me think I'm missing something simple.
Cheers.
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Old 8th October 2012, 04:59 PM   #7
tomst is offline tomst  United Kingdom
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Ok mystery solved. I had the speakers in buts tested them with the 1.5v battery. got the tac noise and a scraping noise (not the coil) when moving the wire over the battery contact. So redid the soldered joints then gave the contacts a good clean with some steel wool.
They work.
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Old 8th October 2012, 09:38 PM   #8
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Great!
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