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Old 9th November 2007, 08:53 PM   #1
JariV is offline JariV  Finland
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Default Need help with Martin Logan speaker

I own a pair of quite old pair of Martin Logan Aerius speakers. Seems that woofers have come to their end and needs to be replaced. Insted of ordering new pair of original woofers I would like to try replace them with aftermarket ones. Problem is that I donīt know TS parametres of original woofer. All I know are facts that it is 8" woofer in 23 litres sealed enclosure, with 89db/m sensitivity and has s 12db/oct crossover in 500Hz. What woofer you would recommed? Speaker is bi-wire able so I can use a separate crossover for woofer.
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Old 12th November 2007, 12:25 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

fortunately you do have some descent info on the speakers, see :

http://www.stereophile.com/floorloudspeakers/312/

The bass unit is used in its pistonic region so no special EQ.
It seems a standard 8 ohm 5.6R or so Re driver.
Changing the crossover would seem to be pointless.

Due to baffle step effects you do need a 89dB or so driver for
85dB midband, this implies 4dB of baffle step compensation.
(can be seen in the nearfield frequency response plots,
but this may not be true due to floor coupling of the driver.)

For a 23 litre sealed cabinet your choice is basically the Q and
Fb - box resonant frequency, the difficulty is finding an 8" driver
suited to sealed box loading rather than reflexing - now difficult.

TBH you should use the original replacement drivers, and then
there would be no need to second guess the driver parameters.
Ideally the nominal sensitivity of the driver needs confirming -
as described above this is difficult to judge without details of
the measuring conditions.

Have you considered the Aerius i bass drivers ?

/sreten.
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Old 13th November 2007, 04:49 AM   #3
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Not the solution you're looking for, but...

I'd love to get a hold of a pair of Aerius electrostat panels, and replace the box woofer with a dipole woofer. The stock crossover would have to be re-engineered, probably easiest to biamp. That removes any worries about efficiency matching, too.

What woofer to use? Beats me. If I had the 'stat panels, I'd try the 15" Hawthorne Silver Iris drivers I already own.

BTW, the inspiration for that setup is Finnish - the Gradient dipole woofers for the Quad electrostats. I once knew a guy with that setup, and it was very nice indeed.

Bill
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Old 14th November 2007, 02:58 PM   #4
JariV is offline JariV  Finland
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Thanks for opinons guys!

Yes I have consired to use Model i woofer, and I made a inquiry to ML`s service / Jim Power wich I havenīt got a reply yet.
Original Aerius woofers are available and costs about 180€ each here in Finland. I guess it would be easiest solution for it. But with that money one could get some up to date woofers also. One I was thinking about is this Scanspeakīs model. http://www.tymphany.com/datasheet/printview.php?id=95
Itīs sbout 200€ each. What you think about it?
The idea to use dipole woofers with bi amping and active crossover units is intresting. I have to think about it.
First I have to get Logans back from service. Other speaker has a problem with charging the esl panel. Or I hope it is only that. New panels cost ONLY 750€ EACH! Oh my god...

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Old 14th November 2007, 06:18 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

The current woofers need new surrounds ? can be done.

If bi-amping (keep passive c/o's) then more choice for
the drivers, as sensitivity does not need to match.

SS driver does look very usable.

/sreten.
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Old 14th November 2007, 08:55 PM   #6
JariV is offline JariV  Finland
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There is no any visible damage in woofers, but other woofer rattles a bit and gives a distorsion like sound. I presume that cone/surrounds are "tired" and it is not centering speaker in a rigth way anymore. In a very small volume the noise is not audible, but in normal listening level it is well noticeable. Would chancing surrounds help?
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Old 15th November 2007, 12:08 AM   #7
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Can you hear any noises when you push the cone in by hand (gently)?

I've seen voice coils come unglued/unwound/uncoiled due to overheating and then you can get a rattle/scrape sound . If it only partially came apart then that might account for noise at the extremes of travel.

Just a thought.
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Old 15th November 2007, 08:37 AM   #8
JariV is offline JariV  Finland
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Good point! I canīt hear any noise when moving cone by hand. When it is attahced to speaker and music is playing the scratching noise is again well audible.
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Old 15th November 2007, 08:37 AM   #9
JariV is offline JariV  Finland
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If it is so, can it be fixed? On the other hand I would like to update woofers anyway.
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Old 15th November 2007, 09:29 AM   #10
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Hmm. It sounds like your initial thought is right, the spider and/or surround is sagging due to age. Either way the prognosis is bad: either recone or new driver.

One last check might settle the question. Turn the speaker upside down and see if the scraping sound improves. This would theoretically apply gravity to correct the sag in the cone/voicecoil.

You have to push in the center of the cone when testing by hand. If you push on the side then you too are twisting the voicecoil in the gap. Alternatively, push the cone at various points around the circumference and see if it scrapes in one place.
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