Rejuvenate old SEAS Drivers?

Thanks Galu.


Excellent reference (blackcones).


The enclosures had fibreglass batts.
Not the nicest thing to have but as the boxes are sealed there's no port from which fibres can be blown out of.


I restricted doping to the surrounds only avoiding the cones themselves.
While doing it I found four distinct straight line tears in the surround of one of the drivers.


Two coats seem to have provided enough material to stop loss of air.
I'm doing some finishing touches on the crossover before I can assemble the second enclosure.


I hooked up the first enclosure and was satisfied with its performance from the little I play through it.


I prefer to wait until I have a pair before doing any more listening.


Your input has been invaluable to me.
This forum is a treasure of experience waiting to be uncovered.


Once again, thanks.


Cliff
 
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Just in case you missed it in post #14, here is the link which gives all the details of your 21 TV G drivers: BLACKCONES

Thanks G.

I finally completed the crossover refurbishment and the woofer doping instead of a radical refoam.
These speakers are really nice to listen too.


Only critical point:
At a high but reasonable volume for bass and treble I found the high notes are almost painful to the ear.
At this volume the tweeters aren't breaking up but just too loud for comfort.


Without resource to measure, could I conclude that the response is too great at the higher frequencies?

I'm using an old Marantz PM-6a Amp but would also like to try the Interdyns on other Amp to verify that it's not the Amp.

If they are too loud, would I compensate by adding a resistor before or after the Cap?


Thanks


Cliff
 
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Assuming the tweeter is nominally 4 ohm like the main driver, you could experiment by placing a 1.5 or 1.8 ohm resistor between the capacitor and the tweeter.

This will result in around 3dB of attenuation and will allow you to judge if your problem indeed lies with the tweeters being over sensitive.
 
Good advice from Sanislav there. Disconnecting the tweeter would be an easy way to attenuate it for experimental purposes!

The Blackcone is said to roll off smoothly after 5 kHz with a single break up at 8kHz. It's possible that it could benefit from some high frequency filtering. That's what Stanislav means when he suggests a 1st order series xover.

I can help you with that if if necessary.
 
Just a final report.
After doping the surrounds on the woofers, recapping, replacement of binding posts, and junking the fibreglass insulation with foam, These speakers are fabulous to listen to.
The Loudspeakers are Interdyn Model 212
These were made in Australia using SEAS drivers.
A 2 x Way design with 3.3mf Capacitor.
Woofer:SEAS 21T/-G 76-=12,210mm wide metal basket
Tweeter: SEAS 5 TV.HE 76-18, 35mm paper dome tweeter
Very enjoyable sound.

And thanks to all the contributors, they remain largely original.
:):):)
 
Hi Galu.
As recommended, I purchased a number of resistors of different value.
The exercise was held up due to family issues.
I went back to the speakers for a final test before experimenting with the resistors, and found that I couldn't duplicate the high end harshness.
I won't go into the detail but I've had issues with an intermittent blocked ear and the good ear might have become sensitive at the time.
After a medical visit blockage has been corrected and I have a new found appreciation of sound.
These Interdyn's sound great.
The can handle power without breaking up.
Reasonable bass.
Crisp detail across the range.
Nice highs without being harsh.
These are keepers.
Thanks to your great input, the surrounds remain original but also sound good. :)
 
Thank you for the update, Cliff.

However, I am left wondering how you addressed the "high notes are almost painful to the ear" issue you mentioned in post #22.

Hi Galu.

Sorry for my absence.
Have been swallowed up by the world.
Only recently have found time to tinker with Hi Fi things.

The Interdyns are still a little on the sharp side.
As discussed earlier I fitted a 1 Ω Resistor between the Cap and Tweeter. The resistor was tested and within spec before fitting.
I fitted the resistor on one of the Speakers and played around with left to right balance, then left to right balance with Reverse.

The result was that it killed the guitar riff on Brian Ferry Slave to Love.
Overall similar volume but neutered what I call the singing of guitar, whilst not eliminating the overly sharp sound.
The resistor has been removed.


I've just restored a pair of B&W DM110's.
The electrolytic caps have been replaced with Jantzen Cross Caps.
Cleaned up the boxes, fitted banana plug terminals and I'm still working on recovering the grills.
They've been an interesting A B comparison with the Interdyn Speakers.
Have been playing Dark Side of the Moon on CD using a Luxman DZ112 CDP, & Marantz PM-6a Amp.

Impressions:
The Interdyns have clarity while the B&Ws sound muffled in comparison.
The Interdyns are much more efficient, needing less volume.
The B&Ws don't produce high enough notes to hurt my ears, even at volume.
The Interdyns in comparison have very sharp highs even at lower volumes.

The Interdyn Tweeter (SEAS 5 TV.HE 76-18, 35mm paper dome tweeter) is currently fitted with 3.3uF Jantzen Poly Cap, but the Woofer (SEAS 21T/-G 76-=12) has no attenuation.

Do you think the overall sound might be improved if I fit Inductors to the Woofers?
I know without measuring and testing, it's guesswork, but what value Inductor would you recommend?

thanks Cliff
 
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As mentioned earlier, the Blackcones are said to roll off smoothly after 5 kHz with a single break up at 8kHz.

You did say you were happy with the treble: "Nice highs without being harsh", and now you say: "The Interdyns are still a little on the sharp side".

The sharpness could be due to the cone break up of the Blackcone at 8 kHz.

To deal with the cone break up, and to properly integrate the drivers, would require a custom built crossover network and full knowledge of the driver parameters.

If you wish to experiment in filtering off the high frequencies to the Blackcone by adding a series air cored inductor, then start with a minimum of 0.15 mH.

However, you may find that this does not solve your problem and, in fact, spoils the immediacy of the sound you enjoy with the current configuration.
 
Thanks for your input Galu.
It was some time ago, but I don't know how I concluded Nice highs without being harsh.
The sound is sharp and immediate but very strong causing discomfort to the ears.
They walk all over the B&W's, but I feel the sharpness makes them fatiguing to listen to.
Do you think that fitting a 0.15 mH air cored inductor has a low probability of rectifying the problem?
When you say the cone break up of the Blackcone at 8 kHz, do you mean that the Blackcone distorts above 8 khz?
 
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So is the cone breakup producing harshness at, and immediately around, 8 kHz, a design flaw needing significant intervention to reduce?


I was thinking that, due to the absence of Induction on the Woofer, that it might be competing with the tweeter. That this was causing the distortion??
 
P.S. If you read the link I gave you again, you will learn that the Blackcones are better than many modern speakers in terms of the smoothness of their roll-off and their breakup characteristics. So I think I am placing too much emphasis on that 8kHz breakup.

BLACKCONES

Also in the link, you can see the frequency response curve of the Blackcone (SEAS 21TV-G) and the low pass filter that Troels used with it.
 
Note also Troel's conclusion number 3.

3. The use of an extended range driver up to 5-8 kHz supplemented by a super tweeter has its shortcomings. Severe beaming is the result with congested treble and increased sibilance. When the wavelength starts approaching the diameter of the driver, we start having beaming. The single-cap people seems prepared to live with this, but to my ears an 8" driver shouldn't be used above 3 kHz.
Your Interdyn system is just that, an extended range main driver, supplemented at the highest frequencies by a tweeter which is high pass filtered by a single capacitor.

That takes us back to limiting the range of the main driver by using a series inductor which will act as a low pass filter.

A series inductor in the region of 0.22 mH should provide a reasonable roll off for the Blackcone - you can but experiment.
 
Cliff, note that I am now suggesting 0.22 mH.

Funny you should mention the B&W DM110 speakers as I have recently been given an unwanted pair in brown livery. I've done no more than check they are working, but they didn't sound too bad at a cursory listening.

My old Hi-Fi Choice 'Best Choice' magazine rates them as good value budget speakers with above average performance.
 

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Note also Troel's conclusion number 3.

Your Interdyn system is just that, an extended range main driver, supplemented at the highest frequencies by a tweeter which is high pass filtered by a single capacitor.

That takes us back to limiting the range of the main driver by using a series inductor which will act as a low pass filter.

A series inductor in the region of 0.22 mH should provide a reasonable roll off for the Blackcone - you can but experiment.
Hi Galu.

It's been awhile.
Hoping you can further advise regarding the Interdyns.

I have a couple of 0.23mH iron core Inductors (measure 0.22 mH) which might do the job, as well as a pair of 0.63mH Inductors which measure 0.53 on my meter.
Should I give them a try?
Do I splice them on the wire between positive Amp terminal and positive terminal on the woofers?
If the sound doesn't improve, are the 0.63mH Inductors (measuring 0.53) too far out to contemplate?

PS: How are your DM110's going?
 
Welcome back Cliff!

Yes, insert the inductor in the positive wire going to the Blackcone driver.

Both of your inductors are worth trying - only your ears will decide which, if either, results in an improvement.

I wired up the DM110s to a creaking old CD receiver which I use in my Man Shed for background listening to CDs or radio while I am hobbying. The speakers sound good in that role, and I have no urge to play around with the crossover components! ;)

I like to reserve my main system for serious and attentive listening, as well as avoiding unnecessary wear and tear of my thermionic valves!