Hello all,
First time poster, so please be kind and patient.
I've inherited a pair of Coral BX-200 speakers. They're going to be my first attempt at a refurb. However, one of the tweeters is blown, based on initial sound tests. Would anyone know where I could find a replacement? Or could I replace both tweeters with more modern ones?
Specs:
CORAL BX-200
Many thanks,
simao
First time poster, so please be kind and patient.
I've inherited a pair of Coral BX-200 speakers. They're going to be my first attempt at a refurb. However, one of the tweeters is blown, based on initial sound tests. Would anyone know where I could find a replacement? Or could I replace both tweeters with more modern ones?
Specs:
CORAL BX-200
Many thanks,
simao
you may give more datas to us
Hello Simao,
Few basic thoughts:
Before choosing a new tweeter, you should be sure than the specs of the link are real. Is it really 98 dB/w/m ? Is it exactly a 4000 Hz XO ? which slope (I bet for a first order often seen in old FR designs) ?
You are in the dark without measurements. Dayton audio has a little kit to measure the drivers specs. You can as well draw the filter shematic and with the marking on the filter caps try to check the crossover frequency with on line filter calculator. You will need to swap the caps of course if you beginn from the original speaker for a refurb.
Based only on the given link you may choose a 96 to 98 (or more) dB tweeter with the same form factor (dome if the original one is a dome, etc)
If no measurements, drawing the filter shematic, photographs of the drivers without the enclosures and name of the drivers (rear magnet marking?) if possible can help the Coral knowledgeable people here... but if you have the luck to meet a Coral enthusiast.
Giving you tweeters ref without more information is just a bet. 🙂
Hello Simao,
Few basic thoughts:
Before choosing a new tweeter, you should be sure than the specs of the link are real. Is it really 98 dB/w/m ? Is it exactly a 4000 Hz XO ? which slope (I bet for a first order often seen in old FR designs) ?
You are in the dark without measurements. Dayton audio has a little kit to measure the drivers specs. You can as well draw the filter shematic and with the marking on the filter caps try to check the crossover frequency with on line filter calculator. You will need to swap the caps of course if you beginn from the original speaker for a refurb.
Based only on the given link you may choose a 96 to 98 (or more) dB tweeter with the same form factor (dome if the original one is a dome, etc)
If no measurements, drawing the filter shematic, photographs of the drivers without the enclosures and name of the drivers (rear magnet marking?) if possible can help the Coral knowledgeable people here... but if you have the luck to meet a Coral enthusiast.
Giving you tweeters ref without more information is just a bet. 🙂
I've seen the pic of a Coral BX-200 speaker and the thing that sounds strange ( indeed it does sound strange ..) is the drivers mounted from the back of the baffle, this to make the grill flat. Also the LS5/2 or WTF referred to the popular two-way 😱 speaker mounts the woofer that way, but not the tweeter.
I'd suggest to mount both to the front.
MMhh talking about sensitivity and efficiency, the latter is specified for the woofer running full range.
A new tweeter and a new driver arrangement ( normal fron mount ) would require also a new crossover; so if you just put a coil in series, the sensitivity goes down because of the added resistance...but it would be 0.5 Ω max.
The decrease in sensitivity ( also efficiency, talking about BW ) happens because you cut the midrange by some dB's , allowing the tweeter to take over.
A tweeter with a wave guide would benefit for such mounting, it may also permit some 1st order filtering...
I'd suggest to mount both to the front.
MMhh talking about sensitivity and efficiency, the latter is specified for the woofer running full range.
A new tweeter and a new driver arrangement ( normal fron mount ) would require also a new crossover; so if you just put a coil in series, the sensitivity goes down because of the added resistance...but it would be 0.5 Ω max.
The decrease in sensitivity ( also efficiency, talking about BW ) happens because you cut the midrange by some dB's , allowing the tweeter to take over.
A tweeter with a wave guide would benefit for such mounting, it may also permit some 1st order filtering...
I would not rely on the data on the picture. It states the BX-200 got a 16cm (6") bass, response from 50Hz up and a spl of 98dB/W. That's physically not possible. I would assume the 98dB are reached at 15W, which would in turn come down to a spl of 87dB/1W, which is reasonable for the size of the driver and the given frequency range.
For a replacement: None of the Coral trancducers are available anymore, especally not pre-80s ones - the company went belly up around 30 years ago.
It is possible only the wires to the voice coil of the tweeter are burnt up and the vc itself is still intact. That can be repaired, needs a bit of skill though. If it's not possible to repair it, I'd suggest to replace it on both speakers. To find matching candidates isn't that hard, the high xo-frequency and very low power rating are very easy to match. For the latter: The speakers are very fragile. Very low power rating and the music of that time wasn't that bass-heavy as todays lead to them easily being overpowered, power wise aswell in excursion.
For a replacement: None of the Coral trancducers are available anymore, especally not pre-80s ones - the company went belly up around 30 years ago.
It is possible only the wires to the voice coil of the tweeter are burnt up and the vc itself is still intact. That can be repaired, needs a bit of skill though. If it's not possible to repair it, I'd suggest to replace it on both speakers. To find matching candidates isn't that hard, the high xo-frequency and very low power rating are very easy to match. For the latter: The speakers are very fragile. Very low power rating and the music of that time wasn't that bass-heavy as todays lead to them easily being overpowered, power wise aswell in excursion.
*shrugs* TBH, that was standard at the time. Ofcourse front mounting the drivers improves the dispersion a lot but given the age, it's not fair to apply modern standards. And - looking at the grill - I am not sure if it's easily doable. I'd try to make it perfect but it's not me who's doing it and I'd change as little as possible at the almost-antique enclosure.
and not to say that tinny alnico magnets had maybe suffer of too much driving/heating and lost their spec... so without measurement, time and money lost !
Dayton Audio DATS V2 Computer Based Audio Component Test System
Coral BX-200 | Audiokarma Home Audio Stereo Discussion Forums
Sometimes the best decision is to give up and invest in a brand new speakers. It's not because there is Coral written on it that it is Worthing the refurb. You may also like them with just the mid-woof FR unit for casual listening or TV speaker ?!
Dayton Audio DATS V2 Computer Based Audio Component Test System
Coral BX-200 | Audiokarma Home Audio Stereo Discussion Forums
Sometimes the best decision is to give up and invest in a brand new speakers. It's not because there is Coral written on it that it is Worthing the refurb. You may also like them with just the mid-woof FR unit for casual listening or TV speaker ?!
To me, these are not sacred treasures. But if they are worth something to a collector, they should be kept as original as possible. The magnets can be re-magnetized. But I totally agree, unless you're a die hard Corel fanatic, it's most likely not worth refurbishing them. More recent speakers will sound better in every regard.
A speaker that is mounted from the front and has no funky grill in front of it, is already modern. Also a crossover for both drivers is accepted to be an improvement. If you're not running in a competition, these can be everyday speakers.
Did I miss something? The LS5/2 was nowhere mentioned except from you, what got that to do with these speakers? The CORAL BX-200 got both speakers mounted from the back, you cannot remove the front grill. If you do, the optics and authenticity is destroyed. So, why do that and mount them from the front then?
Funny, in italian "re-furbishing" resembles the word "furbo" which means clever, but also tricky. So I repeat, why would anyone imitate a bad design ?
He does not want to imitate it. He got the original, he wants to refurbish them, do a restauration, a repair on them. I know, languages can be tricky but he nowhere even remotely mentioned to build it new after original plans. And he also nowhere says something about front mounting or LS5/2. Did you maybe confuse this for another/different thread?
I don't think a magnett and mostly Alnicos, can be re magnetised again if the curie point was reached. It will no keep the magnetism a long time. I know than a lot of brand are selling this service, but it's more a trap than anythingelse. Some cheap Alnicos were not sota made (bad melting and magnetisation process) as for instance Altec drivers which were famous for their bad Alnicos (due to their Alnico magnet provider at that time) with too low curie point which were aging bad if pushed too high (PA environments).
With a power rating of meager 15W I doubt you can even reach anything close to the curie temperature (>700 °C) or the maximum usable temperature (400°). Demagnetizing can happen though, if the speaker gets bumps, loss over time etc.. These aren't high energy AlNiCo magnets or critical in the motor strength, so a re-magneizing actually can help, even if you don't reach the full former strength. I doubt it's worth the effort though, I just wanted to mention it can be helpful and can be done if you want to get as close as possible to the original state.
So if the curie point were not reached there is no reason for demagnetisation with just the aging (but again vey bad Alnico manufacturing, so again doesn't Worth a magnetisation again if biased from the beginning: poles like to travel in a too short Alnico magnet as these old ones 🙂 )
Indeed there is more chance with 15W than the driver would had been broken over its XMech than the curie point reached !
We agree anyway, better to buy Something newer... than investing money in it.
Indeed there is more chance with 15W than the driver would had been broken over its XMech than the curie point reached !
We agree anyway, better to buy Something newer... than investing money in it.
Well, I should probably not have said 'over time'. Alnico can lose a lot of power because of the influence of other magnets (-> coercive force strength) but that also means, it's possible to re-magnetize them easier than other magnets.
Interestingly, the Curie-Temperature of Neodym is much lower (~310°) but are much harder to de-magnetize. Everything got always 2 sides. Neodym magnets are prone to corrosion, so if there are used ones, always look for intact surfaces.
But yeah, we agree, I wouldn't invest much, instead building something else, newer would be much more rewarding.
Interestingly, the Curie-Temperature of Neodym is much lower (~310°) but are much harder to de-magnetize. Everything got always 2 sides. Neodym magnets are prone to corrosion, so if there are used ones, always look for intact surfaces.
But yeah, we agree, I wouldn't invest much, instead building something else, newer would be much more rewarding.
I just don't agree about Alnicos to be magnitsed again : it's a physical non sense according to me, it's not just about curie point and not also because others magnets arounds but more each others South and North pole, the physical structure (form factor) how is melt and colded and mixed the magnet duri,g the process... As you say, just for giving you the last word 🙂 : does an ALnico like physical stress as a chock or loose of its structure : noooope !
Btw, if living in Asia perhaps : this one L Cao alnico matched full range speaker 8 inches pair ! | eBay is a copy of a the most famous FR from Japan which is costing some money today in Japan !
In the link, price is for a "matched" pair...
In the link, price is for a "matched" pair...
Well, think about it logically. If it can't be magnetized that way, then it can't lose the magnetic strength either because it's the whole time not melted. 🙄 Do you realize the error in your logic? Once the crystals are aligned, they do not move around anymore - that goes both ways, not only one. Everything what the magnet loses in strength afterwards can also be gained again.