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The "phenolic ring" tweeter - where did it come from?


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I was wondering if anyone knew anything this ubiquitous tweeter which in the 70s seemed to be used on dozens of different companies' loudspeakers, from entry-level models to respectable "Buick-level" speakers. I've heard them many times and never thought they sounded *bad* and quite a few times I thought they sounded quite good, if a bit on the beamy side as far as dispersion is concerned.

1) what company designed it?

2) what was the phenolic ring - sometimes black, sometimes reddish brown - specifically used for? Why not plastic or some other material?

3) was KLH's cone tweeter the inspiration for it?

I've seen these with small magnets weighing around only 3oz., and versions in better loudspeakers with heavy 8oz. magnets. I think some later models also included ferrofluid.

Until a year ago or so, I saw this tweeter on the PartsExpress site and it was built by Pioneer.

BTW: any thoughts on why cone tweeters fell out of favor? I realize domes are almost always better in most respects, but for 2-way systems their (relative) drawback is that their crossover frequency is usually much higher than the typical cone tweeter's xover point.*

Did speaker system manufacturers finally decide that the advantages of a dome tweeter outweighed its problems in a 2-way system i.e. being crossed over at a higher frequency, say 2500kHz which could affect the system's midrange output?

* I realize some domes had quite low xover points, like the one with the inverted dome made by Genesis in the late 70s/early 80s. I think it had a xover point at around 1500Hz or so.

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  • 11 years later...

Well I don't have definitive answers but here are some thoughts:

Don't know if they designed it but CTS made a lot (all?) of the originals.

Phenolic IS plastic

DK about any KLH inspiration

PE still has them (by GRS). They "had" some nice buyout specials with metal screen grilles but they had different characteristics.

Don't know about the other questions.

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  • 3 weeks later...
  • 2 weeks later...

Here is my CTS phenolic tweeters inserted in Fisher XP6 cabinet.
These tweeters are original USA, dated 75 03, have large ceramic magnet, brick color ring, black paper.
In the photos you see the flange built to adapt the tweeter to the original hole of the XP6 cabinet, the original dome tweeter.
These tweeters, purchased NOS before had been tested in an AR4x cabinet, where they adapt without modification to the original hole.

phenolic1.jpg

phenolic2.jpg

phenolic3.jpg

phenolic4.jpg

phenolic5.jpg

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  • 3 months later...

This is bizarre.  My friend has a pair of Ohm C2s that he bought back in college.  I believe he graduated in 1981, a couple of years after I did.  One of the mid-ranges on his C2s went bad.  He brought to someplace in Providence, RI to have it replaced.  Well we just pulled out his C2s about a month ago and the mid-range that was put in was not an original Ohm mid, but it looks EXACTLY like that phenolic tweeter.  I did some research on this thing online and a place called Simply Speakers still carries these for about 25.00.

But what the hell is it doing in my buddy's Ohm C2 as a replacement mid ???  Is it possible that some clown just popped it in there because it fit ?  I'm scratching my head on this one.  By the way, this replacement for the original mid took place in the early 80s, so the place that put the new "mid" in is long gone.

Just recently I bought a pair of pristine Ohm C2s for 300.00.  They already had the upgraded poly woofers so I ordered the upgraded mids and tweeters from the Ohm website.  Yes they are still in business and still in Brooklyn, NY.  And the President, John Strohbeen, even answers the phone when you call.  I since have found a pair of new, open box original C2 tweeters from a former Ohm parts rep up in Canada.  Never been used.  I like the looks of the original tweeters better so those will be going in.

As for that mid-range replacement on my friend's C2s that seems to be that phenolic tweeter thing.....I'm giving him one of my original C2 mid-ranges to replace that bastardized mid.  We will be putting that in tomorrow night.

I just joined this site, although I have read a lot of threads here.  And stumbling on this thread inspired me to tell this most recent speaker story....

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13 hours ago, Adamo0926 said:

As for that mid-range replacement on my friend's C2s that seems to be that phenolic tweeter thing....

Without seeing pics or specs for the drivers, it is hard to understand what this beef is about. The Ohm C2's midrange driver (see attached) - - which they refer to as a low tweeter - - is in fact some type of phenolic ring unit, according to their product literature. Simply Speakers and other sources sell various phenolic ring tweeters - - in fact, Parts Express sells a 2-inch PRT with a black grille (less than $7), which makes it look very much like the mid drivers used by Ohm. 

My understanding is that CTS first developed the phenolic ring tweeter; and soon thereafter, it was generically copied by other manufacturers (Marantz, BIC, etc). Even within a single manufacturer, all PRT's are not created equal - - I have an early cut sheet of some CTS drivers and within a variety of 1-3/4" PRT models, they have different magnet weights, voice coil diameters, driver depths, and power ratings. All of these have response range that begin at 2000Hz, but there is one 3" PRT that shows a response beginning at 1500Hz. The Ohm C2 calls their low tweeter a 2-inch driver, and the crossover frequency is cited at 1700Hz, so it seems quite possible to me that the Providence-purchased mid in your friend's C2's just might have been a suitable replacement driver that matched the original's characteristics , but without the protective grille. 

We would need to have more information to be able to make a final determination on this matter, but I did notice that there was no mention of deficient performance from the speaker with the replacement driver.

On 4/18/2019 at 2:56 AM, Giorgio AR said:

Here is my CTS phenolic tweeter

According to my CTS brochure sheet, the 2T8 tweeter has by far the heaviest magnet, at almost 8 ounces, and the highest continuous power rating at 10 watts. Response range is noted as 2000 to 20,000Hz.         

Ohm C2 .jpg

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Yes Ohm does call their drivers a high tweeter and a low tweeter.  So perhaps you are right and that mid that is in his C2s does the equal job of the original Ohm low tweeter.  I'd like to see what Ohm's low tweeter looks like without the protective grill.  I have a blown one here that came out of my C2, maybe I could pry the grill off it and take a look.

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28 minutes ago, Adamo0926 said:

I'd like to see what Ohm's low tweeter looks like without the protective grill.

That's exactly what I was beginning to get curious about. If you are certain that you have a dead one, it just might be worth a little exploratory surgery. Can you show us some comparative pics, including backside magnet and markings? If you do try to post pics, keep them small (100kb or so) and jpeg file format works well.  Here is the tweeter with grille I mentioned - - nominal 8 ohms, made in Taiwan. 

https://www.parts-express.com/rt-6-2-phenolic-ring-tweeter-with-grill-8-ohm--279-462

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Here is the tweeter from an Ohm E 2-way speaker. From what can be seen through the grille, it looks like a PRT. The same tweeter was used in the 3-way Ohm L, but there was a Mitsubishi supertweeter (sort of like the AR-2ax design of woofer-tweeter-supertweeter).

Ohm E tweet back.jpg

Ohm E tweet front.jpg

Ohm E front.jpg

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  • 1 year later...

Welcome John.

You can buy tweeters from Ohm https://ohmspeaker.com/legacy-products/b/

But if they are Phenolic Ring Tweeters (I'm not familiar with the Ohm B ) get them Parts Express https://www.parts-express.com/phenolic-ring-tweeter-replacement-for-ar-4x-cts-marantz-and-more-8-ohm--270-252

This thread on AK shows the B+ and it clearly has a PRT https://audiokarma.org/forums/index.php?threads/ohm-model-b.769954/

Kent

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Just now, JKent said:

Welcome John.

You can buy tweeters from Ohm https://ohmspeaker.com/legacy-products/b/

But if they are Phenolic Ring Tweeters (I'm not familiar with the Ohm B ) get them Parts Express https://www.parts-express.com/phenolic-ring-tweeter-replacement-for-ar-4x-cts-marantz-and-more-8-ohm--270-252

Kent

Tried to purchase from Ohm Direct They don't have them, was Hoping for a replacment substitute

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I was typing an edit. Try PE. PRTs are common so if your tweeter looks like a PRT (with or without a screen) you should be able to use the PE ones. Or check ebay for PRTs.

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