Phenolic,Symbiotik,Pascalite Diaphragm

[Jimmy DIY]

Hi all,

Phenolic,Symbiotik,Pascalite, which diaphragm has a better performance at the 250 to 8000Hz in the 288's driver?

Rgds

Jimmy

[Jimmy DIY]

Hi Old Guy,

Thank you very much for your reply, can I use the Pascalite diaphragm in 288 down to 250 or 300Hz?

I have read the old topics and know that the Aluminum diaphragm not suitable to use under 500Hz, some people advised to use the Phenolic diaphragm(Altec 290 or RCA driver)

High frequence is not an issue because I am planning to use the 1003 or 1503 muti-cell horn, high frequrence drop over 8000Hz in this horn, I will add a tweeter to solve the problem.

Rgds

Jimmy

[Old Guy]

I'd have to ask what horns you are using? I HAVE used the Aluminums down to 300, but they certainly won't handle much power. The problem is the excursion. The diaphragm has to move so far to produce a longer (lower frequency) wave. So if you crank them, they will blow.

It helps to have a big horn like the 300 hz multicells. They actually take some of the work off the diaphragm. Compare it to a longer lever if you like. You can lift a heavy object with a smaller force. Ahat analogy will completely fall apart if examined too closely, I am only trying to make a point in layman's terms. Most of the newer small horns just won't work as well.

311-90's would be fine, or 329's if you could find them.

If I wanted to go to 300 LOUD I would use Phenolics. The tweets would have to come in around 6k however. The 290 is one of the best midrange drivers ever made. The 292 is simply an 8 ohm version without the big can on the back. The can was for a 70 volt transformer for paging use.

Later 290's were made in 4, 8 or 16 ohms.

You don't mention what crossover you are using for tweets. Some use only a cap, which is 6 db/octave. The tweets can come in a little higher this way, since they still will be producing appreciable energy at 6k.

If you want to cross at 8k 24 db/octave your best choice is probably Pascalites. They will hold up better at 300 than the aluminum. It will help if you use an active crossover and steeper 18 or 24 db/octave slope as this will reduce LF energy to the mid driver.

As you can see, designing a new system involves a lot of thought and homework. Good to see you are doing yours.

Any more questions just post away. With us old fellows getting us to shut up is often more difficult than getting answers.

[Old Guy]

Sorry noticed the note about the multicells after I posted. I'd try to find tweets you could bring in at 6-7k and use the Phenolics probably. As I said, you'll have to buy 290 series or the less common 292. 290's show up on Ebay, they often don't bring as much as the HF versions.

[Old Guy]

Hi Jimmy- if my info is correct the Phenolic will not fit. It fits only the 290/292 series AFAIK. Anyway they are only good to about 6k.

The Symbiotic is obsolete. This was used in the 291 driver. I don't consider it high fidelity. It has an aluminum dome but a Mylar suspension. It is OK for loud rock in a live situation, even then I would only use them if I already had them.

There are really only two diaphragms to consider for the 288- aluminum and Pascalite. Some say the Aluminum has slightly better highs. At best it's marginal. The Pascalite has a different alloy and a carbon fiber former, allowing it to handle more power. The aluminum should be considered for home stereo only. They blow too easily for live sound use. I use Pascalites. They sound good and last.

Hope this helps.

[Jimmy DIY]

Hi Old Guy,

Thank you for your sharing, it's seem the Pascalite is the best choice, may I know the crossover point of your system now? Are you still cross it at 300Hz same as the Aluminums as you mentioned?

And why the Phenolic not fit for the 288's? Are they use the same phase plug? Can I modify it to fit the 288"s? I'm interesting to know the different sound performance of the diaphragms with 288's. It will be a good experiance for a horn user and it help for tuning the timbre of the horn system.

I'm not yet buy the driver because I am looking for a driver which has the best performance down to 250Hz, the WE555 is good at this range but it roll off at 5KHz, WE594A is my dream driver, it has excellent performancd from 200Hz to 13KHz! but it is too expensive(US$2000 a pair)for me!

I'm now just have a pair of the German Alnico crystal tweeter(3k-30kHz 105db NOS from Germany). I trend to use a passive crossover in the beginning, the tweeter will be cross in frist order at 7-8KHz, I may be try the active crossover later.

The 311-90 & 329 horn is one of my choice, I will buy it if I can buy it in a reasonable price.

Rgds

Jimmy

[bfish]

Originally posted by Jimmy DIY:
Hi
.........And why the Phenolic not fit for the 288's? Are they use the same phase plug? Can I modify it to fit the 288"s? I'm interesting to know the different sound performance of the diaphragms with 288's. It will be a good experiance for a horn user and it help for tuning the timbre of the horn system......

<font size="2" face="Verdana, Helvetica, sans-serif">The phenolic diaphragm has a much heavier coil than the metal ones, the bigger coils require wider gaps. The top plate opening on 290s and 292s is machined to a larger ID than 288s, which is about the only functional difference in corresponding models (Tangerine plugs appeared in both around '76). Phenolic 'frams WON'T work in 288s. I suppose it's physically possible to put a 288 'fram in a 290 though, even if it fit, you'd give up the power handling of the 290, and the efficiency of both. For the more rugged duty down around 300-500Hz (Don't expect much around 250, even at 300 I'd still filter steeply), the 290 can take the higher excursions better, so you can EQ for good power response. Everything comes at a price though, the 290s fall fast after ~6KHz, though they're very clear and loud in that 4 octaves. The horn selected still has control of things though, and it takes some mass to control 300Hz and not ring, so my pick would be the 311, or maybe a well-made wood horn. Whether a 288 or 290 is a preference/requirement call, high SPLs or wide BW.

Installing the Pascalight 'frams in 288s would be my choice, ~same BW as aluminum and handles the rough stuff better ( lasts longer too ). I'd stress the steep XO and proper horn to take any of them to their lower limit, it isn't pretty when they unload from program material below the horn cutoff.

[Old Guy]

As bfish said, they just plain won't fit. there would be no performance increase if they would.


It's just a tradeoff- bandwidth vs power handling. Good engineering is often successfully managing tradeoffs.

[bfish]

250Hz (~4-1/2 ft wavelength) is below the rated BW of either driver, as it's below the Fs of both, not to mention below the horn cutoff of any 1.4" Altec horn I know of. Merely going to 300Hz shortens the wavelength about a foot. For comparison and response plots of both on a 329 horn, see;

http://alteclansingunofficial.nlenet...ers/TL_231.pdf

All I know about the WE and RCA drivers you named is that if I had a few I wouldn't have to work for awhile.

[Old Guy]

I would not recommend 250 even with the drivers you mention. Listening levels are much higher these days. I would not risk the diapragm damage.

I wouls suggest going 4 way. Subs, low mids, 299 with Pascalite, to whatever tweets you want. I would run low mids 80-500. Above about 100 0r so the bass starts to become directional. Subs should be crossed below that.

As an engineer that is how I would solve the problem. Less crossover points is mostly beneficial with passive xovers. With actives like a Beringer DCX 2496 it cures almost all the problems with passives.

A 4 way active system will tear your head off and sound good doing it.