Aluminum vs Pascalite diaphragms

[bigjunglejim]

Hi all...

I have 802?s, 902?s, 288G?s and 291G?s that need new diaphragms. I've been thinking of using Pascalite diaphragms in all of them. I?d like to hear from you folks that have had first hand experience with both Aluminum and Pascalite diaphragms. Is there are any differences in sound between the two?

I was told by Altec employees (when 299?s and Pascalite diaphagms were first introduced by Altec), ?the sound of the two diaphragms is identical?. I was also told, ?there is more difference in sound between production runs than between the two different types of diaphragms? and "if you do an A/B comparison, you couldn't tell the difference between the two". I was also told, ?the only reason Altec continues to make 288?s and Aluminum diaphragms was because some sound contractors refused to use anything but 288?s and Aluminum diaphragms?.

I love the sound of the Aluminum diaphragms in 802?s and 288?s but, the higher power handling of the Pascalite diaphragms is very attractive. IF there is a difference, I?ll stay with the Aluminum and use compressors and/or limiters. I like the sound of a two way system with 288?s better than a three way system using the Symbiotik 291?s with MR902-16HF tweeters (using the same woofers). BTW, this is for sound reinforcement. I know 288?s weren?t intended for SR but, they do SOUND GOOD in SR systems. I?ve never used Pascalite phrams myself but, I?ve liked the sound of 299?s in other?s systems.

[bowtie427ss]

I've never been able to do a direct aluminum to pascalite comparison as i sold my only 8ohm aluminum phrammed drivers a couple years back.

I now have 8 ohm pascalites (new from GPA) in 802-8G's/511B's on my A7's. The only comparison i've made is against aluminum loaded 16 ohm 806A's, there's very little if any difference using an 800hz XO point................... to my ears.

I do however suspect there might be an audible difference if using a 500hz XO as the pascalite (hardened aluminum) should be less compliant than standard aluminum, but that's purely a guess as i won't cross them that low for anything outside of low power tube amplification in my living room.

To my ears there's much more difference in sound between an 811 and 511 horn than there is between aluminum and pascalite phrams.

The pascalite phrams in 802's on 511's are the best sounding 1 inch altec combo i've heard to date, although i'm told that the same driver/phram on the 811 XO'd @ 1.2k with EQ/compensation is quite magical, i intend to try this recipe in 9844's this fall.

I'm sorry i don't have enough experience with large format Altec to comment. In my mind however, it seems that any differences in sound would be even more evident in the large format drivers.

just my sleepy eyed .02.....................

[Old Guy]

I've been conducting an informal poll among people I meet in person- so far it's about 7 no difference, 3 the aluminums have slightly more highs.

That jury would result in the case being dismissed if we were in court.
A personal reprt? Personally I would but Pascalites, if I wasn't 100%, I would play with a parallel R/C filter.. It will definitely make more difference than there is between the 'phragms.

Basically the whole thing is like EPA mileage statistics- they give you some idea, but you won't know till you buy the thing and drive it.

[bigjunglejim]

Old Guy.... You wrote, "I would play with a parallel R/C filter". What is a parallel R/C filter?

[bowtie427ss]

R/C = Resistor/Capacitor, sometimes called an EQ/compensation or EQ/attenuation circuit.

Seems these circuits were employed on some of the "finer tuned" altec systems from the factory.

Model 19's have them, and Altec made a couple stand alone versions too, the 30923 which is just a HF eq/attenuator network, and the 30904 which has the same HF components plus the addition of a zobel for flattening the impedence of the 411 and 413 woofers.

It's also apparent that they used parallel R/C circuits in a few other apps as well.

[bowtie427ss]

I should have elaborated with an explanation of the effect of these "filters".

They are not linear across the frequency spectrum.

If you can visualize a computer model or graphic representation, it would show maximum attenuation at or near the XO and slowly roll off as the frequency rises. This effectively smoothes or flattens, as well as extends the HF response.

This is a big part of the secret behind the superior sound of your 19's as compared to other similarly equipped Altec systems.

Just my interpretation of the riddle..........

[Todd W. White]

I don't think the difference is hearable in the 902 drivers.

Personally, I think it is BARELY hearable in the 288 driver (299), but only barely.

[Old Guy]

Originally posted by Jammin Jungle Jim:
Old Guy.... You wrote, "I would play with a parallel R/C filter". What is a parallel R/C filter?

<font size="2" face="Verdana, Helvetica, sans-serif">Jim I apologize- I should have elaborated.

Essentially in this case, a resistor in series with the driver. There is then a capacitor wired across the resistor. Below the filter's corner frequency, the power goes thru the resistor.. this attenuates the entire signal. As the frequency increase (in this example) more and more power goes thru the cap rather than the resistor. so it is passed rather than attenuated. The result is a power curve that has the power to the driver gradually increasing with frequency.

As Steve Mac so aptly put it, "boost" is a bit of a misnomer. What you have to do is attenuate the HF driver anyway since it's more efficient. So you are gradually bypassing some of that attenuation as higher freqs, resulting in a rising response curve.

Hope this makes sense- if not ask again and I'll try again.

To the engineering crowd- I'm leaving out things I know, just trying to do a class in sound 101.

[Steve Mac]

It just sounds funny when you say you take passive components and then say that something is extended. When you attenuate you decrease...ergo any effect using caps and resistors could never "raise" or add any high end. But I agree, and this is a term used in the recording world, that if you apply subtractive equalization properly, the net effect may yield a "feeling" of more high end. Or maybe I'm not understanding something here. I apologize in advance if this is the case.