Western Electric 1928 - WE 555 Dissect, Design, DIY??

[speaker dave]

Originally Posted by bear

Afaik, almost all the compression drivers operate below their fundamental resonance frequency when loaded with a horn. I find that a bit confusing, but iirc this is correct...

_-_-bear

Yes, I believe you are correct on this. The resonance is revealed in the impedance curve and can be more in the middle of the band.

We are fairly conditioned by our understanding of direct radiators, while horns are different. With a horn the air load is flat (for an ideal horn) rather than rising as it does with a small piston, and constant velocity gives flat radiated power.

Getting wider range out of a horn system still requires more than just a larger horn. Higher excursion with low distortion is still required from the compression driver.

David

[Bill F.]

Originally Posted by bear

Ron, I suspect the stiffness and the mass of the surround is an important design criterion?

Playing with my Hornresp model of a WE555 on a 15ft. expo flare, I noticed something interesting about the diaphragm suspension compliance. Once when I mistakenly had the compliance set two orders of magnitude too high (too soft), I found that it made hardly any difference at all in the system response.

The air load entirely swamps the effect of the diaphragm compliance up to a certain break point.

[myhrrhleine]

So, could we start with an off the shelf driver and go for maximum excursion?
Maybe maximum SPL @ 500 HZ?

[Hentai]

Because it operates below resonance, suspension has a more critical role in compression driver than direct radiators i believe.
If we look at the equivalent electrical circuit we can see that below resonance the driver is controlled by its suspension system. In my mind the best solution is to use mylar. It's also pretty easy to source Ti diaphragms with mylar surround.
Because the diaphragm is very hard to make at DIY level, i think design work should start from here. From available dia to work down to motor structure which can be made accordingly to the WE555.
Designing a phase plug for an available dia will take most of the time. I have found Axidriver to be a very useful tool. Example of a diaphragm/phase plug assembly below:


Parameters that need consideration once a diaphragm diameter is considered, are dome height and compression chamber height.
Although PP structure has evolved ( to better or worse results :P) i find Henricksen's paper a good start:
Henricksen_1978_Tangerine_PP.pdf

[bear]

the 555 does not use the "modern" slit type phase plug...

[Hentai]

yes, of course, my pic was just an example for the software. The WE555 type of phase plug (which is still common today i believe) can also be modeled easily adjusted to the shape of today's diaphragms.

[Alvis]

Wow Bear , this thread is really active.

[bear]

it's my fault/job?

[Alvis]

You catch on quick.

I really wanted to see this thread go somewhere, it is very interesting.

[DavidL]

How can what has already been beat to death go any further? Is anyone going to actually build a 555 type driver or is this just a mental exercise? After the previous 1000+ post thread I think everyone got what needed to be said ..........said.