Speaker Asylum

RE: 6 - 7 octaves if you're into low fi...

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This Post Has Been Edited by the Author

In Reply to: RE: 6 - 7 octaves if you're into low fi... posted by villastrangiato on July 11, 2012 at 13:01:50

Hi,
> Operating a driver at frequencies where the wavelength is smaller
> than the driver's diameter results in frequency combing or destructive
> interference off axis. This is acoustics 101.
Indeed, had you ever progressed to acoustics 102 you could have noticed that your 101 version only applies to rigid pistons, which do not even exist in in Thiel & Patner / Accuton drivers.
So, acoustics 102 is to stop engaging with unrealistic oversimplified theoretical models and to engage with the real devices, something that based on literature I read in my misspend youth was quite common in German acoustics decades before I was born....
> If you wanna argue that fundamental point, go read some basic texts on
> acoustics or talk to the hand.
Look who is talking. I read those decades ago and actually spend time observing said rules in practice.
> "The D130 I mentioned is good to well past 6KHz!"
>
> The D130 was a 15 inch driver.
Correct. It also used a "NAWI" profile cone and a fairly soft paper for the cone. This has, invariably if we observe acoustics based on evidence, certain results.
> The wavelength at 6khz is about 2.25 inches.
And?
> If one were to cross that driver over to a tweeter anywhere near 6khz,
> there would be a very narrow dispersion pattern between 1500 hz and
> the crossover frequency. At the crossover frequency, the dispersion
> would flare out or as is commonly said in the industry- "bloom".
Surely, this would depend on a number of factors.
For example, given the driver does not use a rigid piston, we experience reducing radiation diameters with rising frequency. Of course the cones profile will still provide a waveguide.
So as long as we match the directivity of the 15" Woofer where it hands off to the tweeter we are likely in pretty safe territory. Now the tweeter commonly used by JBL "back in the day" was the 075, basically a 38mm ring radiator with a fitted waveguide that provided 40 Degrees -3dB beam-width from a few KHz to supersonic frequencies.
Unsurprisingly this fits the bass/mid driver very well.
Now you may be considering some Spam Skweek Darkenator or other HF driver designed and employed contra lex naturam as mate, ignoring the hopeless of any SPL match or any attempts of matching directivity, these are quite poor specimens to do HF.
Well, an uninitiated, ignorant novice may try such.
> This may be high fidelity to you. To me and the industry professionals
> I know, it's rubbish.
You expose nothing here than your total lack of understding basic acoustics, or a refusal to put them to work. Come on, we are talking > 60 years ago stuff here.
> All of the JBL drivers I've ever used were extremely well made, low
> distortion units.
So they are.
> But that doesn't fix a novice's poor design or misuse of a driver.
This I agree with completely.
Ciao T
Sometimes I'd like to be the water
sometimes shallow, sometimes wild.
Born high in the mountains,
even the seas would be mine.

(Translated from the song "Aus der ferne" by City)

Edits: 07/11/12

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