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Old 27th January 2013, 12:09 AM   #131
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Default Recommended texts for Nottolkien

Quote:
Originally Posted by Hentai View Post
The first recommendation would be my bible: Acoustics by Leo Beranek.
...
Papers published by manufacturers like JBL,EV or from people like Don Keele offer good information as well.
...
Yes, Beranek is the place to start! I like Olsen too.
Not too much published information on driver theory. Journal of the AES would be my second recommendation.
The JBL papers are helpful but seem to contain a few errors. At first I assumed that JBL was too reputable to have made these mistakes so I must have misunderstood, but eventually decided it was not due to me. Were the papers written by trainees while the real experts did the more important work on actual production? A little misinformation for competitors or just carelessness? There is a handbook by an ex-JBL employee that repeats some of these mistakes.
Don Keele is practically always excellent. The "horn mouth size" paper in JAES is fairly suspect but he is very open about the problems of such old papers.
I believe there are some works in Deutsch and Japanese that are excellent but haven't tracked these down yet.

Best wishes
David

Last edited by Dave Zan; 27th January 2013 at 12:13 AM.
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Old 27th January 2013, 06:44 AM   #132
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Default Harry Olson

Sorry, I misspelled. I recommend Harry Olson for some of the fundamental work on electro-acoustic transducers.

Best wishes
David
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Old 27th January 2013, 01:03 PM   #133
Hentai is offline Hentai  Romania
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VoiceCoil magazine had many articles with insights into driver manufacturing most written by Steve Mowry.
F. Fahy - Foundations of Engineering Acoustics, pretty indepth talk about how wave behave when traveling through different materials and shapes. A good study on mechanical and acoustical impedances.
There are many books, none gives a straight forward recipe for designing drivers (probably because there isn't or there are too many).
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Old 27th January 2013, 01:43 PM   #134
JMFahey is offline JMFahey  Argentina
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When I studied Engineering in the early 70's, in the whole Career there was only 1 "Electroacoustics" , which was basically learning Beranek's book, cover to cover.
The University library also had an old copy of Olson's book, which I kept for so long that they fined me.
Oh well.
There were also a couple other books, but mostly concerned with Architectural Acoustics.
What I found most useful were articles in British Audio magazines, written by real hands-on guys, such as the Fane Design Chief.
I remember a very clever trick (by Fane) on how to *actually* measure VC resistance increase with temperature, which directly indicated power handling (knowing adhesive performance vs temperature).
Mind you, they read it real time, while playing music !!!
I also read there fror the first time about epoxy-fiberglass formers, pioneered by them.
They were the first to achieve 100W RMS power handling (standard for Celestions, etc. was around 20/30W) *and* real 101dB/W/M efficiency.

When People asks me "what did the University give you" ? my answer is : "50% the formal training, 50% shared between free access to their Library and contact with bright people"
"You can find anything in the Net" is a myth; lots of info (the juiciest part) is NOT published, but can be found in real books and specialized magazines.
The IEEE publications are invaluable, but don't waste time on the "modern" ones, at least for speaker stuff; the best parts are in 50's and 60's magazines, maybe something in the 70's, but not further.
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Old 28th January 2013, 08:33 PM   #135
Hentai is offline Hentai  Romania
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True, thats the period of intensive research in the field. Nowadays R&D engineers have to give up space to copywriters, salesmen, so on and so forth... the known issues.

I had my mind on building instrument that can plot VC temp rise in order to use precise electrical models. Thinking of ways to measure the half-inductance parameters. I might get back on that.
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Old 28th January 2013, 11:39 PM   #136
JMFahey is offline JMFahey  Argentina
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Well, they were incredibly simple and clever.
Just quoting from memory (37 years ago ), they built an impedance bridge , similar to a Wheatstone bridge , and, watching the V to I phase relationship on a scope, they found a frequency at which the speaker phase shift was 0 , so it could be considered a pure resistor (at that frequency).
It was then easy to directly measure its DC resistance, while actually playing at high volume.
Knowing the copper thermal resistance factor, they could calculate the temperature in real time within 1%.
As a side note, it was a very safe power rating, because at that frequency (which usually was between 250 and 350Hz for a 12" speaker) the impedance was at its minimum (close to rge DC resistance value) and so the speaker was both the heaviest load for the amplifier and at the same time it received maximum power.
At any other frequencies, the reactive component worked as an attenuator.

Clever chaps.

And yes, that was a time of intensive research and they published papers about it.
I do not doubt that today there's research too, but it usually is kept under covers.
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Old 2nd February 2013, 08:20 AM   #137
Frank40 is offline Frank40  Denmark
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Hello again

I read some where at the membrane has to flex from the voice coil to the edge at high frequency, due to the low wave length. Is that relay true?..... The speed of sound in solid materials is much higher than air, this means a longer wave length. The speed of sound in solid materials is directly to the density of the material, more dens mean higher speed.

Here is a link that shows the velocity in different materials.

Material Sound Velocities / Olympus

Take care
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Old 2nd February 2013, 06:25 PM   #138
Hentai is offline Hentai  Romania
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Hi Frank, what you are describing is called cone breakup and will happen to all cone drivers.
Once wavelength is smaller than cone diameter, the cone will stop moving like a piston and wave will start traveling from the voicecoil to the outer edge of the cone and back. This so called flexing will cause some specific portions or areas of the cone to move out of phase with the voicecoil and this in turn cause dips and peaks in response.
A higher density material will be stiffer and will push this cone breakup frequency higher but usually its magnitude will be higher also. You will see many aluminum and kevlar cones on the market having a high peak in the 4-5kHz region.
It will need some care when designing filters and failure to do so might result in that sound some call "metalic".
Other manufacturers try to damp these resonance by adding a specific voice coil collar that attenuates the high frequency energy but to me it doesnt seem a natural process, solving something that could very well not be there.

Sound speed in paper how ever is very close to that in air and this probably is what gives this naturalness in timbre. Cone breakup still exists but not so evident as with stiffer materials and with proper cone termination much of the waves traveling through cone can be absorbed without adding mass to voice coil.
So as far as cone drivers are concerned for me there is no other material than paper .
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Old 3rd February 2013, 11:37 AM   #139
Frank40 is offline Frank40  Denmark
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Thanks Hentai, you sure know some good stuff. I have leaned allot from this thread... Thanks.

Some notes:

It was noted that the surrounding of the my unit was to thick, so I removed most of it. There was no audible changes ta all, (I have not access to any measure devices).

I added a aluminium cone to the membrane, this give a higher output at high frequency, more or less logical...... It increases the areal in the centre of the membrane. Buy the way the cone was made from the bottom of a beer can

I have decided not to try to make the unit without a spider.....due to the softness of the edge of the membrane. Instead I will bend the edge abut 90 degrees, to make it mechanical stiffer.

At the moment I am trying to make a wizzer with integrated voice coil. Here is some pic's.

Any new on your project Hentai.
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Old 4th February 2013, 04:07 PM   #140
Hentai is offline Hentai  Romania
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Hi Frank,

As test you can have a surround like that (if you are just testing high frequency) for low and mid frequency you need to have some kind of separation from the front side of cone to the back side of cone otherwise you will have shortcircuit.

I like your concept and the pictures, if you can make the whizzers like that from paper i want a pair.

Will update on Ryu soon.
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