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Old 22nd October 2008, 01:26 PM   #4581
gedlee is offline gedlee  United States
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Quote:
Originally posted by Kolbrek

I view it like this: the horn throat impedance forms the load for the compression driver. For steady-state simulations, the average complex throat velocity and pressure can then be found if we know the throat impedance, the parameters of the driver, and the input voltage. Changes in the throat impedance will be reflected in the throat velocity, diaphragm displacement, electrical impedance and so on, so there is a coupling.

-The parameters for the waveguide (throat diameter and angle, length from the throat to where the mouth radius starts, and the waveguide angle [theta0])
-The end areas and length of the internal driver flare, including the phase plug, and if the flare is conical or another shape
-The driver parameters, at least Sd, Bl, Cms, Rms, Mmd, Le and Re
-The volume and size of the rear chamber
-The volume and size of the front chamber

I assume the mouth flare radius is 4 inches, as per your earlier posts.

Best regards,

Bjørn

Yes, the above procedure works, but you just can't assume that the complex throat velocity is independent of the load for a real device, especially at or near the lower cutoff. That was more my point. The resonance that you show presents a large load which reduces the velocity of the driver - an effect not shown in your simulations.

The throat of my larger waveguide is 1" and has a 6 degree entrance. It goes to 45 degrees to a mouth that is 15" in diameter. There is a 4" radius at that junction. Hence the radius would start at 5.6 " from the throat and end at the baffle which is at about 7" from the throat.

The drivers internal flare has to be estimated, but should be close to 1" at the open end, a 6 degree conical section about 2" long, but it could be a little shorter than that. I don't have an exact model of the DE250. I could measure it and get you those exact numbers but that would take some time. I have a model of a typical driver - lumped parameter they are all close to the same. My estimate for the DE250 would be:
Sd = 15 cm^2
Bl = 1.8 Tor
Cms = 1.7 x 10-7 m/Nt (approximately)
Rms = 1 ohm (also a guess)
Mmd = 15 grams (a decent guess)
Le = .11 mH
Re = 6.3 ohms
The volume and size of the rear chamber = just consider this as part of the diaphragm compliance
The volume and size of the front chamber = this is also hard to get, but you can assume that it is about Sd x 1mm = 1.5 cm^3 or less.

When you use these parameters you can adjust them from the simulated impedance curve versus the published data from B&C or your own measurements. I will do that too when I get a chance to see how eell they fit.


I thinks thats all you need.

Thanks - looking forward to it.
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Old 22nd October 2008, 01:38 PM   #4582
Kolbrek is offline Kolbrek  Norway
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Thanks, Earl!

I'll start working on it. It may take some time, though, as I need to do some changes in my SW.

Bjørn
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Old 22nd October 2008, 09:01 PM   #4583
phi is offline phi  Sweden
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Good spirit, Earl, Bjoern!

This is what this forum should be all about, pushing eachother and exchanging ideas. Like it !

Thanks for a good thread Lynn!
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Old 23rd October 2008, 04:25 AM   #4584
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Forums like DIYAudio are one of the treasures of the Internet.

In a corporate environment, with very few exceptions, it's "Not Invented Here" combined with "My Way or the Highway" - as a result, innovation is constrained more by internal politics that physical cost constraints. Tens, even hundreds of millions of dollars are wasted on projects to feed the egos of managers who think that a magic box like a Powerpoint compiler really exists.

There are CEO's and managers throughout corporate America who are confident once the Powerpoint presentation is dreamed up and pitched and sold, the hard part is already done. The wreckage in the military, diplomatic, financial, and economic spheres is mute testimony to the quality of managerial "thinking" - if it can even be called that - over the last decade.

Although we are more heavily cost-constrained than the corporate world, there are no MBAs, managers, marketing directors, magazine reviewers, or a legacy base of customers to satisfy. Thus no reason we can't outperform commercial products, once we leave behind "DIY is only for beginners or cheapskates" mindset.
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Old 23rd October 2008, 05:53 AM   #4585
infinia is offline infinia  United States
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Quote:
Originally posted by Lynn Olson
Forums like DIYAudio are one of the treasures of the Internet.

There are CEO's and managers throughout corporate America who are confident once the Powerpoint presentation is dreamed up and pitched and sold, the hard part is already done.
Yes nicely said!
I've been there when the VP's typical pitch to the troops after the sale, "Now all we have to do is execute". Sometimes I think US management is in different world and language to go with it.
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Old 23rd October 2008, 06:53 AM   #4586
Kolbrek is offline Kolbrek  Norway
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Earl,

The driver parameters look a bit odd - but perhaps I'm using the wrong units? I ran a lumped parameter plane wave tube simulation with these parameters, and the response is in the form of a sharp spike at 3.1kHz.

So just to make sure:
Bl = 1.8 Tesla*meters
Cms = 1.7 x 10^-7 meters/Newton
Rms = 1 Newton*second/meter (or should it be electrical ohms?)

or did you use other units?

To me, both Bl and Cms seem to be too low. The values above gives a driver with a Qes of over 500.

Best regards,

Bjørn
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Old 23rd October 2008, 08:44 AM   #4587
Jmmlc is offline Jmmlc  France
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Hello Bjorn,

a MMd of 15grams fro the DE250 seems to me an indecent guess.

I am using according to Kinoshita a Mmd value of 1.6 grams for my model of TAD TD2001.

Best regards from Paris, France

Jean-Michel Le Cléac'h



Quote:
Originally posted by Kolbrek
Earl,

The driver parameters look a bit odd - but perhaps I'm using the wrong units? I ran a lumped parameter plane wave tube simulation with these parameters, and the response is in the form of a sharp spike at 3.1kHz.

So just to make sure:
Bl = 1.8 Tesla*meters
Cms = 1.7 x 10^-7 meters/Newton
Rms = 1 Newton*second/meter (or should it be electrical ohms?)

or did you use other units?

To me, both Bl and Cms seem to be too low. The values above gives a driver with a Qes of over 500.

Best regards,

Bjørn
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Old 23rd October 2008, 09:30 AM   #4588
Kolbrek is offline Kolbrek  Norway
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Quote:
Originally posted by Jmmlc
a MMd of 15grams fro the DE250 seems to me an indecent guess.
I tend to agree, especially considering that the Beyma 102Nd 10" paper cone driver is specified with a moving mass (possibly including air load) of 33 grams.

From other data I have seen, typical moving mass for 1" compression drivers seems to be in the 1-2 grams range. Perhaps it should be 1.5g?

Bjørn
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Old 23rd October 2008, 12:27 PM   #4589
gedlee is offline gedlee  United States
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Quote:
Originally posted by Kolbrek
Earl,

The driver parameters look a bit odd - but perhaps I'm using the wrong units? I ran a lumped parameter plane wave tube simulation with these parameters, and the response is in the form of a sharp spike at 3.1kHz.

So just to make sure:
Bl = 1.8 Tesla*meters
Cms = 1.7 x 10^-7 meters/Newton
Rms = 1 Newton*second/meter (or should it be electrical ohms?)

or did you use other units?

To me, both Bl and Cms seem to be too low. The values above gives a driver with a Qes of over 500.

Best regards,

Bjørn

Bjorn - I checked on the moving mass and that was a typo, its more like 1.2 grams. Compliance would then be about 2 x 10^-5. See if those numbers work better. I got the flux data from the B&C website and that number is just the flux density not BL. BL would be more like 18. Sorry for the mix-up.
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Old 23rd October 2008, 12:43 PM   #4590
Kolbrek is offline Kolbrek  Norway
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Thanks Earl, that looks better.

I attach the resulting lumped parameter PWT simulation resulting from this. Does it makes sense?

I have included an internal driver flare, per your suggestion 2 inches (5.08 cm) long, 2.54 cm exit diameter (S=5.07cm^2), and a 1:10 compression ratio, giving a start area of 1.5cm2.

Bjørn
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File Type: gif de250_pwt.gif (11.8 KB, 709 views)
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