MJK Offset Driver simulation with PL-18 Help - diyAudio
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Old 16th June 2004, 07:27 PM   #1
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Default MJK Offset Driver simulation with PL-18 Help

Hi

I have played MJK Offset Driver worksheet with Vifa PL-18 measured T/S. Im using MathCad Explorer 8 so I can't save and post results

Could anybody plug values Im using in your WS and check any anomalies.

Farfield SPL Response plot is far outstanding, but Im not sure about the other plots.

Values Im plugging:

Driver T/S:

Fs= 38Hz
Re= 6.2ohm
Lvc= 0.99mH
BL= 6.69N/A
Sd= 132cm^2
Vas= 29 litre
Qe= 0.49
Qm= 2.9

Enclosure Geometry Definition:

L= 73in.
Epsilon= 4.in.L^-1
So= 3.375Sd
Sl= 0.44Sd
Density= 0.45Lb.;Ft^-1

In advance thanks for comments and assistance

JC
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Old 16th June 2004, 08:18 PM   #2
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>I have played MJK Offset Driver worksheet with Vifa PL-18 measured T/S. Im using MathCad Explorer 8 so I can't save and post results
====
Actually you can, though you can't change them. Save them as *.rtf files and open in whatever program you have that can, such as Word.
====
>Farfield SPL Response plot is far outstanding, but Im not sure about the other plots.
====
If a ~IB response in a relatively small cab is the goal then it's fine.

GM
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Old 16th June 2004, 10:33 PM   #3
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Thanks GM

Quote:
If a ~IB response in a relatively small cab is the goal then it's fine.
Its a tower enclosure. 42"x8.5" (1000x220mm) front baffle. Any thoughs?

Did you simulate with my values?

JC
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Old 16th June 2004, 11:40 PM   #4
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Tower/folded, it's still a small cab compared to an IB. Yes, how else could I tell if it had any glaring shortcomings? Whether it meets the needs of the app, I can't say. Don't know what sort of thoughts you're looking for since I don't have a clue what your performance goals are, the room, etc..

GM
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Old 17th June 2004, 06:46 PM   #5
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GM

Ok, my goal is IB response to fit speaker placement away from back wall due to room layout, good transient and so on.

Please refer to MJK "Upgrade Math Cad..." article from 6/06/00

1. Determing lenght and stuffing density: "Adjust so that first peak in ocoustic impendance occurs near driver resonant freq".

In my sim to get near perfect IB, "IB SPL response" plot, after lenght and stuffing adjustments, the resulting peak impedance is at 30Hz, against driver Fs of 38Hz. Is that a serious problem or harmful to driver?

2. I noticed its quite impossible to match resulting curves (red) to predicted ones (blue) in all plots. "Far field TL....", "Woofer and terminus velocity.." etc. What plots I have to focus on and what must be desconsidered.

Thanks again,
JC
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Old 18th June 2004, 03:59 PM   #6
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>Ok, my goal is IB response to fit speaker placement away from back wall due to room layout, good transient and so on.

====

Well, then expect output below the baffle step to sound very rolled off if you do not use a lot of BSC (lowered efficiency).

====

>In my sim to get near perfect IB, "IB SPL response" plot, after lenght and stuffing adjustments, the resulting peak impedance is at 30Hz, against driver Fs of 38Hz. Is that a serious problem or harmful to driver?

====

Hmm, with no stuffing I get a driver resonance of ~29Hz and pipe resonance of ~26Hz, then with stuffing, a ~18Hz Fb.

Anyway, drivers don't like to be loaded below ~0.707*Fs in a vented design, but this is an aperiodic loading so this is not an issue unless it runs out of excursion, which for this driver is around 125Hz if driven to its peak power rating.

====

>I noticed its quite impossible to match resulting curves (red) to predicted ones (blue) in all plots. "Far field TL....", "Woofer and terminus velocity.." etc. What plots I have to focus on and what must be desconsidered.

====

It depends on which of the various performance criteria is most important to you, though when a ~ IB response is the goal, far field and excursion plots are all you need to pay attention to.

====

>Thanks again,
JC

====

You are welcome!

GM
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Old 19th June 2004, 04:31 AM   #7
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Quote:
Originally posted by JC Fardo
G

Please refer to MJK "Upgrade Math Cad..." article from 6/06/00
How can I find that article? I searched here, and I googled, but I came up empty.
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Old 20th June 2004, 06:28 PM   #8
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Dave Jones

You may find here:

http://www.quarter-wave.com/Project01/TL_Sections.pdf

JC
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