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Old 13th May 2004, 12:33 PM   #1
sonu is offline sonu  India
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Default measured thiele para

I am a novice with a whole lot of questions, so please bare with me.

I am a electronics engineer 6-5months back i designed a amp & Subs for my brother who's a DJ, fine the amps are perfectly working since then.

Basically i made 12" woofers on my own but could not measure the thiele parameters so couldn't design the boxes, did a guess work, and luckily those subs also sounded good.

As I always like to design perfect things, I searched the website for measuring thiele para, and found it on ESP Site. After measuring the parameters i found the following.
VAS - 75.19l
Fs - 54Hz
Qts - 0.870
Qms - 5.750
Qes - 1.020

Now I simulated this on WINISD but couldn't come to a conclusin what enclosure size, what fb to use and port size, please suggest me the best ported design I could do with this driver.

Now one more thing I wanna know as how to select a best driver i.e. what parametrs i should look for when selecting. so that i can improve my driver on that basis, what all affects the change in VAS, Fs, Q etc.

Regards.
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Old 13th May 2004, 01:36 PM   #2
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That Qts of 0.870 makes life difficult in a reflex box! Using WinISD beta 0.44 the best I could get was 343 litres and 41.7 Hz. You could go all-out and try a 6th order bandpass with the rear chamber 400 litres at 35 Hz and the front chamber at 100 litres at 70Hz.
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Old 14th May 2004, 07:47 AM   #3
sonu is offline sonu  India
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OK but I wanna know as how to select a best driver i.e. what parametrs i should look for when selecting.
As i have made this driver on my own, I want to know what all affects the change in VAS, Fs, Q etc.
Cause now i am making an 15" Driver, so i will select cone, coil, frame and magnet which should give a good thiele parameter as needed.
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Old 14th May 2004, 07:51 AM   #4
sonu is offline sonu  India
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OK but I wanna know as how to select a best driver i.e. what parametrs i should look for when selecting.

As i have made this driver on my own, I want to know what all affects the change in VAS, Fs, Q etc.

Cause now i am making an 15" Driver, so i will select cone, coil, frame and magnet which should give a good thiele parameter as needed.
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Old 14th May 2004, 08:37 AM   #5
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Do you want to say you were building it up from scratch ?

Regards

Charles
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Old 14th May 2004, 12:10 PM   #6
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For a bass reflex box, I like a Qts of 0.5.
Lower values give a droopy response; higher values give a big peak before they roll off.
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Old 15th May 2004, 02:44 AM   #7
Ron E is offline Ron E  United States
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look here:
Diy dynamic driver

for a spreadsheet tool I posted that helps you figure out where the Thiele-small parameters come from.
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Old 15th May 2004, 03:31 AM   #8
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WinISD Pro from http://www.linearteam.dk/ is a great tool.

When selecting a sub driver for PA, make sure you have: high power handling (>500W), high sensitivity (>90dB/W@1m), relatively low Fs (less than 35Hz), etc. Qts depends on what kind of box (or lack thereof) you'll be putting it in.
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Old 15th May 2004, 11:00 AM   #9
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Building or selecting a driver for a reflex box?

Here is a good place to start.

The Classic Reflex Box, so named by Thiele and Small, and the term was accepted.

Basically, a driver with a Qts of 0.38, (or 0.4, it's okay to round off), goes into an enclosure equal to it's Vas, is tuned to it's Fs, and gets flat response down to it's Fs.

Example A:

Driver A has the following parameters:
Fs=30 Hz,
Vas =60L,
Qts=0.38, (or 0.4)

The ideal box is 60L, tuned to 30 Hz, which gives flat respnse down to an F3 of 30 Hz.


Example B:

Driver B has the following parameters:
Fs=42 Hz,
Vas =40L,
Qts=0.38, (or 0.4)

The ideal box is 40L, tuned to 42 Hz, which gives flat response down to an F3 of 42 Hz.


Reflex boxes work well with Qts ratings other than 0.38, of course. Actually, they work well with Qts ratings between 0.25 and 0.5. As a rule of thumb, with Qts ratings below 0.38, the ideal box will be smaller than the Vas, tuned higher than the Fs, and have an F3 above the Fs.

Drivers with a Qts higher than 0.38 will have ideal boxes larger than the Vas, will be tuned lower than the Fs, and have an F3 below the Fs.

But the Classic Reflex box of Qts=0.38, box volume equal to the Vas is a good place to start.

Anyway, build or locate a driver with a Qts between 0.25 and 0.5, and come back to us and we will show you how to build a reflex box specifically designed for that driver.
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Old 27th June 2004, 08:01 AM   #10
sonu is offline sonu  India
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Thanks all who responded for the support
Now I have made a good 12" driver whose Fs is as low as 26Hz, and it sounds very perfect in a 45liter ported enclosure. Although its vas has increased, and has a Xmax of 14mm.

Regards,
Sonu.
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