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Old 8th November 2006, 04:44 PM   #31
VadimB is offline VadimB  United States
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Quote:
"Also, if you want to add this data to the port output, do not forget to scale the port data by the ratio of port diamenter to driver diameter squared.

How do i do that?
"
Assuming both port and driver are measured near filed, AT THE SAME LEVEL, your data show relative sound pressure at the microphone. Your Panasonic mic is very small, so it does not take into accound that driver has larger radiating area.
The overall SPL (sound pressure level) is proportional to the radiating area of the source. I guess the port is smaller than the driver. Than you have to lower the measured curve from the port by Delta=10*log(D port / D driver)^2 dB.

For example, say the effective diameter of your 4" TB is 3.5" and the ID of the port is 1.5".
Delta = 10*log(1.5*1.5/3.5*3.5)=-7.35 dB.

As soon as I wrote this, I started to doubt myself: do we have to multiply by 10 or by 20 here? I would appreciate a correction, if my memory failed me.

In any case, another good way of checking it is that at very low frequencies, say below 20 Hz the curves should coinside.

Important thing is that you should make these measurements as close as possible to the cone and the terminus of the port (no more than 5mm), and do not change the volume between the two measurements.

VadimB
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Old 8th November 2006, 08:06 PM   #32
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"Important thing is that you should make these measurements as close as possible to the cone and the terminus of the port (no more than 5mm), and do not change the volume between the two measurements."

I did.
But then its mathematics for the pro...
Now i know why i need that!
Keep going VadimB!
But dont brag for us stupid.


Learn us with example.

Solve
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Old 8th November 2006, 08:28 PM   #33
VadimB is offline VadimB  United States
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Quote:
Learn us with example.

Solve.
Solve,

I actually need your help to do just that. Earlier in this thread, I've posted an alternative design for 3" TB driver and promised to post measurements. I have screen shots from Sound Easy for that speaker, however they are large files with higer resoultuion. No matter what I do, the software of this Forum tells me that "attached file is too large".

Can you, please, teach me how to do this?

VadimB
P.S. If there will be some interest in that design - I'll start a new thread on it.
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Old 8th November 2006, 08:33 PM   #34
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Sorry! That user has specified that they do not wish to receive emails through this board. If you still wish to send an email to this user, please contact the administrator and they may be able to help.

?
I help you when you fix it.


Solve

Sorry for this mumbo jumbo.
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Old 8th November 2006, 08:56 PM   #35
VadimB is offline VadimB  United States
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Solve,

I just edited my options on the board. It should work now.

Thanks,

VadimB
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Old 8th November 2006, 09:53 PM   #36
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Dont work.
try this peter_fors.add.hotmail.com
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Old 14th November 2006, 08:43 PM   #37
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VadimB i cant email you?
Sorry for this folks...

Sorry! That user has specified that they do not wish to receive emails through this board. If you still wish to send an email to this user, please contact the administrator and they may be able to help.

Solve
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Old 14th November 2006, 08:53 PM   #38
VadimB is offline VadimB  United States
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Default Sorry for OT

Solve,

I've just openned all the doors there are on the "options" tab of my prophile. If this does not work, I'll have to contact the administrator. I've sent an e-mail to the address you gave (*.hotmail) last week. Did you get that?

Sorry for the bandwidth, folks!

VadimB
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Old 14th November 2006, 08:57 PM   #39
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Didnt get it.
Maybe an dot to much.
peter_fors(@)hotmail.com

Solve

(Sorry for this-have enough of spam)
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Old 16th November 2006, 05:41 AM   #40
VadimB is offline VadimB  United States
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Default Correction

Folks,

I've finally checked the DiAppolito book and, man, was I wrong!

The correct formula for correction of port-to-woofer is:

Delta (dB) = 20*log(D port / D woofer)

Diameters are not squared!

So, in the previous example (woofer 3.5", port 1.5"), the correction is:

Delta = 20*log(1.5/3.5) = -7.34 dB,

so the port near-field response should be lowered by 7.34 dB and then summed with the woofer.

Sorry, but it's better late than never...

VadimB
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