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Discussion Starter #1
Hello Folks,

I would measure the Thiele & Small paramenters of my Behringer B1800D-PRO subwoofer without dismounting it.

Because the unit is brand new (under warranty) and because it is a 18" woofer that is anyway hard to handle, I would first try to measure the T/S paramenters leaving all in place.

I already precisely measured the enclosure net internal volume, the bass-reflex tuning tubes size, and I got an easy access to the loudspeaker wires (I can remove the embedded class-D ampli and have the loaudspeaker's wires in my hand).

Is it possible to do?
I don't need any extrelemy high accuracy, I am just curious to know these params and to try to simulate what it could be if I modify the bass-reflex tuning tube diamter and lenght, or what it could be if I close those.

Many thanks in advance for your help.
Kind regards,
Andrea
 

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Re: T/S params measurement of mounted loudspeakers

Why simulate? You can certainly measure speaker response with sealed port, and you can readily create port inserts that decrease its diameter, and increase its length. Additionally you can estimate internal volume of box, and measure existing port length and diameter. Ports effective length are always somewhat longer than the physical length do to laminar flow of air in port continuing beyond port for small distance, that is roughly proportional to diameter of port, I recall factor of roughly 0.6. Armed with this, and approximate effective diameter of driver (surface area), DC resistance of driver, you can plug into ported box calculator and fudge other parameters until simulation approximates measured performance. All kinds of fun exploration are possible.

Enjoy,

Andrew
 

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Discussion Starter #4
Dear Andrew,

my idea is to get the T&S params of my subwoofer loudspeaker and then simulte what could be possible to do with its enclosure.

In other words, I want to limit my modifications to the number (0 to 2) and size of the bass-reflex tuning.

I already measured the volume of the enclosure and the actual size of the tuning tubes.
I also have the current frequency response (here the graph):
behringer b1800d-pro current settings 20120804bis piccola.jpg
The internal enclosure volume is 125.3 litres
There are 2 bass-reflex tunig tubes being 14.5 cm in diameter and 25 cm long.

So, I was wandering if possible to get out the T&S params without dismounting the unit (very heavy to handle and critical to dismount - easy to damage something).

Many thanks again
Kind regards,
Andrea
 

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Sadly no, you cannot measure T/S with the woofer in-box. Think of it like back pressure changing the way the cone would travel versus being suspended in free-air. You need to measure T/S in open air with the driver all alone by itself.

To confuse things further, there is a single parameter (Vas) that can be measured by mounting the driver in a box of known volume. The box must not have any lining or fill, and must be sealed completely.

Measuring T/S with a driver in-box or measuring T/S on a completed speaker system is used for other things, like verifying port tuning and Qts and such.
 
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