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-   -   sealed vs. ported (http://www.diyaudio.com/forums/multi-way/56724-sealed-vs-ported.html)

sonu 5th May 2005 06:18 PM

sealed vs. ported
 
Please help me which could perform better between the two drivers & why (explained) for pro use,

Thiele Para of driver 1- 18" Driver - 8Ohms
FS- 31.38
VAS - 14.44 L
Qes - 0.849
Qms - 9.809
Qts - 0.781
SD - 190 in^3
Inductance - 1mH
Power Handling - 800W

Thiele Para of driver 2 - 18" Driver - 8Ohms
FS - 23.17
VAS - 118.3 L
Qes - 0.408
Qms - 5.538
Qts - 0.380
SD - 170 in^3
Inductance - 2mH
Power Handling - 600W

As simulated in WINISD the first driver shows its best to be used in sealed, but can i use it as ported, if yes what would be the disadvantages of using the driver recommended for sealed, is used as ported enclosure.

The first driver is tested in a 2.8Cu ft sealed enclosure, it has a very good clean tight bass

454Casull 5th May 2005 06:35 PM

A Vas of 14.4L?

richie00boy 5th May 2005 06:40 PM

Resonance Frequency (Fs), Q of the resonance peak (Qts) and Volume of Air Equivalent to the Suspension Compliance (Vas) are the key parameters to how it will sound. Linear Excursion (Xmax), Surface Area (Sd) and power will give you an indication of how loud it will go.

The first drive unit I would guess is cheap as Qts is high. There is no way it will work in a vented box. I am certain that the value you have given for Vas is wrong as it's far too low for that size of drive unit.

The second drive unit can be used in either a vented or sealed box as Qts is about a medium value. I'd choose a vented cabinet as it would get a bit deeper and louder, but the box will be a bit larger and harder to make. Fs is low so bass will be fairly deep. Again though, Vas looks on the low side.

I would recommend measuring the parameters yourself once you get the drive unit as they can differ a bit because of tolerances and you can't always trust how well the manufacturer measured them.

sonu 6th May 2005 09:56 AM

I HAVE READ THAT ONE SHOULD AT LEAST RUN THE DRIVER FOR HALF AN HOUR TO FREE THE SUSPENSION BEFORE MEASURING THE DRIVER.

The parameters given are tested by me with SW. The magnet design for the first driver is a T yoke design with fem, 1.7T in the gap, how can we get the BL.

richie00boy 6th May 2005 10:21 AM

To break in, half an hour is not enough IMO, a few hours is needed.

I think your method of measurement of calculation of Vas is going wrong somewhere. Both those figures are too low, one massively so.

You can measure Bl by applying an accurately known weight to the cone and measuring how much current is needed to bring the cone back up to the original position, then plugging this data into a formula. I'd concentrate on getting your basic parameters right first though.

sonu 6th May 2005 10:29 AM

I am testing the driver with a 2.8Cu ft sealed box.
Is there anything you can suggest to as how to know if it is correct.

ashok 6th May 2005 11:14 AM

Driver 1 .....
 
Hi Sonu,
What make is that driver No1.
Fs about 31Hz and Qts of 0.78 . Are you sure it is 0.78 .
Where in Mumbai is it available and how much did it cost ?
Thanks,
Ashok.

sonu 7th May 2005 01:38 PM

Ashok its made by me, with a T-Yoke and 30mm deep magnet structure to get good Xmax, Coil design- 35mm length and achieved a lower inductance of 1mH, and tested it with 600W, continious load for 2Hours.
I have tested it in my sealed test box of 2.8Cu ft, its performance is ultimate, but i dont know how good is the performance by knowing the thiele para (like in previous message by richie00boy a high value of QTS is not good). IS IT THAT A HIGHER Total Q VALUE IS NOT GOOD, and I thought higher Q is better.
The gap is also very tightly set, and as per my knowledge it's should definately perform in its best.

Can you please help me how to interpret about the design by the thiele para's.
i.e. - What effects the VAS, Qms, Qes,

richie00boy 7th May 2005 01:57 PM

High Qts is bed because it indicates poor inherent damping within the driver. So high Qes is poor electrical damping and high Qms is poor mechanical damping.

You might like to read through the papers by Thiele and Small on my website www.readresearch.co.uk in the 'papers' section.

kelticwizard 7th May 2005 01:57 PM

Sonu:

You're basically asking for a course in loudspeaker building.

For the engineering minded, the basic parameters and what affects them are explained in the papers by Aussies Richard Small and Neville Thiele-these are the famous Thiele-Small papers from which we get the famous Thiele-Small parameters.

As stated previously, Richie00boy has these papers downloadable for your convenience at his wonderful website:
http://www.readresearch.co.uk/

If you want to know how the Thiele-small parameters work together, an excellent explanation is given by David Weems in his excellent book Designing, Testing and Building Loudspeakers. It is written for the complete novice to get him started, but the explanations are great.


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