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Old 5th November 2002, 05:35 AM   #1
palesha is offline palesha  India
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Default thiel small testing

There r two methods to check thiel small parameters. One is weight method & other is standard box method. Which is better or relable to do? I want to set up my own thiel small parameter set up. Is the test room required to be made soundproof? Any other suggestion for the setup will be appreciated.
Mahendra palesha
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Old 5th November 2002, 12:40 PM   #2
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Default TS measurement

I prefer the mass loading ( weight) method as it is easier. You can use Blue-tack or similar material which is freely available in the local market. You can weigh out the sticky material. I use one with 20gms and another 30gms. For large woofers I use them both. The results are quite accurate. If you do not have any design software you can use an Excel spreadsheet for this. You can find these on the net. One packet of Blue-tack ( or equivalent) usually has about 50 gms of material.

Which ever weight you use, split up the material into half and apply on opposite sides of the cone. To make it stick you should press it on to the cone while holding the rear side of the cone with your other fingers. This way you avoid deforming ( and possibly destroying) the cone. When you remove the blue-tack , it will come away clean and not leave any oily marks. If you plan to use the Buue-tack often, better make sure that it is applied with clean ( no grease) hands and that there is no dust on the cones. That way the Blue-tack will last a long time.
Have fun.
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Old 5th November 2002, 01:22 PM   #3
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The problem with the mass loading method is that you can dirturb the driver compliance while applying the mass, so make sure that the program you use for calculating the parameters can compensate for this. To minimize the errors, apply the added mass first, measure, then remove the mass and remeasure. The compliance is disturbed less this way, as it is easier to remove the mass than to add it.
The best way is to use the reflex enclosure method, which requires just one impedance measurement and optimization, but this technique is not widely practiced.

Andrew
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Old 5th November 2002, 02:03 PM   #4
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Default compliance?

Why would you disturb the compliance which is mainly the springyness of spider and surround?

Eric
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Old 5th November 2002, 04:12 PM   #5
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I've always like the standard box method. It's easy to find an old speaker box to use as a standard volume. You only need the same tools you need to make your speakers with. Unless you have a gram scale handy for other things.

Rodd Yamashita
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Old 5th November 2002, 05:11 PM   #6
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I always use a sealed box between 0.25 and 0.5 manufacturer Vas. I mount the driver from the outside and I add the volume of the driver hole and the volume of the cone. The box must be perfectly sealed (put adesive tape around the driver). A very small leak can affect a lot the calculated Vas especially if it is a small woofer. I never use a "sound proof" room since the software do not use a high power signal. I found the difference very very minor (error order).
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Old 6th November 2002, 12:46 PM   #7
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Many people on this forum haved raved about Speaker Workshop for Thiele-Small testing. I haven't been able to get it set up successfully, but those who have love this program.

It's freeware, you have nothing to lose.
http://www.speakerworkshop.com/

Good luck!
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Old 6th November 2002, 01:10 PM   #8
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I use speakerworkshop. This is one of the most crappy interface that I know of but once you followed the tutorial and did a lot of trial and error you can actually do some useful work. The most important thing is correctly calibrate the system.

Use the tutorial on the web, not the help file (this one is incomplete and you have to interpret and guess a lot of commands).

Even if it has a lot of disadvantage, the software works and it is free Believe me, doing all this work by hand reduce the fun of designing speaker (I did it few times).
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Old 6th November 2002, 02:32 PM   #9
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Eric, the compliance can be affected when attempting to attach the mass just by pulling and pushing on the cone as you attempt to get good adhesion to the cone. Maybe not so much if the drive unit has been well broken in first.
Additionally, depending on the cone strength, the mass can resonate on the cone and cause some errors in the fitting of the calculated impedance curve to the measured one. Finally, added mass can cause the suspension to sag and alter compliance and BL if the drive unit is measured facing upwards.
The added box method can work if the box is properly sealed, and the total volume known accurately. To this end, mounting the driver from the outside, facing in is the preferred way, as it is much easier to calculate the added volume of the cone to the overall box volume.
The vented box method is even better as you only need one measurement, not two!

Andrew
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Old 10th November 2002, 07:48 PM   #10
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Default Reflex Enclosure Method

AndrewJ;

Could you outline the details of taking T&S parameters with this method?
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