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Old 7th May 2005, 02:22 PM   #11
sonu is offline sonu  India
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I couldn't get to the source,
please refer with a full link.

regards,
sonu
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Old 7th May 2005, 03:24 PM   #12
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Sonu:

Don't know what to tell you. The link should work.

Clicking the "Papers" section on Rich's home page should lead you to the following page:

http://www.readresearch.co.uk/HTML/papers.htm

I felt it was preferable to give Rich's home page, instead of the specific page, because Rich has all sorts of useful other stuff on his site you might wish to explore.
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Old 7th May 2005, 03:47 PM   #13
Wizard of Kelts
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Sonu:

A trememndous help seeing the relationship between the parameters is BoxModel, DOS freeware by Bullock and White. Available here:
http://www.hal-pc.org/~bwhitejr/

Caution: Ignore the Transmission Line section of this freeware, Bullock himself admitted it was inaccurate. But the rest of it is fine.

It might take a few minutes to learn to use the arrow keys and Enter key to input data, but it will be worth it.

Using this software, for instance, I can tell right off that speaker number 1 is way off on it's Vas. Why? Because DOS BoxModel tells me that if I input all these parameters, this is what I get:

Bl = 68.23 Tm

That never happens. The highest Tm's you usually see are 25 or so. So this is way off.
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Old 7th May 2005, 03:52 PM   #14
Wizard of Kelts
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By the way, I think I see where you went wrong.

Your Vas is given in liters-metric. Most programs use metric as the default. Dammit.

However, your Sd you listed as 190 square inches. Inches are now used mostly in North America. I think you took the 190 square inches and filled it in a formula as 190 square centimeters. An Sd that small would probably yield a Vas of 14.5 liters.

190 square inches equals 1187, (or 1190), square centimeters. Try putting Sd =1190 square centimeters in your calculations and see how it comes out.
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Old 7th May 2005, 04:11 PM   #15
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The Precision Devices PD2450 has a BL of 32.4 Tm.
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Old 7th May 2005, 04:47 PM   #16
Wizard of Kelts
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454Casull:

Thanks. That is quite high.

Now that you mention it, I think I might have come across a few Bl's of 28 or 29 or so, so I shouldn't be so surprised at one of 32.

I think you will agree, though, that 32 is only somewhat above 25, while a Bl of 68 is pretty far removed from what one is likely to ever come across.
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Old 7th May 2005, 04:52 PM   #17
Wizard of Kelts
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Sonu:

Just to illustrate, here is a screenshot of BoxModel using the parameters you gave us. forget about PE or excursion-for our purposes they don't affect what we are doing right now.

You didn't give Re, for an 8 ohm driver it is useally around 5.7 ohm, that's what I put.

For the dark blue area, we are only interested in the box under "Driver". The other boes have to do with enclosure measurements, which we don't care about right now. The parameters written under "Driver" are the parameters of the driver, in free air-no enclosure.

The way this program works is, we fill in our driver's parameters inthe "Driver" area inthe dark blue. Then the program calculates the other parameters and lists them in the light green area.

We cannot directly change what is written in the light green area. However, we can change what is written in the "Drivers" area in the dark blue, and that will change what is written in the light green area.

As you can see, if we fill in 1190 square entimeters-the equivalent of 190 square inches-the Bl goes up to 68. That is almost impossibly high.
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File Type: gif sonu's boxodel 2.gif (21.2 KB, 149 views)
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Old 7th May 2005, 04:59 PM   #18
Wizard of Kelts
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Now, if we fill in an Sd of 190 square centimeters, we arrive at a Tm of 10.8-a very normal Bl value. This is why I think you accidntally filled in 190 square centimeters for your Sd value, when it is actually 190 square inches-or 1190 square centimenters.
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File Type: gif sonu's boxmodel1.gif (21.2 KB, 128 views)
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Old 7th May 2005, 05:22 PM   #19
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Quote:
Originally posted by sonu
....a high value of QTS [0.78] is not good). IS IT THAT A HIGHER Total Q VALUE IS NOT GOOD, and I thought higher Q is better.
Depends. If this driver was to be used in a dipole construction, the Qts would be considered ideal. Used in a box-probably too high, unless the box volume is at least as large, or larger, than the Vas.



Quote:
Originally posted by sonu
i.e. - What effects the VAS, Qms, Qes,
A lot of things affect each other, but let me illustrate something.

Suppose you have an 8 ohm, 15 inch speaker with an Fs of 40 Hz, a Vas of 200 liters, and a Qts of 0.72. You would like to lower the Qts.

The formula for Qts is:

Qts = (Qes X Qms) / (Qes + Qms)

Now, if you do the math, you are going to find that for most values of Qes and Qms you are likely to run into, Qts and Qes are pretty close. So if you can get Qes to where you want it, Qts will not be far behind.

So, here are the parameters of the 15 inch speaker with the "high" Qts of 0.72, which we would like to lower. Note the Bl value and the Sns, (sensitivity) as well.
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File Type: gif boxmodel 15 in b.gif (21.2 KB, 126 views)
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Old 7th May 2005, 05:29 PM   #20
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Now, we increase the Bl by putting a bigger magnet on the speaker. Assuming the voice coil stays the same, adding a bigger magnet will do that. This cuts the Qes in half, which cuts the Qts almost in half.

As the chart indicates below, we just took the Qts down to about 0.38-a pretty normal value for a Qts, and one which allows you to use a vented tuning, if you wish.

We also increased the sensitivity by 3 dB-pretty nice.

We do all this, but the Fs and the Vas stay the same!

There are other ways to increase the Bl besides using a bigger magnet, but a bigger magnet is one way to do it.
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File Type: gif boxmodel 15in a.gif (21.6 KB, 126 views)
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