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Old 28th September 2012, 12:38 AM   #11
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Quote:
Originally Posted by soundwavesteve View Post
Definitely looks like I am buying the Dayton Audio DATS driver tester. It's probably best that I get exact measurements than rely on published specs anyway. Should be fun!
Unless you actually chart the T/S curves you will not have exact measurements. With the simple PE kit you'll be measuring on another part of the curve from where the factory measures, You will have the measurements for that driver on that part of the curve (there is a margin of error and the measures you take can change with the weather)

dave
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Old 28th September 2012, 12:56 AM   #12
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I use a 1mh steel core coil in parallel with a 4ohm resister, this goes in series with the 4" tb bamboo driver. Nice balance in a small vented box!

Larry
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Old 28th September 2012, 12:58 AM   #13
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Good to know...thanks.
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Old 28th September 2012, 08:35 AM   #14
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In MJKs models you can simulate the predicted response in your listening room based on various parameters. Then you calculate the BSC.
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Old 28th September 2012, 04:20 PM   #15
PKI is offline PKI  United States
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I'd like to start too, can you recommend the best book? It is bad, but I do not have time for tons of books... :-(
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Old 1st October 2012, 09:51 PM   #16
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Default Simulatio BSC

Hi soundwavesteve

I have done some simulations with MJKs models, and the filter as suggested by Emil Attlid is perfect. I have simulated a close listening position, and there is no doubt Emil know what he is doing

I have enclosed some of the plots, which are pretty close to the actual measurements.

Please note: Add 18 gram of stuffing in the cabinet (not the port) to smoothen the SPL.

Hi from
Bjorn
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File Type: pdf SIM01OCT12.pdf (166.3 KB, 12 views)
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Old 11th October 2012, 03:25 AM   #17
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Hey Bjorn and everybody,

I finally got my Dayton DATS speaker tester in today and began doing my own measurements. Plus I took some time today to check my speakers with test tones in the listening position.

First: the mfg specs list R(e) as 6.3 ohms, and my speakers measure 6.291 and 6.285. When I plug those numbers into a zobel calc or even when i do the calc myself, I get 7.8 ohms for the resister. Not 6.8 as Emil suggested.

So, I would assume that I should use the number that I got since it is accurate to my specific speakers. The rest of the Zobel calculation asked for L(e) [Voice Coil inductance], and my speakers measured .000974 mH at 1KHz. That works out to a cap of .015uF. Emil didn't even have a cap, and it almost seems like the number is so small as to be insignificant. What do you guys think?

Two: With no impedance comp or baffle step, just amp wired directly to speakers in the box, I measured the SPL with test tones and Audiotools on my phone, plus a radio shack meter to double check. From 100Hz to 700Hz, my SPLs measured between 67 and 74 db, then a big drop to 55 at 1Khz. From 1400 to 5000 Hz, its between 59 and 64db. With these measurements, it makes me wonder if I even need to build a baffle step - if I did it would bring down the 1400+ range even farther then it already is correct?

*note, these measurements where taken with a 23" LCD between the speakers (no gap) and with the speakers on stands 6" above a glass desk*

If I put back in the baffle step circuit suggested by Emil, everything above 700Hz or so drops even further by 5 db, which is why it sounded so dark and closed in....

Again I am very new to this type of in-depth experimentation, and perhaps it is very likely there is no simple or easy answer, but why does my own calculations differ so much from Emil's and the sim created by Bjorn? For example, the only way to get a suggested zobel circuit of 6.8 ohms is to have a speaker's R(e) be 5.45, a long way off from the published spec of 6.3 and my own measured 6.29....
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Old 11th October 2012, 11:12 AM   #18
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I don't use a zobel on a fullrange driver because it rolls off the top end, great for a midrange or woofer that uses a crossover though!

Larry
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Old 11th October 2012, 08:53 PM   #19
tvrgeek is offline tvrgeek  United States
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PKI, I recommend D'Appolito's Measuring Loudspeakers. It will be tough for a beginner, but if you study, think and measure, it will speed you along better than any book I have.

Steve, yes sims and measures differ. One reason is measurement is not that easy to do correctly and two, sims are only so good. Both are informative. As an example, I learned some time ago how important a large radius on the baffle is for managing diffraction. No sim I know of takes that into account.
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