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Old 27th December 2007, 08:04 PM   #1
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Default Modeling a Baffle Step Correction Circuit

Greetings,

Not sure if this is the right place, as my new custom speaker system doesn't have a full range driver in the Lowther sense, but I am using the Great Plains version of the Altec 604 Coaxial driver....

I need to install a BSC circuit, and based on a calculator I downloaded from Martin King's web site, specific values of resistors and inductors are indicated to achieve "X" dB of correction...The question I have is that the values don't exactly correspond to what is available, so do I get the closest match, or do I run multiple resistors and inductors in parallel to get the exact values?

It seems to me a close match would suffice, as I'm sure there's a +/- range for the actual corrected dB's, but I don't want to go through the process twice...

Also, I've read where the Erse inductors are a better option for a BSC circuit than the air core types, so would you concur?

Thanks a bunch!
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Old 27th December 2007, 09:19 PM   #2
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From what I have seen, you usually select an inductor between 3-4db of correction (works for most rooms with the loudspeakers against the back wall), then get various resistors and find what sounds best to you...

There is no "right" answer, it is purely subjective and dependent on various factors (room geometry, size, etc)...
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Old 28th December 2007, 12:00 AM   #3
Ron E is offline Ron E  United States
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Getting +/- 10% is good enough for any crossover/filter less than 4th order electrical. It just isn't that critical. It is important that they match quite closely left and right, however. You wouldn't want to use a 0.5mH in the left speaker and a 0.56mH in the right, for example.

High DCR in a BSC filter gets you insertion loss, which is usually not a good thing. Try to keep it at less than 5% of speaker DC resistance, and don't forget to account for it in box design.
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Old 28th December 2007, 04:45 AM   #4
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Thanks so much for the input.....I guess I'm working this backwords, as I used a tested design for the cabinet, however it was evidently modeled using a tube amplifier with high output impedance....Something that I'm completely unfamiliar with is the effect of impedance.....

Regarding DC resistance, how do I determine this metric, particularly regarding the components of the BSC circuit?

Thanks again!
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Old 28th December 2007, 09:51 PM   #5
jnb is offline jnb  Australia
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If your existing design was done competently, the BSC should have been incorporated into the crossover, even if it doesn't physically appear to be there. Of course, it's not always safe to assume. I doubt you'll be sure unless you measure for yourself.

If you do BSC, it will be affected by the character of the impedance curve, whatever that looks like.

If they have been designed on an amp with high Zo, your response might look like an inverse impedance curve. A little bass and treble should fix this.

I think you should first add a couple of ohms in series with your speakers and see if you like it.
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