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Old 22nd September 2012, 06:49 AM   #1
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Join Date: Sep 2012
Location: Michigan
Default Get me started....

Ok, I'm not new to speaker building or electronics in general, but I realize I am over my head at the moment and I need some help going in the right direction regarding crossovers.

One day a few weeks ago I decided to build some new speakers for my PC stereo system. I found a simple full range Tang Band 4" bamboo design here and decided to build it. I built it just fine, hooked it up and it made music...but it sounded so lifeless.....

So I began reading a ton of stuff about crossovers, theory, BSC, etc and I feel confident about what the problem is but I don't know how to fix it. Upon testing first and reading later, I figured out that the crossover (or eq + impedance comp) circuit that was created by the designer was meant for stand mounted speakers in a room with the listener seated several feet back....I am using this design on a desktop in a very nearfield position. When I disconnected the crossovers and ran straight wire, the speakers sounded alive again, though it lost some bass.

So, I humbly request help! I want to know how to design the proper BSC and impedance circuits myself for this application. How does one go about figuring out what circuit is required for a desktop full range speaker in the first place?
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Old 22nd September 2012, 07:22 AM   #2
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ah yes, baffle step is critical, isn't it ?

Here is an article using the fx120, notice the different values based on how much attenuation is needed.

Fostex FX120 DIY Bass Reflex Bookshelf Speakers

So long story short, the resistor in parallel with the inductor will need to be smaller, and the inductor a little smaller.

Adjust for your taste.
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Old 22nd September 2012, 10:13 AM   #3
ODougbo is offline ODougbo  United States
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Norm, what size wire would you recommend? 14 gauge Perfect lay coils?

SWS, might want to to buy a lager size and remove wire as needed.

(Resistors don't cost much, copper is expensive)
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Old 22nd September 2012, 04:18 PM   #4
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Another link to check out:
General Speaker Related Articles

Lots of good info on MJK's site.

Cheers, Jim
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A day without music is like a day without food.
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Old 22nd September 2012, 04:26 PM   #5
tvrgeek is offline tvrgeek  United States
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"Adjust for your taste."

One of the most astute comments you will see in this forum.
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Old 22nd September 2012, 11:30 PM   #6
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Thanks guys, lots to read there....

Two questions:

1. I was reading about the zobel circuits and I've got two different ways of doing it and I don't see how how MJK's version is accurate. MJK gives a formula based on the measured DC resistance of the voice coil. The other plays test tones through the speaker and measures resistance at each freq. Once you know exactly where the impedance is the highest, you can correct for it. How does MJK's version correct for impedance when you don't know what freq it's highest at?

2. It seems to me I need to correct for reflections from my desktop surface too don't I? What about my monitor? Since I know where they are and they aren't going anywhere, I can design them into my crossover can't I? Or am I being too complicated here?

Thanks again!
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Old 23rd September 2012, 07:22 AM   #7
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nope. i know someone who would design in a speakers crossover in the room the speakers were to be placed.

Inductor quality, I've no clue, but better caps usually sound better when using minimal component count.
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Old 27th September 2012, 06:43 PM   #8
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Any suggestions on reading material for compensating for desktop placement or having a monitor inbetween the speakers?
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Old 27th September 2012, 11:17 PM   #9
tvrgeek is offline tvrgeek  United States
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Only after you write one. This is DIY, Experiment!
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Old 28th September 2012, 12:43 AM   #10
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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!
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