Crossover frequence and sidemounted woofer - diyAudio
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Old 13th February 2012, 04:15 PM   #1
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Default Crossover frequence and sidemounted woofer

Hi

What are the rules for the crossoverpoint in a FAST system?

What crossover frequence?

How big/small the distance between the woofer and the fullrange?

What about if the woofer is on the side of the enclosure? Is there any thing different then?

If I use a 6" side mounted woofer how high can I cross it? And if I use a 10"?

Best regards

Uwe

Last edited by heinz1964; 13th February 2012 at 04:18 PM.
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Old 13th February 2012, 05:32 PM   #2
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I am thinking about a FAST system with the Scan Speak 10F for fullrange and a 6" or a 5" woofer on each side.

in what range should the crossover frequence be. How high can I crossover to the fullrange.

Is 300 Hz too high?
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Old 13th February 2012, 06:16 PM   #3
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by heinz1964 View Post
I am thinking about a FAST system with the Scan Speak 10F for fullrange and a 6" or a 5" woofer on each side.

in what range should the crossover frequence be. How high can I crossover to the fullrange.

Is 300 Hz too high?
We found that 330Hz worked just fine in a little 2-way with Fostex FF85K and single CSS SDX7 - but to a great extent it depends on the upper mid bass performance of the woofer - if it's smooth enough, you can simplify your total XO, possibly even down to a simple 1st order HP cap for the fullrange. Mind you at those frequencies, the C value can be high enough that a quality film cap can cost as much as some budget full-range drivers, and make bi-amping with passive line level XO far more appealing. (and what self-respecting DIYer doesn't have a few spare amps kicking around ? )
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Old 13th February 2012, 06:24 PM   #4
Swifty is offline Swifty  Netherlands
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You should cross before the side mounted woofer goes from 4 pi radiation to 2 pi radiation, in other words, before the frequencies are high enough for the baffle to start reflecting them. so the deeper the cabinet, the lower you will need to cross. you can calculate the f3 of this point by dividing 11600 by the baffle width in cm. Example: the side the woofer is on is 35 cm wide. 11600/35 = 331.

In this example you should at least cross below 331 hz, preferably at least 100 hz below this point, depending on the order of the filter. Bear in mind that the scan speak should not be crossed much lower than 300 hz or so. So depending on the width of the woofer baffle you might need to either use a very steep filter or look at a different full range driver.

I am actually in the middle of a very similar project, using the Markaudio Alpair 7.3 and a Seas L26ROY. I am using active class D amplification with DSP filtering. This makes crossing very low a lot easier. The Alpair also alows for a lower crossover point than the scan speak.
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Old 13th February 2012, 07:27 PM   #5
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Originally Posted by chrisb View Post
We found that 330Hz worked just fine in a little 2-way with Fostex FF85K and single CSS SDX7 - but to a great extent it depends on the upper mid bass performance of the woofer - if it's smooth enough, you can simplify your total XO, possibly even down to a simple 1st order HP cap for the fullrange. Mind you at those frequencies, the C value can be high enough that a quality film cap can cost as much as some budget full-range drivers, and make bi-amping with passive line level XO far more appealing. (and what self-respecting DIYer doesn't have a few spare amps kicking around ? )
When using such small drivers for the upper frequencies, I'd go steeper than 1st order. Even when driven by a mere 15w Tripath amp, the excursion on the smaller driver hit ~3mm p/p. This was with a 2nd order filter. In order to preserve some dynamic range, I'd make the crossover steeper, and, if possible, higher still.
I'd agree with a first order electrical crossover for the woofers, though - BSC and all that jazz.

Chris
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Old 14th February 2012, 07:14 AM   #6
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Default asymetric sidemounted woofer

Hi

Thanks a lot for the replys

Swifty - What if I mount the sidemounted bas asymetric, not in the middle of the side but closer to the front of the speaker? Does that change anything?

Best regards

Uwe
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Old 14th February 2012, 07:29 AM   #7
Swifty is offline Swifty  Netherlands
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Originally Posted by heinz1964 View Post
Hi

Thanks a lot for the replys

Swifty - What if I mount the sidemounted bas asymetric, not in the middle of the side but closer to the front of the speaker? Does that change anything?

Best regards

Uwe
No. The 4 pi to 2 pi transition is a result of the width of the baffle. It does not change with the position of the driver on the baffle. An assymetrical position on the baffle would help with a better ripple response in the 4 pi to 2 pi transition range but in case of the side mounted woofer the whole issue is to cross below the point where this takes place.

Last edited by Swifty; 14th February 2012 at 07:45 AM.
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Old 14th February 2012, 10:21 AM   #8
Tyimo is offline Tyimo  Hungary
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Quote:
you can calculate the f3 of this point by dividing 11600 by the baffle width in cm. Example: the side the woofer is on is 35 cm wide. 11600/35 = 331.
Where is the 11600 came from?

Tyimo
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Old 14th February 2012, 11:34 AM   #9
Swifty is offline Swifty  Netherlands
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See here

This link shows the calculations expressed in inches (4560 divided by baffle width in inches). Multiply by 2.541 to get to the number I gave: 2.541 * 4560 = 11600 (close enough anyway)
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Old 14th February 2012, 04:12 PM   #10
Tyimo is offline Tyimo  Hungary
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Thanks!
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