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Old 12th April 2007, 02:23 PM   #1
RAYGUN is offline RAYGUN  United States
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Question Scan-Speak crossover help

I'm a first-time speaker builder, and a few years ago I purchased a pair of D2905/9900 Revelators and a pair of 18W/8545 woofers. I have long-since lost the crossover design I had intended to use. The Reference Monitor

http://www.audiocomponents.nl/speake...erence_eng.htm

seems to be an ideal speaker design, but it uses a 18W/8546 woofer instead of the 8545.

I'd be interested if anyone could inform me as to what changes to the crossover I would need to implement in order to use the 8545 for this speaker design? The only other speaker I've been able to find on the net using these drivers is at:

http://www.audiocostruzioni.com/a_d...n-revelator.htm

Any other suggestions would be appreciated as well.

Thanx
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Old 12th April 2007, 11:46 PM   #2
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There are several projects here:

http://www.troelsgravesen.dk/ScanSpeak.htm

Hope you find something helpful.

Specifically this?

http://www.troelsgravesen.dk/SP95.htm
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Old 13th April 2007, 12:25 AM   #3
tinitus is offline tinitus  Europe
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Different driver - but more specifically this one

http://www.troelsgravesen.dk/Amish_8545_9500.htm

But then a different tweeter but might only need different attenuation
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Old 13th April 2007, 03:47 AM   #4
Mingo is offline Mingo  Denmark
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Old 15th April 2007, 07:57 PM   #5
RAYGUN is offline RAYGUN  United States
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Thanks for your help everyone
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Old 20th April 2007, 02:11 PM   #6
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Default a Cross-over

Vance Dickason published a design for a Studio Monitor - LDC6 - in the 6th Edition of his "Loudspeaker Design Cookbook"which is for the two drivers that you have.
He gives several plots he measured of the drivers' responses and final system responses on/off axis, etc ...
It is very well worth reading.
I do not have the facilities to copy the article and post it here, and doing such may contravene his Copyright or that of the Publisher - Audio Amateur Corporation.
There has recently been a new 7th Edition of this book published, and several of the Mail-order sellers list stock.
From the description of added contents on Audio Amateur's own mail-order web-site :- www.audioXpress.com , the added chapter in the 7th Edition about loudspeaker cabinet diffraction, and apparently numerous plots are given of its effects likely including several of Dickason's methods of reducing such, would seem to make this book well worth owning.
I am presuming the LDC6 is still included in the 7th Ed. , but do email and ask "audioXpress" to confirm.

I will list the cross-over components and connections here for you now :-

For the woofer arm there is a series CR network of 10 uF + 1 ohm/10 watt connected in parallel with the 8545 for impedance correction, then a 3 mH inductor connected between the 8545's positive terminal and the amplifier positive connection.
Together with the 8545's own roll-off this network causes a 4th order filter slope.
In his calculations for the component values Dickason says he has included allowance for the Time Delay of the path length difference of the woofer being further from the listener than the tweeter is.

For the tweeter arm there is a 20 uF cap. connected to the 9900's positive terminal, then a 0.2 mH inductor connected from other end of the cap. to the 9900's negative terminal, and an 8 ohm/10 watt resistor connected to that CL junction. The other end of the 8 ohm is connected to an 8 uF cap. and the other end of this cap. is connected to the amp's positive connection.
Together with the 9900's own low end roll-off this network forms a 4th order filter slope.
The tweeter filter is basically a T shape.

The cross-over point is 2 kHz.

This is an often used type of cross-over and no more complicated than necessary. I am confident from all the measurements that Dickason has published as plots that this cross-over does work as he describes.

I have not constructed this Monitor myself, because I am more interested to use the Scan-Speak 18W8531 and D2905/9700 drivers, -{but I haven't bought those yet, nor worked out any crossover component values as I will need to make measurements on the drivers}.

I think this cross-over is worth considering as well as the other cross-over designs that Forum members have posted Links to, as each will have different audible effect - some-what subtle differences between some and more obvious difference between others.

best wishes,
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Old 21st April 2007, 04:37 AM   #7
Mingo is offline Mingo  Denmark
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Here is a link to the Vance Dickason project.
The woofer is the 18W8545K00, though.

http://www.partsexpress.com/resource...e/ldc6kit.html

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Old 21st April 2007, 07:39 PM   #8
Jonasa is offline Jonasa  Belgium
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Hi Raygun,

I've build the studio monitor from Vance that uses the same drivers as you want to use.
But I was not so very happy with the result. The midrange was not so spectacular for the price. Also the hights where to much into the front. When you listen a long time it was very fatigue. (the speaker has large bumps in the midrange)
You can read everything in my tread:"Closed box design:Scan Speak monitor"

But I've good news for you. I've worked more then half a year to improve the crossover. The result is very spectacular.
With the crossover from Vance the frequency responne has large bumps +/- 2.5dB in the midrange. Alse the phase is very poor.
I've my new design of the crossover ready on paper and it looks very spectacular. The frequency respons is +/-1 dB exept one small peak from baffle (reflection agains speaker frontpanel) and the peak above 10Khz but this is normal for the tweeter.

Also the phase of my new crossover is very spectacular. I've a deep null with reversed polarity more then 40dB. With the original studio monitor from Vance I measured less then 20dB

I'm going to post everything on my thread:Closed box design:Scan Speak monitor""in the comming days.
So you can look to my mesurements and my new filter design.

I hope I can build it soon.
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Old 22nd April 2007, 12:11 AM   #9
ttan98 is offline ttan98  Australia
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Jonasa,


flat response from any given x-over does not always sound good....this is not meant to be a critcism of your x-over...just an observation.

With respect to your x-over, you need to listen to it first and like the sound before recommending it.
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Old 22nd April 2007, 07:23 AM   #10
Jonasa is offline Jonasa  Belgium
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ttan98
Yes you are right, but I was a little bit to exited about my crossover because it looks so good on paper.
Ofcourse we will know it for sure if I've build it.
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