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Old 21st October 2003, 11:53 AM   #1
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Default need crossover advice-help

Hi, I've been here looking and reading posts for a little while now.

I am building a pair of two way floor standing speakers using no preset design. They are heavily braced and double wall thick mdf.

I was going to use a basic first order design for the crossover but thought it might be wise to get some advice here first.

I'm not sure if the drivers that i am using are a good choice but they are the ones I have and hope to use.
Please forgive the cut and paste of the drivers specs.



Scan speak
D3806/820000

Characteristic sensitivity (2.83V / 1m) : 90 dB
Recommended frequency range : 1 - 13.5 kHz
Free air resonance frequency, fs : 450 Hz
DC resistance, Re : 5.7 ohm
Voice coil inductance, Le : 0.04 mH
Effective piston area, Sd : 14 cm²
Moving mass incl. air, md : 0.90 g
Force factor, BL : 3.8 Tm
Excursion, lin./max. : ±0.4 / ±1.0 mm
Voice coil diameter : 38 mm
Rated power handling : 100 W (12 dB/oct.
cross-over at 1 kHz)
Net weight : 1.2 kg



Vifa
M21WJ-49-08

Nominal impedance [ohm] 8 SPECIAL FEATURES:
Voice coil resistance [ohm] 5.8
Nominal power [W] 80 Magnesium basket
Short term max power [W] -
Long term max power [W] - Excellent large signal
Operating power [W] 4 behaviour
Sensitivity [dB] 90
Frequency range [Hz] 25-3000 4-Layer voice coil
Free air resonance [Hz] 25
Voice coil diameter [mm] 32 Ideal for bass reflex
Voice coil height [mm] 13
Air gap height [mm] 6 Black coated paper
Voice coil inductance [mH] 1.7 cone
Eff. diaphragm Area [cm²] 139
Moving mass [g] 23.5 High damping rubber
Magnet weight [g]/[oz] 415/14.6 surround
Force factor [Bl] 8.9
VAS [l] 140
Qms 2.20
Qes 0.27
Qts 0.24


Thank you in advance for any advice that can be offered.

Mike
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Old 21st October 2003, 09:48 PM   #2
SY is offline SY  United States
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What's the diameter of the Vifa? If it's a 21 cm, that's probably a bit too large to interface properly with a small dome tweeter.

First-order networks for two-ways can be used in very special circumstances, with drivers specifically made for that, a skilled designer, and a LOT of compensation. Even then, you normally won't end up with something that acts the way you think it will- there's a big difference between electrical slopes and acoustic slopes. In your situation, I'd design with a higher-order filter.
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Old 21st October 2003, 09:55 PM   #3
Vigier is offline Vigier  Netherlands
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Short reply:

with those two together you can get a -3dB response from about 37 Hz to 13 kHz.

The scanspeak can be used from 1 to 13.5 kHz (I say 13 kHz).
You'll miss the highest freq's. I don't know whether that's a problem to you?

Grtz, Joris
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Old 22nd October 2003, 11:10 AM   #4
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Thanks for the replys.
SY the vifa is an 8" and the scan speak is a 1 1/2" tweeter-mid.

So would these be suitable for first or second order crossover?

Vigier, I never really noticed the 13.5kH limit before. It won't really matter with 30 years of using power tools the upper highs are long gone.
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Old 22nd October 2003, 01:35 PM   #5
SY is offline SY  United States
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My own preference in this situation would be to use a 4th order Linkwitz-Riley (acoustic!) at maybe 2kHz. The electrical crossover's order and design will depend on what the frequency response of your drivers is when mounted in your box.
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