What variables need to be considered for crossover freq. and slope??? - diyAudio
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Old 8th March 2005, 05:42 AM   #1
swin1 is offline swin1  Australia
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Default What variables need to be considered for crossover freq. and slope???

I am building a 3-way speaker using a 10" woofer that plays from 28-2500Hz, a Vifa P11WH-00-08 mid and Vifa D19TD tweeter.

I would like to know what to consider in choosing the right slope and frequencies for the crossover. The response and impedance graphs are provided for the vifa drivers, however I have no such information for the woofer, and I understand the voice coil inductance, Le, is important and that figure is not provided. Is it necessary to test the woofer with software if I don't have the Le value?

Any insight into the design of the crossover post-knowing the slope and frequencies desired would be fantastic, I know a lot of questions are asked about crossover design and I hope I'm not repeating other peoples enquiries. I've just had a hard time getting my head around how to actually smooth out impedance curves and response curves for the drivers.

Basically I have the box designed and ready to go, now I need to design the crossovers. BTW I hope I can get away with a 12db/octave slope as I think the usable frequency range between each of the drivers is very high.

Thanks ~Andrew
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Old 8th March 2005, 08:23 AM   #2
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Measure!

All the driver's responses will be different now they are mounted on a baffle. This needs to be taken into account when crossover designing.

You have the right idea about picking smooth parts of the frequency response curve to use for crossing over, but you also need to take into account the smoothness of the phase and impedance curves, as well as any attenuation required to match levels.
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Old 8th March 2005, 09:21 AM   #3
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Also using active or passive can make a lot of difference to the design.
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Old 8th March 2005, 12:38 PM   #4
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Hi,
Regarding the woofer, measure the dc resistance of the voice coil, Re. Then connect a zobel network (R in series with C) in paralell with the woofer, making R=Re and choosing C in order to get a flat impedance characteristic, but you will allways need to measure !!!

The Vifa P11 has a smooth response, and I would try to cross it as high as possible, perhaps using a 1st order network (again, with impedance compensation). I dont´t know the tweeter, so I make no ideia how it sounds...

Final: Why not use an active crossover for the woofer ? It would solve a lot of problems...

Good work!
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Old 8th March 2005, 07:34 PM   #5
morbo is offline morbo  Canada
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You need to measure, then model. The response in-baffle will be very different than the published curves.
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Old 9th March 2005, 12:00 PM   #6
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What is the 10" woofer you are using.

I'd agree that an active for the woofer is going to be the best option.

If you find that active is not possible then design a crossover for the tweeter and mid just as you would for a 2-way with the mid allowed to roll off naturally at the bottom end as the P11's are smooth rolling off, then arm yourself with a bunch of inductors to try and blend in the woofer using a 1st order.

Have a look at your mid's response and look for where the mid is about 3dB down and use that as a starting point for your woofer crossover..... use about 7ohms (for a 8ohm woofer) to work out an inductor. Test, test and test.

You've picked a hard one but good luck and have fun with it. BTW, the P11 mid deserves an better tweeter than the D19TD IMO and a D27TG would be a better choice...... just an opinion.
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Old 10th March 2005, 05:28 AM   #7
swin1 is offline swin1  Australia
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rabbitz I am using the Jaycar response 10" woofer. Basically I want to build this setup with existing parts without having to buy new ones. I have a pair of jaycar response tweeters I wanted to switch out for vifa's to match the vifa mids better, but if I can get away with what I have with little difference I'll just stick with that. I don't have much specs on those jaycars though. I have also been under the impression that those tweeters aren't very good but I think thats due to stereotypical opinion. It's definitely going to be 3-way without the active woofer.

Thanks for everyone elses comments

~Andrew
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Old 10th March 2005, 12:11 PM   #8
rabbitz is offline rabbitz  Australia
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OK........ the Jaycar woofer is the CW2137? It's got quite a high sensitivity which could work in your favour for BSC if you crossover at about 350Hz or a bit lower for a 300mm wide baffle.

If you've got all those drivers, then that's what you use. You could try both tweeters and I think the Jaycar (CT2010) ones might out do the D19TD (have a look at the D19TD response which I never thought was correct as it looks more like a mid..... comments anyone on the D19TD as it has me puzzled).

Good luck and get into it.
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Old 11th March 2005, 10:00 PM   #9
swin1 is offline swin1  Australia
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Yeah thats the woofer I have! I think its a pretty decent one, and the PW11 starts to roll off naturally at 300hz so I wouldn't need to bother high passing it like you said, and just an inductor on the woofer. Although won't i need some sort of rumble filter lower down on the mid? Thanks...
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Old 12th March 2005, 11:32 AM   #10
rabbitz is offline rabbitz  Australia
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Just let the mid roll off naturally on the bottom as it would have a nice slope. If you need to roll off the mid quicker just put in a 50uF cap after the inductor.

Have you got a link to the data sheet on the P11WH?
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