CROSSOVER calculation... - Page 2

AllenB · 29th May 2012, 01:57 PM

This 'classic' formula as you put it would be fine except for a few things, one is of course that the speaker impedance is not resistive. The sqr(2) is indicated for the phase difference between the reactance of a crossover inductor and a pure resistance. It will change when you use a proper impedance (measure or model).

There is a drawback to applying a simple inductor to a woofer in that they each rise with frequency and so tend to share the available drive, rather than one taking over as the frequency rises.

You could either adjust the impedance using compensation (with a resistor and a capacitor to make it behave more like a resistor), or you can move up to a second order filter. These will work better but none of the three options so far will be spot on, unless you either measure or properly model your impedance.

Then, the frequency response may not want to be rolled off at quite that exact frequency...

Tomom · 29th May 2012, 02:55 PM

Here is attached drawing of crossover...Will it work as expected? Sugestions appreciated...

system7 · 29th May 2012, 04:32 PM

Quote:

Originally Posted by Tomom

Here is attached drawing of crossover...Will it work as expected? Sugestions appreciated...

Well, knock me down wiv a fevver me ol' china, an' all that, but it's NOT BAD for something you worked out on the back of a beermat!

Very rough little sim with the 1.2mH W170S, but it does OK. I think you undercooked the Zobel a bit. 30uF just tames a 2dB bump at crossover. This is a freestanding speaker due to the big 2.5mH coil which boosts the bass a lot.

I couldn't get phase nearer than 40 degrees at crossover, but I wasn't trying on the midrange end at all. But mate, this approach seems a bit too rough and ready to me. You need better tools. Some drivers just don't get on together at all. You should tell us what they are.

Inductor · 29th May 2012, 05:03 PM

Quote:

Originally Posted by Pano

Does taking the voice coil inductance into account give you a rough idea of the impedance curve?

Is this your question (if I'm reading it correctly, I will read to the end of the thread), short answer is yes. Higher value inductance gives a more accentuated curve graph.

Inductor · 29th May 2012, 05:15 PM

Quote:

Originally Posted by system7

... You should tell us what they are.

Yes. It's like, "Tell us how to make crossovers in one day" without their correspondent drivers outputs and phases...

or frd's and zma's if you mind me.

Inductor · 29th May 2012, 05:33 PM

Here an estimate of a circuit simulation of a (lf) driver.

Tomom · 30th May 2012, 04:34 AM

Thanks everyone for inputs, it was helpful. I have attached diagram of my final work, please feel free to coment..

Also, I have attached relevant informations for those who were interested, of Midrange and Woofer... Also, Magnitude plot and Phase plot for crossover. I managed to achieve phase diferece between woofer and mid of 10" or just under, which I think is not bad at all,... Oscilloscpe show that sine waves are almost identical (of course, they have to be reversed in respect to each other, once speakers are in the box). If measurements inside the box confirm it, I will be very satisfied...

Tomom · 30th May 2012, 04:45 AM

Actualy, it took a bit more effort than back of beermat

, and longer than one day (inductor)

... Actualy, several months, from the day I received speakers, did some modifications to woofer (and small one to midrange), did measurements, etc...

system7 · 30th May 2012, 09:54 AM

I think you're being far too coy here, Tomom. I still can't visualise what you are doing at all. Is it all "Top Secret"?

This forum attracts a lot of people who are actually absolutely top in the field and have built some awesome speakers that are highly respected. I don't include myself in that category, BTW. To engage them, you have to be very straightforward.

3 way speakers are an interesting topic. Troels has published a couple of very nice designs along with good articles:
Poor Man'
3-Way Classic
High Efficiency Speakers

BTW, I think you may be missing a trick on that bass crossover. A little 1 or 2 ohm resistor on the bass capacitor can do nice things to phase, though the Zobel may affect that a bit.

Tomom · 30th May 2012, 10:23 AM

There is no "top secreet"; I noticed that formula from the book is giving me one value for the inductor, but it does not work in simulator and I have to change it, usualy by the value of the VC inductance. So I just wanted to know if this is the way to go, and why formulas do not mention that. I'm working on a three way system, 15" woofer, 6" mid and a tweeter. I am far from top in the field, but I want to do things to perfection as much as I can...

30th May 2012, 04:45 AM	#18
Tomom diyAudio Member Join Date: Dec 2010	Actualy, it took a bit more effort than back of beermat, and longer than one day (inductor)... Actualy, several months, from the day I received speakers, did some modifications to woofer (and small one to midrange), did measurements, etc...

30th May 2012, 09:54 AM	#19
system7 diyAudio Member Join Date: Aug 2008	I think you're being far too coy here, Tomom. I still can't visualise what you are doing at all. Is it all "Top Secret"? This forum attracts a lot of people who are actually absolutely top in the field and have built some awesome speakers that are highly respected. I don't include myself in that category, BTW. To engage them, you have to be very straightforward. 3 way speakers are an interesting topic. Troels has published a couple of very nice designs along with good articles: Poor Man' 3-Way Classic High Efficiency Speakers BTW, I think you may be missing a trick on that bass crossover. A little 1 or 2 ohm resistor on the bass capacitor can do nice things to phase, though the Zobel may affect that a bit. __________________ Good Night, and Good Luck. Best regards from Steve in Portsmouth, UK.

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29th May 2012, 01:57 PM	#11
AllenB diyAudio Member Join Date: Oct 2008	This 'classic' formula as you put it would be fine except for a few things, one is of course that the speaker impedance is not resistive. The sqr(2) is indicated for the phase difference between the reactance of a crossover inductor and a pure resistance. It will change when you use a proper impedance (measure or model). There is a drawback to applying a simple inductor to a woofer in that they each rise with frequency and so tend to share the available drive, rather than one taking over as the frequency rises. You could either adjust the impedance using compensation (with a resistor and a capacitor to make it behave more like a resistor), or you can move up to a second order filter. These will work better but none of the three options so far will be spot on, unless you either measure or properly model your impedance. Then, the frequency response may not want to be rolled off at quite that exact frequency...

30th May 2012, 10:23 AM	#20
Tomom diyAudio Member Join Date: Dec 2010	There is no "top secreet"; I noticed that formula from the book is giving me one value for the inductor, but it does not work in simulator and I have to change it, usualy by the value of the VC inductance. So I just wanted to know if this is the way to go, and why formulas do not mention that. I'm working on a three way system, 15" woofer, 6" mid and a tweeter. I am far from top in the field, but I want to do things to perfection as much as I can...