Crossover Help/Opinions

[DerrickM]

Hi everybody,

I'm getting ready to build some crossovers, and was hoping somebody would be willing to look at my schematic and let me know if everything looks okay.

I have some Dynaudio mids (MW162) and some Seas 27TFF tweeters. Using the Dynaudio X250 xovers as a starting point, I'm planning on going 2200Hz/6dB on the mids, and 2200Hz/12dB on the tweeters.

The impedance correction (22uf cap and 4.7ohm resistor) are right from the Dynaudio spec sheet.

I'm also planning to put an lpad in there for tweeter adjustment--for $8 each it seems easier and more flexible than individual resistors.

Attached is the current schematic--it's not pretty, as I'm no Visio expert. (The crossover point is wrong--it's 2200Hz, not 1200 as it's shown).

Thanks,

Derrick

PS - Some of you might recognize this issue from my post in 2005. Been busy starting a family, so getting this last system issue resolved hasn't been high on my list... LOL

[owdi]

You have no baffle step compensation in your woofer filter... will this be a 3 way?

Dan

[DerrickM]

I have no idea what a baffle step compensation is!

These are 2-ways, in the rear of my car.

[zega55]

The crossover is to low for that tweeter by my opinion. I would put it more to 3khz. Do you have a tweeter with lower free air resonance this one has 1200 you should get one with 700hz by my opinion . That 8ohm lpad is for changing the speakers impedance if it is then the crossover point is changing and you are attenuating the tweeter by changing the resistance on lpad. You need a normal resistor so the tweeter impedance is set to a constant number and then calculate the crossover.

[DerrickM]

Hi. That's what I was afraid of. I was hoping to be able to use a shallow slope, but with the small overlap from 2k-4k, I guess I'm going to need to go 12dB on both sides somewhere closer to 3k? (The specs on the tweeter were taken with a 12dB slope at 3.5k).

Ironically, the crossover I have now is at 3.5k (as I recall from talking to a Directed rep a couple years ago), but I don't have the specs on it to know what impedance drivers it was made for, or what impedance correction, if any, if has for the woofer. (a/d/s 345is is the crossover).

Btw, the problem I'm trying to correct is distortion at high volumes.

As for the lpad, did I do that wrong? I put it next to the driver so the impedance the crossover sees should stay the same.

As for replacing the tweeters, I'm really trying to do this without spending any more money. I've got a lot in it already, and the wife is keeping an eye on the situation.

[DerrickM]

You know, I was just out on Madisound, and I realize I could buy tweeters for a lot less than I thought. Any suggestions for tweeters in the low end? (I see a lot of Seas in the 25-35 USD range).

[owdi]

If you are considering madisound, I've been curious about the Vifa component kit that is on sale.

http://www.madisound.com/cgi-bin/ind...12289&pid=2129

Dan

[5th element]

Originally posted by DerrickM
You know, I was just out on Madisound, and I realize I could buy tweeters for a lot less than I thought. Any suggestions for tweeters in the low end? (I see a lot of Seas in the 25-35 USD range).

You wont go far wrong with the 27TDFC or the 27TBFC/G. Zaph uses them both iirc with low xovers at 2nd order electrical.

Bafflestep is where the wavelength starts to see the box dimensions as insignificant. At high frequencies where the wavelength is short in comparison to the baffle width, the sound literally sees the box as a solid mass and radiates outwards away from it. When the frequency decreases the wavel increases, when the wavel becomes such that it is now approaching the size of the speaker baffle, it starts to see this mass as insignificant. Simply speaking some of the sound creeps round the side of the cabinet now instead of launching off the front, so instead of having all the sound radiating fowards some goes backwards too. By the time the frequency reaches a certain point the wavelength is long enough so that it doesnt see the cabinet at all, and now radiates infront of the speaker as much as it does round the back. From when this phenominum starts to when it ends it called baffle step, and because the radiation goes from being hemisphreical (2pi) to radiating into an entire sphere (4pi). You lose half the power resulting in a theoretic 6dB drop throughout the smooth transition.

In real world terms room gain gives you some of that back, but you will still need to compensate for ~4dB of this loss.

A analogy to that would be thus. Imagine a flea trying to walk along you arm, its going steady but then comes into contact with a hair. The hair is many times larger then the flea and it cannot walk past it, so instead it just turns around and goes the other way. Now imagine there is a fly walking along your arm, it now comes into contact with some hairs, the fly can walk across them but its hard work. Another fly comes along sees whats happening and decides, pfft, too much work for me and goes the way of the flea. This time a hamster decided to walk along your arm, it marches on and doesnt stop, the hairs on you arm are simply so small its not a consequence to the rodents movement. The animal now gets on its hind legs and signals to its friends that its safe. A stampede breaks out as hundreds of the critters make their way across your arm.

As the wavelength gets bigger and bigger, the box in relation gets smaller and smaller, so eventually the sound doesnt even see the box and walks right through it.

Heh its getting a bit late im making silly things up

Edit - and then I notice this is for a car which changes everything completely due to cabin gain and large parcel shelves etc.

[zega55]

If you need a 6 ohm tweeter you could go with 27TFFC or his newer brother 27TDFC.They are nice price range.Your distortion at hi volume is coming from the car radio wich is using a I.C. amp and from the car battery it cant get much power usualy 15-20W(RMS).

You could get seas 27TFFNC/G(H1396) or 27TFFNC/CG and do a crossover on 2500hz with 12db Butterworth or near that .I would do it like that .


Lpad is ok my bad

[DerrickM]

Okay, I think I'll do that. First I'll build the crossover, somewhere between 2500 and 3000, 12dB slopes on both sides, and see how it sounds before I replace the tweeters. (Which I'll do, I just have to know how much of the current problem is crossovers vs. tweeters). I'll build it for the midwoofer I have, and a 6 ohm tweeter.

Looks like the parts'll cost around $70 (USD).

The distortion is definitely not coming from the headunit. (The fronts don't distort, besides it's probably the best car audio system ever made: the Sony CDX-C90 with a separate DSP/preamp/EQ). Doesn't even have a built-in amp.

I'll try to place my order with Madisound tonight or tomorrow. Looks like I'll have to stack up capacitors to get the values I'll need. (6.25uf and 9.38uf for 300k 12dB Butterworth). How close do I need to get the capacitances? (I mean is 9.2 close enough to 9.38, etc.)