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-   -   A better crossover point (http://www.diyaudio.com/forums/multi-way/7079-better-crossover-point.html)

Westrock2000 25th October 2002 10:41 AM

A better crossover point
 
Just wondering what would be a better place to crossover at, I was thinking maybe using some 2" tang band's and crossing over to woofers at around 500-700 Hz, thus making the treble more seamless. But would it be better to cross to high freqs at say 6000-8000 to get it out of the more sensitive areas? I guess my question is what are the better places to crossover and what are the better off without?


Also I think my first project will be to save my B&W DM302's. I took them apart to see what was inside and they must have a $4 crossover on those things. Good for $250 speakers, but another $50 could probably go along way with a new crossover (maybe series??) and maybe some new drivers.

Redeye 25th October 2002 11:33 AM

What frequencies you set your xovers at depends on your drivers and a fair amount of trial and error as to what sounds good. It really doesn't matter what works in theory if something else sounds better in practice. People can get quite animated on this subject, but the best advice i can give you is to have a go at whatever you think might work and hear what it sounds like.

btw, if you're doing mods on your b&w's then changing the drivers (which will need careful selection) will make much more difference than the crossovers imho.

Westrock2000 25th October 2002 12:08 PM

1: Well just like poeple usually like to crossover in the 2000-2500 area as opposed to the 3500-4000 to skip some anomolies, so they say.....

2: The crossover comprises or iron core inductors and bipolar caps, honestly like $4 worth of stuff. And they sound so harsh after listening to my MMG's for the last year. So I figure some nicer Solen or Dayton stuff and maybe Mills might improve it a little.

Redeye 25th October 2002 12:45 PM

1. Well, it kind of depends on what you're crossing over. A regular 2-way is usually crossed over at around 2-2.5k because the breakup on the LF isn't to horrendous and the HF isn't too far down at that point, so it's a reasonable compromise. However, there is a school of thought in multiway systems (mainly huge PA stuff) which says you should try to avoid crossing over in this range because it's right in the middle of the frequency range which contains a lot of critical voice information and if you crossover here then you'll introduce phase errors in a perceptually important frequency range (hence why decent digital xovers allow you to compensate for filter delays between bands).

Anyway, you're right - using better quality components will improve the sound, so just have a go and see how it sounds.

2. If the xover components are that cheap, I'd have thought that there would be more distortion contributed by the (presumably) cheap drivers than the xover, hence why i suggested that you might notice more improvement by changing them than the xover. Sure, you'll notice the difference by using more expensive xover components, but don't overdo it with those drivers - remember, you can't polish a turd......

diypole 25th October 2002 12:47 PM

Bill Elliot has an excellent article on crossover frequency selection. Search for Elliot sound products and read the article entitled "Bi-amplification: not quite magic but close" (or something to that effect). Very good and easily understood.
regards,
Jason

Westrock2000 26th October 2002 01:11 AM

So in the case of Tang Bands, should i use the smaller 2" or 3" that way that can produce say 300hz-~20000hz and then crossover a real woofer at the bottom or should I use the bigger 4" TB's and then crossover a tweeter real high (maybe 10000+ Hz), this way the treble transitions are real smooth.

planet10 26th October 2002 05:37 AM

Westrock2000,

1st the DM302s. I have a set of these. They are quite good for what they do. With the integration of the drivers into the box, i wouldn't even think of changing drivers. But the XO can be improved. There was a speaker builder article on just that. And you can do the "standard mods" -- ductseal the baskets and stiffen the box. I have also thot about filling all the pyramids in the back -- perhaps some ductseal in the points covered over with epoxy or even just a piece of wood or plastic glued to the back.

As to the best XO points, as has been pointed out, that depends on your drivers. Ideally, the XO point should be out of the critical midband. So the low-frequency turn-over should be between 80-350 Hz and at the top above 4kHz. Getting a driver to cover that kind of range is tricky. Too small to get up high and they tend to not go low, and visa-versa. Fortuneatly good small full-ranges are turning up that give you an edge. With the 2" TB you probably don't need anything on the top, but you probably want to XO it close to the top of the lower band. You would need a woofer with an extended range to keep things as seemless as possible. A 3" might still allow you to run with no help at the top, but would go lower. Personally i am partial to 4", you can usually get down to 100-150 in the bottom, and then run them all the way up at the top with a simple cap XOed tweeter to help or roll the top off and still get away with a T coming in at 5-7k.

My current system uses 4" FR, active XO at 125, run all the way up, with a tweeter coming in at about 10k. My BD-Pipes.

dave

Westrock2000 26th October 2002 07:49 AM

Thanks, that about what I thought with the tang bands. I was looking at the 3" ones, the black phase plug'd ones t be exact as their high freq (10k-20k) seems to be a little more smoother than the ones with the silver phase plug. Im not too scared of lack of ultra top end, because I'm used to my MMG's which are pretty laid back when it comes to lots of treble.

Your right about the 302's with the drivers. I measured openings and it does narrow the choices down, luckily PartsExpress list the physical dimensions of most of their drivers. I think the tweeter would be not so hard, as I have a lathe and could just make the tweeter faceplate smaller to fit the hole.

You know looking though the grills of my MMG's, they appear to have pretty descent XO components, as in polypropylene capacitors and air coils. These things still make me very happy, definently more than twice the speaker of the 302's!

tbla 26th October 2002 08:06 AM

speakin' of the right drivers and the right crossover points......

check this :

http://www.atc.gb.net/PDFs/SCM100.zip

planet10 26th October 2002 05:13 PM

Quote:

Originally posted by Westrock2000
Your right about the 302's with the drivers. I measured openings and it does narrow the choices down, luckily PartsExpress list the physical dimensions of most of their drivers. I think the tweeter would be not so hard, as I have a lathe and could just make the tweeter faceplate smaller to fit the hole.
B&W spent an aweful lot of effort to get the midbass & tweeter to match ezch other very nicely. I would be VERY hesitant to take the effort of changing the tweeter. It will be very hard (or very expensive) to get the overall performance better than you can achieve from the existing drivers with some XO tweaks. I personally haven't found the top to be a problem, but the author of the XO mod article did, and that is one of the things he worked on when rejigging the XO.

dave


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