Midrange Crossover: Choosing the least of all evils?

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Hi folks,

Here's a semi-hypothetical for you all:

If you have a midrange driver with a frequency response that makes it unusable below 400hz or so, where's the best place to cross it over, now that you're already up in the region where most musical fundamental frequencies exist? Assume, for the purposes of the question, that the woofer is good up to about 700hz.

These numbers aren't entirely arbitrary, they relate to real drivers, but no specific system as of yet.

Is it simply a case of "cross it over as low as possible", regardless of the crossover point being in the "coherence band"? Or is it best to push the C/O point up as high as possible, in this case, in order to avoid artefacts around the octave of middle C?

Your insights are appreciated,
- Chris
 
How we perceive sound is partly up to the individual. Thus there is hard to tell an ideal solution. This also apply to to the sparse information about the "virtual" driver and no information at all about the other drivers.

The best way to educate yourself is to compare some crossover points (and even filter characteristics). A good way, although I admit expensive one, is to use a computer interface and cross over in the digital domain. This way it´s easy to "play around" with different options.

http://groundsound.com/
 
I think in deciding how low the xover point can be, you need to consider the order of the proposed xover, and how wide a bandwith the mid driver will be covering, i.e. what it's upper xover point will be...
If the xover point co-incided with the BSC freq, some aspects of design might be easier if driver sensitivities match,
any info on the actual drivers?
 
Cross as low as possible, keeping in mind harmonic distortion. A properly done crossover should be transparent, so the capabilities of the drivers are the only real issue. The best speakers I've ever heard are all 3-ways which have multiple crossovers smack in the middle in the human vocal region (80Hz to 9000Hz, not including overtones), yet vocals sound amazing.
 
The drivers are what they are, and you never have as much overlap as you'd like. Set the crossover frequency based on the drivers. IMO, the argument that there is some magic region where you can tolerate a less then great crossover is flawed. As above, the best systems I've heard (and built) are 3-way, with the crossovers right where you wouldn't want them. It's far easier to go active, so you can experiment, and get the slopes and shapes you planned for, not to mention higher orders.
 
Two things to worry about are lobing at crossover and changes in dispersion going from one driver to the other. The former can be ameliorated by crossover design (the good ol' LR4 is particularly useful), the latter by driver size and positioning on the baffle. Designs which get these bits right tend to sound very "continuous" and integrated.
 
Hi all,

Basically you've confirmed what I suspected - that the only way to be sure is to build it and have a listen.

The drivers in question are from some old junk Sony 3-ways - a friend has asked if there's anything that can be done with them after he destroyed one of the flimsy chipboard cabinets. So I don't have any proper measurements yet, just vague indications from listening to frequency sweeps on each driver.

I was just hoping for a rule of thumb - and in most cases, I think I'll be sticking to the old rule of avoiding crossovers between 300 and 3000 hz.

The reason it was all posted in such a vague way is because I haven't put a lot of effort in yet, because, if it looks like more work than it's worth, I may not do anything with them at all.

Thanks folks, there's some useful advice here.
 
TheSeekerr said:
The drivers in question are from some old junk Sony 3-ways - a friend has asked if there's anything that can be done with them after he destroyed one of the flimsy chipboard cabinets. So I don't have any proper measurements yet, just vague indications from listening to frequency sweeps on each driver.
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A 3-way crossover itself will cost a lot more than what the "Sony junk drivers" are worth. That does not include the costs of setting up measuring equipment and buying measurement software. Are you sure you want to spend several hundred dollars on "junk drivers"? And you still seem to beleive that "crossovers are evil" - as you listen to some high end 3-ways with crossovers within the "300Hz to 3000Hz region" I have a feeling you might change your mind.

Listening Experience >> Theorycrafting
 
I don't think a rule of thumb is useful in this situation, go with the driver's strengths. I recently put together a pair of computer speakers using junk drivers I had lying around, using 1st order, crossover freqs were 1KHz and 6 Khz, the result after a little tweaking was pretty good....
 
I'm guessing we can assume 3 things without knowing about the drivers.

1 Cross the mid over at no lower than 2X the Fs.
2 Cross the woofer over before the onslaught of cone break up.
3 Ensure the power handling of the mid corresponds to that of the woofer at the chosen XO frequency and slope.

EDIT: I just realized I gave advice for driver whose parameters are known. Not much help, sorry
 
Hi folks,

Don't worry about it...the junk drivers are gone - I pointed out to my friend that getting the lot going again was going to cost actual money, and he decided that it might be time to upgrade to some other cheap garbage.

Measurement software isn't that expensive - I've already played with Speaker Workshop, and it's not that hard to use. Getting a mic going is a little more effort, but only because the locally available electrets are garbage.

Really, I was only after some advice, a list of the things to consider. I've scraped together that from this thread.

My belief that "crossovers are evil" isn't particularly deeply rooted. I just have this mental block about having an overlapping section between drivers in vocal fundamental frequency region - I can't shake the feeling that it's going to "smear" the sound. I've got nothing against crossing a tweeter in low, I just don't like the idea of having a woofer reproducing the lower midrange.
 
Hi Andy G - your location has been and is noted - while Australians seem quite well represented on this forum, New South Wales seems strangely quiet!

For all that everyone suggests that you should avoid using rules of thumb, why not, so long as it does no harm?

(I'm rather glad too, I can't do woodwork for peanuts. On the downside, he'll probably go and buy a "stereo" iPod alarm clock or something)
 
Re: cross-overs are not evil...

Andy G said:

"Bad" cross-overs are evil, be they passive or active.

If implemented well, then they shouldn't be an issue where ever you cross.

Having said that, I too, try to avoid crossing between say 300 and 2000.

ps. I'm glad your friend dumped the Sony's.


Note my location.


Yep. Ideally the midrange should have an output that is about 2 db overall higher than the tweeter or woofer. And be so clean it is a nearly a full range driver, all on it's own.

If it isn't those things, it isn't really a midrange driver.

Then you find yourself with a situation where compromise is in order..and fiddling is the order of the day. And, fiddling with ANY point on a midrange driver's crossover, be it the low pass or high pass section.. WILL make a TOTAL mess of the entire crossover balance you may have previously achieved. 'perfect' Three way passive design execution is for masochists. Messing with the LF cut-off on the midrange will screw up the tweeter integration. Big time. and Vise-Versa.

The best you can do is start with a near perfect midrange in the first place. Let's say the better one costs $30-40 more each, than the less perfect one. SPEND THE MONEY. The easing in crossover execution hassles alone -- will make it very much worth the effort required to stretch to the better midrange driver.
 
Andy G said:
I STILL think that Vifa and Peerless mids are some of the best around...because they can be used with minimalist x-os in the low range of 200-300 and upper range of 2000-4000.

I guess that if others want to BASH some of the cheaper metal cone drivers into submission with LOTSA x-o components, that is their decision! :D


ooo, flame war coming !! :angel:


Agreed that Vifa and Peerless mids are downright amazing, but have you tried the Scanspeak mids? You can use those with neither a high pass nor low pass and they will still sound really good.
 
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