Midrange Crossover: Choosing the least of all evils? - diyAudio
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Old 4th November 2008, 09:51 AM   #1
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Default Midrange Crossover: Choosing the least of all evils?

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
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Old 4th November 2008, 10:11 AM   #2
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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 its easy to "play around" with different options.

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Old 4th November 2008, 10:41 AM   #3
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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?
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 4th November 2008, 11:12 AM   #4
cotdt is offline cotdt  United States
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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.
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Old 4th November 2008, 11:32 AM   #5
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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.
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Old 4th November 2008, 11:41 AM   #6
SY is offline SY  United States
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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.
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Old 4th November 2008, 03:20 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

The question does not have enough details for a sensible answer.
The right way of doing it depends on the details, not a generic rule.

/sreten.
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Old 4th November 2008, 06:59 PM   #8
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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.
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Old 4th November 2008, 07:12 PM   #9
cotdt is offline cotdt  United States
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Quote:
Originally posted by TheSeekerr
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.
[/B]

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.

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Old 4th November 2008, 07:46 PM   #10
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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....
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