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Old 4th November 2008, 03:51 AM   #1
Ryan_Mc is offline Ryan_Mc  Canada
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Default Active vs. passive Xovers

I am in the planning stages for a 5.1 setup for my computer. Primary focus is on sound quality for music. I still haven't decided on a speaker design yet but will probably be of the 4.5" + tweeter bookshelf variety. Just planning on starting with the front L&R + sub (two 10" since I have them) for now.

Anyway, in looking through all the speaker designs the crossovers seem to be very complex. I'm OK with making a separate amp for the tweets and 4.5"ers but I'm wondering if that same level of complexity of xover can be carried over into doing it actively. Would that be an advantage or disadvantage?
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Old 4th November 2008, 04:23 AM   #2
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Certainly the woofers should be active... for nearfiled computer use you should consider a satelite system with the best kind of XO -- none at all.

dave
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Old 4th November 2008, 04:28 AM   #3
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Ryan,

There may be a third method worth considering if you have not done so--that of using software based digital XO's in conjunction with your soundcard. See here for discussion: http://www.diyaudio.com/forums/showthread/t-6356.html

First you would not have to build XO units, and much faster to find right frequency and levels. Also much better in some ways sonically as very steep, less phase distortion.

If this were expensive HT project, I would probably not mess around with computer method as it may not have enough flexibility, but for a small PC based system, this seems like a great place to start, and even free, assuming you will be building or buying amps anyway.
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Old 4th November 2008, 09:39 AM   #4
cotdt is offline cotdt  United States
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Since you already have the schematics to building the passive crossovers, it should be much easier than you think. I can put one together in about 10 minutes.

If you insist on avoiding building the passive crossover, the transfer function is usually published and you can use that to program a digital crossover. I strongly beleive that passive is more transparent than digital crossovers. This does not apply to computer based digital crossovers though as you avoid the additional conversion stages.

The other option is analog active crossover, which you would have to build yourself as well. Since you are unwilling to put together a passive crossover, then I assume you would be unwilling to build an active crossover also.
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Old 4th November 2008, 02:09 PM   #5
Ryan_Mc is offline Ryan_Mc  Canada
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@Dave,
Are you suggesting just using a full range 4.5" on each side? That would make supper simpler. I've read a bit about those and I know you guys know your stuff (certainly more than me) but there's that mental hurdle of no tweeter. Got a driver in mind? ....I bet you're thinking FR125S....

@Newmexiconoob,
That's not really what I was looking for but it looks interesting and I'll give it a read! Thanks.
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Old 4th November 2008, 03:33 PM   #6
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Sure, no problem. There are those of us who are convinced that digital XO's are even better than none at all, and certainly superior to analog (whether high or low lovel signals).

Certainly worth reading about--discovered a much more inclusive thread which is here:

A how to for a PC XO.

Best of luck whichever road you take,
John
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Old 4th November 2008, 03:44 PM   #7
Ryan_Mc is offline Ryan_Mc  Canada
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cotdt,

By active crossovers I meant at the line level (analog) using op-amps. I'm not unwilling to make the large active crossovers at the speakers themselves. My concerns were the cost of large high quality caps/inductors/resistors.... and then building an inventory of those to tune or play with different crossover points where I could get many of the same results in the active xovers by changing a couple/few little 1/4W resistors. A quick look into some prices using a fairly complex network for a 2-way that included higher order high/low pass plus additional notch filtering and such to smooth the frequency response, the cost of the xovers was quickly getting very expensive.

Also given effects like stray inductance, coil resistance, ESR in the caps, electrolytic caps having usually widely ranging tolerances, large resistors having an inductive content, most of the above being temperature dependent which I would assume can vary quite a bit given how hard the speakers are driven... blah blah blah.... I thought actives might be better for sound quality, not just easier on the wallet. I'm not suggesting active xovers don't have their own set of issues but I think they can be much easier minimized. At least I think, but that's why I'm asking

Thanks,
Ryan
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Old 4th November 2008, 03:47 PM   #8
Ryan_Mc is offline Ryan_Mc  Canada
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Sorry for the double post but I'm still under moderation (new member) so I can't go back and edit my previous post, but here is an example of the 'complex' xover networks I was talking about.
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Old 4th November 2008, 05:30 PM   #9
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Quote:
Originally posted by Ryan_Mc
Are you suggesting just using a full range 4.5" on each side? That would make supper simpler. I've read a bit about those and I know you guys know your stuff (certainly more than me) but there's that mental hurdle of no tweeter. Got a driver in mind? ....I bet you're thinking FR125S....
Yes. Either FR125 or FE127 (which often comes down to amplifier). Both go into a 4.5 liter box

dave
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Old 4th November 2008, 07:45 PM   #10
cotdt is offline cotdt  United States
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Ryan_Mc,

I see you are refering to analog active crossovers, and in that case assume you know how to design them. Both analog active crossovers and passive crossovers are equally transparent if decent parts are used. Active is even bigger than the passive if you include the power supply for the op-amps and additional amplifiers. For a stereo 3-way, you will need 6 channels of amplication. For me, buying a good aluminum case for my active crossover already costed more than the entire passive crossover, which are usually housed inside the speaker.

There is no difference in sound quality between analog and passive. In listening tests the passives do beat out the digital crossovers though. Most of the arguments against passives assume that the passives are generic designs not tailered to the actual drivers used, which is not a fair comparison for the passive. The extra things that active can do are not that useful IMHO. Active is indeed more efficient but you're using 6 amplifiers instead of 2 so they better be!

My recommendation, go passive for 2-way, and a combination of passive and active for 3-way to save money. If using a ribbon tweeter, going passive is a must. There needs to be a capacitor to protect the ribbon.
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