crossover frequencies by octave

[robotnation]

I am building a large sound system with active crossovers to use for djing, and i used some math to figure out the exact frequencies a crossover should be, or at leat i think i have. I decided maybe i could help some people by sharing my info, or if i was totally wrong, i would be set straight. Most people break crossovers down into what their drivers are capable of handling, and i realized, tht could mess around with sound reproduction. I broke it down by octave and used an exponent sytem. I decided that nice subwoofer speakers (large diameter) can safely go to 20 hz, so thats where i started my scale. Decent tweeters can go up to 20,000 hz, and that is also the limit of human hearing, and a silly number to excede, so that is the top of my scale. This adds up to exactly 10 octaves, meaning, it doubles ten times, so i decided, why shouldn't i try and work the same amount of octaves into each crossover frequency? i assumed that an even distribution would prevent distortion in one region when trying to perfectly reproduce a sound. I did the math for 3 way and 4 way crossovers.

a 3-way crossover should have crossovers from bass to midrange at 20x2^3.3hz, or 200hz, and a crossover from midrange to treble at 20x2^6.6hz, or 2030hz.

a 4-way crossover should have crossovers from bass to midbass at 20x2^2.5hz, or 115hz, a crossover from midbass to midrange at 20x2^5.0hz, or 650 hz and a crossover from midrange to treble at 20x2^7.5hz, or 3675hz.

either design requires high order cutoffs at 20hz and 20,000hz to maximize efficiency, thts a given with any system though. When i build these crossovers i will use 2nd order filters for all crossover points (unless someone suggests something better.)

I hope the math is self explanatory, i just divided 10 octaves by the number of ranges in my system, and then used that number of octaves in each system to determine, using expnonents, just what frequencies to include.

If you are building a sound system, i would suggest finding speakers to fit these ranges witha little room to spare in either direction (obviously thats hard with a subwoofer, but look for one that can handle close to 20hz, if you are willing to invest in a beastly 21 inch sub its worth it)

I really hope this helps at least one person... (i DO know its gonna help me drop some crazy beats )

[DougL]

What you have stated may be a reasonable starting point.
However, the final crossover frequencies and slopes very considerably, depending on the driver capabilities, number of drivers, physical layout, and the target acoustic space.

For example, using Metal cone midranges demand a lower crossover and steeper slopes to keep the driver resonances in check, while a "wide range" driver may need a 10K first order to help it in the top octave, and a 100 Hz LP crossover to keep excursion to a minimum.

All of the choices are compromises, and depend on many factors.

Just My 2 cents.

Doug

[planet10]

Originally posted by robotnation
Decent tweeters can go up to 20,000 hz, and that is also the limit of human hearing, and a silly number to excede, so that is the top of my scale.

It is pretty easy to show the fallacy of that. We may not hear single sine waves above there (for me not even that) but you can hear when it is missing, because an intruments can produce HF sound that produces beat frequencies you can hear.

The logic of your analysis seems flawless, but leaves out practical considerations & the sensitivity to the ear-brain system. Crossovers are nigh-on impossible to get perfect (new digital systems show promise, but sampling rate is still too low), and putting them where the ear is most sensitive is, IMHO, not a good idea.

For a 3-way a bass-mid XO 80-250 Hz, and mid-hF at 5-12kHz. This puts the onus on the mid to be a stellar performer (and i suggest the best place to go looking is in the full-range section).

In a 4-way, the extra driver can be added to handle the lowest bass, and the higher part of the range for the bass-to-mid choosen. Think of the purpose of the woofer to be relieving the driver one up from large excursions. ie i've always held that the biggest benefit of adding an active woofer is the improvement in the midrange.

When i'm doing a multi-way system, i like to find a mid that is musically satisfying all on its own, and then adding help (& relief) on one or both ends. (ie a 2-way should have an XO between 200-350 Hz or 7-12 kHz).

Your approach can produce a speaker with excellent measured FR, dispersion, and power distribution, but in most cases sounds like it has had the life sucked out of it.

And in the end, it is all about enjoying the music.

dave

[EC8010]

Telephone bandwidth is from 300Hz to 3.4kHz because that's where the important stuff is. Anything else is icing on the cake. In other words, we'd really like to avoid having a crossover within that region. Traditionally, 8" drivers could be made to stagger up to 3.5kHz and 1" soft dome tweeters didn't distort too horribly if pushed that low, so that's where the crossover was. Three-way systems tended to leave the 3.5kHz crossover and use a better midrange, then put the other crossover frequency at 300Hz.

These days you can get drivers that almost cover the entire range and just need a little help at the top and the bottom. They make excellent midrange drivers. As planet10 says, a trawl of the full range forum will be rewarding.

[richie00boy]

Your idea is nice, but it seems to me like you are trying to stuff hexagonal shapes into round holes because they are more logical. (lol I sound like Spock!) At the end of the day, a drive unit will have a bandwidth that must be observed and there is no getting around that.

[rjb]

Just a caution on the range determined for telephones. This was to cover speech only.

Music limited to this range sounds horrid.

I agree with previous comments that the mid range is critical, and should cover as much as possible. Removing the demands of the bass from this driver cleans the sound up no end. The treble end seems much less critical, and getting the crossover above 3.5KHz seems adequate.

Moving the crossover a few KHz upwards does not seem to improve matters significantly, and tends to cause beaming with most drivers large enough to go low, say to 100-200Khz. Hence the tendency to use "helper" tweeters.However the most recent drivers are better in this regard, and a 3 or 4 inch "full" range crossing high about 10K could be the thing.

Although I am using a fullrange as my main speakers at present, I find most have limitations. After all like all speakers they are a compromise. I particularly dislike those that use a whizzer cone, although I have not heard the latest Lowther with the damped edge, which may remove my objection to the previous units.

A further comment- cone materials all have their own "sound" and mixing materials brings a further set of problems.

[poptart]

I just wanted to put forward the thought that since your speaker is relaying sound to a human ear rather than a spectrum analyzer you may want to start from the viewpoint of the ear. It's a quirky little thing, perhaps you can find places in it's repsonse where a crossover is better hidden than others.

[robotnation]

wow these are all good ideas... but i was wondering, do all of these little factors change considering the music being played? I am going to be playing techno and using speakers with range limits that are hard to push and break (the drivers i'm looking at are pretty nice.) Another thing, when i dj i have a mixer with EQ settings and i can control what gets sent to my amps. If i have the crossovers i was suggesting, couldn't i bend the music around to be more pleasing before sending it to the amps?

p.s. my crossovers are going to be active not passive

[richie00boy]

The type of music will have no influence whatsoever on the bandwidth that the speakers are capable of producing. You may choose however, that if you like a big vocal picture to run the midrange up a bit higher than normal at the expense of reduced directivity and also possibly some breakup.

[phase_accurate]

Maybe some of the responding people overlooked the fact that he was talking about high-power systems for DJing.
In this case recommendations for 4" fullrangers and softdomes and their usual crossover frequencies don't help much here.

In this case I would say that:

1.) The original poster's proposal is a good starting point (look at it as a flexible design target). 20 kHz is high enough for this purpose BTW.

2.) But there is no way around designing the crossovers matching the driver responses etc.

3.) Higher than 2nd order is recommended for high-power applications of than kind in order to reduce IMD and THD.

Regards

Charles