Crossover points

[3-LockBox]

I know, I'm being lazy, but I was wondering what crossover points were to be avoided as far as midrange and tweeters are concerned.

TIA

[avionic]

was wondering what crossover points were to be avoided as far as midrange and tweeters are concerned.
The incorrect ones...:D Like your avatar..Have no clue on the question though...

[toxcrusadr]

The incorrect ones...:D Like your avatar..Have no clue on the question though...

Ha! I thought of the same thing. "The ones that sound bad."

Truly, it depends on the drivers, box, etc. etc. etc... :yes:

[Bruce221]

This could get quite long but Ill try ----8inch woofers work well to around 1400hz-this wll be the only ex-here---If you want a two way system--lets say a 1inch dome tweeter there are a few optins--first what is the frequency rage of the woofer in the specs --typical 8 inch woffer 50hz-4000hz ok next the tweeter-2000hz -20k--however the tweeter has an absolute low side to it in this case it maybe(resonance)resonace of this tweeter =1000hz WE have some space to work in you see? Fr this ex I could pic quite nicely a crossover of 12db l/r arrangement for the woffer and a 18db odd order crossover @1750hz for the tweeter. the 12 db slope of the woofer would extend out to about 4600hz but the natual rolloff would add some . The tweeter would meet arrond the 4000hz point creating a very nice blended system.Speaker crossover and theary are very large subjects that are hard to explain--for any different 2-way system there would be a diff and yet same method--If you listen to tubes you would want the ohms of the soeaker system to be 7.5 right on the $$

[Paul C]

It depends on the drivers. One does not design a speaker saying, "Self, I'm going to crossover at 1000 hz and 3500 hz."

You look at the woofer, what is the top practical frequency? Does it have a breakup mode near the top you want to avoid?

Tweeters should be crossed at least an octave above the resonant frequency. There may be other considerations such as frequency response dips and peaks, and power considerations. A tweeter that would cross at 2000 hz might only be usable with speaker systems up to 75 watts, but if crossed at 4000 hz that same tweeter might be good in systems up to 200 watts.

A 2-way is necessary, most times, because one driver cannot reproduce the extremes of the human audio range. A three way may be necessary depending on drivers used. The midrange, in this case, is a patch to cover the upper range where the woofer runs out of range, and where the tweeter cannot go low enough.

So, crossover frequencies are entirely dependant on the particular drivers used.

[similost]

hhhmm.. this is kinda like asking, what carb is best for my engine...

well.. wadda ya got?

[3-LockBox]

Well, there are those who avoid x-overs altogether, because they don't want any caps or coils in the middle frequency bands.

As far as the tweeter needing to be x-over an octave above Fs, how do I determine what an octave is? Is there a chart for that?

[similost]

woah woah woah... .you have to have crossovers for mids and highs.. if you don't you'll trash drivers as soon as yyou apply any kind of full range wattage to them. They won't handle it.

now if you are talking about people not using passive crossovers, true, but then you need to run an active crossover to protect your speakers. You can't run a woofer, mid, and tweeter without some kind of crossover...

Otherwise, you will need a full range driver that doesn't require the need for a crossover.

[dnewma04]

An octave is simply a doubling of freq. If the Fs is 900hz, you'd want to crossover at 1800hz or higher.

[3-LockBox]

Otherwise, you will need a full range driver that doesn't require the need for a crossover.


Yes, I was referring to single driver, fullrange speakers (sorry if I distressed you ;))

I've built two or three fullrange designs, but feel they don't do very well with even moderately loud volume - no, I do not mean concert level volumes either. But I do enjoy turning up the volume from time to time, and even my modded/tweaked FRs experience break-up past modest volume levels.

I have built a three-way speaker using a wideband approach to the mid; using a 5" fullrange driver for 400hz and above, and a super tweeter from about 10khz on. I have two 6.5" woofers rolled off at 400hz and below for the bass. This works rather well, actually.

But I have been contemplating making a two way, and I would like to use an 8" driver and a dome tweeter together, mimmicking an old Boston Acoustic design. This would be in a 2 cu.ft. cabinet. Of course my fullrange bretheren eschew any kind of crossover (once again I'm talking single driver FR), especially in two-way designs. I'm guessing that in order to provide maximum protection for a tweeter, it should crossed over about double what he suggested cross-over point would be. That would be around 3khz to 4khz in most cases (going by specs).

My original question should have been more specific. I was wondering if a crossover point at or around 4khz would cause any audible problems in a two way design.

As far as break-up modes, are we talking about peaks and dips (on a frequency output graph)?

And as far as Octaves go: I read where people are referring to certain octaves, such as 3rd, 4th, 5th, etc. Is this the same as a 'harmonic'?
Where does the 1st octave begin on the frquency spectrum.

[dnewma04]

I've never run across that terminology for an octave. I have heard people say "Mariah Carey has a 7 octave range!" or something to that effect.

What you may have been reading was people referring to crossover slopes. A first order crossover would drop the freq response by 6dB per octave. A 2nd order crossover would drop off the response by 12dB per octave. In the case of a 3rd order slope, it's 18dB per octave. So, let's say that you choose a second order slope with your 8" speaker and choose a 4000hz low pass crossover point meaning freq above 4000hz are removed and let's say you are at 90dB at 4000hz. By 8000 hz, your high freq response would be down to 78dB. By 16000hz, it would be down to 66dB. If you chose a 3rd order crossover slope you be at 72dB by 8000hz and 54dB by 16000hz.

The crossover slope would largely be determined by the crossover point and the drivers characteristics above that freq.

I'm afraid there are no set rules to follow here, just a couple of very generalized guidelines to help lead the way.

I would suggest identifying the 8" driver you are considering and we could probably determine whether or not your proposed plan would work well or not or provide some insight into the crossover point/slope you should try.

[Gibsonian]

I was wondering if a crossover point at or around 4khz would cause any audible problems in a two way design.

As long as your low frequency driver is fairly flat up to that frequency and your tweeter fs is 2000 or less, you're good to go. I've heard that it can be beneficial to cross below 300 and above 3000 if you can do it, as that is the midrange/vocal area, but driver selection really determines where you place your points. Experimentation is a great way to find best to your ears Xover points, after you've determined where you can Xover with driver specs and frequency curves.

[3-LockBox]

What you may have been reading was people referring to crossover slopes. A first order crossover would drop the freq response by 6dB per octave. A 2nd order crossover would drop off the response by 12dB per octave. In the case of a 3rd order slope, it's 18dB per octave. So, let's say that you choose a second order slope with your 8" speaker and choose a 4000hz low pass crossover point meaning freq above 4000hz are removed and let's say you are at 90dB at 4000hz. By 8000 hz, your high freq response would be down to 78dB. By 16000hz, it would be down to 66dB. If you chose a 3rd order crossover slope you be at 72dB by 8000hz and 54dB by 16000hz.

I would suggest identifying the 8" driver you are considering and we could probably determine whether or not your proposed plan would work well or not or provide some insight into the crossover point/slope you should try.


I've always known that a first order x-over was -6db, 2nd order -12db and so on, but I never connected that it was per octave. That was intersting info, thanks. I've used first order x-overs before, because I've been told they add the least amount of coloration to the sound of the driver (I use expensive components like Dayton poly caps and Erse perfect layer wound air core inductors). I realize that for a two way system, I need to use a 2nd or 3rd order x-over.

As far as the woofer, I'm still trying to narrow the field on that one. I would like an 8" that was fairly efficient, and still fairly smooth up to at least the crossover point. I want it to go fairly low as well. Depending on the vas of the driver, I think my cabinet is more than big enough.

Oh, and did I mention I was operating on a reletively small budget. :)

[dnewma04]

Im a fan of tight budgets, it makes for a good challenge. can you provide the volume of the enclosure? and give a budget/variance from that budget?

as far as the purists seeking first order crossovers, I tend to find that many people who pigeonhole themselves into such requirements tend to not have a good grasp of speaker building.

[Paul C]

Well, there are those who avoid x-overs altogether, because they don't want any caps or coils in the middle frequency bands.

As far as the tweeter needing to be x-over an octave above Fs, how do I determine what an octave is? Is there a chart for that?

I'm sorry, I should have not assumed.

Yes, an octave is a doubling or halving of frequency. For example, middle C on the piano is approximately 262 hz. C an octave higher would be appx 523 hz. C an octave lower would be appx 131 hz.

Lesson in musical acoustics...

The notes we hear as "harmonies" are whole number ratios of each other.

Just as octaves have a 2:1 relationship, there are other possible relationships, 3:2, 4:3, 5:4, etc.

A "fifth"* would have a 3:2 relationship with the fundamental. So, a G over a C (a "fifth") would have the C appx 262 hz and the G (1.5 x 262) = appx 393 hz.

(* A "fifth"... C would be the first step of the scale or "do", D the second or "re", E the third step or "mi", F the fourth step or "fa", G the fifth step, or "sol", etc. An interval of two notes C and G would be a "fifth" as the other note is the fifth step of the scale)

Interestingly, the difference frequency of these notes, G and C, would be 393 hz - 262 hz = 131 hz... another C an octave below the middle C.

A "major third" would have a 5:4 relationship with the fundamental. So, a C and an E, middle C = appx 262 hz, the E would be appx 1.25 x 262 hz = 328 hz.

These type of simple whole note ratios generate difference frequencies that are also harmonious to the notes being played. They sound "in tune".

Notes that are not simple whole note ratios have very fast difference frequencies, causing the notes to have a "flutter" heard as the notes go in and out of phase with each other. We hear this as dissonance, or as "out of tune", depending on the speed of the flutter.

Pluck a guitar string. It is not just vibrating at f (fundamental frequency) but at 2 x f, 3 x f, 4 x f, 5 x f, 6 x f, etc.

Touch that string very lightly at the exact middle. That will stop the fundamental frequency and now you will hear the tone an octave up. Each half is vibrating at 2 x f. If you hit the string with a strobe light, adjust the light correctly, you can see the string vibrating in two halves.

Pluck the string, then touch it lightly one third of the way from one end, it will now vibrate in thirds, each third vibrating at 3 x f, and the tone will jump up an octave plus a fifth. Clearly seen with a strobe.

So, these musical terms (octave) just can't help but be used in more "techical" discussions of speakers, and other musical acoustics.

[Bruce221]

One bit of advice on woffer selection -woffs that tend to play higher frecs tend to have less bass output-400hz is a good point to crossover midrange in a 3-way system. 2-way systems 8 inch drivers are probably the best choice however there are a few 10 in ones that will also work-if you go to a 12 inch woffer you are probably going to need a horn not a dome tweeter.

[Bruce221]

A 2,0 cu/ft vol inside the cabnet-may make the coopling of the system tword a .7 damped box which if it a sealed enclosure will produce the bass transeints on the money-many music men in bands love these because they hear the true tone- I like my boxes at about .85-many speaker manufactures have boxes at arround 1.0 -1.2-these give a hump at arround 120hz in the responce

[gener8r]

To Paul C,

DUDE! What a great and interesting read. I thought I knew music, but never have I had the notes explained to me in terms of frequencies. Believe me a light bulb came on! Thanks so much for taking the time to write that.

[Paul C]

Thanks. I have lots more, but didn't want to bore you guys.