# Picking driver and crossover points



## -=Jeff=- (Oct 25, 2006)

I know these need to go hand in hand. What I am curious on is if you are doing a 2-way active set-up, how shoudl you pick the drivers?

Meaning, if you wanted a crossover point of 3kHz (that number is picked for the question only) when you look for drivers, what is the minimum freq response you would want the low end to be for the high side (tweeter) and max freq response for the low end (midrange)?


then what is a good range for a crossover point, meaning many cars are different and that will vary the crossover point, so what is a typical median setting and what range from there?

From reading Daytons (rs225) seem to have a lower high end for freq ( 2kHz? approx) so could you crossover at 2kHa or is that not a good idea.

just trying to get a better grasp for some of those basics before determining the drivers.


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## andthelam (Aug 9, 2006)

-=Jeff=- said:


> I know these need to go hand in hand. What I am curious on is if you are doing a 2-way active set-up, how shoudl you pick the drivers?
> 
> Meaning, if you wanted a crossover point of 3kHz (that number is picked for the question only) when you look for drivers, what is the minimum freq response you would want the low end to be for the high side (tweeter) and max freq response for the low end (midrange)?
> 
> ...


If you wanted a median range I believe that your value of 3KHz is pretty median w/ 2kHz-5kHz being a typical for crossong over say a tweeter and a 6.5" mid. Manufacturer's specs are hard to compare A/B. Look through some of the DIYmobile review sites for usable frequency response on different drivers and more importantly the sound you are looking for (Warm, bright, neutral, strong midbass, detailed, nice top-end.....).


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## -=Jeff=- (Oct 25, 2006)

andthelam said:


> If you wanted a median range I believe that your value of 3KHz is pretty median w/ 2kHz-5kHz being a typical for crossong over say a tweeter and a 6.5" mid. Manufacturer's specs are hard to compare A/B. Look through some of the DIYmobile review sites for usable frequency response on different drivers and more importantly the sound you are looking for (Warm, bright, neutral, strong midbass, detailed, nice top-end.....).


Yeah but if your xover point is 3kHz, could you use a driver with the freq response of 3kHz-20kHz and the midrange with a response of 40Hz-3kHz or would 2.5kHz-20kHz and 40Hz-3.5kHz be better with the 3kHz crossover point?


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## fej (Feb 8, 2006)

To hell with what I had to say ... just read what Mini has to say


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## MiniVanMan (Jun 28, 2005)

I'm going to use a couple of examples, and some response graphs to help you understand this. 

I'll start with the Peerless Exclusive 7". Scroll to the bottom of the PDF where the response chart is.

http://www.madisound.com/pdf/peerless/830883.pdf

You'll notice the "blue", "red" and "green" response graphs. Labeled at the bottom you'll see "On Axis", "30 Degrees", "60 Degrees" respectively. 

Looking at the graph you can see that the upper end response of the driver lowers dramatically the further off axis you play them at. Now if your driver side door sits 60 degrees off-axis of your listening position (which most doors fall in that area) then you can get a good idea of what the upper end response will be. In this case the graph shows about 1750 hz before it starts to collapse, and is probably useable up to about 2200 hz. 

Your passenger side driver will yield a considerably higher response due to it be much closer to on-axis than the driver side, so you might start to hear some bias from the passenger side should you try to run the set up to 3500 hz.

Now let's look at the Vifa MG 4" midrange

http://www.madisound.com/pdf/vifa/mg10md09-04e.pdf

Here you'll notice that on-axis response is great. Near 15k flat, with extension up to 20k. Npdang tested this driver and mentioned that it can almost be used without a tweeter. By the response graph we can see that.

However, now let's say we're building some kick pods, and due to some reason, we can't get them completely on-axis, but rather 30 degrees off-axis is the best we can do. You'll see that the 30 degree off-axis response graph basically tells us we can use these midranges up to about 5k before any real degradation of response. Pretty nice. 

Now, for low end response. For tweeters, the general rule of thumb is twice the Fs (Resonant Frequency) at 12 db. A higher slope (i.e. 18 or 24 db) can get you closer to the Fs, but we'll use 12 db for now.

Let's first look at the most common tweeter on this board... The LPG

http://www.madisound.com/pdf/lpg.pdf

The Fs of this tweeter is 1850 hz. Doubled that is 3700 hz. Now, try coupling that with a 7" driver mounted in a door 60 degrees off-axis, and you have quite a gap between 2000-3700 hz. Almost a full octave. Now to be fair, let's look at the upper end extension. The on-axis, 30 and 60 deg graphs look almost flat up to 20k. Very nice. These can be mounted in some sail panels firing horizontally across your front stage and you can get great results from them.

Next is the Seas Neo tweeter.

http://www.madisound.com/pdf/seas/h1396.pdf

Here is a tweeter with a much lower Fs. 1170 hz, using our rule, can be crossed at 2340 hz. The specs say 2500, so we're pretty close. With a 24 db slope you could get 2200 hz out of them. These would be much better to mate with a set of Exclusives mounted 60 degrees off-axis. However, their top end is nowhere near that of the LPGs. You can definitely see that these would lack the top end "sparkle" that so many people refer to when talking about the LPG's. These will be much more neutral and laid back on the top end. Not a bad thing, as a lot of music doesn't go any higher than 15k. You will also notice a huge difference between on and off-axis. A major consideration when considering how to mount them.

These are just some suggestions on how to "guess" at appropriate crossover points. The graphs give you a good idea of how to tell how a driver will perform in a given installation. These graphs in no way indicate how a driver will sound, nor how they will perform at the upper and lower limits of their capabilities. 

I hope this helps you, and hopefully, many others out there. I know it's rather lengthy.


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## azngotskills (Feb 24, 2006)

Thank man...very help guy ^^^


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## evan (Dec 2, 2006)

fej said:


> To hell with what I had to say ... just read what Mini has to say


Boooo! I read what you'd posted earlier and I found it to be really helpful.... unless it was wrong  ...and then it's ok that you deleted it.... But I don't think it was.


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## thadman (Mar 1, 2006)

If you want to determine the ideal LPF for a given midrange driver, observing the manufacturers (or npdangs, zaphaudios, etc) frequency response will give you loads of help. The driver must maintain a flat response 2 octaves above the crossover frequency.

For example, the Seas Excel W18E. It has a nasty breakup at 4800hz, the 2nd harmonic of this breakup is at 2400hz and the 3rd harmonic is at 1600hz. You will DEFINITELY want to avoid the 3rd harmonic of this breakup, and cross below that point (1600hz)

As a generalization (there are exceptions to this rule)

Metal cones are usually the best transducers (most pistonic, some people prefer more distortion :blush: ex. tubes) up until around 1-1.5khz (I wouldnt recommend taking a metal driver past 2khz), where they excite harmonics of nasty breakups  

Paper cones breakup more easily, but the magnitude of the breakup is often quite minimal compared to metal cones and is easily tolerated. They can often be crossed much higher.

Also, you can get an idea of how a driver will perform off-axis with a little math by determining the diameter of the diaphragm.

For example, the Seas Excel W18E. It has a surface area of 126cm^2, A=Pi(r)^2. The diaphragm is ~4.99" across. The speed of sound is 13,397in/s, so divide the speed of sound by the diameter of the diaphragm and you get 2685hz. Above this point, the wavelengths the speaker will be producing will be shorter than the diaphragm and as a result, the driver will begin to beam. You will not want to use this driver off-axis, above this point


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## -=Jeff=- (Oct 25, 2006)

Thanks Guys!!! This does help and it does make sense.. I am still doing my homework on this.. front stage is last on my list, It has been a bit cold here to play around in the garage and try things..


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## fej (Feb 8, 2006)

Haha thanks Evan ... wasn't wrong I don't think, but the explanation mini gave was far more thorough. Mine was more sort of 6th grade style lol. Maybe I will motivate and repost heh.


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## MiniVanMan (Jun 28, 2005)

-=Jeff=- said:


> It has been a bit cold here to play around in the garage and try things..


Cold?? What do you mean cold. Wuss!! Get out there and tear those doors apart damnit. That's what earmuffs are for  

I feel ya, it's been brutal here over the weekend.


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## 02bluesuperroo (Oct 31, 2006)

Great explanation MiniVan. I have one additional questions. When you refer to a driver being able to play to "x" frequency, does this mean it can be crossed over at that point or must be done rolling off by that point?


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## -=Jeff=- (Oct 25, 2006)

MiniVanMan said:


> Cold?? What do you mean cold. Wuss!! Get out there and tear those doors apart damnit. That's what earmuffs are for
> 
> I feel ya, it's been brutal here over the weekend.


LOL, Normally I would be, but I fighting a cold (sinuses), lost my voice on friday and have a bit of a sore throat since Sat. night. 

I also think I am going to sell one of my eD amps, and get either an a/d/s PQ10 or PH15.. to help with the space issue.


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## MiniVanMan (Jun 28, 2005)

Jeff, check out Memphis as well. They make a really nice small profile amp in their M-Class series. Great sound quality as well.

For Bluesuperroo, your question can be simply answered as crossed over at that point. However, it's a great lead in into different crossover types and how they're used. It'll be quite in depth so I'll probably post tomorrow a more detailed answer.


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## 02bluesuperroo (Oct 31, 2006)

Excellent, can't wait.


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## solacedagony (May 18, 2006)

www.passivecrossovers.com for some basics on... passive crossovers! 
A lot of it applies to crossovers in general, but they do have the specifics on setting up a passive crossover (caps, coils, resistors, etc).


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## hyun (Aug 13, 2006)

i don't understand what happens when you play a driver too close to, or at, the Fs resonant frequency. would the ill-effect be easy overexcursion?

e.g. for a 7" midbass with an Fs of, say, 45hz. What happens when you play it near the Fs, at 70, 60, 50 and even 40hz? the impedance rises at the Fs - does that mean the current flow through the speaker is reduced at the Fs? and therefore (as also illustrated in the freq response graph) its output drops at the Fs due to lower current flow?

Fs, being the resonant frequency, would that be equivalent to saying - the speaker's natural resonance is at this Fs - therefore, the little current that it receives at the Fs causes a lot of excursion, which can lead to damage? if that is the case, why does the measured output drop, when there's supposed to be overexcursion? won't there be higher and higher output until the speaker is destroyed?

finally, what is causing this rise in electrical impedance? what happens to the voice coil around that Fs, that causes the impedance to peak, which doesn't happen at other playable frequencies?

thanks! ... trying to understand more of the physics behind all this.


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## 99IntegraGS (Jan 18, 2007)

fej said:


> ... the explanation mini gave was far more thorough. Mine was more sort of 6th grade style lol. Maybe I will motivate and repost heh.


Please repost... I'm thinkin' I need the Fer Dummies version of Mini's post.  

JD


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## thazy2 (Feb 10, 2007)

I was woundering the same thing...........


SUPER explaination! The pics/graphs really helped me out.


thanks..........guys..............


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## ghart999 (Feb 8, 2006)

MiniVanMan said:


> I'm going to use a couple of examples, and some response graphs to help you understand this.
> 
> I'll start with the Peerless Exclusive 7". Scroll to the bottom of the PDF where the response chart is.
> 
> ...


That is one of the best posts I have ever read.


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## Kuztimrodder (Jan 10, 2007)

fej said:


> Haha thanks Evan ... wasn't wrong I don't think, but the explanation mini gave was far more thorough. Mine was more sort of 6th grade style lol. Maybe I will motivate and repost heh.


Some of us understand 6th grade style betterer:blush:

Tis true though, MiniVanMan is the man...man!


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## MiniVanMan (Jun 28, 2005)

Different drivers will behave differently near or at their Fs. 

The most common effect is an increase in distortion. Fs is actually a point at which the speaker itself starts to vibrate. It can overemphasize the frequency due to the vibration, but it will be realized as distortion.

Another common effect is the changing of crossover points due to the rise in impendance. As your impedance rises, the crossover point lowers. This can result in a flattening of your response throughout the attenuated range of the crossover.

Let me see if I can explain that a bit better. 

You're running a 4 ohm tweeter at 100 db. The Fs of the tweeter is 1000 hz. You decide that a 12 db crossover at 2000 hz is what you want to use. It's double the Fs, so it should be good, right?? Well, let's say the impedance starts to rise at 2000 hz, and the impedance reaches 8 ohms at 1500 hz, and tops out at 16 ohms at resonance, 1000 hz. As your impedance is rising the crossover point is lowering. For every doubling of impedance your crossover point cuts in half. So their kind of working against each other. In layman terms you're not realizing a true 12 db drop by 1000 hz. 

God!! I'm trying to figure out a way to illustrate this. Suffice to say, that's highpassing is best left for very steep slopes to realize and real gains in cutoff, when approaching the Fs. 

This is why enclosures are very desireable for controlling a low end on a speaker. They naturally cut of the frequencies mechanically as opposed to electrically. They're not as affected by the impedance spike at resonance, if at all. 

This is a yucky explanation, but barring a much more technical explanation, where I'll have to cut and paste the same stuff you can google, this will have to do.


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## ghart999 (Feb 8, 2006)

I was wondering about this in regards to the Seas Excel W18NX which is very popular here on the forum. It's Fr graph is shown below.

http://www.madisound.com/catalog/PDF/seas/e0042.pdf

According to the graph the 60-degree slope takes a huge dump at 2200Hz and then recovers again at 4200Hz. Should one not play the driver past 2200Hz and LP it at around the 2200Hz? I know that some people, myself included, run this driver with no LP at all. When would it be bad to do this?

Thanks.


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## MiniVanMan (Jun 28, 2005)

ghart999 said:


> I was wondering about this in regards to the Seas Excel W18NX which is very popular here on the forum. It's Fr graph is shown below.
> 
> http://www.madisound.com/catalog/PDF/seas/e0042.pdf
> 
> ...


I wouldn't run it with no LP. That peak at 4.2k is breakup, and just plain nastiness. Sure being the W18, it's probably better sounding nastiness than say the Dayton RS180, but it's still nastiness.


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## ghart999 (Feb 8, 2006)

MiniVanMan said:


> I wouldn't run it with no LP. That peak at 4.2k is breakup, and just plain nastiness. Sure being the W18, it's probably better sounding nastiness than say the Dayton RS180, but it's still nastiness.


So would you LP at 4000Hz? Play with different slopes?

I am still building my system and will be putting in LCY 110 ribbons. But for right now I have just the W18NXs playing with no HP and I don't really hear breakup. But my ear in not very well trained.


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## solacedagony (May 18, 2006)

ghart999 said:


> So would you LP at 4000Hz? Play with different slopes?
> 
> I am still building my system and will be putting in LCY 110 ribbons. But for right now I have just the W18NXs playing with no HP and I don't really hear breakup. But my ear in not very well trained.


Since the breakup is AT 4000hz, making the LP @ 4000hz is only going to put the breakup down 3db. So you're going to want to lower your crossover point as much as possible to limit the audibility of that breakup.


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## hyun (Aug 13, 2006)

MiniVanMan said:


> The most common effect is an increase in distortion. Fs is actually a point at which the speaker itself starts to vibrate. It can overemphasize the frequency due to the vibration, but it will be realized as distortion.
> 
> This is why enclosures are very desireable for controlling a low end on a speaker. They naturally cut of the frequencies mechanically as opposed to electrically. They're not as affected by the impedance spike at resonance, if at all.


that sounds reassuring. currently i'm running the vifa MG10MD09 discussed in this same thread, with a smallish enclosure, estimated not much more than about 400-500ml volume, with about 20% internally polyfilled. (calculated Q=0.707 size is slightly more than 1 litre.) for technical reasons i'm forced to run them down to 160hz, only protected by an active cross of -12slope at 125hz. it's response is flattish down to 160hz but it's awfully close to Fs at about 84hz, which explains my anxiety.

i'm still not noticing excessive distortion (perhaps my ears are too forgiving) but what worries me more is the potential for physical damage - the likelihood of encountering Xmax at low freq at high output levels. i don't know of any magic formula to calculate the SPL limit i could run it before it hits danger level - i suppose using one of those cone-area x freq x excursion formulas would be appropriate. (offhand, i don't know how to apply the formula yet.)

but even then, that would dictate the limit of how loud we can play a 160hz sine wave. from there, we probably have to infer the limit of overall loudness we can tolerate? or calculate from the fact that the 160hz sine test tone was a -1dB signal, and limit gains from there?

therefore i ask this to learn what physical damage happens due to playing at Fs - is it simply hitting Xmax or is there some other form of physical damage that occurs at Fs?



MiniVanMan said:


> Another common effect is the changing of crossover points due to the rise in impendance.


thanks for the effort in explaining. luckily i've dabbled a bit in passive crosses before and understand what you mean. as an addition to your discourse, an active cross would save you this headache since active crosses are not load-dependent and would be precise throughout? unless i'm wrong ... i have NO experience with active cross design.

Another question, very fundamental:

> I'll start with the Peerless Exclusive 7". Scroll to the bottom of the PDF where the response chart is.
> http://www.madisound.com/pdf/peerless/830883.pdf
> You'll notice the "blue", "red" and "green" response graphs. Labeled at the bottom you'll see "On Axis", "30 Degrees", "60 Degrees" respectively.

question is, is there a "convention" whereby plots are always 0deg, 30deg, 60deg? i frequently see charts with varying colours, but NO legend. they could very well be 0deg, 15deg, 30deg, and the legend for the colour coding is nowhere in sight. i don't suppose there's any standard presentation for off-axis freq response but i suppose 0-30-60 is the most common? or 0-15-30?


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## MiniVanMan (Jun 28, 2005)

Don't get so hung up in the graphs as much as use the examples as a baseline to kind of understand what's happening to a driver at its upper limits. I used those particular examples because they're accurate, and have more info than your usual flat line running across a graph that a lot of manufacturers like to give you. As you can see, that kind of graph is useless.

Now, for you midranges. Since you have them in a sealed enclosure, the enclosure itself is acts as a cutoff. Since your Qtc is about .9 (rough guess), the only effect it's really having is a slight hump at a given frequency (probably in the 150-200 hz range. I'm sorry, but I don't feel like modeling it up right now. It won't be realized as distortion, but rather just a peak in response. It may actually be helping.

So, I think you're fine. The extra 12 db at 125 hz is more acting like a subsonic filter would, which is in a lot of cases unnecessary in sealed subwoofer applications.

Good post though, it brought out some more points that are very valid. Thank you.

I think the message to take from this is, enclosures play a huge role in how your driver will respond on the low end.

Enclosures on the low end, and crossovers on the high end.


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## hyun (Aug 13, 2006)

MiniVanMan said:


> So, I think you're fine. The extra 12 db at 125 hz is more acting like a subsonic filter would, which is in a lot of cases unnecessary in sealed subwoofer applications..


i appreciate what you mean. i remember modelling my midrange and, as all modelled graphs go, the rolloff ends up with a minimum of -12db slope, sometimes more.

if the extra 12db at 125hz (subsonic filter) is unnecessary, i'd rather REMOVE it, because a filter at 125hz would induce a phase change up to as high as perhaps 250hz, and would interfere with the phase matching/transition between the midrange, and the midbass taking over.

however, the concern was a very close Fs at 84hz, so the -12db/oct @ 125hz depresses the graph by at least another 6db upon hitting Fs.

May i say then, that, if the modelled graph slopes nicely down, even if it shows a dampened (say, -20dB) response at the Fs of 84hz in this case, it's no big deal? that, even if i can make the speaker play at 120dB, and this Fs ends up being played at -20dB = i.e. 100dB, the act of "playing at the Fs" does not have implications along the lines of "you're gonna destroy your speaker"?

i'm feeling safer now. next, i'll go revise on formulas to calculate SPL with respect to Xmax, to determine max audio output to avoid damage. thanks!


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