UNDERSTANDING CROSSOVERS

[CIGARBUM]

Well I have been writing several posts and asking probably real dumb questions about crossovers, horns and drivers. I feel it's about time I learned some of the technical stuff, please understand I'm dumb as a box of rocks when it comes knowing what I;m doing, so be kind to me. Why I have not getting good answers is that I'm not asking the right question.

That being said, here's where I am. I want to build another set of speakers, I believe it is going to be JWC's DBB. In an effort to ask questions of what components to use, I get information on a whole bunch of stuff I don''t understand, not your fault, mine for not understanding. So far the only thing that is set is the bass bin, it will have 2 of Bob's cast woofers, beyond the when I start asking about horns and drivers for the horns and tweeters ( yes, it will be a three way system ) what I get is a bunch of question about where do you want to roll off or what frequency are you going to cross them, hell I don't know.

I'm going to start with the crossover, it is that bunch of electrical stuff mounted on a piece of wood mounted in the speaker somewhere. So lets assume that I have my components selected, Bob's woofers, ALK tractrix 1" wooder horn, a Great Plains 16 ohm 902 and a Beyma 25 tweeter. Don't ask me why but that's what I used in my Cornscalas. Now I'm not sure these numbers are anywhere close to correct but close enough for discussions purposes.

The woofer: 52 - 2500 Hz

The horn driver: 400 - 9000Hz

The tweeter: 2000 - 25000Hz

Now your recorded media, CD, record or whatever, that signal goes around the player and pre amp and amp to 2 wires that go to the crossover, now this signal has the full spectrum of frequencies recorded on the media and when it makes it to the crossover and goes through all the little tin can things and the little wheels of copper wire and segragates the frequencies to be pushed out the three set of wires to the woofer,horn and tweeter and hopefully it giving each speaker the proper frquencies and nothing it can't reproduce. Bob told me sometimes the speakers aren't really happy producing some of the frequencies, well I want mine to be happy, happy.

Slopes, don't have a clue, but from what I have read from universial to extreme, does that just mean either a bleed over of frequencies or no bleed over and the speaker get just what it can reproduce.

Really, how much of this stuff do I have to know to build a speaker, I want to sound as good as I can afford, without being an Electrical Engineer, my degree is in Civil

Anyone have any good suggestions. Thanks for your attention

CigarBum

[Coytee]

Much of this crossover stuff is also voo-doo to me. That said, you said..

how much of this stuff do I have to know to build a speaker, I want to sound as good as I can afford

I'd speculate that's the thrust of the issue for you. You can put parts together and get 'a sound'. Good/bad/indifferent...is another question. You don't have the tools to genuinely "create" a speaker from scratch so you have to rely on some time tested ideas/parts (nothing wrong with that at all!!)

Question....

Might you consider an active crossover for your project? If you did, you could tinker with the crossover settings on the fly. As it is...if you create a crossover and want to tweak it...you'll have to take it apart, make your changes and put it back together. With an active you can simply change it on the fly.

(I'm becoming a bigger & bigger fan of actives)

Seeing as I don't know much about what all you are doing (I've never built a speaker), I do think if you could consider going 2-way it might simplify some of your problems as you would lose an crossover point.

I'd speculate if you are making DBB's, that you could cross them at least as high as 500?? (that's a question for others who know)

If that's accurate, might you consider a pair of Klipsch K510's with a pair of K69's hanging off the back? (2 inch drivers)

The assembly would probably be small enough to fit inside the box, you are at a 2-way design AND the paramaters for the K510 are well known (although I do not know how it gets integrated with the bass bin)

Trust me when I tell you.... we also want your drivers to be happy, happy drivers!!

[CIGARBUM]

I'm not sure what a active crossover is, never seen one, got any pictures? How much do the cost? Just from the little I have read, they sound compliated.

Tell me more Rich

CB

[Oblio]

I'm not sure what a active crossover is, never seen one, got any pictures? How much do the cost? Just from the little I have read, they sound compliated.

Tell me more Rich

CB

Active crossovers can either be simple, made up of Op(erational) Amp(plifier)s, to the more complex Digital Signal Processors (DSPs). DSPs can be reprogrammed and can give finer control of crossover frequencies, roll off, and phase shift. Your tone controls on your amplifier are examples of actve filters though the output is summed prior to sending the signal to the amplifier stage. Conceptually, you could buy 2 or 3 receivers, set the tone controls so that each receiver had one control up and the others downand feed each output directly to the respective drivers. This would not sound great and may damage the speakers because the slope/attenuation of the tone controls would less than needed but it illustrates the concept.

[Islander]

Lots of info here: http://en.wikipedia.org/wiki/Active_crossover

With Klipsch bi-amped speakers (the Jubilee and JubScala), the most commonly used active crossover/processor is the E-V Dx38 (about $1500 new, $600-800 used) or the built-in DSP of the Crown XTi pro power amps. If you know the settings, they're actually simple to use. You set them and forget them and listen to the great sound of music.

[Guest David H]

I like the active crossovers as well, but it is far simpler to to use a tried and true crossover design, I believe there is one on the ALK site and JWC has one for the DBB as well.

I am currently using a modded Behringer DCX2496 for my active crossover and am amazed at the sound. I also set up an Ashley XR4002 recently for Johnny 5, and like it just as well if not more. The problem with using actives is that it requires 3 amps, pink noise source and an spl meter.

[Islander]

The problem with using actives is that it requires 3 amps, pink noise source and an spl meter.

If you're using Jubilees or JubScalas, which are both 2-way, you need two amps (one stereo amp for the woofers and one stereo amp for the tweeters), the crossover/processor, and that's it. Klipsch will supply the crossover settings, so you just program it and start listening.

[Coytee]

I agree with Pat...even though he has been banished to an island. [:|]

I'm on the dumber side of 50/50 so I'm not into having to re-create anything...especially if the solution has already been laid out. If the passives are already laid out for Bob's project then I say, power to him.

Bob... if you want to make the drive through never land, you're more than welcome to swing up my way and hear the active. I've got a second active crossover that you could borrow if you'd like as well. It's currently being shipped off to EV to fix the display but should be back in couple weeks.

one really nice thing with the active... if I am running my Jubilees I simply select the Jubilee setting. If I want to swap the stock driver on the Jubilee out for the TAD drivers, that requires a reformat of a crossover board. In my case, I would simply adjust my settings inside my active and be done. (actually I have the settings for the TAD driver already saved in slot 2 of user memories)

If I want to put my big horn on top of my LaScalas and make them JubeScalas all I gotta do is put the parts together and on my active, go to that selection and again, I'm done.

Bob... something to know (perhaps trivial though). When someone like Roy is designing a passive he uses the active crossover and his chamber as his main tools (and some kind of signal generator as well I'd imagine). His goal is to figure out what paramaters are needed to get the speaker sounding as good as he can make it sound. He then takes the paramaters configured inside his active and starts designing passive crossovers to try to reproduce the sound of the active.

The point being... (qualified with an "as I understand it") the active creates the standard in which he later tries to duplicate with passive parts. You can dial the sound in much tighter with an active.

If you think you'd build these and be done 'forever' then going passive would probably make some sense. if you think you will use these for while and then perhaps replace them with another project.... in my opinion, the idea of an active which is reusable, starts to make more sense than building passives for all your creations.

You want to borrow my active for a while??

[Coytee]

Bob, here's the scoop on what a number of people are now using. it IS best suited for a 2-way speaker or you could get two units and have one unit per channel so they could do 3 or 4-way...

I think this is one reason why your initial game plan needs to always be well thought out. If you want to go 3-way and bought one of these you'd only be halfway there.

There ARE 3 and 4 way actives, good/better/best I'm sure. I just don't know much about them.

http://www.electrovoice.com/products/50.html

[JohnA]

I'm a Civil Engineer, too.

You realize the questions you've asked have been the subject of several theses? If I were you, I'dpick up a copy of Loudspeaker Design Cookbook.

The Altec/GPA 902 can comfortably run from 500 to 20k on the right horn. It doesn't need a tweeter.

The 908 runs from 500 to 9k on the right horn and absorbs much more power.

Starting with the elementary,

Obviously, the crossovers divide the frequecies between the drivers. They do that by gradually adding impedance (restriction to power) as the frequency rises above the crossover point in a low pass circuit (and as frequencies fall in a high pass circuit). The crossover point is defined as the point where the response drops to -3 dB (1/2 power). When 2 drivers at -3 are in phase they add to 0 dB and have flat response. Each component (cap or inductor) add one "pole" or "order". In most crossover designs each order is 6 dB/octave. An octave is a 2:1 change in frequency.

Each order of a crossover shifts the phase of the frequencies above it by 90 degrees, so you will often see the tweeter in a 2nd order crossover run in opposite phase to the woofer. Horns also shift the phase 90 degrees compared to a direct radiator, or so I've been told.

Crossover points should be selected based on the driver response curves, power handling of the drivers and the dispersion angles of the 2 drivers especially between the squawker and tweeter, most horns begin to beam as frequencies increase. Matching the dispersion angle of the tweeter and squawker should improve imaging and will improve sound quality off axis. Cross tweeters and squawkers at least an ovtave above their resonant frequency to keep them "happy" and buzz-less.

I had to add some contouring to the network when I mated 902s on 511Bs to Peavey FH-1s. You may need to also. I used X-over 3 Pro and recommend it.

If I were doing it, I'd build a 2-way system with a 902-8B (no need for the 16B and it would be undesireable with some amps) on a 511B horn (you could try a Klipsch K510 also) and I'd use a pair of 16 ohm Eminence 15s. I would not use a pair of K-33s in parallel that gives a nominal impedance of 2 ohms and a DC resistance (minimum impedance) of 1.6 ohms. That's a tough load for any amp.

If you are intent on loud and high power, you'll have to switch to the 908-8B and add the tweeter.

[IB Slammin]

CB,

I run ESN 450 dbb passive networks on them. Think I had about $800 in parts and could have spent more for better mid range caps.

I run BEC's CW1526C cast woofers - JBL 2404 tweeters - Altec/GPA 902-16A mid drivers on Altec 511b mid horns (now trying gothover's wooden Trax mid horns[Y] )

I spank the little girls (902's) crossed at 450hz (ESN) without a prob. I intended for the networks to be outboard so looks were an issue. They don't have to look that good if hidden in the top hat. A great friend with great hands assembled them.

Hope this helps as to the cost of passive networks vs active. I love the dbb's. The Slam Factor (that boot in the chest) takes my breath away.

Email me at Ibslammin@gmail.com if I can help.

tc

[IB Slammin]

I'm a Civil Engineer, too.

You realize the questions you've asked have been the subject of several theses? If I were you, I'dpick up a copy of Loudspeaker Design Cookbook.

The Altec/GPA 902 can comfortably run from 500 to 20k on the right horn. It doesn't need a tweeter.

The 908 runs from 500 to 9k on the right horn and absorbs much more power.

Starting with the elementary,

Obviously, the crossovers divide the frequecies between the drivers. They do that by gradually adding impedance (restriction to power) as the frequency rises above the crossover point in a low pass circuit (and as frequencies fall in a high pass circuit). The crossover point is defined as the point where the response drops to -3 dB (1/2 power). When 2 drivers at -3 are in phase they add to 0 dB and have flat response. Each component (cap or inductor) add one "pole" or "order". In most crossover designs each order is 6 dB/octave. An octave is a 2:1 change in frequency.

Each order of a crossover shifts the phase of the frequencies above it by 90 degrees, so you will often see the tweeter in a 2nd order crossover run in opposite phase to the woofer. Horns also shift the phase 90 degrees compared to a direct radiator, or so I've been told.

Crossover points should be selected based on the driver response curves, power handling of the drivers and the dispersion angles of the 2 drivers especially between the squawker and tweeter, most horns begin to beam as frequencies increase. Matching the dispersion angle of the tweeter and squawker should improve imaging and will improve sound quality off axis. Cross tweeters and squawkers at least an ovtave above their resonant frequency to keep them "happy" and buzz-less.

I had to add some contouring to the network when I mated 902s on 511Bs to Peavey FH-1s. You may need to also. I used X-over 3 Pro and recommend it.

If I were doing it, I'd build a 2-way system with a 902-8B (no need for the 16B and it would be undesireable with some amps) on a 511B horn (you could try a Klipsch K510 also) and I'd use a pair of 16 ohm Eminence 15s. I would not use a pair of K-33s in parallel that gives a nominal impedance of 2 ohms and a DC resistance (minimum impedance) of 1.6 ohms. That's a tough load for any amp.

If you are intent on loud and high power, you'll have to switch to the 908-8B and add the tweeter.

John,

Great post and good points as usual.

However, I tryed the 511/902 in two way and missed some cymbal strikes and sizzle to my ear. (but then I am an old guy and might need some extra hf -smile)

I value a speaker that has the same quality sound at 80db peaks as it does at 110db peaks. With proper network slopes, the 902-16a does all of that with grace. The 908-8b misses some upper mid range detail vs the 902 and is not needed for home use at any reasonable SPL (110db) INHO.

Your K33 type woofer load presented to power amps is a good point. I use a tube CDP and Preamp in front of two (re-capped) vintage Luxman SS power amps.The load is no prob here, but could be for for others.

Regards,

tc

[JohnA]

902s are only rated at 10 watts continuous. I think that's a little delicate for heavy duty use. Playing loud crossed at 500 hz is pretty heavy duty. There's still a fair amount of energy at 500 Hz. The crossover I used with my 902/511Bs crossed at 1K (the response curves were better) and had a polyswitch and resistor for driver protecton.

902 Data Sheet

906s and 909s can take much more. Since Bob wants to use a tweeter, the more durable drivers would be more suitable for his application. Terry, I think you are the first person I've ever found to down the sound of Altec's compression drivers. []

I didn't find a data sheet on a 908. The Great Plains 909 fills it's niche.

906

909

[CIGARBUM]

Boy, you guys sure are confusing me.

CB

[Coytee]

They're a bunch of engineers.... you know how confusing it can be to talk to engineers.... don't you?

[dBspl]

Obviously, the crossovers divide the frequecies between the drivers. They do that by gradually adding impedance (restriction to power) as the frequency rises above the crossover point in a low pass circuit (and as frequencies fall in a high pass circuit). The crossover point is defined as the point where the response drops to -3 dB (1/2 power). When 2 drivers at -3 are in phase they add to 0 dB and have flat response. Each component (cap or inductor) add one "pole" or "order". In most crossover designs each order is 6 dB/octave. An octave is a 2:1 change in frequency.

This is basically correct, except two in-phase drivers (operating at the same output level) will acoustically add 6 dB. If the two drivers are down -3 dB and in-phase at the crossover point, the result is a + 3 dB bump.

The drivers don't have to be completely in-phase to sum well. As you can begin to see in this chart, a phase angle difference of less than +/- 45 degrees is close enough to effectively give you + 6dB.

0 degree phase difference + 6dB

45 degree phase difference + 5.5 dB (approx.)

90 degree phase difference +3 dB

120 degree difference 0 dB (approx.)

180 degree phase difference - infinity

Electrically, two in-phase signals would only add 3 dB.

dbspl

[WMcD]

The woofer: 52 - 2500 Hz

The horn driver: 400 - 9000Hz

The tweeter: 2000 - 25000Hz

- - - -

I think we're making things too complicated for a beginner -- and we're not answering beginner's questions -- or confusion.

1) One function of the crossover filters is to keep harmful freqs out of the drivers. Generally this is to keep bass out of the mid and mid and bass out of the tweeter. That is generally accomplished with simple crossover filters. But consider that more recent Klipsch designs are using higher order tweeter filters to protect them.

2) We use the filters to make sure that woofer, mid, and tweeter are only fed with freqs where they work well acoutically.

Contrary to numbers someone gave CB, the woofer (say 15 inch) is not working well above 800 Hz. There may be acoustic output but it only because the pattern is narrowing. Therefore someplace around 400 Hz is used IF you have a mid which can take over. That is the situation here. We need a low pass filter to let "everything" pass below 400 Hz.

The mid probably only works up to 4000 Hz. This is okay because we're going to crossover to the tweeter. This means you need a passband design from roughly 400 to 4000 Hz. Hard to tell without really good technical specs.

The tweeter probably is not going to work well below 4000. So we need a high pass to let "everything" above 4000 to pass

So by the above we have set some points in the electrical design of the filters.

- - - - -

2) Now, talking about passive filters: How to design from a rough starting point. One thing you must know is the impedance of the driver and the target freqs (which we have determined roughly above). The first is the most difficult to determine without sophisticated measuring equipment. Lacking that, you are probably better off to rely on the designs of someone else.

3) From this point on, things get very complicated. I've used "everything" in quotes above because there are the natural roll-off of the electrical filters. They are not brick wall filters. They have overlapping output. While difficult to explain simply, the magnitute and phase of the outputs of the filters (assuming that is all we're concerned with) can lead to some non-obvious results. That is why you read so much about the phase and magnitude issues of the filter outputs. At this point, I say not to worry.

4) If you want to get closer to the truth. Most all of what you read about filter output magnitude and phase is incomplete. This is because the drives-horns themselves act as filters and interact. I believe that dB SPL is talking about the effects of mutual coupling when two acoustic souces are close to each other. He alluded to this in the room boundry subject with John A. Hence 6 dB versus 3 dB debate.

The filter inherent of the speakers themselves is an interesting issue. Horns/drivers have very sharp, but not quite brick wall characteristics which in theory have very rapid phase changes far beyond the electrical filters feeding them.

Wm McD

[seti]

Thanks guys great posts.

[jwc]

I can understand everyones concern about k33's in parallel. I will tell you my experience with doing just that.

I have run sveral different passive with the dbb's. Also different amps.

These amps I've run on the dbb's for extended lengths of time w/o an "apparent" problem.

VRD's

Dynaco 60's

Luxman Vintage SS

McIntosh MC252

McIntosh MC206

Carver M1.0t

Mark1101 has passives on his MWM's and had used a "Bob latino" tube kit amp as well as an MC250 and an MC252.

Nothing has blown up as far as I know.

jc

[mark1101]

I run roughly 2.5 watts on my MC-252 and it will drive you out of the room. So I have never been concerend about the 3.6ohm impedance of the paralleled K-33s. They are not looking for very much power in my application. A couple of time I had them up to 25 watts and that was just idiotic. You could not listen to music at those levels.