cross-overs questions?

[Colin]

plain english version of the types of cross-overs and what difference they make for horns and conventional speakers, please?

if the cross-over doesn't say what kind it is, how do you tell?

what kind is the Cornwall I B2 cross-over?

what kind are ALK's superb models?

what makes some cross-overs so cheap?

[Al Klappenberger]

Colin,

It's difficult to define "type" since there are many definitions of the word in this context. Maybe if you would give us some of the terms you have seen that are confusing you, the explanation would be easy. Once I know what you're thinking of, I can define what type mine are anyhow.

Al K.

[Malcolm]

Wow! Explain crossovers in plain English! Quite a challenge!

Well, there are serial crossovers and parallel crossovers and hybrids of the two. They take their names from how the filter sections for each of the drivers/radiators are connected to each other. The crossovers used in most of the Heritage line, including the B2, use an autotransformer. I am not sure what you would call them.

The differences between the various crossovers used in the Heritage line are basically due to the crossover frequencies and attenuation required to make the particular drivers/radiators and box yield a reasonably flat frequency response.

Generally, the only way you can tell what kind a crossover is to look at the circuit or a schematic of it. The crossover for each combination of drivers/radiators and box pretty much have to be designed for that specific combination, although different crossover designs can be used to achieve similar frequency response from the speaker.

There are active crossovers and passive crossovers. Passive crossovers are what you usually have inside your speaker cabinet. The are composed of capacitors and inductors, and sometimes resistors or protection circuits. They do the work after the power amplifier. Active crossovers live between the preamp and the power amplifiers. They are built with operational amplifiers. They are used by people who bi-amp or tri-amp their speakers.

There is a lot more to crossovers than this, but at least it is a start.

ALK's crossovers are electrically very similar to the original. Al can fill you in, but basically, he uses higher quality components and some circuit tweaks to improve the sound.

Cheap crossovers are usually cheap because they use cheap components, bipolar electrolytic capacitors instead of metalized polypropelene or oil capacitors, ferrite inductors instead of air core inductors. Some are cheaper because they use a less steep roll-off in their filter sections. Crossovers with first order filters are cheaper than those with second order filters because they require fewer parts. Speaker manufacturers have to make compromises in crossover design, and for that matter everything else including drivers/radiators and the box, to get a speaker they can afford to build for the target market. As a speaker enthusiast, you are not faced with that dilema. So you can build crossovers like Al's, use active filters and tri-amp, or do whatever you please, if you have the time and money.

[Colin]

guess I am looking for a definition of the orders - what is first, fourth opder? what does it to the user? how can one tell?

[Klewless]

Colin,

Here is a little bit more. First order means a slow attenuation rate (6 db / octave). In this case there is a great deal of overlap between the two drivers (woofer / tweeter) and very little driver protection for the tweeter. Second order uses twice as many parts to increase the attenuation rate to 12 db / octave and increases driver protection for the tweeter. This decreases the overlap but adds other complications, such as phase changes which affect the sound. Next comes the third order at 18 db / octave, etc. This decreases the overlap even more. But there is a price to be paid for steeper attenuation rates (called the slope). Potential ringing internally within the network (which the speakers intrepret as signal and proceed to reproduce these currents as sound).

It is difficult to to detect just by looking and as Malcolm stated, you'd have to draw the circuit to determine the type. It is not possible to just count parts because there can be other embelishments to the network performing other tasks besides dividing up the signal for the speakers. The auto transformet used by Klipsch for example acts as a volume control for the midrange.

The heritage series used different slopes for each driver. The woofer was very slow, and the tweeter was very fast. The reason for the fast tweeter cutoff was to protect it from low frequencies, which would burn it out in a hurry. So you can appreciate that the crossover was doing more than dividing up the signal for each speaker.

Generally the user does not care. The purist of course cares about everything and looses lots of sleep over it. There is something to be found wrong in just about every approach. Some people believe in crossover types like gospel. Others just accept the facts that crossovers do what they do and leave it at that.

I sincerly hope this does not confuse you any more. Study of crossovers can be very enlightening and is a complex topic.

Anything you do to a speaker can change it's sound whether it is right or wrong, or maybe neither right nor wrong, just different.

------------------

John P

St Paul, MN

[pzannucci]

There are problems with each crossover design as Klewless points out. Each different design introduces a phase shift along with its attenuation of the frequencies. The phase shift usually depends on the slope of the crossover. The 6db per octave is supposed to be the best for phase continuity. Phase shift is not a good thing but is a side effect that designers have to put up with and work around so that their speaker designs don't sound muddy and introduce odd distortions and holes/peaks in response due to the driver overlap.

The several last things that weren't noted (of course this is not all encompassing) but depending on the drivers and their crossover slopes, many times a 12db and an 18db crossover can actually yeild an acoustic equivalent of a 24db per octave slope. So you really can't just look at the components. The components yield the electronic slope.

Lastly, you can even have your crossover at the perfect point at where the driver naturally starts to rolloff at 6db or 12db per octave and you will have to factor in the actual driver acoustic rolloff along with the electronic rolloff to come up with the real db per octave acoustic output drop.

Bottom line though is no crossover is the best crossover. That is why Klipsch is fighting so hard to build two way systems. This minimizes the crossover interaction (badness) but puts much higher stress on the quality and frequency response extremes of each driver.

Hope this helps (or adds to the confusion)...

Peter Z.

[Al Klappenberger]

Colin,

John and Peter have done a pretty good job of answering your question. I'll

just add one other point relating to the networks I am building. They are

third order on the tweeter and second order on the squawker high cutoff. The

La Scala and Khorn both use horns on the squawker and tweeter. These have

natural rolloffs of their own. The K77 (T35) tweeter will operate down to

3500 Hz, so it's roll off is below the crossover, which is at 6000 Hz, so it

does not come into play. The squawker horn cuts off at a bit over 6000 Hz.

This allows its natural roll off to be added to the filter in the network

making the squawker and tweeter slopes nearly the same.

The interesting thing about the second order crossover (Butterworth) is that

the phases of the two drivers is exactly opposite (180 degrees out) coming

out of the network! One of the two drivers should theoretically be reversed

to restore the phase. In practice however, The physical distance between the

drivers also causes phase shifts due to the propagation time of sounds

through the air. This means the only sure way to know how to connect the

drivers is to sweep across the crossover area using instruments and look for

a "suck-out" or notch. This, by the way, is what is holding up my design for

the Cornwall. I am changing to a second order woofer / squawker crossover

and I have only gotten the instruments to do this testing within the last

several weeks.

Al K

[Colin]

Wonderful! Thanks so much for your time and trouble!

[KGeist]

With regard to the 180 degree phase difference from second order crossovers...

When designing crossovers for speakers such as the Cornwall, you must also take into consideration the phase characteristics of the drivers themselves. In the case of the Cornwall, you have a mass controlled woofer and a resistance controlled midrange horn, therefore, there exist a 90 degree difference between the two. When coupled to a second order network, this results in a net 90 degree phase relationship.

This is a really simplified example since the phase characteristics of the individual drivers is quite a bit more complex than this. But it should at least help illustrate the point that the phase characteristics of the drivers must be considered when designing networks.

Kerry

[Al Klappenberger]

Kerry,

Yes, I found out about the 90 degree difference in the driver types the hard way! That's why I am changing the Cornwall woofer / squawker crossover to second order. Nothing in the world quite like 20 - 20 hind-sight!

Al K.

[DougSchaefer]

Hello from a new member:

Sorry if I put this question in the wrong place. I have learned (and laughed) a lot while lurking here the last 2 wks.

Just bought a pair of used Heresy I for music&HT (I'm so happy...). Considering purchasing a 3rd Heresy for the center channel. I would rebox the horns and crossover, and not use the woofer. So a few questinos arise:

1. Does the crossover's woofer output need to be loaded? I would suppose with a high-wattage resistor (8 ohm), even though the center channel signal should not contain much low-frequency energy.

2. Change some crossover component values to allow the midrange (does anybody but me dislike the word "squaker"?) driver to reach a bit deeper?

3. Does this sound like a particularly bad idea to the Klipsch experts assembled here?

If the unanimous opinion is to forget it and buy a new Klipsch center channel speaker box, fair enough. But the idea of the same drivers all accross the front appeals to me.

BTW a Sony STR-DE615 receiver provides the signal.

Thanks for input. Will be making the purchase decision on this particular single Heresy single by 25 Nov 01 PM. That ought to be a pretty good clue as to its identity/location.

Doug Schaefer

[JohnA]

Horns have a low frequency cut-off based on their dimensions (length, mouth area, etc.). Some Heresies used a K-55-V squawker driver with their K-600 horn. The K-55-V is capable of going down to 110 Hz, but the K-600 is not. It is intended for use above 600 Hz. It's true cut-off is probably 450 to 500 Hz; somebody will know. Below the true cut-off frequency the driver diaphragm will unload, there will be little output and it can be damaged by excessive excursion.

You must be intending to use the squawker and tweeter near your TV and let your sub pick up the lower frequencies. It would be a VERY unusual sub that could hit 600 Hz. I think you'll be disappointed with the results. I'd keep the Heresy intact and crossover to the sub at 100 Hz, or get a real center channel.

While it would probably be better for your amp and would make the crossover behave as designed, I don't think inserting a resistor in place of the woofer is necessary. You would need a very high power resistor to ensure it didn't burn out.

Squawker is a term coined by Mr. Paul, so we all seem to keep using it.

John

[DougSchaefer]

First, Thanks John for the reply.

If I explain the setup I have in mind, it may make more sense. You be the judge.

This is a conventional 5.1 system I suppose. With Heresies on the L and R front. I use a JBL powered sub on the Sony receiver's line level sub output. That sub can crossover as high as 150 hz or so I suppose but it's pretty boomy up there so not an attractive option. The current center channel speaker is Yamaha NS-AC3 (I know you guys are laughing now) with 2 5" low/mid drivers and a small dome tweeter. As such it seems similar to many speakers dedicated to center channel use.

My idea (at least prior to the reply) was that the 5.1 center channel received little or no signal below the "voice range", say 300 hz or so. Thus I could put the 2 horns into a smaller box and convert the power directed to the (absent) woofer to heat. Ought to have been just a few watts after all.

Perhaps this approach only makes sense if I suggest that for aesthetic reasons I might not place a Heresy box atop the tv.

The single Heresy that I would buy for center use is said to have a K-55-V, and now I know it is not designed to reproduce to the bottom of the voice range. I did not intend to enlarge the horn to extend the range of the midrange.

Basically I was just trying to get matching drivers all across the front "soundstage" without a 16 x 22 inch box balanced above the tv.

You have nearly convinced me that the best solution may be to just use the Heresy enclosure atop the tv. Would need to be securely affixed here in earthquake country.

Last, I did not know the the origin of the term squawker. I withdraw my objection.

This message has been edited by DougSchaefer on 11-22-2001 at 05:32 PM

[WMcD]

Many things crept into this thread.

I'd like to jump on the bandwagon about the issue of the theoretical cross over of the crossover and its "order."

As mentioned above, the real issue is the charactristics of the crossover, driver, and horn, all taken together.

In my measurements, none of the cook book equations apply. It is a much more difficult matter of testing and design.

As far as the Heresy question. I think the best would be three of them in front. Cross over to a sub at 70 Hz or whatever your amp will give you by default by setting them to "small."

Gil