what makes the RF7 more 'effecient' than the RC7

[Deang]

The RF7 is 102db/w and the RC7 is 98db/w - isn't 4 db/w a fairly substantial difference?

Looking at them, the only difference is that the RF7 has the 2 10's and the RC7 has 2 8's -

It would seem that if the RF7 is more efficient because of the 2 10's - then we should expect to find them overpowering the horn somewhat - but that is not what I hear when I listen to them. They are very well balanced.

If we say the RC7's are less efficient than the RF7's for the same reason (because they have the 8' instead of the 10's) - than we might expect to have the horn overpowering the 2 8's - with a balance tipped to the highs. But I don't hear that either when listening to the RC7's.

What accounts for the difference in efficiency?

Is the horn in the RC7 'throttled' back somewhat using the crossover?

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deanG

[WMcD]

I can't speak to the specific speakers. But generally, you're on the right track.

The overall "problem" with direct radiator bass drivers is that they are relatively small compared to the wavelengths they are trying to reproduce. Therefore they are poor antennae.

They are actually operating in an area where radiation resistance is low, at the deep bass, and getting better up to the cross over point.

This would result in a rising output. The "trick" used is that the motor is relatively weak compared to the mass of the diaphragm. Therefore the effort of the motor is used up to move the diaphragm back and forth as frequency increases. In effect, while radiation resistance is going up, and it is a better antenna for sound, the mass is keeping the diaphragm from moving too much.

This is a form of self equalization, and is called "mass control."

You have to think about this for a while. A small radiator will put out some bass, but less than a larger one. Therefore, there must be more "equalization" to keep respose even. Essentially, this is knocking down the rest of the response.

There are several games to help bass response. They are the use of a port, or a drone driver, or, having a second bass driver start turning on as frequency goes down. None the less, these direct radiators are not as efficent as when a horn is used. In this situation you have a type of sophisticated megaphone in front of the driver.

Consider the LaScala. It's mouth is four sqare feet in area. Larger than most any single direct radiator.

In most cases, tweeters and midrange drivers are more efficent than the bass driver. Therefore their response must be reduced in the circuits of the crossover.

Putting it all together, a small direct radiator is going to less efficent than a large one in the bass. Then the tweeter has to be made less efficent to match.

Gil

[WMcD]

Yes, basically,

The attenuation is most often accomplished by a network of resistors. Or you can have a set up of variable resistors. This is what is called an L-Pad, on some speakers, though not Klipsch stuff. Some others have a type of volume control, or a switch. They allow adjustment of the output of the tweeter. In some technical parlance, these function as "voltage dividers."

Klipsch designs do not typically use resistors. Rather they use a transformer. More properly, an auto-transformer. There are good technical reasons to believe this is the superior approach. Here the transformer "steps down" voltage.

It is another can of worms. But I'll go into it. It may be that the constant directivity high frequency horns used in the Reference series have a related problem. I don't know this for sure. Essentially, the mass of the diaphragm prevents them from working at high frequencies. Here we have the same "mass control" effect, but only because it is difficult to get rid of mass. Hence the use of light weight materials.

Therefore, the combination of components in the network is used in the tweeter circuit, perhaps, to knock down the low end of the tweeter in two way systems.

You can see the overall problem. The bass drivers are not working well in the low end, the high frequency drivers are not working well in the high frequencies. So there has to be a lot of juggling.

The juggling is more easy if the designer is willing to sacrifice efficency.

The most challenging situation is where you want to maintain high efficency, overall. That is the challenge which the Klipsch designers have met well.

Gil