DHAxovers for my '75 Khorns are done

[Marvel]

OT-- driving with the windows down WILL cause high freq. hearing loss.

I drive a 98 Blazer. I get 21-24 mpg on the highway with the windows up and the A/C on.

Bruce

[Al Klappenberger]

Bob,

"The 68 ohms was measured on a new K-33E right out of the box at 35 hz"

Of course! That's the cone resonance! That happens below the usable range of the woofer and it's a very narrow spike, so let er rip! Who cares! I think the back air chamber tends to damp that peak out somewhat anyhow.

Interesting about the MPG study. I think though that you would need to do more than just one pair of cars tested with a single 5 gallons allotment of gass each one time. One engine may have been slightly out of tune or something like that. You would need to at least do it one more time with the window and air conditioner settings reversed to the other car. There's just too may variables.

Al K.

[sfogg]

"Interesting about the MPG study. I think though that you would need to

do more than just one pair of cars tested with a single 5 gallons

allotment of gass each one time. One engine may have been slightly out

of tune or something like that."

Not to mention repeat the test with something other then a couple of

bricks. They have lousy aerodynamics to begin with... opening a window

in them isn't going to have nearly the same effect as in a car with a

much lower Cd to begin with.

Shawn

[Al Klappenberger]

Shawn,

How about repeating the test with a couple of these:

Al K.

[formica]

Greg, Ironically, this is all above my head. [:|]

You too, huh? [8-|] ...

[Al Klappenberger]

Guys,

Have we gotten off the subject here or what? I think we were all picking on Bob about the swamping resistor! [6]

Al K.

[Deang]

Bless his heart -- but he started it! Shoot, you guys took off without me -- I wasn't done yet!

Let's go really off topic -- I just got back from the hospital and I got me another pretty girl: Alexia Hope, 7 lbs. 10 oz. Mom and the baby are doing great. Naturally I'm completely wiped out from all the hard work. While Debbie was pushing, I was thinking about Newton's 2nd Law and impedance.

I wanted to post the following earlier today, but the forum was whacked, so I just emailed it to Bob.

Begin post:

Something's wrong Bob, it doesn't make any sense. How about L-pads? Same deal. Look at tweeter filter John designed for the JBL unit -- he's using a LCR filter AND and a L-pad. This changes the impedance characteristics of the driver -- look at the curves on his website. The curve changes because of the filter, and there can be no change unless the amplifier can "see" -- which is why the curve changes. The resistor does the same thing, but instead of targeting a range of frequencies, it does it across the whole of the driver's response. Other than that, there isn't any difference.

What John explained to us just doesn't fit. I wonder if he thinks when Al says "impedance matching" he's thinking of it in the classic sense -- where you match the source to the load -- which in not what Al is doing. Al designs around a .1 ohm source impedance, not an 8 ohm source impedance. There's a big difference.

End post:

I don't like the engine analogy either. However, the last time it was used I pointed out how the transmission and torque converter is the interface between the engine and differential which allows for the most efficient use of what the engine can do where the rubber meets the road. At any rate, the engine/transmission/differential system is not really analogous to the loudspeaker/network/amplier system -- for the reasons Al already pointed out.

"How about explaining what you think the swamping resistor does that is good? I just have trouble seeing any good from it and can see some bad."

I suppose I should write a response out for the general audience instead of you specifically, since you already know most of this stuff.

"Constant impedance" is a bit of misnomer I think. I say this because the impedance is not this perfectly straight line across the page of the plotted curve -- there is still variation in impedance -- it's just not climbing to the ceiling like the stock networks. I just see the added resistor on the autoformer as a form of impedance correction that's also part of a total design for the squawker that brings it into better acoustic alignment with the other drivers while also smoothing its response. The "total design" includes the addition of a low loss bandpass filter for the squawker that rolls off its response and limits its useable range at the upper extreme. This lowers distortion and also cleans up the sound of the lower end of the K-77's response where the drivers overlap. The K-400/401 needs some help -- and this gives it.

Notice I said "low loss" bandpass filter. Correcting and bringing down the impedance of the squawker is really the only way to accomplish this -- if you don't -- you have to size the bandpss filter based on 30 ohms. The high impedance means you get to use a small capacitor value for the high pass section of the bandpass, but the inductor for the low pass section becomes very large, and the bigger the coil, the more resistance it has. By contrast, leveling out the squawker's impedance means you can now size your bandpass based on 6 to 8 ohms. Now the cap value becomes bigger, but the inductor value becomes 4 times smaller. The resistive element of capacitors is measured in mOhms, and inductors in Ohms -- so you can see that a large value capacitor in series with a small value inductor has significantly less loss than using a small cap value and large coil.

Current driven and voltage driven amplifiers: Big difference here. Tube amps don't have current on demand capability like a solid state amp. Most tube amps only have 4, 8, and on rare occasion you'll see 2 and 16 ohm taps for the output transformer. Tube amps, even those with lower output impedances -- operate, and sound better with a resistive load. Not dealing with the Squawker impedance creates a reactive load that impacts the amp's frequency response. This is one of the reasons the sound of Klipsch speakers can vary so much using different tube amps. For decades, audiophiles have used swamping resistors at the outputs of an amplifier to bring down the impedance of a reactive loudspeaker. In fact, I did it with my RF-7s for the last two years I had them. I did it because it sounded better.

At the end of the day -- the only thing that matters is the acoustic response of the loudspeaker. Most who actually end up comparing the two different approaches hear a better sounding Heritage speaker with the constant impedance networks. My opinion (which incidently Al doesn't agree with) is whether one prefers the ALK, DHA, or Constant Impedance AA -- will for the most part be dictated by the power levels required to meet their preferred listening levels. The required power level is primarily determined by the size of the room and how far away the listener is from the speakers.

The attenuation question: There is a difference between the "technically correct" setting and what "sounds right". It's not so much the action of the resistor on the squawker and the resultant change in impedance that accounts for this but rather the impact of the bandpass filter. Adding any element introduces some loss, and rolling off a driver's response decreases the amount of acoustic energy it produces. The rate of rolloff influences this as well. With the ALK, I think the "technically correct" setting sounds a bit repressed through the middle (taps 4 and X, -6.2dB), and I prefer taps 5 and 2 (-4.6dB). With the DHA and the 3636, taps 5 and 3 are "technically correct", but I prefer taps Y and 1 (-3.9dB). To my ears at least, these settings seem to line up acoustically with what I hear out of the A and AA networks.

[Al Klappenberger]

Dean,

I think you have sumed up the entire picture quite nicely!

AL K.

[Kudret]

Congratulations, Dean for your baby girl.

With the DHA and the 3636, taps 5 and 3 are

"technically correct", but I prefer taps Y and 1 (-3.9dB). To my ears

at least, these settings seem to line up acoustically with what I hear

out of the A and AA networks.

Dean, I tried all the posible settings and the one I ended up using is

4 and 0 (-3dB). The second best to me was 3 and 0 (-6dB).

Strangely, I didn't like the other intermediate settings where 0 was

not the common. Could there be any scientific explanation for this, or is it

just the human perception thingy.

EDIT. With 3636, are 3-0 and 5-3 the same (-6.0dB)?

Kudret

[Al Klappenberger]

Kudret,

The transformer settings that do not connect to zero are ligitimate ratios. The only difference is the levels they set. BTW: What is "technically correct" is different fore each listening room. Without instruments your ear has to make the desision.

AL K.

Dean,

I forgot: Congrats on the new little mouth to feed! []

Al K.

[BEC]

Dean said "Let's go really off topic -- I just got back from the hospital and I got me another pretty girl: Alexia Hope, 7 lbs. 10 oz. Mom and the baby are doing great. Naturally I'm completely wiped out from all the hard work. While Debbie was pushing, I was thinking about Newton's 2nd Law and impedance. :)"

Dean,

Congratulations on Alexia Hope. I understand how tired you would be from that experience. Last time that happened to me, I had to collapse and sleep for 12 hours.

Bob

[Hardhead]

Congratulations, Dean! We're very happy for you and your wife.

[Deang]

Dean,

Don't you have a math error? The K-55-V/PD-5VH is 107 dB on a horn like the K-400 and 110.7 dB (at 1mW) on a plane wave tube.

If the T2A drops its output by 3dB on taps 0-4, then adding the swamping resistor will bleed off additional voltage lowering it's output further. I don't think I'd want it to be dropped too much more than 3 or 4 dB, since the 107 figure could be called 108 easily enough looking at the peaks.

I might want to change taps if I had a live room or one even deader than mine or my brother's.

Uh, I just learned that John is right. Plane Wave Tube response gives maximum sensitivity, and this sensitivity drops a good deal when the driver is mounted to a horn. I read it on the web -- so it must be true!!

Sorry John!

[JohnA]

No probblem, Dean! It was good talking to you this morning! Congrats on the new baby girl, too! I ended up with 2 rough old boys, so I'm a bit envious. OTOH, I won't have to go looking for boyfriends to shoot. :-)