Custom "Heritage" Center

[Deang]

"PWK did design by ear because these fancy programs weren't around back in his day."

He most certainly did NOT design by ear. He did endless calculations and used instruments. When he was finished, he used an EQ to tune the system to taste. He did not trust his ears. This is one of the things Al and Bob actually have in common!

JC -- terrible learning curve with this stuff, and in some ways you have surpassed me in a very short period of time. The box thing hasn't really captured my imagination yet, so take the following for what it's worth.

Six months ago I wouldn't have said this, but I think it's best to let the horn's lower end limit determine the crossover point. What you need to know is the -3dB point of that lower end limit. If you look at the plot I posted earlier, you can see that 400Hz is pretty much it for the K-401. The K-55 will go lower of course, but then you run into things like changing the acoustic impedance (which changes the electrical impedance), higher distortion, and lower power handling. Just keep it simple and straight-forward.

I'm not sure how you got 134 ohms for the squawker on tap 2. I go with 120 there -- how did you come up with that? It's not all that significant, I was just curious how you came up with it.

As for the box, it might best to just let the driver parameters dictate whether you should go sealed or ported.

http://www.bcae1.com/spboxad2.htm

[jwc]

I'd go with the 400Hz crossover...I think it'd sound more cohesive to have the woofer playing for more than a single octave

Just curious, is there any specific reason why you sealed off the LF cabinet from the upper cabinet? Seems like a good 1.5 cubic feet there you could use...

still dunno what is up with that K33 plot...I've always modelled using 8 cubic foot cabinets which go relativtely flat beyond 40Hz. I wonder if there isn't something totally wrong with the T/S parameters we have...I know D-Man said they don't match up with the mouth and expansion rate of the khorn either.

Doc, couple of reasons.

I needed this to be lightweight. This is 1/2 inch birch plywood. If I were to use the same dimension but leave out the middle shelf, I would have a big cube. I was afraid of terrible resonance issues. I also wanted easy access to the crossover and I like to have a HF section in which I could change out the baffle to use different drivers.

Now, it is still possible to convert the cabinet to a large one. Just seal everything off and cut a large hole in the middle shelf. Would make for nice bracing. But does it really matter? I am gonna set the speaker to "small" on HT. Decrease distortion, maybe so. What are the other advantages? I looked at the WinISD for a 5 to 5.5 cubic foot cabinet ported. It isn't really that much difference except that it extends much lower.

By the way, I will have two of the K22 alnicos. I was thinking of building a second cabinet later for a "real" Herescala to see if it would rival the Cornscala. I bet I could port a K22 in a 6.15 cubic cabinet to "thump" more than what the Cornscala/Cornwall will. Curious of the sound. I only have $55 in this current cabinet w/o the paint job coming up. However, if I built the big Herescala, I would have no where to put it. Would have to sell it on this forum as a bad boy heritage center channel.

jc

[jwc]

"PWK did design by ear because these fancy programs weren't around back in his day."

He most certainly did NOT design by ear. He did endless calculations and used instruments. When he was finished, he used an EQ to tune the system to taste. He did not trust his ears. This is one of the things Al and Bob actually have in common!

JC -- terrible learning curve with this stuff, and in some ways you have surpassed me in a very short period of time. The box thing hasn't really captured my imagination yet, so take the following for what it's worth.

Six months ago I wouldn't have said this, but I think it's best to let the horn's lower end limit determine the crossover point. What you need to know is the -3dB point of that lower end limit. If you look at the plot I posted earlier, you can see that 400Hz is pretty much it for the K-401. The K-55 will go lower of course, but then you run into things like changing the acoustic impedance (which changes the electrical impedance), higher distortion, and lower power handling. Just keep it simple and straight-forward.

I'm not sure how you got 134 ohms for the squawker on tap 2. I go with 120 there -- how did you come up with that? It's not all that significant, I was just curious how you came up with it.

As for the box, it might best to just let the driver parameters dictate whether you should go sealed or ported.

http://www.bcae1.com/spboxad2.htm

Dean, those calculations were done by me. Bob gave me the impedance at different taps. I have only a basic knowledge of autoformers but have a good grasp of why they are set differently for different "Heritage" speakers. You know I bought one of those books you suggested a few months ago and it didn't seem to help with the autoformer deal but it sure helped me alot in other ways.

Bob's quote to me

"Impedance of the K-55V connected to autotransformer.

Tap 4 = 34.7 ohms

Tap 3 = 74.5 ohms

Tap 2 = 134.1 ohms"

I only intend to cross at 400hZ for the K401/K55 combo. If the impedance of the K55 on tap 2 is 120, then I need to change my calculation:

C = 1/ (2 x pi x f x z)<?XML:NAMESPACE PREFIX = O />

C = 1/ 2 x 3.14159 x 400 x 120

C = 3.32 x 10(-6) or 3.3uF

Hey thanks for that website. Need to read that thoroughly.

[BEC]

jc,

Those values came off my impedance meter. When you asked me, I just hooked up a K-55V to a 3636 and measured the impedance when it was hooked up to each of the three taps.

Bob

[jwc]

Perfect. Man you're fast. You had that answer for me lickedy split after I emailed you. You must keep a fold-out cot in your audio lab.

[Deang]

From: http://www.peavey.com/support/technotes/concepts/impedance_3.cfm

"In loudspeaker transducer technology, we use a horn as a transformer. The horn couples or matches the loudspeaker to the air in a manner in which the efficiency of the loudspeaker as a system is increased (i.e., with one watt of power going to the loudspeaker, the sound pressure on-axis with the horn will be greater, because all of the acoustic energy radiated from the loudspeaker is focused by the horn). Since the acoustic signal produced by the loudspeaker is now restricted within the walls of the horn, the speaker is said to be loaded by the horn. The horn offers an acoustical impedance to the loudspeaker and, like a transformer, the horn changes the impedance that the source amplifier sees. In this case our amplifier actually sees a somewhat higher impedance or opposition to current flow than the speaker would offer if it were directly coupled to the air itself."

"There is an enclosure in our product line that we have been making for twenty years called, the FH-1 low frequency enclosure. We use a four ohm loudspeaker in this enclosure; however, as long as the enclosure is operated above its cut-off frequency of 60 Hz, the actual load impedance that the power amplifier sees is nominally eight ohms. Likewise, we use a four ohm loudspeaker in the Mid bass horn of HDH-4 and HDH-1 speaker enclosures. As long as these horns are operated above their cut-off frequency of 300 Hz, the midbass of the enclosure will exhibit an eight ohm load to the amplifier."

"The mechanical loading of the loudspeaker by the horn makes an impedance transformation so the amplifier sees a load impedance of 8 ohms within the horns operating bandpass. I mention the horn's operating bandpass because if you operate any horn below its cut-off (-3 dB down point on the low frequency portion of its response curve), the driver reverts back to its original lower impedance. As long as you send horn loaded enclosure frequencies that are above the cut-off, the system will offer a higher load impedance to the power amplifier."

"The DC resistance of the loudspeakers discussed above is 3.2 to 3.8 ohms. Mounting the loudspeaker on a horn doesn't change the DC resistance, but a power amplifier driving that horn will see a load impedance that is more than twice that of the nominal four ohm impedance of the individual speaker. Hopefully some of us now understand how a four ohm loudspeaker can become an 8 ohm loudspeaker system when mounted on a properly designed horn."

So, when you horn load a driver it changes it's impedance. Think backwards and do it like this: What impedance gives you 13uF for a 400Hz high pass?

[jwc]

Dean,

I will have to read that site in it's entirety because I'm gettin 30.6 as the impedance of your question.

[Deang]

Well done. It doesn't sound like much difference, but 34.7 shifts the crossover point down by 60 cycles.

[jwc]

I'm with ya. Need to chew on this a little. Never thought of the backwards calculation. Hmmmm. Now using this method, I calculate the K55 on tap 2 to have a "relative" impedance of 114. This is assuming a cross of 700Hz with a 2uF cap.

[Deang]

Well, that gives us insight on what Klipsch was seeing with the K-55 on the K-700 horn. It doesn't mean we use 2uF if we use a different horn. At any rate, you're getting my drift -- we can use the original values to help us understand the impact horn loading has on the electrical impedance of the K-55. The nice thing about first order filters is that because the slopes are so shallow, there is room for some error without causing any major problems. Still, the more we know the less error there is. Like I said, keep it simple and straight-forward.

[formica]

I don't mind a hijack either, but:

GUYS, GUYS, GUYS....I NEED INPUT FOR THE ORIGINAL QUESION AT HAND.

Here

is a plot of the K22 in my current cabinet. 4 options here.

Ported vs sealed and crossing at 458 vs 216Hz. Which would you

use?

I didn't know we had a choice... I'd go with ported - 458Hz [8-|]

[DrWho]

"PWK did design by ear because these fancy programs weren't around back in his day."

He most certainly did NOT design by ear. He did endless calculations

and used instruments. When he was finished, he used an EQ to tune the

system to taste. He did not trust his ears. This is one of the things

Al and Bob actually have in common!

Sorry, I meant to say there was a lot more trial and error (moreso

at the beginning). I have a video here somewhere where he talks about

it.

Btw, does the lascala use just a 1st order highpass on the squaker?

I could never comprehend crossing over that shallow. And what is the

crossover point on your cornscala dbb's? I think the voicing of the

speaker would benefit from matching the crossover points as best you

can (better timbre matching with your mains).

[formica]

"PWK did design by ear because these fancy programs weren't around back in his day."

He most certainly did NOT design by ear. He did endless calculations

and used instruments. When he was finished, he used an EQ to tune the

system to taste. He did not trust his ears. This is one of the things

Al and Bob actually have in common!

Sorry, I meant to say there was a lot more trial and error (moreso

at the beginning). I have a video here somewhere where he talks about

it.

Although PWK was a strong believer in science (as most engineers are),

you were kinda right in your first post... as Hoffman,

Thiele and Small's mathematical theories had not been developed at the

time of the Cornwalls design.

Actually if I recall correctly, Hoffman only developed a

mathematical formula in the 60s on which Thiele and Small later

perfected and established the TS parameters we all know today.

Trial and error were an important part of developement at the time.

Rob

[colterphoto1]

"PWK did design by ear because these fancy programs weren't around back in his day."

He most certainly did NOT design by ear. He did endless calculations and used instruments. When he was finished, he used an EQ to tune the system to taste. He did not trust his ears. This is one of the things Al and Bob actually have in common!

Sorry, I meant to say there was a lot more trial and error (moreso at the beginning). I have a video here somewhere where he talks about it.

Although PWK was a strong believer in science (as most engineers are), you were kinda right in your first post... as Hoffman, Thiele and Small's mathematical theories had not been developed at the time of the Cornwalls design.

Actually if I recall correctly, Hoffman only developed a mathematical formula in the 60s on which Thiele and Small later perfected and established the TS parameters we all know today.

Trial and error were an important part of developement at the time.

Rob

While at the Heritage Gathering, Chief Engineer Roy Delgado told us that PWK was in communication with T& S during the time they developed the parameters, thus he not only used trial and error prior to the publication of those parameters, but was part of a consortium that developed them.

Michael- PS Dr, bring that vid with you next time you come over please....

[jwc]

"PWK did design by ear because these fancy programs weren't around back in his day."

He most certainly did NOT design by ear. He did endless calculations and used instruments. When he was finished, he used an EQ to tune the system to taste. He did not trust his ears. This is one of the things Al and Bob actually have in common!

Sorry, I meant to say there was a lot more trial and error (moreso at the beginning). I have a video here somewhere where he talks about it.

Btw, does the lascala use just a 1st order highpass on the squaker? I could never comprehend crossing over that shallow. And what is the crossover point on your cornscala dbb's? I think the voicing of the speaker would benefit from matching the crossover points as best you can (better timbre matching with your mains).

Doc, Check out my profile. The CS-dbb's are in a room by themselves. Don't get these confused with My Cornscalas which are my fronts in My HT. They have K401/K55 and K77 just like this center channel I am making. My CS-dbb's use the Altec 511b's/K55v with the JBL 2404 tweeter.

The Type A La Scala network should be first order high pass with a XO point of 400Hz

[jwc]

Just a few pics.

Front

[jwc]

Back

[jwc]

Top section baffle and drivers/horn

[jwc]

again. kinda narrrow...I know. Marvel, I have a baffle here but I bet you would prefer it to be wider...huh.

[jwc]

The start of my "cute" little XO