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Let's Build a Driver Test Box


BEC

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I changed the XO schematic above. I hope that is correct.

You know I am stumped how Klipsch chose the 2.5 mH inductor on the low pass filter. I must be missin something here. To me it seems the "pass" was kinda low. Tell me where I am wrong here. Impedance K33 is 4 ohms for estimation purposes. The inductor on the low pass is 2.5 mH or 0.0025 H.

f = frequency

z = nominal impedance

I = inductance

I = z/(2 * pi * f)

0.0025 = 4/(2 * 3.14159 * f)

0.0025 = 4/(6.28318 * f)

0.0025(6.28318 * f) = 4

0.01570795 * f = 4

f = 254 hZ

I hope that I am way off here. If so its OK...cause I'm a rookie!

jc

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JC,

On the woofer, at least in theory, an older K-33E (before about 1985) would be better for the Cornscala. The old ones had an Fs of about 27 or 28. That would be the ones with the square magnets. They weigh about 2 to 3 pounds more than the later ones and I guess that extra weight is mostly magnet. The only thing in the Heritage line that had a chance of taking advantage of that lower Fs was, I guess the Cornwall or in our case the Cornscala.

The reason that I said "in theory" above is that I have one old K-33E (square magnet) woofer in one of my Cornscalas and one new K-33E (round magnet) in the other. If there is a difference in the two of mine in how low the bass goes, I can't tell it. Probably to take advantage of the ability of the old woofer to go lower would take some messing with the porting and that might also mess with the SPL of the woofer at higher frequencies.

Bob

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Well, a lower Fs would be "lower".

I would like to try different drivers but I don't want to "blow" something. Thats why I wondered about the driver inductance. The 4 ohm woofer I considered has these specs. Notice the true impedance is a little lower as well as the inductance compared to the K33.

RE OHMS 2.71 FS HZ 24

LE MH 0.61 MMS GMS 142.8

QM 6.60 CMS mm/N .30

QE .27 RMS NS/M 3.30

QT .26 VAS LTRS

XMAX MM 4.7mm SD SCM 1159

BL TM 14.8 EBP 90.3

EFF % SPL dB 97

Wattage 800rms

jc

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JC,

I have pondered the formulas a bit before myself. If you want to confuse yourself further, be aware that the updated crossovers for the Klipschorn and Lascala (AL-3 and AK-3) and the Cornwall (B-3) went to 4 mH for the woofer inductor.

Bob Crites.

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Yea, I'm really confused then. With the way I am calculating it, that would make the updated low pass filter at 159 hZ. However, I also would assume the newer XO wouldn't be a first order network either. I could be wrong again.

jc

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  • 7 months later...

Bob, those look really nice. Did you make a pretty pair besides the test units? If so, do you have a finished one? And I'm curious as to how one would go about making a 'decorator' version. Is it as simple as merely routing out the wood on the inside to mount the speakers from the rear to make flush?

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meagain,

No, those are the only pair I made for me. I had a few sets made for others that had nicer wood. Mine are built as test boxes and I use them almost daily to test drivers that I have rebuilt. They are also my choice of all the pairs of speakers I own for music listening. I have Heresys, Fortes, Chorus, Cornwalls and 3 sets of Lascalas.

My new Cornscala II will be in a complete Cornwall size cabinet. I think it may be my new favorite.

Bob

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Jw,

I have not read all the posts very carefully, but maybe you are having trouble reverse engineering the woofer lowpass filters becasue you are forgetting the woofer voice coil inductance. You have to assume 1 higher order than the number of parts you have. The woofer represents 1 mHy loaded with 6 Ohms. For 2.5 mH and 100 uF to ground, it's 3rd order with 1Mh output inductor into 6 Ohms impedance. Try it that way. I can always verify you numbers in the computer.

Al K.

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Ok..Al don't laugh at me here in case I made a bad mistake. I didn't just copy a bunch of yalls stuff to come up with this. I actually did calculate this. I was trying a constant impedance network with both squawker and tweeter attenuation with the woofer/mid crossed at 400Hz anf the tweeter crossed at 6000Hz. Also with a bandpass.

This is for the Cornscala (non dbb) with a K401. Hopefully later with the trachorn as promised if I can get this right. The drivers are K33,K55,K77.

Notice I have a 1.6mHy as the inductor. Calculated with a 4 ohm driver. You seem to think the ported K33 is 6 ohm like the horn loaded version. I guess I haven't firmly believed this yet. Maybe that is my problem. This was for a first order low pass. Now I thought before you said on first order the inductance of the woofer wasn't as important with first order. Maybe I was second order all along and didn't know it. Clear that up for me please.

Now after I made this and tested it, the 2.5mHy inductor sounded better. Tell me why.

Now looking at your graph, I am assuming that it is a plot with a reflex ported K33 with a 2.5mHy and the 100uF cap crossing 3rd order? at 400Hz? Is that right?

jc

post-16499-1381927920127_thumb.jpg

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jc,

Those boxes were $100.00 each in MDF the last time I had some built, but that was close to a year ago. I would have to check on the current price. Would you just want all the cut pieces or some of it assembled? Shipping would be a lot easier if just all the pieces were shipped.

Bob

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Jw,

It's not bad at all! The impedance swing is from 6.1 Ohms to 8.8 Ohms.

It's normally better to move the tweeter filter input (the 2.2 uF cap) to the other side of the 40 uF though. That 40 uF cap is no obsticle to the highs at all but is does obstruct the squawker / tweeter transition a bit. The .2 mHy should be paired with the tweeter filter to work best. The 1.6 mHy and 40 uF are the OTHER pair.

I did an analysis run on this particular design with the tweeter input moved to the other side of the 40 uF cap and found that it wasn't quite as good in this case. I think the reason is that the combination of the 1st order and 3 rd order fiters isn't quite right with these values. This type of circuit casues interactions between the 400 and the 6000 Hz crossovers. I never know what will happen. That's why I like the other circuit! The other circuit is really the "super AA" or ALK Jr. having slightly different values.

I have decided to call this the "Erik Mandaville effect". This is becasue he got me to do some serious investigation about this in another thread. [;)]

AL K.

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  • 1 month later...

Thanks for bumping. I wanted to bump it a few days ago but figured you were busy fielding tweeter questions and didn't need more on your pile.

I SO envision a split version. Horn section nicely veneered to use atop or below TV. Bass bin cube in a shallower cabinet sitting on the floor much like a sub.

Failing that - I'd sure love to hear one of these.

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