books and information on loudspeaker construction

[D-MAN]

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On 12/29/2004 11:12:49 AM elcapitan83 wrote:

ok, admit 20hz is a bit low!

let us go for 32hz, instead.

i dont know, the 'scalas are better from corner placement, but i was thinking of building a set of "bases" that the speakers would rest on. if i opened up the bottom chamber, i could pick up more interior volume, and i could lower the frequency response?

i had heard of some guys opening into the sqwak/tweet chamber and inclosing the back to pick up volume, and instead of doing that, thought it easier to construct my own "base" and tune until i get the response i want.

i use these speaks for stereo hi-fi only, and i really detest subwoofers. i thought that it would be more simple to do it this way...but...apparantly, its not so easy as all that.

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You will not lower the fc very much by simply increasing the back chamber volume. You would need to reflex port the additional space in order to produce lower notes. If it is not ported, you would gain only a couple of cycles lower. Too much space and you introduce a mismatch to the volume of air in the horn resulting in increased IM distortion.

The horn lower cutoff itself is the limiting factor; it is fixed at (somewhere around) 63 Hz. Below that the horn will drop off rapidly, more rapidly than a direct radiator, that's the price of horn efficiency.

Many have done the port thing to the LS. There are some threads on it around here somewhere.

***

Some other thoughts about scaling up a Khorn to 32Hz or there abouts. The horn itself would use a different expansion rate. It could retain the same throat area.

The difference would be 40Hz (normal) is a 22.7" doubling point expansion, and a 32Hz fc would be 24.something" (if I remember correctly) expansion doubling point. So the horn would be about 4" taller and 2" deeper (plus wood) than a standard Khorn cabinet, modifications notwithstanding. Such a cabinet could go down well into the 20+ Hz range.

The horn passages theoretically would not adversely effect the upper-frequencies any more than the normal sized horn does as the folds are still "in scale". Essentially, the horn has only changed in expansion rate and length. Throat size the same (I would think about opening the opening slot to the full throat size as we would probably not be using the K33E).

The main problem is getting an appropriate woofer that has an fc BELOW 32Hz and is capable of horn loading. The unfortunate result would be that it is STILL very difficult to achieve the performance of a K33E in the upper-mid-bass range and have a lower fc. Rubber surrounds or drivers with more cone mass need not apply.

The problem with using an 18" driver is that the mass of the cone is such that the polar response goes to heck. Kiss goodbye to the upper-mid-bass, now you have a crossover and midrange horn problem. Best to avoid an 18" driver for this reason.

PWK went to dual 12" drivers in the Jubilee to keep the upper-mid-bass response, enhanced a bit due to the smaller cone mass of the two 12 inchers.

Seems to me that PWK had the right solution with the dual throated horn, but the increased efficiency requires the top-end to keep up with it, and that's where the consumer Jubilee bit it. Not much available unless one manufactures one specific to the problem.

Extrapolating on the dual throat/dual driver design, one can invision maybe a horn using four 10" drivers and the like; there may be some promise there. That is the direction I took in my latest design ; single throat with enough room for multiple drivers and the means to mate them to the throat opening. Something to think about, but I haven't actually tried it; I LIKE how the K33E sounds!

The main drawback to multiple driver designs is expense. By the time that one arrives at the proper drivers, they EACH cost as much or more as a single K33E. So far, I like to think that I COULD go there if I wanted, but really find no reason to do so. My advice is go with the proven and economical solution that PWK already worked out quite well.

Based on some of his writings, PWK also thought that the best height for the upper frequency horns was around 40-44 inches and kept that in mind in his designs. Something to think about when considering a Patrician-sized monster horn!

DM

[elcapitan83]

thanks for all the replys. here is the original post by djk that got me thinking:

"The taper rate of a LaScala is 100hz,The mouth area is good for 125hz.Below this it is a big woofer in a small sealed box.If we plug the T/S parameters for the K33E into a box program we will see that the Qtc=.85, the Fc=82.5hz, and the F3=70.9hz . If we close in the back of the high frequency cabinet and open the woofer rear chamber up into this volume and fill with fiberglass we now have Qtc=.577, Fc=58.2hz, F3=73.6hz .Bessel=Qtc.577=D2 gives the best transient response and the least group delay of all the sealed boxes.At 30hz the Qtc=.577 has 4.5dB more output than the Qtc=.85 .Compared with sealed enclosures,the transient performance of the best vented enclosure is worse than the best sealed box enclosure.Since we have made great gains in performance some may elect to stop here.But please read on.The next step is to port it.The K33E is not the optimum woofer for this but it works pretty good.With the box size optimized for a D2 we can port the stock woofer to an SC4.The transient response of an SC4 while not as good as an SBB4(more on this later)is better than the more common QB3.Unequalized the F3=49hz and has 3dB more output at 30hz than the D2.The response curves are parallel with the D2 the only difference being the Fc being a half octave lower with the SC4 and the output being 3dB higher from 30~70hz.The output of the SC4 does not drop lower than the D2 until you go below 17hz.Again this may be a stopping point for some.But by adding a simple two pole high pass filter ahead of the power amp we can now have a C6 with a -3dB point of 31hz.Since this is the Fb of the system there is no increase in cone excursion or distortion.The filter consists of a cap an inductor and a pot.The pot allows adjustment at Fb of +/- 3dB.This is similar to being able to change the Qtc of a sealed box from .5~1.0 .If you think about it we have the choice between a D2,SC4,and a C6 in the same box by plugging the port and/or bypassing the eq.If you have a SET amp or simply want to get the most out of the LaScala you will want to upgrade the woofer to something with a lower Qts.The Klipsch K43E does the trick,as do the EV DL15W and the JBL 2205.The EV and JBL drivers require some minor network changes.The lower Qts drivers allow for an SBB4 alignment which has the best transient response of the vented alignments.With no eq they have 3dB more output at 30hz than the stock woofer.With eq we have a maximally flat B6 and the F3 of the system is 27~28hz.If using a solid state amp with the low Qts woofers a small resistor must be added in series with the driver to have the same Rg as the SET does.This mod can be backed out of a stock LaScala with no externally visible changes if you don't like it.No one has ever gone back to stock after hearing this mod.Paul Klipsch was violently opposed to the venting of horn speakers bassed on his experience with venting the K-horn.In retrospect it is easy to see why.The 12" Jensen field coil woofer he was using had an Fs of 60hz and a quick calculation of the vent area vs the Vb based on the photographs of this experiment looks like an Fb of ~80hz.I am sure this sounded horrible.Paul Wilbur Klipsch is a giant in audio.If I appear to see farther than PWK it is only because I am standing on his shoulders."

sorry for the long post, what i had in mind was construct a speaker "stand" the same volume as the top chamber, and fasten it to the base of the la scala. port to taste, and i have a reversible mod if i dont like the result.

which threads to research for the effective porting?

[D-MAN]

I believe that the thread you are looking for is in TECHNICAL QUESTIONS (somewhere). You want the one with the box on the bottom. That is truly the "reversable" version that you are speaking of, and I agree with your reasoning.

There is another example with pics showing a version with the ports rear-firing on a sealed top which is not the "reversable" type, of course.

DM

[m00n]

I want to think you all for successfully making my brain cramp.