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LaScala Bass Extension


Marvel

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Here is the drawing for lowering the bass frequencies output of the LS. This is ten inches tall, making the inside 8.25 inches. The two tubes/ports are PVC pipe, with a 4 inch inside diameter, 10 inches long. The bottom of this needs to be removeable. If you remove the bottom from your LS (use the cover to mark the holes for attaching the new extension) and attach to LS. Stuff with fiberglass or acoustic fiberfill. Attach bottom. Hopefully enjoy lower bass.

I hope djk will post with expected results. I won't try to pull the details out of his posts on Audio Asylum. I think that with the K33 and this, it will go low and solid. Switching to the K43 does even better. Any other speaker (EV DL15W) requires crossover changes as well. If you like this, you can remove this design and cut a hole in the top of the doghouse of the LS and close in the back with ports added. Will do the same thing but drop the height back to normal.

Marvel

post-7149-13819247761154_thumb.jpg

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Since I don't even have a set of LS yet, it doesn't matter to me, but as djk has pointed out:

The flare rate on a LaScala only carries it to 100 Hz. Below that it is a woofer in a sealed box. People have asked, so he gave details. If you already have the LS and like them, why not try it. This is 100% reversible. No wonder he said that PWK would call some of you Luddites. Is it heresy to do all the other mods on PWK designs? Apparently not. I especially like John Warren's removal of the mid horn for his Khorns, and replacing them with the two JBL direct radiators. Very cool. djk says you can get more bass at 30Hz from these cabinets than frm a KHorn. If I had a pair right now, I would be willing to try it and see if he is correct.

Terry,

I used trueSpace for the drawing. My youngest son bought it a few years ago. Last year he switched to Lightwave, so I appropriated it as LW is far better for what he is doing (3D animations and rendering). The version we still have is TS 4.3, but it is now up to 6.0. For what I'm doing, the 4.3 is just fine.

Four Cornwalls would cost a lot more than making these bottoms for a pair of LS. You could make them very cheap to try it out. I have other sketches to mount the ports, so they could easily be removed or modified.

Marvel

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Some interesting ideas. I've got a pair of LaScalas and am using subs right now because they are deep bass shy. I've saved your diagram ( wonderful by the way ) and text and might try it when my leg is better. Just so happens I have some beautiful Baltic birch plywood in the garage from an old primary school cupboard. Should do the trick.

Has anybody done or tried this mod.? Any measurements or listening tests? Thanks. Hamish

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Bass reflex? Is that the type speaker the bass bin would become? I'm not exactly clear on the speaker types, but what is happening is that this extension gives a path for the sound behind the cone to get out of the dog house? Does that have an impact on how the horn would work?

I'll be very interested to hear a report on how this sounds in the real world.

Regards,

Dee

p.s. it is creative way to have an easily reversible option to check this out w/o cutting a hole in the top of the doghouse!

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Below is what djk had posted on the Audio Asylum forum quite some time ago. I was hoping he would post on this. His final "fix" is to open the doghouse on the top side, right under the mid horn if you will. Close in the back and put these ports in it. Don't forget to fill with fiberglass or equivalent material. There are four (4) things he says you can do.

1. just open the space to increase relative size of doghouse.

2. add ports to that

3. 2 plus change to K43

4. 2 plus change to jbl or ev (requires crossover mod as well

Here is his text. He has done these mods, and yes it does make it a bass reflex with a horn. It also seems that with the weight of the LS, if you put some gasket material around the opening of the mod, you might be able to just place your cabinets on top. 123 lbs. is pretty heavy and might seal well enough to try out:

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.

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I see what you are trying to do here adding the ports.

I understand that the undersized sealed cabinets the big K33 or 43 woofers are mounted in and the small slot in front of the woofer were used to cause the woofer to be driven into a compressed state into the entry point of the bass horn cabinet.

Wouldnt porting the sealed cabinet almost totally destroy any means of compressing the bass horn? I don't see how this could work.

JM

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JM,

As I have pointed out to a couple of folks who have emailed me, I don't even have a pair of LS yet. I'm working on that. I DO know that djk has come up with all sorts of mods, and I DO know that his stuff sounds very good. I have heard a set of some LS clones he built back in the '80s. I am more than willing to try what he suggests, I just don't have anything to try it on yet. I figured I could at least make the drawings and make them available. He says he has done this mod, and I have no reason to doubt him.

Marvel

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  • 4 weeks later...

Yesterday I did my first test with the vented LaScala. I used a 4.8 cu.ft backchamber tuned to 30Hz. I didn't have the parts needed for eq'ing, so I'll have to try this later. It sounded great and I'm going to experiment more.

Frode

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Frode,

I have another drawing on the 2 channel, under the subject heading , that has the drawing of this in the top of the LS. DJK pointed out on one thread that with the K33, this would do 31Hz -3db. Do let us know more of your experiments.

Marvel

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