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Hade fabriksbyggda La Scala i butiken för 100 år sedan

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De fick väldigt bra kritik i Stereophile nyligen om jag minns rätt.

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Tackar, var bara nyfiken på hur de såg ut, det finns ju en mk2 version som kanske låter bättre ? De är ju inte så stora och som midbas 60-500 kan de kanske duga.

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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.



None of the stock Eminence Delta,Kappa,etc series drivers will work.The K43Es that I have measured has Fs=31hz and Qts=.25,the TS parameters that Klipsch hands out are bogus.The EV DL15W has an Fs=30 and Qts=.23 and the JBL 2205 has an Fs=30 and Qts=.21 .After taking into consideration the dc resistance of the woofer inductor and the output impedance of the amplifier the optimum Qts for the vented LaScala would be .312 with a Vas of 10.5 cu ft and an Fs of 30hz.

I'm looking for a total net volume of about 4.8 cu ft. I figure the stock back volume is about 2.25 cu ft. Call it an internal height of about 9" (22.5 X 22.5 X 8.70 = 4404 cu in = 2.55 cu ft). Two 4" ID by 10" long ports displace about .15 cu ft so 10" outside is close enough.

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My buddy Thermio and I both scratch built a set of LS bass cabs and he did the djk mod to them. He took measurements on one cabinet as the mods progressed. Here is the data:

200 160 125 100 80 63 50 40 31 25 20 HZ

77 80 79 73 72 78 68 60 61 52 51 dB Stock, mouth braced
76 78 78 73 69 75 65 60 66 56 52 4.5 cuft, no ports
76 78 77 75 74 80 70 60 68 54 54 Two 4"dia 10" ports
76 79 78 76 75 80 71 60 68 54 53 Ports cut to 7"

The interesting thing with 10" ports is the boxes went deep, but the snappy, fast horn
sound was lost! Cutting the port length to 7" brought the snap and speed back to same
as stock, plus the lows remained, esp. at the 31Hz box tuning point. This data is with
K33E driver and light stuffing. We think a K43E in this box would be superb, but haven't tried it yet.

I'm going to try the mods using two 4" ports with both ends flaired (Thermio used 4" PVC). Flaring
is supposed to reduce distortion and possibly increase the gain. Parts Express sells the kits.

Neither of us is going back to stock.

Pete

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Change the woofer to either a K43 or JBL2226G.Down under the JBL will probably be a better buy and easier to find.The JBL will also handle 600W because of the 4" vented gap voice coil. The best way to get a 2226G is to buy a blown 2226H/J and have it reconed with a G kit.This will give new performance at a used price.The correct ports for the 2226G are two 4" dia by 7" long on the back board across the top of the mid-hi box.This gives an Fb=35hz and will handle 600W at Fb without exceeding x-max.

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Stoppa in parametrarna på en Eighteen Sound 12MB600 i Hornresp å lek.
Ett kort horn på en meter med en 8000 cm2 slutarea eller nått sånt, med en tractrix flare borde kunna funka bra.

Gamla konstruktioner i all ära, men dom hade inte potenta datorer och Hornresp.

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