La Scala Bass Reflex Mod

[bliss53]

I have Al's horns and crossovers. I used the crossovers before I got the horns. The horns were an amazing transformation for me. I can wait to hear your impression. Do you have some plans for your ported boxes?

[Al Klappenberger]

Rudy,

Sorry, yours is the first of the next batch. []

Al K.

[DrWho]

I have no reason to doubt the claim that they
extend the response down to the 30HZ area. I remember reading a thread
on here somewhere that published the frequency response curve after
this mod, but I can't seem to find it again...maybe someone can help
with this as I have no way to perform any measurements.

The only numbers I remember seeing were from djk, and he just posted a table of frequencies and their amplitudes.

Also,
you don't get the 40Hz extension without adding the EQ that djk
intended the bass mod to be used with. I believe it is a peaking
highpass filter with about 6dB of gain at the tuning frequency and a
second order rolloff? I don't remember. The point is that you don't
have any cone excursion at the tuning frequency so you're only limited
to the distortion of your port when you add boost. And then the
highpass controls cone excursion below the tuning frequency (since the
driver would otherwise unload and be a danger to itself if you like to
crank it).

Btw, the mod looks real nice. Does the port bin just
get sealed by the weight of the cabinet, or do you have a way of
fastening the two together?

[Guest David H]

Btw, the mod looks real nice. Does the port bin just get sealed by the weight of the cabinet, or do you have a way of fastening the two together?

I was wondering the same, the ones I hade seen had hole cut top and bottom the the reflex mod box could be secured to the lascala through the original holes, and the original box bottom seals the bottom of the lower section.

BTW, it look very well built, and you are definately in for a treat when they are complete.

Dave Harris.

Does anyone know how this mod effects the woofers SPL?

[sootshe]

I have Al's horns and crossovers. I used the crossovers before I got the horns. The horns were an amazing transformation for me. I can wait to hear your impression. Do you have some plans for your ported boxes?

I've found the crossovers pretty amazing & can't wait to get the horns up & running.
I don't have any plans as such, but the bass reflex cabs are built the same width & depth as the LS. The height is 10 inches internal height & the ports are 4 inch diameter & 7 inches long.

[sootshe]

"Btw, the mod looks real nice. Does the port bin just get sealed by the weight of the cabinet, or do you have a way of fastening the two together?"

Dr Who,

I just have the bass & horn section sitting on top of the bass reflex cabinet. The sealing tape I ended up using seems to be soft enough to compress & create a seal, but not too soft that it completely compresses down to nothing. I can't detect any air leaks around the perimeter & there's plenty of air coming out of the ports.

[Marvel]

These figures are from another poster. No eq boost in his amp, as djk mentioned. No idea of the measuring technique.

------------------------------------------------------------------------------------------------------------------------

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.

Neither of us is going back to stock.

Pete

[DrWho]

Here's a plot of that data....which I think makes it easier to see.

[DrWho]

And then just for kicks, here's about what it should look like without room modes...

[IB Slammin]

"Have also just changed over the Crites stamped frame woofers for the cast frame models. Listening impressions are of a huge difference between the two.... not only more extended, but also a lot cleaner from the lower bass to the upper bass.

Sootshe,

Sorry for being late with this reply. I run four CW1526C's in two reflex cabinets.

"Any one else have a similar experience?"

The answer would be yes. Yes I have.[]

tc

[sootshe]

And then just for kicks, here's about what it should look like without room modes...

Thanks for the graphs - I reckon it's pretty similar to what I'm hearing.
I've sent an email to djk to ask him to chime in with some info on the passive EQ & low frequency cut off filter.
No reply as yet.

[Marvel]

Original text from Dennis:

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.

[aj01]

I know that this is off-topic, but has anyone thought about building a double-folded tapped horn to put under a la scala?

[DrWho]

I know that this is off-topic, but has anyone thought about building a double-folded tapped horn to put under a la scala?

I've got plans for one to go under a custom straight tractrix midbass....it wouldn't be too hard to put it under a lascala if you wanted to. []

[aj01]

How would you amp/crossover them? As a starter project I was thinking about getting one of the sub amps from parts express with the built in crossover?

[DrWho]

http://www.crownaudio.com/amp_htm/xti.htm

[Invidiosulus]

I know that this is off-topic, but has anyone thought about building a double-folded tapped horn to put under a la scala?

I've got plans for one to go under a custom straight tractrix midbass....it wouldn't be too hard to put it under a lascala if you wanted to.

What size driver in that tapped horn?

[Ray_pierrewit]

I'm just wondering how the OP is enjoying his mod. Has anyone thought of placing the bass reflex mod so that it fires backwards? I ask because I was reading up on the hornshoppe and I quite like his views on the port opening facing the listener (that it smears the image), though I've never heard his speakers. Plus, I think I read someone here who suggested to redirect that bass bin of split Lascalas to fires backwards. Just a few thoughts.

dna

[Marvel]

Has anyone thought of placing the bass reflex mod so that it fires backwards?

One of the ways to do this mod is to enclose the back of the top section and open the doghouse into the top. Place the ports on the back piece, obviously exiting toward the rear. This will keep the same height for your LS, but provide the improved bass.

Bruce

[Bum]

Marvel,

I am a newbie to the forum, but have been consumed with vintage Klipsch heritage products for the past few months to the point that the little women thinks I need counseling. I've hauled a set of 83 Cornwalls, 83 Standard La Scalas, what I believe are early 80's Pro La Scalas and a pair of 85 Heresy II's into the house since spring, I think I have the bug.

I have been running the Cornwalls beside the La Scalas in my living room for some time, and really enjoy the bass that Cornwalls add to the La Scala sound, but the Cornwalls do make for a rather large "sub". Due to space and mom saying one pair only in that room, I now have to go to just the standard La Scala's in the same room so I have been following the posts on adding the Bass Reflex box to the bottom of the La Scala's.

In the end, I would like to build the bass reflex boxes for both the standard La Scala and for the Pro La Scala, but am not sure if the same design will work for both. In reading the posts, I have assumed that to get the value out of the mod, you have to open the bottom of the doghouse before you set it on the bass reflex box. I have never opened the doghouse on either pair, but the opening on the bottom of the Pro La Scalas appears to open just a portion of the bottom board while it appears that the entire bottom board comes off of the standard LS1. Do you just open what is there to open on either model and set the speaker on the bass box, or is there more to it that that. I would like to avoid cutting into the stock enclosures if possible.

Thanks

Bum