Bass Reflex Mod For LaScala?

[lar418]

I ran a Bass Box Pro bass reflex simulation when I came up with my box size and tuning. The f3 is 46hz and the f6 is 35 hz. Add a little help from the room and your getting usable output in the low to mid 30's. I tried to mimic the Cornwall as much as possible and the shelf port on the Cornwall appears to be tuned to 46hz. My port is tuned to 37hz which should yield a wider bandwidth. The higher tuning of the Cornwall appears to have a peak at about 60 hz. I've seen other post referring to the Cornwall as a shelf port design not a tuned port. I'm not familiar with that design, so I might be off base with my Cornwall assumptions. I used some CD's with low bass to test these speakers and I was pleasantly surprised at the bass output, which was lower then the theoretical response.

The port output is in theory 6 db's below the horn, but I also feel the horn output is reduced with the elimination of the small compression chamber chamber behind the woofer. I ended up moving the squawker from taps 4 and 0 to taps 5 and 2 on the crossover, because the squawker was overdriving the bass horn. I can't prove is mathematically, but it was audible. I used both a test CD and a signal generator along with a sound level meter and measure it in various points in my room. The near field measurement seemed to be the most accurate. It's a crude method, but it does seem to work. If you look at a response curve from an Altec Voice of the Theater, it mimics what we are doing here. The port has less output, but adds to the response.

The best thing about this method is the coherence of the speaker. I've tried to add one and then two subwoofers my La Scala's and had mixed results. Some songs sounded great with the subs and some not so great. I was constantly adjusting the output, phase, etc. Subwoofers can do amazing things, but can be very tricky to get right.

[djk]

The lar418 LaScala mod looks interesting, I can see what he is trying to do. It probably works fine, and doesn't require the high-Q filter my design requires. OTOH, mine will dig a little deeper.

The low Qts K43E is more suited for a horn than a simple reflex, the higher Qts K33E is more suited for a reflex than a horn.

My original concept was for the K43E found in the industrial LaScala, but it also works for the K33E found in the home LaScala.

The idea of a combination horn-flex box is not new, the Altec V.O.T.T. systems are examples of this. The idea of 6th order reflex is not new, the EV Interface systems are examples of this.

The collected AES works of DB Keele are required reading.

http://www.dbkeele.com/papers.htm

Don worked for EV before he worked for Klipsch, and then moved on to JBL. Of particular interest are:

. "What's So Sacred About Exponential Horns?," Presented at the 51st Convention of the Audio Engineering Society, Preprint No. 1038 (F-3), (May 1975).

"A New Set of Sixth-Order Vented-Box Loudspeaker System Alignments," J. Audio Eng. Soc., (June 1975).

"Low-Frequency Horn Design Using Thiele/Small Driver Parameters," Presented at the 57th Convention of the Audio Engineering Society, Preprint No. 1250 (K-7), (May 1977).

"An Efficiency Constant Comparison Between Low-Frequency Horns and Direct-Radiators," Presented at the 54th Convention of the Audio Engineering Society, Preprint No. 1127 (M-1), (May 1976).

"An Efficiency Constant Comparison Between Low-Frequency Horns and Direct-Radiators," Presented at the 54th Convention of the Audio Engineering Society, Preprint No. 1127 (M-1), (May 1976).

"Direct Low-Frequency Driver Synthesis from System Specifications," J. Audio Eng. Soc., (Nov. 1982).

An infine horn is a bandpass loudspeaker. A finite horn looks like a BP4 in the low end, the combination horn-flex looks like a BP6A, a Karlson like a BP6B (using BassBox v5.0 terminology).

BassBox v5.0 does a good job modeling the BP designs, v6.0 can model 6th order vented. Doing a 6th order horn-flex is largely a cut-and-try as there is no exact software model.

A number of people have tried the 6th order horn-flex based on the LaScala, and with a variety of woofers. Best performance (by ear) seems to come from two 4" dia by 7" long ports, although it doesn't measure any different (less than 1dB) than the originally recommended 10" long ports.

When the ear conflicts with measured or predicted performance, I always go with the ear. Some designs measure good and sound less than the best, some measure less than the best and sound quite good. I generally get close with test equipment, within ±1dB or so, and go by ear the rest of the way.

[DrWho]

Dr. Who,

You are obviously not reading the posted links. Below is very old copy

from Dennis that I have posted before. I believe we are talking good

repsonse down to about 31Hz.

================

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 .

If he claims the horn loading ends around 100Hz, then there is no way

in the world the system maintains a 104dB sensitivity below the horn

cutoff....especially an entire octave down. If you look at the

frequency response slopes of the stock speaker, you'll notice that it

is very linear all the way to the F3 of 53Hz (I have been told

that these measurements provided by klipsch were also free field

anechoic). A K-33 in a sealed cabinet of that size has an F3 at 71Hz

(like he pointed out) so there must be something else going on. No room

or corner gain is going to account for being -9dB at 53Hz.

I agree with all his math though....except I still maintain the the

volume coming out of the port will be 5dB less than the wavefront

coming from the horn. At best using a K34E (the cornwall II for some

reason is rated at 101dB) will mean you are 3dB down with the port.

Would anyone happen to have the schenamatic for the peaking 2nd order

highpass filter? I've never seen this trick before and I am quite

impressed with the possible applications of it. I think it should be

mentioned that all of these modifications could also be implemented

with the corwall as well (and since modelling it all for a cornwall

results in a very flat response, I can't see how it would be flat with

the

lascala).

[djk]

The only place a LaScala is 104dB is around 120hz~240hz and 1Khz~2Khz, the Cornwall incinerates it below 80hz or so, but the 6th order vented LaScala bests the Cornwall below 40hz.

It migh help to read everything over again. The high Q filter provides 6dB of electrical boost at Fb=31hz, and system shows bandpass gain between Fb and the horn Fc.

[colterphoto1]

LAR, nice port mod, but I'm wondering, why did you flip your mid/high pack upside down?

Michael

[lar418]

Hi Michael,

My pedistal is 12" high and the tweeter ended up at 47" above the floor. By inverting them the tweeter is now about 39-1/2" above the floor which is more at ear level. I recently added a grill which dresses them up a little. I'll post a pic when I get a chance latter this week.

Larry

[colterphoto1]

The only place a LaScala is 104dB is around 120hz~240hz and 1Khz~2Khz, the Cornwall incinerates it below 80hz or so, but the 6th order vented LaScala bests the Cornwall below 40hz.

It migh help to read everything over again. The high Q filter provides 6dB of electrical boost at Fb=31hz, and system shows bandpass gain between Fb and the horn Fc.

Is that why I love my CW's so much? (I haven't done any mods to anything yet).

I do plan on trying a set of the vented LS this summer.

Michael

[BS Button]

Picture wasn't attached!

How do you connect the additional bass bin with the original cab?

[DrWho]

I think it just rests on top, no?

[lar418]

You are correct, it just sits on top and the weight of the speaker seals the two cabinets. The pedestal has a raised frame that is the same size as the access panel that I removed. Foam sealing tape used for speakers makes an air tight seal. (See attached picture)

[middlecreekguy]

So did you close off the back opening of the doghouse or is that still open?

[Marvel]

So did you close off the back opening of the doghouse or is that still open?

Uh... do you mean the 3x13 inch slot? That is what feeds the horn.

[middlecreekguy]

So did you close off the back opening of the doghouse or is that still open?

Uh... do you mean the 3x13 inch slot? That is what feeds the horn.

Yes, the slot. I was thinking if you open the bottom of the doghouse for the mod, you would have to close the slot.

Guess I was wrong. And glad I'm wrong too.

[lar418]

On the Industrial model the woofer is accessed through the bottom plate. The plate is about 18" x 18" and is just held in place with 8 wood screws. The volume of the doghouse and pedestal combine to provide a 5.9 cu-ft rear volume. The woofer still fires through the slot of the horn.

I have seen posts about opening up the slot to 6" x 13", but I don't know if it will improve the response. Again, I'm using the K-33E woofers.

Any thoughts????

[Loudisbeautiful]

Hi,

I am a bit confused. Does not the horn chamber of the woofer have to be an exact size by design?......IE.... would not the additional volume of the bass mod adversely affect the horn output?

Thanks

[Marvel]

You wouldn't widen the slot for the K33 or K43. They are about a 4 ohm

speaker. I believe you would use the wider slot for an 8 ohm.

Bruce

[lar418]

The output is reduced somewhat, but the bandwidth is increased. Instead of 104 db's it is probably now about 102 db's. This reduced output actually blends better with the port output. As mentioned in an earlier post, I had to reduced the output of the squawker to match the new woofer output.

[DrWho]

Hi,

I am a bit confused.

Does not the horn chamber of the woofer have to be an exact size by

design?......IE.... would not the additional volume of the bass

mod adversely affect the horn output?

Thanks

This is the cool part of the design...you can create the same air

pressure behind the woofer with a properly ported enclosure due to the

way a port loads the driver. So yes, typically increasing the volume

behind the woofer can cause negative results, but in this case it does

not.

[djk]

"Would anyone happen to have the schenamatic for the peaking 2nd order highpass filter? I've never seen this trick before and I am quite impressed with the possible applications of it. "

This is a crossover, the high Q filter would just use the HP output. Ch=0.1µF, Rh=12.1K(the Rh to ground is 200K).

One OPA2134 opamp per channel is recommended with ±12V~15V supplies and 10µF+0.1µF power supply bypass on each rail.

ESP sells the boards quite reasonable too, although it is simple enough to wire on a piece of perf board from Radio Shack.

[DrWho]

Thanks! []