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Opinions needed for LaScala mod


Tony Reed

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I'm thinking of running vertical "strips" cut on a 45 degree angle in the back corners of my LaScala's. These "strips" would run top to bottom filling in the last 90 degree corner somewhat. This would help round out the last turn in the bass section. How would this affect the sound? I thought it might reduce standing waves by helping the air flow.

Thanks,

Tony

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Tony,

Ok... Now that I see it on the drawing I tend to think it might be an improvement. I don't think it will do any harm. In fact, the Belle has a wedge like that right at the throat of the horn, right in front of the woffer driver. The La Scala may have that too. You would have to pull the woffer out to see it though.

Al K.

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Dr. Bruce Edgar published something in Speaker Builder on how such structures were necessary to prevent the area in the turn from being too great and thus effectively widening the duct. I.e. a departure from the approximation of an exponential expansion.

The Speaker Lab near copy of the K-Horn has such pieces at the first turn, i.e. the turn which is actually at the top and bottom just behind the front surface. This is analogous to what you're talking about.

The duct there in the Speaker Lab version, like in in your drawing, is about three inches wide. The diagonal piece is solid. The short sides of the cross section of the piece are 1.5 inches long. Therefore the hypotenuse is 1.414 time that. I mention this as suggested dimension to work with.

I've seen one explanation from Speaker Lab that this is a matter of "reflecting" treble frequencies. I think that is not quite accurate in view of the wavelengths involved. 400 Hz is about the upper limit and has a wavelengths of over two feet.

The other way of explaining it is that the wave has to go a relative long way around the outside of the curve, and a short way around the inside of the curve. You don't want that difference to be anywhere near a half wavelength, because there would be cancellation.

My understanding of the design of the K-Horn, Belle, and LaScala is to keep the width of the duct in the turn to a minimum width. The path is split into two symmetrical structures. Otherwise, one path could have a duct width of six inches. The radius of the outside of the turn would then be greater and thus would be closer to half a wavelength.

The split path may well reduce the purported problem. Especially since there is only one bend in the LaScala. So, that may be a reason for the piece's omission.

However, putting the brace in is probably, IMHO, a good idea and can't hurt.

It would be interesting to see how the turns in the Jubilee are designed. It seems the bass horn is being used up to 800 Hz where such considerations have a larger role.

Gil

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Originally posted by Klewless:

My Peavey FH-1 basshorns (similar to the LaScala horn) have such reflectors in the corners, they help the highend response of the horn. Supposedly the LS horn runs out of gas at 400 cycles, my Peaveys (with K-33E woofers installed) run flat up to 500 cycles. So the reflectors might help the top response of the basshorn but since the LS crossesover at 400 cycles the mod may be of no practical use. However if you CAN get the basshorn to respond to 500 cycles then lots of other mods become possible such as substituting aluminum diaphragm Altec or JBl drivers for the stock mid drivers. Then you could junk the tweeters and go 2-way and play with 511B or Edgar saladbowl horns and on and on, it never ends. :-)

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Tony,

I've tested prototype La Scala's with wedges positioned as you suggest. It does increase the bandwidth of the speaker by a couple of hundred Hertz, but the amplitude response above 400 Hz was pretty choppy (very narrow 6-10 dB dips if I remember correctly). I believe we tried more than one size wedge, but I don't remember the difference it made.

We abandoned the idea after we realized the response wasn't as smooth as we would like. However, we were also concerned about the bass-horns dispersion characteristics above 400 Hz. At these frequencies, the horn is beginning to get fairly narrow. I suspect some of this is due to the bifurcated horn section.

I don't want to discourage you from trying this because we probably didn't explore it as thoroughly as we should have. Extending the bandwidth of the bass-horn in order to relieve some of the burden on the midrange may more than offset some of the problems I describe above.

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Anything that keeps the horn more in a continuous curve would be good but the effect will likely only be at higher frequencies (as suggested) of the bass driver. Don't know how this would affect response of the system as a whole since it was not designed in the crossovers to handle that change in response.

You might like it.

Peter Z.

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This sounds like a good mod but in my experience with the LS I would rather take more of the high frequencies out of the bass horn. It makes some lower vocals sound fat and muddy I think. Wouldn't this mod aid in the hollow upper mids? Just a random though. Ill probably try it anyway though.

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