Preparing for Jubilee build

[bodcaw boy]

Does anyone have the approx. dimensions of the K-402 horn. This is one of the horns on the Jubilee in the Hope engineering lab, right?

It's a tractrix horn, right?

i think dims are in the product section. and until i find a better equation or combo equation or even a fluke equation (or i get replaced or leap frogged or downsized), it will some type of mod'ed tractrix horn. don't get me wrong, i look at lot of horns especially the new kids on the block horns and so far no dice. i don't do tractrix for tractrix sake; i do tractrix cause that is the best that i could find so far....still looking.

roy

[DrWho]

Dimensions:

H: 26" (66cm)

W: 40.3" (102cm)

D: 23.3" (59cm)

And lots more info here if you scroll down all the way:

http://www.klipsch.com/media/Products/Cinema%20Lit%20Aug%2005.pdf

[Deang]

Man, don't you ever sleep?

[Daddy Dee]

Roy,

Thanks for your take on this. Yeh, one thing I can well imagine is that your review of various horn solutions is not a "dog in the fight" kind of audition. You are looking looking for the right solution, in my take. "hornitisiforgetious"... now that's good. I'm plagued by something similar, without knowing much to forget! []

Dr. Who, thanks for the link. That is one big rascal of a horn. It's a challenge for me to keep those horns straight.

[DrWho]

There is a pretty good explanation of the "rubber throat" concept in the JAES article (is that what everyone is calling it?) It was just posted recently in one of these threads - definetly an interesting read...even talks about some of the reasoning behind the compromises being made (which in my opinion is where the real genious in engineering lies).

And no, I never sleep...or if I do I don't realize it cuz I'm probably thinking about speakers then too [][]

[Guest " "]

There is a pretty good explanation of the "rubber throat" concept in the JAES article (is that what everyone is calling it?) It was just posted recently in one of these threads - definetly an interesting read...even talks about some of the reasoning behind the compromises being made (which in my opinion is where the real genious in engineering lies).

And no,  I never sleep...or if I do I don't realize it cuz I'm probably thinking about speakers then too [][]

This one?

AES-Jubilee2.pdf

[DrWho]

That's the one...

On page 5 under the section "4 Analyzing the data" they summarize a reference to some other article written by PWK. Apparently a rubber throat uses a faster initial expansion rate to make the mouth appear larger to the lower frequencies - effectively reducing the likelihood of overloading the throat.

I bet if we bother Gil that he probably has the reference available on pdf somewhere - or should have no problem hunting it down. []

[jt1stcav]

An interesting thread...just finished reading it, albeit not understanding a whole lot due to being mechanically inept, but still an interesting read nonetheless.[]

If I'm guessing correctly, Darell has finished his DIY Jubilees, yes? I'd love to see some pics of the finished products, and his take on their performance with his system and favorite music. And more production pics of the build would be nice if and when he has the chance. I envy anyone who can successfully tackle such a project...I couldn't do it; I'd cut my fool hand off most likely!

[Marvel]

That's the one...

On page 5 under the section "4 Analyzing the data" they summarize a reference to some other article written by PWK. Apparently a rubber throat uses a faster initial expansion rate to make the mouth appear larger to the lower frequencies - effectively reducing the likelihood of overloading the throat.

This is how the LS is made.

[homemadeheresy]

bump

[D-MAN]

Think "Acoustic Transformer"... that's technically what horns are, and multiple horns of differing flare rates connected together transform or transfer the acoustic impedance from the mouth of one section to the throat of another.

The "rubber throat" is typically (but not always, as in the case of the LS) a means to reduce (or increase as desired) the throat reactance seen by the driver by effectively transferring the acoustic impedance to the "next" flare section, using a rapid flare rate at the throat followed by a slower (lower) rate. So the driver "sees" a rapid flare rate and therefore a lower overall throat reactance, due to a rapid flare rate being "easier to push air through" than a lower flare rate which has a higher reactance.

Let me define the terms "impedance" and "reactance"... impedance is "the resistance to air movement", reactance is the property of air to "compress and rebound", if you will. In essence, reactance could be described as a time-delayed "pushing back" property. Reactance has some properties of "storing" energy to a degree, somewhat like a capacitance. Resistance, on the other hand, is the impeding component presented by an enclosed column of air to the movement of air being pushed thorugh in a single direction. The "tighter" or more restrictive the passage as with a slow (low Fc) flare rate, the higher the impedance and subsequent reactance.

Since horns are acoustic impedance TRANSFERING devices, (or acoustic TRANSFORMERS) it is a natural course of events that different horns of differing flare rates can be connected to achieve a desired acoustical impredance at the throat, each respective section's MOUTH being the subsequent section's THROAT impedance.

The original concept was put forth by H.F. Olson of RCA fame in the 40's, which PWK referenced in the original 1945 Khorn patent. The values of the acoustic impedance/reactance is calculated at the mouth of the horn and then is worked backwards towards the throat, a flare-rate section at a time. The use of acoustic impedance values can allow a horn design to present the desired impedance to virtually any driver. The "rubber throat" of higher Fc shows less acoustic impedance to the driver, for instance. A throat section of lower Fc would present more impedance and subsequent reactance to the driver.

One important issue is that the SUBSEQUENT flare rate, whether an intermediate or a terminal (MOUTH) section needs to be LOWER than the preceding section's flare rate.

The Khorn and Jubilee follow this pattern as throat=rapid, intermediate=low, terminal=between the previous values.

Interestingly, it is the terminal (mouth) section that determines the overall Fc of the horn, regardless of how many intermediate flare sections are used. It is NOT an average, etc.

The differing flare rates TYPICALLY allows for a wider bandwidth than a single flare rate horn.

This gets messy like in the case of the LS which uses a low flare rate at the throat, followed by a 125Hz Fc terminal section, the result being a nominal Fc for the horn of approx. 70Hz. The slower throat flare rate is used to provide the acoustic impedance best suited for the driver (the K33). A case of purposefully designing the throat reactance for a specific driver.

The Khorn uses 3 different flare rates, the LS/BELLE uses 2 but reversed from the typical setup, and the Jubilee uses 3.

DM

[Islander]

I'm trying to get these concepts clear in my head and I think it's starting to happen. To use an analogy from something I'm more familiar with (motorcycle induction systems), does the "rubber throat" function sort of like a plenum chamber that gives turbulence a chance to settle down, or am I still confused?

Even though it's challenging, I really enjoy following discussions like this. Learning is fun when it's directly applicable to something you're interested in.

Pat on the Island

[D-MAN]

An expansion chamber? I think that is a close analogy, although the outcome is somewhat different... an expansion chamber is highly capacitive, that is, it has some of the properties of a capacitor, such as "storing and discharging" acoustic energy based on frequency. An expansion chamber DOES alter the acoustic impedance, though, but that's as far as the analogy goes, seems to me...

For our purposes, a "rubber throat" is not the same as an expansion chamber because it expressly does NOT want to store and discharge ANY energy - rather, it wants to transmit it from one end to the other altering the impedance along the way from a relatively high impedance to somewhat lower at the section "mouth". The faster flare rate (one that expands rapidly) is less restrictive to start with, and therefore the impedance seen by the driver is less than if the throat ection was a lower (slower) expansion rate. That is it in a nutshell.

It also doesn't have anything to do with turbulence, either, in a horn.

Think acoustical resistance, i.e., putting the driver "under pressure" or giving it something to push against. The flare rates can be used to control the amount of pressure applied to the driver. Some drivers operate better under alot of pressure, and others not so much, although all tend to "like" some pressure, that is, a higher than atmospheric acoustical resistance to push against.

DM

[Islander]

Actually, the expansion chamber goes on the exhaust side, not the intake side, but you did describe its function quite well. I've never thought of an expansion chamber as a capacitor, but in effect, that's what it is.

The plenum chamber that I mentioned would be the airbox. It allows incoming air time and space to become more coherent in its flow, improving performance.

Although there is no turbulence in a speaker horn in the conventional sense, since the air sort of oscillates rather than flows, aren't there disruptions in air movement around irregularities in the horn, such as corners and steps like at the start of the La Scala bass bin vee? I wonder if adding a piece of filler material to smooth that step might be a good thing?

Pat on the Island

[D-MAN]

No, do not add filler UNLESS you specifically are attempting to filter out the higher frequencies (and/or lower efficiency, etc.).

Filler (absorptive material) is an added viscosity (loss) and slows down the soundwaves, which tend to cancel by phase and losses due to viscosity.

Viscosity is the tendancy of air to "stick" to surfaces. Fibrous material has lots of surface(s) to stick to, slowing the waveform down, enough that phase cancellation can take effect, as well as losses (i.e., motion into heat) from viscous friction. The heat is minimal and is considered adiabatic, but it is still indicative of a loss of energy.

DM

[DrWho]

Sounds like foam might be a good thing for a bend in a horn then...make it wedge shaped, thicker on the inside of the corner and very thin on the outside. There will be slight losses at all frequencies, and moreso once the thickness gets over 1/4 wavelength - but even 1kHz is a good 13 inches. Keep it under 4" at the thickest point and you're home free.

But doesn't sound travel faster through solids???

[Islander]

Actually, I was thinking of wood inserts, like a strip of triangular wood trim with one right angle, which would go in the back outer corners of the LS bass bin, making the corner less sharp. Almost like a strip of quarter-round that goes onto a wall's baseboard, only flat (or even slightly concave) instead of round. As well, a slightly more complex shaped piece (135 degree edge on one side) would smooth off the step at the start of the LS bass bin vee.

Just wanting to streamline the air movement, not dampen the sound. Hopefully neglible losses and reflections. The LS cabinets work, but look like little time was spent on the fine details of their construction.

Pat on the Island

[Islander]

Another way to look at it is that those square corners and steps may cause localized eddying and unsmooth air movement. I'd think that would not help the sound, although the effects are probably minor.

Pat on the Island

[D-MAN]

Think hard-surface reflectors, like mirrors, then. Above 300Hz. Below doesn't matter due to the wavelengths involved.

DM

[bodcaw boy]

Think hard-surface reflectors, like mirrors, then. Above 300Hz. Below doesn't matter due to the wavelengths involved.

DM

no, no....not light rays.....think water pipes......

boy!!