Article: Solving the Klipschorn Throat Riddle (Edgar)

[D-MAN]

Did you see my post in updates and mods about a compression chamber?

I was recently wondering about the effect of different slot sizes on both sides, not a circular opening on one side...

This is a close correlary

DM

III. Acoustic Filters

A. Low-pass filters

An acoustic low-pass filter may be constructed by inserting an expansion chamber in the duct. An expansion chamber serves as a simple model of a muffler, and also has applications in architectural acoustics (the plenum chamber in a building's HVAC system is an expansion chamber). Keeping track of all incident and reflected waves from both junctions, one can derive the sound power transmission coefficient as

(5) Figure 3(a) shows this coefficient for an expansion chamber with dimensions similar to what you will use in this lab. Notice that there are frequencies at which all incident power passes right through the filter, and there are other frequencies where a minimum of power is allowed to pass by. Frequencies for complete transmission correspond to standing waves being set up within the muffler chamber.

In a low frequency limit (kl << 1) the expansion chamber may be treated as a side branch of acoustic compliance C = V/ p c² where the volume V = S₂ L₂. In this low frequency limit, the side branch approximation of the sound power transmission coefficient in Eq. (5) becomes

(6) This low frequency approximation is shown in Figure 3(. The expansion chamber appears to pass low frequencies, and block high frequencies. Thus, it is called a "low-pass" filter.

Figure 3: (a) Sound power transmission coefficient for an expansion chamber; ( low frequency approximation acting as a low-pass filter.

[ajsons]

Which thread is that? My memory is as short as my legs. But I do remember seeing the formula from the thread. The're not showing above.

[D-MAN]

http://forums.klipsch.com/forums/5/633004/ShowThread.aspx#633004

[ajsons]

Ok, now I remember where I saw that.

No extra expense on electronic filters would be great.

[ajsons]

Did you see my post in updates and mods about a compression chamber?

I was recently wondering about the effect of different slot sizes on both sides, not a circular opening on one side...

A double filter?

[homemadeheresy]

bump

[DrWho]

Thanks Gil for posting that article, I think it

shows just how much we still have to learn about acoustics. The

followup posts only emphasize this. Tony

The science of acoustics is very well understood...

The problem with the first article is a series of mathematical

simplifications (basically just assumptions) that happened to work with

the khorn, but turned out to not be a global truth. So obviously there

is more at play than the simplifications made - which is what Edgar's

friend was telling him from an acoustical model.

Ultimately, if you wanna know the true effects then just sit down and

write out the long math equations and spend the next year or so trying

to simplify it down to a function of the height and width of the slot -

and then you'll be able to measure the difference for any horn. [] I

kinda like PWK's method better...trial and error with solid

measurements. It's not like it's very expensive or difficult to

experiment with such a piece in the design.

Btw, I think you can see some of the results using the Horn Response

Calculator...though I'm yet to figure out how to model the

khorn/lascala in that thing.

[Bill Cain]

Btw, I think you can see some of the results using the Horn Response Calculator...though I'm yet to figure out how to model the khorn/lascala in that thing.

Interesting thread. I'm wondering if I might make any actual improvement in bass response of a La Scala (Industrial) with more modern drivers, higher power and compensatory EQ?

I'd like to select a more robust woofer and let the DriveRack properly EQ the system so that more power might help extend the limits a wee bit. I know I can't overcome the horn's limitation due to mouth size, but I do stack the bass cabinets.

Or might I be stuck in Never-Never Land, searching for a correct slot size? I went to Gauss woofers, in the seventies, in University S-9 (Classic) cabinets and never felt as if I accomplished much.

[DrWho]

I think the biggest improvement to be made with the lascala is to

reinforce the bass bin...stick your hand on the side and note how crazy

style it vibrates - even at lower volumes. The problem with dropping a

"better" driver in the slot is that the horn is an acoustical impedance

matching device and by changing the driver you are changing the

original impedance (thus requiring a diffrent kind of matching).

The K-43 woofer is already a pretty beefy woofer - at most you might

gain 3dB with a better driver, but I doubt you'll find one with close

enough T/S parameters.

You should also consider the ported mod - help reinforce that lacking bass.

[DizRotus]

This has probably already been discussed on the forum, if not in this very thread. Nevertheless, does anyone have any experience substituting the larger magnet and more expensive musical instrument speakers in a Khorn that Bruce Edgar referred to in the article?<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Commercial speaker production involves compromises. PWK was very good at making excellent commercially viable speakers. The DIY enthusiast need not use the same driver in a folded corner horn that worked best in the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Cornwall. If spending more for a bass driver would produce a better result, it is worth considering.

In addition to the cost factor, I suspect that digging deeper might compromise the upper limits of the bass driver. Paying more for marginally deeper low end extension, if it dictated the need for a 4-way network, would not be an acceptable compromise.

[Guest " "]

This has probably already been discussed on the forum, if not in this very thread. Nevertheless, does anyone have any experience substituting the larger magnet and more expensive musical instrument speakers in a Khorn that Bruce Edgar referred to in the article?<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Commercial speaker production involves compromises. PWK was very good at making excellent commercially viable speakers. The DIY enthusiast need not use the same driver in a folded corner horn that worked best in the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Cornwall. If spending more for a bass driver would produce a better result, it is worth considering.

In addition to the cost factor, I suspect that digging deeper might compromise the upper limits of the bass driver. Paying more for marginally deeper low end extension, if it dictated the need for a 4-way network, would not be an acceptable compromise.

This is a trick question to say the least...there is a split field on this one. My take

a. i haved used an ACR PA-38 driver in khorns. Both with 3X13 and 6X13 baffle openings. sounded better on the mid-bass using 6X13, better on lower end using 3X13.

b. Used the k-43 in place of the k-33. while folks are concerned that the k-43 has less low end than a k-33, it really depends on which k-33 you have (some are fs 27hz, some are fs 34 HZ), and where are you putting it. I would use it in a lascala or belle, but not in a k-horn.

[Bill Cain]

I think the biggest improvement to be made with the lascala is to reinforce the bass bin...stick your hand on the side and note how crazy style it vibrates - even at lower volumes.

I have never notices that phenomenon. Perhaps the LSI's, being wrapped in Fiberglas and edged with aluminum, are less prone to flexing?

The problem with dropping a "better" driver in the slot is that the horn is an acoustical impedance matching device and by changing the driver you are changing the original impedance (thus requiring a diffrent kind of matching).

I had anticipated that possibility due to this thread....

The K-43 woofer is already a pretty beefy woofer - at most you might gain 3dB with a better driver, but I doubt you'll find one with close enough T/S parameters.

Where might I find the T/S parameters for the LSI woofer? That might be the best place to start. TSC says:

<< Our new PA stuff may be of interest to you. We'll be updating the site with them in about ~2 weeks. We'll list full T/S report and ideal box volumes for bass reflex and maybe even a horn loaded config. >>

You should also consider the ported mod - help reinforce that lacking bass.

I searched the forum and found the mod. Very interesting, but more in line with someone building from scratch. Would not hack my LSI-BG's. Thanks though.

[]

[DrWho]

The DIY enthusiast need not use the same driver in a folded corner horn that worked best in the Cornwall.

I was under the impression that the K-33 was optomized for the khorn and just happened to work well with the cornwall. It seems that most drivers meant for hornloading work real well in bass-reflex cabinets.

[DrWho]

I have never notices that phenomenon. Perhaps the LSI's, being wrapped

in Fiberglas and edged with aluminum, are less prone to flexing?

Well it happens with all of Colter's bass bins, which also includes two

flavors of LSI's. It seriously is a huge problem and something Klipsch

fixed with the new LIII's...they even had to change the crossover to

account for the extra acoustical output.

The K-43 woofer is already a pretty beefy woofer - at most you might

gain 3dB with a better driver, but I doubt you'll find one with close

enough T/S parameters.

Where might I find the T/S parameters for the LSI woofer? That might be the best place to start. TSC says:

<< Our new PA stuff may be of interest

to you. We'll be updating the site with them in about ~2 weeks. We'll

list full T/S report and ideal box volumes for bass reflex and maybe

even a horn loaded config. >>

The specs for the K-33 have been floating around and there seems to

be 3 slightly different versions. I only have one set of specs so maybe

someone will chime in with all 3.

You should also consider the ported mod - help reinforce that lacking bass.

I searched the forum and found the mod. Very interesting, but more in line with someone building from scratch. Would not hack my LSI-BG's. Thanks though.

[]

It is my understanding that the ported mod is completely reversible

and causes no damage? You just remove the hatch door on the bottom and

set the speaker on top of a ported box. Throw in a peaking-2nd-order

highpass filter and you've got strong output down to 40Hz and no

worries of over-excursion below that.

That link to which you refer is definetly not one of the threads I was thinking about...

[Guest " "]

k-33 spec's....the more you search, the more you find

PART # K-33

RE OHMS 3.39 FS HZ 34.46

LE MH .96 MMS GMS 78.59

QM 7.39 CMS mm/N .2714

QE .410 RMS NS/M 2.3037

QT .390 VAS LTRS 301.66

XMAX MM 8.20 SD SCM 889.59

BL TM 11.88 EBP 84.4

EFF % 2.91 SPL dB 96.6

Wattage 150rms

1981 k-33

Re = 3.39 Ohms

Zmax = 46 Ohms @ Fs = 35 Hz

Ro = 46/3.39 = 13.57

Z = Re*SQRT(Ro) = 3.39 * SQRT(13.57) = 3.39*3.683=12.5 Ohms

Fh=49Hz @ Z=12.5 Ohms

Fl=25Hz @ Z=12.5 Ohms

check >> SQRT (Fh*Fl) = SQRT (49*25) = 35Hz = Fs (good numbers)

Qms = Fs * SQRT(Ro) / (Fh - Fl) = 35* SQRT(3.68) / (49-25) = 5.37

Qes = Qms / (Ro-1) = 5.37 / (13.57 - 1) = .427

Qts = Qms * Qes / (Qms + Qes) = (5.37 * .427) / (5.37 + .427) = .395

[D-MAN]

WHO:

Most likely your calculations are for straight (and probably infinite) horns! You probably don't even know WHERE the basis of those calculations come from and the variety of variables and formulas employed in them and who came up with what and how they ended up in the programs in question.

Relying on somebody else's work without doing your own - the main reason I really can't stand your know-it-all posts.

As stated by Kellogg in 1929, which I will paraphrase, "one bend in the horn channel and all the math goes out the window".

Calculate THAT with your horn program.

DM

[sunnysal]

Thanks Gil for posting that article, I think it shows just how much we still have to learn about acoustics. The followup posts only emphasize this. Tony

The science of acoustics is very well understood...

The problem with the first article is a series of mathematical simplifications (basically just assumptions) that happened to work with the khorn, but turned out to not be a global truth. So obviously there is more at play than the simplifications made - which is what Edgar's friend was telling him from an acoustical model.

Ultimately, if you wanna know the true effects then just sit down and write out the long math equations and spend the next year or so trying to simplify it down to a function of the height and width of the slot - and then you'll be able to measure the difference for any horn. [] I kinda like PWK's method better...trial and error with solid measurements. It's not like it's very expensive or difficult to experiment with such a piece in the design.

Btw, I think you can see some of the results using the Horn Response Calculator...though I'm yet to figure out how to model the khorn/lascala in that thing.

I meant more what WE the b-boarders had to learn about acoustics, tony

[DrWho]

Most likely your calculations are for straight (and

probably infinite) horns! You probably don't even know WHERE the basis

of those calculations come from and the variety of variables and

formulas employed in them and who came up with what and how they ended

up in the programs in question.

MY calculations? What the heck are you smoking? Why in the world would

I sit down and write out a long equation for a straight infinite horn

when the specific situation is nothing like that? (especially when

those equations have already been made) Wow - good one. Guess what,

that's close to what Edgar already did using his electrical circuit

model. Heck, I don't even like the khorn []

Relying on somebody else's work without doing your own - the

main reason I really can't stand your know-it-all posts.

I'm glad you are familiar with my research - surely you wouldn't mind sharing about it.

And my posts are certainly not "know-it-all" either - perhaps try

rereading what I actually wrote. You've seriously got issues dude. I

hate when people try to make things personal as it is completely

irrelevant and is usually an indication of one's own insecurity.

As stated by Kellogg in 1929, which I will paraphrase, "one bend

in the horn channel and all the math goes out the window".

Calculate THAT with your horn program.

Good for Kellogg. I'll bet a lot of money that he was referring to

the simplified straight infinite horn model, in which case I completely

agree with him. My suggestion was to have someone sit down and write

out the raw mathematics for the actual khorn. I know it can be done -

it's just the skill in doing it well involves coming up with "simple"

equations that are actually feasible to use/solve. I don't pretend to

be capable of such a task, but I know some who are and I am very

familiar with the process involved. Just because it is out of my scope

doesn't mean I can't comment about it. Heck, you write about horns all

the time []

Spanning on that, the program is not my own and assumes straight

infinite horns simply because the math is easier...I didn't claim it

would model the effects of the khorn at all, but that some of the

effects of slots on a simple horn can be shown in the program. And I

think it would be interesting to enter in the khorn/lascala to see how

close the straight infinite assumption compares to the actual output.

Anyways, you need to work on your reading comprehension. There is a

lack of tone in one's voice when communication through these forums and

you seem to enjoy putting an arrogant tone in my words which is most

certainly not there. Feel free to disagree with anything I write, but

you would have far more credibility if you could do so without making

it personal.

[D-MAN]

A double filter?

Well, my thinking is that in the case of a full circular opening on one side (the cone side)allows for the cone itself to act as a highly variable volume which changes with extenstion and frequency which will effect the overall chamber capacitance much more than a more restictive slot would, which would tend to stabilize the chamber volume to a greater degree across a wider frequency and power (extension) range. Seems to me, anyway.

It would only effect the higher end of the bandpass, and have very little (if any) effect on the low end.

That's the attraction...

DM

[mungkiman]

Shows how simple I am...

I thought the 6" x 13" slot was for a 16 Ohm woofer, while the 3" x 13" slot was for the 8 Ohm woofers.