Channel Folds

[D-MAN]

Hear is what I am thinking. The full channel reflector may extend the high frequencies but at the expense of efficiency of the lows. So if you are going to crossover in the 600 range wouldn't it be better to use the partial reflector to preserve efficiency? Roy am I way off base?

rigma

By all accounts, low frequencies are relatively immune to reflectors due to their very long wavelengths. At best, reflectors only effect the mid and upper bass frequencies where the wavelengths (or sub-multiples) are shorter, respectively.

The full-channel reflectors as put forth by Bruce Edgar (for example) are intended to preserve phase relationships through the folds, again effecting only the upper bandpass.

The low frequencies will not be effected by reflectors.

DM

[DrWho]

Diffraction around the boundary is going to be different for frequency too....I wonder how well these formulas might apply:

There are a number of quite
computationally intensive methods for calculating this reduction, however,
a simple method that suits our purposes is as follows;

R = 10 log(3
+ ((40fd) /c))

where R is the reduction
(dB) over the inverse square law, f is the frequency (Hz), d the
path difference and c is the speed of sound (usually taken as 343m/s).

An alternative method is to
derive the term (u) for which charts exist relating this to dB
reduction.

u
= (1.414h / sqrt(l)) * sqrt((a + / (a * )

http://www.kemt.fei.tuke.sk/Predmety/KEMT320_EA/_web/Online_Course_on_Acoustics/barriers.html
or to get the full website with the menu on the left:
http://www.kemt.fei.tuke.sk/Predmety/KEMT320_EA/_web/Online_Course_on_Acoustics/index_acoustics.html

[D-MAN]

I don't know where diffraction events would be important INSIDE a well-designed horn channel per se, but certainly takes place once the waveform leaves the horn channel(s).

Do you have any specific examples in mind?

DM

[DrWho]

I was just thinking that any sharp bend is going to have diffraction effects that are different at every frequency - I know this is a large room analysis, but the physical system is the same (just a smaller scale inside the horn channel).

[D-MAN]

Well, that's quite probable. One shadow area that I know of, for example, is the Khorn/LS/Belle throat cavity opening is smaller by 1/2 than the throat area cross-section, that would have some diffraction events associated with it. Interestingly, the diffraction would be in favor of the bifurcation taking place at the same point. Sort of using the inevitable slot diffraction to "aid" the turn. Conjecture on my part, but I know it's there.

DM

[bodcaw boy]

have you ever analyzed a curved bend?

Does my wife count?

a little ammunition to hold over deano.......[A]

roy delgado

[bodcaw boy]

Take a look at US patent # 2866513. It's the patent for the Millenium 4D rear loaded horn. The 4D was driven by a pair of 15"JBL drivers. I heard a single unit years ago. The build quality was outstanding. A single unit weighed over 350 lbs.

http://www.stan-white.org/a_hist_adv_1.htm

I've discussed the design with White (by email, he's still around). All he said to me was that should I decide to build it, be sure to use the curved panels otherwise it will not perform very well. He had a single 4D unit on display at a the Chicage HiFi Expo and the engineers at Jensen were all over it, later to introduce the Imperial. The patent came out later (1958).

Isn't Janice cute? The costume is great, so typical of the time.

Stan White is a real character, a lesser known from Audio's "golden era".

Maybe I can get him to chime in here(?)

that would be cool.

jw

Edit-

Note in the advertisments he specifically states the horns are curled and not folded to within 1% of the design formula.

funny how that is...

roy delgado

[DrWho]

the shelves essentially add the waves back at a zero degree angle so they would still see the full mouth and diffract....

Yikes, I originally mistook the problem for a standing wave in the vertical plane...which is totally not what you mentioned before: [A]
(though that begs the question how vertical standing waves aren't an issue)

in the full anechoic measurement, ie no boundaries, the vertical flare
of the lf horn is not expanding; all expanding is done
horizontally.....thus when the wave(think of a bubble) exits the horns,
horizontally the wave is okay but in the vertical it goes from no
expansion to lots of expansion; so the wave diffracts. in a corner and
on the floor one side of the horn in the vertical continues the no
expansion but at the top it still diffracts so it is not as bad as the
full anechoic curve. that is the dip you see around 200 hz.

I've been thinking about this for a while, but can't for the life of me figure out why it affects only 240Hz so severely. The polar plots surely don't show the sound spreading wider in that region (quite the opposite actually). Nearly scratching my head bald on this one []

Btw, is it really that much more expensive to bend a piece of wood for a perfect area expansion through a bend? I think it would even be easier to build the Jubilee with a curved bend (less board to cut). But I'm no woodworker which is why I ask.

[TBrennan]

Stan White eh? I met him at a hi-fi shop where he was touting his little shotglass speakers, they weren't bad at all.

Figures that John would know him. ;-)

[rigma]

Hear is what I am thinking. The full channel reflector may extend the high frequencies but at the expense of efficiency of the lows. So if you are going to crossover in the 600 range wouldn't it be better to use the partial reflector to preserve efficiency? Roy am I way off base?

rigma

well kinda.....you have can have fast flare rate to help the low freq stuff but i am not sure if it improves efficiency. but it is probably best to not radically change the flare rate in the bend. make sense?

roy delgado

Well not really.[:$] Are you saying the partial (45 deg. radius) reflector is the better choice? Does that maintain the flare rate through the bend?

For those who are interested scroll to results at the link below. There are animations of different reflectors and various frequencies.

http://ldsg.snippets.org/HORNS/waves.html

rigma

i saw the website. impressive stuff. what i am saying is that a curved bend whose curvature is dependent on what the area expansion is doing does the best. have you ever analyzed a curved bend?

roy delgado

Can you use a non 45 deg. reflector, say 67 deg. with good results? Maybe even with a short 45 deg section to meeting the 67 deg. section.

[D-MAN]

In the 90 degree turn at the front corners (e.g., Jubilee), the goal is to turn the waveform 90 degrees into the axis of the side channel(s), which would be a 45 degree reflector. A 67 deg. reflection angle would in effect aim the reflected waveform at the channel wall, not the channel center axis. You want to go with the center channel axis to keep side wall reflections to a minimum, otherwise you would just be introducing more inter-channel turbulance that you don't need or want, of course.

However, like I said before, it doesn't really matter whether its a radius (partial) reflector or a full-channel reflector. It would only effect the upper-bass frequencies if at all - HOWEVER - it certainly won't hurt having full-channel reflectors and might possibly help. Being that the Jubilee can naturally make use of upper bass frequencies, why not make it as easy as possible to propagate them through the horn?

DM

[jwc]

Ditto to that.

Dana, did you get my emails over the weekend? jc

[D-MAN]

JC, negative, I'm at home and haven't been to work. Call me.

Dana

[bodcaw boy]

the shelves essentially add the waves back at a zero degree angle so they would still see the full mouth and diffract....

Yikes, I originally mistook the problem for a standing wave in the vertical plane...which is totally not what you mentioned before: [A]

i hope you do better on tests, young man......

(though that begs the question how vertical standing waves aren't an issue)

expanding area, that's how

in the full anechoic measurement, ie no boundaries, the vertical flare of the lf horn is not expanding; all expanding is done horizontally.....thus when the wave(think of a bubble) exits the horns, horizontally the wave is okay but in the vertical it goes from no expansion to lots of expansion; so the wave diffracts. in a corner and on the floor one side of the horn in the vertical continues the no expansion but at the top it still diffracts so it is not as bad as the full anechoic curve. that is the dip you see around 200 hz.

I've been thinking about this for a while, but can't for the life of me figure out why it affects only 240Hz so severely. The polar plots surely don't show the sound spreading wider in that region (quite the opposite actually). Nearly scratching my head bald on this one []

it's just the "critical" freq; it just happens to the physically be the 1/2 wavelength, that's all. leave your hair alone....

Btw, is it really that much more expensive to bend a piece of wood for a perfect area expansion through a bend? I think it would even be easier to build the Jubilee with a curved bend (less board to cut). But I'm no woodworker which is why I ask.

curved wood is expensive.....we looked at some sort of composite/plastic but tooling is expensive.....

roy delgado

[D-MAN]

I found this from 1959. Simplistic, but true. DM

[D-MAN]

I think I proved the validity of this approach in the Jamboree design, which is reliant on reflectors.

DM

[D-MAN]

It certainly won't hurt using reflectors, anyway. Kiss goodbye to the old bass horn "3-octave rule"!

The reflectors were the one part of the design that I wasn't sure about, but looks like they work as intended. Couldn't hope for better, actually.

DM

[ajsons]

Remeber this, Dana...from the Classic thread?

I knew I was headed in the right direction.

http://forums.klipsch.com/forums/5/678109/ShowThread.aspx

(I cut and added the small reflector last night to my Classic. Had to remove a couple of glue blocks that were in the way.)

[D-MAN]

Armando, what is your opinion of the difference in sound?

Like Edgar said about the Classic, which I'll paraphrase, "with the old driver (and the crossover point being 300 Hz), the reflectors are wasted". Are you thinking of changing drivers (or you did already)?

My opinion is that full-channel hard-surface reflectors certainly won't hurt, and will probably help in virtually any horn fold situation.

Dana

[ajsons]

I haven't tested it yet, will do that tonight.

I 'm crossing at 400hz with ALK's. I probably won't be able to tell the difference without any measuring equipment, but I know I'll sleep better, knowing that I put an extra reflector there.

I still have the EV in it.