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post #271 of 448 Old 09-14-2010, 11:42 AM
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Originally Posted by noah katz View Post

the outside dimension of the box stays the same.

The length of the partitions vary.

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post #272 of 448 Old 09-14-2010, 11:50 AM
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the flare angles are typically not that steep, so why doesn't each leg produce the peaks/dips that would attend their lengths particularly for the long legs around the edges?

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post #273 of 448 Old 09-14-2010, 01:27 PM
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Before we get too carried away with this lets think about the standing waves. The standing waves start at half wave lengths, so a reflection point of ~5.5ft is needed before things can even creep down to 100Hz.

The normal areas looked at in a folded horn are the distance between parallel sides of the horn, and the distances around the bends.

The parallel sides SWs are easy: 344m/(Distance*2)= SW frequency.

The bend cancellation is: 344m/((Outside Radius - Inside Radius)*2)


Now when trying to figure the standing waves going with the path length in a flared section you have to remember to do end correction for the bends at each end of the section. A horn is not a pressure chamber, and each section is more like a Helmholtz resonator. As such the effective length of each section is different in anything but a non-tapered pipe.

Note: a stepped pipe would be the same as a flare here.


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post #274 of 448 Old 09-14-2010, 01:31 PM
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what about a single fold horn that is upwards of 7 feet long; how should we think about internal resonances/cancellations in that case?

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post #275 of 448 Old 09-14-2010, 01:51 PM
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Quote:
Originally Posted by LTD02 View Post

what about a single fold horn that is upwards of 7 feet long; how should we think about internal resonances/cancellations in that case?

In the large single folded horns you can get into the area where things are the right size to possibly cause problems, but you can't be sure what will happen until you build it.

If you look at Cowan's 35Hz TH plans, and measurements you would expect something to pop up in the 90-140dB range. The measured response is a little different in that area, but not any more so than you would imagine without SWs.

There are another couple of TH with the predicted peaks missing, that also happen to fall where the SWs would be expected to be. I believe lilmike has one, IIRC.

It is said, the DTS-20 may be using it's size to kill a resonance peak, but the unknown driver parameters in the uber Lab12 clouds the issue.


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post #276 of 448 Old 09-15-2010, 12:01 PM
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[quote=soho54;19191163] A horn is not a pressure chamber, and each section is more like a Helmholtz resonator. QUOTE]

Can you have a Helmholtz resonator without a clear spatial demarcation between the mass and spring?

Otherwise you could say a straight pipe is an infinite number of them, just draw the lines where you want.

I can see where end correction and corner radii are important for a wave traveling through, but I don't see that for a reflection.

To be honest I don't have a good feel for this at all; it would nioce to see a simulation showing how a wave propagates down a FH.

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post #277 of 448 Old 09-15-2010, 02:20 PM
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That is why I said it is, "more like a Helmholtz resonator." What I was trying to get across was that the effective lengths of each section would be different with a taper. They would slightly alter the frequency of the standing wave in each section, and keep them from cascading together. The closest thing most people would "get" where this would be the case, is a resonator with flare and baffle end corrections.

I have a link to a site with a time lapsed view of different frequency pressure waves moving though a bend, but I can't find it right now.


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post #278 of 448 Old 09-15-2010, 02:29 PM
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Quote:
Originally Posted by noah katz View Post

To be honest I don't have a good feel for this at all; it would nioce to see a simulation showing how a wave propagates down a FH.

Very much the same as they do in a room. At very low frequencies/long wavelengths the wavefront acts like a single large object, and it needs no assistance to negotiate the bends. As the wavelength grows shorter the front begins to act like a grouping of individual particles; the shorter the wavelength the smaller and more numerous the particles. They need assistance to go around the bend without all sorts of phase problems. At the lower end of the spectrum simple flat reflectors work OK, see Huygens model. At the upper end of the spectrum rounded bends are required, per the Olson model.

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post #279 of 448 Old 09-15-2010, 07:36 PM
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noah, you are "advanced class", so might find interesting reading the original papers on horn math, some of which go back 70 years, perhaps olson, salmon, et al.

here is a fairly extensive list of references on horn design:

http://www.omegav.ntnu.no/~dunker/refs01.html

http://www.omegav.ntnu.no/~dunker/refs02.html

i'm no horn expert and i have not read most of those papers, so i can't comment on which may be the most relevant to your questions.

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post #280 of 448 Old 09-15-2010, 08:51 PM
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ricci, why the break in expansion in #258? wouldn't a simple conical work just fine?

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post #281 of 448 Old 09-16-2010, 06:41 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

ricci, why the break in expansion in #258? wouldn't a simple conical work just fine?

Sure it would work. The increased expansion towards the end and a smaller s3 allows a larger mouth which increases overall efficiency. A straight conical with a smaller mouth would have greater 25-35hz by a db or 2, the increased mouth expansion and size snags an extra 2db or so from 35-120hz. Plus allows extra room to get at the driver.


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post #282 of 448 Old 09-16-2010, 02:00 PM
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Quote:
Originally Posted by soho54 View Post

That is why I said it is, "more like a Helmholtz resonator." What I was trying to get across was that the effective lengths of each section would be different with a taper. They would slightly alter the frequency of the standing wave in each section...

Do you mean effective length like of a port? I still don't see how that applies here, because I still can't divine the mass and spring.

I think you might be mixing up acoustic and Helmholz resonance.

Acoustic resonance is a function of dimensions and speed of sound.

Helmholz resonance is not acoustic, it's a mass/spring system where both happen to be air (or just one for a PR system).

LTD, thanks for the links, but to be honest my math skills, other than what I use on the job, are quite withered at this point.

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post #283 of 448 Old 09-16-2010, 04:01 PM
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Quote:
Originally Posted by noah katz View Post

I think you might be mixing up acoustic and Helmholz resonance.

I do not believe so.

I used Helmholtz as most people seem to equate them with a ported enclosure, and are able to understand that you have to account for pressure differences at the ends of the duct, which are caused by differences in mouth geometry/boundary position, and that this alters the effective length of the duct. This is what I was getting at, the pressure chamber can be left off here.
Another example could be a simple open end air column formula, but I seem to loose everyone when I bring up air columns, and it requires some tweaking as well.

It was a simplified analogy, that I thought would get the concept across to the greatest number of people.

The thing that is key is that the wave is not forced to reflect off the side at the bend back up the horn, unless the corner dimensions are greater than 1/4WL. It has somewhere to "flow." What you end up with is defined by opposing pressure zones created by the drag of the extreme corner point, and the lesser pressure area on the inside of the bend.

If the wave is small enough it sees the corner as a "wall," and is turned back around.

With a flared horn the measurements at each corner will be different, and will effect the frequencies differently than the last.

If you look at the path time around the bend, the inside track has less distance to cover, while the outside one is forced to cover more distance. This means that when both sides hit the end the inside track is further ahead in time/phase. Where the distance is ahead by 1/2 wave length the two sections are out of phase with one another, and cancel each other out. Well, the middle area blends it all together, so it isn't a total cancellation, just a nice big dip.

Standing waves from parallel walls are your standard SW fare.


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post #284 of 448 Old 09-16-2010, 07:16 PM
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after a few nights to sleep on it, are you happy with the response in #258?

is it time to fold it up?

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post #285 of 448 Old 09-17-2010, 10:54 PM - Thread Starter
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I'm not unhappy with the sim in post# 258. I may still tweak it a bit. This build is some couple of months off still so I'm concentrating on other projects right now. If you have suggestions for improvements or changes, fire away.


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post #286 of 448 Old 09-17-2010, 11:28 PM
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"I'm not unhappy with the sim in post# 258. I may still tweak it a bit. "

i think it looks great for your application. the only points of potential difficulty would be getting the exact expansion that you model in an actual horn and making sure that you have enough volume so the driver will fit. it kind of depends on the design/folding scheme if it will hit spot on your model. in the end, any differences will be a small change though. you have a good driver, a good horn design, so the rest is kind of academic.

for crazy ht apps, the corner could be pulled down to 20-22hz. with a simple 2kw amp, such should punch full reference for ht and upwards of 130db for music--front row at a full blown rock concert spl.

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post #287 of 448 Old 09-21-2010, 07:27 AM
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Originally Posted by Ricci View Post

the Klipschs's and the couple of occasions that I've heard Labsubs is that the sound is very clean at high output levels. It seems that they are freer from distortions or other unwanted noises compared to direct radiators driven to the same levels.

I just came across this from Paul Klipsch, which contains just enough math to satisfy those who must see an equation before believing what can be easily heard.
http://www.readresearch.co.uk/loudsp..._article_3.pdf

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post #288 of 448 Old 09-23-2010, 06:11 PM
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interesting bfm, but i'm not sold.

when used as a subwoofer, amplitude modulated distortion is going to be pretty low because f2 is limited to about 80hz or so. even if A1 is flopping around at an inch, am distortion will be 0.033 * 1.0 * 80 = 2.64%. others report such distortion in the bass in inaudible.

i suppose that real music is never just a pair of frequencies though, so you'd have to integrate across all the frequencies being played simultaneously in the horn in order to arrive at a true distortion number.

my guess is that the lower distortion of the horn is coming from the fact that this just wasn't a fair fight. klipsh is comparing distortion vs. spl for a 12 inch ported driver in a 1.5 cubic foot enclosure to a 16 cubic foot horn!

a better comparison would have been *ten* 1.5 cubic foot direct radiators vs. the 16 cubic foot horn. wouldn't such a system have higher efficiency and lower distortion than the horn?

any chance you could link up parts i and ii?

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post #289 of 448 Old 09-23-2010, 08:03 PM
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a better comparison would have been *ten* 1.5 cubic foot direct radiators vs. the 16 cubic foot horn. wouldn't such a system have higher efficiency and lower distortion than the horn?

Higher sensitivity, no. Lower distortion, maybe. A lot higher cost, most assuredly.

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post #290 of 448 Old 09-23-2010, 10:23 PM
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Originally Posted by Bill Fitzmaurice View Post

Higher sensitivity, no. Lower distortion, maybe. A lot higher cost, most assuredly.

I'd have to agree with LTD02... in that comparing a small box to a large box isn't really a fair comparison.

That's like saying a cube van can haul more in a trip than one pickup truck load. Sure, but what happens when you compare 10 pickups to one cube van load.

Take note of the chart with distortion curve... the 12" in a 1.5 cube box is around 15% distortion at 105 db. The 16 ft ^3 horn is showing about 2-3% or thereabouts.

So what happens when you halve cone excursion by adding another co-located system>? Does it fall by half?

If so, then 4-5 of the small box systems should be able to match the horn in terms of distortion.

The IM distortion would also fall with a reduced test bandwidth, on both systems. Not many folded horns can do the bandwidth that was used in the test. ( 41 hz to 350 hz )

The small box systems will use more amplifier power yes, but will also be much easier to move.

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post #291 of 448 Old 09-23-2010, 11:32 PM
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Originally Posted by LTD02 View Post

a better comparison would have been *ten* 1.5 cubic foot direct radiators vs. the 16 cubic foot horn. wouldn't such a system have higher efficiency and lower distortion than the horn?

How is this any better? Ten subs would give you an almost a 10dB gain in sensitivity, but now you have 10 drivers compared to the Horns single driver. Even then the horn could still be more sensitive, depending on the driver, and bandwidth.

The horn could also still have the same or a better displacement:SPL ratio, and if folded the extra upper out of bandwidth LP filter.

Then you have to look at scale. 10:1 OK, but what if I need more output? 20:2, 30:3, at what point does it get to be to much? 40 small sealed subs to 4 horns?

What about packaging? Ten small sealed subs are going to take up a lot of enclosure surface area.

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Originally Posted by michael hurd View Post

I'd have to agree with LTD02... in that comparing a small box to a large box isn't really a fair comparison.

What is fair? This seems to come up around here all the time, when comparing things. Different alignments are used for a reason.


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That's like saying a cube van can haul more in a trip than one pickup truck load. Sure, but what happens when you compare 10 pickups to one cube van load.

One option costs a crap load more to buy, needs more people to operate, and burns up a lot more fuel.

A better scenario would be pick-ups vs a tractor trailer. For ~$120k for the tractor, and ~10k for a tanker you could pull 8600gal of gas and be right at the legal limit, in the summer, and average 6.5mpg. A regular Silverado (w/v8) will run ~26k, can handle ~300gal of fuel at payload capacity, and should average ~10mpg.

When you get to looking at everything you see that sometimes you need a pick-up(s), and sometimes only a tractor will do.


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post #292 of 448 Old 09-24-2010, 01:03 PM - Thread Starter
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To my mind it goes like this... You have a single driver and you want to make the baddest speaker you can with it. That's a horn hands down. Other enclosure types plateau out and quit gaining significant performance once you get to a certain size. On the other hand if you have plenty of budget and not a lot of space then a bunch of drivers crammed into limited space can be made to out perform horns over an extended bandwidth. It justs costs exponentially more, takes more power, weighs more, etc.


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post #293 of 448 Old 09-24-2010, 07:55 PM
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Ricci, you have a full inbox. I can't get back to you.


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post #294 of 448 Old 09-25-2010, 12:46 AM
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Quote:
Originally Posted by Ricci View Post

To my mind it goes like this... You have a single driver and you want to make the baddest speaker you can with it. That's a horn hands down. Other enclosure types plateau out and quit gaining significant performance once you get to a certain size. On the other hand if you have plenty of budget and not a lot of space then a bunch of drivers crammed into limited space can be made to out perform horns over an extended bandwidth. It justs costs exponentially more, takes more power, weighs more, etc.

it just occurred to me why EAW makes horn subs but JBL ( for the most part ) does not. it's because ( i'm going to oversimplify the math a bit ) JBL makes, and EAW loses money on every woofer they end up using to achieve the same SPL.
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post #295 of 448 Old 09-25-2010, 01:15 AM
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Originally Posted by Ricci View Post

To my mind it goes like this... You have a single driver and you want to make the baddest speaker you can with it. That's a horn hands down. Other enclosure types plateau out and quit gaining significant performance once you get to a certain size. On the other hand if you have plenty of budget and not a lot of space then a bunch of drivers crammed into limited space can be made to out perform horns over an extended bandwidth. It justs costs exponentially more, takes more power, weighs more, etc.

Hmmm

From Bills earlier posts you can never exceed 116db/w with a horn woofer system. Direct radiators have a 3db lower maximum efficiency. I don't know how this affects max output. You could probably put twice the power into the direct radiator system and reach the same output of the horn system given the horn system can only handle half the power of the DR system.

"You can't exceed it because that 116dB/watt reflects approximately a 40% energy conversion efficiency, and that's as much as you can get from a typical woofer horn. You can get that 40% by any number of means, but you can't exceed it. Try modeling in Horn Resp varying the pi space and number of cabs, it's very revealing. I can run 4096 THTs (64 series x 64 parallel) in eighth space and never break 116dB with 1 watt."

"Direct radiators have a sensitivity limit roughly 3dB lower than horns. Direct radiators can never reach the same sensitivity as horns because their maximum attainable efficiency runs about half what horns do, and 1/2=3dB."

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post #296 of 448 Old 09-25-2010, 06:35 AM - Thread Starter
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DL86,
That is all correct. But that is simply efficiency. You'd have to look at driver excursion and thermal handling as well. 4 to 8x the drivers will almost always have huge advantages in those 2 areas.


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post #297 of 448 Old 09-26-2010, 03:47 PM
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"To my mind it goes like this..."

agree.

i'm still curious if there are any additional thoughts on your original question. is the "clean" sound of horns that you are hearing attributable to their high efficiency (and low distortion for small movements in the driver's cone) or is there something else going on (such as low passing harmonic distortion)?

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post #298 of 448 Old 09-27-2010, 05:59 AM
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Quote:
Originally Posted by Ricci View Post

To my mind it goes like this... You have a single driver and you want to make the baddest speaker you can with it. That's a horn hands down. Other enclosure types plateau out and quit gaining significant performance once you get to a certain size. On the other hand if you have plenty of budget and not a lot of space then a bunch of drivers crammed into limited space can be made to out perform horns over an extended bandwidth. It justs costs exponentially more, takes more power, weighs more, etc.


There is always going to be boundaries and constraints. I have never seen the thread where someone picked the ultimate design period (there was always some compromise) because there isnt one design that is the ultimate choice for all applications.

To me "A horn wins hands down" is not really true because to get < 15Hz performance you need a MONSTER BOX. That is actually a compromise in the majority of situations.

So the Monster box tells me the horn does not win and lets face it the horn crowd would never win an interior design award unless they hid all boxes.

On the other hand it takes a lot of money to have great performance in a small box, about $1600 right now on my LMS box/amp. I spent $1600 on another solution in the past too, 4 x 18" woofers in an IB.


Every solution will have a compromise. If $$$ are easy then I would take the looks and peformance over the horn choice every time.

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post #299 of 448 Old 09-27-2010, 11:03 AM - Thread Starter
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You will never be able to get as much performance out a single woofer with any other enclosure type as you will a huge horn. The constraint is the single woofer or money however you want to look at it. Enclosure size is not. Change the constraint to a space issue and remove the money or single driver constraint and things change.


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post #300 of 448 Old 09-27-2010, 11:14 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

"To my mind it goes like this..."

agree.

i'm still curious if there are any additional thoughts on your original question. is the "clean" sound of horns that you are hearing attributable to their high efficiency (and low distortion for small movements in the driver's cone) or is there something else going on (such as low passing harmonic distortion)?

I think it's a combination of perhaps some acoustic lpf and also decreased input power demands and lower average excursion. A large part of it is the cabinet filtering out or masking other contamination noises from the drivers. Hiss, motor noise, suspension noise, leakage back through the cone, all of that various stuff that can pop up once you start to push the drivers well. All of the other noises from a drivers normal operation that are not part of the original signal. Most of the time you don't notice it because its normal with direct radiators. A horn or bandpass system should filter out this above band racket. I believe that this should show up in a spectral contamination test. That's my half baked theory anyway.


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