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Old 6th September 2013, 07:19 PM   #11
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Location: Abingdon, Virginia
Quote:
Originally Posted by weltersys View Post
Dennis,

Your original post does not mention TH, nor does it show speaker position, or exit, or horn path, making it difficult to understand what type of design it is.

Vented designs are known as BR (bass reflex), a Helmholtz resonator.
Front loaded horns (FLH) use a compression chamber.
TH and FLH use a path that expands from throat to mouth.

"Maximize performance" is not a goal unless "performance" is specified in terms of efficiency, SPL, frequency response, distortion and anything else important to you.
A design for maximum output from 30-120 Hz and one designed for 50-150 or smooth response from 50-500 Hz are all different goals and would require different designs (and drivers) to achieve.

Using the free software program Hornresp you could model various designs using the same cabinet volume and speaker parameters and decide which fits your version of "maximum performance".

Art
Art,

The original post does not mention TH, this is true. My follow up question does. The original does specify the location of the "driver compartment" and states various mounting configurations could be used. It also specifically states, though does not show in illustration (something beyond my simple graphics capability in 3D perspective drawing) exactly what the horn path is, including the start of the throat ("horn compartment") and the mouth described by name.

The type of design is not specified for the simple reasons this design is intended to start with the geometry and then try to optimize it by alterations to the geometry as well as selection of the specific design, including driver selection and matching to the other variables. I am trying to design a minimally sized cabinet
with maximum use of internal space, in order to provide the smallest speaker with maximal response. That response should of course include aspects of all the variables you mention. I hope to do for this geometry what is done for most designs, which is to achieve the best balance of those variables. As such, my "goal" is to find the best set of parameters this design is capable of, even including altering the geometry -- just as long as it remains the best possible response that a minimal sized cabinet can achieve.

One of my original questions was whether multiple constant cross section pipes with larger outlet than inlet equate to "expanding from throat to mouth" (ie. providing the same or similar acoustic impedance matching as a path with increasing cross section pipes). This is an example of the very basic level I am attempting to start from in order to determine what design (TH, BR, etc.) is possible to use, and provides the best platform for other alterations and considerations. I realize this is not the "traditional" method of optimizing a given speaker, and so does not lend itself to selecting first what parameter to optimize. My goal, if it fits the definition, is to get the most out of the maximized use of internal space, not matter how many other aspects I have to incorporate into the design, which to forego (sealed box vs. TH for example), and how to balance each against the others in order to find the best possible way to use the design.

I apologize if my intention was not clearly stated. It is obviously a starting point far upstream of that in most designs. To my mind, the complexity and the unusual aspects of it make it something that make it not likely to be modeled well by such as hornresp. Seven pipes, five of what are constant cross section and two expanding, but with the openings and cross section from one to the next getting larger each time, and with seven 90 degree bends -- is hornresp capable of this. I've tried it and I can't tell because of this complexity (including possible resonances of various constant cross section chambers).

Bottom line, I'm trying to start with a particular internal geometry and get the most out of it, so I can see if I can come up with the smallest box with the best response for its size. There are a great many things to be balanced here. I'm just trying to figure out which are most important and so where to start.
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Old 6th September 2013, 07:50 PM   #12
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Quote:
Originally Posted by drmcclainphd View Post
Art,
I am trying to design a minimally sized cabinet with maximum use of internal space, in order to provide the smallest speaker with maximal response.
As such, my "goal" is to find the best set of parameters this design is capable of, even including altering the geometry -- just as long as it remains the best possible response that a minimal sized cabinet can achieve.

My goal, if it fits the definition, is to get the most out of the maximized use of internal space, not matter how many other aspects I have to incorporate into the design, which to forego (sealed box vs. TH for example), and how to balance each against the others in order to find the best possible way to use the design.

To my mind, the complexity and the unusual aspects of it make it something that make it not likely to be modeled well by such as hornresp. Seven pipes, five of what are constant cross section and two expanding, but with the openings and cross section from one to the next getting larger each time, and with seven 90 degree bends -- is hornresp capable of this.

Bottom line, I'm trying to start with a particular internal geometry and get the most out of it, so I can see if I can come up with the smallest box with the best response for its size.
Again, you have not defined a target response- "maximal" regarding a frequency response and output level must be determined.
A simple two fold TH would have maximal upper response, to go low requires more folds to achieve the longer path length needed.

Hoffman's Iron Law applies to all types of sub designs- loud, low, small, pick two. You get to decide what is "best".

Last I checked (been a while and David adds features frequently)Hornresp can model four separate horn segments. Generally the bend can be considered part of a horn segment, but more accurately modeled as a separate part.
If you want to model more parts, you can go to Akaback, and add bits and pieces to your hearts content.

At any rate, the fold pattern presented in the OP seem overly complicated, it seems neither to maximize the use of space or materials.

Is there a reason you want a cubical enclosure?
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Old 8th September 2013, 08:47 PM   #13
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Quote:
Originally Posted by weltersys View Post
Again, you have not defined a target response- "maximal" regarding a frequency response and output level must be determined.
A simple two fold TH would have maximal upper response, to go low requires more folds to achieve the longer path length needed.

Hoffman's Iron Law applies to all types of sub designs- loud, low, small, pick two. You get to decide what is "best".

Last I checked (been a while and David adds features frequently)Hornresp can model four separate horn segments. Generally the bend can be considered part of a horn segment, but more accurately modeled as a separate part.
If you want to model more parts, you can go to Akaback, and add bits and pieces to your hearts content.

At any rate, the fold pattern presented in the OP seem overly complicated, it seems neither to maximize the use of space or materials.

Is there a reason you want a cubical enclosure?
Thanks for sticking with me.

No, I am not defining a target response. There are many possible. I want to try to determine what can be done for each (re: Hoffman's Iron Law), including a fourth -- shall we say clarity? Sharpness? whatever. And then from within the design attempt to maximize the response based on getting the best possible combination.

Hoffman is wrong. You don't pick two. You pick two to try to maximize and either ignore, or try to at least to not do something counter productive with the third. Otherwise it's a plain crap shoot. And I say there's four, not three, and I intend to try to pick and work with all four to get the best possible combination of them.

And I agree, Akaback is the better choice. The bends are where the expansion is and they all need to be accounted for.

The original design is intended to maximize horn length in the most compact form possible because I have to move these things around (requiring space in the truck) and set them up in order to play. Sometimes stage space is quite limited. The "overly complicated" structure is an attempt to to *minimize* the use of material (thus weight; but I do believe that's what you meant). How many other 7+ foot horns require less than a full 4' * 8' sheet of material?

Cubic? Not necessarily. There are probably far more efficient uses of space. The best built from pieces of commonly available materials would probably entail approximating a logrithmic spiral (ie. snail shell shaped) in the manner of an expanding buckytube, built from increasing sizes of equilateral triangles. Everything else would fall in between. And if this were an available choice among possibilities, there would be yet another trade off to make between internal geometry type and the other aspects,.per Hoffman. But in the end, I want something that can actually be built, be reasonably light and compact, and give the best sound I can get within those constraints.

When I did my dissertation research I was told I could get either temporal, spatial or frequency resolution on my EEG recordings, pick two. I picked continuous wavelet transform analysis, got all three, and made a movie of cortical responses that occurred to auditory stimuli only in the prefrontal cortex at 2 msec resolution from 20 to 120 msec, and made the first movie of the dopamine system in action. I learned analysis of functional MRI from the guy who invented it and decried its severe limitations (a statistical technique that made it almost certainly bogus in many cases). He said I could maximize localization or field strength, but not both. I chose tensor calculus as a nonlinear method of analyzing the data and got both. I don't know enough yet about how to analyze the design I'm proposing, but I do know enough to know, as so aptly stated in Clarke's First Law: : "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong." I tend towards the impossible and ask that those on whose shoulders I stand only help how they can with what they know so that I may see farther. On the obverse I ask only that those who can't, accept that fact, and don't tell me I can't.

Last edited by drmcclainphd; 8th September 2013 at 08:49 PM. Reason: missing quote mark
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Old 8th September 2013, 10:56 PM   #14
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Quote:
Originally Posted by drmcclainphd View Post
No, I am not defining a target response. There are many possible. I want to try to determine what can be done for each (re: Hoffman's Iron Law), including a fourth -- shall we say clarity? Sharpness?

How many other 7+ foot horns require less than a full 4' * 8' sheet of material?
There are an infinite amount of possible target responses from just one loudspeaker and a given amount of material.
Narrowing the target response makes achieving a goal possible.
Designs for subs using TH or TQWP designs using over 7 feet of path length with one four x 8 are fairly common.

The very popular SS15 (single sheet 15) TH is bit shorter length, trading LF extension for upper output.
It trades low drive level efficiency for reduced maximum output and increased distortion.

All cabinet decisions need to be done with a specific "weighting", comparing the ranking in importance between the major metrics of 1- size/weight, 2-efficiency, 3-maximum output level,4-frequency extension, 5-smoothness in and out of passband, 6-distortion, 7-impulse/phase response,8-cost.

All eight (there could be further distinctions made, or other qualities bringing the count much higher) metrics have a direct impact on the others.

As you found in your research it is possible to get both temporal, spatial and frequency resolution on EEG recordings, while without a continuous wavelet transform analysis only two of the three are available.

Made me think back to the mid-1990s when using the IBVA (Interactive Brain Visualisation Analyzer) you could see a continuous waterfall plot of brain wave frequency, amplitude, and duration.

With a bit of experience interpreting the three metrics displayed you could identify individuals by their patterns, and also detect whether they were listening or formulating a response, or talking.

Still, the IBVA was not detailed enough to tell you in the least what someone was actually thinking.

Once you become familiar with the relationship of the different metrics and decide what weighting to give each of them, the cabinet choices will become fewer, as it will require a specific design to maximally satisfy the metric "code" you prefer.

You might use your continuous wavelet transform analysis recordings to determine what metrics correlate with your EEG response the most when listening to subs with widely differing response types.

Art

Last edited by weltersys; 8th September 2013 at 11:02 PM.
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Old 12th September 2013, 12:30 AM   #15
colofan is offline colofan  United States
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One design parameter not mention is dispersion pattern at the output and at a distance used for the typical listener location. Horns gain acoustical efficiency in using a very directed wavefront; quite a bit different from some of the other box alignments.
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Old 12th September 2013, 06:05 AM   #16
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Originally Posted by colofan View Post
One design parameter not mention is dispersion pattern at the output and at a distance used for the typical listener location. Horns gain acoustical efficiency in using a very directed wavefront; quite a bit different from some of the other box alignments.
Good point, and since the OP has not decided bandwidth, very important in the upper range where a long narrow horn may only be 30 degrees or so.

Tapped horns and FLH do have quite a bit more directivity in the upper bass range than a bass reflex cabinet.
The radiation pattern from a tapped horn is different than a bass reflex cabinet.

Actual measurements in this post:

Tapped Horn Directivity

The BR cabinet was basically omnidirectional within about 1 dB to 60 Hz, then looses about 3 dB off axis at 125, and around 7 dB at 160 Hz.

The FLH C-horn is basically omnidirectional within about 3 dB to 60 Hz, then looses about 7 dB at 125 Hz, and above. The C-horn has a smaller frontal area than the BR cabinet, the horn is obviously affecting dispersion, not just panel size.

The Keystone TH is basically omnidirectional within about 2 dB to 60 Hz, then looses about 12 dB at 125, and around 9 dB at 160 Hz.
The radiation from the front and back of the cone are imparting a different dispersion at upper frequencies, a different effect than the BR and FLH, which both seem to just narrow more at upper frequencies.

As you said, "quite a bit different".

Art
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