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Thread: Handmade Ersatz M9500 Speakers

  1. #31
    RIP 2011 Zilch's Avatar
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    ESL = English (as a) Second Language....

    [Short form of "EAASL" ]

  2. #32
    Member linear's Avatar
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    Horn (Waveguide) Contour Comparison

    I thought that it would be interesting to compare the contour of Jack's Oblate Spheroid / Tractrtrix Waveguide with a simple Exponential Horn, like the one shown in this thread.

    Assumptions:

    Jack's Waveguide has a 49mm throat dia, a 200mm mouth dia, and a depth of 95mm. Let's create an Exponential Horn with the same dimensions. From simple horn theory, this will result in a flare factor, "m", of 29.6, which in turn defines a cutoff frequency of 811 Hz. This exponential horn contour is overlaid as red dots on Jack's waveguide drawing, below.

    Comments:

    For shallow horns/waveguides (i.e. the mouth diameter and depth are of similar size), the difference between contours is not that great. (Note that with longer horns, the difference is very significant.) In fact, if the wood turner is only a few millimeters off in his axially symmetrical oblate spheroid creation, he could inadvertantly end up with a lowly exponential horn! (or vice versa!)

    Jack, on your original drawing your mention a cutoff frequency of 531.578 Hz. Is this your calculated cutoff for your waveguide, or is it a way of identifying the Tractricx section? (i.e. Is it the cutoff of a fully realized/extended Tractrix, but not this actual waveguide?)

    If the cutoff frequency of Jack's waveguide is 532 Hz, versus 811 hz for an exponential horn version, then those few millimeters here and there are certainly critical!

    Comments?

    Linear
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  3. #33
    Member linear's Avatar
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    Earlier in this thread, there was considerable discussion regarding horn patents. Fun was poked at the issue and sarcasm employed. In that same spirit, it's now my turn!

    [Fun/Fantasy Mode ON]

    I have a friend who works for the NSA (National Security Agency), near Washington, DC, where they monitor thousands of telephone calls a day, all in the interest of national security. They also have incredibly powerful search software, that can locate "key words" (normally of a "terrorist nature") in these conversations. I asked him to search using two names (we will call them "Dr. G" and "Signor Z") and the key words "patent", "cease", "desist", "horn", and "waveguide". He immediately got a "hit". A transcript of this conversation follows.

    Z: Ciao! Hello! This is _____ calling. Please can I speak to Dr. _____

    G: Hello, this is Dr. ______. What's up?

    Z: I regret to tell you that the horns that you are using in your speakers infringe my patent! You must cease and desist immediately! Otherwise, I will be forced to take legal action!

    G: Now hold your horses there, Guiseppe! We DON'T use horns in our speakers! We use waveguides.....

    Z: But waveguides are the same as horns, no?

    G: Absolutely NOT! They are completely different! They are as different as chalk and cheese ... or.....or.... pasta and spaghetti!

    Z: Well, maybe....let me think.....

    G: Furthermore, what we use are "axially symmetric oblate spheroid CD waveguides"! This is leading edge technology, based of course, on my research! Now your exponential horns - that's old technology! They pre-date the internet - they might even be older than that!

    Z: OK, OK! I apologize for my false accusation. Please accept my congratulations on your research. Perhaps I should think about upgrading my old exponential horns to the new, how do you say it, oblate sphero.....

    G: You will have to license that technology from me! But you won't regret it! Nobody wants plain old exponential horns anymore. If you upgrade to my technology, your sales will skyrocket. There's room for both of us in the marketplace. The deal will be win win!

    Z: OK, d'accordo! Send me a contract! But, one problem maybe? I have my computer controlled wood turning machine programmed for the exponential, you know? The cutting heads have a limited travel. For your new completely different contour, how do you say it, oblate sphero.... I may have to buy a new machine, no?

    G: Don't worry! You will only have to adjust the contour a few millimeters here and there. You can use your old machine for sure! Once you sign the contract, I will give you all the details. Wait a minute, what's the tolerance on your machine?

    Z: I'm not sure. It's an older machine. Probably a millimeter, here or there....

    G: You are probably already infringing my intelectual property with that tolerance! I'll add a fee to the contract to cover your past production of horns. They might have oblate contours in them!

    Z: OK, thank you, grazie tante! It will be great to get this new technology!

    G: It's a pleasure doing business with you, Guiseppe!

    [Fun/Fantasy Mode OFF]

    Linear

  4. #34
    Member jack_bouska's Avatar
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    Quote Originally Posted by linear
    I thought that it would be interesting to compare the contour of Jack's Oblate Spheroid / Tractrtrix Waveguide with a simple Exponential Horn, like the one shown in this thread................
    Comments?
    Linear
    Hi Linear – it seems I’m inordinately busy at work these days, a condition which is seriously affecting my spare time available for posting – I will say that I have been doing some offline thinking about your horn-waveguide contour comparison post, and I am in the process of composing a reasoned reply, but my spare time “crunch” has diverted my time at the keyboard to issues more seismic oriented (same problems as audio/acoustics, just not so many octaves, and a much more complicated propagation media). – In the mean time, I am including a .jpg scan of a short sidebar article written by Dr. Keith Holland, which discusses the phenomena of horn cut-off, in relation to horn contour shape (conical vs. exponential).

    I class this material as *essential* reading for anyone who may be contemplating design of their own DIY horn contour. The post I am (mentally) composing will draw on some of the information in Dr. Holland’s article, so I am posting these .jpg’s now, to give any interested parties a couple of days to read and digest the information, before I post my reply related to Geddes-Zingali differences and your particular implementation. The article may require reading in several passes, depending on your particular background level in acoustics. (I re-read it about once every year or so, just to refresh my own memory.)

    Also, if anyone has not done so yet, all interested parties should download a pdf of the Peavey white paper written by C. Hughes (Google: Charlie Hughes peavey )
    The Quadratic-Throat Waveguide:

    http://www.installaa.com/downloads/pdf/qwp1.pdf#search=%22charlie%20hughes%20peavy%22

    Again, the Peavey paper is classed as essential reading for any aspiring horn diy’er.

    All I have time for right now, more to follow, maybe this weekend, (if I first sacrifice a goat to the spare time god’s)

    Jack Bouska
    (thinking about a problem/question is fun, writing about it is more of a chore)
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  6. #36
    Member linear's Avatar
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    Quote Originally Posted by jack_bouska

    Also, if anyone has not done so yet, all interested parties should download a pdf of the Peavey white paper written by C. Hughes (Google: Charlie Hughes peavey )
    The Quadratic-Throat Waveguide:

    Again, the Peavey paper is classed as essential reading for any aspiring horn diy’er.
    I have started working on a chart (graph) that displays several types of horn / waveguide contours, so that the differences in physical dimensions can easily be observed, should anyone want to pick one for a wood turning DIY project.

    So far, I have included Conical, Exponential, and Hughes, as shown in the following attachment. The "Hughes" is from a paper by Charles Hughes (with Peavey at the time), which is referenced earlier in this thread.

    Speaking of the Hughes paper, considering that it is "essential reading", has anyone else noticed that his equations have several serious typos that make them useless for working out the data points for his waveguide???? I had to go back to Pythagoras and re-derive them. I would appreciate a "sanity check" from someone else, that I'm correct in that observation.

    I intend to add some more contours to this plot. I am "normalizing" everything to a horn / waveguide with a 2 inch throat diameter, a 15.5 inch mouth diameter, and a depth of 6 inches. This is my favourite size, as it is a drop in "replacement" for a standard 15 inch driver. Someone could retro-fit a cabinet with two 15" speakers, to a horn / bass driver configuration with this size of horn / waveguide.

    Jack, when you get some time, could you send me an email, or post some data points (x,y) on your "Oblate Spheroid / Tractrix" waveguide? Would anyone else like to contribute their favourite contour? About 20 data point pairs should be enough, as long as the values at any "contour transistion" (e.g, Spheroid to Tractrix) are included.

    Linear
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  7. #37
    Administrator Mr. Widget's Avatar
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    This is an interesting comparison. Thanks for doing the leg work and sharing this with us. I would love for someone to produce a prototype of each horn and objectively and subjectively compare them along with a true tractrix horn and possibly one of Jack's horns.

    Are Jack's "Oblate Spheroid / Tractrix" derived from any real world product or are they unique to his speakers? Has anyone ever listened to them? (Besides Jack obviously... we tend to be biased about our own babies.) Jack if you posted their full history I am sorry, I must have missed it.


    Widget

  8. #38
    Member jack_bouska's Avatar
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    horn shape comparison

    Quote Originally Posted by linear
    I have started working on a chart (graph) that displays several types of horn / waveguide contours, so that the differences in physical dimensions can easily be observed, should anyone want to pick one for a wood turning DIY project.

    So far, I have included Conical, Exponential, and Hughes, as shown in the following attachment. The "Hughes" is from a paper by Charles Hughes (with Peavey at the time), which is referenced earlier in this thread.

    Speaking of the Hughes paper, considering that it is "essential reading", has anyone else noticed that his equations have several serious typos that make them useless for working out the data points for his waveguide???? I had to go back to Pythagoras and re-derive them. I would appreciate a "sanity check" from someone else, that I'm correct in that observation.

    I intend to add some more contours to this plot. I am "normalizing" everything to a horn / waveguide with a 2 inch throat diameter, a 15.5 inch mouth diameter, and a depth of 6 inches. This is my favourite size, as it is a drop in "replacement" for a standard 15 inch driver. Someone could retro-fit a cabinet with two 15" speakers, to a horn / bass driver configuration with this size of horn / waveguide.

    Jack, when you get some time, could you send me an email, or post some data points (x,y) on your "Oblate Spheroid / Tractrix" waveguide? Would anyone else like to contribute their favourite contour? About 20 data point pairs should be enough, as long as the values at any "contour transistion" (e.g, Spheroid to Tractrix) are included.

    Linear
    Linear: so much to post, so little time

    - sorry I did not get any spare typing time last weekend, or this week, so my promised horn shape reply is still in the works (I have been composing it in my head, just no time to type).

    -I remember the Hughes paper had some incorrect assumptions in it, which I was planning on commenting on, but I never tried graphing a contour based on his equations, I’ll take a look over the next few days (or weeks) and get back to you.

    - I’ll send you an excel spreadsheet with both my horn contour x,y’s, as well as a small program to generate oblate spheroid horn curves. Send my your normal email address by PM and I’ll package up a zip and send tomorrow.

    - The Oblate/Tractrix shape needs to be built “by hand”, essentially designing a oblate spheroid horn which is shorter, and has a smaller mouth than the final horn length and diameter, then running the tractrix curve generator multiple times until the exit angle and mouth size of the oblate exactly match the throat diameter and input angle of the tractrix.

    - Later this month, I will create a new hybrid (Oblate-Tractrix) contour to match your 15.5” standard, it only takes about a half hour of fiddling, but not tonight (I have a couple of weeks holiday coming, so bear with me)

    - In the mean time, this (and the next four) posts will contain some graphs from a horn directivity study that I did (using the McBean hornresp program) prior to constructing the ones I am using now. With some compromise, the input Mcbean Hornresp program can be adjusted to simulate using a compression driver on a front loaded horn, which opens up the possibility of doing directivity studies using a computer, instead of a lathe.

    - Eventually, I will re-run this study (with the four horn types) conforming to your 15.5”mouth, 2”throat standard, but for now the four horn types use a 1”throat, 6.3”mouth.

    - The various graphs have reasonable labels for title and axes, and should be self explanatory, if you need more information, then you will have to download Mcbean hornresp, and read the help files.

    - The obvious conclusion from this directivity study is that only the Oblate and the Conical shapes provide reasonable constant directivity coverage. The Exponential and Tractrix curves both show strong narrowing of directivity with increasing frequency.

    More later
    Jack Bouska
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  9. #39
    Member jack_bouska's Avatar
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    Mcbean Horn Directivity Study: Exponential

    Mcbean hornresp
    Horn Directivity Study: Exponential horn, frequency response and directivity curves:
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  10. #40
    Member jack_bouska's Avatar
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    Part 2: Mcbean hornresp directivity study

    Mcbean hornresp
    Horn Directivity Study: Tractrix horn,
    Frequency response and directivity curves:
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  11. #41
    Member jack_bouska's Avatar
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    Part 3: Mcbean hornresp directivity study

    Mcbean hornresp
    Horn Directivity Study: Oblate Spheroid Waveguide,
    Frequency response and directivity curves:
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  12. #42
    Member jack_bouska's Avatar
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    Part 4: Mcbean hornresp directivity study

    Mcbean hornresp
    Horn Directivity Study: Conical Horn,
    Frequency response and directivity curves:
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  13. #43
    Member jack_bouska's Avatar
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    Quote Originally Posted by Mr. Widget
    This is an interesting comparison. Thanks for doing the leg work and sharing this with us. I would love for someone to produce a prototype of each horn and objectively and subjectively compare them along with a true tractrix horn and possibly one of Jack's horns.

    Are Jack's "Oblate Spheroid / Tractrix" derived from any real world product or are they unique to his speakers? Has anyone ever listened to them? (Besides Jack obviously... we tend to be biased about our own babies.) Jack if you posted their full history I am sorry, I must have missed it.


    Widget
    The directivity study (above) shows some objective (simulated) comparisons.
    In my post on Oblate Spheroid horns I show measurements which compare a tractrix horn against the pair of Oblate Spheroid designs that I built. I could comment on the sound from each, but you know that only two types of listening are valid (Either double blind scientifically controlled testing, -or- personal audition)

    “Are Jack's "Oblate Spheroid / Tractrix" derived from any real world product..?”
    Answer is: they are my own concoction

    “Has anyone ever listened to them? (Besides Jack obviously….”

    Apart from those in my immediate family, (and a good part of the neighborhood when I crank up the volume with the window’s open…..)

    I’ve had four people over from the LLDIYHiFi club for a listen. A quote from the last fellow (a devout ribbon fan) was “nice treble”

    Also, John W. just built a pair (see big blue thread) and so he will likely report on the sonic quality when the sawdust and solder settle on his latest project.

    “Jack if you posted their full history I am sorry, I must have missed it.”
    I’m sure you must have seen my thread called:
    DIY Axially symmetric oblate spheroid CD waveguides, in solid Oak
    At:
    http://www.audioheritage.org/vbulletin/showthread.php?t=12126

    In that thread, I discuss (in gory detail) the waveguide contours, shape, measurements etc. In particular post #3 describes why I chose a hybrid oblate – tractrix shape for the horn mouth.

    Before retiring for bed tonight, I’m going to post some additional graph comparisons on the Big Blue thread
    http://www.audioheritage.org/vbulletin/showthread.php?t=12671

    In the big blue post, I will show comparisons of the Oblate spheroid vs the JBL PT-H95HF waveguide and a 2381. I wouldn’t go so far as to say the waveguides that I built are the be-all and end-all of sonic excellence, but they do perform, and measure just as I expected them to when they were on the drawing board (gotta like that)!

    Jack Bouska

  14. #44
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by jack_bouska
    “Are Jack's "Oblate Spheroid / Tractrix" derived from any real world product..?”
    Answer is: they are my own concoction!

    I’m sure you must have seen my thread called:
    DIY Axially symmetric oblate spheroid CD waveguides, in solid Oak
    At:
    http://www.audioheritage.org/vbulletin/showthread.php?t=12126
    Thanks for the concise answer, and thanks for posting those interesting sims.

    Yes, I have glanced at your thread, but I simply haven't found the time to go through the "gory detail"... based on your sims... why would you want such a contour? The on axis response is far from linear and the off axis ringing seems really problematic.

    I freely admit to be in the exponential/tractrix camp. I have yet to hear a demonstration of conical, bi-radial, or other true CD horns that makes me want to go there.


    Widget

  15. #45
    Member jack_bouska's Avatar
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    Quote Originally Posted by Mr. Widget
    Thanks for the concise answer, and thanks for posting those interesting sims.

    Yes, I have glanced at your thread, but I simply haven't found the time to go through the "gory detail"... based on your sims... why would you want such a contour? The on axis response is far from linear and the off axis ringing seems really problematic.

    I freely admit to be in the exponential/tractrix camp. I have yet to hear a demonstration of conical, bi-radial, or other true CD horns that makes me want to go there.


    Widget

    Widget – please re-read the post above (#43), I just finished editing it (again)

    The Mcbean simulations are not perfect; most of the ringing is due to the compromises in my specification of the diaphragm and motor, along with the poor termination from the straight sided front chamber-to-throat, and the complete lack of fully curved round-over to alleviate the mouth-to-free space acoustic impedance discontinuity.

    My actual measured curves don’t show anywhere near the same level of ripple, (on or off axis) as the simulations. Have a look at the directivity measurements in post #3 of my oblate spheroid thread, the off axis curves (+ - 40deg) track each other quite closely, and do not display excessive ripple. Post #4 shows some high resolution FFT graphs, (with spatial average) which also show the relatively low level of ripple from the Oblate devices). Also, if your interested, watch out for more info in my next post in the big blue thread, later tonight.

    I have never used exponential horns; however they *should* provide the optimum diaphragm loading, right down to cutoff frequency (if that's required). I have built and used a couple of different Tractrix horns, on JBL 2426 and TAD2002 drivers, and found that they sounded very good, however I needed to aim them correctly, and sit within the high frequency “sweet spot” to get the full treble experience. They also worked better in over damped (Live-end Dead-end) rooms. (quite bad with wood floors and bare walls/ceilings.).

    With the Oblate Spheroid horns, I get excellent frequency response regardless of what position I take in the room, as long as I am in front of the speakers. I can stand, or sit, and even walk across the entire width of the room, barely 3 feet in front of the speakers (or at the back of the room), and I hear *exactly* the same frequency response (and high frequency extension) as I would in my sweet spot favorite listening position.

    I could never do that with my tractricx horns.

    Hope that helps?
    Jack Bouska

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