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Thread: Information on bass horn construction

  1. #1
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    Information on bass horn construction

    Does anybody have any info on the construction of the VS125HS basshorn?

    2 X 2225 folded horn from the venue series:
    http://www.lansingheritage.org/image...pro/page15.jpg

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    Senior Member grumpy's Avatar
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    Thank You

    Quote Originally Posted by grumpy View Post
    I appreciate it I had found that already but was searching for a better idea of the horn folding.

    I'm trying to assuage my guilt. Some time ago I bought a pair of new 2226H's because they were a good deal from PE, intending to put them in a reflex cabinet. Since then I've built a pair midrange horns and decided to pursue a horn bass/midbass to put under them and still use the 2226's that never found their way out of their boxes.

    I haven't been able to come up with a 2226-based horn that models worth a damn and I can't bear the thought of buying another pair of drivers

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    Senior Member 1audiohack's Avatar
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    What do you use for modeling?

    I am just digging into the bass horn thing and could use a leg up on calculation. Any recomended references?

    Thank you.

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    Senior Member Hoerninger's Avatar
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    Hey,
    I have made a simulation for a JBL 2226H with HORNRSP by David McBean on the quick. Are you looking for something like this?

    Throat area 350 cm2, back chamber 45 l, brutto volume ca. 600 l, heavy. Placed in a corner or two side by side.

    The deeper the horn the easier the folding.
    ___________
    Peter
    Attached Images Attached Images    

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    McBean Sim

    Quote Originally Posted by Hoerninger View Post
    Hey,
    I have made a simulation for a JBL 2226H with HORNRSP by David McBean on the quick. Are you looking for something like this?

    Throat area 350 cm2, back chamber 45 l, brutto volume ca. 600 l, heavy. Placed in a corner or two side by side.

    The deeper the horn the easier the folding.
    ___________
    Peter
    Thank you for this, Hoerninger. Yes, 1audiohack, I was trying to use McBean to model a suitable horn but, very inexperienced, I couldn't get a sim that didn't look like a pie-wedge.

    I didn't consider 1/8 space since I can't place them anywhere near any corners and my wife ain't Mrs. Klipsch (tolerance for false corners is just about zero).

    Thanks again for something to go on.

    Best,
    Charlie

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    1/8 space

    I didn't consider 1/8 space

    Well done Charlie,

    The claim that just the horn mouth could be made smaller when placed in corners is obviously wrong. It came up from a concept common in electrical engineering called "mirror source".

    As it is a perfect reflector the wall is considered as being a symmetry plane. Insofar o/k. But one has to think it further down the throat (bad english, sorry): the throat has to be made smaller too. The driver has to be smaller, the volume ... - just an other horn, ain't it? But the flare rate has to be taken from the virtual bigger one. Complicated. I don't know what "hornresp" does.

    I never found someone really validate the results of a so called horn simulation at home. Simulations that can't be validated have to be considered wrong. Why do audio people disagree with that conservative statement? Idealism?

    Auf Wiederhoeren!

  8. #8
    Senior Member Hoerninger's Avatar
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    .. the horn mouth could be made smaller when placed in corners is obviously wrong.
    Is this statement really true? Things are connected, as you have pointed out, and a horn into full space cannot be simply divided by eight when radiating only into one eighth ("corner") and the speaker is the same. But the mouth area which has an influence on the lower cut off may be one eighth - radiating into one eighth of space. And as the speaker is the same, the length may be shorter when the flare rate is maintained.

    Some formulas for the geometrical calculations you can find in this forum. They are only for exponential horns. But why do "by hand" if a programm HORNRESP can do it for you, this is one part of this program.

    The other parts are predictions of SPL, impedances, displacement phase and others. HORNRESP has a high reputation by their users, look into some forums. And using this programm can help you to get the idea of some modifications of a certain horn. This will help not to waste time, money and efford on a real horn, which you will have to build for real life testing.
    There is one simulation which turned out to meet reality quite nicely:
    http://audioheritage.org/vbulletin/s...749#post152749
    And this was simulated before building with good conformity concerning the choosen speaker:
    http://www.audioheritage.org/vbullet...58&postcount=3

    "Mirroring" is a good approach to understand for example the two horns of a Paragon. They are close together and mirroring. The corner is obsolete, this reduces room resonances. But when the ceiling is low, the situation is difficulty to predict. And when the room is small then the horn mouth is working on a compression chamber, this must be treated differently.
    __________
    Peter
    Last edited by Hoerninger; 06-18-2008 at 07:44 AM. Reason: not (!) to waste

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    Quote Originally Posted by Hoerninger View Post
    Is this statement really true?
    ...
    And when the room is small then the horn mouth is working on a compression chamber, this must be treated differently.
    __________
    Peter
    Hi Peter,

    You are right in asking for a further explanation. I read Your formulas #5 and #6. We want to account for the "mirror"-idea in understanding the effect of nearby walls - or neighboring horns.

    The mirror idea leads to a horn of half, quarter or eighth cross sectional area from the mouth through-in to the throat. Including diaphragm piston area of the driver, rear chamber volume and so on. But the length is not affected.

    From that concept regarding Your formulas #5 and #6 we understand that with the mirrors the horn is physically smaller in volume first. But second it can't be made shorter if the same cut off has to be yielded. The exponent, the "flare" is the same as with the virtual "free standing" horn.

    I checked that with hornresp, that I didn't knew before. One may calculate a horn 1xPI radiating for a given driver e/g S0= 100, S1=10000, Sd=100 ... then calculate the same horn with all cross sectional areas and back chamber volumes multiplied by four (take 4 drivers), radiating 4xPI.

    The latter gives exactly the same acoustical impedance, same ripple etc. The output is +12dB frequency independent due to multiplying the electrical input by 4 ...

    Hornresp confirms my suggestion. It falsifys common wisdom in that stacking or wall mounting really has no effect on the lower cut off frequency (or ripple). It remains questionable wether the idea of mirroring holds in real life. To validate means to measure responses in real living rooms. Even with closed boxes that purpose may become a burdEn.

    Good luck!

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    ... may become a burdEn.

    Hi,

    Once again because of possible "loss in translation".

    - Just making the mouth - and only the mouth - of a horn smaller to compensate for positioning near to walls is no good.

    - Just stacking horns will give unpredictable results too: where are the symmetries (mirrors) with example given 3 horns?

    - Websters horn theory relies on plane wave propagation. Obviously this is faulty at least for folded horns. So exponential flares or from that derived polygones will not work as it is predicted by analytical methods. Simulations have to handle the wave equation numerically. The latter is a very demanding task. It is prone to misconception or plain error. A simulation that hasn't been proven in many different circumstances has to be considered as wrong. Me myself didn't work with hornresp yet.

    - Validation of hornsimulations within rooms is near to impossible due to so far unknown interactions. To only consider the walls right beside the horn-shaped enclosure is a little bit to optimistic, I assume.

    - The initial statement repeated: to fit the horn to a wall/wedge/corner calculate the horn for 2/4/8 "virtual" drivers in parallel acting on that very horn, radiating into 4 PI. To build it with one driver devide all cross sectional areas and every volume by 2/4/8. If the horn equation is given as

    x = a0 * exp(f *L), a0 throat area

    use the same "f" to calculate the cross sectional areas at any axial position "L". The total length is kept as calculated. Nerver ever the length can be reduced. The length does determine the lower cut off independently from nearly all circumstance. To yield 40Hz a minimum length of ~4 meters (~12 feet) is unavoidable.
    This holds if and only if You trust the sim. Countercheck for validity. Report, as reports are highly appreciated - especially if they show the sim as being - misleading.


    I hope I killed my reputation - if any - in the end!

  11. #11
    Senior Member Hoerninger's Avatar
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    Mini,

    it is difficulty to follow your intention, here is the DIY section.
    What would you do to build a bass horn from scratch?
    Some must have done it, because there are appreciated plans.
    I for my part used a simulation to find a slight improvement. And the result showed me, that (in this aspect) the simulation was right.
    __________
    Peter

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    Arrow filthy intentions

    Quote Originally Posted by Hoerninger View Post
    Mini,

    it is difficulty to follow your intention, here is the DIY section.
    What would you do to build a bass horn from scratch?
    Some must have done it, because there are appreciated plans.
    I for my part used a simulation to find a slight improvement. And the result showed me, that (in this aspect) the simulation was right.
    __________
    Peter
    Hi Peter,

    My intention is to change the misconception of the n x PI space issue. It is by no means possible to shorten the horn if the same cut off has to be provided. Period. A horn placed in a corner behaves as an other horn that is very different from that placed under 4 PI condidions. The same is true for stacked horns. But if You shorten it, cut off will be higher in linear proportions.

    To calculate a horn from scratch is very difficult. As shown by Geddes Websters theory is incomplete not to say wrong. Therefore an analytical derivation of some basic measures is not possible e/g length, flare angle. This is at least true with folded horns which I think is all to obvious, if You think of Websters plane waves. May be I didn't got the magic though ...

    If in spite of that it comes to DIY calculations taking nearby walls into concern I gave You an apropriate methodology. I checked that for plausibility using HORNRESP. If You use it is left to Your own of cause.

    Yours, Sauerkraut

  13. #13
    Senior Member Hoerninger's Avatar
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    The theorie of Arthur Gordon Webster: "Acoustical Impedance, and the Theory of Horns and of the Phonograph " (PNAS 1919 5: 275-282) is not wrong.
    The question is whether it is applicable to real horns. Any theorie will have its limits and there will be improvements - the normal way in science.

    Historically it was a great approach to develop new better sounding horns. Webster had been "accused" for that he did not publish this work immediately after writing. The result of his work was much longed for.

    In this forum I can't remember a forumite who was confused by simulation vice versa reality. If you accept the limits of a simultion it can be a great tool.
    ____________
    Peter

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    Hi,

    As a German I have to insist (Jefferson Airplane)

    Websters theory is wrong in that it doesn't hold for its own outcome. If a horn is calculated with Websters premises, this horn will never behave as predicted, as this horn does not fulfil the premises - granted.

    The most prominent premise is plane wave propagation to keep the problem in a single spacial dimension. With that You do Your calculations. What You get is an - example given exponential horn with a certain dimensioning. But with this horn the desired plane wave propagation is not given. In that the outcome of the theory will not fulfil its premises. It is conflicting itself, while hoping for the best like: "If I was a Millionaire ..."

    The theory might not be wrong utterly. It could hold for the 0-th order of an approximation as You will. But again, taken as it is it is wrong. At least with folded horns - remember the premises!

    If You have to check for the validity of a simulation every time You do one, what is the use of it at all? A simulation should allow to have an idea how valid it is right before I take my time to play.

    To repeat my initial claim. To take account for nearby walls/corners the horn must not be shortened. Even with Webster.

    No offence!






    Quote Originally Posted by Hoerninger View Post
    The theorie of Arthur Gordon Webster: "Acoustical Impedance, and the Theory of Horns and of the Phonograph " (PNAS 1919 5: 275-282) is not wrong.
    The question is whether it is applicable to real horns. Any theorie will have its limits and there will be improvements - the normal way in science.

    Historically it was a great approach to develop new better sounding horns. Webster had been "accused" for that he did not publish this work immediately after writing. The result of his work was much longed for.

    In this forum I can't remember a forumite who was confused by simulation vice versa reality. If you accept the limits of a simultion it can be a great tool.
    ____________
    Peter

  15. #15
    Senior Member Hoerninger's Avatar
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    Mini,

    I do not feel offended. Due to what I have learned I know too well the modelling of horns is far from being satisfying.
    And I can not see contradictions in judging using a corner or about mirroring.
    Look at the premises: "... calculate the horn for 2/4/8 "virtual" drivers in parallel acting on that very horn, radiating into 4 PI". In practise you have one speaker and will have to decide whether it is in a corner or not.

    My approach is very pragmatical, and so the last horn I built was much better than the first (ca.1965). And my theoretical insight today is better than way back.
    Consider the wavelength of say 50 Hz which is ca. 7 m. If you take a small horn with a mouth area of for example 6000 cm2, the diameter is so small that I do not ponder about plane or spherical wavefronts.

    Why hesitate about the theorie? It should not be a brake block.

    Have you ever built a (bass) horn? And have you listened to a horn system? It is about the magic ...
    _________
    Peter

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