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Author Topic: Good Mid Bass Horn  (Read 40811 times)

Peter Morris

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Re: Good Mid Bass Horn
« Reply #20 on: May 18, 2006, 03:32:52 AM »

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Phil Pope

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Re: Good Mid Bass Horn
« Reply #21 on: May 18, 2006, 08:56:41 AM »

Antone Atmarama Bajor wrote on Thu, 18 May 2006 08:12

     I used a T of .55 Like the Lab and BT7 (Hyperbolic flare).  I don't know if there is a better expansion constant for mid bass???  
Antone-  


have you tried a tractrix expansion. some of my models look quite promising. IMO there is not much point in reactance annulling for a horn that is going to crossover to a larger horn because the crossover point is going to be limited by excursion not by the response below cutoff. Using hyperbolic you can achieve a long horn without having a small throat which can stress the driver or a large mouth which is cumbersome. this isn't so much of an issue in a mid-bass horn so you can get away with exponential or tractrix expansions.

have you tried using a rubber throat? use a relatively small throat and double the horn area in the first 10-20 cm from the throat.

cheers
Phil
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Antone Atmarama Bajor

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Re: Good Mid Bass Horn
« Reply #22 on: May 18, 2006, 02:35:00 PM »

I was wondering what happened to the Xtro tops.

Has anyone done any measurements????

Antone-
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Antone Atmarama Bajor

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Re: Good Mid Bass Horn
« Reply #23 on: May 18, 2006, 02:46:30 PM »

Rubber Throat???  For Diffraction?  I just don't like diffraction in general.  Starts to smear the Top end but that's the price we pay for good coverage using one horn to try and cover too many octaves.
 
    No I'm only in the daydreaming stage right now.

    I know a couple of people have patented the use of Damped Resonant cavities in the horn to help absorb would be reflected energies, one of the Japanese engineers at TAD, and Jerry Steckling.

    I'm not sure what the mathematical relationship for tractrix is.  Don't they have more of a problem with beaming in their high end.  (Not that Hyperbolas don't have beaming problems.

    Does Horn Resp model Tractrix????  It isn't immediately obvious that it models hyperbolic curves.  I happened across that by pushing the H key where it only gives the options to use exponential/conical/or linear expansion.

Antone-
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Antone Atmarama Bajor

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What Space Loading
« Reply #24 on: May 18, 2006, 03:41:00 PM »

     I was wondering how would you model these if they are typically going to be on top of a 45" stack of subs.  Would it be free spaces since the BT7/LABS are not  an effective boundary?

    and does floor reflection come into play at Xover???

    Will I actually get a dip in response from floor reflection?  Or will the fact that the cabs are both operating -6dB @ Xover that this is a non issue???

Antone-
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Peter Morris

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Re: Good Mid Bass Horn
« Reply #25 on: May 18, 2006, 10:43:55 PM »

The advantages of a Tractrix is reduce length / size and reduced colouration.  I believe that because of the rapid expansion at the mouth the reflections are reduced at this point.  They are usually considered a good choice for mid range.... Don’t know about how well they array.

The disadvantage is poor loading of the driver at the cut of frequency -  it will not be as efficient as exp, or hyp. in the bottom octave.

And yes Hornresp and AJHorn will model tractrix.

A conical Tractrix horn:-

x = a * ln((a + sqrt(a^2 - r^2)) / r) - sqrt(a^2 - r^2)

x - is the distance from the mouth of the horn,
a -  is the radius at the mouth, and
r -  is the radius at distance x from the mouth.
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Antone Atmarama Bajor

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Re: Good Mid Bass Horn
« Reply #26 on: May 19, 2006, 03:52:35 AM »

     Can Tractrix expansions be succesfully implimented using non circular horn?

    I was thinking of maybe buildig a square straight horn.  Maybe???  Proabably rectangular.

Antone-
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Walt de Jong

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Re: Good Mid Bass Horn
« Reply #27 on: May 19, 2006, 08:15:47 AM »

I don't think tractix is optimal voor proffesional applications. It needs a large cabinet front. You want to impress people with great loud sound, not very big looking cabinets.

The 2x15" section of the X-tro is aimed at the 80-300Hz range. The use of a double driver allowed for a short (bandpass) horn without needs to fold it. The throat geometry is optimized to get a good 'kick' out of the design. It has a relatively small frontal area, the downside is, this means limited efficiency (larger effective mouth = more efficiency) but the second driver gets you an additional 3dB. Of course this means more amplifier power.

For more information about the X-tro look at the specific forum at www.speakerplans.com:

http://www.speakerplans.com/forum/forum_topics.asp?FID=19

The design of such a cabinet is full of compromises. But for its bulk (it is quite small) it packs a lot of power. But you need some serious amps to get best performance. Think about 1500-2000W midbass/400W mid/200W high.

Best regards,

Walt
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Peter Morris

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Re: Good Mid Bass Horn
« Reply #28 on: May 19, 2006, 11:05:36 AM »

Hi Walt,

I have to agree – unless you want to have a huge mouth there has to be a compromise.

I like what you have done with the X-tro - the other practical alternative is to fold it like KV2 or Funktion 1 or port it like the old JBL 4560.

Operating below 200 - 300Hz I would almost call it a bass horn, however it will probably have to operate in full space not half space like most subs, so the mouth, unless it’s a compromise will be quite large.

Here is an excerpt from an interview with Bruce Edgar that may be of interest  ...


Bruce: Yes, those particular horns were made for me by Bill Firebaugh, the Well Tempered arm inventor. He's also been interested in horns. He showed the paper horns to me. I said, "I've got to have a pair of these." So he made up a pair of horns. They are a round Tractrix horn and a round exponential horn. You talk through them like megaphones. When you talk through the exponential horn, people can hear the coloration to your voice, which is a certain resonant quality that wasn't there before. You talk through a Tractrix horn and you don't hear it. It's completely open.
The explanation goes back to the difference between spherical and plane waves. When the plane waves travel down to the end of the mouth of the exponential horn, suddenly there's a bulge where they exit into space, and that bulge is essentially a discontinuity. So, you have reflections at the mouth, which travel back to the throat and set up a quarter-wavelength resonance condition. With the Tractrix horn, since the waves are spherical going through the horn, they exit the mouth with very few reflections. When I first started building Tractrix horns, I heard this immediately. They didn't have the same horn colorations I'd heard before. I said, "Well, I ought to build all my horns this way," so when I built a 70 Hertz Tractrix Bass Horn (Speaker Builder, 1983), I was in for a surprise. The problem is that the Tractrix is a short horn. If you take the equivalent Tractrix and equivalent exponential horns (same mouths, same throats, same flare rates), the Tractrix horn is shorter. At the low end, the response on any horn is limited by the throat reactance, which peaks at the flare frequency. The exponential horn is long enough that if you can put on a back chamber and resonate it with your loudspeaker at the flare frequency, you can partially cancel out that throat reactance. With a hyperbolic exponential horn, you can cancel it out exactly. With a Tractrix horn, you don't cancel it out at all, so the 70-Hertz horn rolled off at 100 Hertz. It sounded very good, but the problem is that the Tractrix horn response just does not extend to the flare point. There is no way that you can do it, so you have to live with the consequences. Well, for a midrange horn that's not too bad. The 300-Hertz horn that I make turns on at around 400 Hertz, and since its size is not huge, I can build a full-size 300-Hertz horn. It sounds very nice, but it won't turn on until 400 Hertz.

Peter
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Phil Pope

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Re: Good Mid Bass Horn
« Reply #29 on: May 19, 2006, 02:14:41 PM »

i am not sure whether there are other ways around this but because beaming is an issue you will need to look at the directivity plots in Hornresp and get the on axis plot reasonably flat. hopefully the off axis response will be OK to a reasonable angle. if you get this right the constant directivity plot will show a gentle roll off from about 200Hz.

phil
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