sumsound said:
I built a couple of subs that are almost identical to this last summer. There is only two differences really. In the old one, the back chamber is sealed. And it uses a eight inch driver instead of a twelve.
One unexpected problem was that the WEIGHT of the pipe makes them unstable. I wound up using expanding foam to "bind" the pipes together in a few spots. And some duct tape too
It's not pretty, but it works. The sub doesn't even rattle a bit!
It's an unconventional approach, but it worked surprisingly well. I wound up building two of them, which really smooths out the response.
Here's the pics:
http://www.audiogroupforum.com/csforum/showthread.php?t=62292&page=2
sumsound said:
Groan, that's something I hadn't considered. The one I built last summer has a high compression ratio at the throat, but the mouth has a much lower compression ratio. The one I built last summer doesn't suffer from any kind of rattles or buzzing. It really works well. The eights don't go low enough for HT though; it was designed for car stereo.
As you discovered, the TH likes a driver with a high FS. Once I played with the model a bit, I noticed that the SMALLER tapped horns have smoother response that goes very low. Paradoxically, the BIG tapped horns have a higher F3. But the BIG tapped horns have higher efficiency.
My preference is to give up efficiency for extension.
As long as you have the power and enough sub to sacrafice the additional SPL and still have at least proportional Headroom to the rest of your spectrum.
I happen to think more headroom in the sub bass region is really necassary to play with equal loudness curves and what not.
My Subs I like to use for small PA and 5 String Bass. Even with Equal SPL in the fundamental ranges its very hard to compete with the loudness of something like a Martial/Marshall stack. Trying to acomplish Equal loudness down to a low A 27.5Hz takes a lot more Equivalent SPL.
Any how it looks like fun.
Antone-
I happen to think more headroom in the sub bass region is really necassary to play with equal loudness curves and what not.
My Subs I like to use for small PA and 5 String Bass. Even with Equal SPL in the fundamental ranges its very hard to compete with the loudness of something like a Martial/Marshall stack. Trying to acomplish Equal loudness down to a low A 27.5Hz takes a lot more Equivalent SPL.
Any how it looks like fun.
Antone-
I checked out the MCM version - very cool design. So do you feel it outperforms the Autotuba in most aspects except efficiency? And would you still build it that way for home use - as opposed to the open back, non-tapered design on this thread?
Ive got a couple hours, a MCM 55-2421 laying around, lots of PVC and an old sonotube sub I had a Soundstream 8" in. Just too easy to not try.
amt
Ive got a couple hours, a MCM 55-2421 laying around, lots of PVC and an old sonotube sub I had a Soundstream 8" in. Just too easy to not try.
amt
Patrick Bateman and Freddi, re the horn that patrick bateman linked too, I was wondering if you have thought about a Karlson slot in that sonotube cover or final third of the horn. I believe that this would make it the closest I've seen yet to the theory in his patent. Maybe Freddi would care to comment. This would also be how I intend to try the theory at some point.
jamikl
jamikl
hi Jamikl - I don't see that in Karlson's patents (?) to my way of thinking, Karlson's invention (K15) had a wedge shape coupling chamber and its cross-sectional area decreased.
The invention mentioned in Karlson's 1950 list also added reverb. I'm not sure if slotting the pipe for 1/3 would do much other than effectively shorten the pipe. Maybe Planet 10 and others have observations. I think RCA-Fan spoke once of a horn slotted its full length - it may have required a lot more length (?) - perhaps one can get Bill to elaborate over at AA's High Efficiency speaker forum.
Karlson's open-end waveguide microwave antenna and his X15 HF slotted waveguide HF tube had constant cross-section and a large amount of energy is propagated perpendicular to the tube's long axis.
Here's a few excerpts from Karlson's first installment of Acoustic Transducers" I took the liberty to underline a few items. There's probably typo :^(
Best, Freddy
J.E. (John Edward) Karlson “Acoustic Transducers” US 2816619 filed Dec. 1951
"----Basically my invention consists of a pipe or elongated chamber closed at one end and open at the other. The size and shape of the opening are controlled to give the desired acoustic properies and differs from horns and similar devices in that the principal radiation occurs with a directiivity which is essentially normal or perpendicular to the axis of this pipe.
Stated differently, the sound comes out of the side of the pipe rather than out of the end. The advantages of this approach and the theriy thereof are explained in the following paragraphs.
When sound waves are initiated in a pipe they travel towards the ends of the this pipe. At the closed end these waves are reflected back into the pipe and at the open end another reflection occurds due to the sudden rarefaction of the wave front of these waves. At certain wavelengths reinforcements of the incident waves occur due to these reflections which create the condiions for resonance. Therefore, a pipe open at one end and closed at the other end will resonate at a frequency whose wavelength is equal to four times the length of the pipe. The strengthness of this resonance is largely dependent upon the abruptness of the discontinuities at the ends of the pipe and the losses within the pipe. thus if only minor discontinuities exist at one end of tbis pipe, correspondingly weak reflections occur with the result that this pipe can only be weakly resonant. Also, if the energy within the pipe were gradually dissipated before it reached the end of the pipe, resonsnace would be further weakened. Then these conditions hold for a wide range of frequencies then we have the essentials for a non-resosnat enclosures for use as an acoustic transducer for wide band applications.
This invention relates to a practical means of accomplisthing these objectives. In order to present a minimum discontinuity at the open end of said pipe, a small opening is made in the pipe near the closed end of said pipe; said opening garduallay being made wider untial a maximum width of the aperture thus formed is realized at the other end of the pipe. The cross section of the pipe is also narrowed so that the energy being propagated toward the open end of said pipe is gradually forced through the opening formed by this tapered aperture.
This action continues until a minimum cross section at the widest end of the tapered aperture forces the remaining energy out of the enclosure. By this means, it is therefore possible to present a minimum discontinuity at any point in the opening in said pipe while at the same time providing a means of gradually dissipating the energy in said pipe in a useful fashion.
>>> (further down)
An elongated chamber is used in all thse designs in order to take advantage of the propagation effects inherent in a sound duct whose length is not small relative to the wavelengths transmitted, The parameters associated with these structures may then be regards as distributed constants and the ensuing acton may be analagous to electrical transmission lines and antennas.
The tapered apertures used in these figures although of different dimensions and shapes present a means for gradually varying the distributed constants of said chambers so that the high impedance driving sources may be adequately matched to the low impedance of the air.
The shape of the aperture largely determines the rate of release of the energy begin propagated toward the opent end of any individual chamber. In order to have a minimum pressure gradient introduced at any point of efflux, it is necessasry that equal amounts of energy be released for equal increments of distance along the aperture. This is done in several embodiments of my invention by varying the width of the aperture as the square of the distance along the axis of the elongated chamber.
Other rates of release of the included enegy may be realized by changing the rate of taper.
>>>
An examination of Figs 1, 2, 3, 4 will show that all of said tapered aperture coupling chambers have be desinged with a diminishing interior cross section starting near the apex of each apertuer and narrowing down to a minimum at each base of said apertuer.
The inclined planes thus present to the energy being propagated toward the the tapered apertures end of each coupling chamber deflects said energy over the entire length of said aperture. This action ensures a more uniform release of energy over the entire length of said aperture than would be normally experienced by a uniform cross sectional area. In addition to this feature a minimum discontiuity is also presented at the open ends of said coupling chamber by this structural design.
A less obvious result of the inclined plane so created in the path of the enclosed sound waves is in its influence of the radiation pattern of said coupling chamber. Properly designed relative to the rate of taper in the aperture, a uniform distribution of energy can be realized over the entire length of said aperture, especially for the high frequencies. When this occurs a roughly semi-cylindrical wave front results. This constitutes an ideal manner of propagation of these sound waves since the high frequencies will not be sharply beamed in any one direction.
If the angle of said inclined plane makes with the plane of said tapered aperture is greatly increased, several effects may be observed. Among thse are (1) lower frequency limit (2) increased reverbration time (3) poorer transient reponse and (4) less uniformity in the radiation patter thoughout the frequency range. Obviously optimum results of any particular application would be subject to some trial and error tests...."
The invention mentioned in Karlson's 1950 list also added reverb. I'm not sure if slotting the pipe for 1/3 would do much other than effectively shorten the pipe. Maybe Planet 10 and others have observations. I think RCA-Fan spoke once of a horn slotted its full length - it may have required a lot more length (?) - perhaps one can get Bill to elaborate over at AA's High Efficiency speaker forum.
Karlson's open-end waveguide microwave antenna and his X15 HF slotted waveguide HF tube had constant cross-section and a large amount of energy is propagated perpendicular to the tube's long axis.
Here's a few excerpts from Karlson's first installment of Acoustic Transducers" I took the liberty to underline a few items. There's probably typo :^(
Best, Freddy
An externally hosted image should be here but it was not working when we last tested it.
J.E. (John Edward) Karlson “Acoustic Transducers” US 2816619 filed Dec. 1951
"----Basically my invention consists of a pipe or elongated chamber closed at one end and open at the other. The size and shape of the opening are controlled to give the desired acoustic properies and differs from horns and similar devices in that the principal radiation occurs with a directiivity which is essentially normal or perpendicular to the axis of this pipe.
Stated differently, the sound comes out of the side of the pipe rather than out of the end. The advantages of this approach and the theriy thereof are explained in the following paragraphs.
When sound waves are initiated in a pipe they travel towards the ends of the this pipe. At the closed end these waves are reflected back into the pipe and at the open end another reflection occurds due to the sudden rarefaction of the wave front of these waves. At certain wavelengths reinforcements of the incident waves occur due to these reflections which create the condiions for resonance. Therefore, a pipe open at one end and closed at the other end will resonate at a frequency whose wavelength is equal to four times the length of the pipe. The strengthness of this resonance is largely dependent upon the abruptness of the discontinuities at the ends of the pipe and the losses within the pipe. thus if only minor discontinuities exist at one end of tbis pipe, correspondingly weak reflections occur with the result that this pipe can only be weakly resonant. Also, if the energy within the pipe were gradually dissipated before it reached the end of the pipe, resonsnace would be further weakened. Then these conditions hold for a wide range of frequencies then we have the essentials for a non-resosnat enclosures for use as an acoustic transducer for wide band applications.
This invention relates to a practical means of accomplisthing these objectives. In order to present a minimum discontinuity at the open end of said pipe, a small opening is made in the pipe near the closed end of said pipe; said opening garduallay being made wider untial a maximum width of the aperture thus formed is realized at the other end of the pipe. The cross section of the pipe is also narrowed so that the energy being propagated toward the open end of said pipe is gradually forced through the opening formed by this tapered aperture.
This action continues until a minimum cross section at the widest end of the tapered aperture forces the remaining energy out of the enclosure. By this means, it is therefore possible to present a minimum discontinuity at any point in the opening in said pipe while at the same time providing a means of gradually dissipating the energy in said pipe in a useful fashion.
>>> (further down)
An elongated chamber is used in all thse designs in order to take advantage of the propagation effects inherent in a sound duct whose length is not small relative to the wavelengths transmitted, The parameters associated with these structures may then be regards as distributed constants and the ensuing acton may be analagous to electrical transmission lines and antennas.
The tapered apertures used in these figures although of different dimensions and shapes present a means for gradually varying the distributed constants of said chambers so that the high impedance driving sources may be adequately matched to the low impedance of the air.
The shape of the aperture largely determines the rate of release of the energy begin propagated toward the opent end of any individual chamber. In order to have a minimum pressure gradient introduced at any point of efflux, it is necessasry that equal amounts of energy be released for equal increments of distance along the aperture. This is done in several embodiments of my invention by varying the width of the aperture as the square of the distance along the axis of the elongated chamber.
Other rates of release of the included enegy may be realized by changing the rate of taper.
>>>
An examination of Figs 1, 2, 3, 4 will show that all of said tapered aperture coupling chambers have be desinged with a diminishing interior cross section starting near the apex of each apertuer and narrowing down to a minimum at each base of said apertuer.
The inclined planes thus present to the energy being propagated toward the the tapered apertures end of each coupling chamber deflects said energy over the entire length of said aperture. This action ensures a more uniform release of energy over the entire length of said aperture than would be normally experienced by a uniform cross sectional area. In addition to this feature a minimum discontiuity is also presented at the open ends of said coupling chamber by this structural design.
A less obvious result of the inclined plane so created in the path of the enclosed sound waves is in its influence of the radiation pattern of said coupling chamber. Properly designed relative to the rate of taper in the aperture, a uniform distribution of energy can be realized over the entire length of said aperture, especially for the high frequencies. When this occurs a roughly semi-cylindrical wave front results. This constitutes an ideal manner of propagation of these sound waves since the high frequencies will not be sharply beamed in any one direction.
If the angle of said inclined plane makes with the plane of said tapered aperture is greatly increased, several effects may be observed. Among thse are (1) lower frequency limit (2) increased reverbration time (3) poorer transient reponse and (4) less uniformity in the radiation patter thoughout the frequency range. Obviously optimum results of any particular application would be subject to some trial and error tests...."
jamikl said:
Yes, I thought about that for a few minutes. And then I realized there's a flaw in that line of thinking.
In a tapped horn, we WANT a deep null, don't we? The null facilitates a steep crossover, and makes it harder to localize the sub.
I could see the advantage of using something like what you describe with a single reflex bandpass or a vented enclosure. But with a tapped horn, I'd say Tom Danley's on the right track.
As a side note, Earl Geddes sells a single reflex bandpass subwoofer that leverages a technique he invented to spread out the resonances of the vent. As the *inventor* of single reflex bandpass, it's always interesting to see him take it to "the next level." I don't want to reveal what the technique is, as I believe he hasn't patented it.
Looking at DTS-20, imo a deep null (or even 6dB) is a defect from reference-qulity graphs which Tapped-Horn inventor Tom Danley can achieve - - but good for the hobbyist - who knows how to make use of a dip :^)
I was trying to compare a TH's excursion to a reflex using AJ-horn for reflex. AJ looked "optimistic" giving too much edge to BR What freeware besides WinISD which crashes gives accurate excurison for bass-reflex? (Bullock &
White? - stupid Win XP won't allow freezes - grrr)
btw - here's AJ with BM15CXA specs on 4.5M BIB - look at that dip
http://img402.imageshack.us/img402/4195/bm15cxbibvscondn6.gif
I was trying to compare a TH's excursion to a reflex using AJ-horn for reflex. AJ looked "optimistic" giving too much edge to BR What freeware besides WinISD which crashes gives accurate excurison for bass-reflex? (Bullock &
White? - stupid Win XP won't allow freezes - grrr)
btw - here's AJ with BM15CXA specs on 4.5M BIB - look at that dip
http://img402.imageshack.us/img402/4195/bm15cxbibvscondn6.gif
It seems like a luxury: for movies it is possible to play non-musical events but really in music we have few instruments that reach 15Hz and we also hear little of this frequency. Decades earlier there was a transmission line design called the "air coupler". I built some great subwoofers, the house shook.
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