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How to determine the best midrange enclosure?
How to determine the best midrange enclosure?
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Old 10th January 2017, 10:24 PM   #11
Jonathan Bright is offline Jonathan Bright  Australia
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Hi twinter, Thanks for that post. Your last line needs stressing more often I think.

I think that points 2 and 3 from Moriyasu article could profit from further discussion. In fact all three points are linked. A spherical enclosure will have the advantage of only one reflection as opposed to several with rectangular enclosures. I have seen people who advocate them for this very reason...... I.e. they avoid parallel surfaces at all costs. But if you go down that path and have only one resonance then point one becomes relevant (Q). Now of course you can damp "till the cows come home" which at first sight seem sensible until we get those results from Barlow (Goodmans 1960's or poss '70's) and others telling us that sometimes very well damped resonances which cover a wider frequency range are MORE audible than some narrow res' with high Q's! 0.5-0.7 may well be optimum.
Oh well! The "black art" of speaker designing.....never a dull moment.
Cheers Jonathan
"It was the Springtime of the year when aunt is calling to aunt like mastodons bellowing across primeval swamps." P.G. Wodehouse.

Last edited by Jonathan Bright; 10th January 2017 at 10:28 PM.
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Old 10th January 2017, 11:32 PM   #12
joetekubi is offline joetekubi  United States
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Originally Posted by twinter View Post
Jim Moriyasu published a two issue article in Speaker Builder, Issues 7&8 in 2000, titled, "A Study of Midrange Enclosures". He performed frequency response and subjective testing on numerous midrange enclosure configurations. Some of his recommendations were 1) size enclosure volumes for lower Qts', from 0.5 to 0.7 2) avoid spherical, egg shaped, or cubic enclosures due to internal wave resonances 3) rectangular enclosures with sound damping material performed well.

Also, chamfer the baffle opening rear edge, through which the rear of the midrange mounts, to prevent cavity resonances.
IIRC, he also showed that the very best sealed enclosure was one with no parallel walls.
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Old 11th January 2017, 04:02 PM   #13
twinter is offline twinter  United States
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When I get a chance, I will reply again. I just looked at Moriyasu's article, and my memory was not 100% correct. For those interested, two links of interest are listed below. You may have to Google for a working link to download the B&W paper.

The B&W paper, Development of the B&W 800D, pages 26 - 29

Jim Moriyasu's published several articles in Speaker Builder & AudioXpress. He spent considerable effects on the testing.
AudioXpress, 2/2002, "Panel Damping Studies: Reducing Loudspeaker Enclosure Vibrations"
Speaker Builder, 7&8/2000 entitled, "A Study of Midrange Enclosures"
They are available on archive CD's, by annual issues at:

Last edited by twinter; 11th January 2017 at 04:05 PM.
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Old 11th January 2017, 04:33 PM   #14
badman is offline badman  United States
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I'm with planet10 here- a non-resonant (well damped) TL for a midrange lets you damp the impedance peak and makes passive XOs a lot easier, and really has no downsides unless you're trying for max power handling/trying to use the acoustic slope of the mid enclosure as part of your filter. I'd suggest that electrical or active XOs are generally superior to that solution (sometimes excepted when the driver's a big high-power mid like a JBL 10") as more power into the motor, regardless of whether excursion is damped, is more flux modulation distortion.
"The dawn of Bose created the "Man Cave" and reduced testoterone levels worldwide by 18.5 per cent" Peteleoni
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Old 11th January 2017, 08:28 PM   #15
ernperkins is offline ernperkins  United States
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Here's a link to an innovative midrange TL: Construction info on my winning MWAF speakers, the Amaroso (long) - Techtalk Speaker Building, Audio, Video Discussion Forum

From the link:

"The rather unique midrange enclosure uses a short, tapered TL, having a ľ-wavelength resonant frequency of ~400 Hz, to raise the falling lower-end response of the Neo8. The exit end of this tapered TL coincides with the apex of a triangular-shaped diffuser/deflector. Sound waves travel down the tapered TL, wrap around the diffuser/deflector into secondary tapered chambers to the sides of the box, then around the back of the diffuser and out the back of the cabinet through a vertical slot. All of the midrange enclosure contains fiber filling, mostly polyester and some fiberglass, with densities varying from 1.2 to 2.1 lb/ft3 depending on location and material. Fiberglass is used in the secondary side chambers; these chambers attenuate the lower frequency output from the rear slot, which results in a generally flat frequency output over its effective range, at about 5 dB below the front, on-axis output. The primary goals of the midrange enclosure design were to eliminate back-wave reflections through the driver and reduce standing waves, while providing a controlled rear output for a small enhancement of soundstage spaciousness and depth, yet allowing the cabinet’s back to be fairly close to the wall. Dan Neubecker conceptualized this midrange enclosure configuration. I built a midrange test box with an adjustable fore-and-aft location for the diffuser/deflector and shipped it to Dan. He used it to perform extensive testing of both front and rear outputs, using various stuffing densities and materials, various positions of the diffuser/deflector and a variety of rear slot sizes. Through this testing, the optimum geometry, stuffing densities and stuffing materials were determined."

Whew! Pics of the enclosure are in the link.
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Old 11th January 2017, 09:35 PM   #16
Bob Richards is offline Bob Richards  United States
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The thing about midrange frequencies is that some of their wavelengths will often fit inside the sub enclosure, which means the energy reflected back out through the cone will vary a lot in intensity over frequency. Ideally you want a totally non-resonant enclosure with gaussian padding that will dissipate most of the energy at any frequency, so little or nothing gets reflected back through the cone.

It was well documented in the Audio Cyclopedia decades ago that a sphere is the best shape internally, IF it is stimulated from the surface, not the center (where it would be the worse shape). In the real world a sphere would have pretty bad baffle step response on the outside.

I made a sub enclosure out of ABS pipe, 4 inch inner diameter, about 9 inches deep, for a Tympani/Peerless TG9FD1008 3 inch driver, and it measures almost ruler flat from about 400HZ to above 10kHZ. I cross it over at 500HZ and 7kHZ 4 pole in a triamp'd system I built. To seal the back end of the pipe (bought at Home Depot), I just let the pipe go all the way to the back of the main enclosure, and sealed it with lots of contact cement (several applications each 24 hours apart - same thing where the pipe meets the front baffle board).

Very important is that I packed about 1-2 inches of stiff wool felt in the back end of the pipe (actually upholstery padding - much cheaper and works fine), then an inch or 2 of regular cheap foam rubber, then an inch or so of the more conventional fluffed synthetic cotton type stuff (whatever they are calling it these days), all glued in place, leaving maybe half of the pipe tube empty so the midrange driver isn't too impeded by the stuffing, which can raise the Q if the driver "feels" the enclosure is too small (which can cause a low freq. peaking effect). I glued regular thin felt to the inside of the pipe in that unstuffed region. So I created an approximation of a gaussian arrester with all the padding. It works very good. It's wise to drill a hole for the wires to go through before doing the rest.

Cutting the pipe exactly square is necessary and is the hard part, unless you've got the right tools. Not a trivial project, but worth it. When you get above about 1kHZ, the wavelengths start fitting inside the enclosure, but the padding eats the energy up pretty well. Any resonant energies inside the front part of the pipe are focussed to the center of the pipe, which the driver magnet blocks. I of coarse front mount the 3 inch driver to minimize cavity effect on the front side of the cone, and so the driver is replaceable if it ever goes bad. I also routered the back side of the approx. 3 inch hole in the baffle board, so the air could disperse from the back side of the driver with less impedance into the subenclosure. I mount the driver with wood screws and silicone rubber glue.
Attached Images
File Type: jpg ABS pipe 1 wb.jpg (567.6 KB, 193 views)
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Old 15th January 2017, 02:54 AM   #17
twinter is offline twinter  United States
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Jim Moriyasu authored an article in the 7 & 8 2000 issues of Speaker Builder Magazine, "A Study of Midrange Enclosures". He tested 18 different midrange enclosures mounted on an IEC baffle, 1.65m x 1.35m. He measured frequency response and Cumulative Spectrum Decay (CSD) or waterfall plots at a near field 2". He used a Focal 5NV4212 Neoglass midrange with a phase plug, flush mounted on the baffle. Enclosures were tested with and without damping material, Acousta-Stuf at 1 lb/cu. ft..

Cube (2), small (Qtc = 0.7) & large (Qtc = 0.5)
Rectangle, golden ratio (2), small & large
Tube w/ flat end (2), small & larger
Vifa tube with hemispherical end
Pyramid, three sided
Pyramid, four sided (2), small & large
Transmission line, tubular (2), small & large
Transmission line, square
Transmission line, triangular
Anechoic Enclosure, with rigid foam insulation wedges
8" x 8" x 6" Enclosure

So much information is shown in the plots of the articles, with so much for personal interpretation, that paying for the e:files is worthwhile.

Summarizing the articles results, hopefully doing the article justice :
Appropriate use of damping material and a sufficient internal volume for a Qtc of 0.5 or less is more important than shape. In general (not always), the larger enclosures performed better than the small enclosures. The damped transmission lines performed well. The undamped and damped cubic enclosures were not as resonant as expected. The undamped flat-backed tube and the undamped Vifa tapered tube were very resonant. While performing well, the justification of using a spherical or egg shaped enclosure for actual improved performance is very questionable. Beveling the rear edge of the baffle midrange opening is important.


Last edited by twinter; 15th January 2017 at 03:04 AM.
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Old 15th January 2017, 04:42 AM   #18
Bob Richards is offline Bob Richards  United States
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I definitely agree that a tube would be the worse of the bunch, if it isn't almost half full of padding . End to end it's a disaster without the padding, but side to side seems not a problem. I actually got the idea from the Linkwitz Pluto speaker system where he has a woofer/mid mounted at the end of a pipe about 3 feet long. ABS pipe 1/4 inch thick walls, is much lighter than wood and subtracts less internal cabinet volume from the woofer, if that matters. Thanks for the link info above.
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Old 15th January 2017, 09:00 AM   #19
Mario Pankov is offline Mario Pankov  Europe
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How to determine the best midrange enclosure?
I have to redesign my own loudspeakers and want to use a 18cm Scanspeak as a driver to cover upper bass and midrange but had a problem - I didn`t want to put an electrical highpass filter and did some simulations in WinISD to see if there is an alternative and noticed something interesting. If the midwoofer (in this case) is put into a very small, about 10 times smaller than its sealed 0.7 allignment, enclosure which is extremely lose, Ql being somewhere 0.75 (yes that low) - the end result is a smooth 3rd order roll-off which can be adjusted in frequency by varying the enclosure size and amount of stuffing in the improvised variovent, twice lower than sealed group delay and better cone control - in my case with 14V of input voltage in 1.5l aperiodic, very loose enclosure, the Revelator stays within its linear stroke down to 26Hz, more than enough, in sealed with Qtc of 0.7 it would be above its max stroke at about 40Hz, big difference in behaviour. I don`t like the idea of a big capacitor bank before the mid which would also cost the same or much more than all other crossover components and no matter what caps are being used, they`d introduce their own scent in the overal output.

Has anyone else experimented with such driver loading? I will do some real tests in the following weeks to see what the actual result would be (using a different driver I have on hand).

Last edited by Mario Pankov; 15th January 2017 at 09:08 AM.
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