Omnidirectional Speaker Project, any interest, help?

[dlneubec]

I finished my first open baffle speakers a couple months ago (NaO Mini’s), which I’m extremely happy with. I love the huge sound stage they project and this got me interested in the concept of omnidirectional speakers. In doing a little research, I ran across the Duevel loudspeakers. They use up or down firing drivers that utilize a cone shaped horn/deflector to create a 360º radiation pattern. The reviews on the Duevel speakers are very good.

I have been thinking of doing somewhat of a clone of a cross between their Bella Luna
Bella Luna



and their Venus models
Venus



The Bella Luna seems to be very efficient for a two driver, 2-way system and a concern I had was how to make a reasonably efficient DIY version. I was hoping to use drivers that are fairly typical to the type of DIY projects we see on this forum regularly, ones that are well known and well measured. My thoughts were to use a body like the Bella Luna, but with a deflector/horn more like the Venus. I believe someone reasonably skilled with a lathe could turn these, once a design shape was determined.

The attachment below shows various conceptual plans for the speakers that have been bouncing around in my head.

My first thought was to add a second 7” or 8” driver on the opposite end of the main body firing down to increase efficiency. Perhaps a 2.5way arrangement?

My second thought was to go 3-way, using an up firing 7” or 8” driver, a down firing tweeter, but add a low frequency driver that fires down toward the floor, perhaps a ported 10” or a sealed 10” powered sub driver.

The third through fifth concept us based on the idea of an array of 4”-5” drivers, with a small flange, 2.5” or so, dome or ring radiator tweeter located in the center of the array. My thinking was that since the array would be evenly deflected 360º off the horn/deflector, that it would not suffer the same problems that it might if it was firing directly at the listener. I did a little modeling in Unibox and found that four RS125S-8’s, wired parallel in series, would match the efficiency of the tweeter and allow pretty high SPL’s with an F3 of 118hz in a 8L box. Combine this with either a down-firing or up-firing 10’ driver or powered sub and it looked interesting also.

The concepts I show below use 12”x12” boxes with a total height in the range of 38” to 40”.

I’d love to get feedback from anyone who is interested in the omnidirectional concept, or who wished to comment on or give me direction/guidance on how to move forward.

Thanks for any thoughts.

[cjd]

The tweeter doesn't need to be loaded behind the funnel or whatever you call it - as long as it doesn't have a phase shield, that is. You can simply mount it up top. Which opens up your tweeter options quite a bit.

I wonder how dispersion will be with the 4-mid arrangement.

I would probably lean toward the 3-way. This might be a great application for an Extremis on the bottom paired with a 150 (or 180mm) mid.

The last omni I heard was very picky about room, or so I understood from some folks that had heard it previously and found the sound so improved they swore a change had been made (yet, no changes were made).

C

[JonW]

Interesting idea. And I really can't help you at all. (I really can't ever help anyone, it seems. ) But before going to the effort of this build, I might recommend first trying to hear a similar speaker. See if you like it at all. I find that I like speakers with tack sharp, really precise, pinpoint resolution. And I don't really like speakers as much with, say, a rear firing "ambience" tweeter (or even mid). It seems some of the precision of a really good speaker is lost that way. Just to my tastes, of course. So omnidirectional speakers might be even worse in this regard. It might be good for surround speakers in a home theater setup. But for music I'd think it will only appeal to some people and not to others.

But if you've got plenty of time on your hands, it looks like it would be a very cool, quite fun experiment. Definitely something different. :T

[joecarrow]

Make sure you check these guys out: http://www.sawonline.com/index_flash.html

They license the ALT technology to B&O for the Beolab 5 speaker. I've heard the Beolab 5 in person, and it was an extraordinarily fun speaker.

Edit: The shape they use is well photographed. You could probably figure it out and prototype it with some sort of sculpting clay and a hard veneer made of epoxy.

[sliceofhogan]

Funny, i was thinking about exactly the same thing, but then, ofcourse completely different 8)

I am currently trying to fiddle some sort of a "speaker ball".... they used to be popular at the end of the '70's and beginning of the 80's. Companies like JVC, Grundig and lots of other had their "balls" for the then hot "quadrophonia-mania" - the hype that never was that is :twisted:

Am thinking about using a lot of RS125 (or otherwise the CSS 125, depending on the number of units i need to get a nice "ball", as these are also available in 16ohm). Tweeters are still to be selected, suggestions are welcome.

Like a soccer ball i am now fiddling with (cardboard) pentagrams, to get the proper shape. Afterwards i will make a master from which i can make copies with my router....

I think Visaton (Germany) also has cone diffractors, for testing a suited chair or table foot could suffice, perhaps

[joecarrow]

Something like this? http://www.music.columbia.edu/%7Edan...ces/index.html

One of the music professors from my college plays a sensor bass through one of those. It sounds really interesting.

[Dennis H]

I am currently trying to fiddle some sort of a "speaker ball"....

Am thinking about using a lot of RS125 (or otherwise the CSS 125, depending on the number of units i need to get a nice "ball", as these are also available in 16ohm). Tweeters are still to be selected, suggestions are welcome.

That's one application where so-called fullrange drivers make some sense and you might not need tweeters. With enough drivers, bass shouldn't be a problem and you would never be far off axis of one driver or another so the power response of the treble should be okay too. Maybe the CSS FR125 (expensive) or some the smaller and cheaper drivers like Zaph tested -- Aurasound, HiVi, Tangband, etc.

http://www.zaphaudio.com/smalltest/

[dlneubec]

Thanks for the comments. There is no place close by that I know of where I could hear something like the Bella Luna. However, I figure they might be quite simple to open baffles. In some of the reviews, I have seen them compared to the top end Magneplanars and Martin Logan Dipole Electrostatics.

Here are some reviews if anyone is interested.
6 Moons Audio review: Duevel Bella Luna Diamanted
6 Moons Audio review: Duevel Jupiter
Enjoy the Music.com Bella Luna Review
Buyer Review from audio site
Ultra Audio Review of the Venus

One of the interesting things to me is that these are not like pointing drivers in all different directions to get some type of ambiance. Instead, they would seem to provide a very coherent 360º wave of music.

CJD, my take on using the conical shape to disperse the tweeter is that it would take away the concern about off axis response dropping off. Whether on axis or 60º off axis, the sound quality and frequncy responce would be the same. I woudl think an up-firing tweeter, especially if it covers from 2000Hz or so on up would be somewhat dissapointing since you would be listening around 180º off axis. Does that make any sense to you?

Joe, I'll check out that link, thanks.

[RonS]

I've been giving this idea some thought too. I'm still finishing my dipoles, but am thinking of a small omni speaker for the living room.

You don't need to have the cone/whatever for the bottom speaker, as the floor will spread the sound out for you. Just fire the woofer into the floor and it will disperse evenly in a 360 degree circle.

Have you seen the Morrison speakers?

http://www.morrisonaudio.com/index.htm

[dlneubec]

Yes, I have seen the Morrison. I have the same picture saved. It looks a bit simpler than the Duevel acoustic lens concept and might be easier to make or buy a premade ball (or half ball).

My wife didn't like the look of it as well, however ;x(

It would be worth experimenting with.

On the lower deflector/lens, I was thinking that it might be beneficial if depending on how high that driver was crossed to the mid. would there possibly be less diffraction problem since the sound would be deflected out rather than down into the base plate, or are the wave lengths just too long to worry about?

[mmoeller]

On the lover deflector/lens, I was thinking that it might be beneficial if depending on how high that driver was crossed to the mid. would there possibly be less diffraction problem since the sound would be deflected out rather than down into the base plate, or are the wave lengths just too long to worry about?

I think you maybe right on having less of a diffraction issue in the traditional sense. There is however a quarter wavelength associated with the end of the deflector. There might be a diffraction in that range that would have to be accounted for.

Is there a specific pass band associated with the lenses. The crossection pics on the Duevel site, at least on the tweet, look more like a waveguide than just a deflection gradient. Even with the mid would wavelengths longer than what the deflector would "redirect" be attenuated. For example say the longest distance from the cone to the deflector is about 50mm. That would represent a quarter wavelength of about 1.7kHz. Would the reflector continue to efficently direct frequencies with longer wavelengths than that.

One of the white papers on the SAW site talks about the waveguide effect, and the effect of the wavelengths on dispersion. Mentioning that at the longer wavelengths the lens would act more as a horn. There is definately something going on there.

[dlneubec]

mmoeller,

I'm not capable of answering your questions. I hope there are folks out there that can. I'm sure there is much to consider in deciding on the shape of the delfector/horn/waveguide, whatever it is. I have another question. Could the deflector/horn have an effect on system efficiency?

I do notice that as you go up in price on the Duevel models, that they do more treatments to the edges of the baffle the drivers are mounted on. Also, on the Venus, the tweet looks to be mostely deflected, whereas on the Bella Luna and up, they use much larger voice coil compression drivers and definitely create a 360º horn/deflector. This would seem too complicated for DIY, so I was thinking more along the line of the Venus treatment and using a simple dome tweeter.

Where is the SAW site you mentioned?

[mmoeller]

Post #4 for the SAW site. It has some very short and simple white papers. Looks like they have a patented lens design.

It seems to me that Dueval probably used some Finite Element Analysis (FEA) at low frequency to simulate response. Most likely a mechanical design package. I have access to electrical field analysis tools, but they don't like to work at audio frequencies.

You can try this for a simple wave applet.

http://www.falstad.com/mathphysics.html

Ripple tank in fun. Try to use the plane wave source. I'm assuming that it will act much like a pistonic speaker cone. Only flat.

[knifeinthesink]

www.decware.com has a project like this. Interesting site.

I was walking through my workplace one day and suddenly heard someone playing a cello. This didn't make much sense considering my workplace had nothing to do with music or cellos. When I got closer to the source of the sound I realized someone was playing a cd of cello music on a really cheap portable unit that was lying on its back with the speakers face up. I was really intriqued by the fact that I was so sure there was a cello in the building. Seems to be something to be said for omnidirection sound reproduction. Im sure someone around here must be well acquainted with the pros and cons since its not exactly a new idea.

Im curious to see what people come up with for the cone shaped thingy that redirects the sound waves. I suppose if you had a lathe it wouldn't be that tough but I doubt the average diy'er has one. Ill bet there is a readymade solution lurking in a home depot somewhere though.

Looking forward to seeing what comes of this.

[dlneubec]

I've been thinking that there is probably something ready made to use for the deflectors, lie some kind of large funnel. Somebody just has to stumble upon it.

On the other hand, there are wood shops everywhere that should be able to turn these out relatively quickly and I would think, not too expensively, depending on the material and if they do any finish sanding/etc., especially if you were to get a multiple order of them together. Ideally you could make them modular so they could be stacked back to back to make a two sided lens or use them single sided, which would open up more design possibilities.

I hope there is enough interest to keep this thread going.

[dlneubec]

I just looked at the decware site and they do have another interesting take on a "radial" speaker. Here are some quotes from them I found interesting.

"HOW THEY WORK
The Radials create a radial wave front that emanates from the speaker and expands into the room across all 360 degrees. Since room reflections are what destroy focus and coherent imaging, many audiophiles have to resort to expensive and ugly wall mounted diffusers to bust up these reflections. That is because these audiophiles use a conventional speaker with forward firing drivers. Conventional speakers emit all of their energy into a 30 degree dispersion pattern or beam directly at the listener. That means that all of the speakers output (that misses you head) reflects off the back wall in a con centrated beam or pattern. By using quadratic diffusers these beams can be phase grated into a hemi-disk that radiates into a180 degree pattern that greatly reduces the adverse effects of those reflections. In stark contrast the Radials have 90 percent less energy hitting that same surface. They also load all wall surfaces evenly so that the sound is already diffused. This makes it possible to have imaging that normally is only possible after spending 1000’s of dollars on a dedicated and treated listening space."

"POINT SOURCE
Unlike the original Ohm Walsh speakers that radiated sound into a 360 degree pattern, the Radials do NOT try to shoot high frequencies off in all directions. We have found that there is a point in the overall frequency response around 2500 cycles where the advantages of having 360 degree wave fronts start to work against you. In other words you do not want to spit high frequencies all over the room. Using a specially selected ribbon tweeter the Radials gradually become a point source starting around 2500 cycles. They become predominately a point source by the time they reach 4500 cycles on up to 25000 cycles. This combination is what makes the Radial loudspeakers own the term “holographic”."

There is a nice review of the RL1.5 speakers there also.
Decware RL-1.5 speakers

[knifeinthesink]

interesting comment about the transition to point source radiation. Worth discussing abit i think

[dlneubec]

I'm not sure I buy the argument, but it is certainly worth discussing and proibably experimenting with. I sure don't like the way the tweeter site right in front of the forward part of the radiation pattern from their top mounted driver. That seems counterproductive to me.

I once owned a pair of Infinity 2000 II speakers. They had a walsh gold foil-like cone supertweeter on top, that stuck up about 4-5" and supposedly had a 360º radiation pattern. It came with an oak top that sit a few inches above this tweeter, supposedly out of the way of the radiation pattern, but also with a second top that was open with grill cloth. The speaker sounded much more open and spacious to me with the open top and more closed in with the system sounded.

[Landroval]

Have you seen Bolzano Villetri: http://www.bolzanovilletri.com/

[JonP]

Well... I saw the reference to these earlier, very interesting technically as well as visually striking. And it did occur to me that the Venus' reflectors would be DIY feasable to replicate.... so it's cool that there are like minded folks getting a thread going.

After stalling out on my router created waveguide experiments, this is getting me fired up again. Don't have a lathe, do have a master woodworker/sculptor friend who does...

interesting comment about the transition to point source radiation. Worth discussing abit i think

An interesting concept... and of course, that's Siegfried's point with the Plutos, more or less, ommni at the lower end, point source (but somewhat
directional) in the higher frequencies...

I have a buddy who has a set of Ohms... the later models also had a directional tweeter facing the listener. Seemed like the evolution for them as well.

[knifeinthesink]

Have you seen Bolzano Villetri: http://www.bolzanovilletri.com/

WOW!!!

Only the Italians could make a speaker that beautiful.
:drool:

[knifeinthesink]

ahh, and the russians... apparently.

[dlneubec]

Hi Guys,

I decided to explore some further ideas for an omni speaker last might. In order to be able to make it flexible to adapt to a variety of configurations that folks might want to try, I came up with the idea of a modular build concept. Here’s how it would work (see attached pdf below).

First I had to pick a modular size. I decided to go with 13”x13” square for the speaker, since that would allow as much as a 12” driver to be shoe-horned into it, or if any array was used, you could go as high as four 6” drivers. Then I wanted to make some increments that would allow a wide variety of driver and interior volume sizes and types. I picked 9L(.32 cu.ft.) increments, which worked out to be an interior space of roughly 4”x13”x13”. The idea is that one would build the sides of a 4.5”x4.5”x13” box and have interchangeable tops an bottoms for the boxes. For example, you might have a top of bottom that is intended as a speaker baffle, or the backing piece to a thicker baffle, but you also might have one that is for bracing, for a port or for different sized drivers.

The idea is you would build the boxes with no top or bottom. You would then assemble them by adding the appropriate top and bottom and stack them to make whatever configuration you are interested in. I think if you look at the pdf, this will make more sense. Since you have a potential brace every 5.5” or so, it would also make for a very rigid cabinet. It might even allow you to make the sides of the box out of thinner material than ¾”, or use something like solid hardwood stock. The largest unsupported inside panel would be 4”x 11.5”, so box resonances should be well controlled. The interior divider/brace pieces, are notched so that the boxes easily can stack.

In order to keep the sides the same, there is a slight change in size of the boxes. For example, a single sealed box is 8.7 L(.31 cu.ft.), whereas when you add boxes with brace-type dividers, each additional box adds about 9.5L(.34 cu.ft.). So, you can have a sealed box as small as 8.7L, but you could stack them using brace-type dividers, for volumes of 18.2L(.65 cu.ft.), 27.7L(.98 cu.ft.), 37.2L(1.31 cu.ft.), 46.7L(1.65 cu.ft.), etc.

I’ve added an extra ¾” piece at all baffle locations so that the baffles are 1.5” thick. This would allow a solid piece of hardwood to be used over mdf for example, as a composite. It would also allow for some serious chamfering from the edge of the baffle as I’ve shown on the attached concepts and as you see in the upper end Duevel speakers, which should help with edge diffraction.

Right now, I picture two types of deflector/horns, one for tweeters and one for everything else. I don’t know it that is valid in that it may turn out that different driver sizes or frequency ranges will need a different shape, but with this concept it would be easier to a bunch produced in bulk.

As far as the concepts I have shown, I’ve got a TMMW concept, with a sealed downfiring 10” sub in about a 27.7L space, with two 6”-7” drivers firing toward each other, but separated by the deflectors, and a top mounted tweeter, for a 3-way configuration. The second concept is similar, sort of a TMM, but instead of the sub, it shows a passive radiator and just one big 37.2L box on the bottom and probably a 2-way or 2.5-way configuration. The third option is the same as the first, a TMMW, but instead of the top mounted tweeter, it has a traditional front mounted tweeter. The fourth option shows a MMTMMW configuration, with a small downfiring 4-driver array, using something like the RS125 or RS150, in a 8.7L sealed box with a small flange tweeter centered in the array, and an upfiring 10” sub driver with a downfiring passive radiator in a 37.7L box. Finally, I did one in a two-way, TM configuration with an upfiring driver, downfiring passive radiator and an upfiring tweeter. They range in height from about 32” to 41”.

It was a lot of fun playing with the modules to create various configurations. I think it has a lot of flexibility and potential to adapt to various types of driver configurations and if constructed with gaskets between sections, might even be able to be disassembled and changed to a different concept.

What do you all think of it?

[eb15]

Daniel Queen, the well known acoustical consultant, had a similar "cylindrical wave launch by standard drivers and waveguide/horn design" patented loudspeaker with a good reputation in the early 1980s. Let's see it's US patent number 4,134,471 from Jan 16, 1979 and had a related article in Journal of the Audio Engineering Society May 1979 volume 27, number 5 titled "The Effect of Loudspeaker Radiation Patterns on Stereo Imaging and Clarity"

About the PDF drawing... Can you add some arms and make them look like
robots.

[cjd]

interesting comment about the transition to point source radiation. Worth discussing abit i think

This has been found with dipoles as well. I am not surprised to see this comment there. In fact, it's been discussed on HTGuide before.

I want to test it myself before I buy it completely though.

C

[mmoeller]

This has been found with dipoles as well. I am not surprised to see this comment there. In fact, it's been discussed on HTGuide before.

I want to test it myself before I buy it completely though.

C

It seems as if this would happen regardless of the speaker being a dipole or a 360 radiator. As the freq. increases is it not true that the radiation pattern of any speaker shifts to more of a beam/lobing pattern. The benifit may be seen in the need for baffle diffraction or lack there of, or the lack of mid to tweeter transition radiation interference. May allow the mid to creep a little higher in the frequency range.

However I am nuts and like to make things up.

[knifeinthesink]

maybe this would work as a readymade diffuser.

http://www.target.com/gp/detail.html/ref=br_1_9/601-0286469-7245745?%5Fencoding=UTF8&frombrowse=1&asin=B000E8POV8

Not the concave shape you usually see but similar to the shape used for the morrison speaker.

[dlneubec]

It seems as if this would happen regardless of the speaker being a dipole or a 360 radiator. As the freq. increases is it not true that the radiation pattern of any speaker shifts to more of a beam/lobing pattern. The benifit may be seen in the need for baffle diffraction or lack there of, or the lack of mid to tweeter transition radiation interference. May allow the mid to creep a little higher in the frequency range.

However I am nuts and like to make things up.

I read in another forum where a guy was commenting on how he thought sound changed from naturally omnidirectional at low frequencies to more directional through the mids and lower highs, but then got omnidirectional again at the upper end of hearing.

He was taling about testing with various tones and how the sound got omnidirectional again up in the 15-16kHz range, at least to his ears. I remember thinking the same thing recently when I ran through some test tones. I couldn't locate where the tones were coming from at all, once I got up into 14-15khz, as I recall.

[dlneubec]

maybe this would work as a readymade diffuser.

http://www.target.com/gp/detail.html/ref=br_1_9/601-0286469-7245745?%5Fencoding=UTF8&frombrowse=1&asin=B000E8POV8

Not the concave shape you usually see but similar to the shape used for the morrison speaker.

There do seem to be two schools of thought around, one concave and one convex to rounded. Even Duevel has round balls over the drivers on the "Planet" model. I also noted that some seem to have a reflector that is larger than the width of the driver and some have them the same size or smaller. Maybe the size is depending on the frequency range and the beaming of the driver.

I suspect it would be easier to find something ball shaped, than a concave cone.

[sliceofhogan]

Something like this? http://www.music.columbia.edu/%7Edan...ces/index.html

One of the music professors from my college plays a sensor bass through one of those. It sounds really interesting.

No, i meant something like this JVC Ball .....

Seems like JVC goes retro, complete with omnidirectional technical mumbo-jumbo :T The orginal had a metal ball-shaped surround grill, which made it look "high-tech" but livingroom acceptable.
Anyhoo, JVC says lots of speakers in a sphere shape is better, fwiw.

Might try a test with some cheapo tangbands (fullrange), thanks for the pointer!

[Dennis H]

Re the Decware thing:

Conventional speakers emit all of their energy into a 30 degree dispersion pattern or beam directly at the listener.

Well that's clearly nonsense so anything else they say can be taken with a huge grain of salt. Conventional speakers radiate 360 degrees at low frequencies, 180 degrees at mid frequencies and something less than 180 degrees at high frequencies.

[mmoeller]

There do seem to be two schools of thought around, one concave and one convex to rounded. Even Duevel has round balls over the drivers on the "Planet" model. I also noted that some seem to have a reflector that is larger than the width of the driver and some have them the same size or smaller. Maybe the size is depending on the frequency range and the beaming of the driver.

I suspect it would be easier to find something ball shaped, than a concave cone.

The different reflector styles led me to ask myself, "if the two shapes are used to get the same effect, what about the two shapes is the driving factor?", and "what makes them different?".

I am starting to think that the concave or convex curvature may be related to the phase shift the signals will undergo when coming in contact with the boundry. At any infinitely small segment of the curve the wave will undergo a 180deg phase shift. At that same segment a given frequency will be at either a quarterwave (90deg shifts to -90deg) mabey for a sphere, or a threequarter (-90deg shifts to 90deg) mabey the deflector type. This might not be 100% accurate, due to the varying angle of incident, but its close. I would think either could be use effectivly.

[dlneubec]

The different reflector styles led me to ask myself, "if the two shapes are used to get the same effect, what about the two shapes is the driving factor?", and "what makes them different?".

I am starting to think that the concave or convex curvature may be related to the phase shift the signals will undergo when coming in contact with the boundry. At any infinitely small segment of the curve the wave will undergo a 180deg phase shift. At that same segment a given frequency will be at either a quarterwave (90deg shifts to -90deg) mabey for a sphere, or a threequarter (-90deg shifts to 90deg) mabey the deflector type. This might not be 100% accurate, due to the varying angle of incident, but its close. I would think either could be use effectivly.

I'm not knowlegeable enough to comment on the phase shift. Maybe someone else can.

I wonder how the shape of the reflector might change where the sound is reflected? Would one tend to give a taller dispersion and more vertically dispersed soundfield and another a more focased horizontal soundfield? Would one shape tend to have less negative diffraction effects? I'd like to understand more about how sound is reflected.

Here is a pdf that shows the two reflector types together. I carefully traced the Duevel shape from photos, so I think it is now very close to the one they use.

[mmoeller]

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

This site has a lot of great basic information about alot of different things. Including sound reflection. The section on plane waves is uniquely interesting. It says that concave surfaces tend to focus sound waves. I'm sure the focal point of the concave deflector for each frequency might vary, or it is designed to have more of a wide focal range, or depth of field (i.e. microscopes, telescopes).

As far as diffraction goes. I would suppose where ever there is an edge, sound would diffract. I'm definately not sure about all the particulars of diffraction. The shape of the sound wave could be changed as it travels through the reflector. It might lend itself to a decrease in diffraction at the reflector edge. It might affect the vertical sound field more than the horizontal as well, given the orientation of the reflector.

I have been studying a fundamentals of acoustics text to try and understand some of the science about what is going on here. I'm definately a beginner in acoustics, but I deal with electromagnetics for a job. Very similar. I have a buddy that works for Shure, the microphone company. I have been thinking on sending him some pics to see what he thinks. He's a heck of an engineer.

This looks like a very complicated topic that may require some simulation to expect to get good results, or just build one and measure a lot.

[dlneubec]

On a whim, I stopped by a local "Hobby Lobby" store at lunch. I was able to find styrafoam balls from about 2" through 7" or so. I can cut one in half, carve out the center, glue a wood baffle to the flat end to hold the tweeter, and serve as the deflector ball for the upfiring woofer, like the Morrison setup (see pic). they were all no more than a couple bucks each.

I also found wooden balls with apartial flat side, I guess intended to be used as knobs, in 1", 1.5", 1.75" and 2", and also cam with various sized holes drilled in the end for mounting. There were also solid round ones in those sizes. I picked up some 1.5" and 1.75" ones for the tweeter deflector in the Morrison approach.

I also found some styrafoam round disks in about 1" depths in sizes from about 14" on dowm. I bought enough of those to see if I could make a Duevel-like delfector, buy gluing the layers together and then sading them down to a concave cone shape. I might use it on the bottom of a prototype.

Anyone have any idea what and how to apply something to the surface of the styrafoam pieces to make a hardened surface, or at least one that is not absorbant? As long as I can glue the styrafoam peices to a wood backing piece, I think it might work fairly well, at least for prototyping something.

I think I may try to use these parts and my modular concept to build a simple TMM cabinet like shown in the attached pdf. I will use the drivers from a currently stored 2.5way system, that uses 2-RS180S-8's and a RS28a. I'm thinking of putting the .5 woofer down and just using the crossovers I already have for the MTM just to see how it sounds. I'm thinking for this test to make the RS180's sealed, though the modular approach will allow me to take it apart and change to ported, larger volume, etc. I will set them on my stereo subs for now.

Anyone have any thoughts?

[Martyn]

I wonder how the shape of the reflector might change where the sound is reflected? Would one tend to give a taller dispersion and more vertically dispersed soundfield and another a more focased horizontal soundfield? Would one shape tend to have less negative diffraction effects?

I have a sneaking suspicion that it's not very critical. If we were dealing with an optical system with a point source of light, then it might be more important (you can imagine hanging a convex or concave mirror over a point source), but with sound waves eminating from a large diameter source and spread across a wide frequency spectrum? Nah.

Of course, if my natural scepticism is misplaced, I'm missing an enormous market opportunity. Just imagine the scope for marketing departments to expound on the relative benefits of parabolas and exponential or Fibonacci curves; and what about whether they're made of MDF, Baltic birch, maple, or sitka spruce; and should they be gold-plated or simply finished with a wipe of snake oil? :lol:

More seriously, why don't you mount a single mid-range driver in a box, hang a variety of shapes over it, and take some free-field measurements? At least you'd get a rough feel for what's going on before you commit to some major woodwork...

[dlneubec]

More seriously, why don't you mount a single mid-range driver in a box, hang a variety of shapes over it, and take some free-field measurements? At least you'd get a rough feel for what's going on before you commit to some major woodwork...

Therein lies the real rub for me. I'm a relative noob and have not started to do my own measurements yet. :cry:

I'm hoping to get some ideas generated and early protoryping done to the point that I get someone interested who can do measurement and crossover design. Failing that, I'll end up hiring someone to do it, if it looks promising enough. 8O

[knifeinthesink]

costs aproximately $80us for a berhinger mic and single channel pre-amp.

[Martyn]

Anyone have any idea what and how to apply something to the surface of the styrafoam pieces to make a hardened surface, or at least one that is not absorbant?

Plaster of Paris will set in minutes to give you a rough shape that you can then refine with subsequent applications of thinner layers. Then finish off with drywall mud. You'll have to work fast with Plaster of Paris, so it's better to apply not quite enough than to make yourself lots of sanding.

[dlneubec]

Well, I got a good amount done on building and testing my modular prototype idea (see the attached pics).

I think the modular concept is going to be pretty nice. I'll report more on that later, with pics. I'm still working on the concept, but I think it may have the potential to allow me to build up various systems sort of like Lincoln logs, from TM's, to TMM's, to TMW's, with some part sealed, some ported, etc. and still disassemble them and change to another concept.

What is shown in the pics is my first concept, which is an RS180S-8 on top, firing up, into a 5" ball-shape (like the Morrison speaker). The RS180 is in a sealed cabinet at about 9L. The ball shape houses and RS128AS firing up into a 1.5" hardwood ball. The 5" ball is made from a styrafoam ball cut in half and then mounted to a MDFround. The MDF is the support for the whole thing. I painted several coats of truck bed liner spray on the styrafoam ball to close the cells. I see this as a temporary solution to allow me to test this concept. I'm anticipating trying to find another source for the 5" ball, maybe a wooden bowl, with the lip on the bottom sanded off.

The bottom 4/5's houses a RS225, firing down. It is in a 39L enclosure that will be ported, probably at the 4 corners, firing down also, but I didn't have the right ports.

I'm planning on trying a 2.5way crossover with this setup, an existing crossover made to use with two RS-180's and the Rs28, but instead the .5 will be the RS225. I got the idea that this might work from this thread, where Dennis H suggests the two might be interchangeable.
RS180 drop in for RS225 and Vice-Versa?
We'll see how it sounds anyway.

I'm working on getting a deflector made like the ones that Duevel uses and plan to experiment with this concept, as compared to the ball concept as well. I have not decided whether to use a ball or cone-type deflector for the RS225, but will probably start with a ball, since that is what I have on hand.

[mmoeller]

Pretty slick rig.

Looks like you made it so that you can change the spacing between the ball and the cone of either driver. I think that might be key in adjusting the dispersion.

[mmoeller]

I have a sneaking suspicion that it's not very critical. If we were dealing with an optical system with a point source of light, then it might be more important (you can imagine hanging a convex or concave mirror over a point source), but with sound waves eminating from a large diameter source and spread across a wide frequency spectrum? Nah.

Of course, if my natural scepticism is misplaced, I'm missing an enormous market opportunity. Just imagine the scope for marketing departments to expound on the relative benefits of parabolas and exponential or Fibonacci curves; and what about whether they're made of MDF, Baltic birch, maple, or sitka spruce; and should they be gold-plated or simply finished with a wipe of snake oil? :lol:

I might disagree that it wont have a signifigant effect. A speaker is definately different than a point sorce or optical emitter. However, there are physics that can predict the response of plane waves. Simplifing the problem to a simple 2D cross section might explain alot in terms of function. I'm not an expert but it seems the shape of a horn determines the dispersion a great deal. Although this may only be considered a horn at a certain range of frequencies. There in lies the rub.

If you need some marketing, I can BS with the best.

[dlneubec]

Pretty slick rig.

Looks like you made it so that you can change the spacing between the ball and the cone of either driver. I think that might be key in adjusting the dispersion.

Yes, the entire project is made so that it is as adjustable as possible, from the modular build concept on the cabinet that allows increments of 9-10L enclosures, sealed or ported, to the legs, which are 3/4" aluminum tubing, used as spacers with long 8" carriage bolts to hold the base to the body, to the small diameter aluminum tubing which also act as spacers for the upifiring woofer and tweeter.

I originally thought that the modular box concpet for the cabinets would be simply temporary, and once a final build was selected, I would glue it together or make whole new cabinets. However, I now have some ideas that I think might work to allow the whole thing to be assmebled or dissasembled, even after finishing. So one could start with a small sealed TMM that sits on a stand or a sub and finish it. Disassemble it later, and change it to a TMM tower or TMW, etc.

[knifeinthesink]

Nicely done.

This thread is becoming extremely interesting. I cant recall coming across an actual discussion of the details of a diy omni speaker anywhere else.

[JonP]

Wow.. you work fast! I do like the modular idea....

I was going to mention that for rough surfaced sytrofoam (though this looks like the finer stuff) you would want it very smooth for the tweeter... looks like you were already thinking of that for the woofer, and the tweeter is wood. Higher frequencies = shorter wavelengths = need smoother surfaces.

My other guess is that a larger diameter for the tweeter might work better... it will be interesting to see how the effects change with different size/shapes of reflectors.. Hmmm.. I am basically set up for measurment, need to clear some working space in the garage and get at it... (for other projects as well!)

Overall though, just diving in and listening to various things can tell you a lot! Have at it and let us know...

Well, I got a good amount done on building and testing my modular prototype idea (see the attached pics).

What is shown in the pics is my first concept, which is an RS180S-8 on top, firing up, into a 5" ball-shape (like the Morrison speaker). The RS180 is in a sealed cabinet at about 9L. The ball shape houses and RS128AS firing up into a 1.5" hardwood ball. The 5" ball is made from a styrafoam ball cut in half and then mounted to a mdf round. The mdf is the suppoort for the whole thing. I painted several coats of truck bed liner spray on the styrafoam ball to close the cells. I see this as a temporary solution to allow me to test this concept. I'm anticipating trying to find another source for the 5" ball, maybe a wooden bowl, with the lip on the botom sanded off.


I'm working on getting a deflector made like the ones that Duevel uses and plan to experiment with this concept, as compared to the ball concept as well. I have not decided whether to use a ball or cone-type deflector for the RS225, but will probably start with a ball, since that is what I have on hand.