Hello -
I'm in the process of designing and building what I call a "branched waveguide" loudspeaker (read: a wad of PVC pipe with multiple outlets). I had initially planned on driving the waveguide with a 5" Carbonneau speaker that I've had lying around, with its back open to the air but I've recently hit on the idea of using a midrange compression driver instead, connected with a conical adapter that's threaded on one end for a 1-3/8" driver and on the other for 4" PVC.
And so I've been hunting for compression drivers on eBay, and I've noticed that there are definitely "tweeters" and "midranges" among the breed. But I'm concerned that midrange CDs' frequency ranges mostly seem to bottom out at 500-1500Hz, which concerns me because the fundamental on a guitar's lowest note goes down lower than that. I found one, shown here, that states a range down to 100Hz, which is so much lower than anything else I've been able to find that I'm not sure if that's for real, and without any make or model shown in the auction I can't look up specs independently (I've tried to contact the seller but there has been no response yet). So my question is, how low can midrange CDs be expected to go?
I'm in the process of designing and building what I call a "branched waveguide" loudspeaker (read: a wad of PVC pipe with multiple outlets). I had initially planned on driving the waveguide with a 5" Carbonneau speaker that I've had lying around, with its back open to the air but I've recently hit on the idea of using a midrange compression driver instead, connected with a conical adapter that's threaded on one end for a 1-3/8" driver and on the other for 4" PVC.
And so I've been hunting for compression drivers on eBay, and I've noticed that there are definitely "tweeters" and "midranges" among the breed. But I'm concerned that midrange CDs' frequency ranges mostly seem to bottom out at 500-1500Hz, which concerns me because the fundamental on a guitar's lowest note goes down lower than that. I found one, shown here, that states a range down to 100Hz, which is so much lower than anything else I've been able to find that I'm not sure if that's for real, and without any make or model shown in the auction I can't look up specs independently (I've tried to contact the seller but there has been no response yet). So my question is, how low can midrange CDs be expected to go?
Greets!
Nothing in the link, but the lowest I'm familiar with is the 4", 200 Hz Community M4. Below this point one normally designs/builds it using a mid or mid-bass horn driver depending on how low it needs to load, though there's been some available in the past such as these 12" Community stadium horns:
Low Mid Range Community Speaker | eBay
GM
Nothing in the link, but the lowest I'm familiar with is the 4", 200 Hz Community M4. Below this point one normally designs/builds it using a mid or mid-bass horn driver depending on how low it needs to load, though there's been some available in the past such as these 12" Community stadium horns:
Low Mid Range Community Speaker | eBay
GM
Not nearly low enough to cover the full output of a guitar, unless you're talking about esoteric ones that are really more like conventional drivers turned into compression drivers, and gigantic and extremely expensive, i.e. not the kind of thing you slap onto some bits of PVC.
My dear fellow DIYers that have suggested that 1" exit compression drivers are not capable of output down below 80 Hz evidently are unaware of this thread:
http://www.diyaudio.com/forums/multi-way/239472-new-ideas-k-55-pd-5v-compression-drivers.html
The large horn used extends response well below 80 Hz.
There are a number of "old school" PA drivers that can drive down low, as anyone that has heard a talk box knows (Frampton "Do you feel Like I do", Zapp/Roger etc.). I wish we would have collected all the old RCA drivers from under the Met Sports Center bleachers in Bloomington, MN, before it was demolished and turned in to the Mall of America.
Those RCA drivers made great talk boxes..
However, a wad of PVC pipe with multiple outlets is nothing like the large, very long Sato horn used in the above thread link, and won't have much LF at all with any compression driver.
Also, it won't be a "branched waveguide", it will be a "Branched Frequency Dependent Diffraction Unit"
.What is it you are actually trying to achieve with the BFDDU?
Art
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Thanks for the replies. It turns out that since I started the thread, the seller on eBay has changed the description from 100Hz to 1000Hz although I never did get a message back.
Just the same, in looking around further on eBay, I've found a Samning Sound S-100S with specs of 275-8000Hz, 100W, and 11 ohms. Guitars in standard tuning run down to 82.41 Hz. I can't find a spec sheet for the S-100S but the sheet for the similar S-60S, that's specced down to 375Hz, shows that it's down about 11dB SPL from peak at 200Hz and falls off even more steeply below that, so I dunno...
Just the same, in looking around further on eBay, I've found a Samning Sound S-100S with specs of 275-8000Hz, 100W, and 11 ohms. Guitars in standard tuning run down to 82.41 Hz. I can't find a spec sheet for the S-100S but the sheet for the similar S-60S, that's specced down to 375Hz, shows that it's down about 11dB SPL from peak at 200Hz and falls off even more steeply below that, so I dunno...
And the second harmonic of the low E (164 Hz) is usually quite a bit louder than the fundamental.
We still "dunno" what you want to do, so hard to help you.
Not really "below", but that's an interesting thread. I'd love to hear one of those. I couldn't be more skeptical
. Neither here nor there for the OP, as you said.Well, let me elaborate a bit on the thinking behind this.
Right now the guitar world is positively awash in "before-amp" effects and I have a couple of vintage distortion boxes and delay effects. But in the interest of differentiating myself and doing interesting things for an audience, I am exploring "after-amp" effects to include acoustic ones.
And so I thought of using PVC pipe starting with a long section at 4" wide that branches off a 2" line and drops to 3", which branches off in a few more 2" lines of varying lengths such that there winds up being perhaps 6 to 10 2" lines in total, which exit in different directions. I figure that the interactions between the sound, the locations of the branches, and the lengths of the pipes in between will more or less be randomized but that the end result will be that any one note from the guitar will have a certain power distribution of harmonics among the outlets while for another note, that distribution will have changed. And of course there will necessarily be differing amounts of delay at each outlet, so I'm expecting that this will have a very ambient and animated sound when played in a room.
I have a video where I experimented with the 5" Carbonneau and a 6'7" length of 4" pipe here. That this length of pipe happened to resonate at the guitar's low E suggested to me that I perhaps should make the length to the first branch point just a bit longer than this.
I was prepared to mount the Carbonneau to a 6" threaded plug with the center cut out, facing in, and I'd screw that into a 6" fitting than I'd immediately adapt down to 4" for the first pipe but a few days ago I was thinking about how some of the power would be getting lost out of the back of the speaker in a roughly cardioid pattern and it got me thinking about using a compression driver the way a Leslie does.
I've got enough pipe and fittings accumulated that I can experiment with some arrangements with everything just laying out in the driveway. And if my cousin fabs me an adapter to go between a compression driver and a 4" PVC threaded socket like he offered to, perhaps this Sanming or the JBL one of you mentioned would be the way to go.
Right now the guitar world is positively awash in "before-amp" effects and I have a couple of vintage distortion boxes and delay effects. But in the interest of differentiating myself and doing interesting things for an audience, I am exploring "after-amp" effects to include acoustic ones.
And so I thought of using PVC pipe starting with a long section at 4" wide that branches off a 2" line and drops to 3", which branches off in a few more 2" lines of varying lengths such that there winds up being perhaps 6 to 10 2" lines in total, which exit in different directions. I figure that the interactions between the sound, the locations of the branches, and the lengths of the pipes in between will more or less be randomized but that the end result will be that any one note from the guitar will have a certain power distribution of harmonics among the outlets while for another note, that distribution will have changed. And of course there will necessarily be differing amounts of delay at each outlet, so I'm expecting that this will have a very ambient and animated sound when played in a room.
I have a video where I experimented with the 5" Carbonneau and a 6'7" length of 4" pipe here. That this length of pipe happened to resonate at the guitar's low E suggested to me that I perhaps should make the length to the first branch point just a bit longer than this.
I was prepared to mount the Carbonneau to a 6" threaded plug with the center cut out, facing in, and I'd screw that into a 6" fitting than I'd immediately adapt down to 4" for the first pipe but a few days ago I was thinking about how some of the power would be getting lost out of the back of the speaker in a roughly cardioid pattern and it got me thinking about using a compression driver the way a Leslie does.
I've got enough pipe and fittings accumulated that I can experiment with some arrangements with everything just laying out in the driveway. And if my cousin fabs me an adapter to go between a compression driver and a 4" PVC threaded socket like he offered to, perhaps this Sanming or the JBL one of you mentioned would be the way to go.
Your Carbonneau will be a compression driver if you simply enclose the back.
It has far more excursion than most compression drivers, it will work better for what you are trying to achieve than PA compression drivers, which require a (very) long exponential expansion to go low at rock and roll levels.
You might find a PVC plumbing cap or tin can that fits the speaker, or make one out of laminated plywood doughnut rings with a back cover.
You can choke the speaker exit down to 2" or 3", (compression cone mids often have a ratio of 4/1) reduce pipe size and expense and increase output.
Got a 4x4" Leslie for sale if you want some more movement!
The 4x4" work better than the compression driver on a 3 foot horn did, saved a lot of space.
For your project, you can maintain long tube lengths and reduce size further by using 90 degree elbows and "U" plumbing parts, will also make it easier to mic if you want to record or use it through a PA.
The elbows will also create more comb filter sounds, which for what you are doing will enhance the harmonic effects.
Have fun!
Art
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Just mount the cone driver in a sealed box (or pipe) with a wad of insulation in it, and attach your experiment to the front of it. I don't think a compression driver is gaining you anything here. edit: whoops, Art beat me to it. If you can avoid a shrinking cross section, you'll probably like the results better, so maybe have your "branching" start at the same place on the large tube, rather than tapering to a small one. I suppose if you had a series of branches coming off the large tube, each one would be a high pass filter...
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weltersys - Quite a piece of hardware there; very interesting!
Okay, so at this point I'm fairly well discouraged from using a CD at all. I had wondered about potentially closing in the back of the mounted Carbonneau but I was wondering about setting up resonances or just losing power by squishing air, but if I made that enclosure larger in response...well, I'd might as well just take PVC away in both directions! I won't want to make that a mirror-image run lest I have a net phase cancellation but I would certainly get the power captured in the pipes.
Dumptruck - I just bought a big pile of 2" pipe and elbows off a guy whose son built a Blue-Man-Group-style "tubulum" (five and a half feet long!) for a high school project...I even got all their extras. So I'm going to try to design this in such a way that I've got pipe arranged as densely as possible so I can still get this thing in the car!
Okay, so at this point I'm fairly well discouraged from using a CD at all. I had wondered about potentially closing in the back of the mounted Carbonneau but I was wondering about setting up resonances or just losing power by squishing air, but if I made that enclosure larger in response...well, I'd might as well just take PVC away in both directions! I won't want to make that a mirror-image run lest I have a net phase cancellation but I would certainly get the power captured in the pipes.
Dumptruck - I just bought a big pile of 2" pipe and elbows off a guy whose son built a Blue-Man-Group-style "tubulum" (five and a half feet long!) for a high school project...I even got all their extras. So I'm going to try to design this in such a way that I've got pipe arranged as densely as possible so I can still get this thing in the car!
By the way, here's what that would look like.
An externally hosted image should be here but it was not working when we last tested it.
The compression chamber volume of that enclosure, even with the back covered, is likely too large for optimum results with your project.
You can reduce chamber volume incrementally by filling a plastic bag with sand and placing it inside the compression chamber.
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