Unconventional Speaker Design - thread carried over from multiway forum - diyAudio
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Old 27th September 2012, 07:13 AM   #1
morgoe is offline morgoe  Australia
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Default Unconventional Speaker Design - thread carried over from multiway forum

Hi guys,

I posted this initially in the Multi-Way forum, but I've since decided to make this a fullrange speaker, so I'll continue on the thread here. The old thread is located here.

For those who didn't see the original thread, a quick recap:
I'm designing a speaker for an Object Design class at university. I'm an audio engineer, but I've never delved much into acoustics. I want to make something that sounds good, but unfortunately a major component of the course is making a challenging and interesting looking design, so I can't just make it look like a box on the outside, despite the research and science that goes into the architecture. I've got a great wood workshop available at university, but I can't use MDF there, so I'm trying to stay away from that if possible.

I'm tossing up between two ideas at the moment, and I'll decide in the next couple of days.
The first would look something like this
Click the image to open in full size.
but in a cylindrical (U shaped box) or spherical shape. I'd cut up all the blocks into tiny little segments, and then put them together.

The second idea is to use rings to create the design, but this may waste a bit of material.

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Quote:
Originally Posted by Remlab View Post
" Innerchoic" design, by PBN.
Sammy
Interesting design. I found this pic of the inside:
Click the image to open in full size.
It does look quite similar to my design. Couple of questions:
-There's no material on the inside of that pic. Is that because they've taken it out to show you the inside, or does the speaker design not require any dampening?
-Could I do a design similar to this using hardwood instead of MDF? Or would the horizontal length warp?

Thanks again.
I'm also looking into drivers. I'm not overly restricted by money, so I've been looking at the EL70's which seem to be quite popular here. Thoughts?

Last edited by morgoe; 27th September 2012 at 11:36 AM.
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Old 27th September 2012, 09:29 AM   #2
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If they put damping in there, you wouldn't be able to see the coathanger. It's either staged shot, or they're using a lightbulb for tweeter protection.

Properly cured hardwood doesn't warp unless you have humidity problems.
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Old 27th September 2012, 11:30 AM   #3
morgoe is offline morgoe  Australia
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I'm reading over the "MDF vs Baltic Birch" thread at the moment.

I should have put some more details in the OP for those who didn't see the previous thread, so I'm doing that now.
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Old 27th September 2012, 10:11 PM   #4
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I'm interested in what happens with diffusive surfaces inside cabinets. The inside in that one pic looks like the egg crates people put on their studio walls- lots and lots of diffusion at only one frequency.

I think it's possible that breakup style diffusion- edges creating diffusion- inside cabs will lead to larger enclosure losses. I'm looking at using some convex curves inside a rectangular cab to avoid standing waves, but I've been leery of having edges sticking out inside- seems like it could easily cause turbulence. Turbulence is not good news in your duct, except perhaps for a bit around the edges to "grease" the flow of the main plug of air, according to the Salvatti et al AES paper on ports. Then again, I'm not sure this is a vented cabinet you're working on, so I may be on apples and oranges.

I'm building cabinets out of seasoned (14 year old, in fact) solid maple. I just can't get excited about plywood and mdf.
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Old 28th September 2012, 12:47 AM   #5
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Greetings. May I ask what is the problem you want to solve?

You want to solve problems in the order of greatest impact. The box's -outer- geometry will arguably have greater impact than its -inner- geometry. And that's not even the biggest fish you have to fry!

But anyway, I'm not sure diffusing internal standing waves is of such great importance, nor that you can do it better than simply attenuating them through absorption with e.g., wool.

If you want to explore the (rather massive) impact that the baffle has on frequency response, consider downloading The Edge and get ready for some surprising results, e.g. a massive 3db lump and lots of ripples in the response, all courtesy of a "normal" baffle with center-positioned driver.

Also, on this forum under "Articles," read the "Arpeggio" article which is a general overview on fullranger design decisions and tradeoffs.
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Old 28th September 2012, 02:30 AM   #6
benb is offline benb  United States
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Yes, it looks like you're wanting to put diffusors on the inside walls, something like this:
PME Records QRD Diffusor Construction

From the last post, the immediate thought is to put a "diffusor" on the front panel, but after a short moment's thought you don't want anything for the high frequencies to hit on, reflect off of, or diffract around.

Here's the page for that "Edge" software, I've seen it before but haven't used it:
Home of the Edge
Unfortunately it doesn't appear to show the effect of rounding off the front baffle edge around to the sides, top and bottom, which as I understand can significantly soften the bumps and dips along and above the baffle step response. I see this edge rounding in the smaller Infinity cabinets as well as others.

Here's more info:
Baffle Step Compensation
The sphere shape is "ideal" shape for the baffle, but perhaps the worst shape for the inside of the cabinet (maybe fighting it out with a cube, with all X Y and Z dimensions the same, giving a big resonance at the corresponding frequency). Maybe the front half be a hemisphere and the back half be something else to give appropriate internal volume?
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Old 28th September 2012, 11:58 AM   #7
morgoe is offline morgoe  Australia
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Thanks guys,

Just a quick update, I've spent all day checking out various drivers, playing around with the "Edge" software. I think at this point in time I'm going to go with a U shaped box, as thin as possible (these as desktop speakers would be nice), so maybe 150mm max. As tall and as deep as is necessary. Still not sure whether I should go for the rings or the blocks, I'm thinking blocks.

I'm also tossing up between the following drivers:
Alpair 6p, Alpair 5, CHP-70, Audience A3.

If anyone's got any further input that'd be great, otherwise I'll just keep researching and updating this as I go.
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Old 28th September 2012, 02:34 PM   #8
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Okay, so the problem you're addressing is the need to build something with unconventional construction. I had thought you were addressing specific design goals of the final result.

So what you're doing sounds like fun, and you're exploring what's possible. But it's not really speaker design (yet) because there is no defined objective, e.g., (random example) a flat frequency response for Driver X, in dimensions no bigger than Y, down to bass frequency Z, given the desired positioning,etc.
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Old 28th September 2012, 02:45 PM   #9
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Quote:
Originally Posted by benb View Post
... but perhaps the worst shape for the inside of the cabinet (maybe fighting it out with a cube, with all X Y and Z dimensions the same, giving a big resonance at the corresponding frequency).
It can be a theoreticaly myth, because many guys that built spheres haven't notice any resonance...
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Old 28th September 2012, 02:45 PM   #10
morgoe is offline morgoe  Australia
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Quote:
Originally Posted by rjbond3rd View Post
Okay, so the problem you're addressing is the need to build something with unconventional construction. I had thought you were addressing specific design goals of the final result.

So what you're doing sounds like fun, and you're exploring what's possible. But it's not really speaker design (yet) because there is no defined objective, e.g., (random example) a flat frequency response for Driver X, in dimensions no bigger than Y, down to bass frequency Z, given the desired positioning,etc.
Yeah sorry I should have made that clearer. I do have some specific goals in mind at the moment, I'll do a bit for research tomorrow and hopefully post my requirements like the ones you just listed.
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