A Study of DMLs as a Full Range Speaker

Bertagni Electroacoustical Systems, BES. Lots of info available... typically used for sound reinforcement for small conference rooms, designed to fit into suspended ceilings. Installed hundreds of these critters.

An exciter is mounted to an aluminum frame. Frame attaches to the outer edge of a moulded polystyrene foam panel. The molded foam incorporates the surround and eggshaped cone all of which is polystyrene. Typical panel size is 2' x 4'. Stupid simple to make.
 
You know, this forum is really a hindrance to those of us trying to get their MA degree (ok not very hard ... BFD, my exams were two weeks ago.) Did I pass? Who knows? Just some reading and a few papers for the rest of the month otherwise. * ahem * Where was I? Oh yes, my favorite hobby...f-----g with audio!

I've been reading the NXT thread at audiocircle and ... fun! I have yet to buy "proper" exci ters because...I am still destroying my own spare parts :)

Somewhere in that thread it mentioned the "broken speaker" method. Having none of those, and quickly tiring of the 12" sub (meh!) I browsed for the next likely victim. Not having any broken drivers, I grabbed two Bose 901 (type) full rangers -- many people in this forum would say they are the next best thing to a broken driver :rolleyes: -- and have done unto them just like I did with the subwoofer: cat food tin, Gorilla Glue and illicitly acquired sign from last year's elections :)

In the aforementioned thread there is much discussion about mounting the exciter to the panel. Having never seen an exciter, I am not completely sure of what's going on. However, since I have some experience with the "broken driver" method, I have some qestions: many of the exciters rely on inertia of their mass to transmit the vibration? Tsk tsk. Much more efficient would be if the panel is "mostly" connected to the voice coil and we have a substitute for the "surround". Here the crystal ball grows foggy...

At issue is the added mass of the panel upon the voice coil assembly, maybe not so much if the voice coil will remain vertical but most of us probably will have the panel more or less facing us, so voice coil goes horizontal. Well, not quite, since it has several grams added mass pulling it down. Thus the need to better affix the basket to the panel somehow....and minimize damping of said panel.

Since tuning the panel is somewhat hit-or-miss, here is an idea: if some damping is needed anyway, it can be supplied by the mounting points of the basket (new "spider"?) for the combined contriviance.
 
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duh...

xrk971 (post #39) had my solution. So I will add stand-offs that will answer my long-winded need for achoring the driver to panel as well as the "suddenly I understand!" moment of keeping the voice coil in the right place.
 

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X,

You're welcome. :)


Soldermizer,

Here is a sketch to show the structures of the exciter and bass shaker I have on hand:

exciter_bassshaker_zpszn4fvm1o.png~original


I haven't actually dismantled them, but I guess it's reasonable enough for how they work.

The cheapo tiny exciter is on the left, its VC is exposed and intended to be coupled with the panel. For itself, it's "moving coil" structure.

In the middle is the Dayton bass shaker I have. Its VC is fixed on the inner wall, while the magnet block is suspended by several spiral-shape plastic cantilevers. So, this can be seen as "moving magnet" structure.

No matter they are MC or MM, when coupled with panel, eventually it's a mass mated with a spring / motor onto the panel.

So, the inertia of the mass, resilience of spring, and the motor are cooperating to deliver the driving force.
 
Interesting! I'd like to consider building a completely DIY exciter. Yes I know they can be bought for $20 or even less. But if people can build DIY planar magnetic speakers, why not a DIY coil? I know there are "science fair" project type things on YouTube etc. Yes, you can make a speaker out of a styrofoam dinner plate or a flower pot (well, maybe it is a coffee cup?) But oh no, not me.

I want an obscenely powerful "linear motor" or voice coil. In fact, for this type of speaker design, why not a variation of the "fixed coil" (or moving magnet, same thing?) Just embed a permanent magnet on the panel where you'd put the exciter (easy) and then nearby we place the yet-to-be-designed monster coil/electromagnet. Not the least of advantages would be the coil is fixed and presumably could be scaled to be tolerant of high power. I have several hundred watts available albeit Behringer watts :smirk:

Why can't coil be as large as needed? Good heat dissipation? OK, now is the time for you propeller heads to explain the high frequency losses and other inevitable facts of physics that squash my dreams :)
 
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Muchas gracias! This afternoon I also did some reading about how a dynamic speaker works. And magnets. I did the make a magnet with wire, a battery and a nail thing when I was young. (And even with Iron filings -- we were affluent !) :)

News to me that a permanent magnet can have its N/S pole on the inside of a cylinder and the opposite outside. It also occurs that while I love to tinker, that the cone speaker and audio in general is > 100 years old, and it is quite likely that the best of the simple designs (the dynamic speaker) has been pretty much perfected by now :blush:

Still...perhaps someone has overlooked something, and it truly is possible to make a 1000 watts exciter with a few meters of magnet wire, a nail (a really big one!) and some Gorilla Glue :rolleyes:
 
You really don't need that much power, unless your goal is shaking the whole floor and house.

The exciter is not driving the whole mass and air load of the panel. It's not like ordinary driver. In general, panel is a light load and doesn't take much power to be excited, and to be loud.

18x24" panel is too small for your powerful self-made exciter. Try larger.
 
Interesting! I'd like to consider building a completely DIY exciter. Yes I know they can be bought for $20 or even less. But if people can build DIY planar magnetic speakers, why not a DIY coil? I know there are "science fair" project type things on YouTube etc. Yes, you can make a speaker out of a styrofoam dinner plate or a flower pot (well, maybe it is a coffee cup?) But oh no, not me.

I want an obscenely powerful "linear motor" or voice coil. In fact, for this type of speaker design, why not a variation of the "fixed coil" (or moving magnet, same thing?) Just embed a permanent magnet on the panel where you'd put the exciter (easy) and then nearby we place the yet-to-be-designed monster coil/electromagnet. Not the least of advantages would be the coil is fixed and presumably could be scaled to be tolerant of high power. I have several hundred watts available albeit Behringer watts :smirk:

Why can't coil be as large as needed? Good heat dissipation? OK, now is the time for you propeller heads to explain the high frequency losses and other inevitable facts of physics that squash my dreams :)

Hey, Soldermizer
You on right track. It has been donewith 40(!!!) inch cone and 3 inches of xmax! Look https://www.youtube.com/watch?v=yt8NLFsBWxw and here AV: Huge New Avalon Hollywood Subwoofer Installation Driven By Powersoft M-Force - Pro Sound Web
Subscribe.
 
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CLS: Yes, no doubt too small the panels. I was hoping for a bit more bass. Probably my alignment of the voice coil is not perfect (there was more bass while adjusting it.) Still, they have very good mids and fun to listen to.

I think I will be buying some 4x8 of neutronium panel or similar next time at the home improvement store :)

PartsExpress has exciters as cheap as <$2.00 each but they are really small and I do want something that will shake the panel, if not the entire house :)
 
Neutronium panel? What is that?

I haven't built any panel with frame. They are all free edged. I remember seeing one vibrating quite a lot when playing loud bass. The amplitude was about several mm, clearly visible. The exciter is actually riding on the waves actuated by itself. Very interesting.
 
Neutronium = "unobtainium"; actually neutronium probably does exist but not on Earth, and if it did it would be way too heavy to lift. :) I was being silly, as I often am.
'
I have already found two more full rangers to use: I have a total of 4 small coax auto speakers from a year ago (also a project I was "infected" by someone here ... the stereo speakers in a box for PC monitor.) More realistic: I am going to Lowe's and will get one or two 4x8' panels of whatever is cheap! For my "exciters" rather than completely disassemble them which is much trouble for little gain, I'm going to try something lazy with (of course!) Gorilla Glue: make the "puck" to be hardened foam inside the existing cone. I will advise on how/whether this works...
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How hard is the foam? How does it sound when you tap on it with knuckle?

For 'rigidity' here, you need a microcosmic view.

For example, a piece of paper can't stand up straight by itself, it'd mostly bend down. OTOH, a piece of PS foam board is strong enough to be flat and straight by itself against gravity regardless of orientations.

However, for transmitting sound waves, paper is more rigid.

For you foam block, if it doesn't sound like a piece of wood when you tap it, it's not hard enough.
 
I think I have to use 3 different meterials to handle all the spactrum, 3 isolated zones: for lows (porus material), mids (the pink material) and highs (glass or aluminum). No crossOver just phisical atenuation...semipistonic...Soldemizer style for bass, but 80 watts for me will be enough.