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Multi-Way Conventional loudspeakers with crossovers

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Old 29th April 2008, 12:29 PM   #361
gedlee is offline gedlee  United States
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Default Re: Re: Re: No More Re's!!

Quote:
Originally posted by MJL21193



Here's the way I see it: With the drivers mechanical motion you have inertia. The lower frequencies need a longer excursion of the cone to produce the same spl as a higher frequency at a lower excursion. The further the cone travels, the more opposing force,


Unfortunately this statement is not true. F = ma , acceleration not displacement. The force between the voice coil and the frame is constant with frequency. The kinentic energy of the cone decreases with frequency above resonance.

Quote:
therefore more kinetic energy to deal with. It's easy to visualize when you think about how a long throw woofer will make a box "walk", as opposed to a midrange or tweeter that, even if hanging in free air, will not move very much (if at all).

I agree about the driver flanges. It's not practical to leave it loose on the baffle. I do like Dave's solution, where the magnet is directly coupled to a brace. This channels the mechanical energy from the driver into the box structure, and not into the baffle.

The question remains: What happens to this energy if there is nothing to dissipate it? (such as panel damping).
If properly done this energy is all radiated as sound from the speaker.
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Old 29th April 2008, 12:30 PM   #362
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Simple funny "experiment"

Hold a playing woofer in your hands, and there will be no bass
Then place it on its magnet on the floor, and suddenly there will be pounding bass

btw, if its true that lower frequencies than box plate ressonance wont exite the plates to ressonate...THEN a sub used below 50hz wont need any bracing at all
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Old 29th April 2008, 12:54 PM   #363
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Default Re: Re: Re: Re: No More Re's!!

Quote:
Originally posted by gedlee


Unfortunately this statement is not true. F = ma , acceleration not displacement. The force between the voice coil and the frame is constant with frequency. The kinentic energy of the cone decreases with frequency above resonance.
I find it interesting that you would disagree.
Here's a screen shot from Linkwitz' site.

It clearly illustrates what I'm saying.
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Old 29th April 2008, 02:56 PM   #364
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I do not think this has been mentioned, but here is an interesting link to add to the debate. It is written by Peter Comeau of " World-Designs ", and you can find it at, " www.speaker-parts.eu/info/ ". Peter is a highly regarded speaker designer with extensive experiance in the commercial sector ( Heybrook Mission ). Here he explains his preference of 3 core particleboard to MDF plus the qualities of Birch ply. Peter now offers DIY designs which have been published in Hi Fi World. He recommends particle board for the main enclosure covered with 4mm mdf for better finishing, and MDF for the front baffle for ease of machining. I am surprised that Dave of " Planet 10 ", has not mentioned this as he took part in the various debates on thier forum, still go and read it.

My interest in " CLD " was recently revived by watching a documentary on the deHavilland Mosquito, the ledgendry WW11 fighter bomber, which I think a lot will know was largly constructed from wood. It was known as the " wooden wonder " or " timber terror ". This was briefly debated in a thread on " Balsa Cabinets " back in Jan 2006

The fuelage and wings were constructed from a Birchply / balsa composite, namely 2mm ply skins with 9mm balsa centre. The strength of the structure allowed minimal bracing for lightness. The wings had a load capacity of 41 tons, each of which carried a 12 cylinder 1620HP engine. Then of course you had the crew, fuel, instrumentation, bomb load, plus the overall stresses and strains, and G forces, all of which shows the strength of the structure.

So perhaps we ought to take an other look at this type of panel. Using say, solid wood edging for attaching the front baffle, etc, some bracing, damping pads ( ? ), this may well be an excellant cabinet material, though obviously not off the shelf. If it is good enough for the above I think it should handle some loudspeakers

Roy
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Old 29th April 2008, 04:32 PM   #365
GM is offline GM  United States
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For sure this is a good way to go and at least one prosound manufacturer feels it's worth the extra effort, though IIRC it's based on foam core structural wall technology.

GM
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Old 29th April 2008, 06:24 PM   #366
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Quote:
Originally posted by Roy Lewis


The fuelage and wings were constructed from a Birchply / balsa composite, namely 2mm ply skins with 9mm balsa centre.

This is a structural sandwich, which will allows an exceptionally strong panel (resists deflection) from relatively light and weak materials.
Hollow core doors are built this way, except they use a cardboard honey comb on the inside.
We talked about this before, on the other thread (linked by Dave at the start of this one).
This method is effective, but is it less complicated than proper bracing techniques used with regular panel material?

If you could make the interior layer for the entire box in one piece and the exterior layer the same way then fill the void between with urethane foam, this would be quite dead, don't you think?
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Old 29th April 2008, 11:50 PM   #367
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Quote:
Originally posted by MJL21193
If you could make the interior layer for the entire box in one piece and the exterior layer the same way then fill the void between with urethane foam, this would be quite dead, don't you think?
This is what Rockport is doing for their megaBuck speaker.

http://www.stereophile.com/floorloudspeakers/644/

Click the image to open in full size.


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Old 30th April 2008, 12:01 AM   #368
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There's a more indepth discussion on construction of newer Rockport models here:

http://www.soundstage2.com/tours/rockport_200702/

Not very often I lust after commercial gear but the Rockport Altair is one of the few. They'd have to do something about those dome tweeters though.
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Old 30th April 2008, 01:47 AM   #369
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Default Rockport

And here I thought your latest creations were of devine inspiration...

That high gloss finish is my next addition to the cherry dipoles,btw...as I recently refinished the doors on my sons car with automotive clearcoat...

John L.
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Old 30th April 2008, 02:35 AM   #370
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Default Re: Rockport

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Originally posted by auplater
And here I thought your latest creations were of devine inspiration...

That high gloss finish is my next addition to the cherry dipoles,btw...as I recently refinished the doors on my sons car with automotive clearcoat...

John L.
They are most definitely poor man's Rockport's, I borrowed heavily from their styling cue's.

Be sure you take up Buddhism, you'll need the meditation once you start spraying wood/MDF.
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