file FSP-MAGICBOX

12 years 2 months ago #3780 by jake_fielder
Replied by jake_fielder on topic FSP-MAGICBOX

tommysb wrote: Call it 'the gash frother'


Jesus! thats a bit too hardcore

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12 years 2 months ago #3786 by deadbeat
Replied by deadbeat on topic FSP-MAGICBOX
Thanks, guys...

simon, the secret reason for me borrowing your drawings was for me to view their folding, they're similar to a Martin 215 Mk III as you have been told, but have a difference which allows me to save a bit of space, I think. Thanks!

Hmm....

If worst comes to worst we could buy empty chassis and make our own servo loudspeakers! or skint diy recones for custom specs on an existing chassis. I have a few ideas on voice coil winding, think XBL2 technology (double gap, single coil) inverted (split coil, single gap) for similar results. Actually, this one has me thinking...
[img]smileys/smiley36.gif I'm dreaming alright.
[img]smileys/smiley36.gif
Edited by: Deadbeat

[url=\"http://users.ece.gatech.edu/~mleach/beraneklaw.html\"]Beranek\'s law[/url]
\'bits of ply round a driver\'

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12 years 2 months ago #3788 by steve_b
Replied by steve_b on topic FSP-MAGICBOX
@deadbeat the nexo reference was regarding their high frequency horn which is basically folded. The only relevance to this thread is that if they can get very high frequency sounds round a fold, then it should be posible to do the same with a bass horn

Nexo uses what they call a Hyperbolic Reflective Wavesource which consists of an acoustical reflector (i.e. mathematically calculated hyperboloid acoustic mirror, derived from rigorous geometrical transformations) this creates path lengths from the virtual and real sources,
to the horn mouths that are identical at the coupling points. Where the two wavefronts touch they will therefore be in phase because the pressure wave takes the same amount of time to travel an identical path length to the coupling point, regardless of where its real source is located in relation to that coupling point .

With some rigorous head scratching, trying to remember my A level maths I believe that the equation for a hyperbola is:

x^2 / a^2 - y^2 / b^2 = 1

Obviously deriving a curved reflector from that equation makes all the difference.

For my version, I shall use the more impressive looking equation of an ellipse:

(x - h)^2 / a^2 + (y - k)^2 / b^2 = 1

The fact is that any surface will act as a reflector. Changing the rate of curvature just changes the focal length Saying that one particular curve is optimum is a bit like saying that there is an ideal pair of glasses that will work for everyone with impaired eye sight. It is still a folded horn and having a curved back section won't eliminate the problems associated with folded horns.

Also the idea that if the sound sources all emanate from the same virtual acoustic centre all will be well is wrong. If you had a row of say four of these horns and stood directly in front of one then if you are in the coverage area of the other horns the path length will be different. The problem is that the path difference after the sound comes out of the horn is the problem.

What has all this got to do with bass cabinets. Simple, stop worrying about the design and concentrate on the marketing.

Meanwhile, back with the ported horn.....

Consider collapsing the mouth of the horn down so that it is a simple tube. Drilling a hole in the side of the tube and connecting a chamber to it with a short pipe will create an acoustic notch filter. Moving away from the resonant frequency the attenuation reduces to zero. As I said before, if the port is to increase efficiency below the operating range of the horn, it, the horn, won't increase the gain of the sound radiating from the port. It will to some extent alter the tuning of the port so conventional calculations used for tuning may be wrong.

If you have not seen it already, there is some interesting reading on horns at Martin King's web site.

<a href="http://www.quarter-wave.com/Horns/Horn_Theory.html" target="_blank">http://www.quarter-wave.com/Horns/Horn_Theory.html </A>

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12 years 2 months ago #3790 by deadbeat
Replied by deadbeat on topic FSP-MAGICBOX
Hi Steve,

I now visualise this as a cutaway Newtonian telescope- I think that's sort of right...
If it is, I completely agree about that statement. Thanks for the explanation.

Thanks for the link to Martin's website, I've read his stuff, nevertheless others should too.

[url=\"http://users.ece.gatech.edu/~mleach/beraneklaw.html\"]Beranek\'s law[/url]
\'bits of ply round a driver\'

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12 years 2 months ago #3793 by deadbeat
Replied by deadbeat on topic FSP-MAGICBOX
Back to the design.

jake, how's it going?

My 215 is taking shape slowly but surely. I'm not sure about the form factor though, I have two sketches - one is dimensioned within the constraints, but the other is like a Martin cab - long and flat.

[url=\"http://users.ece.gatech.edu/~mleach/beraneklaw.html\"]Beranek\'s law[/url]
\'bits of ply round a driver\'

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12 years 2 months ago #3797 by deadbeat
Replied by deadbeat on topic FSP-MAGICBOX
Triple Post! I make a new post for each idea...no point sharing posts.

i've got an idea so crazy, it might just be worthwhile.

When these bins are done (or during this), I am thinking of doing a highly modular midtop that would get down to here. It would be done like this:
http://www.delicate.com/f2system.htm
Yes, you read that, it's the Martin F2 system.

The bass bins would replace the F2B, and the mid tops would be highly configurable.

Still a pipedream though.

come on simon, i know you have some interesting dreams.

[url=\"http://users.ece.gatech.edu/~mleach/beraneklaw.html\"]Beranek\'s law[/url]
\'bits of ply round a driver\'

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12 years 2 months ago #3805 by jsg
Replied by jsg on topic FSP-MAGICBOX

Steve_B wrote: Meanwhile, back with the ported horn.....

Consider collapsing the mouth of the horn down so that it is a simple tube. Drilling a hole in the side of the tube and connecting a chamber to it with a short pipe will create an acoustic notch filter. Moving away from the resonant frequency the attenuation reduces to zero. As I said before, if the port is to increase efficiency below the operating range of the horn, it, the horn, won't increase the gain of the sound radiating from the port. It will to some extent alter the tuning of the port so conventional calculations used for tuning may be wrong.


You're right that the throat-ports would tend to attenuate radiation travelling from the front of the driver cone through the horn near the resonant frequency of the rear chamber. But I don't care about that, because at those frequencies the resonance is loading the driver so it is hardly moving anyway.

What I care about is the transfer function from the rear of the driver cone, through the rear chamber and throat port and then through the horn (which would probably be acting as a half-open pipe at these frequencies).

Say we're an octave below the quarter-wave frequency and/or flare rate limit. The horn duct is still givinga littlegain because the gain decays gradually as you move away from resonance. That's gain that can be added on to the output of the rear resonant chamber.

Edit: just been looking at Martin's papers. In Horn_Pysics.pdf figure 5.4, the volume velocity ratio graph clearly shows some remaining gain below 100Hz (which is the horn's nominal cutoff frequency). It may not be much, but at low frequencies every little bit of gain helps, and it therefore makes sense to exploit this one or two dB of gain rather than simply leave the horn doing nothing at these frequencies.
Edited by: jsg

Ars est celare artem

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12 years 1 month ago #3900 by deadbeat
Replied by deadbeat on topic FSP-MAGICBOX
<strike>
I'd just like to say that I'm not dead yet, am still working at my own little box!

Might take a bit of time, this is the grunt stage of development.

Omar

</strike>Screw that, I'm on more exciting pastures. More later.

Edited by: Deadbeat

[url=\"http://users.ece.gatech.edu/~mleach/beraneklaw.html\"]Beranek\'s law[/url]
\'bits of ply round a driver\'

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12 years 1 month ago #4054 by rich_gale
Replied by rich_gale on topic FSP-MAGICBOX
how about a hybriddesign using 2 high excursion 12" drivers and a18" passive radiator in a config similar to a scoop? so the PR unit would be placedat the throat of the scoop.The direct radiating12" drivers will move aboutthe same air as an 18, but will extend upto 200hz a lot easier.



i suppose the design could be labeled as a horn assisted passive radiator cabinet.

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12 years 1 month ago #4060 by jake_fielder
Replied by jake_fielder on topic FSP-MAGICBOX
Do you mean the passive radiator could be placed at the mouth of the scoop, (not throat)?

That sounds like a very interesting idea, although i have never delt with passive radiators, I dont know anything about them... But... do they move in and out far enough for this use? and wouldn't the efficiency of the horn be lost if there was a passive radiator at the end?

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