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Old 28th February 2021, 07:21 PM   #41
David Morison is offline David Morison  Scotland
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Well, I know a lot less about amplifiers than I do about WinISD, so I don't think I can really answer that, I'm afraid, sorry.

The conversion of watts to volts for the output of the amp should be pretty straightforward, though: Volts = square root of (Watts x Impedance). Basically it's just combining Ohm's & Watt's laws. It shouldn't matter what topology the amp itsself uses, if it does 280W @ 4R, that should be the output voltage.

Cheers,
David.
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Old 1st March 2021, 03:16 PM   #42
kipman725 is offline kipman725  United Kingdom
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in an ideal case a single rail BTL amp can generate a peak to peak voltage swing of 2* its rail voltage.

E.G 48V supply,
1) Maximum peak to peak voltage = 96Vpp
2) This coresponds to a sine wave with RMS = Vpp/(2*sqrt(2)) = 33.94 V
3) Power can then be calculated P=V^2/R = 288W (into 4ohms)

Thinking about it in terms of what is the maximum voltage swing the amplifier can put across the load will allow easy calculation of any design. E.G a non BTL amplifier would only get 1/2 the voltage swing and so would have 1/4 the output power.

Real world power is a bit lower as 100% modulation can't be achieved by the output stage and there are Rdson and other losses in the output devices and filter.
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Old 2nd March 2021, 08:36 PM   #43
zerokelvin99 is offline zerokelvin99  United Kingdom
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Thanks David,

And cheers kipman,

RMS not peak... Suddenly everything makes sense! Thanks for the simple step by step for the maths too

-

Turns out as well, never trust bags internal dimensions when they list them online. Turns out the actual internal measurements take off near 10L of volume.

Been doing some creating mock fitting of MDF in this bugger to see how I can squeeze it back up to 40L usable volume. (And the layout has swapped round to fit w/ ports next to the H100 horn, pictures soon)

It's 'only' 1-1.5dB of gain at Fb, but would be nice to get it back if possible..
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Old 3rd March 2021, 12:12 PM   #44
kipman725 is offline kipman725  United Kingdom
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Mylar bags filled with Sf6?

or more praticaly activated carbon:
KEF - ACE - United States
I heave heard that pearlite also works.
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Old 11th March 2021, 03:51 PM   #45
zerokelvin99 is offline zerokelvin99  United Kingdom
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Hmm, looking into pearlite, I can't see any direct evidence or proof of it working unfortunately.

Funnily enough, in a previous role one of my projects was integrating activated carbon as a lowband absorber into commercial products. The absorption below 1kHz left traditional foams in the dust. Dust being exactly the problem we weren't able to overcome unfortunately, as acoustically transparent and almost gas tight were often at odds. (Even with some ultra-thin latex from ""special"" sources )


Been a bit stalled on this, as realistically the bag I had was too small. Ended up buying a new one, and now have the MDF mockup fitting nicely inside with resultant internal back to 45L. Found a local source of poplar, so just need to generate some DXFs!

Oh, and these arrived. The 12" is hilariously light, and the 1" is simply minuscule

Edit: Didn't see your SF6 comment.. Not sure about that hah!
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Old 12th March 2021, 10:24 AM   #46
kipman725 is offline kipman725  United Kingdom
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Some info on SF6 as a speaker filling here:
Filling a small subwoofer box with Sulfur Hexafluoride?
realistically though some other ultra dense gas would have to be used as SF6 is been phased out as its a very bad greenhouse gas. There is also someone in the thread claiming it works but I haven't tried it myself.


I also found this paper on the activated carbon, I think you would put it inside some kind of sock that allowed the gas to flow freely but prevented dust escape:
https://pdfs.semanticscholar.org/572...c311fe32ca.pdf
it seems to work very well at reducing the tuning frequency of their Helmholtz resonators by upto 35%. The question for me reading this is in a ported system is the port output also going to be reduced significantly by the activated carbon?
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Old 12th March 2021, 01:06 PM   #47
kipman725 is offline kipman725  United Kingdom
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I also found this Thesis which looks to be embargoed till August:
Acoustics of activated carbon - University of Salford Institutional Repository

*various whispering on the internet that pore size is critical
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Old 12th April 2021, 03:04 PM   #48
zerokelvin99 is offline zerokelvin99  United Kingdom
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Nice, will probably give the activated carbon a go once I've built this up!

Bit of an update since it's been a month..

Design and FEA modelling has been finalised. All parts have been CNCd / 3D printed & sheet work cut+formed.

Attached a couple of images of brace subassembly, elliptical port flares and connection plate. Will try to get a screenshot of the full design CAD up at some point too.
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File Type: jpg 2.jpg (486.5 KB, 38 views)

Last edited by zerokelvin99; 12th April 2021 at 03:06 PM.
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Old 12th April 2021, 03:52 PM   #49
kipman725 is offline kipman725  United Kingdom
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Elliptical port flares? something like this? https://www.comsol.com/paper/downloa...zola_paper.pdf
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Old 12th April 2021, 04:11 PM   #50
zerokelvin99 is offline zerokelvin99  United Kingdom
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Exactly, based off a different white paper but same approach.

Velocities are in the mid 30s, so hoping to keep flow profile sensible on port exit, minimising losses at high output. Will be interesting to measure the effectiveness.

Mid section is straight pipe (less flow critical) to enable length changes.
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