Originally Posted by acras13
Is the reason I can't really take your design concepts seriously .
That's ages ago.
Since then I did simulations that showed that these two use the same material amount per square foot:
Even though one is clearly superior to the other in panel movement.
And I also discovered that diagonal bracing uses half the material but achieve nearly the same panel movement:
Thus if we combine the two, like in my design for example:
Then we get darn good results.
Internal air pressure: 1000 pascals.
Such internal air pressure achieved at driver wattage: 1800w rms.
Bottom frequency that can achieve such air pressure without exceeding xmax: 120hz (so it is assumed 150hz to be well within safe limits, using 3.5 out of 5mm xmax then).
Power handling of 15" mid that can handle this: 1700w AES (1700w rms pink noise 2 hours).
Noise achieved from panels: 65db at 150hz.
Internal pressure drops off from 150hz upwards, but I will check what the panel movement is at lower internal pressures as well just to be safe that the noise produced by the panels isn't higher than 65db towards 1000hz where the mid will hand over to the compression driver.
Radiation pattern assumed in all db figures: 2.0 X Pi (so floor loaded, no walls or ceiling).
Signal/Noise ratio achieved: 65db (65db noise, 130db output, 130 minus 65 equals 65).
It stands to reason that we can assume the ratio is true for lower putput, so 120db has 55 db noise, 110db has 45db noise, etc.
In day to day use the enclosure will be used with 50hz highpass filter instead of 150hz highpass filter, and instead there will be two woofers on either side. As such the output level will be limited to about 120db a piece (all assumptions about db is in 2.0 x Pi radiation). But it stands to reason that the noise will then be equally far below, so 55db or so from the panels at 120db. Which is darn good I'd say.
For special occasions (read: parties and demos) the mids will be cranked up to 150hz filter and then:
The cross-members in the middle that you can see are cut off in the middle are also held in place with frictionless constraints so they can't move towards the camera or away from the camera, but they can move in the two other axis. But these cross-members show significant resonance so they too must be braced in the final version. Probably vertically in this view.
If someone on AVS forum could just have told me this to begin with, I would never have bothered to share my WRONG idea of how to most effectively brace enclosures. And I also would not have to bloody teach myself this if someone already had designs which could say how much noise they produced from flapping panels. "These window braces cause little enough
panel movement" is hardly enlightening.
PS: Does anyone remember what 21" subwoofer thread it was that measured with and without pillow stuffing?
If I remember correctly it was -2db that was the result with two extra pillows in a 21" enclosure with very low tune. I'm betting you will lose more db if you have a higher tune and get higher overall output. I really want to test that on this enclosure.
PPS: The simulation is a quarter of the enclosure, in case you hadn't worked that out. The other pieces are equal to this piece, just mirrored across one or two axis.
PPPS: I worked out db noise from using this tool.
We can argue a lot about what speaker diameter to use and which average xmax figure to use, of course. I arrived at about 65db from my guesstimate. If we take the wavelength of 150hz and see how much the other four sides can add to each other (sum up) in db we could probably do some more accurate figures.