Vent surface area affects db output?
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Originally Posted by NoTLaDStyle
It seems like the surface area reduces the auduble output.
I had been using a single 3" round vent for my 12 so far and when I lowered the tuning freq from 35 to 31 I lost 3db in sound, Im pretty sure the lengthening of the tube clipped the backwave and lowered my db output. I doubled the area by adding another pipe and recomputing the lengths/volume and it seems to have opened up the low end significantly.
From this:
To this:
I wasnt sure if the fact that the port was at a 0 degree phase and now is at a 90 degree phase would have anything to do with it either.
WinISD doesnt computer port efficiency beyond whether or not it will whistle. Anyone (toby) able to compute the loss of output due to insufficient port surface area?
I had been using a single 3" round vent for my 12 so far and when I lowered the tuning freq from 35 to 31 I lost 3db in sound, Im pretty sure the lengthening of the tube clipped the backwave and lowered my db output. I doubled the area by adding another pipe and recomputing the lengths/volume and it seems to have opened up the low end significantly.
From this:
To this:
I wasnt sure if the fact that the port was at a 0 degree phase and now is at a 90 degree phase would have anything to do with it either.
WinISD doesnt computer port efficiency beyond whether or not it will whistle. Anyone (toby) able to compute the loss of output due to insufficient port surface area?
I can't find anything that would effect pure output, once you are over the whistling point. What I think it is, is the effect of port harmonics, which is basically the vents tendancy to resonate.
Insert cool graph here. This is just something I threw into bassbox, but you can see that one plot is almost 6db louder at 40 hz. All I did was give the port 3x the area. Tuning frequency remained the same. If I used a pure response curve, and didn't plot vent resonance effects, these curves would lie on top of one another.
Since this is just resonance, it would probably have a negative effect on sound quality, since phase and group delay will both be off at that point, which will effect transient response. But, it will be louder, and at lower frequecies, the phase and GD probably aren't real noticable to most people.
I don't think the 'phase' of the port has anything to do with it. Output at the tuning frequency is almost exclusively from the port, so there is really nothing to be in or out of phase with (except the original music, but that's another story). And your 'clipping of the back wave' just made me chuckle.
Toby
Last edited by TJElite; Jul 25, 2006 at 07:11 AM.
