Uncle Ants said:Hi Graham, Thanks for this. Just by coincidence I did a google trawl and downloaded this program a few hours ago and been messing with it. Is the aim to adjust the volume and port tuning to get an absolutely flat response that tails off or is the aim to get the response as wide as you can between the 0 and -3db lines?
I can go bigger (by quite a bit - probably up to 150 litres). If for example I plug in 150 litres and a the port tuned to 25Hz, the reponse extends a bit lower (though admittedly not by a whole lot) but starts to drop off far earlier, albeit very gradually so that it doesn't dip below -3db until it gets down to 25Hz (see attached graph nb. the pink line is the recommended 87 litre box and the green a 150 litre).. Sounds like not a lot gained for a lot more box, but I've got no experience interpreting what these things mean in practice.
Any idea roughly how much extra volume would be needed to account for X over and cable resistance?
Lordy mama - where to start? First off, your graph and analysis are spot on..as you said, you can either have a 'bit more' at the very bottom - and lose a few dB @ 45Hz or have a 'maximally flat' curve to use the jargon. Not a lot gained is also how I would describe it
The trouble with modelling the passive bits is too many unknowns.
If you use their x-over, you would start by measuring the DC resistance of the inductor that feeds the bass driver, then add the resistance of your speaker wire. It might come to say 1 ohm..
Re = 6.3 ohm [datasheet] + 1 ohm = 7.3
7.3/6.3 = 1.159
1.159 x Qes = 0.5005
Qms = 5.32 [datasheet]
[ 1/.5005 ] + [ 1/5.32 ] = 2.186
1/2.186 = 0.45746
This is the new Qts and has gone from 0.4 to now 0.457 which sounds trivial but isn't. If the Q is above about 0.5 you will never achieve a curve like your 150 litre box line because the Q is too high. Try making a new driver model in WinISD with the new Qes and Qts [ call it DC 200 + 1ohm] and see how the new curves need much bigger boxes