Originally Posted by Ricci
... ports are only effective over a limited bandwidth of about 2 octaves.
I'm trying not to dispute every single thing point by point but finding it difficult to resist...
WinISD (with port resonances turned off) might agree with you but that's a very simple model.
That's just a random model I pulled up, first graph is summed response, second graph is port vs driver contribution that makes up the summed response in graph 1. This port response should be remarkably accurate if you do an accurate port near field measurement. Ports are not restricted to a single massive spike. They have a big influence way up high. In fact that's exactly why they visually contribute to spikes up high in frequency way above the port tuning. I don't know what software you use (I assume WinISD with port resonances turned off) but it doesn't seem to accurately reflect reality.
I've seen at least a couple of examples of people doing a near field port measurement and being completely confused about what they see. Then I model it for them with 1/4 wave software and it's clear to see why the port has significant output way above where WinISD says it should.
Hornresp and Akabak will also show the same thing as shown in this pic. WinISD with port resonances turned off will not, it shows a single spike with much higher q. This 1/4 wave model simulation software shows the generally accepted way that ports work and it's pretty easy to measure if you don't believe it. Just be very careful to only capture the port output.
(blue dotted line in graph 1 is IB response, just disregard that.)Edited by diy speaker guy - 12/10/12 at 5:15pm