Straight ML-TLs are two summed resonant structures of which one is a 1/4 WL and the other a 1/2 WL resonator, so there's an unbalanced number of both even and odd order harmonics, ergo the system is non-harmonic in its passband, comb filtering with the driver's harmonics, screwing up its response until the vent's output has decayed to ~ -25 dB.

GM

As an example of what I am trying to say, please refer to Appendix C of my TL alignment tables article. I have displayed the results for three TL's (tapered, straight, expanding) all tuned to 30 Hz. The fundamental 1/4 wavelength resonance is at 30 Hz for each geometry but the 3/4 wavelength resonance is at 120 Hz only for the straight TL. I won't go into the mode numbering schemes because I use a different method of labeling. Maybe we are talking about different things or I have misunderstood the thread discussion.

Martin

?

The only way that a 1/2 wave mode can be supported is to have a node at the top and closed bottom of the pipe, and this fundamental would be twice that of the 1/4 wave mode. In this case, that would be 80 Hz. Since the 1/2 wave mode is trapped between the ends, it would produce no output but would modulate the driver. I don't see it in the model above, nor do I remember you mentioning 1/2 wave modes in stopped pipes.

See Modeled/actual comparisons.

Bob

What is the pipe diameter and length?

Martin

Would you like to see the plans, just for grins?

Bob

Martin

The vent is a 1/2 WL resonator with its own harmonic structure activated by the 1/4 WL pipe's pulses, creating a very non-harmonic summed system as clearly shown in the 'woofer and Terminus Far Field Sound Pressure Level Responses' plot. Driver and/or vent locations away from the ends just screw it up more.

GM