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Thank you for the very informative post!. Considering the level of dificulty in the actual tuning of the transmission line system, is there any instrument that one can use to insure that the phase of both port and driver are the same?
Thanks; Wade
You are not so much concerned about the phase of the line opening signal anyway, so measuring this might be somewhat misleading.The best way to assure T-line tuning is to measure a very accurate and detailed impedance curve, so as to assure a nice flat curve at driver resonance. To little damping causes the classic double hump of a vented cabinet, while too much starts to look like a selaed box, with a single mild peak at system resonace.
The frequency of this dip or slight hump is the tuning frequency, and it should be in the middle of the impedance lumps/humps that are residual.
Ideally, a perfectly tuned line would look like a resistor, but most well tuned lines have a hint of a very braod and mild hump, due to a slight amount of overdamping. This is preferable to ANY amount of dip.
Jon Risch
Jon;
Please correct me if I'm wrong, but once I have the impedence curve as flat as possible, if the TL does not reverse the phase of the drivers rear output, then, rather than reinforce the frequencies near the drivers Fs, Ill get a cancelation or a "blurred" sound in that frequency area.Plus I feel that if I slow the rear energy enough I can shorten the TL to a minimum. What do you think?
Wade
I suggest you re-read my T-Line note, and realize that once you get the impedance curve right, the line output will be approx. in the correct phase. However, this is still immaterial, as the rear wave from a true transmission line is not a significant portion of the output.Jon Risch
Thing is, Jon, that the impedance curve is right, and I still havent started with he TL yet. I did this with a special aperiodic fiberglass mat.All I want the TL or PORT to do, is reverse the phase of the rear output, which, becasue there is only a 2" mat covering it, is a considerable portion of the output.
Thanks for any ideas.
Wade
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