If, for instance, a line has a decreasing area with a taper ratio of 10:1, its effective length will be about 63% longer than its actual length as far as the 1/4-wavelength resonant frequency is concerned. Similarly, a line tapered at 5:1 will have an effective length that's about 40% longer than its actual length. In addition to having a longer effective length, a tapered line also reduces the magnitude of response ripples at higher multiples of the 1/4-wave resonant frequency.
Paul
Paul
Looking at reviews and specs of the PMC DB1 Gold the quoted effective line length is 1.5 metres, but looking at sketches and a cross section the actual line length is about a meter or so.
I wonder what the difference between effective line length and actual is?
Thanks
Simon
I agree it is more an extension of the TL with an offset terminus. If you wanted to make a band stop filter (or stub) the aspect ratio should be long and then and not a square box. Also, as a band stop filter it should be densely stuffed. When modeling such stubs in AkAbak I use basic 1/4-wave equation to size them. So pick a peak you want to flatten out, take freq of peak and multiply by 0.03266 in/Hz and you get the length of your stub. The efficacy can be quite dramatic if placed in correct location. For instance in the compression section of a TH and you really smooth the first peak overshoot at the HF.
Just so. They can be useful, although like all notch filters, they have their disadvantages too. I've used variations a few times in QW boxes, horns (OK, another QW box type, albeit a different subtype) etc. I believe Martin King has also. In general, I prefer other methods of killing harmonic modes, but it's one to keep up the sleeve if necessary.
For reference:
1. There's nothing special about the transmission line on a PMC monitor. The output IS NOT in phase.
2. The speaker being demo'd there has a vifa tweeter and SB Acoustics woofer.
3. Capacitors on tweeter are typical solen, with cheap electrolytics on bass and compressed ferrite dust cores (if I remember correctly)
4. PMC have built there trade by mastering the art of squeezing high performance out of strictly mid-range components. With strong engineering in the design phase and excellent control of component tolerances they produce products which they claim to be 'more than the sum of there parts'.
For what it's worth, I think PMC make some great sounding speakers and offer excellent value for money for what you get, but just a personal opinion.
I also think you can improve almost any mid-range PMC speaker with a re-designed crossover, but I feel that about most speaker companies... ah well.
1. There's nothing special about the transmission line on a PMC monitor. The output IS NOT in phase.
2. The speaker being demo'd there has a vifa tweeter and SB Acoustics woofer.
3. Capacitors on tweeter are typical solen, with cheap electrolytics on bass and compressed ferrite dust cores (if I remember correctly)
4. PMC have built there trade by mastering the art of squeezing high performance out of strictly mid-range components. With strong engineering in the design phase and excellent control of component tolerances they produce products which they claim to be 'more than the sum of there parts'.
For what it's worth, I think PMC make some great sounding speakers and offer excellent value for money for what you get, but just a personal opinion.
I also think you can improve almost any mid-range PMC speaker with a re-designed crossover, but I feel that about most speaker companies... ah well.
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