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 12th January 2011, 12:25 AM #3 mashaffer   diyAudio Member   Join Date: Jun 2004 Location: Indiana Might find this interesting... http://6p3s.com/images/articles/ML_TQWT.pdf __________________ Generic Signature
 12th January 2011, 01:45 AM #5 MJK   Account disabled at member's request   Join Date: Feb 2002 Location: Clifton Park, NY From my site, this is the best description of what I have called mass loading of a TL or TQWT. I am guessing that this is what you are referencing. Enclosure Design and Construction for the Lowther DX Series of Drivers "The ML TL enclosure can be thought of as a form of transmission line where quarter wavelength standing waves are used to provide the spring for the mass of air in the port. To physically model a straight uniform TL, clamp a yardstick to the edge of a counter or desk and pluck the free end so that it starts to vibrate. The vibration pattern is analogous to the air velocity in a TL. The TL's air velocity is zero at the closed end as is the yardstick's motion at the clamped end. The TL's air velocity is a maximum at the open end as is the yardstick's velocity at the free end. There are two ways of changing the frequency of vibration for the yardstick. If you shorten the length cantilevered off the counter, the frequency of vibration will increase. Make the length longer and the frequency decreases. This is how straight TL's have traditionally been tuned by adjusting the length. The second way of tuning the frequency of the yardstick is to add a lump of mass to the free end. Put a piece of modeling clay on the free end and watch the frequency decrease. What I have done to the classic TL is put a lump of mass at the terminus end using a restrictive port. For a given frequency, I can shorten the TL (make it stiffer) increasing the tuning frequency and then add mass (air in a port) to pull the frequency back down and get a similar tuned result. One other benefit of having a lump of mass at the terminus is a rolled off port output above the first quarter wavelength resonance. This result is similar to a bass reflex port's response. I did this first with the ML TQWT and then with a straight TL. If you try the yardstick analogy, I think by changing the length and adding mass to the end you can demonstrate to yourself exactly what I am doing in my MathCad computer models."
 12th January 2011, 07:07 PM #6 chrusion   diyAudio Member     Join Date: Jan 2011 Location: Chattanooga, TN, USA Martin, Thank you! That was very helpful. I had a suspicion that the mass referred to had something to do with air volume/pressure/damping/etc. when coupled with QWL designs rather than the three definitions above. Your analogy of the vibrating ruler was superb. . __________________ Dean A. Scott, mfa owner / animator, chrusion | FX
 13th January 2011, 08:53 PM #7 Thawach   diyAudio Member     Join Date: Dec 2007 i ever had the simple thought when no has mass loading. it's like i flying on the moon with my apollo 11. this make the sense to understand the mass loading __________________ The Four Noble Truths & Mental Factors
bentoronto
diyAudio Member

Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Quote:
 Originally Posted by head_unit snip Mass loading thus means techniques which increase the air mass load. For instance, sticking the speaker on a horn lets the speaker "grab" the nearby air more efficiently. snip
Right

Thoroughly stupid, when think about it, trying to vibrate the thin air with any kind of precision by shaking a massively heavy block of cardboard, even with a very strong motor (magnet).

Mass loading is crucial to good sound production just as shock absorbers are to a car and for analogous reasons.

(In reply to head unit, woofer horns do try to create air mass loading. And in such cases, they do increase efficiency through impedance matching - although efficiency per se tends not to be an important goal now-a-days.)
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Last edited by bentoronto; 14th January 2011 at 08:49 AM.

David McBean
diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by chrusion That is, it seems to be used more frequently as a generic term in many cases of enclosure design and less often as a specific procedure.
Hi Dean,

Mass loading usually means that the enclosure design includes a port or tube open at both ends that is short enough so that the air in the tube moves as a whole, without appreciable compression. In other words the component behaves primarily as an acoustic mass.

If a tube rigidly closed at one end is used instead, then the air will be compressed and the component acts primarily as an acoustic compliance.

Kind regards,

David
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