Pipe organs suffer from resonance?
Pipe organs don't suffer from resonance, they use it. But for the resonance of pipes, the king of instruments would be silent. Each pipe is tuned to a specific pitch. Most pipes are flute type, flue, pipes open at both ends. The shaping of the pipe, its metal content and many other factors determine its harmonic content. The open pipes radiate even harmonics. There are sets of pipes with one for each note. These are the ranks. Each rank "speaks" when the appropriate stop is pulled. Each stop has a different harmonic balance. This gives each stop its unique sound.
The ranks are laid out in order on the wind chests to make a division. Now the keys are the y axis of large graph board and the stops the x axis. When a given x and y line up a pipe speaks. In the mechanical organ this is done with sliders actuated by trackers. The keys go up and down the x axis and the stop sliders the y. There is a hole in each slider, for each pipe to allow air from the wind chest to get to the pipe. When holes in two sliders line up the pipe speaks.
There are reed stops that have a vibrating reed at the mouth, such as the trumpet, tuba and genschorn stops. In organ pipes you need lots of harmonic content in addition to the fundamental (the tuning) frequency of the pipe.
There are also the pipes, usually made of wood, that are closed (stopped) at one end. These are the gedackt pipes. A pipe closed at one end has a fundamental half the frequency of an open pipe of the same length.
Now it is these latter gedackt pipes that are of interest to the speaker designer. The closed pipes radiate odd harmonics. These are not generally considered as pleasing as the even harmonics.
Now an organ builder wants rich harmonic content, the speaker builder does not. However the gedackt pipe can be adapted to the speaker builders needs.
The crudest adaptation is the cylinder speaker mentioned in this thread. This is a straight cylinder, whose length is half the wavelength of the fundamental. The fundamental, and therefore the area of reinforcement to the speaker driver is narrow. The odd harmonics are generated because the speaker is at the closed end of the pipe. These are suppressed with the fiber fill.
Now if we take our gedakt pipe, give it a reverse taper, that is to say make the area of the closed end three or four times grater than the open end, you broaden the fundamental greatly. This is now much more promising for loudspeaker loading. Now if you place the diver a little further down the pipe from the closed end you can position it to greatly discourage the generation of odd harmonics, especially the loudest third harmonic of the fundamental. In other words you place the diver at the node of displacement of the third harmonic. If we then fold the pipe we suppress HF radiation completely, this is important if the speaker is not a sub. We then fill the pipe uniformly with fiber fill to suppress any residual harmonic content.
Now the pipe tuning frequency and the volume of air in the pipe have to be matched to the Thiel Small parameters of the driver. As I have previously shown this form of loading will augment the bass output of a driver from F3 to 100Hz, 2 to 3db over other alignments. I regard this method as the optimal bass loading for drivers that have suitable parameters.
It is absolutely suited to making the finest of subs. If you ever hear one you will regret it until you have one of your own.
These pictures will give you are good idea of how it is done.
http://mdcarter.smugmug.com/gallery/2424278#127083295
So Joe, you see resonance is not a bad thing. The trick is to make resonance work to your needs for the task in hand.
