Toon Town Dave wrote:SoundInMotionDJ wrote:That said, a 5" speaker at head height is not able to couple to the ground at all...and it likely 180deg out of phase at between 50Hz & 60Hz. That is not good for lows.
Huh? How can the out put of a single speaker be out of phase let alone out of phase at particular frequencies? What do you mean "couple to ground", do you mean in a mechanical or electrical sense?
Ahhh...so many questions...here goes:
By "coupling" I am referring to "boundary loading". The floor is a boundary. If the source is within 1/2 the distance of the radiating plane, then the boundary loading "coupling" will occur. For a 15" direct radiator, that means within 7.5"...which can be rounded to "on the ground."
Below 100Hz, sound is "omni directional."
At 40Hz, a sound wave is about 28ft long.
At 100Hz, a sound wave is about 11ft long.
If a reflective surface is 1/4 wavelength away from the source, then the reflected wave will be 180deg out of phase (i.e. 1/2 wavelength total travel).
At 40Hz, 1/4 wavelength is 7ft.
At 100Hz, 1/4 wavelength is 2.8ft.
So, the Prime directive of speaker placement is "never put a sub between 2.5ft and 8ft from a boundary".
If you have PC speakers with a separate sub woofer...try this experiment. Place the sub on the floor, and point it into the corner. Keep the sub about 3-4" from the walls. Notice the increased low frequency sound.
Here is a distance -v- frequency chart for boundary cancellation:
http://www.padrick.net/LiveSound/CancellationMode.htm
Toon Town Dave wrote:The frequency response spec for the SRM150's is 100Hz - 17.5KHz so I'd expect little at 100Hz, and nearly nothing at 50Hz anyway.
Well then...nevermind. That would certainly explain the lack of low end.
--Stan Graves