Please check my measurement space math!

[head_unit]

I posted the below in another thread, but it has been a long time since I did this calculation and I am suspicious I made a mistake. Please take a look and see where I goofed, thanks! (I think the process is correct, but I just don't believe the 88 Hz figure)

"To get a proper measurement really needs a big chunk of open space. At one job I used to measure transducers mounted in a drop-ceiling baffle, 8 feet above the floor = 2.44m.
For a 1 meter measurement distance, this meant I had 2x2.44-1=3.88m before the floor reflection would bounce back to the microphone. Using the acoustic formula v=f*l (in this case, speed of sound = frequency* wavelength) then 343=f*3.88 and f=88Hz. So I would be getting "real" data points every 88 Hz.
Anyway, to match that reflection-free distance all around, imagine a half-ellipsoid with the tip on the floor and the equator at the ceiling. The width of the ellipsoid would need to also give 3.88m of clear space. This means roughly the nearest furniture or protrusion of any kind must be roughly >1.9m away.

[head_unit]

Nobody?

Let me simplify greatly: if I had, say 8 mS before reflections contaminated the direct sound from a speaker I'm trying to measure, what frequency can I measure down to? (Assuming an FFT measurement system, windowing out the reflections)

[dantheman]

this should help:
Frequency, Wavelength, Time and Distance Calculator

Seems like you're in the right ballpark, but the impulse response will let you know.