Bass "speed" (or timing) as it pertains to frequency response

[Gordonj]

Make sure you keep in mind that any solid reflective surface (reflective to a sub that is) will add 3dB of level. Therefore, place on the floor add 3dB. Place against a back wall and the floor = 6dB. Place in a corner add 9dB to the level of the sub out put. On top of that you will also add and subtract certain frequencies as they combine and subtract due to phase anomalies caused by the reflections. Those reflections can be calculated by 1/4 & 1/2 wave calculations. This is also refered to as "comb-filtering".

Also remeber that LF are very large waves by nature. Some can exceed 4,5,6 feet in size or large and can be very long and take a while to form. As you move the sub, or yourself around the room you can move in and out of certain LF waves.

For the "tightness", that is caused by two more things that have not been discussed here so far - 1) how the sub and system has been tuned ( certain freqs impact the tightness of the sub) and 2) a cohesive wave front. Since the LF take longer to form due to the size of the waves, the subs need to be moved "back" behind the mains. That can be done physically or by the use of a time delay. In most cases a few milliseconds aligns things ( each millisecond is approximately 1.75 feet).

Hope that helps.

Gordon

 

[Gordonj]

I realized that my tendency to over simplify things might have got the best of me here so, I wanted to clarify some things i suggested -

The size or length of a wave can be determined by looking at the following -

Since we know speed travels at 1087.42 ft/s at STP (standard temp. sea level) we can figure the wave size by the following math.

1087.42 ft/s / f (f=frequency)

Therefore, a 1,000Hz freq wave is 1.09 ft.

A 400Hz wave is 2.718 ft.

A 150Hz wave is 7.249 ft.

A 80Hz wave is 13.592 ft.

A 60Hz wave is 18.592 ft

A 20Hz wave is 54.371 ft.

All that being said. Those are the sizes of the waves that we are talking about (in the lower ones). So, placement of a sub in a room and where the listener is sitting can have a profound effect on if the listener can even "hear" the LF as you could imagine.

If you drop two subs in a room and separate them then you can also add in something that is referred to as "power ally". This is an effect where two waves actually combine at some freqs and cancel at others. This effect creates a comb filtering effect where bass frequencies cancel each other. Please keep in mind that this comb filtering only impacts a system when the speakers are sending out the same signals, as in subs. One sub in a room is generally better then two separated subs. If you need additional sub output, combining the subs in the center (side-by-side) would eliminate the opportunity for the comb filtering. And of course we all know that two subs in the center is not very doable no is it.....

Hope i did not make things worse!

Gordon