At what frequency does bass become directional??

[Kevin K.]

You see all of these subwoofers with the drivers facing different directions; downfiring, twin woofers side-mounted in the enclosures, etc. When does the bass become directional and require the driver to face you?

While on this subject, is there a rule for distance from the floor for a downfiring subwoofer?

[Sydney]

Re: At what frequency does bass become directional??

... When does the bass become directional and require the driver to face you? .

There is a bit of confusion in regards to 2 areas:
One: The limitation of human hearing and perception and localization ability at low frequency.
Two: It is more of a case of how big does something have to be to control directivity:
Think instead about the size of the sound radiator and the size of the wave it is propagating.
To control directivity the radiating surface ( or baffle or horn mouth ) has to be LARGE in relation to the wavelength involved.
A 2.0 cm radius piston (ka= 1.0) would be about 3 kHz.
Significant directivity ( Ka= 2.0) does not happen for a 2 inch piston until about 10 kHz.
( Ka= 2.0) for a 20 inch piston until about 1 kHz.
( Ka= 2.0) for a 200 inch piston about 100 Hz.
( Ka= 2.0) does not happen for a 400 inch piston until about 50 Hz. :rolleyes:

[billfitzmaurice]

Re: At what frequency does bass become directional??

Bass goes from omni-directional to directional at the baffle step frequency, where the baffle is one wavelength. But as one wavelength at 100Hz is eleven feet, and it only gets longer as you go lower, directional subs are for all intents and purposes non-existent, in the home at any rate. The driver never has to face you.

[Ray Tremblay]

Re: At what frequency does bass become directional??

Bass goes from omni-directional to directional at the baffle step frequency, where the baffle is one wavelength.

This.

[nigelb]

Re: At what frequency does bass become directional??

This.

If this is the case wouldn't a 1ft baffle have a baffle step frequency of 343 hz? If so that would mean frequencies below that would be omni directional? So therefore difficult to to locate?

[craigk]

Re: At what frequency does bass become directional??

use the KISS method for this. basically any thing below 100 hz is going to be Omni directional 99 % of the time.

[ROTECH]

Re: At what frequency does bass become directional??

use the KISS method for this. basically any thing below 100 hz is going to be Omni directional 99 % of the time.

And with this being said, if you can still clearly and honestly locate the sub with your ears...... Turn it down and get more sub/amp. Hearing the driver/enclosure is different than localizing the bass notes.

[ErinH]

Re: At what frequency does bass become directional??

I'm not so sure about the use of the term "bass", but to determine when a drive unit is no longer omni, the beaming point is what I go by. which is approximately speed of sound divided by the effective diameter of the drive unit, divided by 2. ( you can use 1/4 wave if you like, but 1/2 wave is my rule of thumb)

speed of sound = 13500 in/s (varies with temp; close enough for rule of thumb calculations)
effective diameter = half-surround to half-surround. if it's a non-circular unit, use the smallest dimension.

i.e.;
Driver with 2" effective diameter: 13500/2"/2 = 3375hz
Driver with 10" effective diameter: 13500/10"/2 = 675hz

[craigk]

Re: At what frequency does bass become directional??

yep +1

[scholl]

Re: At what frequency does bass become directional??

For deep bass the baffle isn't important but room boundaries are. Positioning is everything to determine when the boundaries stop re-enforcing bass and we can determine location.

So, for every system in its room that point will be different but 100-300hz is the range.

[Pete Schumacher]

Re: At what frequency does bass become directional??

You can begin to localize the source of the low frequencies somewhere above 100Hz. If the subwoofer has higher distortion, you can localize it even easier.

If you don't want to know where the subwoofer is placed, cross it over as low as possible, preferably well below 80Hz.

[billfitzmaurice]

Re: At what frequency does bass become directional??

If this is the case wouldn't a 1ft baffle have a baffle step frequency of 343 hz? If so that would mean frequencies below that would be omni directional? So therefore difficult to to locate?

A wavelength at 1130Hz is one foot. But that has nothing to do with directional location, which is based on the distance between your ears. We directionally locate via triangulation, comparing the difference in arrival time and phase shift of the sound at the two ears. If the wavelength is sufficiently long we can't directionally locate it because our ears are too close together to discern enough difference in arrival time and phase shift to triangulate the source.

[Wolf]

Re: At what frequency does bass become directional??

So, for every system in its room that point will be different but 100-300hz is the range.

Bingo!
Wolf