Sub questions

[Paul H]

I have a couple of questions about subs and bass frequencies.

Can anyone explain or point me to a good explanation of at what frequency in a given room (ie 24 x 17 for mine) sound becomes non-directional? Alternately where should the LF crossover be set to ensure that you can't tell where the sub is by sound alone?

Second, a lot of subs point downwards at the floor. This certainly works for a sub with a 40 Hz crossover. How high can the crossover be set before the sub should be pointing horizontally into the room rather than at the floor to avoid losing sound detail?

Thanks,

Paul

[JonMarsh]

Hello Paul,


By directional or non-directional, are you referring to your ability to localize the sound source? I.E., what direction the sound is coming from?

For a sub, this point is complicated by two issues. One, the crossover frequency isn't a brick wall; things are rolled off, so you have some output above the crossover frequency. More important, though, is that 2nd and 3rd order harmonic distortion, which can be at levels over 10%, are at frequency multiples of the fundamental- and those higher harmonics are easily localized.

Now, another side matter aobut "localization" is that the real question being asked is, how far away from my mains can I locate my sub and still have the sound integrate properly, and the subs not call attention to themselves?

At 100 Hz, the sources shouldn't be more than a quarter wave different in Z axis localization; that's about 3 feet. Laterally it's about 12 feet before you have directionality. Of course, with most pre-pro's you can compensate for driver distance.

The downward firing situation is a subset of any woofer that loads into a controlled space, like the W dipole frame woofers, or IB manifold arrays, or slot loaded woofers like I used to build in the 70's and 80's. It does mess up the frequency response, usually putting some peaking into it starting around 100 Hz or so and peaking in the 200-250 Hz region or higher, depending on dimensions. To avoid the effect on the crossover transistion, without using additional EQ, you have to move the crossvoer frequency. For this reason, downward firing woofers are usually not used above 50 Hz, so that they can be down 20-25 dB by the time these affects kick in. In the case of systems like an IB woofer with manifold, our preferred "technique" is to equalize the IB system flat to 200 or 250 Hz, then use the "classic" electronic crossover (whatever that is) or LFE crossover.

Bottom line, IME, I like 75 Hz or lower crossover points in almost all systems, for the above reasons and other considerations. 63 is nice, and where I start to be really happy.... :T

~Jon

[Paul H]

As always Jon, a considered and well-written response - I will definitely purchase your speaker design book - I know you haven't written it yet, but hey, start a rumour and see where it leads

Thanks and Merry Christmas,

Paul

[taz13]

I'm in, I'll buy that book. :T :T :T :T :T :T :T :T :T :T :T :T :T