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Speaker Beaming

#2
The wider a driver is, the more its highs and upper mids move to the middle of the cone and the less they can be heard off to the side.

Multiple drivers affect it because if you have two 10" drivers side by side, they will act as a 20" driver when it comes to beaming.

For me, though, there are no real world effects because I think my rigs sound great wherever I stand, and most of the time I'm going into the PA anyway so it only affects me on rare occasions.
 
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#4
There are physical filter devices called beam blockers that help rectify the problem in guitar amps. They provide some details as to how the disk works. Some amps, such as the B-15N, have a two inch wide wooden strip positioned horizontally infront of the center of the speaker, part of the baffle. According to the designer, Jess Oliver, his intent was to have it serve to protect the speaker. But you never know what sonic effect it is having, even if limited.

Invalid Link Removed
 
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#7
Beaming frequencies on charts rely on the assumption that cones act like piston, and they don't, so it is a generalisation that isn't too useful.

Beam blockers that are a disc over the middle of the speaker just make the beam less predicable and consistent so it is harder to spot, rather than fixing the dispersion issue, Foam donut sorts work a bit better.
 
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#8
monkeyfinger said:
Found this chart at [Invalid or Expired Link Removed]
speaker diameter beaming limit in Hz
18" 903
15" 1052
12" 1335
10" 1658
8" 2105
6.5" 2672
5" 3316
4" 4224
3" 5381
2" 6840
1" 13680
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That's pure poor man's math which does not represent partial cone resonance of drivers and also does not regard to the damping factor of cone material as well it does not represent the abiity of distinct cone curves to improve radiation pattern at the treble frequency band

If all the speakers available where kind of a flat made of stone the math was true.
 
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#9
ThisBass said:
That's pure poor man's math which does not represent partial cone resonance of drivers and also does not regard to the damping factor of cone material as well it does not represent the abiity of distinct cone curves to improve radiation pattern at the treble frequency band

If all the speakers available where kind of a flat made of stone the math was true.
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Correct, plus the re-radiation capabilities of the dust cap and how it couples with the bobbin can make a big difference in the polar response curves.

If you look as some of the popular Faital drivers, you will immediately see that the polars are very different than what the simplistic math might suggest.
 
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#11
for most part yes, just a rule off thumb for basic formula figure out beaming frequency. its not set in stone but still roughly falls and will start happening where the formula suggest. cone shape/ cone depth can improve or raise beaming frequencies. likewise dust cabs can be used change depth to help reduce beaming, likewise dual cone or whizzer shaped dust caps to improve high frequency / reduce beaming
 
#12
monkeyfinger said:
Can someone fill me in on what beaming effect is and how it relates to speaker size? How does multiple drivers affect beaming? What are the real-world consequences?
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In my opinion, dispersion (which includes beaming effects) is usually a part of tone. Let me explain:

Most of the sound that most of the people hear at an indoor gig is reflected, or reverberant, sound. (At an outdoor gig, there is pretty much nothing but direct sound, but dispersion still matters for listeners who are off-axis somewhat). So indoors the tone that most people hear is a weighted average of the direct sound and the reverberant sound, and the exact "weighting" depends on a lot of variables, but we can make some generalizations that will be in the ballpark:

- The bigger the speaker cone, the "warmer" or "darker" the spectral balance of the off-axis sound from that speaker, which will therefore make the actual tone warmer or darker than we would have expected from merely eyeballing the on-axis frequency response curve.

- The more speakers we have in a cluster (like an 810), the "warmer" or "darker" the spectral balance of the off-axis sound from the cab. The lows from the different speakers all combine in-phase whether on- or off-axis, but higher up in frequency the shorter wavelengths in effect combine in semi-random phase off-axis. The higher the frequency and/or the greater the spacing between the cone centers and/or the greater the off-axis angle, the less effectively the different drivers reinforce one another. So what happens is something like this: an 810 is 12 dB louder than a 210 at low frequencies, transitioning to something like 6 dB louder than the 210 at high frequencies, assuming identical woofers. So despite using identical woofers, and despite having nearly identical on-axis response curves, their real-world in-room tone is quite a bit different.

I happen to prefer fairly wide-dispersion cabs for bass. This way, the "weighted average" of direct + reverberant sound is more consistent across a wider angle, so more of the audience is hearing the same thing. Various techniques exist for getting good dispersion, including crossing over to a midrange or tweeter before the woofer's beaming gets too bad.
 
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