Forward Lobe

Another important aspect of speakers is their vertical polar response. Every typical two-way speaker will have lobes and nulls in the response formed by the non coincident sources playing the same frequencies. In the near field--before the reflections become a major player--these lobes/nulls are audible with fairly small head movements if the nulls are not spaced very far apart. So ideally a "near field" monitor would have a broad forward lobe. The forward lobe is dictated by the distance between the drivers, the crossover frequency and slope, phase, and driver directivity at the crossover frequency, but that can be a heavy topic. Essentially you want to forward lobe to point at your ears. Check this out for a great visual on lobing: Falstad's wave interference applet.

Let's have a look at the studio monitors we have on hand.

You can see in the top graph that there are 3 lines that are basically flat. Since the speaker is rotated in 11.25 degree steps toward the tweeter, that corresponds to a 22.5 degree forward lobe that is angled 11.25 degrees toward the tweeter. Behringer lists the crossover frequency at 2 kHz for the B2031P(the speaker graphed). Seems pretty darned accurate. This is pretty good performance for the near field, but not ideal. The graph toward the woofer is 5 dB down at 11.25 degrees off axis. I got to do a little more precise measurements in smaller increments on this at a friends house and it's actually a bit better performance than what this indicates and the lobe is centered at 10 degrees toward the tweeter. I didn't include the graph toward the woofer

The next is the Behringer 1030A--graphs 2 and 3. The 2nd is toward the tweeter and the 3rd is toward the woofer. Combining those 2 you can see four lines that are basically flat. That is impressive performance--33.75 degrees of good behavior. The wide directivity of the drivers (small mid/woofer and shallow waveguide--see horizontal polar pattern for evidence), low crossover frequency, and close driver spacing contribute to this.

Now let's check out the Mackie HR 624 mkII, the 4th and 5th graphs.

The Mackie looks to have a bit more narrow lobe than the B2031P and it seems almost perpendicular to the baffle but slightly toward the tweeter. Not necessarily a bad thing, but good to know info. Placement is critical with these speakers. To be sure, these are my favorites out of the bunch, but they are the most difficult to get right. In the near filed, small head movements can definitely alter the sound. The 1030A seems immune to them. I listen to these Mackie monitors from 6-9 ft away. That gives you a vertical window of a little over 2-3 ft respectively. Of course you are also into the reverberant field at 9 ft so you can all but totally ignore the lobe. At 6 ft in my room I can still hear it with pretty dramatic head movements unless placement of me and the monitors is just right. At 3 ft away and a 1 ft vertical window, head movements can be an issue if monitor placement is not precise.