Using the LD-3
In addition to the 160 Hz high-pass filter on the LD-3, the LD-3 compensating line driver provides additional filtering capabilities to help you further fine-tune an M2D/M2D-Sub system.
Table 4.2: M2D and M2D-Sub frequency response results with different filter configurations
HPF | LPF | ø Reverse | Result |
| | Switch | |
Off | Off | Off | Flat response (small rise on 70 Hz |
| | | -160 Hz area) |
| | | |
80 | Off | Off | Very flat response, +3 dB sub gain |
| | | recommended |
| | | |
80 | 80 | Engaged | Very flat response, +3 dB sub gain |
| | | recommended |
| | | |
160 | OFF | Engaged | Very flat response |
| | | |
NOTE: For more information on the LD-3 line driver’s atmospheric and array correction
features, please refer to the LD-3 Operating Instructions or visit www.meyersound.com.
Digital Signal Processors
Full-range signals may be applied to Meyer Sound’s self- powered loudspeakers because they have built-in active crossover circuits; external crossovers and digital signal processors (DSP) are optional and should be used very carefully due to phase shifts that can cause cancellations.
If a DSP is used, both M2D and M2D-Sub loudspeakers should be fed from the DSP in order to keep their delay time the same. Otherwise you may experience phase shift differences between the M2Ds and the M2D-Subs. In addition, you should verify the delay time between channels: Some DSPs may develop channel-to-channel delay errors when the DSP is near maximum throughput, which becomes more likely as the number of filters the DSP is using increases.
In no case should a filter higher than 2nd-order be used. The additional phase shift introduced by steep sloped filters deteriorates the impulse response and higher roll-off does not improve crossover interaction. In fact, it is highly recommended that the crossover/filter are set to emulate the low-cut LD-1A, LD-2 and LD-3 (at the 160 Hz position) characteristics themselves, as shown in Table 4.3.
Table 4.3: LD-1A, LD-2 and LD-3 (LD-3 at 160 Hz) “Lo-Cut Filter” Parameters
Type | Order | Pole | Q |
| | Frequency | |
High Pass | 2nd (-12 dB/oct) | 162 Hz | 0.82* |
| | | |
*If the DSP does not have variable Q for high-pass filters, the filter should be set to “Butterworth” (Q ≈ .7).
If the loudspeakers are going to be driven directly from DSP, verify that the outputs of the processor have the driving capabilities to drive the total load presented by the loudspeakers connected to it.
NOTE: When precise array design, subwoofer integration, DSP and delay
systems, and compensation for acoustical conditions all come into play, measurement and correction tools are a must. Meyer’s SIM audio analyzer and the CP-10 parametric equalizer are both highly recommended.
USING THE 650-P WITH THE M2D
In some applications – for instance, in a system design where the subwoofers do not need to be flown in the array – it may be desirable to deploy an M2D array in combination with Meyer Sound’s 650-P high-power subwoofer. The 650-P subwoofer extends the M2D system frequency response down to 28 Hz, and can accommodate daisy- chain, line driver, and DSP connection options.
NOTE: The 650-P subwoofer does have a polarity switch, and you will need to ensure
that it is set to pin 2 + (same polarity respect to the M2D loudspeaker’s pin 2 +) when co-planar and in close-proximity to and M2D array.
NOTE: When driving M2Ds from the Mid- Hi output of the LD-1A, LD-2 or LD-3 line
driver with the Lo-Cut filter engaged and 650-P subwoofer in their full-range configuration, their polarities should be kept the opposite if they are co-planar or near each other. If your M2D and
650-P loudspeakers are separated by a greater distance – or delay must be used between them – a measurement system such as SIM should be used to determine the correct delay and polarity.
