In addition, the use of high-pass filters to drive an M2D system with the M2D-Sub flattens overall frequency response and slightly increases M2D headroom in the lowest end of its usable spectrum.
The ideal ratio of M2D to M2D-Sub loudspeakers depends on the configuration of the system, the application, and the frequency content of the signal being reproduced. For most applications, two M2Ds for each M2D-Sub yields good results in frequency response and headroom.
NOTE: The M2D-Sub limit LEDs indicate when its safe power level is exceeded. If
the M2D-Sub loudspeakers used in a system begin to limit before reaching the required SPL at low frequencies, you may need to add more M2D-Subs to satisfy the SPL requirements without exposing the drivers to excessive heat and/or excursion.
The M2D and M2D-Sub loudspeakers can accommodate three basic connection options.
Daisy-Chained
When M2Ds and M2D-Subs are daisy-chained using the loop feature on the user panel, the result will have a fairly flat frequency response. However, at a ratio of two M2D to each M2D-Sub loudspeaker, the response will have a rise in the 70 to 160 Hz range where the frequency of the M2D and M2D-Sub overlap.
CAUTION: Always ensure that the source equipment can drive the total load of the
paralleled system.
NOTE: When both and M2D and M2D-Sub loudspeakers are used in their full-range
configuration (e.g., looped audio or the same audio feed), their polarities should be kept the same if they are co-planar or near each other. If they are separated by a greater distance – or delay must be used between them – a measurement system such as the SIM audio analyzer should be used to determine the correct delay and polarity.
Adding a Line Driver
Driving an M2D/M2D-Sub system with the same signal from different outputs using a line driver allows adjustments to the gain and polarity of each sub-system, and could be used effectively to compensate for the ratio of loudspeakers or
acoustical conditions. If the gains are adjusted to the same level, the combined response is identical to a daisy-chain configuration with a rise in level on the overlapping range. Meyer Sound makes available three different line drivers.
Engaging the Lo-Cut Filter
Using the LD-1A, LD-2 or LD-3 Lo-Cut filter (the 160 Hz HPF position on the LD-3) can produce an M2D/M2D- Sub system (in close proximity and co-planar) with very flat frequency response and a minimal area of overlap. The M2D loudspeakers in the system receive their signal following a high-pass filter, while the M2D-Subs apply their normal internal crossover frequencies to a full range signal.
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 M2D-Sub loudspeakers in their full-range configuration, their polarities should be kept the opposite if they are co-planar or near each other. This can be achieved by engaging the polarity reverse switch on the subwoofer output of the line driver. If your M2D and M2D-Sub loudspeakers are separated by a greater distance – or delay must be used between them
–a measurement system such as the SIM audio analyzer should be used to determine the correct delay and polarity.
TIP: How flat the response will be is, in any case, dependent on proximity to boundary
surfaces.
While the change of polarity with respect to a daisy-chained configuration is needed due to the phase shift caused by the high-pass filter at overlapping frequencies, placing M2D-Sub loudspeakers more than 4 feet apart from M2D loudspeakers may require reversing the polarities once again to compensate for the delay propagation.
Table 4.1: M2D and M2D-Sub frequency response results with LD- 1A, LD-2 and LD-3 (160 Hz filter)
Lo-Cut | ø Reverse | Result |
| Switch | |
Off | Off | Flat response (small rise on 70 Hz -160 |
| | Hz area) |
| | |
Engaged | Engaged | Very flat response |
| | |
