In many AV rental or fixed installation applications, there may be the need to set up a number of loudspeakers that will all play the same audio content. The simplest way to implement this is to daisy-chain a number of active loudspeakers together.
QSC active loudspeakers feature two different kinds of outputs. First, QSC K.2, KW and KLA Series feature “Thru” or parallel Outputs. These are always the closest to the Inputs and are labelled with a single arrow between Input and Output. These line-level outputs are hard-wired to their respective inputs. Simply put, they are identical copies of their respective inputs, therefore are unaffected by any gain adjustments made to the loudspeaker. We refer to this as Pre-Gain.
Note: the KLA Series has a single output and although simply labelled “Line Out”, it is in fact a Pre-Gain “Thru” Output.
The second type of outputs are called “Mix” Output (or “Line Out/Post Gain” on the older K & KW models). This line level output produces a post-gain mix of all the input channels (A, B and C). Any adjustments made to the gain of any of the three channels affect this Mix Out signal, which is still free from any DSP processing. QSC K.2, KW and CP Series feature this Mix Output.
So let’s have a look at how many active loudspeakers you can safely daisy-chain, whilst keeping an uncompromised audio quality:
Thru Outputs
A very large amount of loudspeakers can be daisy-chained using the Pre-Gain “Thru” Output. Eventually – after many tens of units – some line-level signal loss will occur, depending on the length of the cable run. Note: the CP Series does not feature a “Thru” Output, but only a “Mix” Output.
Mix Output
With any Post-gain Mix Output, there is always some small noise added due to the signal running through the gain circuitry and this noise will grow with every additional loudspeaker that is daisy-chained. It is recommended to daisy-chain no more than four (4) units using their Mix Output. Because CP Series only has Mix Output, four units is the limit.
Hybrid use-case
A common practice is to use the first loudspeaker in the chain as the “mixer” using its Mix Output, then daisy-chain many other loudspeakers using their Thru Outputs. This practice is perfectly safe and because you are only running through a single Mix Output, you can daisy-chain many tens of units using the Thru Outputs.