you would be fine without a spl meter, it just makes setup more foolproof and gives you the ability to tinker with settings more. however "ideal" may not be how you like the room to sound, so keep that in mind. i would use the "ideal" (based on spl testing) setup just as a reference, and then slightly modify it to suit your tastes. there are a variety of different quality units out there, so be sure to get an adequate one.
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