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[hispls 5,000+ posts]

The installer is recommending the addition now of a DSP to help control the unwanted frequencies.

Your installer is correct. Replacing the LOC with something with more powerful DSP features. Proper DSP is the tool you need to correct trouble frequency peaks and nulls. I guess if you had an RTA, lots of patience, and the ability to custom fab mounting locations AND a willingness to audition a bunch of different component speakers you could probably get around it without DSP, but modern DSP will allow you to brute force past a lot of the issues we are faced with the acoustic environment of a car.

 

[1aespinoza 10+ year member]

AND a willingness to audition a bunch of different component speakers you could probably get around it without DSP,

I was going to reply with "In the old days..."