Yep, did the shop that built the custom box discuss it with you, need to know the box size, vol cubic ft, port size and length, what is it tuned to? Check winisd to see what it looks like on the graph. Is it too boomy, try adjusting your gain setting, if there too high you can get boomyness and delays. If the box is tuned too a higher frequency you can experience issues there as well. Since you paid to have the custom subwoofer enclosure built I would go back to the builder let him listen to it, explain how it's tuned and what your amp settings are at. If they are good this shouldn't be a problem and they will assist you with explaining how the box is built and what your amp settings are and how to adjust to your preference. I built my own box with the help of an experience installer and it took me a few days to adjust and change setting on the amp to get it to where I'm 100% happy with it. I have enough materials and am going to build another ported box tuned a bit lower with a flatter curve and build a sealed box and listen to the differences. Building a custom ported box is a bit more challenging in that you have to build it according to the subwoofers specifications, your listening preferences, and the car and stereo system itself. An experienced customer builder has the advantage of having built a lot of boxes and I think can get it closer than the novice such as myself but even then what the customer builder thinks you are looking for may not turn out exactly as you invisioned...
