I recently received some PMs asking me about why some industry veterans  said they don’t believe in the “house curve philosophy” because “every car is different”. 

Obviously, I can’t speak for them. 

But I was reminded of an article I read a long time ago by a pro sound guy named Bob McCarthy. I looked it up, and I went ahead and ordered his book –  On Sound System Design –  and here’s a bit of what he said in the article:

“Where do you aim the speakers in a lively hall? At the people. And in a dead hall? At the people again. In what kind of hall do we intentionally aim sound at anything other than the seats? None that I have ever been involved with. Do we approach this differently for pop music than speech in a house of worship? Do loud shows need to aim away from the walls while quiet ones don’t?

This might seem like a silly line of questioning, but I am bringing this up to make a simple but important point. Sound system engineering is not about the room. It is about the sound system.”

He goes on to make some excellent points, some specifically for pro, some I’m going to test out in my own car – but the gist of it is this:

A house curve approach isn’t an approach of where to set the sliders. That truly would ignore differences from car to car. 

A house curve is a frequency response target. You can change that target for personal preference or system deficiencies (or because you don’t want to rattle one trim panel you aren’t going to fix the rattle in, I guess), but you should start somewhere. 

Speaker designers – and I mean speaker-system designers, not speaker driver designers –  start somewhere. They have a goal in mind. They select drivers and build crossover networks and add attenuation and reverse polarity in the wiring in order to reach an objective. 

Room-correction-algorithm engineers – the guys at Dirac and Audyssey –  have a goal in mind. They use EQ and phase processing and delay and level to reach an objective. 

Pro audio guys have a goal in mind, whether they have quantified it, or they know it when they hear it. 

When we design, install, and tune a car audio system, we are acting as speaker-system engineers and also as manual room-correction engineers. If we want to avoid quantifying anything, and simply “know it when we see it”, we can do that to try to preserve the mystery that only a few of us can possibly understand. 

But I don’t believe it’s a mystery. I don’t believe it needs to be and I don’t believe it should be. 

Now, I will meet you halfway. I completely believe that you can have two audio systems which, when measured with all speakers playing with a 1/3-octave RTA, measure the same and sound very different (both tonally and from a stereo presentation point of view). I think that the deficient system can be improved without changing its gear, through better tuning beyond what you see with a 1/3-octave RTA with all the speakers playing. (It might also benefit from better product, of course.) That doesn’t mean much, though. I think that’s just misusing a tool, and I’ve written about the early measurement mistakes I made in this regard. I also believe what Dr. Floyd Toole has said about measurement, which I will paraphrase as “if you want to know why two speaker systems sound different, you need more than 1/3-octave resolution”. There is a question about whether or not you need greater than 1/3 for tuning, as opposed to speaker-system R&D, and I prefer to look at measurements in resolutions higher than 1/3-octave as an educational activity – but I digress. 

The use of a tuning process that includes a target curve is intended to efficiently get you, as a beginner or novice, to the point of fine-tuning without a lot of wrong turns or wild goose chases. 

Now that said, I can’t tell you how many beginners or novices have heard a car I’ve tuned to a target curve, and been unable to find anything to change or tweak afterwards. It was better than anything they’d heard in a car. I could, though. I could show them something to change and improve, and I would explain what I would do. I believe that after those folks listened to fifty or so tuned systems, they would start to notice where to improve as well. It takes practice. 

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So, if you have a mechanism that works for you, God bless you. We have too few people in our industry who can tune a car, and we need them all. 

But using a target curve doesn’t ignore the acoustics of the vehicle, or the problems in the vehicle, or the rattles in the vehicle. It’s an objective. For some who’ve never tuned a car, having an objective demystifies the whole thing. 

Wouldn’t it be great if everyone could tune a car by ear and not need to do measurements? Well, in the words of Charlie Brown, “Wouldn’t it be great if potato chips were good for you?” I can’t tune a car by ear. I can’t. But I made a good living tuning a car with test equipment – ONCE I understood what the hell I was doing and stopped spending my time going down rabbit holes. 

I’ve been collecting target curves. I have one, Andy Wehmeyer has one, Harman probably has that same one if they remember, JL has a couple, and on and on. The thing is, until you understand how to reach one of them, you can’t reach any of them. The interactions of phase and time arrival and acoustic summing are what make tuning harder, and if you don’t sort those out, you can’t hit any curve at all. It’s not the shoes. 

I have a tuning process. Some others have tuning processes. If you follow one of the good processes, you’re sorting out the interactions of phase and time arrival and acoustic summing, even if you don’t know it! The point of a good tuning process is to help you correct the problems in that car. 

So, I don’t teach a process with a target curve in it because I ignore that cars are different. I don’t ignore that cars are different, but I also don’t ignore that humans  – and our hearing systems – are very similar. Our basic audio designs need to have a commonality among them so that we can make this into a business. In the words of a forgotten comedian, “we can’t stop serving baked potatoes because the guy with the recipe and the tin foil went home!” After we bake the potato, we can put the stuff on top that we want – but we need a potato first.