sub sound output explanation

Ok, so I have been working on a friends 2000 Chevy truck, full size standard cab, and I built and installed an enclosure for a single 10" Diamond CM3 sub, which sits between/ behind the 2 seats with the sub basically positioned over the center console, so its right next to your head. It is powered by a JBL CS 300.1 amp, 400rms @ 2 ohms. So, we started with the enclosure sealed, .75 ft^3, and while waiting for the JBL amp he had the sub powered by an old Pioneer 2 channel that put out like 75 watts, and sounded pretty good, just not very loud. So, we got the JBL amp in and installed and the sub was alot louder, but sounded like it was distorting real bad when we really cranked it up, so I decided to port it since I have better luck with ported boxes anyways. So, got it ported and back in and better, but still some distortion. So i'm getting frustrated at this point and then the weird thing happens, he opens the door to get out and bam, this sub is pounding and sounding great! So, the sub doesn't sound worth a crap with doors closed and windows up, but open up both windows and the thing sounds awesome, why is that? Is it the fact that the trucks cab is too small for this sub to perform well? First time I have experienced this so looking for information as to whats going on. Thanks guys.

not really sure but i tend to have the oppisite with ym setip with the trunk on my car down it sounds great but with it open sounds kind of sad

I have heard something about tuning to the wavelength of the vehicle or something. I do know that in my Camry when I had my 10, it did sound better with the windows down. In my first car, two 12's, sounded better with everything closed/rolled up.1999 Toyota Camry

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Pioneer DEH-P3700MP

Lightning Audio Strike S4.15.VC2

Lightning Audio Strike S4.500.1

Majestic 6.5"

So, any ideas on this? Has to be a common occurrence I would think.

I agree with dwarren. Cancellation is probably what is going on. Try moving the box to different spots in the back. Having it centered may be causing some of the cancellation. Also check the gains and boost if it is truly distortion.The Flakman

I feel strange. I have deja vu and amnesia at the same time.

John | Manteca, CA

I will try reversing the wires tomorrow when I see him again, see what that does. As far as the box size, per Diamond, sealed boxes .5 to 1.0 ft^3, ported .75 ft^3, so based on that, I built it with porting in mind. And with this vehicle, there is no moving the box around to different positions, it is the way it is because there absolutely no room behind the seats.

Is the .75 cu ft you have provided gross (box volume ONLY) or net (box volume, plus vent, plus woofer, plus bracing)? What I mean is this: If your woofer displaces .1 cu ft, (typical) and your vent displaces .2 cu ft (again, typical, for a deep tuning), and your bracing displaces .2 cu ft (hopefully AT LEAST that much...), did you add those, for a NET box volume of 1.25 cu ft, or did you build your box to .75 cubes, and then stuff everything into THAT volume... If you stuffed everything into .75, you're working with a volume that is FAR too small to be vented. Now, this isn't an answer to your question, but it IS an issue. As to your answer, I can't tell you, but it most likely has something to do with the transfer function of the cab. In my car, my bass drops off DRAMATICALLY when I close the windows, but with them open, I get deep, tight, LOUD... I don't hear "distortion" as you say, but there is a noticeable difference in response, open vice closed I'll ask someone I know if they might have an idea...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

The .75 is the net volume. I had built the box with the idea that if we didn't like the sealed, we could port it and be at the recommended size. I had meant to swap the wires around today at work, but never got time to so, maybe in a couple of days when i see him again I can try that.

So a little update, plus still looking for answers. I reversed the wires, no change at all, we laid the box on its side so the sub was facing the back of the lower passenger seat, seemed to make it hit lower and clearer, but still not near as loud than when we opened the doors. So, still at a loss here. Thinking about asking Diamond if they have any recommendations.