Sub distortion

So I just installed a JL audio 10w1v3 in a sealed box behind the rear drivers side seat in my double cab. The sub is being powered by a jl audio jd250/1 and is spec'd for .55 cubic feet in a sealed box. Attached is a *rough* drawing of my box which came out around.57cuft. The sub isn't very clean with punchy rock bass... it almost has a flap/ vibrations noise when it hits. My question is, should I be looking at the geometry of the box or stuffing it with something to clean up the hit?

 

Did you play test tones to set up the amp? Sounds like it may be too much gain?

 

Sealed boxes generally require large volume to maintain accurate sound reproduction. Have you set your sub volume accurately using pink noise?

 

What did you build the box out of?

If it's a sealed box, any leak will make noise.

Generally, it's a good idea to staple or glue some insulation to the walls of the box to help damp any vibration.

Could the subwoofer be hitting something, like the back of your seat?

 

Gain is turned down quite a bit. I couldn't get a bigger box back on that side and it was just a little bigger than what JL recomended

 

⅝ mdf . It's got a ring around the sub preventing the cone to travel beyond the ring and contact anything

 

Since I have no clue what pink noise is... thats a no.

 

That’s about the size of the box I have and I have a 12” image dynamics in there that thumps pretty well. You have to play the test tones and dial up the gains until you hear distortion, and then dial it back a bit from there. There’s a bit more to it than that for the setup sequence, but I suspect that may be the problem.

 

Well then download a pink noise sound file and stick it on repeat (or an app) and measure the dB waveform using another app if you don't have anything better.
Ideally you'd run a frequency sweep, adjust your equilizer, then adjust with a real time analyzer (RTA) over pink noise

 

Pink noise is the test tones. There are some good articles online on tuning the amp to the speakers and it’s a crucial step. It will allow you to get the most out of each speaker. You’ll need to download test tones. The lowest one is for the sub. I downloaded them and played them from a flash drive.

 

So, the ring sticks out beyond the (foam or rubber) surround?

5/8 seems flimsy to me, but IDK what's typical in car subs.

I would suggest taking the box out of the truck and playing it to see if it still makes the same noises. Then, you can feel the panels to see if they are vibrating excessively.

It's possible that the panels of the car are just vibrating due to the SPL. If that's the case, you'd need to damp the truck with Dynamat or something similar.

 

5/8 is fine for anything under about 700W RMS; normally, I[d recommend additional bracing and damping fill, but he has a minuscule enclosure

 

When you play the test tones:

decide how loud your max operating volume will be. Typically this is 3/4 of the max volume.

set up and decide how you want your EQ settings first, because this will effect your max gain levels before you reach distortion.

make sure that your source is taken into account. For example, I play a lot of Spotify, so my Spotify settings on my phone are set on flat. The EQ is all through my head unit. I then tuned the gains based on that setup.

I think crutchfield has an article on all of this that will help. Playing the test tones and finding the distortion limits is a big deal.

 

I would think it would be based on cabinet size more than wattage.

My home speakers are only rated for 300 watts rms, and are 3/4 or 1" MDF. But, they're larger and produce more bass than anything most people would ever put in a car.

 

FTR you should not ever be using something to physically clip the mechanical extension of a cone. For sound quality, the driver should be recessed behind the enclosure based on maximum extension of the cone, but that doesn't seem to be your goal. I would very much reconsider a vented design, then refocus on setting the SPL to the correct level.

 

I mean, thicker is always better. You just don't want transmission obviously, so you're right that a smaller enclosure would suggest thicker walls

 

Don't you mean that a smaller enclosure would suggest thinner walls?

 

No. You have more force pressing on a smaller area (greater PSI), so you want thicker walls to resist that motion, and therefore resonance and distortion.

This is all considering a sealed design, of course

 

Ah. I would think a larger panel would be more likely to vibrate, unless there is internal bracing. I get what you're saying, though.

 

Ya I mean without modal resonance modeling, it would be impossible to say for certain which walls should be braced further (I'd assume the back wall should be the thickest in most cases), but in a spherical enclosure, smaller should theoretically be thicker