I have a question concerning sub boxes for the C5. I have had numerous types of sub boxes in my vette including JL Stealth boxes and many others. My question is, Why does the sub sound like it's popping when you have the deck lid open? If it is closed it sounds awesome in the cabin, although the whole car rattles like everything,lol. This has happened with every sub box I have had in the vette and in other vehicles. If you are right up near the sub, there is a popping under good loud bass, but when you are a little ways away the sub sounds perfectly normal. Sitting in the cabin of the vette, the sub will about blow your ears off and sounds great, but when you go back and pop the deck lid, you can hear the sub popping or whatever you want to call it,lol. I know I need some dynamat to help with the rattle, but it appears to me that the popping is normal since this has happened everytime I have used a sub enclosure.

Thanks
-Jason

 

Usually when the subwoofer is popping, it is normally due to distortion created at high volume levels. You can turn the gains down on the amp to eliminate this... typically, when the trunk is closed, you may not hear it as well as you would when the trunk is open... that may be the cause of the problem...

 

OK, I have a Hifonics BX1505D amp and I assume the level is the gain. It is adjustable from 0.2v-9v. I have it set in the middle. The headunit bass adjuster is set at 0 and the bass boost on the amp is off. I am using a Kenwood KDC-MP828 deck with preamp output voltage of 5. I am using a Old School Farenheit CK12D sub. I'm also thinking it's something to do with the gains, but am a little puzzled. I'm not out at the car at the moment to check to see what everything is set at, but here is what is listed on the side of the amp:

Subsonic: 15hz-35hz
Bass Eq: 0db-18db
Low Pass: 35hz-250hz
Phase: 0-180
Level: 9v-0.2v

I know the bass eq is at 0 and the low pass is set around 80hz. Am I supposed to have the level ( Gain ) match my output voltage of 5 on my HU? Someone told me something about this but I didn't understand them.

Thanks for your response!

-J

 

Yes, generally the gains, or level, is to be adjusted to closely match the head unit RCA output for best sound. What is the amp rated at, and do you know if the box is the correct airspace for the sub? Generally, the Corvette sub boxes that fit in the well are usually about .8 to 1.0 cubic ft. If the box airspace is too small for the sub, that could be part of it as well... your adjustments seem to be good, so that eliminates most of the troubleshooting, unless of course, the sub is by any chance, fixing to blow. If the sub is close to going out, any amount of adjustments may be futile, as the sub will still sound bad.

Overall, your sub may not be bad, but just getting a little distortion. Try to check the gain level, and match them as close as possible to the head unit for the best sound. Let me know what you find...

 

I'll try and look at it again tomorrow. This particular sub requires around 0.75-1.25 cu ft of air space. I have a overhang box with this sub, so it's a little bigger than your stealth boxes. I will also add some rubber/foam under the sub to help in case of an air leak. I will post the exact adjustments on the amp tomorrow. The amp is rated @:

RMS @ 4ohm = 500 watts x 1
RMS @ 2ohm = 1000 watts x 1
RMS @ 1ohm = 1500 watts x 1

I have the sub wired in parallel to produce a 2 ohm load and then it is bridged at the amp.

This is what the box looks like:



-J

 

The easiset way to set the "gains" properly if you don't have an O scope is with a sine wave CD and a multi-meter that can read AC Voltage. Make sure that the signal you're using recorded at 0dB reference and is in the x-over band (50 Hz will be good). If you don't have a CD, you can download it from the net and burn it.
A little Ohm's Law - Voltage = SqRt (Power x Resistance).

So if your amps is 500 Watts @ 4 ohm we need to turn the "gain" until we read 44.7V AC.

There is a flash movie that illustrates the whole procedure here: "gain" setting guide

 

Part of the reason that you hear a difference in the bass response when you have the deck lid open is that the sub's sound wave no longer has a significant area to bounce or load off of, it now has open space, which means a good portion of your bass just floats out of the opening and does not "bounce around". You can mess around with this yourself in your house by throwing your sub enclosure out into the middle of the room, and then puting it into a corner. Very measureable difference.

As for the gain adjustment, what percentage of the max volume on the HU are you using? If it is not 75% or so of max you probably have the gain on the amp a bit high and are not using your main volume control as efficinently as you could be. Which then sends the sub amp into clipping when you do crank it up to get the front stage as loud as you like.

One other thing, that formula above represents a "perfect world" scenario where your amp manufacturer actually provides you with advertised watts. This can be a problem if they under deliver on the watts as your voltage will send you into clipping/distortion. If they over deliver, then you are not getting the true max power/volume from the combination.

I still like my ears unless you have an oscilloscope.

G'luck
Fej

 

The gains on the amp are set to a HU volume of 30. The highest the volume on the headunit will go is 35. That's what I was thinking FEJ, cause it pounds when everything is closed up, but when you open the hatch it just sounds like a speaker popping with minimal bass when you are back there looking at it.

 

Hmm, is the HU an alpine? With 35 being the max I think that it is. Anyways with Alpine HU's I always shot for a 27 or 28 max because I found that most of them began to send a clipped signal beyond that point, which could be causing a bit of your popping or distortion as well. Generally only the high end SQ decks will play clean up to and beyond 80% of max .. my Eclipse 8053 is clean to 78 of 80 ... and most real high end stuff (alpine f1, Denon, top end clarion, pioneer and eclipse) will play to max unclipped.

You always have to account for road noise, and a general loss of what I consider approximately 2 points of volume when driving vs when you are tuning with the engine off, not moving etc. Really noticeable in the 60hz to 200hz range.

Try a minor retune with that new max volume number and see how things go bro

Fej

 

Hey Fej, the HU is a Kenwood.