Hey guys,

Been a while since I posted, but I have a few questions. I built a 3/4 MDF sealed box for my (2) ARC 10D2 subs. They're rated at 250 watts rms, and I'm powering them with the KAR 1000.2T. I went for a very small box because apparently less volume = more accurate bass. ARC recommends 0.5 cu. ft. as the "minimum volume" for each sub. Don told me that I'd be fine anywhere between 0.4 and 0.5 per sub. The box I built comes out to just under 0.45 cu. ft. per sub. Another problem is my power wiring. I didn't ( ) take my sub amp into account when I bought wiring. I have 4 guage running to the dist. block in the trunk and 8 running to each of the amps. I have a KAR 400.4 and 1000.2T back there. So does that mean I'm starving my amps? I'm pretty sure I'll have to run 1/0 AWG, but I really don't want to deal with the hassle if it's not necessary.

My problem is mainly that the subs, though they sound good, are very quiet. I'm by no means going for an SPL setup back there, but these things just seem to have no power.

How much of a difference does box size really make? If I jumped from 0.45 cu. ft. /sub to 0.65 cu. ft., would I notice much more SPL? How about upgrading the wiring?

And one more question. Can using a distribution block for the ground on the amps lead to system noise? When I first installed my speaker amp (the 400.4), I had really bad noise. Then I switched the grounding point to a better location from which I had scraped the paint, and the noise went away for the most part. Then, when I added my sub amp, the noise got much worse again.

Thanks for any help guys.

-Brian

 

Well, generally speaking, 8AWG is rated for around 73 amperes. IIRC, our alt supplies around 120 amperes, so, depending on the impedance, I think upgrading the wire ould be in your best interest.

4 AWG is capable of handling around 135 amperes, you might be better off with an upgrade. My 4150XXK states in the manual that 4AWG is REQUIRED for the amp...I would think your manual says the same thing, but I did not see any reference to minimum AWG in the Kar series amp guides.

 

Yeah, I don't recall seeing any numbers for that either, but I will take another look. Guess I'll have to look into the upgrade. See how much it'll cost me and such. Thanks Metal.

 

as for the box size...the larger the box, the easier it is for the sub to work since the air volume has more 'play' in it. also, the sub can play the lower notes more easily when compared to a smaller box. i've always been a fan of large sealed boxes. nice sq, and decent low end extensions

btw, larger the box, lower the sub's power handling. but i don't think it will be anything too drastic since you're going from .45 to .65 cu ft.

 

You might notice a difference but it might be the large one your going for. The only way I can think of is ot maybe build a bigger ported box tuned low. You'll still maintain the SQ although you may lose a little and should get a lot louder. Im not familar with Arc subs but sometimes manufactures dont accurately display the optimal enclosures for there subs. For Ex. Kicker says the minimal cu ft for a 12" L7 is like .75 and I can guarantee it will sound like total @$$ in that enclosure. Your wiring is fine and nothing to be worried about. 4 gauge is rated at 125 amps for about a 12 ft run and a 2-4 ft of 8 gauge is about equal to that of the 4 gauge because of the lenth. You should also check all your settings, X-over should be about 80, and set the gains using the DMM method.

 

You mind quantintativley elaborating on this? I don't agree with you...AT ALL. So what you're saying is that an 8GA wire will be capable of handling the SAME load as 4GA in shorter runs? BS.

 

Its exactly what im saying. The lenth of the wire dictates how many amps it can handle. Im not saying its equivalant but a 3 ft run of 8 gaue will handle the same amount of power as a 12ft run of 4 gauge.

 

Wow, you just made teh profile...j/k, you are right.

 

I couldn't find a 10D2 sub with a 250w RMS rating on the Arc web site. The Extreme models are 350w RMS. Do you have the T/S parameters of your sub? I can model it and give you a frequency responce comparison of the two different boxes.

No. If you are smaller than optimum, the Q of your sub will be close to 1. You get a hump in your frequency response and a steeper roll-off. Some people like that sound so it's not bad, just not what I shoot for.

You have just learned lesson #1 of Hoffman's Iron Law

Hoffman's Iron Law states that the efficiency of a woofer system is directly proportional to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can usefully reproduce)

-Robert

 

i have no idea, sorry.

 

glad you're contributing something useful to the thread

 

It's actually an ARC series sub. It's the most expensive line before the new Flatline subs. There is a PDF on the site with all the relevant specs.

Thanks again for the help guys.

 

It would help if I learned to use the scroll bar.

You get a very small 1db hump because of the smaller box. What stands out is how much you are choking the sub. I modeled it in the Unibox recommended 20L (.7cf) and your 13L (.45cf) boxes. I picked 300watts as an arbitrary power input. In the 20L box, that 300w will push the sub to the limit. In the 13L box, 300w only gets the excursion to 10mm. You are wasting 1/3 of your sub's xmax. Here are the graphs.

-Robert

 

^^^

Wow. Thanks Robert. That's pretty interesting.

Damn, wish I had something like this before I built my box. Oh well...live and learn, I guess.

 

It's free. link

-Robert

 

Don't worry Dan. 0.05 cu. ft. won't make an audible difference.

 

Have a hard time believing that a nice setup like that is not booming... my tiny polk db10 in it's ultra tiny box hits really hard and clean...


I'm running dual 4GA lines for about 1100W RMS... put one in with a JBL BP600.1 integrated into a aftermarket CD + Factory Amp + Factory Speakers + Sub, then decided to just scrap the factory system entirely and ended up getting a bigger than planned 4 channel PG Ti500.4, so just ran another 4GA line to that one...

Also, which way are your sub(s) facing? Had mine facing forward towards the cabin (single 10") and it sounded pretty poor, flipped it around and the difference was incredible... also, may be getting cancellation, could try only connecting one sub and seeing how that sounds?

Do you have polyfill in the box? Supposedly polyfill tricks the sub into thinking the box is bigger than it actually is...

What GA speaker wire are you running to the subs from the amp? Lower GA = less resistance = more power to the speaker.

 

Hey, let me answer some of your questions here. I really want to get this figured out. I was hoping Don would chime in at some point.

My subs are facing rearward (toward the back of the car). There is no polyfill in the boxes because I was told I wouldn't need it.

For the wire, I have 4 AWG from the battery to the dist. block, 8 AWG from the dist. block to each amp, and 12 AWG from the KAR 1000.2T to each sub. I think for the in-cabin speakers I'm using 16 AWG, but that's not the issue here.

 

That all sounds good... I would think that the amps would cut out if they did not have enough power... but those are a lot higher quality amps than I've ever dealt with, so they may just be scaling down output based on the power available? Could just try to run the sub amp and not the 4 channel and see if it's a "not enough power available" sort of issue?

May be a bad ground? I've actually never grounded on a scraped spot, I always ground on an existing bolt and test for that ground using a 12V light bulb with aligator clips soldered on... if the bulb lights up fully, it's a solid ground, if not it flickers.

Sorry I can't help more... I've fiddled with my system quite a bit to get it to sound the way I wanted (Ended up setting HP on my 4ch amp at 120hz, and LP at 120hz with bass center freq @70hz, MX=2, Sub level at +10 (of 15) and MX on the head unit turned on (Alpine))... may just be a head unit settings thing?

 

That's a good idea about disconnecting the 4-channel to see if the subs get louder. I'll give that a shot when I get a chance.

Other than that, I've screwed with the settings a bit already and haven't been able to get the desired results. I have the 9835 (which I'm less than pleased with). IMHO, the MX thing kills the audio quality, so I won't be turning that on.

I'll let ya know about what happens when I disconnect the 4-channel. Thanks again.

 

kinda late to chime in, but make sure your subs are in phase with one another. if not, the bass won't be as loud due to cancelation.

 

BigDu...that Kar 1000.2T NEEDS 4gauge....its a kilowatt rms amp,it needs bigger wire. That being said you'd really benefit from 0/1 gauge power wire to have enough current flow for both amps....its like sucking ice cream through a straw, I'd be afraid that could be harmful to the amps. I guarantee you are not seeing full rated power from either at the moment- perhaps thats the culprit as to why output is not satisfactory.

And even though the subs work well in smaller air spaces for those that have no choice, a 0.6 or whatever Arc claims is optimum sealed is what you should go with for best overall performance.

 

I play primarliy a burned mp3 discs and without MX on (MX level is 1 of 3), everything sounds flat...

Since you have an alpine HU did you incease the sub output level? On mine it's in the volume button menu (w/Balance, fader, defeat)... I think it is more of a output level limiter rather than an amplifier, so I don't think it introduces any distrortion... Usually have mine set to +10 out of a possible +15, get a quite a bit more thump with that set... Also, may want to fiddle with the bass engine's center freq / width, I think my center freq is 70hz, width is 2, level at 0... Then again my HU is 4 or so years old (CDA-7892)

That may fix the bass spl, but may still be starving the amps... then again 400.4W + 250Wx2 = 900W RMS with A/B eff being like ~60%, D at ~80%, gives you like 540 + 600 = 1140W actual RMS / 13.8V = 82A RMS, so maybe ~164A peak through a 125A cable in worst case scenerio? Then again if you were truely starving the amps, you'd be popping your "by the battery" fuse, right?