Sub amp tuning

[bmk6795 10+ year member]

Ok guys ive spent all day attempting to tune my sub amp to my liking and just havent been able to get it. Equipment is as follows: ab vfl 4480, 2 12" c2 threatcon 2 D4s wired at 1 ohm, Jvc aresenal hu (i forget the model number, it has 3 sets of 4v pre outs), 4 cube box, 16 sq in of port area tuned at 32, AT wiring including rcas. I am setting my gains with a Fluke dmm, and have used multiple test tones. I set the gain with the hu volume at 42/50 I've used 0, -3, -5, and -6 db test tones. Every time i set the gains, they slam on the test tones. No matter what db level the test tone was they got down on the test tones only. After i put in a cd the subs just will not preform. If i turn the hu up a few notches (45-46) they start hitting pretty good. Its like this no matter what db test tone i use. No bass boost is being used. The bass setting on the hu is set to 0, the sub level is set to 8/8. Anyone have any ideas as to what is going on?

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[Side Show 10+ year member]

check your deck settings, some of the jvc headunits let you choose the rca pre-out voltage

 

[bmk6795 10+ year member]

check your deck settings, some of the jvc headunits let you choose the rca pre-out voltage

I dont believe this one lets you. I've sorted through most of the options since i've had it and i havent seen anything like that. Ill double check that in the morning though.

 

[bbeljefe]

Sixteen inches of port area total or 16" per cubic foot?

 

[bmk6795 10+ year member]

Sixteen inches of port area total or 16" per cubic foot?

Lol thats the second time ive been asked that, i need to be more specific. Its 16" per cube.

 

[bbeljefe]

Okay thanks. And yeah... that's pretty important with respect to sound quality and loudness. Put a good bit of power on a sub in a 4 cube box with a 16in² port and it'll sound like a sealed box with a leak. ;-)

Just to clarify the maths... how much power should the amp produce and what voltage are you looking for/setting to?

It sounds like you've got the head unit at a correct volume level but has it been checked for clipping level? My Alpines don't clip until 29 of 35 without a processor and with one they don't clip at all, so I'm wondering if there is some usable headroom on your HU that's not being utilized at the volume level you're using to set gain. 42 of 50 is 84% and that should be about right but it never hurts to clarify.

It also may help to clarify the box parameters, if you know them.

 

[bmk6795 10+ year member]

Okay thanks. And yeah... that's pretty important with respect to sound quality and loudness. Put a good bit of power on a sub in a 4 cube box with a 16in² port and it'll sound like a sealed box with a leak. ;-)
Just to clarify the maths... how much power should the amp produce and what voltage are you looking for/setting to?

It sounds like you've got the head unit at a correct volume level but has it been checked for clipping level? My Alpines don't clip until 29 of 35 without a processor and with one they don't clip at all, so I'm wondering if there is some usable headroom on your HU that's not being utilized at the volume level you're using to set gain. 42 of 50 is 84% and that should be about right but it never hurts to clarify.

It also may help to clarify the box parameters, if you know them.

The amp should be producing 1200 watts, 34.64v at 1 ohm.

Hu hasnt been checked for clipping as i dont have the tools necessary to clairfy that, so i just used the 85% rule.

box parameters are as follows, 14H x 35W x 25D (outter dims) port dims are, 12.5H x 32L x 5W, double baffled, 45s in the back corners. After port/bracing/woofer displacement i am left with 3.95 cubes, 15.83 sq in of port area per cube, and a tuning of 32.34 hz.

When building the box we used titebond 2 wood glue, 2" course threaded screws 5-6" apart, and dap caulk around the edges on the inside.

I set the gain for 1500 watts on a -6db 50hz tone today and once again it got down on the test tones, from 20hz-70hz (i dont have any tones higher than 70hz). But once i started playing music the output was less than that of my single sa 12 i had before. I have no idea what is going on.

 

[bbeljefe]

Sounds like you've got everything set up properly, although I always set gains with a 40hz tone. But that difference is really not much so you should be slamming.

That said, those subs have a low EBP for ported enclosures so even though Sundown recommends up to 2 cubes per, your box may be a bit too large. Since it would be easy to do, why don't you put some mass in the box and see how they perform? I would say add about 1ftⁿ of mass. That should bring the tuning up to ~38hz but with cabin gains it should still be pretty hot in the mid 30s.

 

[bmk6795 10+ year member]

Sounds like you've got everything set up properly, although I always set gains with a 40hz tone. But that difference is really not much so you should be slamming.
That said, those subs have a low EBP for ported enclosures so even though Sundown recommends up to 2 cubes per, your box may be a bit too large. Since it would be easy to do, why don't you put some mass in the box and see how they perform? I would say add about 1ftⁿ of mass. That should bring the tuning up to ~38hz but with cabin gains it should still be pretty hot in the mid 30s.

I'll try that, also though, if i set the gains with the bass boost on 6, (has 0, 6, 13) it does pretty good but without the bass boost on its ****

 

[bmk6795 10+ year member]

Sounds like you've got everything set up properly, although I always set gains with a 40hz tone. But that difference is really not much so you should be slamming.
That said, those subs have a low EBP for ported enclosures so even though Sundown recommends up to 2 cubes per, your box may be a bit too large. Since it would be easy to do, why don't you put some mass in the box and see how they perform? I would say add about 1ftⁿ of mass. That should bring the tuning up to ~38hz but with cabin gains it should still be pretty hot in the mid 30s.

my rcas are only reading .65v, it's a 4v system, could this cause the issues I'm having? i tried 2 different rcas, one knu, one at and got the same readings

 

[bbeljefe]

Well, yeah. Something isn't right about that.

Check voltage at 85% volume from center pin to shield and center pin to chassis ground. Should be the same reading and should be ~4v.

EDIT: And to clarify, check it at the head unit, not at the ends of the RCAs. That way we can rule out RCAs.

 

[bmk6795 10+ year member]

Well, yeah. Something isn't right about that.
Check voltage at 85% volume from center pin to shield and center pin to chassis ground. Should be the same reading and should be ~4v.

EDIT: And to clarify, check it at the head unit, not at the ends of the RCAs. That way we can rule out RCAs.

ok so i put in a different hu and used the same rcas and got a .6v reading at the end of the rca. how would i check the voltage at the input of the hu? unplug it abit so i can touch the probe to the prong?

thie hu i swapped was a 2.5v hu btw.

 

[bbeljefe]

ok so i put in a different hu and used the same rcas and got a .6v reading at the end of the rca. how would i check the voltage at the input of the hu? unplug it abit so i can touch the probe to the prong?
thie hu i swapped was a 2.5v hu btw.

You can send the probe into the center of the RCA out on the head unit and ground it on the chassis or the shield. Just don't go jamming it in there like you're trying to make a new hole, lol.

 

[bmk6795 10+ year member]

You can send the probe into the center of the RCA out on the head unit and ground it on the chassis or the shield. Just don't go jamming it in there like you're trying to make a new hole, lol.

lol alright. will test that tomorrow and report back.

 

[bmk6795 10+ year member]

You can send the probe into the center of the RCA out on the head unit and ground it on the chassis or the shield. Just don't go jamming it in there like you're trying to make a new hole, lol.

Correction, the system has 4.8v preouts. I tested them just a little bit ago, and i got 2.4v from each rca input on the hu on a 50hz -6db test tone. Assuming this is right since 2.4+2.4 = 4.8?