Gain Setting on Amp?

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mrdragon

Copper - Posts: 121

Joined: October 08, 2003

Location: Australia

Posted: September 21, 2004 at 4:03 PM / IP Logged

Guys i got a Kicker 12" rated 125WRMS @ 4 Ohms, and an amp i can BRIDGED to 125WRMS into 4 Ohms as well.

Is this how i calculate to set the amp gain...

125WRMS x 4 = 500

Square Root of 500 is = 22.36

So is that how i should set the gain on the amp to 22.36 if i go over 22.36 i risk damaging the sub right since it's rated @ 125WRMS???

Cheers:)

stevdart

Platinum - Posts: 5,816

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Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: September 21, 2004 at 4:12 PM / IP Logged

You are correct! Give that man a cigar...

And when you're all done with the adjustments and have had some time to listen to your different music sources for awhile at full volume...if you notice something wrong with the sound at the high volume levels...then you can turn the amp's gain back a hair. Sometimes amplifiers aren't quite what they are spec'd to be, and it is in the sound that you would notice that.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

mrdragon

Copper - Posts: 121

Joined: October 08, 2003

Location: Australia

Posted: September 21, 2004 at 4:20 PM / IP Logged

But the thing is the amp gain setting is not even reach 1/4, beside from that it's not loud at all, is that mean my amp is underated in term of real RMS power??

Lastly the recommended box for this sub is 1.75 cu (ported) Is that the minimum i need to build the box, i want to save some space and just wondering if i could make it smaller (ported)sub???

Cya

stevdart

Platinum - Posts: 5,816

Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: September 21, 2004 at 6:23 PM / IP Logged

The thing to know about amp gain setting is this... it doesn't matter where it ends up, 1/16 of a turn, 1/8, 1/4...whatever it ends up. The gain is adjusted to the:

1. Output of the amp, or

2. RMS of the speaker(s) connected to it, if less than the output of the amp.

That does not mean anything about the amp being either overrated or underrated...it is just an adjustment of amp sensitivity to head unit output. Seriously. Don't even pay attention to the knob's relative position when you are done adjusting. Don't even look at it. It's not important.

It's not "loud at all" because...you guess. 125 watts. You've been around long enough to know subs are usually provided more power than that if you want "loud". Just read some of the posts on the forum here. But that is what you got, so that is what you get.

If you need a smaller box you should look at building it as a sealed instead of ported.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

/r7

Silver - Posts: 340

Joined: July 30, 2004

Location: Canada

Posted: September 21, 2004 at 7:08 PM / IP Logged

you could also play with dimensions of a sealed box, to allow more headroom in the trunk, or more space in any which way, so long as there is at least 1" of wood around the edge of the cut for the sub to be placed in, and i read 3/4" for a specific sub someone was helping another person with, but i would say 1" as well. 1.75cu could allow you some various shapes and sizes.

also - to add to making the box smaller, maybe stev can correct me, or anyone with more knowledge about it than i. but Polyfill should allow you to create a smaller box then what was recommended. im going to take a stab and say this will be the first box you'll make. unless your adept in the carpentry skills, you may want to consider a sealed box anyways, it would relieve you of make having to design a 'quality' port for the box, which is more than just a hole and a pringles tube stuck in it. (love that analogy)

so witha sealed box, and every wall covered in 1" of polyfill, you should beable to cut down the recommended size of your box (which was specified to be ported) enough to meet your needs.

if im wrong about the polyfill let me know.

stevdart

Platinum - Posts: 5,816

Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: September 21, 2004 at 8:23 PM / IP Logged

Nothing to correct there, IMO, /r7...and I like that Pringles thing too. The only reason I would say stick with ported in this case is the very little bit of power the amp has to offer. You would get a little more out of the power with ported. But polyfil wont do you any good here. Ultimately, when you are able to upgrade: get more power, a more apt sub, and use sealed for the enclosure. You'll take up less space. Meantime, like /r7 said above, the box can be oddly shaped to fit the car best and take up minimal space.

But how is it you know how loud this amp/sub is when the box isn't built yet?

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

mrdragon

Copper - Posts: 121

Joined: October 08, 2003

Location: Australia

Posted: September 21, 2004 at 11:20 PM / IP Logged

Ok for now i think i am going to build a sub and run wat i got at the moment. Does it matter where u place the ported? does it have to be on the same size as the sub?

Cheers:)

/r7

Silver - Posts: 340

Joined: July 30, 2004

Location: Canada

Posted: September 21, 2004 at 11:49 PM / IP Logged

heres a couple links to take a read through, i havent used either my self, but i've found great use of other tutorials from JLaudio's website

[QUOTE]

Ports

Covers the basics of duct/slot port construction and round port calculations including multiple port calculations.

Designing subwoofer enclosures

This tutorial concerns itself only with the physical construction of the enclosure and discusses enclosure shape, materials, bracing, strength and sealing. [/QUOTE]

hope that explains a bit :-)

btw read up about the bracing, that will help you out too.

EDIT: the 2 urls and descripts are ripped from the JL website, not taking any credit for writing that ;p

mrdragon

Copper - Posts: 121

Joined: October 08, 2003

Location: Australia

Posted: September 21, 2004 at 11:52 PM / IP Logged

Ok one last question do i really need 6x9 at the back if i got a 12" sub, 4" at the front plus a tweeter?

/r7

Silver - Posts: 340

Joined: July 30, 2004

Location: Canada

Posted: September 22, 2004 at 12:01 AM / IP Logged

4" is the only mid bass?

you may want some rear fill for the lower mid-bass i dont know how low the 4's can go, but im sure the 6x9 would offer more. i would say leave the 6x9's unless you get enough midbass the 4's, if your heavily relying on alot from your 6x9's right now, then you may want to lean towards keeping them.

thats an option. may just want to replace the fronts with something bigger if its an option you can take,

or leave them, if you cant make your 6x9's work with your 12" when you get it put in, disconnect them from the HU, saves having to take them out of their place, unless you plan on changing them.

hth

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Gain Setting on Amp?

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