Determine Ohm for Gain Setting

[jrwalte]

What's the best way to determine your ohm to place in the formula for setting your gains based off its AC voltage output with a test tone?

Do I just take the basic ohm of 4 ohm sub wired parallel is 2 ohm and speakers bridged on a 4 channel is 4 ohm? Or do I take an actual ohm measurement of the speaker wire? The ohm reading of my speaker wire for my fronts are about 3.4 ohms and my sub was around 2. Do those differences make a difference in the formula?

Thanks

[BEAVER]

Nobody uses the DMM method around here. Set your gains by ear.

[jrwalte]

Originally Posted by BEAVER

Nobody uses the DMM method around here. Set your gains by ear.

I do both. I use the DMM to set the max I should go on my amp gains and then I'll fine tweak it by ear from my HU. But then I have the baseline to not go past. Added security I guess

[BEAVER]

most who use this method use the nominal impedance, not the actual. i guess that's what i'd do if i were you.

[jrwalte]

Originally Posted by BEAVER

most who use this method use the nominal impedance, not the actual. i guess that's what i'd do if i were you.

thanks

[MarkZ]

Originally Posted by jrwalte

I do both. I use the DMM to set the max I should go on my amp gains and then I'll fine tweak it by ear from my HU. But then I have the baseline to not go past. Added security I guess

What happens if you listen to music that doesn't reach its peaks at 0dB?

[BEAVER]

I used to use the dmm method. Take a look at this...

DMM Dilema

[jrwalte]

Originally Posted by MarkZ

What happens if you listen to music that doesn't reach its peaks at 0dB?

I used a -3 db test tone to help with that. I typically listen to rock/alternative. Both my amps over power my speakers (fronts by 50 RMS and sub by 500 RMS). I wanted to set a level I know I shouldn't typically go past to help protect them. Since I have the 'headroom' in power I don't think I'm shorting myself.

So I guess I'm more using the DMM method to not over power my speakers...not to prevent clipping. It also allowed me to make sure I set the left and right bridged channels on my 4-channel to the same level.

[MarkZ]

Originally Posted by jrwalte

I used a -3 db test tone to help with that. I typically listen to rock/alternative. Both my amps over power my speakers (fronts by 50 RMS and sub by 500 RMS). I wanted to set a level I know I shouldn't typically go past to help protect them. Since I have the 'headroom' in power I don't think I'm shorting myself.

So I guess I'm more using the DMM method to not over power my speakers...not to prevent clipping. It also allowed me to make sure I set the left and right bridged channels on my 4-channel to the same level.

You're much more likely to blow your speakers by running at a high average level and low crest factor than you are by having excessive peaks. In other words, whether or not you reach an arbitrary peak is of no consequence. Remember, the heating and cooling of a speaker's VC is a very *slow* process compared to the dynamics of music.

The gain setting really isn't there to keep you from blowing your speakers...

[jrwalte]

Originally Posted by MarkZ

Remember, the heating and cooling of a speaker's VC is a very *slow* process compared to the dynamics of music.

Would excessive heat transfer to anywhere on the outside of the woofer that I could touch to know if the VC is getting too hot? If so, how warm/hot would be too much?

[XC-C30]

rip off the dustcap j/k

[MarkZ]

Originally Posted by jrwalte

Would excessive heat transfer to anywhere on the outside of the woofer that I could touch to know if the VC is getting too hot? If so, how warm/hot would be too much?

No, you want heat to transfer to the outside of the motor (and therefore away from the coil). The effectiveness of the heat transfer differs from driver to driver, and so does the max temperature that the coil and former can withstand.

IMO, there's no practical way of alerting the user to impending damage. The most reliable way may be the smell, actually. But obviously that's not terribly reliable either.

So I think the best method would be:
1) Buy drivers big enough and sensitive enough to do what you need them to do.
2) Filter them appropriately. In other words, don't use their frequency response measurements as the sole determinant of where your crossover points will be.
3) When you feel it's getting too loud, maybe back off a bit. *
4) If you're really ambitious (or paranoid), you could use some sort of limiter that's based on power content in large-ish windows. I don't know off-hand who makes such an animal for the car.

* = a note on #3... I think most people won't get full enjoyment out of their listening experience if they're paranoid about blowing the speakers. This is why I almost never buy equipment that's expensive to replace.

[GlasSman]

Originally Posted by jrwalte

Would excessive heat transfer to anywhere on the outside of the woofer that I could touch to know if the VC is getting too hot? If so, how warm/hot would be too much?

The only way to do that would be to place a temp probe inside the rear vent on the bump plate ....if your sub has one.

But keep in mind 2 things.....theres no way to overpower a speaker....and unless you're playing PURE TEST TONES....

You have nothing to worry about.

[GlasSman]

Another thing to add to the temp probe suggestion.....you'd have to monitor the resting temp when the sub isn't operating and compare any temp rise from that temp.

[jrwalte]

Well I'm playing my RD Elite 15" rated at 1000RMS on a 1500 RMS amp. I play it to a level that I enjoy and if I start to hear it distort I turn the volume down or select my second EQ setting for a slightly lower bass. I'm not overly concerned about blowing the sub to lower the quality of bass response that I enjoy but I don't mind extending the life a little bit by tapering back a little

I currently have it in a sealed 2.25 cu ft box. The guy in the store told me it's fine 2-3 but when i talked to RD myself they recommend 2.5-3. The guy also told me it was rated for 1500 RMS, hence why I bought a 1500RMS amp (not from him), but RD said it was 1000. I may try placing some polyfil in it to give it the affect of a 3cu box and to help dissipate heat better.

[Hillbilly SQ]

Originally Posted by MarkZ

No, you want heat to transfer to the outside of the motor (and therefore away from the coil). The effectiveness of the heat transfer differs from driver to driver, and so does the max temperature that the coil and former can withstand.

IMO, there's no practical way of alerting the user to impending damage. The most reliable way may be the smell, actually. But obviously that's not terribly reliable either.

So I think the best method would be:
1) Buy drivers big enough and sensitive enough to do what you need them to do.
2) Filter them appropriately. In other words, don't use their frequency response measurements as the sole determinant of where your crossover points will be.
3) When you feel it's getting too loud, maybe back off a bit. *
4) If you're really ambitious (or paranoid), you could use some sort of limiter that's based on power content in large-ish windows. I don't know off-hand who makes such an animal for the car.

* = a note on #3... I think most people won't get full enjoyment out of their listening experience if they're paranoid about blowing the speakers. This is why I almost never buy equipment that's expensive to replace.

that pretty much sums it up. actually, i only have $290 total in tweets, mids, and sub. team cheap bastard sq ftw!

[jrwalte]

Originally Posted by GlasSman

But keep in mind 2 things.....theres no way to overpower a speaker....and unless you're playing PURE TEST TONES....

You have nothing to worry about.

I don't play test tones on a regular basis and it's not for comps. Like you said, I'm probably fine. In addition, I mostly listen to rock/alternative so I don't think they'd have a huge output on the sub like a test tone would.

I also cross it at 65Hz with a 18DB slope. I have 4 bass ranges on my EQ, 20s, 30s, 50 and 80, that would most directly impact my sub. I turn down the 20, 30 and 80 slightly and up the 50. I like the big 'thump' from the bass drum