intel

iTrader: (1)

Hey,
I have a pair of JBL GTO 638s in the front and a pair of JBL GTO 938s in the back.
The RMS value of the fronts are 60 watts and the rears are 100 watts.

I want to know if I can adjust the gain on my amplifier for the fronts to around 90 watts rms and the rears to about 120 watts rms.


I have a voltmeter and access to an oscilloscope. My amplifier starts to clip at around 130 watts per channel. So I would be able to give a clean signal with no clipping
to the front and rear speakers if I were to go with 90 watts for the front and 120 watts for the rear.


Am I at risk of damaging the speakers? I have been reading mixed responses and wanted to get some opinions from you guys.

Thanks-

EmperorJJ1

iTrader: (5)

the reason ur getting mixed responses is because of the nature of speakers in general. there is no correct yes or no to if you were able to give them more power. but you can solidly say you can be at risk of damaging the speakers.

if you listen to clean music and dont clip the HU much and trust yourself then you should* be ok

intel

iTrader: (1)

Aight, thanks for the input EmperorJJ1.
I ended up tuning my setup to be at RMS value, my Kenwood BT952hd puts out a clean signal all the way to volume 34, I clip at 35/35, which is pretty impressive.
So I set the fronts for 60w rms and the rears for 100w rms.

EmperorJJ1

iTrader: (5)

hows the volume at RMS unclipped?

Cobalt ss/sc Jake

i have mine up all the time with no probs

intel

iTrader: (1)

Are you asking how I figured it out or how it sounds lol? If it's the latter, I am actually quite happy with the way they sound. I haven't had time to try different genres of music to fully test out my headunit, I still haven't messed with the equalizer options as well.

EmperorJJ1

iTrader: (5)

how it sounds i know all about oscopes. the reason why im asking is i can go more in-depth with my response to give u a better idea of what ur looking at if u want that is assuming ur werent happy with the sound which it sounds like u might be at least for now

intel

iTrader: (1)

Ah I got ya, do you mind explaining..? I am pretty curious and would like to get a better idea of what I am looking at.

EmperorJJ1

iTrader: (5)

there's 2 limits of a speaker mechanical and thermal. While a speaker can fail in many different ways those 2 pretty much sum up how you would damage a speaker with too much power and the reason why there isn't a "real" rating of a speaker is because neither of those happen on a consistent measurable basis.

Example if we are looking at mechanical failure the speaker broke due to too much movement. the more power the speaker gets the more theoretical movement it has. so at 91w it will move more then at 90w. but the speaker moves more or less depending on the frequency being played. at 20hz the speaker may end up moving much more on say 30w then it would at 100w at 5khz. so a crossover plays a big role in preventing mechanical failure. This one is hard to judge especially on a door speaker because you aren't going to see it when its laying behind the door panel. However you could theoretically play white noise and check its movement prior to wrapping up the install to get an idea of mechanical movement vs real world power ur amp is giving

Thermal failure somewhat easier because theres a 100% limit on the power the copper voicecoil can carry. if its 90w then 91w is blown simple as that. The spin on this is when a speaker is playing it releases the heat when air passes the voicecoil. So while the copper has a limit of power it can handle before burning if the speaker is cooling the voicecoil down you would have to exceed that limit before the VC actually sees that temp/power limit. You also need to look at this similar to an engine. when you start it up in the morning its going to be cold regardless and if your playing it all day its going to be easier to break that thermal barrier vs a short blast of overpowering. This is why you see competitors in SPL comps exceed their RMS ratings by so much. also why people post how many runs they do at a time. if you pump a gigantic number of watts into the speaker for the 3 seconds it takes to win then doing a second run right after of 30 seconds playing music is going to be disadvantageous as compared to waiting a few hours for your sub to cool down, your batteries to charge up ect ect

You also have to factor in impedance rise. the nominal impedance of the speaker say 4 ohms. is always going to be wrong. when u get the speaker your resting impedance will be slightly higher or lower. When you apply power to the speaker and it moves the impedance will change as well. So every millisecond your amp is giving the speaker a different amount of power due to this change.

I've never worked in the speaker manufacturing business so i cant state facts but one can assume after building a speaker they compile this information and make an educated guess at power rating based on these "limits" and changes as well as an attempt to prevent warranty returns. Speaker manufactures know that most people are idiots and most warranty claims are going to be not that the speaker had a manufacturing defect or didn't deliver its full performance but instead "user error" SO it makes sense that they would lower the RMS rating to lower warranty costs.

intel

iTrader: (1)

Awesome, thanks for the explanation.

intel

iTrader: (1)

Had another question emp,

Before I got a chance to mess with my subwoofer I tuned my headunit for the speakers (front+rear) at a volume of 34/35

I used the oscope on the sub out from my headunit and I found out that it clips at 32/35 volume.

I take it that I have to go back and set the gains on my amp for the speakers at a volume of 32/35 now right?

EmperorJJ1

iTrader: (5)

you should ya

intel

iTrader: (1)

Aight, thanks for all the help again.
Have it all set now.

tru2nrtt777

iTrader: (1)

I was wondering if you were going to get into impedance rise Emp although if you were going to get that technical you could also get into the fact that no two speakers are exactly the same, the exact same model speaker can handle and sound completely different from the one it was packaged with at the factory. Crossovers and individual channel gains can correct it but even if not corrected the bare ear will not be able to tell.

Also the wattage ratings are all based on thermal capacity, every maker is different in their tests on determining rms but most run the speaker at fs on different wattages for certain amounts of time until they reach certain temps. Mechanical damage is usually loosely referred to as rating the x-max. In theory if it exceeds x-max it is creating heat and mechanical damage because the cone is now no longer traveling in a linear fashion. Most good companies underrate both parameters for warranty and qc purposes.

EmperorJJ1

iTrader: (5)

right since no two coils are the same. Audison used to offer a service for their Millie line of speakers where if u paid an extra thousand or whatever you would get tweeters that were as close as possible in specs (they built however many then tested them and paired based on specs)

as far as xmax thou that's not necessarily the point of mechanical damage.... speakers not so much but subs especially have alot of mechanical leeway so you might be able to exceed the linear travel without necessarily breaking the speaker immediately (however if u continue to do it it will eventually break) That would still quality as damage now that im rethinking it as i type so ya i see your point however i was originally thinking of immediate damage. (ive seen speakers that were played so hard the voice coil smashed into the magnet making the former crinkle and destroying the speaker. The coil itself was still copper colored with no discoloration so in that case the thermal barrier wasnt met. Now you could always argue the speaker was defect from the manu if the coil wasnt properly aligned but it could also be a case that it got too much power. since the coil wasnt burnt it would have had to be clean or semi clean power clipped signal would have discolored or blown the coil