Now that we got that out of our system, lets go over rise.
Two components of rise are:
We discussed these however, we should really go over the real world of what happens.
In the real world subwoofers warm up, in my experience I have found this to reeealy depend on the application. Spl subs, or daily subs seeing a whole lot of power especially now adays seeing all these giant beefy subs and cheap priced amplifiers will have a lot of what's called:
- Thermal compression
With thermal compression there is degrees of it. You can have an extreme of all out thermal compression where say you are feeding a poor sub 4kw RMS, if you feed it any more even if it can handle it without dying it does not increase in output because the resistance conversely increases as it gets hotter from more power added. A coil can only handle so much current after all. God for forbid it dosnt die first. So at this point you would be wasting money if you wanted a larger amp. In fact I should not even say that you are increasing power after thermal compression what you are doing is increasing voltage drive from the amp which ideally
is supposed to increases power draw, but the power is not increasing.
Vdrive * current from sub = power output(well Apparent power anyway but this is irrelevant to the point)
Increasing Vdrive * propotionaly less current via impedance increase for trying to drive more juice to the sub(heat) = canceling out of increased voltage effect to cause more current draw.
This is how you increase power:
V*I=P So, if you increase V
and keep I
static then you get an increase, if you increase current flow but keep voltage static you get an increase of power aswell, if you increase both then you still obviously increase power. Now, if you increase one but propotionanly decrease the other by the same ratio then you gain nothing at all as far as power goes.
In audio, the amplifier is a constant voltage source meaning it is static it means if any of the other two values change the voltage will still remain the same. Ohms law tells us there is 3 components, V I R. It shows that if just one changes then only one other has to change. Power also changes with any variation in change. So anyway, we have the ability to change the voltage amplitude of the amplifier output. We do this by moving the volume knob at the Head Unit. This tells the amp to increase the output(literally, amplification). When we do this, the voltage applied to the speaker by the wires creates a current draw depending exactly on the impedance of the speaker/sub. Vdrive/Imp=I.
So with fully blown thermal compression, V increases,
But R also increases proportionally, not necessarily at the same ratio at all in fact there are plenty of degrees of thermal compression it can be very little depending on power and sub model or be full fledged where no more power is drawn.
Thermal compression is always around it just may be so negligible at little power levels however it realllly also depends on speaker model because different sized subs, perhaps built with tank-like parts may withstand and put to use a lot of power. This is all relative. A small 3" 10w speaker may compress at say 20w for instance. In SPL we see the very little gain by going from already great power, to more.
A lot of SPL guys always say: oh wire real low wire real low an here's the thing:
Reactance is all over the place and dynamic to the music. The q and Ts parameters are linked to the reactive impedance profile which is why the box size both dictates the q(resonance) of the system and the impedance profile.
Misconception, or misuse of term
Alot of competitors refer to their rise as a reactive load. This is wrong because we cannot really effect the reactive impedance in the first place it is the resistance which we have most trouble with and you will also notice that you cannot beat that either by wiring low. Also if you have a musical system it is much more impossible to try and lower reactance as you are effecting your sound quality, or response profile. Low-end bass, linearity across the line(flat) is linked with whatever reactive impedance you will see. Changing it directly changes the Q outcome, FB etc of the box design and in fact the only common and real way to change it is to change box size, go figure...We should all know beter, musical quality and overall response is linked to reactance. In spl burping you have a better posibilty of messing with reactance for a better outcome such as a smaller box but IME, since it's related to efficiency aswell you may be reducing efficiency while increasing power and you know by now how opposites cancel out, efficiency gives you more then more power will anyway because of more possible heat losses and changing reactance gains you very little if you take notes on a change. In other words the smaller box used may reduce the efficiency enough to where the reduction in impedance is not helpful. You may notice something at a higher frequency since upper end efficiency may increase but this is not due to reactance decrease anyway.
Resistive, thermal rise
We know how there are the two components, well, now were looking at compensation misconception for thermal rise aswell, at least to a point, and it is much more possible then messing with reactance.
As I wrote about power compression, this term thermal rise is caused by it, so most of it is already explained but a misconception is that wiring low helps. Well it can help however people who are already in the compression zone are wanting to do it the most it seems. If you are already thermally compressing because you already have like 5kw to one sub think about it: if thermal compression is the cause of heat from a lot of current flow and its basically saturated with current to where you cannot draw no more through the subwoofer's coil, wiring lower will simply cause an even lower threshold for compression. Say it compresses at 5k and you wire it lower so now let's say it's already i the zone at 4k now and
with more power added you are def spinning your wheels on this one. I'd say its better to to choose one or the other, wiring low or more power not both if you are already up there in limits.
If you are on much less power and have some thermal rise already but not too much then you can wire a little lower. If you have no thermal rise at all practically and you wire too low you are going to be destroying your amp, straining it, protection etc. so on the flip side, thermal compression actually allows
you to wire maybe one step lower due to a safely idle impedance(higher then normal due to thermal rise) well not long idles only short idling as it can cool off, but this really depends I mean idling as in between music notes, etc...
On to the quest of True power:
Ideally, RMS Voltage / Nominal impedance rating is actually a very simple way to get the True power . This is because resistance creates no reactance. Nominal is a resistive value and not reactive.
The reason why we cannot simply say hey this sub is going to be wired at 1 ohm nominal so with 100V measured from the Amp output we don't even have to measure anything else, 100v/1=100A so well have 10,000 watts. The thing is, with the resistive rise, the speaker will rest up at a higher resistance. So a test or something to determine the actual total resistance will be required.
Also, as I have told people before just because the power appears to be less doesn't mean it isn't "hiding". With speakers, they store energy it is a conversion from one form of energy to another, electrical to mechanical. So you cannot see it with a meter.
There are other calculations for true power and reactive however the easiest and most ideal method is to invest in a true power meter...should be more reliable then an invention We all have seen, the "amp dyno" since you can measure with a true subwoofer load hooked up and it will see the true power after thermal rise from an actual sub. The reactance figure from a sub may not be the true power but the subwoofer has it's own thermal rise profile depending on power going to it. A True watt meter will see the full resistance because the sub is connected and you can play the amp. Something like the amp dyno uses a predefined resistance and not an actual subwoofer for a thermal profile.