Going below the ohm load

 

Silver Member
Username: Heavyb

Hopkins, Sc Usa

Post Number: 102
Registered: Jul-04
i want to do 3 12s but when i bridge my amp it can only go to 4ohms stable. would it be that big of a deal to go down to 2.67 ohms. i have a guy that has done many installs telling me he used to break this rule all the time and nothing major ever happened. will it ruin my equipment for sure or can i just be careful with it.
 

Bronze Member
Username: Fishy

Post Number: 27
Registered: Sep-04
If you've got a little physics under your belt read this:

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html

Theoretically, optimum power transfer occurs when the internal impedance of an amplifier is matched to the external impedance of its load. At this point 50% of its power is provided to the load and the other 50% is dissipated as heat. Below this load more power is dissipated as heat than is transferred to the load. In the real world I'm not sure if car amps are designed to be played at this "optimum" load but if you reduce the impedance far enough it is possible to turn your basic SPL producing device into a space heater.

What this means is that if you reduce the load too far your amp will get hot as hell and may actually produce LESS power than at the optimum load plus the damping factor(how well your amp controls your speakers) goes down as well.

My advice is to lose a 12 or get a different amp(JL 500/1 mebbe?) or 3 12 ohm subs.

-Fishy
 

Bronze Member
Username: Fishy

Post Number: 28
Registered: Sep-04
If your subs are DVC(dual 4ohm?) there's another option. I've been told that it is generally a better idea to run speakers in parallel than series but if you've got dual 4 ohm subs just wire the voice coils in parallel. That'll give 3 2 ohm subs. Wire those guys in series and that'll give ya a 6 ohm load. Bridge your 700s into that and you should get about 470 watts total. If "bridged 4 ohm" is the optimum impedance of that amp then this actually the same amount of power you would get bridged into 2.67 ohms with like 1/3 the heat and a much better damping factor.

If your dead set on using 3 12's, are stuck with the equipment you have(and you have DVC subs), and find that a little over 150 watts a sub is sufficient power the I'd go with it.

Of course this is all theory. Jonathan or someone else would probably be able to give you the definitive answer on how to go, but I know Jonathan doesn't like maxxing out amps so would probably agree.

-Fishy
 

Bronze Member
Username: Fishy

Post Number: 33
Registered: Sep-04
OK, I just found something that may make this idea not so good. If you look here:

http://www.jlaudio.com/tutorials/wiring/index.html

Its says, "Please note that when wiring multiple drivers, whether DVC drivers or their SVC brethren, it is recommended that series connections between drivers be avoided at all costs."

I asked an installer once why this wasn't a good idea, but I can't remember his explanantion(probably because I don't think it made much sense to me at the time). Ya might want to drop JL Audio a line and try and get an explanation before you get too far in this endeavor.

Hmm, mebbe I'll start a thread.

-Fishy
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 1644
Registered: May-04
Make sure to note down a little further: "This does not include series connections made between voice coils on the same driver." I know you're talking about wiring the subs in series, but anyone reading this, this doesn't apply to the voice coils. As far as wiring subs in series, it is mainly because the voltage will be different between each sub b/c of minor build differences due to tolerances. Also, it is considered more desirable to have more voltage(rather than current) going to speakers for numerous reasons, which parallel wiring does. Remember that when wiring in parallel, the voltage is the same throughout each load, and current divides. With series, the current is the same and voltage divides between the loads.
 

Bronze Member
Username: Fishy

Tamarac, FL USA

Post Number: 46
Registered: Sep-04
Ok so difference in impedances, both electrical and mechanical, due to design tolerances means that each woofer in series affects its brother in a such a way that each sub just doesn't get a "like" voltage relative to the amplifier output? i.e. the mechanical behavior of woofers in series will be much more dispraportionate or out of synch and just sound plain ugly than if they were wired in parallel.

whew!

Is that it? It seems like they are just more effectively "damped" in parallel.

Oh well, "series bad", "parallel good" mo bettah.

thanks Jonathan

-Fishy
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