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scb Unregistered guest | I heard that, for example, 300 wrms @ 8 ohms is better than 300 wrms @ 2 ohms. The 8 ohm load will give better control over the speaker, will sound cleaner and the amp will run more efficiently. That is why home audio generally uses greater impedances. Regardless of application, more impedance w/ all else being equal is better...from an SQ/reliability standpoint. Anybody else heard this before? Is it true? |
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Bronze Member Username: Tj80Vancouver, BC Canada Post Number: 20 Registered: Aug-05 | Good question.. I've wondered this too. I have the option of buying either the 2 ohm or 4 ohm version of Image Dynamics components... 100 watts @ 4 or 200 watts @ 2 They suggest 150 watts RMS... I'd get the 2 ohm ones, but I was concerned about exactly the same thing... am I sacrificing SQ by dropping the impedance? |
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Silver Member Username: MixneffectOrangevale, Ca. USA Post Number: 335 Registered: Apr-05 | In D/C circuitry 4 Ohm loads are optimal, due to the law of physics, just as 8 Ohm loads are optimal in A/C circuitry. They are optimal because they allow ample amount of current with the least restrictions. High resistence require more current(amps) or power(watts) to get the same output. Lower resistence does not filter out enough harmonic distortion, which is caused by electricity and magnetism. Heres an interesting far fetched analogy; You know that buzzing sound you hear coming from high voltage power lines. Well that would be called Harmonic Distortion in audio specifications. Harmonic distortion is any alteration in the sound after is goes through any given electronic device (CD player, amp, pre-amp, etc...) Audio systems have become so precise, in recent years, that only approximately .008% of the sound has been altered to the original recording, when played back through most decent quality audio systems. As far as higher resistence is concerned, you get the same problem if you have a high ohm load. To get the same output, you may need a higher current amp or an amp that cranks out more watts. Either way, you will need a bigger/stronger power supply. When you incerase the current, you get more harmonic distortion. To get more watts, you need a higher current amplifier. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 9851 Registered: Dec-03 | 4 ohms is pretty much optimal on most class AB car audio amplifiers. lower loads will produce more THD, and a higher S/N ratio, offer less damping, and less head room. Basically at 2 ohms, you're pushing the amplifier harder, and continuously closer to it's limits. This generates more heat, and runs the internal components at closer to their tolerances. You're not going to get as good of a result doing this, but you will get more power. Now if you'll be able to really hear this difference is a different question. Most times it won't be an audible difference in comparison to the increase in output gained. The other drawback to running amps at 4 ohms (not bridged) is price. price per watt doubles by doing this so while running the whole system at 4 ohms like I did in my car improves overall SQ, and generates less heat, it's also considerably more expensive. |
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scb Unregistered guest | GlassWolf, So, the ONLY con to running everything @ 4 ohms is cost. The pro is SQ and reliability. Correct? |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 9871 Registered: Dec-03 | yup that's pretty much it. That downside can be a big one to most folks though. Especially in this age of multi-kilowatt systems. I suppose realestate is another minus though. You do end up with larger amplifiers as well, which eats up more space, and adds weight. I mean heck, I use three amps rated for 250 x 2 @ 4 ohms and each amp is 24" long and heavy as sin. That takes up a LOT of trunk space. |
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scb Unregistered guest | What about dampening factor and control over the speaker? That would be part of the SQ though...I think. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 9891 Registered: Dec-03 | damping is better at 4 ohms than at 2 ohms, due to the increase in headroom, and dynamic range of the amp at the higher impedance. |
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Silver Member Username: Matt12490Benicia, California Post Number: 180 Registered: May-05 | what do you mean when you say headroom? |
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Gold Member Username: Jonathan_fGA USA Post Number: 4637 Registered: May-04 | It refers to the reserve level capacity of the amplifier, in relation to the average output. Say your amplifier will produce enough power to achieve 120db of output at it's output capability (maximum power before clipping). If you were listening to material at an output level that averages around 110db, you would have 10db of headroom. As far as the amplifier itself, this relates to the capabilities of the power supply and the output devices. Lower impedance loads draw more current, which puts more stress upon both the power supply and the output devices. Higher impedance will equate to less current draw, lower heat, and thus, more headroom. Basically, the power supply won't sag as much when stressed. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 9906 Registered: Dec-03 | Jon got it before me, and put it very nicely. think of it like an athlete. The harder a runner runs, the less reserve energy that runner has in store for quick needed bursts of speed. Same sort of reasoning applies to amplifiers being pushed harder at lower loads in a sense. |
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Silver Member Username: InvictuzSeattle, Wa Usa Post Number: 153 Registered: Jan-05 | so let me dive a bit further into this with another question: Would the dampening and headroom difference between 2ohm and 4ohm exsist on a class D amp that can run either 2ohm and 4ohm? So is there a difference between class A/B 4ohm and class D 4ohm? |
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Silver Member Username: JeremycGermany Post Number: 806 Registered: Jun-04 | Yes, your dampening, and headroom will still be greater at 4 ohm, even with a class D. The only real diffrence with a class D and a class A/B is the way they amplify music. Instead of amplifing the original ac wave, a class D recreats it at a higher wave length. Thats why class Ds are more effeciant, but don't have as good of sound quality. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 9951 Registered: Dec-03 | yes class D amps are affected as well, but not in exactly the same way as a class AB. both amplifiers have finite power supplies, so that limits both amps in headroom and damping, but a class AB amplifier actually amplifies the input signal in a different manner to that of a class D amplifier, which digitally samples the input signal then reconstructs that signal at a greater amplitude at the output stage. There's no sampling involved with a class AB amplifier, so the damping is a little different, but the power supply still only has so much reserve available at any point in time, and that amount of reserve is also a factor of the load presented to the amp. |
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Anonymous | I got a 8ohm sub. Its 125w RMS. My Mono Amp puts out 120w @4ohm. I'm wondering if I got the same sub but at 4 ohms if I'd be more happy, or somewhat of a increase? I cant believe how loud it is with only 65-68 watts right now. |
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Platinum Member Username: GlasswolfWisteria, Lane USA Post Number: 10034 Registered: Dec-03 | you'd be ideal with the same sub if it were a 4 ohm model if it's rated for up to 125w, and you'd get 120w @ 4 ohms. you'd increase about +3dB in volume going from 8 to 4 ohms |
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Anonymous | Yeah Its a 12WO. I got the Amp and Sub from a friend because he had TWO 12wo's running on that Mono Amp, when they're BOTH 8ohms. Doesnt that mean they BOTH were sharing 65watts each? 30-33 watts a sub. No wonder he wasent happy with it. Of course, this is the same kid that traded me that 12WO and the E1200 JL amp for my old 12" Rockford HE2, and says he loves it lol. I was so excited when I got my hands on that for trading a RF HE2 LOL. Im almost tempted to sell the 12WO, and get a new 12W1V2 4ohm..it'd be getting around 125. It's rms is 150 though. What do you think Glass? |
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Platinum Member Username: GlasswolfWisteria, Lane USA Post Number: 10054 Registered: Dec-03 | that'd work out very well. you'd like it a lot. the e1200 is a good amp, but I'm not real excited about HE2s. and yes he was getting 65 watts to each sub.. or there abouts. Only about +3sB louder tahn what you have with the single sub. |
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Anonymous | Oh, EACH sub was getting 65Watts? But the amp only puts out 120@4 ohms. Or wait, does two 8ohms subs hooked up together make a 4 ohm load? I thought only DVC subs can make different independeces? |
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Platinum Member Username: GlasswolfWisteria, Lane USA Post Number: 10067 Registered: Dec-03 | ok 60 watts each. yes two 8 ohm subs in parallel is a 4 ohm load at the amp. in parallel, current is divided, so both subs "split" the power of the 4 ohm total output. www.bcae1.com may be a site well worth reading, if you have the time and inclination to get a getter grasp of basic electronics in relation specifically to car audio. nothing too complicated, but there's some math on the site. |
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New member Username: TjmutlowPost Number: 9 Registered: Sep-05 | Everything i have heard, lower the ohm load, raises the distortion rate of amp.Even though gives more power. |
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Platinum Member Username: GlasswolfWisteria, Lane USA Post Number: 10074 Registered: Dec-03 | yes ty. that's been stated above. lower loads produce more heat, higher THD, and lower S/N ratio, among other things. the only real plus to a lower load is more power from a smaller amplifier that costs less per watt. for strictly SQ purposes, a larger amp at a higher load will always be superior. |