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#### npdang

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I've seen many people say, "Well I want to use this speaker, but I'm put off by the fact that it's 8 ohms."

Let me explain why it's ok to use an 8 ohm speaker, and why it could actually be better than a 4 or 2 ohm speaker.

First of all, using a higher impedance than what your amp is nominally rated for is always ok. In fact, if your amp is rated for 4 and 2 ohm impedances, typically you will get less power into 8 ohms meaning that your amp will run cooler and more efficiently at higher impedances. It won't hurt your amp, and in fact it's actually much better for your amp's longevity.

Now, you're probably saying how is getting less power out of my amp a good thing? Think of your amp's power reserves as your bank account. Just because you have 100 dollars in your bank account doesn't mean you have to spend it all. Quite the opposite. Wouldn't you rather spend LESS and get MORE? That's exactly what you're doing when you use less power from your amp, and get the same amount of output from a high efficiency speaker.

Remember, most speakers are rated at 2.83V. A 4 ohm speaker rated for 90db spl at 2.83v is really being rated at 2 watts! Whereas an 8 ohm speaker rated for 90db spl at 2.83v is only being rated at 1 watt. You can do the math for yourself, Power = Voltage^2 / resistance. At 2 watts, we can assume that same 8 ohm speaker is actually rated at 93db spl (remember, every doubling of power gives you a theoretical 3db gain in spl). So using that 8 ohm speaker will give you the same amount of output, at half the power required as a 4 ohm speaker. Your amps run cooler and draw less power from your vehicle's charging system, your speakers run cooler, and everyone is happy!

Ok, now let's look at another example of an 8 ohm versus 4 ohm voice coil. Typically, the efficiency of a speaker is given by:

Efficiency = ( B^2 * L^2 ) / ( R * Sd^2 * Mms^2 )

B = magnetic field strength
L = length of wire
R = resistance
Sd = surface area
Mms = mass

So for your 8 ohm voice coil, using the same wire as a 4 ohm voice coil, you would need twice the L or length to get an 8 ohm impedance. That makes sense doesn't it? A longer wire will have more resistance. Now, looking at the formula above, doubling L actually causes your efficiency to rise, even though the impedance also rises. So in this very oversimplified example, raising the impedance actually causes efficiency to go up and lowering the impedance actually causes a loss of efficiency.

What's important to remember is that it's the overall output and efficiency of the speaker that's important, not the impedance. A high impedance, high efficiency driver can get just as loud off a small amount of power as a low impedance, low efficiency driver that sucks a ton of power! Just because you have a 100 watt amp doesn't mean you have to use all 100 watts.... it's all about being efficient.

I also found this excellent post by Dan Wiggins over at carstereos.org:

"I think one thing to consider is that going to a higher impedance voice coil will result in better packing of the voice coil, meaning a higher cross-sectional-area of copper in the flux, for a given mass.

If you take a given driver, and simply swap out voice coils, you end up with more efficiency as you increase the impedance. Take a voice coil, say 2" diameter, 1" winding length, 24AWG 4 layer, and swap it with a 2" diameter, 1" winding length, 27AWG 4 layer, and you double the impedance, but the efficiency also goes up - less mass and better packing density."

It's because the moving mass has dropped, and if desired - because of the thinner wire diameter which packs in tighter - you can put more layers in the voice coil and potentially raise the BL."

#### mitchyz250f

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Please help me understand this better. Let us say I have an amp (Orion SX150) that puts out:
-150 watts per channel @ 4-ohm,
-300 watts per channel at 2-ohms
-600 watts bridged @ 4-ohm

Lets say I have sub that has two 8-ohm coils (tempest) or a sub with two 2-ohm coils. What would be the performance difference being with running the amp bridged, non-bridged with the sub in parallel or series? If you could answer this I would be very grateful.

#### npdang

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I'm not sure that I understand the question. WIth that amp, and a dual 8 ohm sub you would want to wire the sub in parallel for a 4 ohm nominal load.
For a dual 2 ohm sub, you would want to wire the coils in series for a 4 ohm nominal load. In all instances, you'd want to run your amp bridged into a 4 ohm load.

However, if you were to chose between a sub that was 4 ohm vs. 8 ohm, and the 8 ohm sub was more efficient by ~3db or more... I would choose the 8 ohm sub since you would be pushing your amp alot less harder and achieving same/more output.

MrHarris

#### calvinhpk

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ok...for this senario....
i have this amp that can output 4x150w @4ohm

and i have 2 choices of mid same manufacturer, same series, but different impedance,
i) 18W/4531G00 - 4ohm
ii) 18W/8531G00 - 8ohm

which one would give me more control, better sound?
will I lose out on some kick-bass in the 8ohm series?

#### 10K2HVN

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revelators.. yawn....

you wont hear the difference, just get the 4-ohm because you can.

what are you planning to run with those mids..?

If your planning to run them in the doors, NpDang says the Seas CA18RNX sound better in the doors, freeair.

#### calvinhpk

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noted. planning to put at the door. In consideration also the 15W version instead of the 18W.
the matter is, i've never listen to the Seas CA18RNX
i've listen to the revelator 4ohm version, and love it.

running with an a/d/s/ P850.2, bridged.

#### Tirefryr

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I was down to the Revs or Lotus for In-door app. After doing research, the Lotus/Excel drivers seem to be far better suited. If you have the room for the proper enclosure (and the extra cash), I'd suggest the Revs. Well, then again, that depends on the overall application you are looking for.

#### Kramerica

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So does this also mean that an 8 Ohm driver will pull halve as much current than a 4 Ohm driver?

Just trying to figure out the total current draw if I were to add another amplifier.

Thanks

#### demon2091tb

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I would think it would, as he said the amp would run cooler and be more efficient with an 8ohm driver over a 4ohm driver at the same sensativity. Say you have a driver with 88db/2.83v at 8ohms, and then you have one that is 88db/2.83v @ 4ohms then its basically 1/2 the power as the formula states, to get the same sensativity of the driver. Because the length of wire for the 8ohm driver is 2x as long as the 4ohm driver, making the 8ohm driver as effecient as the 4ohm driver with 1/2 the power.

Hope i re-itterated that correctly.

The big question i have is, Would cutting down the amount of power that an amp can possibly put out at 4ohms rather than 8ohms have a huge difference on overall spl levels? I probobly already answere my question but besides the obvious benefits of having an amp run cooler and lengthening the life of the amp, how amount actual power differences in question. Like having an amp that does 100rms @ 4ohms, and 50rms or less at 8ohms make a huge impact on the overall sound and possible spl levels?

#### npdang

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#### demon2091tb

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Haha Figures well good deal then, thats the only thing i really wondered about in using an 8ohm driver over a 4ohm driver, as all of the drivers that i will be using in my current build up are 8ohm drivers, except the Tempest and thats a duel 8

The only other thing i worry about is how loud the CA18 and the LPG 26 could be with ~40rms each @ 8ohms, as my amp puts out 82rms @ 4ohms. Somewhat off topic but any ideas Dang? Will they be loud enough to suffice?

#### Kramerica

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What I meant to ask was, will an amplifier powering an 8Ohm speaker pull halve the current then if it was powering a 4Ohm speaker?

Say an amp pulls 20 amps to power a 4Ohm speaker.

Will the same amp only need 10 amps to power the 8Ohm speaker?

Thanks, and I will be getting a Dayton Reference tweeter and midrange to replace some CDT's.

#### minitruck_freq

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demon2091tb said:
The only other thing i worry about is how loud the CA18 and the LPG 26 could be with ~40rms each @ 8ohms, as my amp puts out 82rms @ 4ohms. Somewhat off topic but any ideas Dang? Will they be loud enough to suffice?

40 watts will be loud with that combo. i have the ca18's and lpg 25nfa's running off an arc 4050. around 50x4 rated power. they get quite loud. even with the gains all the way down.

#### npdang

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40 watts will be very loud... however, keep in mind that with music an amp will very rarely be outputting it's max. continuous power.

#### minitruck_freq

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i played a 1 khz. tone at my normal listening level...measured ac voltage across + and - terminals... used the formula to convert to wattage blah blah blah. my ca18's are getting just over 17 watts. they are really loud with that little power to them. that myth about needing alot of power is just rediculous. IMO of course.

#### pervo

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finally registered thanks npdang!

wanted to bring attention to some issues

an 8 ohm driver compared to a 4 ohm, all things being equal outside of the voice coil windings have these trade offs

the 8 ohm will be slightly thinner and longer
resulting in more turns in the gap.... thus higher bl

making a 4 ohm will have a lower bl and thus needs to compensate

one meathod is to double the layer of voice coils, often facilitating the need for a different voice coil winding... ie flatter wires in order to fit in the same gap. thus bl will most likely not surpas the 8 ohm because even more windings are lost

so dirrect conclusions cannot be drawn form exactly how much inductance differs on the 4 layer vc vs the longer (winding wise) 2 layer

but it is safe to say that inductance will be higher on the 4 layer
also increased mass plays a factor also

this is my understansing at least

#### dwyers99

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I HAVE A QUESTION. I AM CURRENTLY RUNNING AN AUDIO ART 100HC THAT CLAIMS STABLE TO 1/2 OHM A CHANNEL

also have 2 oz matrix elite subs dual 4 ohm coils

in this case i had wondered how much difference i would get in the different loads i applied to this amp

i mean 1000 to 1200 watts bridged at 1ohm should give me that bass i need but i am worried it might be overkill both for my front stage and my electrical system not to mention running now at a 2 ohms load bridged is making it considerably hot even at mid listening levels.

i honestly dont think this amp can handle much lower impedence than 1 ohm/channel

however running each channel straight to each sub w/ say a 2ohm load drops the wattage of the amp significantly, nevermind running it to each sub w/ an 8 ohm load

i will try it tonight for kickS (BOTH 2 AND 8 PER CHANNEL)but i would like to hear your feedback on this

I understand what this thread was saying and it makes a great point btw!

#### kckon

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So in conclusion does a 2 ohm load have an increase in spl over an 8 ohm speaker?? we know that the amp will run hotter. Also so why make 1 ohm stable amps?

#### npdang

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It may or may not. It depends on the speaker. The key is to pay atttention to BOTH the efficiency and the impedance of the speaker.

I was just pointing out that there are tradeoffs in getting a low impedance driver that may lower efficiency if not compensated for. Of course for dual voice coil speakers it maybe different.

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I think another thing that DIY types overlook is the distance from the driver. Granted sensitivity is rated 1W/1M BUT coming from a home/pro environment we tend to go by experience and dictate a sensitivity number and involuntarily/mentally calculate that to "Listening Position Loudness" Knowing that sound pressure level decreases 6dB for every time you double the distance in an anechoic environment, one can conclude that in a vehicle interior the level perceived with one watt input will be MUCH greater than that it would be in a home or other surrounding. This also proves that the reduction in power going to an 8 ohm driver will be negated by early reflections, cabin gain and lack of appreciable distance from the driver. So not only is it an electrical calculation it’s a matter of the intended application that keeps the SPL of the driver up well within acceptable limits.