Question about Ohms

[elitism]

What is better to have low ohms with low watts ie 6 or 4 ohms at 90w or 40 watts, or high ohms with high whats ie 8 ohms with 100+ watts? Thanks in adavance!

 

[JVC]

Doesn't really matter about ohms, as long as the receiver matches the ohms of the speakers. If you use 4 ohm speakers with an 8 ohm receiver, you could possibly damage the receiver. Can make receiver run very hot. But receivers today have the protection mode, to save them from frying.

This didn't really answer your question, the way it was asked, but I hope it helps you understand a little better?
Good luck!

 

[jcPanny]

Amp power and impedence

In general, all amps and receivers can drive 8 ohm speakers and most are fine with 6 ohms. I dedicated amp or good mid-fi receiver is required to drive speakers with a 4 ohm impedence.
Also note that most amps and receivers will deliver MORE power into a lower impedence (i.e. 100 Watts @ 8 ohms, 120 Watts @ 6 ohms, etc.)
Finally, the power delivered by the amp, the eficiency of the speaker (90 dB @ 1 Watt/1 meter etc.), and the size of the room determine the volume level at the listening position.

 

[agarwalro]

Finally, the power delivered by the amp, the eficiency of the speaker (90 dB @ 1 Watt/1 meter etc.), and the size of the room determine the volume level at the listening position.

Good reply. To expand...

A good amp will deliver twice the power every time you reduce the speaker impedance by half. So,
100W into 8 Ohm load
200W into 4 Ohm load
400W into 2 Ohm load.

That is why 8 Ohm speakers are easier to drive than 4 Ohm, which is easier than 2 Ohm.

 

[WmAx]

Good reply. To expand...

A good amp will deliver twice the power every time you reduce the speaker impedance by half. So,
100W into 8 Ohm load
200W into 4 Ohm load
400W into 2 Ohm load.

That is why 8 Ohm speakers are easier to drive than 4 Ohm, which is easier than 2 Ohm.

A good amp does not have to double maximum power as the load is halved. In fact, very few even 'good amps' actually double power. This usually comes down to power supply constraints. A switching amplifier is more likely to come closer to doubling output power, because of it's vastly increased energy efficiency(much smaller power supply needed to achieve same power output as conventional Class AB amplifier).

-Chris

 

[majorloser]

Ohm's Law

Ohm's Law states that V=I*R or voltage = current X resistance.

The lower the resistance the higher the amperage output required from the power supply (amplifier).

Also, wattage is the measurement of power supplied.
Wattage = Voltage X Amperage

With that said, if you cut the resistance (ohms) in half you should double the wattage. But speakers and amplifiers aren't perfect. The resistance of a speaker will vary under operation as will an amplifier under load. Unfortunately with electronics some of the power required to run the item is wasted in heat production. (damn physics ) I can't wait till we get superconducting audio equipment. Liquid nitrogen cooling systems........

I'm no expert and I'm sure one of the "pros" around here will correct me. It's been over 20 years since I went through electronics tech school.

 

[j_garcia]

Doesn't really matter about ohms, as long as the receiver matches the ohms of the speakers. If you use 4 ohm speakers with an 8 ohm receiver, you could possibly damage the receiver. Can make receiver run very hot. But receivers today have the protection mode, to save them from frying.

While the receiver will heat up, the speakers are more likely to be damaged by clipping (if pushing it too hard) before any damage will be done to the receiver (or it will shut off due to the protection circuitry). Some receivers will shut off when the impedance drops too low as well. If the receiver/amp is not stable at the nominal impedance of the speaker, you will most likely have issues. I guess the simple answer to the question really is, pick the speakers then find an amp that has sufficient power for them.

 

[WmAx]

With that said, if you cut the resistance (ohms) in half you should double the wattage. But speakers and amplifiers aren't perfect. The resistance of a speaker will vary under operation as will an amplifier under load. Unfortunately with electronics some of the power required to run the item is wasted in heat production. (damn physics ) I can't wait till we get superconducting audio equipment. Liquid nitrogen cooling systems........

I'm no expert and I'm sure one of the "pros" around here will correct me. It's been over 20 years since I went through electronics tech school.

It should be noted that common amplifiers will double/2x (well not exactly, more like 1.98x) the power into a lower impedance load so long as it's not near the maximum output power range. For example, amplifier B has 100 watts @ 8 ohms or 150 watts @ 4 ohms. But these are just maximum power specifications. If you measure amplifier B at, for example, 25 watts @ 8 ohms, the power will essentially be almost doubled to something like 49.2 watts @ 4 ohms, assuming that the input signal to the amplifier is the same in both conditions, and that the amplifier has a very low output impedance as is typical of most solid state amplifiers. The determining factor that decides the actual ratio under the maximum power rating is output impedance.

-Chris

 

[Francious70]

What is better to have low ohms with low watts ie 6 or 4 ohms at 90w or 40 watts, or high ohms with high whats ie 8 ohms with 100+ watts? Thanks in adavance!

To answer your question, neither will sound any differnt than the other. It's just more efficient to run 8 ohm speakers.

 

[agarwalro]

A good amp does not have to double maximum power as the load is halved. In fact, very few even 'good amps' actually double power. This usually comes down to power supply constraints. A switching amplifier is more likely to come closer to doubling output power, because of it's vastly increased energy efficiency(much smaller power supply needed to achieve same power output as conventional Class AB amplifier).

-Chris

To put in a quick response I left out some info. Let me rephrase my earlier response,

An ideal amp will deliver twice the power every time you reduce the speaker impedance by half. So,
100W into 8 Ohm load
200W into 4 Ohm load
400W into 2 Ohm load.

That is why 8 Ohm speakers are easier to drive than 4 Ohm, which is easier than 2 Ohm.

Barring other considerations, the closer your amp to the ideal, the better.

 

[MDS]

I'm assuming the underlying question is whether the amp will be louder when it is producing 200 watts into a 4 ohm load instead of 100 watts into an 8 ohm load and the answer is no. You can't look at the higher watt number and conclude that it is louder. See the v= i x r and power (watts) = i x v lesson above.

The V is constant as the amp has a maximum rail voltage it can supply. It doesn't get louder because the wattage number is higher - it MUST produce more power to maintain the same output level when the load increases.

In other words, if the amp can produce 100 dB SPL when it is producing 100 watts into an 8 ohm load, it MUST produce ~200 watts into a 4 ohm load to maintain the same 100 db SPL. The 8 ohm load is far easier to drive for all of the reasons already cited.

 

[WmAx]

In other words, if the amp can produce 100 dB SPL when it is producing 100 watts into an 8 ohm load, it MUST produce ~200 watts into a 4 ohm load to maintain the same 100 db SPL. The 8 ohm load is far easier to drive for all of the reasons already cited.

I don't quite get what your saying. Because a watt is a unit of power. If you design the same speaker, but only change the coil resistance, so that one is nominally 4 ohms and the other is 8 ohms, they will still have the same 1watt/1meter sensitivity. But if the amp produces twice as much power into 4 ohms, it will drive the 4 ohm version 3 dB higher then the 8 ohm version of the same speaker.

-Chris

 

[Buckeyefan 1]

What is better to have low ohms with low watts ie 6 or 4 ohms at 90w or 40 watts, or high ohms with high whats ie 8 ohms with 100+ watts? Thanks in adavance!

You mean low ohms with high watts, or high ohms with low watts - assuming you are talking about speaker ohm ratings compared to receiver/amp ratings.

In laymans terms:

It's less expensive to have high ohm speakers with a lower watt receiver/amp. To drive demanding low ohm/low spl speakers, you'll want a more powerful receiver/amp. These amps will have larger capacitors, heat sinks, and power supplies to deliver the power needed to drive demanding speakers to similar spl levels (compared to high ohm speakers driven off lower wattage amps).

You also need to pay attention to the spl ratings of the speakers. You can have a 4 ohm 90dB speaker which will play louder than an 8 ohm 85dB speaker given 1 watt at 1 meter.

When you purchase demanding speakers, you are limited to spending more on a higher quality, powerful amp/receiver. When you purchase efficient speakers (say 8 ohm 93dB), you can purchase just about any receiver on the market. Keep in mind efficient speakers don't necessarily equate to better sound, just more volume - quicker.

 

[MDS]

I don't quite get what your saying. Because a watt is a unit of power. If you design the same speaker, but only change the coil resistance, so that one is nominally 4 ohms and the other is 8 ohms, they will still have the same 1watt/1meter sensitivity. But if the amp produces twice as much power into 4 ohms, it will drive the 4 ohm version 3 dB higher then the 8 ohm version of the same speaker.

-Chris

Yes, I did leave out that little detail, but my point is that alot of people like the big numbers and think 200 watts into 4 ohms is *double* the loudness of 100 watts into 8 ohms, simply because 200 is twice as much as 100. 3 dB is a small increase.

 

[lonsdale3]

I have a question about ohms. I am choosing equipment for a home theater for a room that is 15' x 17' with an 8'6" ceiling.

The current plan is for a Marantz SR 8500 with 125 watts into 8 ohms. It is a 7.1 receiver. The speakers will be PSBs. The towers and surrounds are 6 ohm nominal and 4 ohm minimum. The center is 8 ohms nominal and 6 ohms minimum.

The Marantz has the following notice on the rear by the speaker connections:

"Front A or B, Center, Surround, Surround Back - minimum 6 ohms. Front A and B, minimum 8 ohms"

Will the Marantz drive speakers with these ohm ratings?

Thanks very much for your help.

 

[MDS]

The Marantz has the following notice on the rear by the speaker connections:

"Front A or B, Center, Surround, Surround Back - minimum 6 ohms. Front A and B, minimum 8 ohms"

The word 'minimum' there doesn't actually mean the minimum impedance of the speakers - it refers to the nominal impedance. It would probably be better phrased 'At a minimum, use speakers with a nominal impedance of 8 ohms or greater'. Nearly all 8 ohm nominal speakers dip to a minimum near 4 ohms (impedance varies with frequency). The specs listed for the PSB speakers are pretty standard and I doubt the Marantz would have any trouble driving them.

 

[Fastnbulbous]

There's an interesting table that shows recommended watts to use according to speaker sensitivity (dB) and room size.

http://timefordvd.com/hardware/receiver/HomeTheaterReceiverBuyingGuide2.shtml#RoomSize

For my 2,700 cubic ft room and Rega R3s with 89 dB sensitivity, I need a minimum of about 51-61 watts per channel. Not a problem. However, the Regas have Nominal Impedence of 6 Ohms, which still confuses the hell out of me. Does it mean I need 76 to 80-something?

So if I got an Harman Kardan AVR 635 at 75 watts per channel, I should just hope for the best?

 

[majorloser]

Buy the biggest, baddest and meanest amplifier your wallet (and WAF) can accept! ARR, ARR, ARR