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my current home theatre is with 6ohm speakers and i want to replace the front with Sony SS-B3000 bookshelf speakers (8 ohm, 120W power). The receiver manual dont specify what is the impedance it can support, it just says the provided speaker impedance as 6 ohm. I am considering a different 8 ohm floor standing speaker as well.

Also the receiver supports 135 watts per channel at 6 ohm.

Can I connect the SS-B3000 speakers to my current receiver?

Is it a safe assumption that the power delivery to the speakers increase as the volume is increased ?

@Arjithin, while I am no expert in this area, but one point (in Electronics) is that for best output, you need to match the impedance. Hence if your HT has a 6 ohm impedance, then it will be best if you can use speakers of the same rating.

(Do you remember the Max Power transfer theorum ? )

Agree with you, but the question is should I change the complete set up for a defective front speaker. I am not finding a good/budget friendly 6 ohm speaker. My assumption is that it wont make a big issue as long as I keep the volume to moderate levels. but expert opinions always help.

Hi Arjithin,
A higher impedance speaker wouldnt harm the receiver. On the other hand a speaker with lower impedance speaker than the receiver's recommendations would certainly load the amplifier. You can very well go with 8 Ohms, but replace both the front speakers so that you get symmetricity in volume. Otherwise the 8ohm speaker will be more pronounced.

Actually your speaker impedance changes with the frequency.
So your speaker can present a load of 6 ohms at say 1000 Hz, whereas at the same time present a load of 8 Ohms at 10000 Hz, and 4 ohms at 100 Hz.

The receiver (actually amplifier) needs to be built and rated for lowest possible impedance and highest possible power delivery.
That way the receiver output can be fed to higher impedance / lower power speakers as well.

As far as I remember - if your amp can take load of 6 Ohms speakers, then it can surely take 8 Ohms speakers (but not the 4 Ohm speaker - these speakers will draw far too great current and heat up your amp).

In that case, you can safely connect 8 ohm speakers. 8 ohm speakers will draw lesser current and would not cause any harm to receiver.

Yes, you may. Speakers with 8 ohms nominal impedance will draw slightly less power, so no worries that the receiver will *force* power into the speaker and burn it. If you replace only 1 front speaker with an 8ohms speaker, you may have to adjust the balance to get the image right.

It is not an assumption at all - that's how it actually works. Unless there is a severe mismatch between the power capabilities of the amp and the speaker, e.g. amp can supply > 2x power that the speaker can handle, you are safe.

If there *is* a large mismatch like that, chances are (refer to @alpha1's explanation of impedance varying with frequency) that some loud passage of sound, which has high power coinciding with a low impedance, heats up the voice coil.

Short bursts are unlikely to cause damage, but if such conditions are sustained, the voice coils of the speaker will give up their ghost due to overheating. However, in your case this is unlikely to happen since the amp and the speakers are more or less within each others' range.

One good way to visualise this relationship is an electric bulb, a water heater and the mains supply.

Both the bulb and heater have a heating element. The bulb's element is designed to put out light, and the heater's is built for heat.

The main supply does not care what the load is, it delivers a constant 230V to either of them regardless of their magnitude.

The loads, on the other hand, draw a current which depends on their own internal resistance and convert this current to energy. The mains circuit basically maintains a stable voltage irregardless of load. You will see in backward areas the voltage dips as the load increases. This is when the mains supply is overloaded beyond limits (+/- 10% is considered acceptable).

A good audio amplifier is a voltage source, much like a mains supply. It is load-agnostic upto its limits. For practical and cost reasons most commercial amplifiers are limited to a minimum of 4ohm loads and some are even less capable, only accepting 6ohm and above loads. Some older tube amplifiers could only handle 8 or 16ohms.

Basically 8 ohm speakers are fine on a receiver rated for 6 ohms. Speakers draw current, amplifier do not 'push' current. The magnitude of current drawn is dependent on the voltage the amplifier is putting between the speaker terminals, which in turn depends on the volume control position. The safest way to avoid overload is avoid distortion.

An amplifier with low output capability can also be assumed to be one that will damage speakers severely when overloaded. Tweeters will be destroyed outright by clipping distortion, which is the niche specialty of cheap and underpowered solid-state amplifiers.

On the whole, it is better to have an amplifier that can deliver more power than the speaker can demand. Though this sounds counter-intuitive, it is far easier to hear speakers in trouble than make out distortion at high volumes, and prevent damage.

And yes, speaker impedance does change with frequency. However that is a far more complex discussion maybe outside the scope of this thread.

how to find how much watts one speaker is consuming at some level on volume knob. If I go by rating of 100 watts/ chl, does that mean 4 speakers will consume 400 watts ( but at what level of volume knob?). what if I switch off source in (STB, TV) to receiver now, will receiver still present the same voltage level to speakers. I am wondering if I should keep the receiver always in switched off state when not in use. pardon me if it is really a dumb question.

Wattage depends on input signal too. If there is no input to receiver, power consumption by speakers would be zero (ignoring error/noise and power required to keep the receiver on).

Even in real life, no movie would have all channels driven at 100% all the time. Most of the signals would be sent to front left and right speakers.

To actually feed 100W to speakers:
1. You need a "test" signal that is a sound with fixed frequency. just a very long beeeeep
2. Then very volume knob to get 100 W output. To measure, wattage you need some equipment (measure ac current/voltage being fed to speakers).

Example of test tone:

10kHz 44100Hz 16bit funny music - YouTube

No easy answer really.

The only way to find out is to measure the actual output current, and this is not trivial to do. You could measure the voltage across the speaker but that will not be very accurate as the impedance (and current) change with frequency.

Normally most high-quality amplifiers present zero gain with the volume control at maximum, and there is a fixed gradation of the volume knob. These amplifiers usually mark the knob in dB, and it goes from -infinity to zero. At zero dB, the amp is producing maximum power, at -6dB it is producing half power, and so on. The complicated thing here is that each song has a slightly different recording level and for some songs the 0dB will be a slightly different situation.

So to answer your question, there isn't an answer.

As long as the impedance is more than the minimum specified you are Ok. Plus better damping, minus lower power.

No problem in using 8ohm in place of 6ohms. Max power transfer is a thing of the past, when transformer coupling was used. Even if you were to use a 4ohms in place of a 6ohms the sky would not fall on your back. If you used lower impedance load and drove the volume to crazy max then perhaps the amplifier would tend to heat up a bit more and would shut itself down in case of thermal run out. Most modern amplifiers do that. Best bet is not to jack up volume too high anyway; that would keep your ears functional till older age, hehe.