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post #1 of 56 Old 09-08-2013, 05:10 PM - Thread Starter
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I am probably buying an Emotiva power amp (XPA-200) . It isnt exactly a powerhouse (my receiver by itself is powerful enough, I just want my speakers to open up with a separate unit).
The Emotiva descriptions says:
"Equally at home powering a superb stereo system, or the front channels of an audiophile surround sound system, the XPA-200 delivers 150 watts per channel into 8 ohms, or 240 watts per channel into 4 ohms of powerful, clean, audiophile grade audio power."
My amp is a Pioneer Elite VSX-53, speakers are Polk LSi-9s (4ohm, power hungry). So, the Emotiva will be providing 240 watts of power into the Polks because they are 4ohms? Or 150W? Why the difference? If I had an 8ohm speaker set, would they be less loud because of 150W power? Or this has nothing to do with how loud the signal will be?
I am sure this is a basic question, but I never got a straight answer to it from anyone before.
Thanks a lot.
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post #2 of 56 Old 09-08-2013, 05:16 PM
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So, VSX will be providing 240 watts of power into the Polks because they are 4ohms? Or 150W?

The VSX wont be providing 240 watts of power into 4 ohms, the Emotiva amp will.

http://www.ehow.com/facts_5913837_speakers-ohm-vs_-ohm.html
Quote:
Considerations
When choosing four or eight ohm speakers, it is important to consider the minimum ohm rating of the amplifier. Connecting four ohm speakers to an amplifier designed for eight ohms can overdrive the amplifier, damaging both the amp and speakers. However, a four ohm amplifier can handle eight ohm speakers.

Considerations
All other things being equal, four ohm speakers will play louder than eight ohm speakers. This is because the four ohm speakers have less resistance to the flow of voltage from the amplifier.



Read more: http://www.ehow.com/facts_5913837_speakers-ohm-vs_-ohm.html#ixzz2eLofowxa

You also have to consider the sensitivity of each speaker and take that into account.

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post #3 of 56 Old 09-08-2013, 05:30 PM - Thread Starter
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Quote:
Originally Posted by afrogt View Post

The VSX wont be providing 240 watts of power into 4 ohms, the Emotiva amp will.

Yes, thanks for pointing that out. I corrected the post. The VSX is 110W into 8ohm, the Emotiva is 150W.

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post #4 of 56 Old 09-08-2013, 05:51 PM - Thread Starter
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My guess is that 4 Ohm speakers (all other things like sensitivity being equal) will produce a louder sound from the same signal. I think that because the impedance of a speaker is its opposition to the flow of A.C. current. The lower the impedance, the higher the current flow. Increasing the impedance will decrease the current flow (all else being equal). Decreasing (from 8 to 4ohm) - in a stronger signal and sound.
Is this accurate?
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post #5 of 56 Old 09-08-2013, 06:02 PM - Thread Starter
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Quote:
Originally Posted by afrogt View Post

The VSX wont be providing 240 watts of power into 4 ohms, the Emotiva amp will.

http://www.ehow.com/facts_5913837_speakers-ohm-vs_-ohm.html
You also have to consider the sensitivity of each speaker and take that into account.

Fantastic, Afrogt. Your post appeared simultaneously with mine above. That is the information I was looking for. Thank you so very much.

Regarding
Code:
Connecting four ohm speakers to an amplifier designed for eight ohms can overdrive the amplifier, damaging both the amp and speakers. However, a four ohm amplifier can handle eight ohm speakers.

I gave the Polks run for the money for an hour or two. I gave them hell. No distortion, no issues, the Pioneer Elite VSX amp didnt even become more than slightly warm. This could have been because my speakers are crossed over at 150Hz, everything below going to a subwoofer which has its own 1000W internal amplifier. So, some of the power was handled by the sub.

Here is what i dont understand:
Code:
Connecting four ohm speakers to an amplifier designed for eight ohms can overdrive the amplifier.

What does "ovverride" mean in this particular context?

Thanks
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post #6 of 56 Old 09-08-2013, 06:46 PM
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When you have a music or movie passage that ask for a peak and the amp has no more headroom (ceases to increase in wattage or level out) then it clips or distorts which if played long enough will cause damage.Some mfg provide a 8/4ohm switch but doing this limits rail voltage to protect the amp and limits output at the same time.
All speakers vary in impedance throughout the audio spectrum they do not maintain a constant ohm they dip and peak.
4ohm will draw more current from an amp than 8ohm thats why you should stay clear of amps that have the same or barely more wattage at 4 than 8ohm.
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post #7 of 56 Old 09-08-2013, 07:01 PM - Thread Starter
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Quote:
Originally Posted by oztech View Post

When you have a music or movie passage that ask for a peak and the amp has no more headroom (ceases to increase in wattage or level out) then it clips or distorts which if played long enough will cause damage.Some mfg provide a 8/4ohm switch but doing this limits rail voltage to protect the amp and limits output at the same time.
All speakers vary in impedance throughout the audio spectrum they do not maintain a constant ohm they dip and peak.
4ohm will draw more current from an amp than 8ohm thats why you should stay clear of amps that have the same or barely more wattage at 4 than 8ohm.

Thank you for the explanation.
And how is Emotiva XPA-3 or XPA-200 in that regard?
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post #8 of 56 Old 09-08-2013, 07:19 PM
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Quote:
Originally Posted by grigorianvlad View Post

Thank you for the explanation.
And how is Emotiva XPA-3 or XPA-200 in that regard?
They meet the requirements as for specs but I personally have not listened to them in a long time.
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post #9 of 56 Old 09-09-2013, 09:12 AM
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Quote:
Originally Posted by grigorianvlad View Post

My guess is that 4 Ohm speakers (all other things like sensitivity being equal) will produce a louder sound from the same signal. I think that because the impedance of a speaker is its opposition to the flow of A.C. current. The lower the impedance, the higher the current flow. Increasing the impedance will decrease the current flow (all else being equal). Decreasing (from 8 to 4ohm) - in a stronger signal and sound.
Is this accurate?

so generally your volume control setting defines the voltage gain that your preamp plus amp will demonstrate. So if you plug an 8 ohm speaker in, you'll see, say 1 watt with a fairly loud test signal (ket;s say it happens to hit 85 dB with one watt in your listening space.. Plug in a 4 ohm speaker, change nothing else, and you will be using 2 watts from the power amp. It's ohm's law. Cut the impedance in half, leave the voltage (volume control setting) the same, and the current HAS TO double. It's the law. Since it's physics, you can't even bend it a little. At least at the scales we're engaging here. Power is voltage times current, so doubling current while keeping voltage constant doubles power.

But which will be louder? depends. If the 8 ohm is a modern efficient speaker design and the 4 ohm is my former Magnepan 1.6s, probably the 8 ohm speakers will be louder. Because the Maggies are inefficient - IIRC, 86 dB for 2.86 volts (which translates to 2 watts into a 4 ohm load).

From the amp's perspective, it should double power with a halving of the impedance, all else being equal. Leaving aside the unlikelihood of such equality, a properly operating amp will do exactly that - double down- until it gets to the limits of its ability to cleanly deliver power. Realities of physics as well as design decisions dictate that (AFAIK) no amp will reliably double it's maximum output into successively halved impedances.

The real question is whether it matters. And the answer is it depends. I was able to drive my Maggies as loud as I wanted them with my now-semi-elderly Denon receiver. Same is true with the Paradigms that replaced the Maggies eventually. But I don't need 105 dB peaks - - I tend to listen to movies at -10 or more from reference, which means I'm using one tenth the power I'd need in a (futile) attempt to reproduce sound at reference levels. I say futile because my small Paradigms, even with the help of a sub, likely would compress before reaching the 105 dB potential peaks at reference level (so the amp may be sending the power to push the speakers to 105 dB but they only put out 102 or maybe less - - that's basically what speaker compression is).
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post #10 of 56 Old 09-09-2013, 10:16 AM - Thread Starter
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Originally Posted by JHAz View Post

so generally your volume control setting defines the voltage gain that your preamp plus amp will demonstrate. So if you plug an 8 ohm speaker in, you'll see, say 1 watt with a fairly loud test signal (ket;s say it happens to hit 85 dB with one watt in your listening space.. Plug in a 4 ohm speaker, change nothing else, and you will be using 2 watts from the power amp. It's ohm's law. Cut the impedance in half, leave the voltage (volume control setting) the same, and the current HAS TO double. It's the law. Since it's physics, you can't even bend it a little. At least at the scales we're engaging here. Power is voltage times current, so doubling current while keeping voltage constant doubles power.

But which will be louder? depends. If the 8 ohm is a modern efficient speaker design and the 4 ohm is my former Magnepan 1.6s, probably the 8 ohm speakers will be louder. Because the Maggies are inefficient - IIRC, 86 dB for 2.86 volts (which translates to 2 watts into a 4 ohm load).

From the amp's perspective, it should double power with a halving of the impedance, all else being equal. Leaving aside the unlikelihood of such equality, a properly operating amp will do exactly that - double down- until it gets to the limits of its ability to cleanly deliver power. Realities of physics as well as design decisions dictate that (AFAIK) no amp will reliably double it's maximum output into successively halved impedances.

The real question is whether it matters. And the answer is it depends. I was able to drive my Maggies as loud as I wanted them with my now-semi-elderly Denon receiver. Same is true with the Paradigms that replaced the Maggies eventually. But I don't need 105 dB peaks - - I tend to listen to movies at -10 or more from reference, which means I'm using one tenth the power I'd need in a (futile) attempt to reproduce sound at reference levels. I say futile because my small Paradigms, even with the help of a sub, likely would compress before reaching the 105 dB potential peaks at reference level (so the amp may be sending the power to push the speakers to 105 dB but they only put out 102 or maybe less - - that's basically what speaker compression is).

Perfectly explained, thanks
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post #11 of 56 Old 09-09-2013, 12:48 PM
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There are two factors to power, the maximum voltage and the maximum current a given amplifier will put out. So if you look at ohms law, V = I x R and the power equation P = V x I, you get two equations by combining those two, P = I x I x R and P = V x V / R.

A given amplifier will have a maximum voltage that it can output, usually limited by it's internal power supply. Then it will also have a maximum current that it can handle, usually limited by the output transistors or drive components. It will probably have a maximum power that is likely somewhat less than the product of the maximum voltage times the maximum current related to how much waste heat the amp can dissipate.

So you could look at your "XPA-200 delivers 150 watts into 8 ohms, or 240 watts into 4 ohms"

Plug those numbers into the above equations to find V = 34.6 volts and I = 4.33 amps with 8 ohms.
And with 4 ohms, you get V = 31 volts and I = 7.75 amps.

So you can see at 8 ohms, that XPA-200 amp is likely voltage limited and can only supply enough voltage to the 8 ohm speakers to produce 150 watts. With 4 ohms, it has plenty of voltage but is likely current limited so does not quite supply twice the current as it did at 8 ohms. You could look at those above numbers and guess that the maximum voltage the amp can put out might be around 35-36 volts and the maximum current might be around 8 amps, so could theoretically put out 280 watts or so, but in real life 240 or 150 watts depending on the speaker load.

So as mentioned above, it comes down to how the amp was designed.
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post #12 of 56 Old 09-09-2013, 05:13 PM
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Quote:
Originally Posted by 4Crawler View Post

There are two factors to power, the maximum voltage and the maximum current a given amplifier will put out. So if you look at ohms law, V = I x R and the power equation P = V x I, you get two equations by combining those two, P = I x I x R and P = V x V / R.

A given amplifier will have a maximum voltage that it can output, usually limited by it's internal power supply. Then it will also have a maximum current that it can handle, usually limited by the output transistors or drive components. It will probably have a maximum power that is likely somewhat less than the product of the maximum voltage times the maximum current related to how much waste heat the amp can dissipate.

So you could look at your "XPA-200 delivers 150 watts into 8 ohms, or 240 watts into 4 ohms"

Plug those numbers into the above equations to find V = 34.6 volts and I = 4.33 amps with 8 ohms.
And with 4 ohms, you get V = 31 volts and I = 7.75 amps.

So you can see at 8 ohms, that XPA-200 amp is likely voltage limited and can only supply enough voltage to the 8 ohm speakers to produce 150 watts. With 4 ohms, it has plenty of voltage but is likely current limited so does not quite supply twice the current as it did at 8 ohms. You could look at those above numbers and guess that the maximum voltage the amp can put out might be around 35-36 volts and the maximum current might be around 8 amps, so could theoretically put out 280 watts or so, but in real life 240 or 150 watts depending on the speaker load.

So as mentioned above, it comes down to how the amp was designed.

Kinda correct...
Ohms Law is a reasonable comparison when driving a load resistor on a test bench.
However....
In the real-world a traditional loudspeaker provides a reactive load to the amplifier not just resistance, and its power output may vary greatly depending on the loudspeaker's actual inductance and phase angle...
In certain instances, with some highly reactive loudspeakers the power output of the amplifier may drop by up to 50-70% compared to the power output into a load resistor. We have measured amplifiers delivering 100W into an 8 Ohm resistor but when driving a stubborn, insensitive, sealed enclosure loudspeaker the power output may be <50W..

Just my $0.05... 👍😉🔊
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post #13 of 56 Old 09-09-2013, 05:58 PM - Thread Starter
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Another question. How does amp power translates into loudness (actual decibels)? Does a hundred watts amp produce a louder signal than a 50W amp (all other things being equal)?
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post #14 of 56 Old 09-09-2013, 06:39 PM
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Originally Posted by grigorianvlad View Post

Another question. How does amp power translates into loudness (actual decibels)? Does a hundred watts amp produce a louder signal than a 50W amp (all other things being equal)?
it should be 3db louder.
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post #15 of 56 Old 09-10-2013, 06:18 AM
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The bottom line is unless you're driving your amp to near clipping levels, the speaker impedance shouldn't be an issue. It's amazing how hung up on impedance people get. I have many 4 ohm speakers and I've never had an issue using them on any receiver or amp. If I didn't read the manual, I would never have known the nominal impedance.

There is no such thing as a 4 ohm amp or 8 ohm amp. All amps can drive any impedance that's not a short or open. The issue is really how hot they get at a certain volume since overheating is almost always what ultimately leads to failure.
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post #16 of 56 Old 09-10-2013, 08:13 AM
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Originally Posted by KidHorn View Post

The bottom line is unless you're driving your amp to near clipping levels, the speaker impedance shouldn't be an issue. It's amazing how hung up on impedance people get. I have many 4 ohm speakers and I've never had an issue using them on any receiver or amp. If I didn't read the manual, I would never have known the nominal impedance.

There is no such thing as a 4 ohm amp or 8 ohm amp. All amps can drive any impedance that's not a short or open. The issue is really how hot they get at a certain volume since overheating is almost always what ultimately leads to failure.

Incorrect..
Many entry-level AVRs have an impedance sensing circuit if the load impedance is 4 Ohms or less it prevents tha AVR from outputting any signal. The subject AVRs are built very cheaply with no overdesign in either the power supply or output stage. Check out their weights now they are down to 11-13 LBs as just a few years ago they were 21-25 LBs they are stripped down significantly which means less output voltage/current capability. And since the current is doubled @ 4 Ohms, they are unable to handle this.
Perhaps...
They may play @ low levels into 4 Ohms but crank it up and it shuts down... 😡

Just my $0.05..... 👍😉
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post #17 of 56 Old 09-10-2013, 09:27 AM
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Tons of misinformation here. As we know from ohm's law, power (watts) = Current (amps) X Pressure (volts). Impedance is a restriction to the flow of AC current. When you lower the impedance, you cause the speaker to draw more current to reach the same power level. Going back to Ohm's law, you can see that when you increase the current flow, you also lower the voltage delivery because less pressure is required to deliver the power. More current, lower voltage and vice versa. Increasing the current draw from the speaker also increases the heat generated by the amplifier because amplifiers aren't 100% efficient. The amplifier has a thermal sensing circuit that shuts it down when the temperature hits a dangerous point because excessive heat can damage the amplifier circuitry. So what low impedances do is cause the amplifier to run hotter for the same power as a higher impedance. That's the whole issue.

How hot the amplifier runs depends on many factors - the major ones being the current draw we described above, the sound pressure level at which we listen and ventilation. Impedance ratings for amplifiers are based on full power output. Understand that we rarely if ever use our amplifiers at full power. My home theater will play quite loudly with an average power consumption of 1 watt average and 10 watts or so on peaks. Just check the sensitivity of your speakers and you can work out the math very easily. Sensitivity rates the db of sound pressure with 1 watt of power at 1 meter. Then moving away from the speaker, the sound pressure level decreases by 3 db for each doubling of the distance. So most of us are running somewhere between 1/2 a watt to 3 watts on average with our hundred watt amplifier in a normal room.

Impedance ratings for amplifiers are based on full output power.. Although it isn't that simple, amplifier X is rated to deliver 100 watts into 8 ohms. If we keep the voltage the same, that same amplifier will deliver somewhere near twice the power into 4 ohms but we stand a chance of overheating the amp if we run full output power long enough to heat up the circuitry. As we know, however, we don't keep the voltage the same. It reduces as the current flow increases to keep the same amount of power. But if we run the same amp at, say 50 watts or 1/2 of its rated power, then the current flow is reduced by about 1/2 and the thermal emergency is over. If we run the amp at 1 watt, it has little problem at all with the speaker impedance. In other words we could take the same amp that is rated for 100 watts into 8 ohms and rate it at 50 watts into 4 ohms. Now everybody is happy. We now have a 50 watt amplifier which is still way bigger than we need, rated at 4 ohms.

If you followed all that, it attempts to explain why audio consumers are hung up on speaker impedance but probably should not be. The reality is that speaker impedance is not constant. It varies by frequency and it varies a lot. The nominal impedance rating that manufacturers put on speakers is an attempt to guide the consumer in mating an amp to a speaker. Actually it only describes the impedance curve at a few points along the frequency spectrum. You can view it as an average even though it isn't an average. If we were using 5 watt amplifiers those nominal impedance ratings would be critical. Since we're using 100 amplifiers, they aren't so critical. Our 100 watt, 8 ohm rated amplifier will probably deal just fine with 2 ohm impedance dips in the curve as long as we don't turn the volume up too high or hit 2 ohms for a significant amount of time.

Consumers, for some reason, are concerned about amplifier power, not speaker impedance so amplifier manufacturers rate their power output for continuous duty into 8 ohms (about as high as speaker impedances get in practice) because that makes the power number higher. Speaker manufacturers then have a tendency to rate nominal impedance as high as they can get away with so that the consumer won't worry about the impedance that he shouldn't really worry about in the first place. Any amplifier rated at 8 ohms is also rated at 4 ohms at a lower power output level and 2 ohms at an even lower one. It is a numbers game. The reality is that it would be stupid for a speaker manufacturer to make speakers that would cook the average home amplifier and it would be equally stupid for an amp manufacturer to make a product that couldn't survive driving all those available speakers out there. They aren't stupid.

The average consumer knows nothing of Ohm's law or speaker impedance. He just goes to a store and buys what he likes and hooks it up and enjoys the audio. If there were actually a good chance that he would burn up his amplifier, we would hear stories about cooked amplifiers all over the place and we don't. The only ones I've seen involve abuse like wiring a dead short across speaker output terminals and things of that nature. Quit worrying about speaker impedance. For the vast majority of us, it simply isn't an issue. If we listen in an auditorium where we will stress the amplifier's capabilities, then it can be a problem but few of us listen in an auditorium. Hope this helps clarify a few things. If I wasn't clear somewhere, let me know and I'll correct it.
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post #18 of 56 Old 09-10-2013, 09:36 AM
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Quote:
Originally Posted by M Code View Post

Incorrect..
Many entry-level AVRs have an impedance sensing circuit if the load impedance is 4 Ohms or less it prevents tha AVR from outputting any signal. The subject AVRs are built very cheaply with no overdesign in either the power supply or output stage. Check out their weights now they are down to 11-13 LBs as just a few years ago they were 21-25 LBs they are stripped down significantly which means less output voltage/current capability. And since the current is doubled @ 4 Ohms, they are unable to handle this.
Perhaps...
They may play @ low levels into 4 Ohms but crank it up and it shuts down... 😡

Just my $0.05..... 👍😉

You do realize that it's very common for all speakers to show a resistance load at times below 4 ohms regardless of the nominal impedance rating of the speaker. it what you state is true then those receivers would routinely shut down for no apparent reason.
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post #19 of 56 Old 09-10-2013, 10:01 AM
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Quote:
Originally Posted by M Code View Post

Incorrect..
Many entry-level AVRs have an impedance sensing circuit if the load impedance is 4 Ohms or less it prevents tha AVR from outputting any signal. The subject AVRs are built very cheaply with no overdesign in either the power supply or output stage. Check out their weights now they are down to 11-13 LBs as just a few years ago they were 21-25 LBs they are stripped down significantly which means less output voltage/current capability. And since the current is doubled @ 4 Ohms, they are unable to handle this.
Perhaps...
They may play @ low levels into 4 Ohms but crank it up and it shuts down... 😡

Just my $0.05..... 👍😉

It would pay you to read the post above where I try to explain the realities of speaker impedance. The reason AV receivers are lighter is that they tend to use switching amps now instead of AB biased amps like they did in the past. The 300 watt class D amp in my subwoofer only weighs about 2 lbs. They aren't stripped down and they don't have less current handling capacity. In fact they have more thanks to the efficiency of switching designs and can get by with less substantial power supplies. Actually they can play at ear splitting levels into 4 ohms . We would need to get somewhere near full rated output to be concerned about thermal shutdown (not current shutdown.).
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post #20 of 56 Old 09-10-2013, 11:23 AM
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Quote:
Originally Posted by FMW View Post

It would pay you to read the post above where I try to explain the realities of speaker impedance. The reason AV receivers are lighter is that they tend to use switching amps now instead of AB biased amps like they did in the past. The 300 watt class D amp in my subwoofer only weighs about 2 lbs. They aren't stripped down and they don't have less current handling capacity. In fact they have more thanks to the efficiency of switching designs and can get by with less substantial power supplies. Actually they can play at ear splitting levels into 4 ohms . We would need to get somewhere near full rated output to be concerned about thermal shutdown (not current shutdown.).

Very few AVRs use Class D amplifiers, only certain Elite models. Previously Panasonic and Samsung AVRs had Class D output stages but have been discontinued due to poor sonics and sales. As of now, Denon, Marantz, Onkyo, Integra, Yamaha and NAD AVRs continue to implement analog Class A-B amplifiers. Harman/Kardon AVRs are lighter because they now utilize an SMPS (Switch Mode Power Supply) instead of the traditional linear power supply but the output stage is analog Class A-B. As posted previously, today >90% of the home theater systems, HTIBs and all--1-systems are driving subwoofer/ satellite speaker systems so that primary power output stage does not require the voltage /current required to drive full-range loudspeakers. Additionally, the product costs are higher due to more digital processors including audio, video, connectivity, higher HD royalties and appreciating exchange rates. AVRs sold today in the entry-level price segment <$599 SRP are lacking for higher current and capabilities to drive lower impedance loudspeakers (4 Ohms). Check out their specs, all type of stretched specs are being published such as:
  • 1 Channel driven
  • Power output @ 1kHz
  • Power output @ 1% THD
  • Power output into 6 Ohms
  • DIN power output

The AVRs are lighter because costly material like larger heat sinks, power transformers and shielded metal chassis have been sized down to lower the material costs..
If one wants the full bandwith, lower distortion, higher current output power capability and able to drive lower impedance loudspeakers they better think about getting separate components not an AVR.



Just my $0.05... 👍😉
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post #21 of 56 Old 09-10-2013, 11:39 AM
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Originally Posted by KidHorn View Post

You do realize that it's very common for all speakers to show a resistance load at times below 4 ohms regardless of the nominal impedance rating of the speaker. it what you state is true then those receivers would routinely shut down for no apparent reason.

>90% of the loudspeakers mentioned are little, inexpensive satellites which only go down to 200Hz..
Connect an entry-level AVR up to a quality, full-range, sealed box, 4 ohm, lower sensitivity (<87dB) loudspeaker and guess what happens when you drive the AVR hard...
Hint.. hint..
It will shut down.... 😱

It has to, as it is not designed to deliver robust, high current, continuous power output..
If the protection circuit doesn't kick in, the AVR will simply self-destruct...
I don't like car analogies but it is like running a KIA 2.4 4 cylinder against a Dodge Viper V-10, 175HP/150LBs of torque vs. 650HP/625LBs of torque... No contest..

Just my $0.05... 👍😉
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post #22 of 56 Old 09-10-2013, 11:49 AM
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Quote:
Originally Posted by M Code View Post

>90% of the loudspeakers mentioned are little, inexpensive satellites which only go down to 200Hz..
Connect an entry-level AVR up to a quality, full-range, sealed box, 4 ohm, lower sensitivity (<87dB) loudspeaker and guess what happens when you drive the AVR hard...
Hint.. hint..
It will shut down.... 😱

Maybe. Hint, Hint. But you defined neither the amplifier power, nor what drive it hard means. In most cases it will not shut down. In most cases the loudness will be uncomfortably loud for the listener well before you reach thermal shut down. Have you even reached thermal shutdown with an AVR?
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post #23 of 56 Old 09-10-2013, 02:19 PM
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Quote:
Originally Posted by FMW View Post

Maybe. Hint, Hint. But you defined neither the amplifier power, nor what drive it hard means. In most cases it will not shut down. In most cases the loudness will be uncomfortably loud for the listener well before you reach thermal shut down. Have you even reached thermal shutdown with an AVR?

Absolutely..
Thermal shutdown is very common for entry-level AVRs...
Another major reason is the lack of adequate free-air clearance, many AVR users never read their setup guides..
The major AVR brands including Pioneer, Denon, Onkyo specify @ least 8" for the L/R sides and top cover, also they advise against stacking any component on top..
If the heat cannot exit the AVR enclosure its internal temperature will accelerate upward,,
Todays AVRs regardless of price segment, generate considerable heat... 🔥
Originally, the output stage and power supply generated the most heat but now the HDMI video board is the major contributor due to the overclocking of the video processor..
In fact several brands including Onkyo/Integra, Pioneer/Elite and Harman/Kardon are now putting a small cooling fan for just the video processor...

Just my $0.05... 👍😉
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post #24 of 56 Old 09-10-2013, 07:19 PM
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I have to agree with M Code on this and as an installer have seen this from clients they either try to play it too loud ,pair it with low ohm low sensitivity speakers, they simple shut down or the units cooks and a flashing trouble light code is present.
We always recommend mid level and up Flagship if they will let us and speakers with at least 91 db 1w/1m and definitely crossed over to a good sub at 80 Hz.
But amp quality in almost every AVR with the exception of the Flagships are subpar to what they were a few years ago and the test bench on the different brands show this in Home Theater Magazine.
This may be because they are now squeezing 9 cheap amps where 7 nice amps use to go or profit margin took a hit so parts and quality naturally get to take a hit.
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post #25 of 56 Old 09-10-2013, 10:12 PM
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About amplifier weight and heat. While reading the manual on my new Onkyo TX-NR929, i noticed the 8" per side and 4" on top clearance required, as mentioned above. Well the second half of my Integra DTC 9.8's life was with less than ideal ventilation and I think it suffered HDMI board overheating problem. With my electrical background I should have known better. Shame on me. Makes me wonder how many Joe Sixpacks weren't honest with Onkyo/Integra about their clearances. Joe certainly doesn't need to understand the above electrical theory to know when something is too hot.

About the weight, weigh this. Any reasonable person would think at 41 lbs, my 9 channel @ 135 watts 929 is heavy. But consider the Integra DTC 9.8 pre-pro it is replacing, with 0 amps, is almost as heavy. Then there is the amp portion it's replacing. That would be my Outlaw 7 channel amp @ 200 watts/channel that tips the scales at 90 lbs. Now to confuse the issue, we'll consider my Sunfire True Sub. Heavy little sucker. The 11" cube weighs in at 48 lbs. But wait, there's more. After meeting Bob Carver and reading about his new subs, I had to have one. But I was leery about the published specs. Especially his Tracking Downconverter amp rated at 2700 watts!!! I figured they took the engineer's rating and multiplied it by the number of people in the marketing department. So I traipsed down to Century Stereo in San Jose with my CD of Fanfare For the Common Man with it's kettle drums and my Fluke meter and devices to read amps at the 120 volt side. With the receiver volume at about 75% the sub quickly jumped up to 14 to 16 amps. Then 18 to 20 and as those drums got louder I saw a peak of 22 amps. Of course sustained would have tripped the breaker. Due the math. I did, and realized it was a legit 2700 watts. No wonder it was so heavy. WRONG!

A couple of years ago I had to take it apart. That 2700 watt amplifier was the size of a candy bar!

Patrick
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post #26 of 56 Old 09-10-2013, 11:44 PM
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Quote:
Originally Posted by M Code View Post

Absolutely..
Thermal shutdown is very common for entry-level AVRs...
Another major reason is the lack of adequate free-air clearance, many AVR users never read their setup guides..
The major AVR brands including Pioneer, Denon, Onkyo specify @ least 8" for the L/R sides and top cover, also they advise against stacking any component on top..
If the heat cannot exit the AVR enclosure its internal temperature will accelerate upward,,
Todays AVRs regardless of price segment, generate considerable heat... 🔥
Originally, the output stage and power supply generated the most heat but now the HDMI video board is the major contributor due to the overclocking of the video processor..
In fact several brands including Onkyo/Integra, Pioneer/Elite and Harman/Kardon are now putting a small cooling fan for just the video processor...

Just my $0.05... 👍😉

OK. it must be my limited experience with the latest gear. My main AVR is a high end model from 7 years ago. In those days I never even heard of anyone seeing a thermal shutdown. It can drive me out of the room with 4 ohm speakers. I do have a late model entry level AVR in my bedroom but I imagine I don't play it loud enough to stress it. I'm actually stunned to hear that thermal shutdown is common these days.
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post #27 of 56 Old 09-11-2013, 03:16 AM
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Quote:
Originally Posted by M Code View Post

>90% of the loudspeakers mentioned are little, inexpensive satellites which only go down to 200Hz..
Connect an entry-level AVR up to a quality, full-range, sealed box, 4 ohm, lower sensitivity (<87dB) loudspeaker and guess what happens when you drive the AVR hard...
Hint.. hint..
It will shut down.... 😱

It has to, as it is not designed to deliver robust, high current, continuous power output..
If the protection circuit doesn't kick in, the AVR will simply self-destruct...
I don't like car analogies but it is like running a KIA 2.4 4 cylinder against a Dodge Viper V-10, 175HP/150LBs of torque vs. 650HP/625LBs of torque... No contest..

Just my $0.05... 👍😉

I don't disagree with any of this, but what you're stating isn't the same as a receiver sensing a low impedance and shutting down. I don't see how any receiver could operate if any time a 4 ohm load was detected, it shut off. Maybe 2 ohm or lower, but not 4 ohm. The cheap receivers that can't handle a higher rail current would have the same issue with an 8 ohm load as a 4 ohm. The only difference is the problem would occur at a lower volume with the 4 ohm load.

The nominal impedance listed for speakers is basically a ball park guess. That's why the numbers are nice round numbers like 4, 6, or 8 and not 6.34. Generally the number is based off the DC resistance of the speaker coil rounded up to the nearest even number. In reality since capacitance and inductance are wave form dependent, the number is all over the place in real world use.
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post #28 of 56 Old 09-11-2013, 05:36 AM
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Quote:
Originally Posted by KidHorn View Post

I don't disagree with any of this, but what you're stating isn't the same as a receiver sensing a low impedance and shutting down. I don't see how any receiver could operate if any time a 4 ohm load was detected, it shut off. Maybe 2 ohm or lower, but not 4 ohm. The cheap receivers that can't handle a higher rail current would have the same issue with an 8 ohm load as a 4 ohm. The only difference is the problem would occur at a lower volume with the 4 ohm load.

The nominal impedance listed for speakers is basically a ball park guess. That's why the numbers are nice round numbers like 4, 6, or 8 and not 6.34. Generally the number is based off the DC resistance of the speaker coil rounded up to the nearest even number. In reality since capacitance and inductance are wave form dependent, the number is all over the place in real world use.

They don't sense impedance. They sense heat. It is heat that can damage an amp, not low impedance. Low impedances simply cause the speaker to draw more current and that can heat up the amp given enough level and time.
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post #29 of 56 Old 09-11-2013, 06:35 AM
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If you look at enough threads in these forums you will read more often of people complaining it shut down during the movie or a piece of music .
The advertised wattage numbers mfg.'s are playing these days don't quite match bench tests especially the lower end models.
To those that state all channels driven does not matter either don't listen to multichannel music with a lot of dynamics or Blu-Rays with action scenes galore.
To those that state they have not had an issue with these great you probably listen to it at lower volume levels and won't have a problem crank it up and watch the nightmare began.
The weight issues means nothing on digital amps they are lighter do to design but on class A/B if the weight dropped open the top gone is the high output toroidal transformer and large caps along with multiple transistor outputs per channel meaning gone also is the great power output this or that brand had in the past.
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post #30 of 56 Old 09-11-2013, 08:03 AM
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I had no problem running my 7.2 Home Theater at near Reference Level with the Denon AVR-4802R/4806ci, which were both THX Ultra II certified and heavy. The for a year I drive the same system with a Denon AVR-3805 and with SPL meter in had found I had to listen a good 6 dB lower on multichannel music and action movies...Now I have a Denon AVR-4311ci and I am back enjoying things at Reference level.

After comparing everything I could came to the conclusion it was the ability of the power supply to drive 4 Ohm speakers, but don't discount that Audyssey also may have something to do with it. With this in mind I noticed that the 7 channel AVR-3805 weighs 37 lbs 8 oz and the 9 channel AVR-4311ci weighs 38 lbs 2 oz and is rated to drive speakers that are 4 Ohm...I have seen the Benchmark test on the AVR-4806ci but would be curious how the lighter AVR-4311ci stacks up if anyone has a link or ideas how it can accomplish this in a lighter unit.
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