Question about Speakers Ohms rating - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 21 Old 03-30-2019, 07:26 PM - Thread Starter
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Question about Speakers Ohms rating

So I need someone that has a good understanding of this to help me understand something.

I have seen speakers rated commonly at 8 ohms, and then I have seen some at 6 and then some at 4

From my understanding if you have an 8 ohm speaker and a 4 ohm speaker the 4 ohm speaker would require more power from the amp to sound as loud as the 8 ohm speaker?

So I was looking at the Elac Uni Fi UB5 that is 4 ohm rated with a low sensitivity rating of 85dB just confuses me

Are 4 ohm speakers for people with high powered amp then?
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post #2 of 21 Old 03-30-2019, 09:57 PM
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Quote:
Originally Posted by the7mcs View Post
So I need someone that has a good understanding of this to help me understand something.

I have seen speakers rated commonly at 8 ohms, and then I have seen some at 6 and then some at 4

From my understanding if you have an 8 ohm speaker and a 4 ohm speaker the 4 ohm speaker would require more power from the amp to sound as loud as the 8 ohm speaker?

So I was looking at the Elac Uni Fi UB5 that is 4 ohm rated with a low sensitivity rating of 85dB just confuses me

Are 4 ohm speakers for people with high powered amp then?
The UB5 is rated with a voltage sensitivity of 85 dB at 1m for 2.83V RMS. 2.83V RMS would give 1W for an 8 ohm speaker, but 2W for a 4 ohm speaker. The power sensitivity of the UB5 is then 82 dB/W. That's fairly low.

Voltage sensitivity may be a better way of specifying the sensitivity, as speakers don't have constant impedances as a function of frequency.

4 ohm speakers require more current (amperage) from the amp than an 8 ohm speaker to get the same power. That may cause some amps to overheat or clip, if you drive the speakers at high volume.
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post #3 of 21 Old 03-30-2019, 10:25 PM
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It's complicated....I'll try to keep it as simple as I can (or can't)....

EXPLANATIONS:
A typical Class AB (Push-Pull) Amplifier TRIES to be a Constant Voltage Source, irrespective of Frequency or Load Impedance. So, without a Load, the Maximum Voltage Output would swing between Vout = +/- (Vcc - Vloss), where Vloss is the Voltage Loss in each Output Stage and +/- Vcc are the Power Supply Voltages applied to the Output Devices (Tubes, Bi-Polar Transistors or MOSFET Transistors, such as are used in my Pioneer AVR).

IF equipped with a Voltage Regulator in the Power Supply (my Marantz 250 is NOT), it TRIES to keep +/- Vcc Constant, irrespective of the Current Demand....which is usually the case for "typical" Standardized AVR Spec Tests [with or w/o Voltage Regulator], which very rarely have more than one or two channels fully driven [also the case for REAL Music & Movie Tracks]. Only when ALL Channels are fully driven should we [maybe] expect to see an AVR's Voltage Regulator no longer provide the full +/- Vcc voltages.

Now I'm going to use my antique Marantz 250 Amp as an example...mostly cuz it's about the only component for which I had a Service Manual and could readily FIND apples-to-apples specs for both 4-ohms (150 wpc) and 8-ohms (125 wpc) Loads...and even 16-ohms (64 wpc)....for 0.1% THD from 20 - 20 kHz. Per Service Manual, Vcc = +/- 58-volts and Vout = 31.6-volts (rms, or 44.7-volt peak) for 125 wpc into 8-ohms [hence Vloss = 13.3-volts under these test conditions]. Note that Vcc/Vout = 0.544, which is significantly less than 0.707 Peak/Avg Ratio we would expect if there was NO Loss in the Output Stages. For additional examples, download manuals for Onkyo TX-NR656, Pioneer VSX-LX103, and/or Yamaha RXV-621 [IHF/IEC test conditions for last two are NOT stipulated...based on Onkyo and comparisons to other specs, they appear to be with just One (vice typ. 2) Channels Driven and maybe just 1 kHz or perhaps 20-20kHz].

Pout = (Vout)^2 / Zload. IF Vout was indeed Constant, then Zload = 4-ohms should result in TWICE as much Power being delivered to the Load, as for 8-ohms. This is roughly True if you compare Amp spec power for 8-ohms vs 16-ohms....but specs for 4-ohms (150 wpc) are considerably short of 2x125=250 wpc for 8-ohms (125 wpc spec). That is because the higher Current Demand at 4-ohms results in considerably higher Vloss in the Output Stages....plus higher voltage loss in subsequent speaker cables and internal Speaker Crossover Filters.

BTW: Although more Power can be delivered to 4-ohm Speakers, it is likely that Twice as many Voice Coil Windings are used in an 8-ohms Speaker...which explains why it's DC Resistance is much higher....and hence it would also likely have a 3 dB higher Speaker Sensitivity, diminishing the difference...although other factors are also involved which complicate simple comparisons:
http://www.jlaudio.com/header/Suppor...DVC%29+/287542

========================================
BOTTOM LINE:
IF you can find an AVR or Amp that actually has [Apple-to-Apple] SPECS for both 4-ohms and 8-ohms loads [most only go down to 6-ohms], plug those WPC numbers, along with the Speaker Sensitivity Spec into the fol. On-Line Calculator and compare max Sound Pressure Levels (SPL).
PS: IF Amp specs don't explicitly specify 4-ohms WPC at an acceptable Distortion Level (1% or lower....NOT 10%), then it is NOT designed for 4-ohms....and will likely trip the self-protect circuitry at a [Loud] WPC level perhaps LESS than Max SPC at 6 or 8-ohms.

PPS: For most Dynamic Woofers and Sub-Woofers, Highest Current Draw occurs at a Frequency about 2x to 3x higher than it's -3 dB Low Freq Rolloff, where the Impedance is Minimum and equal to the Voice Coil's DC Resistance (Re), easily measured by a VOM/DVM. THAT is the Impedance that should be used when looking at Amp specs...which are tested using purely resistive test loads. OTOH: Speaker "nominal" [average?] Impedance Specs are inexplicably & dangerously HIGHER:
https://imageevent.com/holl_ands/fil...akercomparison
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Last edited by holl_ands; 04-01-2019 at 03:02 PM.
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post #4 of 21 Old 03-31-2019, 09:53 AM
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Originally Posted by the7mcs View Post

Are 4 ohm speakers for people with high powered amp then?
That seems to be the consensus of most people who own 4 ohm rated speakers on AVS.

Emotiva owners seem to be the exception however Emotiva themselves, understandably as they sell outboard amps, begs to differ and thinks AVRs in general are a poor choice especially if the lack pre outs.

This is their latest take on the matter albeit a bit self serving.

https://emotiva.com/blogs/info-hub-1...n-a-v-receiver
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post #5 of 21 Old 03-31-2019, 10:12 AM
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Quote:
Originally Posted by the7mcs View Post
So I need someone that has a good understanding of this to help me understand something.

I have seen speakers rated commonly at 8 ohms, and then I have seen some at 6 and then some at 4

From my understanding if you have an 8 ohm speaker and a 4 ohm speaker the 4 ohm speaker would require more power from the amp to sound as loud as the 8 ohm speaker?

No. The sensitivity rating of a speaker tells you how much power it takes to generate a specific sound level.


The impedance is an electrical property of the speaker, that tells you nothing about the sensitivity of the speaker. The reason the impedance matters is that different amplifiers have different capabilities with regard to the impedance that will work properly with them. Usually, one finds on the back of an amplifier (or receiver) writing near the speaker connections saying that there is some minimum impedance speaker that is suitable for it (such as, 4 ohms minimum, 6 ohms minimum, or whatever). Basically, impedance is the resistance to the flow of electricity, with zero being a dead short (i.e., just a wire going from + to - on your amplifier output terminals, which, unless the amplifier has protection circuitry, is likely to destroy the amplifier [for the pedantic, the wire will have some slight resistance, and so it will be ever so slightly above zero ohms, but that will not matter for your amplifier being destroyed; it will be practically zero ohms]). So with an impedance that is too low, the amplifier can be damaged. The actual impedance of speakers vary with frequency (that is, the speaker actually has a different impedance at different frequencies), and can be represented in a graph. The nominal impedance figure is supposed to be a number you can pretend the entire speaker is, for matching with amplifiers, though many manufacturers essentially lie about this, as they want to sell you the speaker and many people notice that, on the back of their equipment or in the manual, it specifies a minimum impedance, and if they tell you the truth about it really being, say, 4 ohms instead of 8 ohms, some people will not buy it because they do not want to damage their amplifier. To be safe, look at the minimum impedance and pretend that the nominal impedance is that or about 10% higher.


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Originally Posted by the7mcs View Post
So I was looking at the Elac Uni Fi UB5 that is 4 ohm rated with a low sensitivity rating of 85dB just confuses me

The sensitivity rating is 85db @ 2.83V @ 1 meter (and assuming it is accurate), if that speaker is fed 2 watts of power, the sound level will be 85dB at a distance of one meter. The amplifier connected to it must output 2 watts @ 4 ohms to do this. That is a fairly low sensitivity speaker, and so, to play very loud, it will require some power. However, for soft background music, a couple of watts is likely all you would ever need.

Typically, amplifiers have different capabilities with different impedances. For example, the old Pioneer SX-1250 was rated at 160 watts RMS continuous from 20-20KHz @ <0.1% THD into 8 ohms, and 200 watts RMS continuous from 20-20KHz @ <0.1% THD into 4 ohms. And one is not supposed to use speakers lower than 4 ohms with it.


So, if you were wanting to use the speakers you mention, you would want an amplifier rated for use with 4 ohm speakers. Of course, you might be able to get away with one that is not rated for such speakers, because amplifiers can deliver some power into lower impedances than is recommended. But, it tends to run hotter. Also, since impedance varies with frequency, two different speakers rated the same nominal impedance will likely present different levels of difficulties, and, the louder you play the music, the more power is demanded, etc. And different amplifiers have different protection circuits, some of which work better than others, etc. Because of the number of variables, it is difficult to be certain of when you can get away with violating the warning on the back of an amplifier; if you want to be safe, don't violate the warning on the back of the amplifier. Worse case scenario can result in fire and death, though that is unlikely.

If you want to be safe, use an amplifier rated for the minimum impedance of the speaker. Of course, even then, you can damage things, as there are limits to the power handling of the speaker, and there are limits to the power output of the amplifier. If, when turning up the volume, the sound becomes audibly distorted, turn down the volume to a level such that there is no audible distortion.


Quote:
Originally Posted by the7mcs View Post
Are 4 ohm speakers for people with high powered amp then?
No. Low sensitivity speakers are speakers for people with high powered amplifiers, if they want to be able to play them loud. Low power is fine when the speakers are high sensitivity, or when people don't want to play it very loud.

4 ohm speakers should be used with amplifiers rated for use with 4 ohm speakers. It does not have to be high power.

If, hypothetically, one had a 4 ohm speaker with a sensitivity rating of 105dB @ 1 watt @ 1 meter, one would not need much power at all to have very high volumes. Of course, it is power into 4 ohms that one needs for this.

I hope the above is simplified enough to be intelligible, but not too simplified to be unusable. Ask any questions you have about this. Or, if you prefer, you can read this:

https://www.audioholics.com/loudspea...er-sensitivity
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post #6 of 21 Old 03-31-2019, 10:15 AM
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You are looking at the ELAC Uni-Fi UB5.

I own these speakers. Maybe this will be of value.

I have had the UB5s connected to a NAD C 316BEE (40 watts), a NAD C 326BEE (50 watts) a Marantz HD-Amp1 (70 watts at 4 ohms) and a NAD C 275BEE (150 watts). The UB5s sounded great with all of these. I realize that my listening tests are not scientific nor controlled, these are just my observations. None of these sources had any difficulty driving the UB5s to very loud levels.

The UB5s are currently connected to my C 326BEE using a CD player and streaming ALAC files as sources and I am very happy with the sound.

Of course, your room size, the type of music you listen to and the loudness you listen at, will all come into play.

Check this out:
http://myhometheater.homestead.com/splcalculator.html
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post #7 of 21 Old 03-31-2019, 01:33 PM
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Quote:
Originally Posted by the7mcs View Post
So I need someone that has a good understanding of this to help me understand something.

I have seen speakers rated commonly at 8 ohms, and then I have seen some at 6 and then some at 4

From my understanding if you have an 8 ohm speaker and a 4 ohm speaker the 4 ohm speaker would require more power from the amp to sound as loud as the 8 ohm speaker?

So I was looking at the Elac Uni Fi UB5 that is 4 ohm rated with a low sensitivity rating of 85dB just confuses me

Are 4 ohm speakers for people with high powered amp then?
Buy 8 ohm speakers. Then you can use any modern receiver and enjoy watching movies instead of getting an engineering degree reading the avs forum, which is really hard.
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post #8 of 21 Old 03-31-2019, 02:05 PM
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Originally Posted by Mingo Sanders View Post
Buy 8 ohm speakers. Then you can use any modern receiver and enjoy watching movies instead of getting an engineering degree reading the avs forum, which is really hard.
Unfortunately, speaker manufacturers have noticed people doing that, so some of them rate their 4 ohm speakers as 8 ohms to sell to people who know nothing about impedance. Judging by how common this is, there must be no legal meaning for "nominal impedance" or a lot of them could be in trouble. Here is an example:

Although Harman rates the Infinity Primus P363 as 8-ohm speakers, what I measured tells a much different story. These are clearly 4-ohm speakers. They appear to be tuned just below 50Hz, but the saddle points are quite asymmetric. This indicates a system tuning too low for the available box size needed to produce a more optimal response. The 4 ohm dip between 100Hz to 200Hz is a bit concerning for those wanting to use these speakers with budget A/V receivers. Even if bass managed, these speakers can present a rather strenuous load if the amplifiers in the A/V receiver don’t take kindly to 4-ohm loads. I found that Infinity employed a 4-ohm tweeter as evident by the impedance dip above 10kHz. I believe they did this in attempt to increase speaker sensitivity.
https://www.audioholics.com/tower-sp...3-measurements

So, if you don't learn about it, that does not mean it won't result in your amplifier being damaged.

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post #9 of 21 Old 03-31-2019, 02:19 PM
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Originally Posted by Jack D Ripper View Post
Unfortunately, speaker manufacturers have noticed people doing that, so some of them rate their 4 ohm speakers as 8 ohms to sell to people who know nothing about impedance. Judging by how common this is, there must be no legal meaning for "nominal impedance" or a lot of them could be in trouble. Here is an example:

Although Harman rates the Infinity Primus P363 as 8-ohm speakers, what I measured tells a much different story. These are clearly 4-ohm speakers. They appear to be tuned just below 50Hz, but the saddle points are quite asymmetric. This indicates a system tuning too low for the available box size needed to produce a more optimal response. The 4 ohm dip between 100Hz to 200Hz is a bit concerning for those wanting to use these speakers with budget A/V receivers. Even if bass managed, these speakers can present a rather strenuous load if the amplifiers in the A/V receiver don’t take kindly to 4-ohm loads. I found that Infinity employed a 4-ohm tweeter as evident by the impedance dip above 10kHz. I believe they did this in attempt to increase speaker sensitivity.
https://www.audioholics.com/tower-sp...3-measurements

So, if you don't learn about it, that does not mean it won't result in your amplifier being damaged.
I trust Harman. I live on the edge.

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post #10 of 21 Old 03-31-2019, 06:20 PM
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Originally Posted by Mingo Sanders View Post
I trust Harman. I live on the edge.
It is a very curious thing, trusting them when they have just been proven to be lying. If this site had a political section, I would make a guess about your favorite politician.

But however you personally feel about the matter, I do not recommend that people trust proven liars. You, of course, may do as you please. You would anyway.

I am also reminded of how James Randi proved that Peter Popoff was a con man:

https://en.wikipedia.org/wiki/James_Randi

Peter Popoff (born July 2, 1946) is a German-born televangelist. He was exposed in 1986 for using an earpiece to receive radio messages from his wife, who gave him the names, addresses and ailments of audience members during Popoff-led religious services. Popoff falsely claimed God revealed this information to him so that Popoff could cure them by faith healing.[1]

He went bankrupt the next year, but made a comeback in the late 1990s. Beginning in the mid-2000s, Popoff bought TV time to promote "Miracle Spring Water" on late-night infomercials, and referred to himself as a prophet.[2] Business Insider remarked: "No matter how many times his claims are debunked, he seems to bounce back with another version of the same old scam."[3]
https://en.wikipedia.org/wiki/Peter_Popoff

For some strange reason, many people continue to believe other people when those other people have been proven to be liars and untrustworthy. If someone has a link to a psychology website that might explain this, I would like to see it. It is something to which I cannot relate. When someone lies and I detect it, I automatically do not trust them in the future. Why would one trust someone when one KNOWS that the person is a liar?
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Originally Posted by Jack D Ripper View Post
It is a very curious thing, trusting them when they have just been proven to be lying. If this site had a political section, I would make a guess about your favorite politician.

But however you personally feel about the matter, I do not recommend that people trust proven liars. You, of course, may do as you please. You would anyway.

I am also reminded of how James Randi proved that Peter Popoff was a con man:

https://en.wikipedia.org/wiki/James_Randi

https://www.youtube.com/watch?v=lTn0t_7pGZo
Peter Popoff (born July 2, 1946) is a German-born televangelist. He was exposed in 1986 for using an earpiece to receive radio messages from his wife, who gave him the names, addresses and ailments of audience members during Popoff-led religious services. Popoff falsely claimed God revealed this information to him so that Popoff could cure them by faith healing.[1]

He went bankrupt the next year, but made a comeback in the late 1990s. Beginning in the mid-2000s, Popoff bought TV time to promote "Miracle Spring Water" on late-night infomercials, and referred to himself as a prophet.[2] Business Insider remarked: "No matter how many times his claims are debunked, he seems to bounce back with another version of the same old scam."[3]
https://en.wikipedia.org/wiki/Peter_Popoff

For some strange reason, many people continue to believe other people when those other people have been proven to be liars and untrustworthy. If someone has a link to a psychology website that might explain this, I would like to see it. It is something to which I cannot relate. When someone lies and I detect it, I automatically do not trust them in the future. Why would one trust someone when one KNOWS that the person is a liar?
"integrity in the internet age ".. a proven myth .... people believe whoever can give them a straw man to dislike.. no facts needed...

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Quote:
Originally Posted by Jack D Ripper View Post
It is a very curious thing, trusting them when they have just been proven to be lying. If this site had a political section, I would make a guess about your favorite politician.

But however you personally feel about the matter, I do not recommend that people trust proven liars. You, of course, may do as you please. You would anyway.

I am also reminded of how James Randi proved that Peter Popoff was a con man:

https://en.wikipedia.org/wiki/James_Randi

https://www.youtube.com/watch?v=lTn0t_7pGZo
Peter Popoff (born July 2, 1946) is a German-born televangelist. He was exposed in 1986 for using an earpiece to receive radio messages from his wife, who gave him the names, addresses and ailments of audience members during Popoff-led religious services. Popoff falsely claimed God revealed this information to him so that Popoff could cure them by faith healing.[1]

He went bankrupt the next year, but made a comeback in the late 1990s. Beginning in the mid-2000s, Popoff bought TV time to promote "Miracle Spring Water" on late-night infomercials, and referred to himself as a prophet.[2] Business Insider remarked: "No matter how many times his claims are debunked, he seems to bounce back with another version of the same old scam."[3]
https://en.wikipedia.org/wiki/Peter_Popoff

For some strange reason, many people continue to believe other people when those other people have been proven to be liars and untrustworthy. If someone has a link to a psychology website that might explain this, I would like to see it. It is something to which I cannot relate. When someone lies and I detect it, I automatically do not trust them in the future. Why would one trust someone when one KNOWS that the person is a liar?
Yup, I still trust Harman. My politics? I trust people who vote.

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Yup, I still trust Harman. My politics? I trust people who vote.
that's a *very large pool* of people you trust...i might suggest being a bit pickier, your wallet will thank you

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@the7mcs


The short and dirty version


While Ohms is no indication, on how a speaker will sound.
Your AVR need to be rated for lower resistance, if using a lower resistance Speakers.
If not when playing at higher level. The AVR will be struggling to keep-up, and might go into protection mode.
Since most AVR are rated at one or two channels, for Power and Ohms rating.
That said, no damage should not occur. Just been annoying in the middle of a movie.


Ray
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post #15 of 21 Old 04-01-2019, 01:21 PM
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Quote:
Originally Posted by holl_ands View Post
The Voltage Regulator in the Power Supply TRIES to keep +/- Vcc Constant, irrespective of the Current Demand....which is usually the case for "typical" Standardized AVR Spec Tests, which very rarely have more than one or two channels fully driven [also the case for REAL Music & Movie Tracks]. Only when ALL Channels are fully driven should we [maybe] expect to see the Voltage Regulator no longer provide the full +/- Vcc voltages.
With very rare exceptions, only amps with switchmode power supplies have regulated rails. The only regulated voltages in your Marantz are for the meter circuits.
Sometimes it's the voltage of the power line to the amp sagging that limits max output.

Quote:
Now I'm going to use my antique Marantz 250 Amp as an example...mostly cuz it's about the only component I could readily FIND that had apples-to-apples specs for both 4-ohms (150 wpc) and 8-ohms (125 wpc) Loads...and even 16-ohms (64 wpc)....for 0.1% THD from 20 - 20 kHz. Per Service Manual, Vcc = +/- 58-volts and Vout = 31.6-volts (rms, or 44.7-volt peak) for 125 wpc into 8-ohms [hence Vloss = 13.3-volts under these test conditions]. Note that Vcc/Vout = 0.544, which is significantly less than 0.707 Peak/Avg Ratio we would expect if there was NO Loss in the Output Stages.
From the manual, it looks like the only reason your Marantz 250 doesn't swing the output fully to the rails is because the current limiting protection is set to kick in well before then.

Quote:
For additional examples, download manuals for Onkyo TX-NR656, Pioneer VSX-LX103, and/or Yamaha RXV-621 [IHF/IEC test conditions for last two are NOT stipulated...based on Onkyo and comparisons to other specs, they appear to be with just One (vice typ. 2) Channels Driven and maybe just 1 kHz or perhaps 20-20kHz].
For the Pioneer at least, the VSX-LX103 lists several different specifications for the power amplifier section:

"Rated Output Power (FTC) (North American)
With 8 ohm loads, both channels driven, from 20-20,000Hz: rated 80 watts per channel minimum RMS power, with no more than 0.08% total harmonic distortion from 250 milliwatts to rated output.
Rated Output Power (IEC) (Others)
7ch x 135W at 6 ohms, 1kHz, 1ch driven of 1% THD
Maximum Effective Output Power (North American)
170W at 6 Ohms, 1kHz, 1ch driven of 10% THD
Maximum Effective Output Power (JEITA)
7ch x 170W at 6 ohms, 1kHz, 1ch driven of 10% THD
Dynamic Power (*)
*IEC60268-Short-term maximum output power
160W (3R, front)
125W (4R, front)
85W (8R, front)
THD+N (Total Harmonic Distortion+Noise)
0.08% (20-20,000 Hz, half power)"

That seems pretty well-stipulated to me? Certainly enough to do useful comparisons and draw conclusions?

Quote:
Pout = (Vout)^2 / Zload. IF Vout was indeed Constant, then Zload = 4-ohms should result in TWICE as much Power being delivered to the Load, as for 8-ohms. This is roughly True if you compare Amp spec power for 8-ohms vs 16-ohms....but specs for 4-ohms (150 wpc) are considerably short of 2x125=250 wpc for 8-ohms (125 wpc spec). That is because the higher Current Demand at 4-ohms results in considerably higher Vloss....plus higher voltage loss in speaker cables and internal Crossover Filters.
Have you actually measured the max power output at specified distortion? Some of those vintage Marantz amps put out a lot more power than their nominal specs.

Quote:
BTW: Although more Power can be delivered to 4-ohm Speakers, it is likely that Twice as many Voice Coil Windings are used in an 8-ohms Speaker...which explains why it's DC Resistance is much higher....and hence it would also likely have a 3 dB higher Speaker Sensitivity, diminishing the difference...although other factors are also involved which complicate simple comparisons:
If simply doubling the driver nominal impedance always gained 3dB in efficiency, nobody would use 4R drivers. Why stop there? 16R speakers would be even louder for even less power. Keep increasing the number of turns until you have a speaker that is infinitely loud but consumes no power at all...

Of course that's impossible. What's missing is that efficiency, and thus sensitivity, is affected by the resistance of the voice coil. Consider a flat-wound coil, with ribbon wire (rectangular cross-section that can completely fill the gap so we can ignore packing density). If you wish to change a 4R voice coil to an 8R one, squish the wire to 0.707 of its original thickness. At the same time, increase the length(l) by 1.414 times. The new coil will have twice the resistance (Re). The equation for reference efficiency includes (Bl)^2/Re. The B stays the same because the magnetics and geometry haven't changed, and the increase in l and Re cancel each other out. So the 4R and 8R coils in the same driver design will have the same efficiency of converting electrical power into acoustic power.

Quote:
PPS: For most Dynamic Woofers and Sub-Woofers, Highest Current Draw occurs at a Frequency about 2x to 3x higher than it's -3 dB Low Freq Rolloff, where the Impedance is Minimum and equal to the Voice Coil's DC Resistance (Re), easily measured by a VOM/DVM. THAT is the Impedance that should be used when looking at Amp specs...which are tested using purely resistive test loads. OTOH: Speaker "nominal" [average?] Impedance Specs are inexplicably & dangerously HIGHER:
https://imageevent.com/holl_ands/fil...akercomparison
The driver/speaker manufacturer usually judges over how wide a range as well as how low the impedance minima are, and whether they are located in regions of likely intended use. And of course then they're usually rounded to a nominal value.
Driver reactance and crossover design can contribute to *even more* current through the amp than the DC resistance of a driver might indicate. Reactive loads at a higher impedance can be a much more difficult load for an amp than resistive loads of a lower impedance. It also depends where the heavy loads occur, most amps don't like heavy loads at highest frequencies.

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post #16 of 21 Old 04-01-2019, 02:53 PM
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See clarification...I was trying to make a point about AVR's being only lightly loaded during Spec Tests as well as normal use:

"IF equipped with a Voltage Regulator in the Power Supply (my Marantz 250 is NOT), it TRIES to keep +/- Vcc Constant, irrespective of the Current Demand....which is usually the case for "typical" Standardized AVR Spec Tests [with or w/o Voltage Regulator], which very rarely have more than one or two channels fully driven [also the case for REAL Music & Movie Tracks]. Only when ALL Channels are fully driven should we [maybe] expect to see an AVR's Voltage Regulator no longer provide the full +/- Vcc voltages."

Back when I was still working [abt 2004/5] and had access to a room full of Test Equipment, I refurbished my antique Marantz 250, including replacing Power Supply Electrolytics and Meter Light Bulbs. Although I did not have Dummy Load Resistors that could dump 125+ wpc, I did have some that could dump 50 wpc, which is more than I ever need anyway, driving a pair of Altec 15-in Voice-Of-The-Theater Woofers [Eff. ~ 94 dB SPL for 2.83-v at 1-m]....repurposed as my Sub-Woofers with a 1/3-Octave Band Equalizer. At the same time, I also refurbished my Antique Phase Linear 1000 Auto-Correlator [Rumble & Hiss] Noise Eliminator.

Specs for Marantz 250 only stipulate Power at 0.1% THD, so obviously it's going to provide quite a bit more at 0.8% THD (a frequently cited THD spec point).

Since a Speaker mfr can vary the Magnetic Force (B) as well as ALL of the other physical properties, I would NOT try to generalize as to whether 4-ohm or 8-ohm Speakers (or 2-ohm in Cars) are somehow "better". The only thing that we CAN compare is the resultant SPL for a given Efficiency [as I advised]...which unfortunately IGNORES the OTHER limitation on how much LOW Frequency SPL is possible....Xmax, the Maximum Voice Coil Extension before it smacks into the mechanical structure....which is usually reached AFTER non-linearities result in excessive Distortion....and don't forget to adjust Xmax curves found in LOUDSPEAKER link I cited above for whatever ROOM EQUALIZATION is being applied before you consider whether Sealed or Vented Box is somehow "better".

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post #17 of 21 Old 04-01-2019, 03:47 PM
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I checked Service Manual for my Pioneer VSX-1015TX-K AVR (pre-HDMI so I use 5.1/7.1 Analog RCA I/F from Oppo BD-Player) It uses Push-Pull Power MOSFET Output Devices....which do NOT use Regulated Power...although there are a total of 9 Voltage Regulators for OTHER Circuits.

I also checked Owner's Manual for my old Dynaco ST-120 Stereo Amp (60 wpc into 8-ohms at 0.5% THD), a pair of which were used in early '70's for Stereo and later QUAD set-up....until I got tired of replacing the Output Transistors (which was a common problem) and bought an early AVR. It HAD a well Regulated Power Supply, as described in the Owner's Manual and below White Paper. Note that a Voltage Regulator MiGHT be more useful in a STEREO Amp where both channels are likely to be heavily loaded, unlike an AVR where many/most of the channels are very infrequently...if EVER...driven to full power at the SAME Time:
https://davidreaton.com/dynaco/stereo-120
https://www.updatemydynaco.com/docum...ptionRev10.pdf [Note Regulation occurs on GROUND side connection.]

Voltage Regular performance for the Original ST-120 Design described here, along with a recommended reliability mod:
https://www.google.com/url?sa=t&rct=...GzofsGoJCn440a

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A survey of amp and speaker specifications

If you want to learn a lot about speakers and rooms, get my book: https://www.amazon.com/Sound-Reprodu...=UTF8&me=&qid=

If you want some useful free information there is an interesting perspective on amplifier power ratings and loudspeaker impedance and sensitivity ratings in Part 3 of "How to Design a Home Theater" at the open access companion website for the book: www.routledge.com/cw/toole

Click on the title at the top of the web page and download it.

It shows persuasive evidence that misrepresentation is widespread - it should be expected.
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Quote:
Originally Posted by Floyd Toole View Post
If you want to learn a lot about speakers and rooms, get my book: https://www.amazon.com/Sound-Reprodu...=UTF8&me=&qid=

If you want some useful free information there is an interesting perspective on amplifier power ratings and loudspeaker impedance and sensitivity ratings in Part 3 of "How to Design a Home Theater" at the open access companion website for the book: www.routledge.com/cw/toole

Click on the title at the top of the web page and download it.

It shows persuasive evidence that misrepresentation is widespread - it should be expected.
While I was not able to download-it, I strongly agree with this last sentence.

I also understand that most consumer only need an AVR.
Personally, I prefer a power amp with a good AVP. Since most power amps, are rated with all channels driven from 20-20000Hz.
That said, the price of entry is a lot more. But worth the price in my opinion, but not for everyone due to budget restriction.


Ray
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post #20 of 21 Old 04-01-2019, 09:30 PM
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Quote:
Originally Posted by fill35U View Post
.... the VSX-LX103 lists several different specifications for the power amplifier section:

"Rated Output Power (FTC) (North American)
With 8 ohm loads, both channels driven, from 20-20,000Hz: rated 80 watts per channel minimum RMS power, with no more than 0.08% total harmonic distortion from 250 milliwatts to rated output.
Rated Output Power (IEC) (Others)
7ch x 135W at 6 ohms, 1kHz, 1ch driven of 1% THD
Maximum Effective Output Power (North American)
170W at 6 Ohms, 1kHz, 1ch driven of 10% THD
Maximum Effective Output Power (JEITA)
7ch x 170W at 6 ohms, 1kHz, 1ch driven of 10% THD
Dynamic Power (*)
*IEC60268-Short-term maximum output power
160W (3-ohms, front)
125W (4-ohms, front)
85W (8-ohms, front)
THD+N (Total Harmonic Distortion+Noise)
0.08% (20-20,000 Hz, half power)"

That seems pretty well-stipulated to me? Certainly enough to do useful comparisons and draw conclusions?
.....
Although 6-ohm and 8-ohm Power Specs are fairly complete, I find that the "Dynamic Power (*) *IEC60268-Short-term maximum output power" specs (which include 8, 4 and 3-ohms) are very incomplete since it does NOT stipulate the THD Test Criteria for these MAX Power values. [At least 4 and 3-ohm loads don't trip the self-protect circuitry!!!]

The very next line re THD+N probably [??] applies to preceding IEC60268 specs....but they are AT HALF POWER...which says NOTHING about what THD (or THD+N) might be at the MAX POWER spec points....so it's of NO USE in explaining them. They read as follows:

"THD+N (Total Harmonic Distortion+Noise)
0.08% (20-20,000 Hz, half power)"


BTW: It would cost about $353 just to download the fol. IEC 60268 spec that may or may NOT be the correct "-part" anyway:
https://global.ihs.com/doc_detail.cf...132531&csf=ASA
Or maybe this "-part" for an additional $301 [???]:
https://webstore.iec.ch/publication/28687
And if that isn't the right "-part"....keep guessing at abt $300 ea....

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post #21 of 21 Old 04-02-2019, 10:22 AM
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Quote:
Originally Posted by holl_ands View Post
I also checked Owner's Manual for my old Dynaco ST-120 Stereo Amp (60 wpc into 8-ohms at 0.5% THD), a pair of which were used in early '70's for Stereo and later QUAD set-up....until I got tired of replacing the Output Transistors (which was a common problem) and bought an early AVR. It HAD a well Regulated Power Supply, as described in the Owner's Manual and below White Paper.
Wow, talk about a dinosaur! The only reason the ST-120 had regulated rails was to try to keep from blowing the 2N3055 outputs. The ubiquitous 2N3055 is a terrible choice for output devices (or input devices, or most anything in between...). They were even worse in those early days before the gradual improvements. Not surprised you blew a lot of them. Tremendous upgrades would be from the zenith of TO-3 audio transistors in the mid-1980's, then you can throw away all the regulator circuitry. Or take the popular option of gutting the case and dropping in a couple of 3886 chip amps, again no regulator necessary.

Quote:
Note that a Voltage Regulator MiGHT be more useful in a STEREO Amp where both channels are likely to be heavily loaded, unlike an AVR where many/most of the channels are very infrequently...if EVER...driven to full power at the SAME Time:
I'm not sure you understand how a linear voltage regulator works: You start with a higher voltage than you need, and the regulator drops it to a precisely maintained lower voltage. The difference is wasted as heat in the regulator. The heavier the load, the more the input to the regulator will sag (if it didn't, you wouldn't want a regulator in the first place). So the higher the expected load, the higher the starting voltage, the more the regulator wastes as heat under light load. High current, high voltage, high dissipation linear voltage regulators are big, heavy, expensive, would dissipate roughly the same heat as the amp itself, and sometimes generate significant noise. All they would do in the process is throw away headroom as heat.

In an audio power amp, there's no reason to regulate the main rails. Whether the rails sag from one channel or all 17 at once, they're still sagging and all rails see the same voltage. If there's more than one rail power supply, the heavily loaded channel will have low rails and the lightly loaded channel(s) won't. Why does this even matter? If you want less sag, use a bigger power supply, or a more efficient topology.

For the OP, using 4 ohm speakers instead of 8 means more current throughout the entire amp, and more heat. There will be *measurably* more distortion, but it will almost certainly be well below audibility.

Quote:
The very next line re THD+N probably [??] applies to preceding IEC60268 specs....but they are AT HALF POWER...which says NOTHING about what THD (or THD+N) might be at the MAX POWER spec points....so it's of NO USE in explaining them.
Just because you don't want to pay for access to standards doesn't give you the right to claim they don't exist or are useless. Or do you not care that UL1492/6500/60065 protect you? Since you don't own copies, do you consider them pointless?

You also seem obsessed about distortion and rail voltage performance at exactly full output. You do realize that edge is fairly arbitrary, depending on how much distortion you're willing to accept? The specs show a reasonable variance in output power over a reasonable range of distortion and conditions. If you're running continuously near maximum output, you have very little headroom. The practical approach would then be upgrading to a substantial increase in output capability, so you could comfortably run around... half power or less. That's why the "half power" spec, it's silly to always run the amp right on the edge. If that's how you like to roll, you probably won't mind a little extra distortion at that point anyhow...

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