Should I change the impedance to 6 ohms on my AVR? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 20 Old 04-12-2019, 02:25 PM - Thread Starter
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Should I change the impedance to 6 ohms on my AVR?

Hi guys, so I just came across someone's random review of my Denon AVR-S740H AVR on Best Buy. He said, "don't forget to change the ohms to match your speakers". I wasn't aware that this was a "thing" and thought after I run Audyssey then everything would be all good (including setting the impedance automatically).


I currently have a 5.1 setup with Sony Cores for the left, right, and center and JBL B15's for the surrounds. My sub is the JBL 550p (not sure what ohms). The Cores' are 6 ohms 100W and the JBL's are 8 ohms 100W. According to what I've read, once I set the AVR to a specific impedance, it's global, meaning it'll set it for everything.


So I have a 3 part question. 1.) Should I be setting my AVR to 6 ohms or keep it at 8 ohms? 2.) How will this affect my speakers in general? The stats on the AVR is:


Power Output (8 ohm, 20 Hz - 20 kHz, 0.08% 2ch Drive) 75W
Power Output (6 ohm, 1 kHz, 0.7% 2ch Drive) 110W
Power Output (6 ohm, 1 kHz, 10% 1ch Drive) 165W


3.) Also what's the 10% THD all about? Isn't that a lot of distortion right? I'm not sure what 1ch Drive is vs 2ch Drive. If I change it to 6 ohm, will I be getting 0.7% or 10%?
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post #2 of 20 Old 04-12-2019, 02:48 PM
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Originally Posted by t0md0 View Post
Should I be setting my AVR to 6 ohms or keep it at 8 ohms? 2.) How will this affect my speakers in general?

No, keep it at 8 ohms. It will just limit power if you switch it to 6. If for some crazy reason you drive them very hard and it makes the receiver go into protection, then switch it to 6 ohms.
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post #3 of 20 Old 04-12-2019, 03:36 PM
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Originally Posted by t0md0 View Post
I currently have a 5.1 setup with Sony Cores for the left, right, and center and JBL B15's for the surrounds. My sub is the JBL 550p (not sure what ohms). The Cores' are 6 ohms 100W and the JBL's are 8 ohms 100W. According to what I've read, once I set the AVR to a specific impedance, it's global, meaning it'll set it for everything.

So I have a 3 part question. 1.) Should I be setting my AVR to 6 ohms or keep it at 8 ohms? 2.) How will this affect my speakers in general? The stats on the AVR is:

Power Output (8 ohm, 20 Hz - 20 kHz, 0.08% 2ch Drive) 75W
Power Output (6 ohm, 1 kHz, 0.7% 2ch Drive) 110W
Power Output (6 ohm, 1 kHz, 10% 1ch Drive) 165W

3.) Also what's the 10% THD all about? Isn't that a lot of distortion right? I'm not sure what 1ch Drive is vs 2ch Drive. If I change it to 6 ohm, will I be getting 0.7% or 10%?
OK - leave the impedance setting alone. It won't affect the sound, just tweaks the shutdown (auto-protect) parameters. 2ch (vs 1) data basically characterizes the receivers 'current' & 'voltage' budgets. Not significant, unless you're really trying to crank it. 10% THD distortion is high, audible, & something to avoid (i.e. dial the volume down from 11). With that setup, would make sure that the speaker size(s) are set to small, & the receiver's crossover frequency is somewhere in the 80Hz..110Hz range.
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post #4 of 20 Old 04-12-2019, 03:53 PM
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Switching to 6 Ohms limits the available current... This will result in having less power available, less dynamics.. Leave in 8 Ohms..


Just my $0.02...
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post #5 of 20 Old 04-12-2019, 03:55 PM - Thread Starter
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Originally Posted by zeus33 View Post
No, keep it at 8 ohms. It will just limit power if you switch it to 6. If for some crazy reason you drive them very hard and it makes the receiver go into protection, then switch it to 6 ohms.

Limit power if I switch to 6? As in reducing power? Maybe I'm not understanding this whole impedance thing but the receiver specifically states it'll do 110W @ 6 ohms (or 165W 1ch Drive still not sure what these means). Aren't I actually increasing output power to the speakers if I switch to 6 ohms?
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post #6 of 20 Old 04-12-2019, 03:57 PM
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Originally Posted by t0md0 View Post
Limit power if I switch to 6? As in reducing power? Maybe I'm not understanding this whole impedance thing but the receiver specifically states it'll do 110W @ 6 ohms (or 165W 1ch Drive still not sure what these means). Aren't I actually increasing output power to the speakers if I switch to 6 ohms?
6 ohm speakers draw more current than 8 ohm speakers, so the amp runs hotter. The 6 ohm setting limits the power output to keep the amp from overheating.
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post #7 of 20 Old 04-12-2019, 04:30 PM - Thread Starter
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6 ohm speakers draw more current than 8 ohm speakers, so the amp runs hotter. The 6 ohm setting limits the power output to keep the amp from overheating.

So in other words, I'll be pushing the amp harder if I switch to 6 ohms. Therefore, limiting the "overhead" of available power left over which will probably mess with my over sound/dynamics?


Is there a case to be had to ever switch the impedance to 6 ohms? Based on the Denon site it states to switch it to 6 ohms if ANY of my speakers are 6 ohms. In any case, I trust you guys I'm just stating what I read. Thanks everyone.
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post #8 of 20 Old 04-12-2019, 04:44 PM
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So in other words, I'll be pushing the amp harder if I switch to 6 ohms.
Not exactly. You'll be pushing the amp harder just by using 6 ohm speakers, irrespective of how you set the AVR. The 6 ohm setting will limit how hard you can push it.
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post #9 of 20 Old 04-12-2019, 05:25 PM
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OK... Lets make this simple..
If there was NO impedance switch the amplifier puts out more power as the impedance decreases...
The switch is designed to reduce the power supply voltage capability so U don't over stress its components... But the byproduct by the limiting circuit is less power, especially for dynamics...

Just my $0.02...
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post #10 of 20 Old 04-12-2019, 05:27 PM - Thread Starter
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Originally Posted by lightbox View Post
Not exactly. You'll be pushing the amp harder just by using 6 ohm speakers, irrespective of how you set the AVR. The 6 ohm setting will limit how hard you can push it.
Ooh ok. Gotcha. Since my speakers are 6 ohm and the AVR is set to 8 ohm, what's the wattage going into the Cores in this case? 75W? 110W?
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post #11 of 20 Old 04-12-2019, 08:01 PM
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Originally Posted by t0md0 View Post
Ooh ok. Gotcha. Since my speakers are 6 ohm and the AVR is set to 8 ohm, what's the wattage going into the Cores in this case? 75W? 110W?
By Cores I'm assuming you mean the Sony SS-CS5?

If that's the case, the speakers sensitivity is rated at 87 dB 2.83V @ 1 meter.

If you calibrate using Audyssey at 75dB, you'll be using less than 1 watt @ 1 meter.

The sensitivity rating is telling you that you would use 1 watt for a sound pressure level (SPL) of 87dB at a 1 meter distance.

If your sitting 3 meters back, or ~10 feet, from the speaker, you'll have an ~9.5 dB drop in SPL for something like 77.5dB SPL (87dB - 9.5dB = 77.5dB).

It requires a doubling of power to increase the SPL 3dB. So to get back to an ~87dB SPL you would need 2 watts to go from 77.5dB to 80.5dB. 4 watts would take you from 80.5dB to 83.5dB. 8 watts would take you from 83.5dB to 86.5dB with consideration to sitting ~10 feet in front of the speaker.

Most people listen at something around 75dB or less. So you will never be using more than a a few watts with the exception of very loud passages where there is an increase in dynamic range or volume from the movies sound mix.
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post #12 of 20 Old 04-12-2019, 09:59 PM - Thread Starter
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Originally Posted by b curry View Post

By Cores I'm assuming you mean the Sony SS-CS5?

If that's the case, the speakers sensitivity is rated at 87 dB 2.83V @ 1 meter.

If you calibrate using Audyssey at 75dB, you'll be using less than 1 watt @ 1 meter.

The sensitivity rating is telling you that you would use 1 watt for a sound pressure level (SPL) of 87dB at a 1 meter distance.

If your sitting 3 meters back, or ~10 feet, from the speaker, you'll have an ~9.5 dB drop in SPL for something like 77.5dB SPL (87dB - 9.5dB = 77.5dB).

It requires a doubling of power to increase the SPL 3dB. So to get back to an ~87dB SPL you would need 2 watts to go from 77.5dB to 80.5dB. 4 watts would take you from 80.5dB to 83.5dB. 8 watts would take you from 83.5dB to 86.5dB with consideration to sitting ~10 feet in front of the speaker.

Most people listen at something around 75dB or less. So you will never be using more than a a few watts with the exception of very loud passages where there is an increase in dynamic range or volume from the movies sound mix.
Wow thanks man. I guess it's really not as simple as I had originally thought. There's a lot that goes into what the sensitivity of a speaker means and now I understand what that spec actually is when looking at speakers. That's very detailed info and I really appreciate it.
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post #13 of 20 Old 04-13-2019, 01:32 AM
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The impedance switch is a safety thing. When the manufacturer submits their amp for safety certification (think UL, CSA or ETL Intertek) they submit which speakers it's to be used for. The safety test lab hooks up a special load that simulates a speaker then places the amp under worst case conditions that severely stress it. The amp has to survive without getting too hot, catching fire or being dangerous to the owner.

The manufacturer may request lower impedance speakers be tested with a lower impedance setting - these impedance setting limit the amount of power the amp has, which lowers the dissipation and heat produced by the amp.

The best setting is to leave it at the 8 ohm or higher setting, as this will make all the power the amp available. However, if it results in the amp going into protection mode then you will have to lower the setting as you're stressing the amp enough where it overheats. Also lower the setting if you feel uneasy since it is related to product safety. But realize that the test lab is putting the amp through very stressful conditions - conditions that will unlikely ever be reproduced during normal use.
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post #14 of 20 Old 04-13-2019, 06:19 AM
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Originally Posted by t0md0 View Post
Wow thanks man. I guess it's really not as simple as I had originally thought. There's a lot that goes into what the sensitivity of a speaker means and now I understand what that spec actually is when looking at speakers. That's very detailed info and I really appreciate it.
Yes, there is a lot. My example is a close approximation for your speaker and based on one speaker. You have two of the Sony SS-CS5 speakers so that can increase the SPL by ~3dB for a given power level. How the speakers are placed in the room and/or interact with the room can also boost the SPL which in turn will offset some of the SPL lost for distance or the power needed.
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post #15 of 20 Old 06-25-2019, 12:27 AM - Thread Starter
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Need help understanding AVR specs and should I be concerned about THD?

Hey guys, new to the AVR world and home audio in general. Sorry for the newb questions but I was just looking over my manual the other day and noticed that it stated:

Power Output (8 ohm, 20 Hz - 20 kHz, 0.08% 2ch Drive) 75 W
Power Output (6 ohm, 1 kHz, 0.7% 2ch Drive) 110W

So my first question is regarding THD. Like if I plug in 6 ohm speakers to my AVR, does that mean theoretically any sound above 1 kHz I'll get 0.7% THD? Obviously lower is better but when shopping for speakers, ideally, should I be looking for speakers that are 8 ohm and not 6 ohm for the lower THD? Or is the difference so small it doesn't really matter?

And also lastly, I also see it says 110W if I use 6 ohm. What does this mean exactly? Does that mean more power will be available to a set of 6 ohm speakers vs an 8 ohm speaker? 110W vs 75W respectively? Like, should I be trying to match the wattage on the AVR to the speakers wattage to get the most out of them?

Just trying to get the most out of my AVR and want to make sure I'm powering speakers correctly. Maybe it's not as simple of answer like, oh hey 75 watt speakers will be perfect with a 75 watt amp? Lol.
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post #16 of 20 Old 06-25-2019, 12:50 AM
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Quote:
Originally Posted by t0md0 View Post
Hey guys, new to the AVR world and home audio in general. Sorry for the newb questions but I was just looking over my manual the other day and noticed that it stated:

Power Output (8 ohm, 20 Hz - 20 kHz, 0.08% 2ch Drive) 75 W
Power Output (6 ohm, 1 kHz, 0.7% 2ch Drive) 110W

So my first question is regarding THD. Like if I plug in 6 ohm speakers to my AVR, does that mean theoretically any sound above 1 kHz I'll get 0.7% THD? Obviously lower is better but when shopping for speakers, ideally, should I be looking for speakers that are 8 ohm and not 6 ohm for the lower THD? Or is the difference so small it doesn't really matter?

And also lastly, I also see it says 110W if I use 6 ohm. What does this mean exactly? Does that mean more power will be available to a set of 6 ohm speakers vs an 8 ohm speaker? 110W vs 75W respectively? Like, should I be trying to match the wattage on the AVR to the speakers wattage to get the most out of them?

Just trying to get the most out of my AVR and want to make sure I'm powering speakers correctly. Maybe it's not as simple of answer like, oh hey 75 watt speakers will be perfect with a 75 watt amp? Lol.
A speaker with lower impedance will cause more current to be drawn through the amp. When you're near the top of the amp's volume range, this extra current will cause an increase in THD. That's all it's really saying, but I don't think it will have any real world impact on your system.

Most regular consumer speakers will be 8 ohms. What you care about more is the speaker's sensitivity, i.e., how many dB it can create per watt of power. More sensitive = more efficient = less power needed for a given loudness.

The 6 ohm spec on the receiver is basically saying it's OK to also use 6 ohm speakers if you want. 4 ohm speakers would not be recommended, as you are taxing the amp too much if you turn the volume up.
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post #17 of 20 Old 06-25-2019, 12:53 AM
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Originally Posted by t0md0 View Post
And also lastly, I also see it says 110W if I use 6 ohm. What does this mean exactly? Does that mean more power will be available to a set of 6 ohm speakers vs an 8 ohm speaker? 110W vs 75W respectively? Like, should I be trying to match the wattage on the AVR to the speakers wattage to get the most out of them?
The wattage rating on a speaker is how much power it can handle. So basically don't buy a speaker capable of only handling 35 watts, but then send it 100 watts. You'll blow the speaker. Other than not overpowering the speaker, this rating is fairly meaningless as well.
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post #18 of 20 Old 06-25-2019, 09:43 AM
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The 20hz-20khz rating with at least 2 channels driven is a better indicator of the watts per channel available.

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post #19 of 20 Old 06-25-2019, 10:39 AM
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A few points,

First thing is the distortion is rated at the power level stated--this does not mean in any way that is the distortion you get when not driven at that level.

For instance, a Texas Instruments chip amp is rated at verious points, it puts out 0.004% distortion at 5 watts, 0.1$ distortion at 60 watts and 10% distortion at 110 watts (roughly)

Distortion on amplifiers is not linear, it starts fairly high at very, very low levels (1/100th of a watt) then rapidly falls to very low levels which riase as it gets near it's limits.

It is not uncommon to have an amp output 0.01% or less distortion at 1 to 25 watts and stay really low until it gets close to max level (say 100 watts) The more power it puts out, the more distortion it has as ALL amplifiers will do 10% and higher distortion as you get close to maxing it out. The level of distortion is up to the manufacturer. You can have the exact same amplifier and rate it verious ways. Say you want impressive THD specs, just rate the amplifier output lower to get those 0.005% specs. If you want more impressive power numbers, just go up the power output scale to get those numbers but at higher distortion levels. A 100 watt per channel amp at 0.01% distortion can be the same exact amp as one rated for 140 watts per channel at 0.7% distortion or rated for 200 watts at 10% distortion.

They call those distortion charts "hockey sticks" because the start with medium distortion at very, very low levels which declines rapidly as you approach 1/10th of a watt then it stays very low for most of the chart but then kicks up rapidly as the amp maxes out.

For this reason, it is best to get a distortion CHART that shows all the information with multiple impedances--say 8 and 4 ohm and make your decision from that chart. In professional sound, it is common to state the output at 0.5% distortion, this gives a very high output rating and generally will the limiter will start to engage to protect hte amplifier (and the speakers to a certain point) The actual operating distortion level can be lower, much lower at 0.01% to less than 0.1% for most of the range. It is just how they are rated. Slam a speaker with 500 watts of power and it will distort far more than 0.5% so amp distortion does not matter at that level, the speaker will be creating far more distortion which will mask anything the amp does. (as long as you keep the limiter light at bay)

The other interesting things amps do is generate more power at lower impedance levels but that also creates more distortion--another game the manufacturers can play.

In summation, numbers really don't mean anything so get a THD chart for the amplifier desired at the impedance you plan to use. Yes, a $5 chip can go down to 0.005% distortion at 5 watts of output so you don't need to spend a huge amount to get the numbers you desire--no point in having a numbers battle when the chart will show you the full story. Try to find the charts that do full bandwidth testing, 20Hz to 20KHz for your mains and 5 Hz to 200 Hz for your subwoofer amplifiers if you desire ULF for Sci-Fi and war movies. Some amplifiers will filter out frequencies blow 10 to 20Hz so getting a chart that shows you the ULF band will guide you to the proper subwoofer amplifier.

For this reason, I don't waste time with amplifier "reviews" and look for actual amplifier testing with full bandwidth THD charts with 8 ohm and whatever the minimum impedance of the amplifier tested (1 to 6 ohms depending on amplifier) Hope this helps you in your quest for amplifiers to meet your needs.
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post #20 of 20 Old 06-25-2019, 10:49 AM
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