speaker impedance game

[daddyora]

I'm doing research on a speaker upgrade (the fun stuff) but I'm getting a headache over speaker impedance ratings. I understand some of the tech about impedance and frequency & loudness but it seems that there are games being played with how speakers are rated vis-à-vis impedance. "Nominal" ratings (wink, wink) seems to be part of this game. Sometimes they will list a minimum but often this minimums seems to belie the nominal (ie a nominal 8 ohm speaker may dip to a 3.2 ohm minimum). Reviews on speakers often use subjective terms like "robust", "quality", or "expensive" to describe amplifier requirements for low ohm speakers. I did see one interview with Andrew Jones where he stated that a speaker minimum should be around 80% of the rating but this guideline certainly doesn't seem to be an industry standard. How do we as consumers deal with this problem ? Specifically, I have a Yamaha Aventage RX-A660 avr this is listed as a 6 or 8 ohm speaker amplifier. Am I stuck with 6 or 8 ohm speakers for the life of the avr or can I drive a 4 ohm center speaker with it in a 5.1 system ?

 

[highfigh]

I'm doing research on a speaker upgrade (the fun stuff) but I'm getting a headache over speaker impedance ratings. I understand some of the tech about impedance and frequency & loudness but it seems that there are games being played with how speakers are rated vis-à-vis impedance. "Nominal" ratings (wink, wink) seems to be part of this game. Sometimes they will list a minimum but often this minimums seems to belie the nominal (ie a nominal 8 ohm speaker may dip to a 3.2 ohm minimum). Reviews on speakers often use subjective terms like "robust", "quality", or "expensive" to describe amplifier requirements for low ohm speakers. I did see one interview with Andrew Jones where he stated that a speaker minimum should be around 80% of the rating but this guideline certainly doesn't seem to be an industry standard. How do we as consumers deal with this problem ? Specifically, I have a Yamaha Aventage RX-A660 avr this is listed as a 6 or 8 ohm speaker amplifier. Am I stuck with 6 or 8 ohm speakers for the life of the avr or can I drive a 4 ohm center speaker with it in a 5.1 system ?

I would recommend looking into the FTC rating requirements that started in the early-'70s and how it has changed over the decades.

A lot of the reason AVRs aren't rated for low impedance is that most home theater systems use a subwoofer and that's where a lot of the grunt work happens. If the satellites don't require the amplifier to drive high current, the 6-8 Ohm rating is fine. If the system is full-range, that's going to result in gutless sound.

 

[ryanosaur]

Hi Daddyora.

This was shared by another cat here who's helped me along my way, @lovinthehd: https://www.audioholics.com/audio-amplifier/impedance-selector-switch-1/amplifier-and-power-supply-basics

If you haven't already stumbled on it, it has some good info that might help out as it does cover lower impedance speakers and the impedance switch.

My solution is matching the front 3 and getting a separate amp to juice them... letting my avr run the surrounds, and if/when I upgrade to a surround pre-pro, I'll upgrade to an amp suitable for the surrounds, too. (I've been looking at Emotiva amps, XPAs: affordable and people seem to be happy with their performance.)

Cheers!

 

[Dennis Murphy]

I would recommend looking into the FTC rating requirements that started in the early-'70s and how it has changed over the decades.

A lot of the reason AVRs aren't rated for low impedance is that most home theater systems use a subwoofer and that's where a lot of the grunt work happens. If the satellites don't require the amplifier to drive high current, the 6-8 Ohm rating is fine. If the system is full-range, that's going to result in gutless sound.

I'm not sure which changes in the FTC testing protocol you're referencing. We did make some peripheral changes in the pre-conditioning requirement and allowed more flexibility in the choice of impedance for powered speakers, but other than that the protocol hasn't changed. The primary disclosure is supposed to be (but often isn't) continuous power into 8 ohms with two channels operating at a stated frequency bandwidth and maximum distortion.

 

[shadyJ]

I'm doing research on a speaker upgrade (the fun stuff) but I'm getting a headache over speaker impedance ratings. I understand some of the tech about impedance and frequency & loudness but it seems that there are games being played with how speakers are rated vis-à-vis impedance. "Nominal" ratings (wink, wink) seems to be part of this game. Sometimes they will list a minimum but often this minimums seems to belie the nominal (ie a nominal 8 ohm speaker may dip to a 3.2 ohm minimum). Reviews on speakers often use subjective terms like "robust", "quality", or "expensive" to describe amplifier requirements for low ohm speakers. I did see one interview with Andrew Jones where he stated that a speaker minimum should be around 80% of the rating but this guideline certainly doesn't seem to be an industry standard. How do we as consumers deal with this problem ? Specifically, I have a Yamaha Aventage RX-A660 avr this is listed as a 6 or 8 ohm speaker amplifier. Am I stuck with 6 or 8 ohm speakers for the life of the avr or can I drive a 4 ohm center speaker with it in a 5.1 system ?

You can probably get away with running a 4 ohm speaker on that AVR. Low impedance speakers are not going to kill that thing unless you run them loud. And if they do kill that thing, than you can get an AVR that has a better amplifier, so it's a win-win.

 

[TLS Guy]

I'm doing research on a speaker upgrade (the fun stuff) but I'm getting a headache over speaker impedance ratings. I understand some of the tech about impedance and frequency & loudness but it seems that there are games being played with how speakers are rated vis-à-vis impedance. "Nominal" ratings (wink, wink) seems to be part of this game. Sometimes they will list a minimum but often this minimums seems to belie the nominal (ie a nominal 8 ohm speaker may dip to a 3.2 ohm minimum). Reviews on speakers often use subjective terms like "robust", "quality", or "expensive" to describe amplifier requirements for low ohm speakers. I did see one interview with Andrew Jones where he stated that a speaker minimum should be around 80% of the rating but this guideline certainly doesn't seem to be an industry standard. How do we as consumers deal with this problem ? Specifically, I have a Yamaha Aventage RX-A660 avr this is listed as a 6 or 8 ohm speaker amplifier. Am I stuck with 6 or 8 ohm speakers for the life of the avr or can I drive a 4 ohm center speaker with it in a 5.1 system ?

You have hit on a big problem. Ideally every speaker should have a published impedance curve together with a graph of the phase angle between current and voltage with frequency. So you actually can have an impedance lower then the trace on the impedance curve.

Minimum impedance is a guide if the frequency is stated where this occurs. Usually it is right on the power range of 80 to 600 Hz. If that is so then the rough rule of thumb is that the impedance is minimal impedance plus 10%.

Now the use of subwoofer is totally irrelevant but goes on being repeated. In the sub range this almost always occurs at the twin peaks of impedance in a ported enclosure and the mass loaded TL. It occurs over the single impedance peak for sealed speakers and the traditional non mass loaded TL. In addition there is actually not a lot of power below 80 Hz. People think there is because people want small subs which are inefficient.

So lets get this straight subwoofers offload the bass and bass mid drivers of the other speakers and NOT the receiver.

Unfortunately there are a lot of speakers with adverse load characteristics and you are right the manufacturers usually hide the fact.

I would say that if a speaker has two woofers it is almost certainly 4 ohms or less. If it has more than two woofers don't drive it with a receiver unless you know the phase angles and impedance curve.

I personally think that driving speakers with a receiver unless you play it very quietly is not to e recommended. Good external power amps are a wise investment, unless you are driving bookshelf speakers in a small room. But essentially I regard receiver amps as pretty nasty contraptions, and I don't listen via receiver power amps.

If you are concerned this woofer tester is strongly recommended. It will test a complete speaker and is very accurate.

Actually if you intend to put together a decent system, and keep it in good order, investment in some sensible test gear should be part of the budget. Members here do not invest in test gear like they should. It would save them a lot of trouble and expense if they did.

 

[highfigh]

I'm not sure which changes in the FTC testing protocol you're referencing. We did make some peripheral changes in the pre-conditioning requirement and allowed more flexibility in the choice of impedance for powered speakers, but other than that the protocol hasn't changed. The primary disclosure is supposed to be (but often isn't) continuous power into 8 ohms with two channels operating at a stated frequency bandwidth and maximum distortion.

IPP (Instantaneous Peak Power) power was used until the mid-'70s as one of the specs, then RMS became the one people selling stereo equipment used. Didn't mean they understood it, but they used it. I asked and the only 'explanation' I got was "It stands for Root Mean Squared'. Thanks, Elliot.

The equipment manufacturers helped themselves by connecting the speakers in series when the switch was set to Speaker A+B, too. I don't remember seeing many receivers or integrated amps stating they could handle 4 Ohms and most showed something about using only 8-16 Ohm speakers. OTOH, some companies would publish their specs and the equipment would usually overshoot by a good margin- I had an integrated like the one in the link and while rated at 100W/ch, I had one of the service techs test it with the store's BPI distortion analyzer and it put out 176/channel, both channels driven, at rated distortion.

http://www.thevintageknob.org/sony-TA-F6B.html

 

[Dennis Murphy]

IPP (Instantaneous Peak Power) power was used until the mid-'70s as one of the specs, then RMS became the one people selling stereo equipment used. Didn't mean they understood it, but they used it. I asked and the only 'explanation' I got was "It stands for Root Mean Squared'. Thanks, Elliot.

The equipment manufacturers helped themselves by connecting the speakers in series when the switch was set to Speaker A+B, too. I don't remember seeing many receivers or integrated amps stating they could handle 4 Ohms and most showed something about using only 8-16 Ohm speakers. OTOH, some companies would publish their specs and the equipment would usually overshoot by a good margin- I had an integrated like the one in the link and while rated at 100W/ch, I had one of the service techs test it with the store's BPI distortion analyzer and it put out 176/channel, both channels driven, at rated distortion.

http://www.thevintageknob.org/sony-TA-F6B.html

No argument there. But your original post seemed to say the FTC had changed its protocol, which isn't the case. The industry switched to continuous power ratings rather than peak specs in 1974 because that's when the FTC Rule took effect. Continuous power into 8 ohms is still the required spec, although a case could be made for allowing a primary spec based on shorter term power capability. Manufacturers are free to disclose additional power ratings based on different protocols. as long as the FTC spec is the most conspicuous.

 

[highfigh]

No argument there. But your original post seemed to say the FTC had changed its protocol, which isn't the case. The industry switched to continuous power ratings rather than peak specs in 1974 because that's when the FTC Rule took effect. Continuous power into 8 ohms is still the required spec, although a case could be made for allowing a primary spec based on shorter term power capability. Manufacturers are free to disclose additional power ratings based on different protocols. as long as the FTC spec is the most conspicuous.

No, the FTC didn't change its protocol, the industry stopped abiding by it. They now use 1KHz as the reference frequency and we all know of amplifiers that are very capable of high output at that one frequency, but as soon as the bass hits, the wheels fall off. Power supplies that aren't SMPS are smaller than ever and they just can't deliver. We had discussions about whether all channels driven is a valid requirement for power specs and my rationale was that I want the power supply and amplifier circuits to be able to handle more than it should need in normal operation. Do we use all of the power our car can deliver? No, but it's there if we need it.

 

[kini]

I would say that if a speaker has two woofers it is almost certainly 4 ohms or less. If it has more than two woofers don't drive it with a receiver unless you know the phase angles and impedance curve.

I personally think that driving speakers with a receiver unless you play it very quietly is not to e recommended. Good external power amps are a wise investment, unless you are driving bookshelf speakers in a small room. But essentially I regard receiver amps as pretty nasty contraptions, and I don't listen via receiver power amps.

Not even close to being true. The number of drivers has little to do with the overall impedance.
Also, even if the speakers are 4 ohms, that still doesn't mean that an AVR, any AVR can't be used. Pretty much any modern AVR can drive 4 ohm speakers just fine at normal listening levels. It might be an issue at very high volumes in which case the AVR will let you know by shutting down.

 

[Dennis Murphy]

No, the FTC didn't change its protocol, the industry stopped abiding by it. They now use 1KHz as the reference frequency and we all know of amplifiers that are very capable of high output at that one frequency, but as soon as the bass hits, the wheels fall off. Power supplies that aren't SMPS are smaller than ever and they just can't deliver. We had discussions about whether all channels driven is a valid requirement for power specs and my rationale was that I want the power supply and amplifier circuits to be able to handle more than it should need in normal operation. Do we use all of the power our car can deliver? No, but it's there if we need it.

Well, it's a matter of how often you need it and how much it costs to insure against a rare event. But I agree that the current specs are a mess. People are always asking whether this or that AVR has enough power for the BMR's and AA's, and sometimes I can't answer because the published specs are incomplete or misleading. Very few companies are spotlighting or even disclosing the FTC specs.

 

[PENG]

IPP (Instantaneous Peak Power) power was used until the mid-'70s as one of the specs, then RMS became the one people selling stereo equipment used. Didn't mean they understood it, but they used it. I asked and the only 'explanation' I got was "It stands for Root Mean Squared'. Thanks, Elliot.

If they understood it they would have known that there is technically no such thing as RMS power. Surely, it can defined the same way as we define RMS voltage and current, but then it would have no practically meaning. Manufacturers should know better so they should have stick with the technically correct/text book term "average power" (some still do, sometimes anyway..), but they continue to use the incorrect term. Many common errors in English have become acceptable over time and no longer considered as errors, so I guess the same applies to such technical terms too.

 

[Johnny2Bad]

The speaker manufacturers have to put in a value for compatibility with power amplifiers and in particular amplifier stability. If a speaker is an easy load (impedance and phase together) and generally is above 4 ohms, maybe they rate it at 6 or 8 ohms "nominal". If it's a difficult load, say dips to 3 ohms and has a difficult phase relationship at the same frequency as the low impedance, then maybe they rate it at 4 or even 2 ohms nominal.

The nominal impedance is not meant to represent the lowest measured impedance dip (typically at low frequency), rather it's a general representation of the difficulty of the load the amplifier will see. Most amplifiers have some combination of impedance, inductance and phase that will cause the amp to either go into protection or shut down entirely or even damage the amplifier's output transistors. Other designs are stable into difficult loads, like the QUAD 303 which was designed to drive an electrostatic speaker and will reduce power output as the impedance falls until into 0 ohms it produces 0 watts ("unconditionally stable" is QUAD's specification). It's useful to know the nominal impedance for these reasons.

 

[Irvrobinson]

If they understood it they would have known that there is technically no such thing as RMS power. Surely, it can defined the same way as we define RMS voltage and current, but then it would have no practically meaning. Manufacturers should know better so they should have stick with the technically correct/text book term "average power" (some still do, sometimes anyway..),but they continue to use the incorrect term. Many common errors in English have become acceptable over time and no longer considered as errors, so I guess the same applies to such technical terms too.

Not only do I agree, but I've personally always blamed this RMS power nonsense on Marantz, who had "watts RMS" in their advertising years before the FTC issued their notorious amplifier measurement requirements. They made such a big deal about it. I remember even asking my high school physics teacher about RMS watts, because I thought RMS applied to voltage and not power, and I also remember he just laughed when I showed him a Marantz ad in Stereo Review. His suggestion was that I read textbooks and not ads stuck with me, but unfortunately I didn't follow it as soon as I should have.

 

[highfigh]

If they understood it they would have known that there is technically no such thing as RMS power. Surely, it can defined the same way as we define RMS voltage and current, but then it would have no practically meaning. Manufacturers should know better so they should have stick with the technically correct/text book term "average power" (some still do, sometimes anyway..), but they continue to use the incorrect term. Many common errors in English have become acceptable over time and no longer considered as errors, so I guess the same applies to such technical terms too.

RMS power just takes the number and uses the formula, without bothering with units.

Perreau introduced a power amp just before CES in the early-'80s and the specs showed current at a certain voltage. Rather than express the power in Watts, it showed 'Power- adequate'.

 

[highfigh]

Well, it's a matter of how often you need it and how much it costs to insure against a rare event. But I agree that the current specs are a mess. People are always asking whether this or that AVR has enough power for the BMR's and AA's, and sometimes I can't answer because the published specs are incomplete or misleading. Very few companies are spotlighting or even disclosing the FTC specs.

If you have never sold electronic components like receivers and amplifiers, you haven't felt the joy when someone would come in and ask "How many Amps does this put out?".

I think the solution would be for the consumer companies to use the same data as commercial/industrial audio- it's logical, not emotion-inducing.

 

[PENG]

RMS power just takes the number and uses the formula, without bothering with units.

Perreau introduced a power amp just before CES in the early-'80s and the specs showed current at a certain voltage. Rather than express the power in Watts, it showed 'Power- adequate'.

That's incredible!! Any link?

 

[highfigh]

That's incredible!! Any link?

It was early-'80s- everything was on paper.

 

[Johnny2Bad]

That's incredible!! Any link?

They must have been taking a page from Rolls-Royce (and Bentley). Until very recently (1996 was the first year) when UK legislation required that automobiles indicate horsepower and torque as part of the spec sheet, Rolls used to simply state that "power is adequate".

 

[ryanosaur]

They must have been taking a page from Rolls-Royce (and Bentley). Until very recently (1996 was the first year) when UK legislation required that automobiles indicate horsepower and torque as part of the spec sheet, Rolls used to simply state that "power is adequate".

Isn't this the same concept you see in fine dining, art studios, etc... "if you have to ask, this isn't for you." Not saying it's right, but that's the feel of what you guys are saying. At the root, as a newcomer to hifi gear, I have been confused by the way this info is communicated. Peng, Tls, Highfigh, Shady (and many others), you've all helped me peel back the curtain and begin to make sense of it. And yes, I wholeheartedly agree that a clarity is needed. Speaker to amplifier to pre-out/pre-amp/processor to source component.
But we still love it