Question about OHMS

[mnatiq]

i have been reading that the onkyo 806 can work speakers at 4ohms compared to the normal 8ohms. what are the advantages of that, can someone tell me if my polk monitor 70s can work at 4ohms. if so how can i do it? dont know to much about the ohms factor. thanks

 

[Haoleb]

Your speakers are 8 ohms, So you have nothing to worry about, You cant change it. Its a characteristic of the speaker by design. If the reciever is rated to drive 4 ohm speakers that means it has a better amplifier section than other recievers that are not rated for such speakers. 4 ohm speakers are generally a harder load for an amplifier because they require more power.

If you are intersted in learning more about such topics the "av university" part of this website has many well written articles. Some of them may be a technical but dont be overwhelmed by it, Your not supposed to fully "get it" after reading through a few paragraphs.

http://www.audioholics.com/education/

 

[Seth=L]

Speakers don't handle ohms, they are the ohms. Ohms is a measure of resistance. The less resistance, or impedance, a speaker has the more current it will demand of an amplifier. So an 8 ohm speaker would be easier to drive than a 4 ohm speaker. Also, speakers are rated for nominal impedance or average impedance. This means the speaker doesn't stay at one impedance all the time. A 8 ohm nominal rated speaker may be at 8 ohms at one frequency and 4 ohms at another. So assuming the same output level a speaker at 8 ohms is drawing 20 watts from the amplifier/receiver and then it drops to 4 ohms it will now be drawing 40 watts.

Of course these are all very rudimentary figures as there are more factors that are considered.

What is important for you is that your receiver is rated to handle most speaker systems designed for use in a home theater. You will be fine.

Also, don't set your receiver to the 4 ohm setting (it should be a menu option now, it used to be a switch located on the rear of some receivers and not all receivers have a 4 ohm setting that can be used). All the 4 ohm setting does is reduce the output current of the receiver to protect it from careless use.

 

[highfigh]

Impedance varies with frequency and when it dips, some amps have a major problem with handling it. If the amp only shows the power output for 8 ohms, pass and look for one that shows 4 ohms, as well. Also, look for a receiver or amp that is rated with all channels driven. Any amp will work with one channel but who listens to true mono? All channels driven presents a lot more load to the power supply and if it sags, the voltage that's available to the output devices drops, so you get less power and more distortion.

 

[PENG]

Impedance varies with frequency and when it dips, some amps have a major problem with handling it. If the amp only shows the power output for 8 ohms, pass and look for one that shows 4 ohms, as well. Also, look for a receiver or amp that is rated with all channels driven. Any amp will work with one channel but who listens to true mono? All channels driven presents a lot more load to the power supply and if it sags, the voltage that's available to the output devices drops, so you get less power and more distortion.

Unfortunately it is not that simple. For example, one may benefit more from one that is test rated for 150W 2 channel driven, 50W all channel driven, than another one that can manage 90W 2 channels driven, 75W all channel driven. It really depends on your needs too. Some receivers are more power supply limited while others are more amplifier limited. Manufacturers can only put so much money into a particular product in order to compete in the open market and be profitable. They all have to do their balancing act in allocating X$ to features, quality, amp sections, power supply, connectivity etc.

 

[highfigh]

Unfortunately it is not that simple.

It really depends on your needs too. Some receivers are more power supply limited while others are more amplifier limited. Manufacturers can only put so much money into a particular product in order to compete in the open market and be profitable. They all have to do their balancing act in allocating X$ to features, quality, amp sections, power supply, connectivity etc.

How detailed does this need to be for the original question? I was addressing that, not market-driven decision making by a manufacturer.

"For example, one may benefit more from one that is test rated for 150W 2 channel driven, 50W all channel driven, than another one that can manage 90W 2 channels driven, 75W all channel driven."

I would say the first one is only managing to put out what it does- it's only 50%, while the other is hitting 80%.

Why put great output devices on a bad power supply? That makes no sense, unless they really designed it as a pre-amp and put the power section in as a courtesy.

 

[PENG]

How detailed does this need to be for the original question? I was addressing that, not market-driven decision making by a manufacturer.

"For example, one may benefit more from one that is test rated for 150W 2 channel driven, 50W all channel driven, than another one that can manage 90W 2 channels driven, 75W all channel driven."

I would say the first one is only managing to put out what it does- it's only 50%, while the other is hitting 80%.

Why put great output devices on a bad power supply? That makes no sense, unless they really designed it as a pre-amp and put the power section in as a courtesy.

I felt that the original question has been addressed quite well by you, Seth and others. The markert driven... thing was directed to you, (just food for thought regarding ACD vs individual channel ratings) it really has nothing to do with the OP's question. Obviously you are entitled to your opinion and I am entitled to mine. Sorry I wasn't clear.

 

[Seth=L]

I felt that the original question has been addressed quite well by you, Seth and others. The markert driven... thing was directed to you, (just food for thought regarding ACD vs individual channel ratings) it really has nothing to do with the OP's question. Obviously you are entitled to your opinion and I am entitled to mine. Sorry I wasn't clear.

PENG, you are being very modest and polite. I am much more blunt when it comes to these sort of things.

Mr. Highfigh,

Look at the actual benchtests of your so called ACD rated receivers.

Harman Kardon AVR 630 benchtest Suggested retail price: $1,299

AVR 630 published specs

Onkyo TX-SR606 benchtest Suggested retail price: $579

TX-SR606 published specs

And for another comparison...

Harman Kardon AVR 8000 benchtests Suggested retail price: $2,799

Onkyo TX-SR875 benchtest Suggested retail price: $1,699

Sherwood Newcastle R-965 Suggested retail price: $2000

Granted the H/Ks are older than the units I chose for comparison, so to be fair I will find a comparable units from that time period. The two following Denon's are comparable to the AVR-630

Denon AVR-2803 benchtest Suggested retail price: $799

or...

Denon AVR-2805 benchtest Suggested retail price: $899

Now compare those Denon's the similarly priced AVR-330 from H/K

Harman Kardon AVR-330 benchtest Suggested retail price: $899

And so you don't think I have a bias against one company that uses ACD ratings, let's take a look at another that also does ACD ratings....NAD

NAD T-753 benchtest Suggested retail price: $999

Compare to Onkyo TX-SR606 which has a suggested retail nearly half that.

Harman Kardon and NAD are secure as manufacturers so long as their are people that think ACD is such an important factor. I wouldn't buy a receiver if it was rated 100 watts per channel and it benchtested 20 watts ACD, but the results have shown on many receivers that they don't rate that low. NAD and H/K are using ACD ratings as a marketing gimmick, just as another manufacturer might use PMPO as their marketing gimmick.

I am also not incinuating in any way that H/K or NAD make a bad product, and often times they are fairly comparitive in performance and features with the competition. I often don't consider H/K or NAD because of their missleading advertised ratings and they both seem to be a year or so behind the leaders in getting the newest of the new technology integrated into their products. They eventually catch up, but only after something else new has come out (so in reality they are never fully caught up).

 

[fmw]

Good heavens, Seth. Do they give you a vacation from these exhaustive analyses?

 

[highfigh]

PENG, you are being very modest and polite. I am much more blunt when it comes to these sort of things.

Mr. Highfigh,

Look at the actual benchtests of your so called ACD rated receivers.

Harman Kardon AVR 630 benchtest Suggested retail price: $1,299

AVR 630 published specs

Onkyo TX-SR606 benchtest Suggested retail price: $579

TX-SR606 published specs

And for another comparison...

Harman Kardon AVR 8000 benchtests Suggested retail price: $2,799

Onkyo TX-SR875 benchtest Suggested retail price: $1,699

Sherwood Newcastle R-965 Suggested retail price: $2000

Granted the H/Ks are older than the units I chose for comparison, so to be fair I will find a comparable units from that time period. The two following Denon's are comparable to the AVR-630

Denon AVR-2803 benchtest Suggested retail price: $799

or...

Denon AVR-2805 benchtest Suggested retail price: $899

Now compare those Denon's the similarly priced AVR-330 from H/K

Harman Kardon AVR-330 benchtest Suggested retail price: $899

And so you don't think I have a bias against one company that uses ACD ratings, let's take a look at another that also does ACD ratings....NAD

NAD T-753 benchtest Suggested retail price: $999

Compare to Onkyo TX-SR606 which has a suggested retail nearly half that.

Harman Kardon and NAD are secure as manufacturers so long as their are people that think ACD is such an important factor. I wouldn't buy a receiver if it was rated 100 watts per channel and it benchtested 20 watts ACD, but the results have shown on many receivers that they don't rate that low. NAD and H/K are using ACD ratings as a marketing gimmick, just as another manufacturer might use PMPO as their marketing gimmick.

I am also not incinuating in any way that H/K or NAD make a bad product, and often times they are fairly comparitive in performance and features with the competition. I often don't consider H/K or NAD because of their missleading advertised ratings and they both seem to be a year or so behind the leaders in getting the newest of the new technology integrated into their products. They eventually catch up, but only after something else new has come out (so in reality they are never fully caught up).

Seth- it seems that you think I was the one to say that an amp that develops 150W in 2ch mode and only 50W all ACD is the better one. I disputed that and agree with your point about not buying one that did 100W 2ch/20W ACD. We listen to multi-channel music, so I can't see any good coming from an amp that can't perform well when all channels are in use. Adequate power should go where it's needed but this industry is a classic case where people are cowed by all kinds of fancy gimmicks and specs they don't necessarily understand. I'm actually a firm believer that the ears should be the final arbiter and specs are great for engineers to use for verifying their design goals. If the amp is run below the level that causes clipping, it should be fine but with extremely dynamic source material, low dynamic headroom doesn't cut it.

Back in the late '70s and early '80s when all of the receiver companies were having their specs race, it was a many times per day occurrence to have people waltz into the store with their freshly read copy of Stereo Review and Consumer Reports, asking for equipment and asking about its slew rate, rise time and how many amps it put out (actually happened, a lot). They always looked at me like I was an idiot when I would tell them that a 100W/ch receiver might put out around 3-5Amps.

Voltage sag is great for an old tube guitar amp when someone wants it to break up early but I want a good, stable power supply with a nice, strong amplifier section that can drive whatever loads are thrown at it for listening to music.

Also, measuring output with a 1KHz sine wave- any idea why they still do that, other than to show that it gets really loud at that frequency? Did I read that new amplifier testing standards were being discussed?

 

[highfigh]

I felt that the original question has been addressed quite well by you, Seth and others. The market driven... thing was directed to you, (just food for thought regarding ACD vs individual channel ratings) it really has nothing to do with the OP's question. Obviously you are entitled to your opinion and I am entitled to mine. Sorry I wasn't clear.

No problem- I was just wondering how someone would benefit more in your example. I agree with your point, though. Any manufacturer is doing a balancing act when they make decisions. Unfortunately, in some cases, they make the wrong ones. The H-K 300 series from the late '70s-early '80s were a good example. Great sound and the 330B replaced the 330A because the A blew up and then, the 330C replaced the 330B. Sansui had their R series a little later and not only did they sound bad, they blew up because they biased them too hot. The service techs would order outputs and bias resistors by the bag-full and lower the boas a bit and those particular ones wouldn't come back. I did car audio exclusively from '88-'98, so I didn't really pay very much attention to home audio during that time, but the store from '88-'94 did sell Mac, Klipsch, KEF, ADS and some other nice gear.

I have heard an awful lot of hype in my 30 years in the business and as I posted to someone else before, people who are extremely interested in this type of thing are incredibly opinionated. If the objective measurements were the only reason to buy something, think about how boring this would be.

 

[Seth=L]

No problem- I was just wondering how someone would benefit more in your example. I agree with your point, though. Any manufacturer is doing a balancing act when they make decisions. Unfortunately, in some cases, they make the wrong ones. The H-K 300 series from the late '70s-early '80s were a good example. Great sound and the 330B replaced the 330A because the A blew up and then, the 330C replaced the 330B. Sansui had their R series a little later and not only did they sound bad, they blew up because they biased them too hot. The service techs would order outputs and bias resistors by the bag-full and lower the boas a bit and those particular ones wouldn't come back. I did car audio exclusively from '88-'98, so I didn't really pay very much attention to home audio during that time, but the store from '88-'94 did sell Mac, Klipsch, KEF, ADS and some other nice gear.

I have heard an awful lot of hype in my 30 years in the business and as I posted to someone else before, people who are extremely interested in this type of thing are incredibly opinionated. If the objective measurements were the only reason to buy something, think about how boring this would be.

Sorry you find it boring. I would rather pick the correct amount of power needed, with ample headroom, and get my speakers situated so I can "bore" myself with music.

Maybe there isn't a whole lot wrong with knowing how much power a receiver has while driving 5-7 speakers. However, basing your purchase decision based on the fact that a company publishes an ACD spec doesn't warrant choosing their product, especially when I have shown you multiple less expensive alternatives that offer more clean undistorted power with 1, 2, and 5 channels driven.

Although, it's unlikely that even at reference levels of output that a mid level receiver in a mid sized to larger room would have any trouble driving most arrays of speakers to reference levels using less than half of their potential output power.

My Sony STR-DA1000ES drives my home theater to levels beyond necessary in a mid sized room. My speakers are moderately efficient and I release some of the load off the receiver by setting all speakers to small and letting the subwoofer handle all the potentially hazardous low frequencies. I don't have the measuring equipment to prove it, but I probably hardly use more than 150 watts total out of that receiver with a few dynamic peaks that don't seem to be stressing the receiver in any way. I don't necessarily consider Sony to be a great AVR manufacturer, and my AVR is probably comparable to most mass market middle of the line gear. I've owned countless receivers and only had a couple that where anemic (one bottom of the barrel Yamaha and a Pioneer OEM, also bottom of the barrel).

 

[PENG]

Good morning highhigh and thank you for being open minded. I cited a purely numerical example to make a point and I am glad you now actually agree with that one point.

If money is no object then we would have been in full agreement. I regret not making this point clear in the first place. If there is a fix budget, then we cannot just advise people to go for an ACD rated receiver unless we understand one's specific wants and needs. Seth's post highlighted some of my own thoughts as well. Feel free to read back and forth between his and my post and I welcome further debate on this topic. Well, may be in another thread in order not to hijack this one.

Before I forget, this is a good read:
http://www.audioholics.com/education/amplifier-technology/the-all-channels-driven-amplifier-test-controversy/?searchterm=the all channel driven controversy

For something more real than just numbers, let's say I have L/R speakers with modest 86 dB sensitivity in a 12X20X9 room and I listen to mostly classical and jazz music in stereo. I also use the system to watch movies in 5.1 but I do not listen to any 5 ch stereo at all. In this case, something like the Onkyo 606 (7X90) or Denon RX-V663 (7X90) can do a better job for me than a low end NAD or HK 254 (7X50 ACD) because I would benefit from that extra power for my 86 dB sensitive L/R speakers. Someone may remind me about the 663's poor bench test numbers (7X40 approx.) S&V and HT mag published recently. A British review measured much better numbers for the 663. This is the first time I have seen such severe discrepancies among these three magazines. By the way, Seth listed a bench tests that show many receivers in the same price range as HK/NAD or less that turned out better ACD numbers but I believe those the tests were done for a short duration. That would have been the right thing to do though because real music/movies do not have peaks that sustain any more than a few seconds, may be slightly longer but not continuous or they won’t be called peaks.

Lastly, let me say that I actually do listen to multichannel SACD and DVDA a lot and the surround channels really do not (I know Ms Frizz may disagree) need much power at all. If anyone wants to tell me not to rely on measurements, well I must tell you every time I want LOTR I the surround channels were loud. They were, but they still took much less power than the front channels. Such facts are measurable.

 

[PENG]

Good morning highhigh and thank you for being open minded. I cited a purely numerical example to make a point and I am glad you now actually agree with that one point.

If money is no object then we would have been in full agreement. I regret not making this point clear in the first place. If there is a fix budget, then we cannot just advise people to go for an ACD rated receiver unless we understand one's specific wants and needs. Seth's post highlighted some of my own thoughts as well. Feel free to read back and forth between his and my post and I welcome further debate on this topic. Well, may be in another thread in order not to hijack this one.

Before I forget, this is a good read:
http://www.audioholics.com/education/amplifier-technology/the-all-channels-driven-amplifier-test-controversy/?searchterm=the all channel driven controversy

For something more real than just numbers, let's say I have L/R speakers with modest 86 dB sensitivity in a 12X20X9 room and I listen to mostly classical and jazz music in stereo. I also use the system to watch movies in 5.1 but I do not listen to any 5 ch stereo at all. In this case, something like the Onkyo 606 (7X90) or Denon RX-V663 (7X90) can do a better job for me than a low end NAD or HK 254 (7X50 ACD) because I would benefit from that extra power for my 86 dB sensitive L/R speakers. Someone may remind me about the 663's poor bench test numbers (7X40 approx.) S&V and HT mag published recently. A British review measured much better numbers for the 663. This is the first time I have seen such severe discrepancies among these three magazines. By the way, Seth listed a bench tests that show many receivers in the same price range as HK/NAD or less that turned out better ACD numbers but I believe those the tests were done for a short duration. That would have been the right thing to do though because real music/movies do not have peaks that sustain any more than a few seconds, may be slightly longer but not continuous or they won’t be called peaks.

Lastly, let me say that I actually do listen to multichannel SACD and DVDA a lot and the surround channels really do not (I know Ms. Frizz may disagree) need much power at all. If anyone wants to tell me not to rely on measurements, well I must tell you every time I want LOTR I the surround channels were loud. They were, but they still took much less power than the front channels. Such facts are measurable.

 

[highfigh]

Sorry you find it boring. I would rather pick the correct amount of power needed, with ample headroom, and get my speakers situated so I can "bore" myself with music.

Maybe there isn't a whole lot wrong with knowing how much power a receiver has while driving 5-7 speakers. However, basing your purchase decision based on the fact that a company publishes an ACD spec doesn't warrant choosing their product, especially when I have shown you multiple less expensive alternatives that offer more clean undistorted power with 1, 2, and 5 channels driven.

Although, it's unlikely that even at reference levels of output that a mid level receiver in a mid sized to larger room would have any trouble driving most arrays of speakers to reference levels using less than half of their potential output power.

My Sony STR-DA1000ES drives my home theater to levels beyond necessary in a mid sized room. My speakers are moderately efficient and I release some of the load off the receiver by setting all speakers to small and letting the subwoofer handle all the potentially hazardous low frequencies. I don't have the measuring equipment to prove it, but I probably hardly use more than 150 watts total out of that receiver with a few dynamic peaks that don't seem to be stressing the receiver in any way. I don't necessarily consider Sony to be a great AVR manufacturer, and my AVR is probably comparable to most mass market middle of the line gear. I've owned countless receivers and only had a couple that where anemic (one bottom of the barrel Yamaha and a Pioneer OEM, also bottom of the barrel).

I don't know how you came to decide that I find this boring, I said "If the objective measurements were the only reason to buy something, think about how boring this would be." and that's a big difference. I also am left wondering why you're showing less expensive alternatives to anything when I never A) said I was looking for anything, B) said that I rely much on spec sheets or C) said there was a problem with knowing the specs.

One thing about operating at a reference level and being required to reproduce strong peaks- a 60W/ch amplifier section can't do this accurately if it's running a, say 5W and a 30dB peak is needed. However, because of the way human hearing works, if some of the spectrum is removed, the failure to accurately reproduce this peak won't necessarily be apparent. That's one of the main reasons subwoofers became available in the first place- people wanted smaller speakers and less expensive receivers, so the bass was directed to a speaker that was made for it.

There's nothing wrong with your receiver, at all. I use an ES integrated amp/tuner combo in my system now and have owned several of their "higher" line pieces, although nothing from the Esprit line. When ES came out, there was little in the 'mainstream' that sounded as good without going into the lower esoteric area.

Main point- if it sounds good, enjoy it, but if it sounds good and the spec sheet makes someone want something else anyway, that's irrational. The whole reason for this equipment is so we can listen to and enjoy the music but some can't stop listening to the equipment.

 

[highfigh]

PENG- "...and I am glad you now actually agree with that one point."

I didn't change my view but I think we have clarified a few points.

I also addressed some of the points about power vs what part of the spectrum is being sent where. If bass isn't needed from the surrounds, I agree that those channels don't need to be as powerful, but to accurately reproduce peaks, I want an amp that can do this better than something that fails miserably. However, speccing a system to have 5/7 identical speakers and amp channels has a reason. The surround processor can direct the signal at whatever level is needed but accuracy is definitely enhanced when it's done this way, instead of big power to the mains and little power to the rest.

"How much is necessary?" is a question that will never be answered, IMO. An amplifier from Perreaux Audio that won some awards at CES in about 1980 had a power rating of "Adequate". IIRC, they stated something like 30V @20A.

As always, the budget determines what can, or will, be purchased and there's nothing wrong with this. I don't usually enjoy dealing with the highest end equipment or people who think it's the only kind worth using. The equipment tends to be too temperamental and the people are too neurotic. That said, I don't like to compromise when it comes to certain things- reliability and durability are in a dead heat with the importance of sound quality. As I said, some specs tell an important part of the story and that's why I want a strong power supply and amp section. There's no such thing as a great amp with a bad power supply.

Re: the article you linked- I lived through all of the spec wars and changes from the EIA, et al. IIRC, NAD was one of the only lines that could provide a 3dB peak in the Dynamic Headroom tests. Some brands were rated at 0dB DH. One thing that necessitates the ability to reproduce dynamic peaks and sustained high output is synthesized music and sound effects. When the first CD players became available, one of the most commonly used discs to demo'ing amps and speakers was the 1812 Overture section that was recorded with real cannon. That registered peaks of about 30dB, according to the VU meters on the recorders we would connect and unless the deep bass is removed, most amps and speakers yak all over their shoes when this part shows up at anything above a moderate level.

Again, even with engineers and testers, complete agreement on power requirements is impossible, but the fact that nobody has given up trying to make the best, benefits all of us.

 

[Seth=L]

Here's a good example of a receiver I would not buy purely based on clear amplifier limitations.

http://hometheatermag.com/receivers/808piorec/index2.html

 

[fmw]

Here's a good example of a receiver I would not buy purely based on clear amplifier limitations.

http://hometheatermag.com/receivers/808piorec/index2.html

Why? Looks OK to me. It would drive my home theater just fine.

 

[highfigh]

Here's a good example of a receiver I would not buy purely based on clear amplifier limitations.

http://hometheatermag.com/receivers/808piorec/index2.html

I think I need to clarify something regarding my previous comments. I want a beefy power supply, so I would look at the specs as a basis to weed out some specific equipment but as I said, my ears have to be happy, so that's how I actually make the decisions.

However, commercial and pro sound gear is chosen mainly by specifications and a reputation for durability. This practice works and although we don't usually think of commercial sound gear as great sounding, I think you would be surprised by how 24) 8" Atlas speakers in enclosures can achieve a very flat frequency response and sound very neutral with human speech or music as the sources, when equalized properly. This, in a large room with acoustical ceiling tiles, commercial grade carpet on the floor and plaster coated walls, in a church. The equipment I'm referring to was all spec'd by an engineering firm in TX, for use in LDS facilities and none of it is considered "high end" or "consumer" grade.

If someone sets their system to THX standards, 85dB is the level from all speakers when the test signal is sent, right? Since the power output will be determined by the speaker sensitivity, room size/acoustical properties and distance from the speakers to the listening position, it's very possible that a speaker with 85dB/1m/W(2.83V@8Ω) sensitivity will require more than 16W to achieve 85dB at 12'. That will change +/- with more/less absorptive acoustics, but with a 6dB loss every time the distance doubles, it's pretty close. Now, assuming the front/center channels will see a 20dB peak, the amplifier power will need to increase by 100 times to be totally accurate. Subtract 2 octaves of bass (crossover at 80Hz), and you still need a bunch pf power to have really clean reproduction. Assuming a real world room, where the surround and rear surrounds (if used) are 8' from the listening position, it's safe to add about 2dB to the reference level SPL, so a reduction of needed power is in order. Now, change to a speaker that yields 91dB/1m/W and the power needed will be cut to 25%. That's a livable number- 4W average with peak power of 100W should work and to ballpark an RMS number, a receiver with 70W/ch should be fine. More is better and a sustained loud event will really show what has the cajones to pull it off, but this is the reason I want more power with all channels driven.

Is my logic more apparent, now? All of this aside, if the ref level is used during setup, 20dB peaks will be in the 105dB range with only one speaker driven, so adding another at 85dB adds 6dB (+/- to account for phase reinforcement/cancellation) to the overall SPL, with equates to quadrupling the power. Add another 6dB from the surrounds (just a ballpark for more speakers and closer proximity), and maybe the average power needed will be in the range of 1W, but the 20dB peaks can still be an issue.

In a small room and with sensitive speakers, that receiver you linked to may be perfectly fine as long as live concert/movie theater levels aren't used.

If you get the chance, check out the equipment room at a good movie theater. What they use is chosen because it meets spec, but I'm sure a lot of people would turn their nose up at it. Most people don't actually pay that much attention to the sound quality when they go to a movie, they listen for the deep, thundering bass and really loud explosions.

 

[PENG]

If someone sets their system to THX standards, 85dB is the level from all speakers when the test signal is sent, right? Since the power output will be determined by the speaker sensitivity, room size/acoustical properties and distance from the speakers to the listening position, it's very possible that a speaker with 85dB/1m/W(2.83V@8Ω) sensitivity will require more than 16W to achieve 85dB at 12'. That will change +/- with more/less absorptive acoustics, but with a 6dB loss every time the distance doubles, it's pretty close.

The inverse square law works in open field but not in a room. If you have a sound meter you can find out for yourself. You are right in saying that "this will change +/- with more/less absorptive acoustics", but in terms of the in room distance effect the change is invariably on the favorable side. How much room gain you get depends on the geometry of the room. In my room I do not lose much at all from 1 meter to 4 meters. There is no question that in open field one would need tons of power but in a room of say 12X20X8, I would take a $5,000 Luxman class A 20X2 amp any time over a $1000 200X2 class AB amp just to satisfy my curiosity. I am not not sure if I can hear a difference but I am confident the 20W class A will do fine in a small room.