Wattage help for a newbie - AVS Forum
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post #1 of 19 Old 01-26-2012, 08:32 PM - Thread Starter
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So yes, I'm new to this whole high-end audio thing, and it will likely not be until sometime in 2013 til anything is bought, but I need help understanding the relationship between amp and speaker wattage.

The basic idea, is that most speakers (I've been primarily looking at either the KEF Q or R series) show a huge range of wattage that can drive the speakers. I'm only interested in 8ohm speakers, just seems like 4ohm speakers are theoretically (not counting component quality) inferior to 8ohm in how they handle power.

It seems like it would be ideal to match an amps rated wattage/channel output with the max wattage suggested for a speaker, but how close do you need to get to have a negligible real-world difference?
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post #2 of 19 Old 01-26-2012, 09:27 PM
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Mfg's rate speaker impedance where it spends most of its time in the bandwidth it covers .No speaker stays flat from lets say 30Hz to 20 KHz they all very at the extremes some dip to 2.5 ohms at the bottom end while hitting upward of 16 ohms at the top and varying in the middle somewhat depending on the brand. Thats why they
use the word nominal.
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post #3 of 19 Old 01-26-2012, 09:34 PM
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Quote:
Originally Posted by Swingline39 View Post

So yes, I'm new to this whole high-end audio thing, and it will likely not be until sometime in 2013 til anything is bought, but I need help understanding the relationship between amp and speaker wattage.

The basic idea, is that most speakers (I've been primarily looking at either the KEF Q or R series) show a huge range of wattage that can drive the speakers. I'm only interested in 8ohm speakers, just seems like 4ohm speakers are theoretically (not counting component quality) inferior to 8ohm in how they handle power.

It seems like it would be ideal to match an amps rated wattage/channel output with the max wattage suggested for a speaker, but how close do you need to get to have a negligible real-world difference?

1) There's nothing wrong with 4 ohm speakers; but receivers are rarely spec'd to handle them (but that does not mean they won't)

2) You don't need to match amplifier power to speaker handling; some claim that you want twice the amp power as the speaker's average power handling - but I think that's impractical for home setups. One concept is to buy as much power as you can afford. Your power needs depend on a number of factors - speaker sensitivity, room size and desired SPL to name some.

"But this one goes up to 11"
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post #4 of 19 Old 01-26-2012, 09:37 PM - Thread Starter
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Alright. And I was reading the AVR faq, and it's really interesting how loud 1 watt can be, and subsequently how quiet 100 watts can be.

It sounds like the very common 140w/channel amps would be able to drive a 90db speaker like the KEF R900's fairly well. My volume would be capped, but I'd still be looking at 105 db @ 1m only needing 32watts. however 111db would be maxing things out at 128watts.

I guess the most important thing is to figure out how far away you want to listen to the speaker, and how loud you want it to be.
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post #5 of 19 Old 01-26-2012, 09:40 PM
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Hope you enjoyed the FAQ

One problem is that receiver ratings seem useless.

"But this one goes up to 11"
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post #6 of 19 Old 01-26-2012, 09:55 PM - Thread Starter
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I always love a well written FAQ haha.

I must be and odd one, but my plan at this point is have a setup for HDTV/HTPC that's just a 2.0 setup consisting of 2 floorstanding speakers.

In a perfect world I would have a Pro/Pre feeding XLR to an amp which can bi-wire the KEF towers.
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post #7 of 19 Old 01-27-2012, 05:53 AM
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Play with this SPL calculator to get an idea what you might really need, and how changes in power and speaker efficiency affect loudness (SPL). Be sure to read the SPL chart at the bottom so you have an idea how loud things are in the real world.

http://myhometheater.homestead.com/splcalculator.html

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #8 of 19 Old 01-27-2012, 06:36 AM
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Down the road, try to get an amp that is stable into 2 ohm (or at least 4 ohm) loads. That'll give you more options with speakers. Some solid state amps actually double their power as impedance is halved. So a 100 wpc amp (spec's into 8 ohm) might put out 200 wpc into 4 ohm speakers.
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post #9 of 19 Old 01-27-2012, 07:11 AM - Thread Starter
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So it seems like 140 watts should be enough to drive a 90db speaker at a reasonable listening distance. The issue is wattage spikes, which could result in clipping. Or can the amps power go past the spec'd watts/channel to handle a sudden change?
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post #10 of 19 Old 01-27-2012, 08:13 AM
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Quote:
Originally Posted by noway1 View Post

Down the road, try to get an amp that is stable into 2 ohm (or at least 4 ohm) loads. That'll give you more options with speakers. Some solid state amps actually double their power as impedance is halved. So a 100 wpc amp (spec's into 8 ohm) might put out 200 wpc into 4 ohm speakers.

As mentioned previously, many speakers, even ones rated at 8 ohms, dip down to 2.5 ohms.

If you are an audiophile, then you DO want a receiver/amp capable of driving the 2.5 ohms.
Most receivers, with the exception of one or two top of the line models, just are not built to handle 2.5 ohm loads.
Some brands like Sony (even their ES line) exaggerate their ratings.
Look at all channels driven rating, which gives you a good indication of the power supply quality. Good amps/receivers have only a slight drop off.
Sony 120 w/ch receivers, in all channels mode are only capable of ~35 w/ch.

Another key item to keep in mind with your selection of speakers and amplification, is dynamic peaks, which can easily be 15+ dB above your current listening level.
Remember for every 3 dB increase in output, your amp needs to supply twice the power output.

Thus for your 90 dB speakers, running at 105 dB using 32 watts, if a 15dB dynamic peak comes along, you need 1024 watts to reproduce it without clipping and distortion. A typical receiver/amp can't handle this.
Now on the other hand, if you choose well designed speakers with good efficiency, i.e 99 dB, your power requirement is only 128 watts.
And there are dynamic peaks that exceed 15 dB.

If you have never listened to high efficiency speakers, with good amplification capable of reproducing dynamic peaks, then you may not even know what you are missing.
The key to true audiophile sound reproduction is choosing a combination of speakers and amplification that CAN reproduce these dynamic peaks.
So you have 2 choices:
1 - lower efficiency speakers with 1,000+ watts/ch amplification, or
2 - quality design, high efficiency speakers that can be driven with reasonable amplification
This is something to keep in mind as you go through your selection process
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post #11 of 19 Old 01-27-2012, 08:54 AM
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Curios. So how would my B&W 604 S3's perform with my HK AVR 354? The B&W's are rated at 90db efficiency I believe, and the AVR is rated at 75wpc ACD, and is listed as a High Current amp. I have noticed that with this setup, music does not "Feel" loud though it is loud enough to interfere with conversation in the house, and although it is loud enough to interfere, it remains entirely clean. I just want to understand this better.
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post #12 of 19 Old 01-27-2012, 09:33 AM
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^^
So then at an average seating distance of 10-12' from the front mains there is roughly a 10db loss in volume .. therefore the following would apply for your speakers ...

1W - 80db
2W - 83db
4W - 86db <-----
8W - 89db
16W - 92db
32W - 95db

So at an average volume of 85db or less (which is quite loud), those speakers are using < 5W/CH with plenty of headroom for any peaks.

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post #13 of 19 Old 01-27-2012, 09:40 AM
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Quote:
Originally Posted by Tweaked05 View Post

Curios. So how would my B&W 604 S3's perform with my HK AVR 354? The B&W's are rated at 90db efficiency I believe, and the AVR is rated at 75wpc ACD, and is listed as a High Current amp. I have noticed that with this setup, music does not "Feel" loud though it is loud enough to interfere with conversation in the house, and although it is loud enough to interfere, it remains entirely clean. I just want to understand this better.

I have never listened to your combination.
However, one needs to be careful when using the term "loud".

In my experience, many speakers that tend to sound "loud" as you turn up the volume, is often due to distortion and some clipping.

Quality high efficiency speakers when turned up tend to get more life like reproduction without necessarily sounding "loud".

I have 100dB efficient speakers that I drive with a 250 w/ch (8 ohms, 500 w/ch - 4 ohms) and I can turn up the volume to reference level and they do not sound loud, just have incredible dynamics (punch).

Bad speakers, with cheap amp can sound loud with 20 w/ch - but the loud is due to headache causing distortion, not excess decibels.

Hope this helps
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post #14 of 19 Old 01-27-2012, 09:50 AM
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Quote:
Originally Posted by jdsmoothie View Post

^^
So then at an average seating distance of 10-12' from the front mains there is roughly a 10db loss in volume .. therefore the following would apply for your speakers ...

1W - 80db
2W - 83db
4W - 86db <-----
8W - 89db
16W - 92db
32W - 95db

So at an average volume of 85db or less (which is quite loud), those speakers are using < 5W/CH with plenty of headroom for any peaks.

Please take a look at the following table for Sound Levels of Music:

Piano Fortissimo 84 - 103dB
Violin 82 - 92dB
Cello 85 -111dB
Oboe 95-112dB
Flute 92 -103dB
Piccolo 90 -106dB
Clarinet 85 - 114dB
French horn 90 - 106dB
Trombone 85 - 114dB
Tympani & bass drum 106dB
Walkman on 5/10 94dB
Symphonic music peak 120 - 137dB
Amplifier rock, 4-6' 120dB
Rock music peak 150dB

As you can see, most classical music instrument go from 85 dB to 110 dB peaks, with full orchestra peaking at 120-137 dB. Rock music peaks can be higher yet.

Thus there is nowhere near enough power for "realistic" (meaning average levels at 80-85 dB with dynamic peaks 110-130 dB) music reproduction with those speakers.
Now if all you are after is background "musak" then power is not an issue.
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post #15 of 19 Old 01-27-2012, 11:38 AM
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Those measurements are not in the audience, and peaks that loud are rare (but not unimportant, I'll grant you that). 100 dB average level is very loud to me; in fact, 75 dB is pretty durn loud, at which point if the system can play 105 dB you have 30 dB headroom for peaks.

I have been in concerts with 120 - 140 dB peaks. Probably part of the reason I am getting tinnitus now. Never again, thank you.

BTW, I am quite insulted your table does not list trumpet, which as we all know is king of the instruments.

- Don (principal trumpet, Pikes Peak Philharmonic, lead in various other local groups)

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #16 of 19 Old 01-27-2012, 12:40 PM
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Quote:
Originally Posted by DonH50 View Post

Those measurements are not in the audience, and peaks that loud are rare (but not unimportant, I'll grant you that). 100 dB average level is very loud to me; in fact, 75 dB is pretty durn loud, at which point if the system can play 105 dB you have 30 dB headroom for peaks.

I have been in concerts with 120 - 140 dB peaks. Probably part of the reason I am getting tinnitus now. Never again, thank you.

BTW, I am quite insulted your table does not list trumpet, which as we all know is king of the instruments.

- Don (principal trumpet, Pikes Peak Philharmonic, lead in various other local groups)

Good comments Don.
Sorry for not having trumpet, but this is not my table.

Agree with you that most will not be listening at 105 dB for any extended periods.

The key is what type of listening on is doing.
The lower your base volume, the more headroom you have.

If you sit down specifically for critical listening and are trying to reproduce live performance, you will be significantly above 75 dB, which reduces your headroom.

I disagree strongly with your view that peaks are rare (except for 120+ dB). It is these peaks, dynamics that bring music to life. Where peaks are rare is in much pop music, where idiot recording engineers are after max overall sound volume, rather than realistic and faithful reproduction of music, which has a huge difference between quiet and loud passages (dynamics). Classical and jazz recording engineers tend to apply less compression and thus produce much better recordings. Try to find some good recordings so that you can experience these dynamics.

Additional issue that one needs to be aware of with low efficiency speakers (below 95 dB) is compression. The more power you apply to the driver, the less efficient it becomes for the corresponding increase in power (due to heat). Thus applying 1,000 does not give you the expected increase in output due to compression.

Thus if one is after "realistic" live performance, then you are much better off choosing well designed high efficiency speakers that do not require thousand watts of amplification.

With low efficiency speakers you are having to apply tons of power to overcome shortcomings of bad speaker design (low efficiency)
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post #17 of 19 Old 01-27-2012, 05:55 PM
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Sorry, I did not mean that peaks were rare by any means, just that peaks that loud (110 - 120+ dB) are rare. I know what that sounds like, from inside the orchestra even, and peaks that loud just do not happen very often. Maybe if I played in the CSO... In any event I have lots of music recordings with high dynamic range; I was not clear and as you surmised I meant 120+ dB kind of peaks are rare. 10 dB over average all the time, 20 - 30 dB less so, and even for an orchestra soft can be pretty durn soft. And, 30 dB over 75 dB is still "just" 105 dB, loud enough for me (and probably about as much as my system will put out).

Now, the peak-to-average ratio in music runs around 17 dB, meaning you need 50x your average power, but most of us are probably running around a watt or two on average so have plenty of headroom. I have read ~30 dB for movies, which is 1000x average power and really getting up there. Again, I suspect peaks that loud happen pretty infrequently.

I agree with the rest of your post, and have pretty inefficient speakers myself -- I just can't bear to get rid of them. I would quibble about inefficient being "bad design", though -- the efficiency is intrinsically low in most planer speakers due to the physics of the design. They are among the cleanest (lowest distortion) within their dynamic range. All in life is compromise and trade-offs...

Thank you very much for an excellent post! - Don

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #18 of 19 Old 01-27-2012, 08:51 PM - Thread Starter
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So if the speakers I'm looking at are 90 or 91 db speakers in terms of efficiency, what should the minimum wattage amp be that i'm looking at?
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post #19 of 19 Old 01-28-2012, 08:23 AM - Thread Starter
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A bit of a bump, but oh well...

So the two potential pairings I'm considering right now are the
Marantz AV7005 and MM7025 which gives 2 140w channels
or
NAD M15 and M2 which gives me 2 250w channels as well as it seems more power available for dynamic spikes.

Looks like the Marantz setup would cost around $3000, I don't know about NAD
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