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Watts and Current - Page 8

post #211 of 227
Thread Starter 
With regards to power supply stiffness - in the case of 'difficult' speakers - is that where a beefy power supply on a low wattage amp becomes useful and where it can potentially outperform an amp with a lesser power supply and higher rated power?
post #212 of 227
Quote:
Originally Posted by Heinrich S View Post

With regards to power supply stiffness - in the case of 'difficult' speakers - is that where a beefy power supply on a low wattage amp becomes useful and where it can potentially outperform an amp with a lesser power supply and higher rated power?

In a sense yes, but probably not what you think.

The absence of a beefy power supply can produce a low wattage amp becomes useful and where it can potentially outperform an amp with a beefy power supply and higher rated power.

The absence of a beefy power supply gives you an amp that produces less power on the test bench where it is tested with steady pure tones, and that gives the appearance of low wattage.

The difficult speaker often has an impedance curve that wanders all over the place, which means that its impedance that is high over much of the audio range. Here's a real world example:

post #213 of 227
Thread Starter 
Quote:
Originally Posted by arnyk 
The absence of a beefy power supply can produce a low wattage amp becomes useful and where it can potentially outperform an amp with a beefy power supply and higher rated power.

The absence of a beefy power supply gives you an amp that produces less power on the test bench where it is tested with steady pure tones, and that gives the appearance of low wattage.

I don't follow, especially the top one. Could you elaborate more on what you meant as the way you described it doesn't make sense to me. Thanks.
post #214 of 227
Quote:
Originally Posted by Heinrich S View Post

Quote:
Originally Posted by arnyk 
The absence of a beefy power supply can produce a low wattage amp becomes useful and where it can potentially outperform an amp with a beefy power supply and higher rated power.

The absence of a beefy power supply gives you an amp that produces less power on the test bench where it is tested with steady pure tones, and that gives the appearance of low wattage.

I don't follow, especially the top one. Could you elaborate more on what you meant as the way you described it doesn't make sense to me. Thanks.

I build a power amp with a weak power supply - plenty of voltage but limited current capacity. It has poor regulation.

If I test this power amp with pure sine waves, the power supply's poor regulation means that its output voltage drops quite a bit in a steady-state test and its maximum power output on the test bench is poor.

If I test this power amp with music, the power supply's poor regulation is not stressed , and its maximum output voltage does not drop appreciably.

A power amp with a beefier power supply might have good current reserves and better regulation, but its maximum output voltage may be less.

The bottom line is that good engineers built equipment that provides the desired service. If you define the desired service as producing steady sine waves then you build the amplifier a certain way and along the way it can become suboptimal for other kinds of service such as music. Correspondingly, if you define the desired service as producing music, then you build the amplifier some other way.
Edited by arnyk - 7/18/13 at 8:30am
post #215 of 227
Can someone please double check this amplifier power calculator for me. It seems like a lot more power is required to hit a given SPL than I thought.

http://www.crownaudio.com/elect-pwr-req.htm

Do the figures include room gain?
Edited by OllieS - 7/22/13 at 11:39pm
post #216 of 227
Ollie, it doesn't appear so, seems more for free space or large venues. Try this one, which does allow for room gain, and seems to track actual measurements I've made fairly closely.
post #217 of 227
Quote:
Originally Posted by Wayne Highwood View Post

Ollie, it doesn't appear so, seems more for free space or large venues. Try this one, which does allow for room gain, and seems to track actual measuremetnts I've made fairly closely.

three dB for room gain seems consistent with what I've seen elsewhere for home-sized room. But do be aware that the added gain due to multiple speakers could be misleading if a person is seeking reference levels. Reference implies peaks of 105 dB from each speaker. Hitting 105 with 5 speakers (at 97 dB per speaker) is not reference, and actually only happens, I think, when every speaker is emitting the exact same thing in phase. SPL calculators differ depending on whether the multiple sounds are correlated (the same) or not. Tr full tile at reference the theoretical total SPL (leaving the sub out of the equation) would be 113 dB, but it's generally accepted that movie content does not actually push all speakers to their max all the time, and I don't think it's common to have five or channel mono in the original mix . . .
post #218 of 227
Quote:
Originally Posted by OllieS View Post

Can someone please double check this amplifier power calculator for me. It seems like a lot more power is required to hit a given SPL than I thought.

http://www.crownaudio.com/elect-pwr-req.htm

Do the figures include room gain?

The Crown calculations don't include room gain, loudspeaker directionality, or the fact that most audio systems are composed of more than 1 loudspeaker. The absence of an adjustment for loudspeaker directionality makes sense because that is included in most specifications of loudspeaker sensitivity. All other omissions are more difficult for me to explain.
post #219 of 227
Quote:
Originally Posted by arnyk View Post

The Crown calculations don't include room gain, loudspeaker directionality, or the fact that most audio systems are composed of more than 1 loudspeaker. The absence of an adjustment for loudspeaker directionality makes sense because that is included in most specifications of loudspeaker sensitivity. All other omissions are more difficult for me to explain.

Bolded mine. Neither does the calculator I linked to. It had some large deviation from the omnimic readings on some higher sensitivity, narrow directivity, corner horns I tried it with. But that's a rare case, I would think.

Also, in response to JHAz, I only compared using two channel rigs. It's crude, for sure, but not too bad without real measurement tools available. Hopefully it's useful for Ollie.
post #220 of 227
Thread Starter 
So is music and home theater sound made up of sine waves at different frequencies? Test bench uses sine waves.. correct?
post #221 of 227
Quote:
Originally Posted by Heinrich S View Post

So is music and home theater sound made up of sine waves at different frequencies? Test bench uses sine waves.. correct?
Fundamentally yes-all sounds are "sine waves". A square wave is basically a bunch of sine waves of different freq -with the highest freq ones being on the leading and trailing edges-but of a limited height.

The sine waves are "modified" to produce all kinds of different shapes-which provide the particular 'sound" and harmonic content.

But it is not as simple as it may appear.

A sine wave is basically a pure tone-with no harmonics and a very high crest factor, 3dB.
post #222 of 227
Quote:
Originally Posted by Heinrich S View Post

So is music and home theater sound made up of sine waves at different frequencies? Test bench uses sine waves.. correct?

Music is made up of many sine waves at many different frequencies, each with a unique envelope or time-versus-amplitude characteristic, all mixed together. The magic word is multitone. In a typical musical track thousands of different frequencies are present. Some are harmonically related but many are either near misses of harmonics or aren't harmonics of any other tone at all.

Test bench tests for amplifiers are generally done with one pure tone or two pure tones or a pure tone whose frequency is steadily varied across the audio band over a period of a few seconds. Audyssey users are familiar with swept tones or chirps.

Multitones necessarily have high crest factors, but single pure tones whether steady or swept have low crest factors.

One exception to the rule I just gave about multitones and crest factors is pure square waves which contain odd harmonics with carefully defined amplitudes and phase, and have a very low crest factor of 0.0 dB. Pure sine waves have a crest factor of 3.0 dB. The crest factor of music varies from as low as 8 dB to more than 30 dB with 17-20 dB being a very high number.

The classic "boat anchor" high mass power amplifier is generally designed to handle signals with a very low crest factor. If you are running a shaker table, its probably exactly what you want. ;-)
Edited by arnyk - 7/24/13 at 7:56am
post #223 of 227
The ability to recast a complex sound as the sum of mulitple sine waves at different frequencies is unintuitive to me, apparently well proven, and old as dirt: French mathematician and physicist Baron Jean Baptiste Joseph Fourier (1768-1830) realized that any complex waveform could be decomposed into a group of sinusoids of different frequencies and amplitudes. Okay, maybe dirt is older than 280 years, but still . . .

So when I strike an open E on my guitar, with a fundamental frequency of about 80 Hz, the string and guitar conspire to establish the harmonics that will be heard as part of te tone. The idea that you can describe that sound as a series of sine waves seems quite intuitive to me. Different acoustic guitars will accentuate different frequencies, so the harmonic content of that open E differs from guitar to guitar. It also differs depending on whether you strike it harder (harmonics become relatively a greater part of the sound) or if you strike the string near the bridge (excites the fundamental less, again resulting in more accentuation of harmonics (twangy sound). That all makes sense to me, and I can see how even if I play a six tone chord, the sound could be defined by the fundamentals and harmonics of each of the notes of the chord.

But it turns out that you can also describe the sound of a bass drum and snare being struck at the same time as a guitar chord, bass guitar note, piano chord and four part horn section as a series of sine waves. Or the sound of a real or made for movies explosion. Really.
post #224 of 227
Quote:
But it turns out that you can also describe the sound of a bass drum and snare being struck at the same time as a guitar chord, bass guitar note, piano chord and four part horn section as a series of sine waves. Or the sound of a real or made for movies explosion. Really.

Fairlight CMI used additive synthesis back in the early 80's.
post #225 of 227
Quote:
Originally Posted by kiwi2 View Post

In audio I don't think I've ever seen two experts (be that professionals or self appointed experts) say the same thing.

Agreed Kiwi. Audio is a funny hobby; I've experienced first-hand one engineer only use solid state, another only tubes, and another even more expensive cabling (OCC copper he informed me) in their systems. The last one surprised me, being everything I've read about cables. It made me realize after only a couple years into this hobby that not everything is set in stone and that there's a diverse lot out there who cherish/value different things in their systems, and what they find important or what leads them to musical satisfaction, let's say.
post #226 of 227
Quote:
In audio I don't think I've ever seen two experts (be that professionals or self appointed experts) say the same thing.
That's because, in audio, there are way more "experts" than there are experts.
post #227 of 227
Quote:
Originally Posted by ThumbtackJack View Post

Quote:
Originally Posted by kiwi2 View Post

In audio I don't think I've ever seen two experts (be that professionals or self appointed experts) say the same thing.

Agreed Kiwi. Audio is a funny hobby; I've experienced first-hand one engineer only use solid state, another only tubes, and another even more expensive cabling (OCC copper he informed me) in their systems. The last one surprised me, being everything I've read about cables. It made me realize after only a couple years into this hobby that not everything is set in stone and that there's a diverse lot out there who cherish/value different things in their systems, and what they find important or what leads them to musical satisfaction, let's say.

You appear to be weighting a tiny minority equally with a huge majority.

For example, compared to SS amp sales, tubed amp sales are just about nil. Ditto for vinyl versus digital media. In the latter case people claim a resurgence of vinyl and the death of digital every time vinyl comes near 0.5 % of overall sales.
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