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Fun Fact: Does everyone know why the THD+N curve takes the shape it does, not only increasing in percentage as power increases but also as power decreases? First, what is THD+N? It is the total harmonic distortion (THD) of the amplifier plus the amplifier's noise (N), and in the graph it is expressed as a percentage of the signal. Now, THD is strongly correlated to the signal.....as the level of the signal increases (i.e. as power output goes up), THD increases. As the level of the signal goes down, so does THD. The right hand portion of the graph makes sense then.....we see the % of THD+N increasing as power increases. But if we look at the left hand side of the graph, in the lower power output levels, we see that the % of THD+N increases as power decreases? Well, that's because the "N" portion of the THD+N, or the noise, is uncorrelated to the signal. The level of the noise is going to be relatively the same at low power levels as it is at high power levels. Because of this, as the level of the signal decreases, the noise becomes a larger percentage relative to the signal ! So the percentage of THD+N is going increase as power decreases because, even though "THD" is decreasing, "N" is increasing as a percentage of the signal. So the THD+N starts out high because N is a larger percentage of the signal at low power levels, then the graph slopes downward because "N", as a percentage of the signal, is decreasing while THD is increasing (although not at as rapid a rate as "N" decreases, so the overall slope of the graph is still downward) until it reaches a point where THD begins to become more significant as power increases and the graph swings back upward again. This is why the SNR (signal-to-noise ratio) of an amplifier is completely dependent on the level of the signal. As the power output of the amplifier increases, it's SNR improves. So if we measure the SNR of an amplifier at 1w, it will be worse than the same amplifier measured at 100w. This is a typical marketing trick by amplifier manufacturers.....some of the less scrupulous manufacturers will list the SNR of their amplifiers at full power output, while others will list it as a 1w measurement. Which is why it's important to know the test conditions of a SNR measurement before trying to compare them between amps. The SNR measurements of two amplifiers can not be directly compared unless they were taken at the same power level, or you adjust one of their SNR measurement numbers to account for a difference in the power level the measurement was taken at. So, there's my attempt at posting something educational today.

It has been debated rather hotly for years, and now it has become pretty much accepted that MP3 and sound quality do not mix. But why is it? Why do some people hear so much loss in their systems and others don’t? Are my old ears really better then someone 30 years my junior? Someone who still has a large amount of their hearing range left, while mine has deteriorated over the years should be able to hear these losses better then I! I started with home tower speakers in the back seat of my old Delta88 back in the days when we had no real systems, and we still had post mounted tape decks and 8-tracks. Then times changed, and we started putting in tape decks with trunk mounted CD cartridge changers with $60 coaxials and $50 amplifiers and maybe a bazooka tube subwoofer for those of us with “discriminating” tastes. Eventually I wanted to just go boom and spent money on several thousand watts and some monster excursion subs. Then we learned about XBL2 and how these high output subwoofers could be very accurate. Finally I finished my journey with $1200 component speakers and $1000 amplifiers, all filled in at the bottom with very capable sound quality based subs dialed way back. My journey started out as just wanting to get some sounds, to wanting to get loud, to wanting to sound good. Now that I have found a really nice sound quality install, my music seemed to really lack. I have been using MP3 for years, but eventually I started looking for higher bit-rate MP3s, and now I am at a level where only .flac or .wav or other lossless files suit my tastes. I have listened very critically to how the advancement of definition brought about by higher quality speakers and amplification, and source caused my MP3 listening experience, no matter the bit-rate to become bland, and I really felt more of the emotion brought out in music by using lossless formats in my car. But then I asked myself, “Why does my lossless not only sound better, but seem to bring about a more emotional experience?” So I started to learn about how lossy formats work, and how they can stick so much information in such a small space. Let’s discuss music reproduction first, so we can get an understanding of what we are listening to. All we are listening to is really a reproduction of an instrument or a voice, and to simplify this writing I will include the vocals as the instrument as well. Musical reproduction is usually characterized as fundamentals, harmonics (and as I will discuss below, low fundamentals can be included in this grouping), and finally overblow, breath, or air. The very heart of these sounds are called fundamentals. The fundamentals, are what I call meat and potatoes or music, are the essentials of the reproduction. They are what the instrument actually delivers, directly. But then we have carry over, which are termed harmonics. These are not as much a base of the delivery of the instrument, as they are an extension of it. You might also see the lower frequency carry overs dubbed as a “low fundamental”, as they are more apparent in low frequencies, where they tend to be less noticed in higher pitches. I like to call this the emotion of the music. Finally you have overblow, which is usually only noticed in wind instruments and vocals. I personally like to classify this as emotion as well, and therefore will include them as a group when I say emotion or harmonics. While it takes a trained ear to listen for image and stage presentation, younger people with a naturally better range can hear losses in the “emotional” frequencies or the harmonics of the sound easier than us old fogies. So why is it that those of us who are older tend to hear these losses better then the young folks? I would dare to venture that it is simply because we tend to have more money invested in our component systems (and when I say system, I mean everything from source material, source equipment, sound processing, amplifiers, speakers, and installation techniques) with a higher definition then the younger folks who are running a simple inexpensive component system install. This is not to say our systems are better for all purposes, as I will discuss in this writing. In fact, for the vast majority of folks, a lower definition system makes more sense, as many are more concerned with the ease of storage media and they tend to use MP3 or other lossy formats. When we have these high definition systems, many of the weaknesses inherent in lossy encoding really jump out glaringly. So, sandt38, what is it that we really listen to? Well, the human brain perceives and retains everything it sees, hears, thinks, etc. It is actually an amazing organ that captures far more then we are able to drag out of it. We simply do not have all the doorways opened up in the brain, so we forget, or don’t notice many of the things that we actually perceive. The mind actually only directly notices the loudest things we hear. So while there may be several instruments may be reproducing the same frequency at the same time, we only perceive the loudest of this information we actually hear. We ignore the other lower volumes of the same frequencies, but we still hear it. Our mind processes this information but determines that it is not that important so it will file it away in that subconscious part of the brain we do not actually consciously notice. So let’s look at how these MP3 encoders work. In order to save space, an MP3 encoder usually selects certain information to discard, and other information to retain. The most common method of MP3 encoding functions similarly to how we perceive the music. Just like our brain, it ignores the lower volumes of the same frequencies, and all it retains it the higher volume material at that frequency. We fill in the rest subconsciously. Please be aware that many encoders eliminate only certain lower frequencies altogether, but they variably retain the higher volume information up to a certain point. For example, the encoder may retain ½ of the information at a certain frequency. But it will retain the higher volumes at a greater rate. While these are not the only methods of encoding MP3s, they are the most common. So you see, by considering the way the encoder works we can get an idea of what happens to the music we listen to. The fundamentals tend to get retained, while the harmonics tend to be lost. So we lose the emotion, which is why MP3s sound so bland on systems with very high quality components. Now, there are other things to consider when it comes to MP3 compression. Bit-rates, and not only the rate, but variable or constant bit-rates, are the biggest consideration here. Very quickly, the higher the listed bit-rate, the more information that is saved, and therefore the better the quality. But to be frank, these don’t alter what occurs with the music. Yes, these higher bitrates do sound much better, but there is still something that is lost. So what can we gather about speaker selection from our source material? Well, we can help decide whether it is really worth it for us to spend $1000 on components, or if a $200 set will suffice. I am not trying to say that if you spend a grand on a set of components it will automatically be a better set then a $500 set. My mention of pricing basically assumes a basic cost/quality ratio. Clearly a $200 set of Sony Xplod coaxial speakers is nowhere near as good as a $180 Image Dynamics CTX65CS component set. So take these generalizations to assume a similar cost/quality ratio. The high dollar sets that you see out there are far more true to source then the lower priced units. This is a good thing if the source material is pristine. But if your source is not that great, these more accurate speakers will start to sound like crap. It isn’t the speakers that suck, it is the material you are putting through it. But when we get down into the lower dollar sets, these weaknesses are not quite so apparent. I do want to point out this article, no matter how poorly the whole test was conducted the results still prove my point. The guy used some of the most awful source and speaker combinations. Why you would ask people to listen for nuances using a $200 receiver and a $200 subwoofer and satellite set using 5 3.5 inch full range units is beyond me. Sheer idiocy. But the end results are very significant, the differences between MP3s and lossless were detected by all listeners in the test. All this considered, please keep a few other things in mind. I cannot stress the importance the rest of your signal chain has on the final product. The higher end speakers will also show off weaknesses in them as well. Be prepared to make some really high dollar signal chain investments when you decide to buy these high end components. I also think it should be noted that while amplifiers of the same class may sound different while sitting still with little ambient noise, but once we get moving these nuances really disappear. I do feel that differing class amplifiers can have a different overall sound, and can be distinguished while moving.

You want me to get the SAZ-3500 to put it up against the RF 2500? I didn't test my RF 2500's to put it up against anything else. I tested it because I wanted to know for myself what it actually put out. I'm a skeptic when it comes to Birth Sheets also, but I saw the proof, and I'm happy with it. Ive heard nothing but good things about Sundown and will be getting one or installing them for my next customer. When I get one I will gladly test it. But like i said, i'm not doing testing to put any brand down. I think most people knew that. Some people have boners for a specific brand. Nothing wrong with that, just like there is nothing wrong with seeing value in other brands too. I like the test and I am sure Sundown would be right there too. We are lucky to have so many quality choices.

As M5 said, the entire reason amplifiers have a gain knob is to allow the amplifier to provide full power output with a wide range of input voltages. If you properly readjust the gain, there would be zero difference in output levels between a 2V headunit and an 8V headunit. What happens most of the time is that someone switches from a lower preamp voltage headunit to a headunit with a higher preamp voltage output, and then don't readjust the gain on the amplifier to compensate for the increase in input voltage the amplifier receives. In those cases the output increases because of the higher preamp voltage, but only because the installer did it wrong and didn't properly readjust the amplifier's gain setting.

It is completely unrelated to output as long as you have a half way decent amp. It is functionally the reason there is a gain knob on the amplifier.

If there is no more power then there is no additional headroom. Headroom is power available beyond what is needed for normal sound production. If the amp is capable of producing 200W and the normal power used on music is 50W you have 6dB of headroom in the system. Gain setting is not related to headroom. Gain setting is not related to how "hard" the amp works. Setting it correctly allows you to get full power from the amp regardless of source voltage. Having it set incorrectly does one of two things. If it is set too high, you have a very limited range of usable source volume control before the amp is driven into clipping. If it is set too low, you simply will never get full power from the amp. It is really that simple. The only benefit that you might see from higher signal voltage is the reduction in gain can keep noise out of the system. Every signal cable has a noise level present in it. The voltage of that noise stays constant. With an extremely low signal voltage, the gain on the amp has to be turned up and that amplifies not only the signal, but also the noise. Higher signal voltage essentially increases the s/n ratio of the signal cabling. 2V is way more than enough to completely overcome the line noise in most any system. Beyond that its all about marketing. Sounds like my kind of gig.

You want me to get the SAZ-3500 to put it up against the RF 2500? I didn't test my RF 2500's to put it up against anything else. I tested it because I wanted to know for myself what it actually put out. I'm a skeptic when it comes to Birth Sheets also, but I saw the proof, and I'm happy with it. Ive heard nothing but good things about Sundown and will be getting one or installing them for my next customer. When I get one I will gladly test it. But like i said, i'm not doing testing to put any brand down.

Higher voltage HU's allow amplifier gain settings to be adjusted lower which will allow more amplifier headroom. If you have a strong input signal you can set your gain lower than if your input signal was weak. A lower gain setting allows for more dynamic headroom. What this means is that the amplifier can produce a cleaner output signal without clipping. Music has peaks and dips some peaks can be +3db stronger than others (0db signal). That 3db signal requires the amplifier to work much harder than baseline; often this is where clipping occurs. Just my very brief comment on a complicated subject.