The physics and understanding of low frequencies - Page 4

I am not the smartest or most experienced on this subject, but it seems that with the bold part of your quote, you have already admitted that different speakers sound differently. Maybe I'm wrong, but isn't the whole point of equalization to cater the sound towards a certain goal? If all speakers sounded the same and were perfectly accurate, we wouldn't need it.

Bottom line is, you seem to simply be disregarding all sorts of obvious facts. Different drivers use different materials, and those materials will affect their output in various ways thus creating different sounds. That's way before you even put any of the other variables into account.

Don't take any of this the wrong way, if I'm wrong, I am more than open to correction. After all, this is a great place to learn.

Heres some physics for you that may explain how speakers sound different:

An object in motion tends to want to stay in motion. Otherwise known as inertia.

Now, let's take a tweeter made from aluminum, and a tweeter made from titanium, which is heavier than aluminum.

Now, we excite this tweeter with a frequency of some sort. What happens when the sine wave reaches it's first peak? The cones on both tweeters will want to continue moving in that direction at the same speed. What happens when the sine wave passes the peak? The decreasing voltage is telling the tweeter to start moving in an opposite motion.

Now, the lighter tweeter will respond faster than the heavier one. Reason being, it takes more energy to reverse a greater mass than a lighter one. So ultimately, the two tweeters will have a slightly different sound.

So why not make all tweeters aluminum? Maybe because Titanium holds it's form better, and is less likely to flex at the highest frequencies. So there is a trade-off.

Now, extend this to midranges and woofers. They can be made from paper, aluminum, kevlar, ceremetallic, coated paper, plastic, any number of materials. Each of these materials is going to weigh differently. So their inertia can make them sound different.

So why aren't all speakers made out of the same material? Cost. Paper is cheap. But play at too high a volume, and the paper can literally catch on fire. Aluminum is more expensive to work with, but it can act as a heat sink, so you ca play at louder volumes. But the speaker will cost more. Or maybe another manufacturer uses an expensive alloy because it's light, but holds its shape under high stress, and dissapates heat well.

The sound of a speaker can vary because of many factors. Heavier or lighter drivers have more or less inertia. Different materials can flex differently under stress.

Let's try this way, when the speaker is good it is more accurate, so an orchestra should sound like an actual orchestra and you should be able to hear not only the overall music, but the part of each instrument, as well as being able to locate that instrument spatially.

If the speaker is not good enough you can still hear the overall music, but the location get fuzzy, and instruments seem to blend together.

This is not something you get from an equalizer as you said, the distortion due to the speaker can vary if the signal is simple or have a lot of harmonics.

No it still produce a sound but not a perfect sine wave.

Yes but the signal is more complex, so if you lose some of the details you tend to lose more in that case.

Think of a picture, if it is very simple like 4 square of different colors, even if you add noise and distortion you can still perceive the original picture very clearly.

If the picture is complex, like for example a high res satellite picture, the smallest amount of noise or distortion will mean you wont be able to figure out the details. For example you can still see there are roads and cars, but you cannot distinguish the pedestrians, or the car models on the road.

Both tweeters can vibrate at that frequency. But how well they reproduce the input signal is the difference. If you were to look at the tweeter's actual waveform on an oscilloscope and compare it with the input waveform, there will be differences.


EXACTLY! Therein lies the issue. The enclosures, material, and diaphram of any speaker do make their own sound. If you want to build a cheap speaker, you don't worry about that. But if you want to build a speaker that is as true as possible to that 50Hz tone, then you need to spend extra time and $$$ into researching how to best reduce and eliminate these undesirable traits. And so a manufacturer will spend more money on better enclosures, better engineers, better driver materials. That added cost gets passed on to us, the consumers, in the form of more expensive (and better sounding) speakers.

You mentioned enclosures making their own sound. That is a perfect example. Lets say you put a 12" driver into a 1/2" thick plywood box and play 50Hz. What is that thin plywood going to do? It is going to vibrate at 50Hz as the driver pressurizes and depressurizes the box. That will create an undesireable noise which was not in the original 50Hz sine wave you fed it.

Now, let's say you use 1" thick plywood, and install internal bracing. That box is now going to vibrate a lot less, and as a result, it will not add as much of it's own undesireable sound. So now you have a speaker which plays a better sounding 50Hz tone. And you've spent more money doing it, so you need to charge your customer more.

Now let's say your customer doesn't like the look of raw plywood. So you put a polished wood grain veneer on the cabinet to make it look pretty. Now you need to charge your customer even more because it cost you time and money to make a pretty box.

Now let's say your customer has issues with room modes. So you build a parametric equalizer into the subwoofer box. Now you need to charge even more!

That's why there is such a huge variety of speakers. Maybe I'm a struggling college student, and all I can afford is the 1/2" plywood box. I might want the sub with the PEQ, pretty veneer, and thick box, but I can't afford it. So I get the cheap one. On the other hand, maybe I'm a Sheik from Saudi Arabia. I don't want the cheap box that sounds bad. I want the thick pretty box with PEQ. And I want it diamond encrusted. And I want the driver to look pretty, so I want you to make it gold plated.

I think the big picture thing that's being danced around a bit here is distortion. It sounds like your main premise is that if speakers were EQ'd to have the same FR they'd then all sound the same which is intuitive for most I'd think. The problem is speaker drivers cannot 100% accurately reproduce the input signal they're asked to and the enclosures they're placed in have a large effect on the speakers' acoustic frequency response. If you ask a speaker to play 50hz they will play 50hz but they'll also be playing a lot of other notes that they weren't asked to because of the inaccuracies (distortion - harmonic and non-linear). That alone can cause two speakers with the same measured FR to sound differently but we can extend that even further. Now imagine you have two speakers. One has a naturally flat FR curve, the other has a large 10dB bump in the FR at 200Hz caused by the enclosure. You EQ the 2nd one to be flat by bringing down the bump at 200Hz though and expect them to sound the same. Now you play a loud 100hz note on the first speaker then the 2nd speaker and they sound very very different. Why would this be??? Even though you've electronically "fixed" the 200hz bump of the 2nd speaker the harmonic distortion produced by the 100hz note (at 200hz) is still being boosted significantly by the enclosure.

Another example that's not too complicated is off-axis frequency response. Due to speaker baffle size, driver layout, crossover, and even whether the edges of the baffle are rounded over, chamferred, etc the FR of different speaker designs will be significantly different then each other as you move off axis vertically and horizontally. Since the majority of what we hear when we play a speaker is reflected sound rather than direct these differences have a significant effect on how a speaker sounds. Another oversimplified example. Say we have two speakers again, both with flat on-axis FR. Speaker one rolls off very smoothly both vertically and horizontally - say it's -3dB at 15 degrees off axis at all frequencies and -6dB at 30 degrees off axis at all frequencies (NO speaker would be this "nice"...). Speaker two has a narrower vertical window around the crossover frequency - say 2kHz. In most of the FR it matches speaker one but at 2kHz it is -6dB at 15 degrees off axis vertically and -12dB at 30 degrees. Now, even though on-axis they measure the same FR = flat, they will sound significantly different at 2kHz when placed in a room as speaker #2 is contributing less energy toward the ceiling and floor to be redirected to the listener. For more details on directivity see the polar maps near the end of this paper posted by Earl Geddes (the paper is actually sales literature... I didn't read the entire thing but the polar maps are very interesting): http://www.gedlee.com/downloads/directivity.pdf

These are just two simple examples of why speakers with the same measured FR would sound different. There are lots and lots and lots of things that affect the sound of a speaker that cannot be seen by a simple FR measurement (and cannot be fixed by EQ alone...).

Assuming each was equally able to exactly replicate the signal (shape, amplitude, etc - far more things than the frequency affect the sound) this is correct.

This is NOT the way things actually work however. If you measure the waveform generated by each speaker it will not perfectly match the input signal. Some may be closer than others. In general, the more expensive speakers will be closer than the cheaper speakers. This is an inherent of mechanical systems.

Many of your questions seem to ignore this fundamental issue with speakers and sound replication. Two main things:

1. There are more elements to a sound wave than frequency (such as amplitude, shape, etc)
2. No mechanical device can 100% replicate an input signal (speakers are mechanical devices)

Does both of these statements make sense?



There are two types of "fast." One is "can the tweeter vibrate at a certain frequency indefinitely." The second, which is the important one in understanding speaker differences (assuming the speaker isn't so bad of quality it cannot even do the first) is "how quickly can the tweeter change to vibrate at the given frequency."

ie

You go from 0 to 15 kHz. The tweeter will not go from 0 to 15 kHz immediately. It will likely take a short amount of time to go from 0 to 1kHz to 2kHz, etc, all the way to 15 kHz. This happens so fast we barely notice it. Factors like this contribute to speaker differences.

The graph I showed previously really illustrates this.


Without knowing your background, it is difficult to say. My background contains a lot of math and science. I will say though that understanding those equations is something I do not necessarily think is required to having a pretty good understanding of why speakers sound different. Perhaps this would benefit you in understanding more mathematically why you feel bass instead of hearing it.

(disclaimer: the following is just my thoughts on the matter, and while there is a scientific background here, everything I am saying are conclusions I draw from that )

My assumption would be as the wavelength of the sound increases (with decreasing frequency, a 20 Hz soundwave has a wavelength significantly longer than a 1000 Hz soundwave) it eventually hits a point where your ear can no longer determine its characteristics and therefore you do not "hear" it. This is the same as if you tap someone on the shoulder, and increase the speed at which you do it - eventually you will be tapping them fast enough they cannot tell individual taps apart. Well if you are able to move your hand fast enough I guess. Probably would require a non-human 'tap' to move quickly enough to have this be possible.

Waves also transmit energy. For a simple wave, as the wavelength increases, the distance between a peak/trough (hi/low amplitudes) also increases. Eventually this becomes enough to remove a "constant" pressure. As this distance decreases we perceive the relative differences less and less. For lower notes (lower frequencies) these differences might be enough where you can "feel" the energy from the wave. Instead of a constant pressure, there is a perceptible oscillating pressure wave (very roughly at 20 times a second for a 20 Hz wave; wavelength of roughly 17m and a speed of 343m/s means you get about 20 waveforms per second).

*shrug* Not sure on the math of that or even if what I said above is right.

No. The fact that equalization exists proves that speakers sound different and are inaccurate.

The only real asanine statement here is to say that computer speakers sound the same as a set high end floor standers. Not being mean, it just is.

The dynamics of a speaker is how well it responds to those changes in signal input and its ability to remain accurate over a given volume range. Saying that two speakers using completely different drivers, crossovers, cabinets and materials will produce the same results is just silly.

It also seems a bit odd to ask me to watch a youtube video as an example of dynamics when you yourself said you cant get a fair listen over the internet.

Once again, not being combative, these are good discussions to have.

It is true that some tweeters go higher than others. Some tweeters don't make it all the way to 20KHz. Some go further. For example, the Axiom M80 speakers have tweeters that go to 20KHz. But the Klipsch RF-7 speakers have tweeters that go to 24KHz.

My main point about tweeters is that while it can vibrate 15,000 times a second, how cleanly is it vibrating? Does it's waveform look like a sine wave, or does it look more like a sawtooth?

Bass has more energy than midranges. That's why it takes more wattage and bigger woofers to recreate bass. More energy moves more air. Less energy moves less air.

What would .5Hz feel like? Ask Adam Savage from Mythbusters. I think they subjected him to .5Hz during the "brown note" myth.

this question really points out that you don't understand the fundamental aspect of "sound"...

you need to buy "the master handbook of acoustics"...

That's a riot,

Too bad most here won't get it.

That's okay. I've long since made peace with the fact that almost nobody gets my humor.

I have no problem continuing this discussion, but if I am going to continue it you have to adress this. Because otherwise all my efforts here are a waste of time --

1. There are more elements to a sound wave than frequency (such as amplitude, shape, etc)
2. No mechanical device can 100% replicate an input signal (speakers are mechanical devices)

Does both of these statements make sense?

So you agree that different guitars can have different sounds but not speakers? I'm curious about this.

Here is what the waveform of a violin looks like...


Image from: http://musikality.net/general/audio-...riertransform/

That is not a pure sine wave. There are waves there, but it is not a sine wave. However, that signal is what your speaker will see. And that is how your speaker will have to vibrate to reproduce that sound.

As explained on the site I sourced the image from, the sound of a violin is made up of several frequencies. The fundamental, and all the harmonics of that frequency. Now, let's examine this waveform.

Right near the zero crossing line, there are little ripples in the waveform. Very small, but there nontheless. A cheap speaker may not be able to recreate those ripples accurately. Perhaps it's mass overshoots, and exaggerates the ripple. Perhaps it's not sensitive enough to react to such a minute change.

Sensitivity is an important spec in any speaker. Lets say that speaker A will generate 85db when fed a 1KHz tone at 1 watt. Lets say that speaker B will generate 101db when fed a 1KHz tone at 1 watt. Which speaker is going to be better at reproducing that slight ripple in the violin's waveform? Speaker B, because it's much more sensitive to variations in sound.

An interesting thing to note is that while in the above example speaker B is the better of the two, there are cases where it will sound worse. If you feed speaker B a well recorded signal, you will get great sound out of it. But let's say you play a vinyl record on speaker B. You'll hear the music, and you'll also hear every scratch, pop, and other imperfection in that record wonderfully reproduced on the highly sensitive speaker. Garbage in, garbage out. But the less sensitive speaker A, will still reproduce some of the imperfections, but they won't be as easy to notice.


Okay, let's try another exercise. Total Harmonic Distortion, or THD. THD is how much distortion is introduced to a sound. In another thread I started, I did a hearing test where I asked people to listen to a 10Hz - 19Hz tone to see if they could hear it. Here is a spectogram of the source file:


The sound file starts at the bottom of the picture, and slowly works its way up to the top, from 10hz to 19Hz. Notice how there is one single vertical line per tone. This is the sine wave. The second and third harmonics of 12Hz would be 24Hz and 36Hz. Looking over at the 24Hz and 36Hz portions of the graph, we see only inky blackness. So our source signal has no harmonic distortion. Just a clean 12Hz sine wave, and nothing else.

Now, this was recorded from my headphone output:


Now look at the 12Hz fundamental (3rd orange line from the bottom) Look to the right. There is another line at 24Hz, and a third line at 36Hz! That audio was NOT in the source file. But the speakers in my headphones produced it nontheless! This is distortion. This is the speakers in my headphones not reproducing the 12Hz (or any other frequency on this chart) accurately.

Let's look at a different chart. This is my headphones producing 10Hz.



Recall that the original source file had zero distortion. However, on this graph, note the areas marked 2 and 3. These are the 2nd and 3rd harmonics of 10Hz (20hz and 30Hz) Those little spikes there standing above all the others are distortion. They were NOT in the source signal. But they are there now.

Now, let's look at a slightly more expensive sound system built by notnyt:



My headphones produce about 5.7% THD at that frequency. But notnyt's system produces 3.8% THD at that frequency. (and notice his level is over 30db louder than mine).

There they are. Objective measurements from two sets of speakers being fed the exact same 10Hz tone. Yet one is clearly doing a better job than the other. If a speaker is a speaker is a speaker, and they all sound the same, then both I and notnyt should have the same results. But we don't. Why? Because different speakers do sound different.

If a speaker could play with 0.00% THD, then that would be correct. But speakers can't do that. Some speakers get closer to 0 THD than others. So while the input might be +8 -4 +2 +4 -2 +8, what the speaker actually does might be more like +8.22 -3.91 +1.86 +4.13 -1.95 +8.13. That is exactly what distortion is - a speaker not playing a signal accurately.

Check out the "Servo Subwoofer" section of this wikipedia article: http://en.wikipedia.org/wiki/Subwoofer#Servo_subwoofers

The point of a servo subwoofer is the engineers who made it know that the cone is not going to replicate the input signal exactly. And so they put a sensor on the cone which measures actual cone movement. A microprocessor compares the input signal to actual cone excursion, and adjusts the output in an effort to get the cone to more precisely reflect the actual input signal. If all speakers truly replicated the input signal exactly with no distortion, there would be no need for a servo subwoofer.

I think there is a very serious language barrier here.

By the way, I asked how old you were to determine your age, period, don't worry about what I was assuming, I was just asking.

You seem to be a person whose natural first language is not English. If that is true, I think that is contributing to some of the confusion.

The other possibility is, well unkind and I won't say it. Good luck.

Guitar speakers have VERY different sounds. That's why, for example, for at least much of his carreer Malmsteen has used a Celestion speaker that is not "native" to the cabinets he is using. I can't imagine switching all four speakers in 28 separate cabinets to a speaker that many, especially vintage buffs, think is "inferior" (but it's really all about horses for courses) because it doesn't make any difference(!).

Your desire to rest on your untutored assumptions is wrecking any capacity to learn the answers to the questions you are asking.

While the differences may be subtle in some cases, and utterly irrelevant to you in all cases (i mean if you can't hear the difference between speakers, be happy and buy cheap) you can come very close to turning a Marshall into a fender just by switching to Jensen-style speakers, and LOTS of people get somewhere in the Vox/Marshall sound world with Fender Blues Jrs simply by putting a celestion Blue (or alternative aftermarket speaker like a Weber equivalent). It makes what to me, and to folks who heard me audition celestion-based amps with a Weber Jensen-style speaker. Changes the character of the sound a lot. Easy as pie for anybody who would bother to look at the speaker websites that I have twice suggested you visit to see the beginnings of the reason why: their FRs are significantly different at low power. But even more differences come as you pour on the power - - how each speaker's FR changes, the way they compress (or don't) and how the cones break up really makes a difference.