The physics and understanding of low frequencies - Page 2

Originally Posted by MichaelJHuman

Efficiency (usually measured as sensitivity) indicates how much power must go IN to the speaker to get power out. You can make really efficient subs if you don't mind them being very, very large.

Power handling is what it sounds like. Better speakers handle more power to some extent as they use better speaker drivers with better venting and such.

I mention accuracy because speakers differ in how accurate they are. Accurate = better if you want sound output that's as similar to the sound input as possible.

I am saying that speakers don't produce sound 100% accurately. And remember they are not just trying to produce single frequencies normally. They are trying to reproduce many at once, which is probably harder. I am no expert on speaker physics, but I would think that there's interference going on because it's trying to vibrate at various frequencies at once, so to speak.

Originally Posted by JHAz

Probably at least 7 sentences. But why bother with punctuation when you can make things really hard to comprehend by foregoing it?

Higher frequencies have shorter wavelengths. Put a woofer in a box and at some relatively high frequency the wavelength exceeds the distance from teh center of the woofer to the edge of the box. Then it starts to wrap around. So while a tweeter's output goes essentially forward in a pattern of 180 degrees or less (thinking just 2 dimensionally) the woofer is radiating in 360 degrees. Since more of the tweeter's response is coming your way, it's relatively louder than the woofer. Also, when a woofer operates without either a huge baffle or a box, the back wave wraps around, too, and being 180 degrees out of phase with the front wave cancels it out.

When you press closed phones tighter you seal them better so none of the tiny amounts of air movement constituting the bass can leak out. Result, louder bass because you've turned them into pressure chambers more directly connected to your ear drums. I think

In a ported sub designed for flat response down to the tuning frequency, the tuning frequency defines the point at which the most sound is coming from the port rather than the driver. You can design a sub to be very flat even with a port. On the other hand, many car subs are designed to be one-note as you described. Because no musical note is a single frequency but they all contain harmonics, a one note box will basically amplify the bejessus out of the harmonics close to the tuning point and will always be inappropriately loud at that frequency. So it will pound out about the same note no matter what the fundamental of the note being played in the source material. In my experience.

WRT in a car versus in a field, two words: cabin gain. Look it up.

Originally Posted by MichaelJHuman

Go look at a pipe organ in a church. Ask them whether the longer or shorter pipes produce the lower tones...

Go check out some drums. Are the drums bigger, which sound lower?

Just some food for thought (it's not an exact analogy, because now we are talking about stuff tuned to a certain freq, but think about it...)

Originally Posted by JHAz

from what I've read most mixers seeking to punch up a bass drum are eqing around 60 Hz or so. Give or take (probably mostly take) 20 Hz. How loud to feel it I don't know.

Originally Posted by JHAz

You need to do some independent study. Google sound frequency wavelength and you will find a wavelength calculator. If the particular frequencyps wavelength is 2 inches or 1 inch, it won't wrap around the enclosure. If the wavelength is 10 feet, it will sure enough wrap around a 15 inch wide enclosure. Google geometry for what 180 and 260 degrees mean.

I'm no expert and don't have either the time or inclination to write a treatise on these topics. WRT speakers sounding different, take a look at the guitar universe. You can spend 300 on a 12 inch Celesetion that handles only 15 watts precisely because it has a very unique sound that relates to distortion in the cone. You can surf around on the Eminence site and listen to different speakers of the same size playing the same input and hear how different they are. While hi fi speakers are theoretically not designed specifically designed tohave an intrinsic sound, the cones still have breakup modes. I lost the link but there are sites that show how the cone vibrates in sections that change size and shape at different frequencies.

It's actually not much fun to try to help somebody who simply chooses not to believe accurate statements and demands that volunteer folks trying to help them work harder to convince them. the truth is out there. Fire up your favorite search engine.

Originally Posted by penngray

Did my post above not make sense????


I will repost....

Drivers have different measurements and T/S Specs, they perform differently and they can sound different. Some has more stored energy then others, some have higher distortion, some have different harmonic signatures, some require a sealed box and some love big ported boxes, some need 100Watts and some need 500Watts or 4000Watts. Large woofers can run really low and sometimes do not go very low at all. Look up Hoffman's Iron Law on reasons why. I guess Im trying to post that there are many, many reasons why two drivers can sound different.

You have to learn about all the measurements that can be done on a driver, See zaphaudio.com then you have to look at those measurements to see the differences.

Yes, measurements matter!!

We are not even getting into the discussion of speaker design, XOs with 1st through 4th order slopes and how they change sound. Phase coherence, stuff. Box harmonics, etc. Stick a 2 uF cap on a tweeter and watch it have a high pass rolloff above 5000Hz.... Its really not that hard to figure out why speakers will sound different.

Originally Posted by enderland

Do you have a piano around? A simple example should demonstrate this - play an identical note on the piano and on a guitar.

They might be exactly the same frequency and volume but clearly sound different. Simply because the frequency and volume are the same does NOT mean the actual sound you hear is the same. The piano/guitar example should make this completely clear.

If this doesn't convince you that speakers can sound different in spite of the same frequency you should be really confused how a guitar and piano can play the same note yet sound different

Originally Posted by JHAz

Seeriously, try a little google. Do something for yourself. Heck go to a store and listen to different speakers and see if they sound the same. You can find arguments almost daily here about whether amps can or do sound different, or whether you can hear any difference with different cables. I've just never ever ever seen anybody argue that spepakers don't sound different from each other. The idea is so self evidently ludicrous that all I can think to do is suggest you conduct your own research. The feac that I can't understand exactly how the sun works does not stop it from providing heat and light to the planet.

The basic reason for the differences, I guess, is that no real world material is perfect, so the imperfections of the materials used result in different departures from perfection.

Originally Posted by enderland

After supplementing my background (mechanical engineering) with some quick googling to verify what I was thinking -

One definite reason the same frequency will sound different is the shape of the wave. Frequency tells you NOTHING about the actual shape of the waveform itself. If you have a perfect sine wave it should sound different than a sawtooth waveform or an imperfect sine waveform or a squarewave form, etc.

This is the stuff I wanted to talk about. OK if a guitar has all the same frequency harmoincs as piano and the different levels in the harmonics make them sound different than what factors then determine two guitars or two pianos sounding different?If the human voice has its own waveform than what about the waveform makes my voice different than yours or a girls distinguisable from a guys?

If each speaker was capable of creating the exact same waveform (shape, frequency, amplitudes) and the speaker case, either a box or whatever the speaker was contained within, had identical acoustic properties (they never will be exactly the same for this purpose even within the same brand) you should get the same exact sound.

Not sure what you mean the speaker it self should have no trouble reproducing the sound exactly cause its just reacting to a signal. I understand the box it is in making a huge difference. Basiclly if you send a 200hz frequency to two different kinds of speakers what would be the audible difference.I know youre going to say real sounds are not simple waveforms but real sounds are made up of a combination of sinewaves.

They can't however. The more advanced speakers presumably can more accurately match the recorded waveform. Unfortunately, physics exists and there will almost always be difficulties in matching a given signal. For example



If the sound waveform being given to the speaker is the blue waveform, differing speakers will have difference responses - indicated perhaps by the differing curves. It is physically impossible to instantly reproduce a given waveform. It just is. By the way, the above graph is from a PID controller in case anyone is wondering, which while technically not limited to audio, the principle applies to nearly any waveform replication. This example is probably far 'worse' than most speakers would be.

Each replicated waveform will have imperfection when compared to the source signal. This will lead to the waveform sounding different, even for the same frequency. Speakers will tend to react to the source sound in the same way consistently - which will result in different sounding "tone" for speakers, ie bright or deep or however else you want to describe them. This is partially (perhaps completely) caused by the speaker output varying similarly to the above graph results varying.

I can understand this but what I cant wrap my mind around is if a flat frequency reponse(would like some clarification on what this means) is ideal but the thinng that makes instruments sound different is the fact that they have different volumes of their harmonics so basically the only thing people would be looing for in speakers is how they vary from a flat frequency repsone not too mention some speakers could sound like other ones depending on the original levels of the harmonics in the recoriding.

Not to mention the fact that even if two drivers can reproduce the exact same waveform from the exact same source signal the container they are in will likely affect the sound too. Or that the input signal to the speaker will in no way be as simple as a step function waveform (the blue waveform in the above image) considering it will have a lot more instruments, vocals, etc.

Your comment regarding coke/pepsi is actually a really good one. For some people, they can quickly discern the difference between the two. Many if not most cannot depending on the test conditions (as an aside, if you think you are good at this, have someone take the typical test with a twist - instead of 1 cup of each, have 2 cups of 1 and 1 of the other, for a total of 3 cups, and see if you can still replicate your success) can not do this. And obviously, someone who has drank more pop would be far more likely to succeed than someone who drinks pop on a semiregular basis. I would probably fail at the coke v pepsi test.

Yes totally agree that if someone didnt have expierence with them they would probably fail the test several times but to me this is more because they dont have expierence with which one is which not they cant taste the difference. I can tell the differncee between speakers if im switching between them with same material but I wouldnt know what to listen for that I wold consider that i would like. What would some of the basic things too listen for a begginging auidophile?

However, speaker evaluation can be similar. My background involved me playing trumpet in a very good youth orchestra. My ears and mind are acutely tuned as a result (or so I think, hah!) to hear differences in sound. In an orchestra setting, tone makes all the difference. I bought Polk speakers because I listened to a variety and found that to me, Polk speakers were very defined - this is likely a turn off to some people, as it might be too bright, etc. Anyways, the point is people have different talents for finding differences in things they are familiar with. A machinist can probably look at different plates of steel and identify them far better than either of us. Just the same, those more experienced and versed in speakers can definitely see the differences.

It might be more difficult for you than others here. This is, afterall, a forum for people who like this sort of thing greatly and are much more likely to have invested huge amounts of time/money into listening to speakers and therefore have a much larger knowledge and experience base than you.

Anyways, this turned into a book, but this should answer all of your concerns regarding speaker differences. If not I guess I would suggest reading through it again.

edit - You might also be interested in reading about Fourier series based on your discussion of sine waves on the previous page.