In a stereo speaker woofers are big-ass speakers to render that chocolate fudge bass realistically. But the bass in my earbud headset is actually pretty bass-y. How does such a tiny membrane provide such relatively good bass?
It doesn’t really. Hold the earbud away from your head and re-evaluate how good the bass is.
But it doesn’t matter how lossy the little membrane is in open air. When in your ear, almost all the acoustic energy is utilized, since it only has to travel through a small-diamater channel before reaching your eardrum.
Balancing the bass vs treble is still tricky for an earbud; an issue of matching their losses.
The trick is that the lower the frequency, the more prone it is to diffraction, i.e. the greater the tendency to disperse from its original trajectory to a more lateral path. So if the earbud is jammed into your ear, the bass has nowhere to go but toward your eardrum. If the earbud is held away from your ear, then the bass frequencies kind of spray out in a fuzzy-edged cone, with only a tiny fraction of the original intensity reaching your ear canal - but the higher frequencies disperse less, and reach your ear canal at something much closer to their original intensity.
I have some Soundmagic ear-buds, and it is very noticeable that the bass response can be adjusted by how far they are pushed into the ear. Further in = more bass.
I assume that this applies to all earbuds, and is a function of the volume of air trapped in the ear canal. Can anyone direct us to a more detailed explanation?
Referring straight back to this thread is not exactly helpful.
Diffraction is nothing to do with it because I am talking about earbuds IN the ear holding a trapped volume of air.
Actually, that’s kind of poetic, pointing out that the closer you are to the source, the clearer the response.
Speculating: maybe it’s not about the volume of air between driver and eardrum. Maybe the farther in you jam the earbud, the better a seal you’re creating around its perimeter?
along with the above i think being in direct contact with your skin would help cos sound is better transmitted through dense stuff like you than air
No.
feedback.
A lot of it is an auditory illusion. Don’t have time to quote the details but see here: http://www.forbes.com/sites/nickmessitte/2014/04/19/how-earbuds-have-changed-the-sound-and-business-of-pop/2/
A better seal will help. A complete seal means sound can’t get out through small gaps between the earbud foam and the ear canal. A tighter seal, meaning the foam of the earbud is compressed more, will mean the foam will absorb less of the sound.
Pushing the earbud in farther also means the sound will travel less distance through the ear canal. The sides of your ear canal will absorb some sound, so a shorter distance means the sides will absorb less sound. Having a better seal is probably more important. But the air absorbing sound will be even less important. The ear canal sides will absorb more sound energy than the air in the canal.
The question was answered correctly: it’s because the energy is all trapped inside your ear canal, so it doesn’t take much energy to get all that bass. Bass is what takes almost all the watts, in a stereo system (relatively speaking) because you have to move lots of air.
Let’s look at it another way. Start with what’s happening at the ear. There’s a low frequency wave with a given sound pressure level (SPL). The further you go from your ear, how much more sound pressure is required to deliver that pressure at your ear? The answer is that it goes up with the square of the distance (ignoring T-line issues that I’ll touch on below). When the distance from speaker to eardrum is measured in millimeters, just a few extra millimeters doubles the distance the first time. Twice that to double it the second time. And so on. You don’t have to get very far before you have doubled it quite a few times, and each time you double the distance, you square the amount of pressure required at the distance to get the same pressure at your ear. (That’s a bit of an oversimplification, of course.)
Why does it take a bigger driver to deliver more pressure? Well, the actual requirement isn’t driver size, but volume displacement, which is speaker cone area times linear displacement (that is, area times how far it moves). There are practical limits to the latter, so we make the woofer bigger to get more bass.
Furthermore, your ear canal is a “transmission line”. Once the speaker is in the canal and sealed off, the “distance squared” relation no longer holds; instead you get the equivalent of sending an electrical signal down wires. This fact is used in many speaker designs to emphasize the bass to get more oomph with smaller drivers. (It comes at a cost of resonance, but I’ve heard it applied extremely well.) For details, see the wikipedia article on transmission lines. The article inaccurately limits the discussion to electrical signals, but as a first order approximation (ignoring air friction), it applies to sound in a tube as well. Or so I’ve been told.
It helps to have a large resonance chamber between your ears…
We don’t seem to be making much headway here.
I really do not think this is a sealing issue. The increase in bass as the buds are pushed further in is completely consistent and the same for each ear. That would not be the case if it depended on odd leaks here and there.
Why should that enhance the bass?
If you’re telling me that the walls of the ear canal selectively absorb bass, I am afraid I simply don’t believe it. I don’t accept that the walls of the ear canal absorb any significant sound at all- they are evolved to get sound to your ear-drum efficiently.
Not at bass frequencies, if at all. To act as a transmission line a tube has to be a substantial fraction of the wavelength involved. At 100 Hz the wavelength is 3.4 metres.
The adult ear canal is about 2.5 centimetres (1 in) in length and 0.7 centimetres (0.3 in) in diameter.
Read the whole quote. As you push it in, first you achieve a more complete seal. As you go further, the foam gets compressed more, and so absorbs less sound. None of that is going to cause a sudden change, so as you push it in further, less of the sound energy will be lost.
They absorb sound because they are made of flesh and are soft. At lower frequencies, the sides of your ear canals have more time to respond to the changing air pressure in your ear canal, absorbing more energy.
Not sure why you think this. I’m not even sure if you mean the tube’s length or its width.
I doubt if insults are going to get us further with this issue.
No. My Soundmagic in-ear phones do not have foam- they have very flexible rubber flanges. As far as I can tell, pushing them in a little way gives a complete seal.
I don’t accept that this is a significant factor. Audiologists agree- see Essentials of Audiology By Stanley A. Gelfand (viewable on Google)
Because it is generally accepted by everybody. In a transmission line, be it electric or acoustic, the general criterion is that you only have to start allowing for transmission-line effects when the length is greater than 1/6 of the wavelength.
I was hoping that some kind soul was going to direct me straight to the answer, but looks like that ain’t gonna happen. I thought the increase in bass with depth of insertion would be a well-known phenomenon, but looks like I was wrong.
I only have one type of earbud to try, but I doubt if they are unique in this behaviour.
So I set to, and soon found myself studying tympanometry, a science I never knew existed until today.
To cut to the chase, the air trapped between the eardrum and phones diaphragm has a certain springiness, described as the acoustical impedance. The smaller the volume, the higher the impedance, and the better the coupling of low frequencies to the eardrum. The question now is why this doesn’t apply to middle & upper frequencies. Something to do with the mass of the air?
Is there an acoustics expert in the house?