FI SSD12 frequency response

[Immacomputer 10+ year member]

Bottom line, I can't tell what the difference in experience is between 15hz and 35hz. To me, I perceive it as hearing. And yes, by hearing it seems like it's coming from my ears but I know that it's not. The trip is what you make of it and that's how I take it. I know the difference between taste and touch and feeling and hearing. What I'm saying is that I'm experiencing the "hearing" sense when I play any frequency below 20hz. I do feel it as well, just as I feel higher bass and midbass. Call it what you will, but I will call it hearing through a medium that is not my ears.

 

[newusername 10+ year member]

Bit of a weird thread!

First, you must eliminate your ears if you're trying to hear flat frequency response. Our ears do not hear all frequencies equally, and have equal loudness contours associated with them. Basically, your ears have their own frequency response curves: we are most sensitive to sound in the frequencies our speech normally include, and are especially insensitive to sound at low frequencies. Worst of all, our ears/brain don't have good memory and aren't very reliable. Nick already nailed another important point: you simply won't have flat response in your vehicle without some equalization.

As for what hearing is, hearing is the perception of a sound wave. Pretty simple, if you ask me. It is true that the commonly acknowledged bandwidth of human hearing is 20 Hz - 20 kHz, but this is only a very general model. In fact, most humans have a smaller range over which they are capable of hearing, particularly on the top end where they may not be able to hear above ~14-15 kHz. Likewise, there are some whose hearing exceeds the "accepted" bandwidth on either end.

At frequencies below 20 Hz, sensitivity is usually extremely diminished, though many can hear down to 17-18 Hz. Can people hear at frequencies much lower than 17-18 Hz? You bet they can. Of course, it depends on many things, including the amplitude of the signal and your own sensitivity. A lot of people who say they have heard sound below 20 Hz haven't actually done so, but have detected resonances in the vehicle or harmonics from the driver; harmonic components are almost certain to be there, considering the high degree of non-linearity at low frequencies. The 1st harmonic of a 12 Hz signal is 24 Hz; 2nd harmonic is 36 Hz; 3rd harmonic is 48 Hz, and so on. Any harmonic with a reasonable amplitude will be quite audible.

By the way, "sub-sonic" has nothing to do with it. Sub-sonic refers to the speed of sound, which does not vary with frequency. The speed of sound is determined by some very well understood properties of the material through which the sound wave passes; in classical mechanics, it is the density and coefficient of stiffness of the material. Frequency, though, has nothing to do with it. Low frequency sound waves travel at the same speed as high frequency sound waves (although the rate of absorption of the medium is different). It doesn't matter how long the wavelength is: the speed of sound will remain the same as long as the properties of the medium are the same.

The correct term for sound below 20 Hz is "infrasonic". Unfortunately, the entire audio industry has adopted the wrong term and it is hard to get people to change.

edit: By the way, when hearing, the medium it passes through is still the air. Hearing is just a few little bones in your ear vibrating at a certain frequency and amplitude, which are converted from an analog sense to a digital perception by your brain.

 

[NDMstang65 10+ year member]

Son of a ***** it is infrasonic, sorry about that. But how could it not have anything to deal with the subsonic speed of sound? It's totally dependent on the density of the atmosphere in which a given wave form is in that you are considering...

Whether it be motor oil, water, air, salt water, milk shake, ice cube, or even a car. Whatever it may be the speed and amplitude and frequency for a given scenario will change..

If the wavelength is so long, and travels so slowly that you simply can't hear it...

Put a elephant in the air on dry land in the middle of a desert and play a 12Hz tone at 120dB at however many feet 1 wavelength of 12Hz is and buzz his brain a little...

Put that same elephant at the 1 wave length distance away from the source in water and play at the same amplitude and you'll kill it...

But which one did it get there faster in? 12Hz is 12Hz, but there's a big difference in water and air...

The speed changes...it just depends on the atmosphere in which it is considered.

Just the way I look at it...I could be mistaken, but I could have sworn the speed changes.

 

[NDMstang65 10+ year member]

Sealed should yield the flattest response with respect to +/-3dB response...you should be around in that ballpark...

However you will still have a peak at resonance in your vehicle...

 

[Immacomputer 10+ year member]

Nick already nailed another important point: you simply won't have flat response in your vehicle without some equalization.

For the bass range? I'm easily flat within +3dB from 20 to 70hz without any EQ and with exception to 22hz in which I could bring that peak down with a little more polyfil. There could be some sharp nulls that I didn't get since I only used 1hz increments but the response was very flat compared to the other enclosures I have had in the car.

If the wavelength is so long, and travels so slowly that you simply can't hear it...

I think you are having a problem with understanding what pressure waves really are. Full waves do not need to develop in order for sound to be hear. When you imagine a sine wave, don't think of it as a line that comes out of a driver but as a bunch of air molecules closely bunched together from the start of the waveform (the driver) to the end of 1 cycle (distance will be frequency dependent obviously). Now think of how a sine wave looks. That wavy shape is not a physical description of the sound wave but rather a velocity over distance graph. Each molecule of air is going to be moving with some displacement when there is a sound. Those molecules are not going to shoot from the driver to the end of the wave but they will change their velocities from positive to negative how many times per second that corresponds to the given frequency. If a full wave is developed with no reflections, the half way point will have air molecules that are not moving and basically sit still. At 1/4 wavelength distances, the air molecules there will be highly excited and will alter their velocities but they will have a peak velocity that will be higher than any other portion of the wave.

Thinking that way, it's easy to understand why you can still hear frequencies when you're closer than a full wavelength away from the speaker. Even though the wave has not fully developed, the air molecules are still stimulated right from the driver and have some velocity component to it. If the air molecules are stimulated, then your body can be stimulated and you can hear that sound, no matter how close you are (with exception to being right at 1/2 and full sine wave locations given a completely echo free chamber).

 

[NDMstang65 10+ year member]

For the bass range? I'm easily flat within +3dB from 20 to 70hz without any EQ and with exception to 22hz in which I could bring that peak down with a little more polyfil. There could be some sharp nulls that I didn't get since I only used 1hz increments but the response was very flat compared to the other enclosures I have had in the car.


I think you are having a problem with understanding what pressure waves really are. Full waves do not need to develop in order for sound to be hear. When you imagine a sine wave, don't think of it as a line that comes out of a driver but as a bunch of air molecules closely bunched together from the start of the waveform (the driver) to the end of 1 cycle (distance will be frequency dependent obviously). Now think of how a sine wave looks. That wavy shape is not a physical description of the sound wave but rather a velocity over distance graph. Each molecule of air is going to be moving with some displacement when there is a sound. Those molecules are not going to shoot from the driver to the end of the wave but they will change their velocities from positive to negative how many times per second that corresponds to the given frequency. If a full wave is developed with no reflections, the half way point will have air molecules that are not moving and basically sit still. At 1/4 wavelength distances, the air molecules there will be highly excited and will alter their velocities but they will have a peak velocity that will be higher than any other portion of the wave.

Thinking that way, it's easy to understand why you can still hear frequencies when you're closer than a full wavelength away from the speaker. Even though the wave has not fully developed, the air molecules are still stimulated right from the driver and have some velocity component to it. If the air molecules are stimulated, then your body can be stimulated and you can hear that sound, no matter how close you are (with exception to being right at 1/2 and full sine wave locations given a completely echo free chamber).

I fully understand how wavelengths work, but if your ears can not detect it and make it to an audible 'analog' signal then the wavelengths themselves are too long for them to be processed into sound that you are actually hearing, not perceiving. Again 'thinking' when you can hear when you can't. Hearing is hearing, not perceiving in different ways other than your ears. If you heard a ultra low subsonic frequency then you would 'hear' your bowls relieve themselves at 12Hz at ~118-122dBa...but your not actually hearing it. Your experiencing your bowls relieving themselves and having a very unpleasant mess...

Most of the larger anechoic chambers are pretty much useless at anything below 100Hz...there are very very very few that are large enough to be able to do in the lower frequency range that we're interested in in this conversation...

Ultra low frequencies are not dissected in a chamber, they are tested in a plain open field for the most part...to stay away from echo's and refraction/reflections.

 

[Immacomputer 10+ year member]

Hearing is hearing, not perceiving in different ways other than your ears.

Have you ever heard of a "sneaky path" when referred to electronics? It's basically radiated noise that is picked up by a receptor and the processor will process that noise and the true signal that is received. This sneaky path can cause all sorts of issues in data communication. Sneaky paths usually will cause problems only in very low SNR situations. The sneaky path signal can become very high amplitude and might be used in the processor. The same thing can happen in our brain. A sneaky path can be implemented to supplement the low SNRs that the ears are receiving. If the sneaky path is similar to the applied signal, those signals can be joined and thus your brain tells you that you're hearing this frequency because the signal is still present at the ears.

Think about this too: Saying humans can't hear anything below 20hz is like saying your sub's low pass crossover filter does not allow ANY frequencies above the cut off point. That is just not true at all and it can never be true based on the laws of physics as we know them.

 

[SHOemup233 10+ year member]

Think about this too: Saying humans can't hear anything below 20hz is like saying your sub's low pass crossover filter does not allow ANY frequencies above the cut off point. That is just not true at all and it can never be true based on the laws of physics as we know them.

It is not like saying that at all. You guys keep comparing ears and the human body to other things, when it doesn't apply.

I understand that you feel that hearing is more than just your ears. That is your opinion. It is known that the ears alone can only process sound down to 20 hz, maybe lower for some people. Beyond that it is not your ears "hearing," it is your body feeling the sound. Immacomputer disagrees. I accept that. Whatever.

 

[NDMstang65 10+ year member]

Have you ever heard of a "sneaky path" when referred to electronics? It's basically radiated noise that is picked up by a receptor and the processor will process that noise and the true signal that is received. This sneaky path can cause all sorts of issues in data communication. Sneaky paths usually will cause problems only in very low SNR situations. The sneaky path signal can become very high amplitude and might be used in the processor. The same thing can happen in our brain. A sneaky path can be implemented to supplement the low SNRs that the ears are receiving. If the sneaky path is similar to the applied signal, those signals can be joined and thus your brain tells you that you're hearing this frequency because the signal is still present at the ears.

Think about this too: Saying humans can't hear anything below 20hz is like saying your sub's low pass crossover filter does not allow ANY frequencies above the cut off point. That is just not true at all and it can never be true based on the laws of physics as we know them.

No it's not like a crossover, your ears simply do not roll off you do not have electrolytics built into your brain to filter the sound, they stop turning waves of pressure into an analog response known as noise at a certain frequency. Most people it's in the 20Hz range, some are lower to an extent.

http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/earsens.html

Again, you can't hear it. Not with your ears at least..unless you are some weird breed of human that is missing a few parts that is illustrated in there or has a few extra ones like those of the elephant then you are full of ****.

For the last time, you can perceive it in may different ways. But it is not with your ears and you can NOT hear it.