[Ramtha604]

A few days ago I was experimenting with my Beyerdynamic DT 250/250. While listening to a few THX woofer tests on them I seemed to notice them going really low and felt very much like trying the 10 hz test tone on them. Until then I never was brave enough to go below 30 hz but this time I thought I just had to.

In another thread I posted that i heared a 10 hz tone. Of course this is wrong, I even knew myself that humans cannot hear tones below 20 hz, but I was so much in awe I just posted I did.

Well then, if I cannot hear a 10 hz tone, how can I hear something from the headphones when they only play a 10 hz tone? Well, from my point of view there are two possible versions of basically the same answer: I heared the membranes moving at 10 hz. I've come up with an analogy: The eye does not recognize movement that happens at less than 25 hz. But does that mean it cannot see that something changes when it changes at a frequency of 10 hz? Of course it does see that something changes at a frequency of 10 hz but it doesn't see it _as_ movement, just as change. The same way of thinking I can apply to the 10 hz tone. A membrane that vibrates at 10 hz does move air, even more than a membrane that vibrates at 100 hz. That the brain does not regnoice the sound/noise that the membrane makes when it moves at 10 hz as a tone does not mean that i cannot a hear a membrane that moves at 10 hz at all, does it? Well maybe it's true none the less. In that case my explaination would be that I was hearing the distortions that the headphones playing at 10 hz were of course producing. And of course these distortion will have some 10 hz-character to them. And that's what I heared.

Or is the whole story that we never hear tones, but only distortions and the brain interpretes the distortions as tones (so what we call distortions in headphones would be distorted distortions, so to say

).

Whatever, I'm sure someone can explain it all and then I and probably some people else here are gonna be another bit smarter.

 

[elnero]

I'm not really sure what you heard but you described like this "it sounded like a machinegun firing at 10 times per second (just "softer")"

A tone implies that it is pure without harmonics so what you heard wouldn't have characteristics of a 10Hz tone but could be distortion of some sort related to the driver at least trying to recreate the tone but, given how hard it would be to reproduce a 10Hz tone, I somehow doubt that as well .

I don't know enough to give you a definitive answer as to what you heard and why but my suspicion is that there is something completely different going on in your system when you play this tone. What were you using as a source and amp?

 

[Ramtha604]

i would _guess_ that to create distortions that show 10 hz characteristics the membrane had to move at 10 hz, not just try to.

signal path was 128 kbit mp3 -> herculess fortissimo II -> porta corda (26 volt wallwart) -> DT 250/250

 

[elnero]

My guess is it's actually the soundcard spazzing out. I tried to find a freq. response for that card but the Hercules site doesn't mention anything. I highly doubt that it does anything below 20Hz though so that's probably where the answer lies. I've had problems with my souncard reproducing high frequency tones. It just clicks, sounds like it might be a similar thing.

Edit: It is strongly recommended to convert your tones to wav's and burn them to a CD and use a real cdp to test with.

 

[Ramtha604]

i don't know if what I heared were just distortions coming from the struggling soundcard, but it kind of had too much "body" to sound much like classic distortions (like an increased noisefloor or the bassdistortions from severely underpowered drivers). you could be right about the soundcard, but I am still puzzled.

 

[chillysalsa]

Chances are you are hearing noise - harmonic distortion, and intermodulation distortion. Sub frequencies are very taxing on electronics, and the distrortion levels generally increase with lower frequencies - even for the very best equipment.

 

[Duncan]

Elnero, the problem with that theory ~ A CD is incapable of playing a 10hz note

I myself have heard a 23hz note on my CD1700s, and I agree with the phenomenon that ramtha604 mentioned, it sounded like a guttural growl, but very consistent...

The CD1700s laughed in the face of the V6 on that one

Cool

 

[Snow]

Is there somewhere on the Internet where you can download test tones?

Thanks, Snow

 

[gerG]

Snow, go to Trueaudio.com and download Truerta. It has a built in signal generator that will make sine waves at any frequency down to 10 hz.

Ramtha604, humans can indeed hear below 20 hz. That is just an average. I can hear a tones down to 16 hz, but they are falling away fast. 25 hz is about where my sensitivity starts falling off. I tried 10 hz on my DT250-250, but didn't actually hear a tone. What I got was the pressure sensation (guess I can't tell 10hz from DC) and a bit of extraneous noise from the diaphragms. I wasn't driving them very hard. LF signals also reveal themselves by masking and distorting higher frequency sounds, and by spawning higher frequency harmonics.

I first ran across the pressure sensation several years ago when a friend let me try out some early noise cancelling headphones. When I switched the control on, the left channel did what it was supposed to, but my right ear felt like I had just gone under water, and everything got choppy and muffled. Closer inspection showed that the right side had freaked out and the diaphragm was running wide open throttle at about 10 hz. Pretty cool, but not a good approach for noise control.


gerG

 

[jip]

Quote:

Originally posted by Duncan Elnero, the problem with that theory ~ A CD is incapable of playing a 10hz note

i'm curious, just quite _how_ is a cd incapable of playing 10Hz or any lower frequency? you mean cd players aren't normally capable, or are you trying to say redbook can't store a 10Hz tone? the latter makes no sense to me. and i made a cd with a 10Hz tone and could hear 10 'puts' per second.

 

[Tim D]

CD's IMO can go lower than 20hz..., the 20hz-20khz is just printed specs but the upper limit is pretty accurate. As far as limitations with DSP, I think that is more with the high frequencies which is limited by the sampling rate. I don't think low frequencies should be limited as far as PCM CD format, however it can possibly be limited by perhaps the analog output stage or amp stage with insufficient caps maybe and of course the roll off that may be in the transducers.

And I also hear tones below 20hz that aren't just distortion from either bought CD's with low test tones, or burned ones. It should be entirely feasible to burn a signal of lower cycles accurately(just think of stretching out a given sine signal)...its the highest ones that are limited (sampling resolution limits the ability to squeeze in the cycles). Wheter or not this low sub-bass signal is reproduced properly by the player, amp, and headphones, or heard by your ears is another matter.

What do sub-bass tones sound like? Certainly not like any machine guns or flapping of diapghrams against plastic...but quite simply how you would figure them to sound like...just extremely low bass tones until it becomes more of a sensation/feeling as it passes out of audibility.

 

[ServinginEcuador]

Using the Bass Mekanik's Quad Mazimus CD, you can playback notes from 10-100Hz in 1HZ increments of 5 seconds each. I tried using everything from 10-30Hz using some W1000s, CD3Ks, and Senn 600s, none produced anything but weird noise below about 25Hz, and nothing noticable as bass until closer to 32Hz.

I used to own a 600W amp in my car running (4) JL Audio 15" subs in a 15 cubic foot enclosure. I could play a note of 18Hz that would move everything in the car around, but was sub-audible to nearly everyone. It was noticable as sound to me, but barely. I doubt I could hear it now.

 

[setmenu]

I have a 'test' cd that has amongst others a 0-22k sweep.
And yes it is produced,I can watch a diaphragm just slowly
move up until ,well I guess 25 hertz.

I do hear 'tones' at that frequency but in reality like Ramptha604
I don,t really know what I am hearing.
It also varies from transducer to transducer, also only one
of my ears is able to detect the sounds.

What I hear varies between a distinct pulsing and modulating but
distinct tone,more subliminal than anything else but a tone nonetheless.
I have no doubt we can hear/detect very low frequency's as this
would have been a useful thing in past times.
But is it a case of the brain labeling an input with something near
to rather than an actual tone?

It has got me thinking, hearing a high[er] frequency sine-wave the
the impression is of a single constant tone but as with vision
the ear/brain can only differentiate between two impulse events
if there is sufficient time between them ,so HF or a frequency higher
than that threshold would appear constant.
So would I be right in thinking that LF tones under that threshold
would indeed be heard as pulsing rather than constant .
If so a correctly heard 10HZ would be a clean pulsating sound.
Perhaps I am stating the bloody obvious here, but how the brain
perceives a 'sound' at LF thresholds is interesting.

I do find my Stax good in respect to LF reproduction but obviously
one does not want to go turning em up at these frequency's[or any
other transducer for that matter] as diaphragm excursions are slow
but high and the 'stops' are reached quickly.

Setmenu

 

[elnero]

Quote:

Originally posted by Duncan Elnero, the problem with that theory ~ A CD is incapable of playing a 10hz note I myself have heard a 23hz note on my CD1700s, and I agree with the phenomenon that ramtha604 mentioned, it sounded like a guttural growl, but very consistent... The CD1700s laughed in the face of the V6 on that one Cool

There is no reason a CD can't play a 10Hz tone that I'm aware of. I think Tim D described it pretty well. Especially when he says low bass tones sound like just that, low bass tones until they become more of a sensation/feeling as they pass out of audiblity. We can sense low bass below audiblity through bone conduction but we can't actually "hear" it.

I have no idea of the limits of the CD1700's so it is quite possible that you heard a 23Hz tone, it's well within the audible range, but Ramtha's claim of hearing a 10Hz tone in my view is ridiculous, even taking into account Greg's statement of 20Hz-20KHz being an average, a 10Hz tone is just too damn low, especially given the description of what he heard.

 

[chillysalsa]

I've generated a bunch of tones down to 0.5 hz with Cooledit and burned them to CD. You can't hear them, but those woofers move like crazy. (For every drop in frequency by 1/2, the travel of the diaphram must increase by 4 I believe). I even made one that 'holds' the tone at the top of the last peak for a couple seconds - you can see the woofer stop at the top if its travel, and slowly fall back to rest position as the power reserve in my amp is depleted. Maybe this can be used to estimate the reserve supply of an amp by timing how long it takes?

I've found sub frequencies mixed into normal music have some benefits. They seem to improve the soundstage, and I think it has more to do with room interactions and harmonics. I haven't noticed as much of a benefit with headphones.