Low bass in your space? Are you sure?

[dragonfyr]

one more

InvestigatingStanding Waves1.pdf

[dragonfyr]

and one more from Sam Berkow that illustrates aspects of measurement concerns over the frequency spectrum

SoundRoomInteractions.pdf

[D-MAN]

Very cool. Thanks.

DM

[pauln]

https://myeporia.eporia.com/resources/company_38/techpaper107.pdf

"Small Room Acoustics De-Mythologized"

[WMcD]

Nope. I'm sticking to my guns.

What I wrote is correct. But please note the limitation of same frequency.

Smile.

Gil

[D-MAN]

Well, that's a fine thing! after we went to all that work!?

DM

[WMcD]

Well I expected to get some flack on the math but did not expect flack on the real effect.

I must apologize because the real world explanation is almost moronic.

Suppose you put a mono 60 Hz signal into two stereo speakers. Sit in the center. Plug one ear if you demand one sample going to your brain. You hear 60 Hz. The amplitude and phase of the signals at your ear are the same.

It is here easy to visualize that two identical sine waves add up to one bigger sine wave.

Now move off axis to the left. Use the left signal as a reference.

The signal from the right speaker has decreased in magnitude at your ear because you're more distant and the distance inverse square law applies. Up close loud, far away, less loud.

The signal from the right has also shifted in phase because the path length difference.

So what you have is the mixing at your ear of two sine wave of the same frequency but with different amplitudes and phase.

What do you hear? It is still 60 Hz. No overtones, no harmonics etc. Intermod? No. There is no intermod of identical frequencies.

By logical extension, a reflection from a wall can't do anything but mimic the right speaker. Yes amplitude and phase is going to be different than the original souces, and may indeed sum to a very low level. But there are no new frequencies.

I wanted to point out that there is some magic to the sine wave when two of the same frequency are summed. There is so much out there about harmonics and intermod that we fail to realize that this particular function can be summed without introducting new freqs.

Yes there can be filtering by delay. That is how digital filters work. Nonetheless, simple delay does not introduce new frequencies.

Gil

[DrWho]

The animation on that webpage that shows the standing wave also shows that the frequency remains the same...so like Gil said, all you got are amplitude changes due to phase and arrival time differences. The arrival time usually falls in the 20ms window which makes them "inaudible." I forget the study that showed that, but basically anything that arrives within 20ms of the original signal sounds like it's arriving at the same time. Anything greater and you get the smearing effect.

As far as room effects and all that go, they apply to all frequencies and I'm not sure how making the room smaller is inherently always going to have a different effect on the lower frequencies. Explain that and you've got yourself a case. But even if it did make a difference, the same difference that the room puts on your speakers would be the same difference as if the original instrument itself was playing in the room. If you want it to sound like some other hall or something, then make your room sound like that hall...

I also wanted to point out real quick like that you don't have to hear a complete cycle of a frequency for your ear to be able to detect it. In fact, you only need to hear it for a fraction of a second for it to be heard correctly (I wonder if this correlates to the 20ms smearing window). Usually, the low frequencies from any source material are lasting just as long as the high frequencies which means they are both experiencing the same magnitude of the room's influence on the sound. Of course the net phase result is different for each frequency, but the time arrivals are the same (between the high and low frequencies). The phase of the direct + indirect sound is dependant on the frequency itself...in other words, you can have both constructive and deconstructive interference for any frequency (low or high). Looking at the modal response of "small" rooms shows that this usually results in boosting the amplitude of the bass because the reflections tend to remain in phase (notice how the number of modes decreases with frequency and room size). Correctly treating these modes is just like treating the reflections at higher frequencies. In fact, it's exactly the same because it's all due to reflections.

Also, just because a sound wave hasn't completed a full cycle before it hits the wall doesn't mean that it's going to reflect any differently from a wave that has completed even many cycles. The wave just bounces off the wall and continues the wave in whatever the new direction is.

[sunnysal]

this thread has been interesting but in the end, IMHO, kind of wasted time.

room size has nothing to do with how low a note can be played in the room, proof? headphones can produce 20hz into your ear with almost no space to "propagate", another? cars...you get down into the low teens inside a car with no problem. 1 hz could be played in a phone booth...so room size has nothing to do with limiting bass response.

it is easy to get wrapped up in formulas, etc. and lose sight of what is in front of you. obviously bass reproduction is not limited by room size...a little knowledge can be a dangerous thing...tony

[sfogg]

"The arrival time usually falls in the 20ms window which makes them "inaudible." I forget the study that showed that, but basically anything that arrives within 20ms of the original signal sounds like it's arriving at the same time."

You are describing the Haas Precedent effect but have it a little wrong. What arrives within that 20ms window will be localized to the same direction as the direct sound. However it is not inaudible. If it causes amplitude changes with the direct sound that is audible.

For example the Allison effect is almost always within that 20ms window but the Allison effect is audible.

Shawn

[Erik Mandaville]

Tony:

"this thread has been interesting but in the end, IMHO, kind of wasted time.

room size has nothing to do with how low a note can be played in the room, proof? headphones can produce 20hz into your ear with almost no space to "propagate", another? cars...you get down into the low teens inside a car with no problem. 1 hz could be played in a phone booth...so room size has nothing to do with limiting bass response.

it is easy to get wrapped up in formulas, etc. and lose sight of what is in front of you. obviously bass reproduction is not limited by room size...a little knowledge can be a dangerous thing...tony"

Given the amount of time some have spent contributing, it would seem that a few people have found it a worthwhile subject for discussion -- and you have added your thoughts on the matter, as well. I agree with you on the headphone point, although I've been told that if I'm hearing notes with headphones I don't with the Klipschorns that something is wrong with my speakers, room, me, or all of the above.

Erik

[sunnysal]

erik, I did not mean to say that the discussion was totally without merit, just that in all its wanderings the thread had NEVER even strayed close to establishing that room size can limit low frequency reproduction, a lot of material was produced and none showed that 20hz could not be reproduced in a car or phone booth, etc. as was initially suggested. So I felt, and stated, the thread was kind of a waste, good intentioned, but utimately got no where. Part of the problem is our limited knowledge among board members, we know just enough to be dangerous to ourselves.

re: Headphones, they can accomplish amazing feats compared to speakers due to the fact that they do not have to contend with room effects and the need to move a LOT of air to reproduce music, you have not really "lived" until you have heard some high-end phones or ear speakers, go out and try to find a pair to audition, they are amazing. regards, tony

[Erik Mandaville]

Tony:

Headphones?! LOL! I listen to my Sennheiser 650s every weekday evening instead of watching TV.

Why am I laughing? Because of an eight-page-long thread which I started that deals with this very topic -- I called it "Into the deep with headphones." Here's what started a rather long-winded adventure on the Klipsch forum: I quote my initial post.

"I need/want a subwoofer!

As I've been doing each evening, I've just been listening to the Moth/KR2A3 combination with headphones, and am just astonished with the Sennheiser's bass response. I was listening to a Narada CD of harp music, and was particularly struck by one track with bass response so low down -- that sort of very low, earthy rumble that's almost more of a sensation than a musical note -- that I've never heard before on our main system. It may have been present, but just not at a level that made it nearly so much an integral part and foundation of the music. With phones, it was really neat to hear, and makes me think even more that there may be information on CDs that we are not getting nearly enough of. This isn't to say that the Klipschorns are not good bass performers. They are. It's that I have heard some very subterranian sounding stuff recently with the Sennheisers that just does not come through nearly as much as I now know I would like it to.

Erik"

and again,

Erik

[pauln]

I am amazed at the fundamental ignorance of some of my fellow beings concerning physical, physiological, phenomenological, and psychlogical realities concerning sound and music.

Some of these arguments sound like weighing a duck and a women to see if she floats (ergo to determine if she is a witch).

[dragonfyr]

----------------

On 6/7/2005 11:02:52 PM William F. Gil McDermott wrote:

Well I expected to get some flack on the math but did not expect flack on the real effect.

I must apologize because the real world explanation is almost moronic.

Suppose you put a mono 60 Hz signal into two stereo speakers. Sit in the center. Plug one ear if you demand one sample going to your brain. You hear 60 Hz. The amplitude and phase of the signals at your ear are the same.

It is here easy to visualize that two identical sine waves add up to one bigger sine wave.

Now move off axis to the left. Use the left signal as a reference.

The signal from the right speaker has decreased in magnitude at your ear because you're more distant and the distance inverse square law applies. Up close loud, far away, less loud.

The signal from the right has also shifted in phase because the path length difference.

So what you have is the mixing at your ear of two sine wave of the same frequency but with different amplitudes and phase.

What do you hear? It is still 60 Hz. No overtones, no harmonics etc. Intermod? No. There is no intermod of identical frequencies.

By logical extension, a reflection from a wall can't do anything but mimic the right speaker. Yes amplitude and phase is going to be different than the original souces, and may indeed sum to a very low level. But there are no new frequencies.

I wanted to point out that there is some magic to the sine wave when two of the same frequency are summed. There is so much out there about harmonics and intermod that we fail to realize that this particular function can be summed without introducting new freqs.

Yes there can be filtering by delay. That is how digital filters work. Nonetheless, simple delay does not introduce new frequencies.

Gil

----------------

Gil, with your condition of signals being the same frequency, I agree with your idealized math. But when we move into the later examples in the real world, where one might expect a frequency to be cancelled based on the ideal example, that is overly simplistic.

The reason is 'multi-fold'. Rather then the room exhibiting the very simple one factor example you first posited, the real world room exhibits a mix of a GREAT number of conditions that are 'not allowed' within your initial ideal model! For example, when you mention that your ideal reflection is not experienced as a complete cancellation, and that moving off center that you still hear the fundamental frequency, what you actually experience is a high order reflective environment with a commensurate high order number of signal paths and corresponding delay times - each having a distinct phase shift. So there is no way that the signal will disappear! Thus, the summation of the complex response is comb filtering, and not absolute cancellation! We are not experiencing your initial defined condition! The world has introduced a myriad additional list of factors not accounted for in your initial model!

First there is the masking effect, dependent upon the relative gain of each of the reflected signals...

Second and more importantly is the Haas effect - ranging from the inability to localize the sound to fusion dependent upon the separation in time of the reflected signals...

As you cannot ignore the psycho-acoustical effects of the instrument you are perceiving the effect with! Your ears!

And some have even suggested that all of this is a waste of time!! Lets take a look! Let's take a moment to step back and look at the process we are employing for a second!

Maybe! But ONLY IF you (erroneously) think that you can simply extrapolate complex reality from one isolated ideal classroom example! Does anyone really think that reality is not comprised of a myriad combination of that and so many other conditions!??

Any oversimplified model will fail to predict real world performance! And any ideal model that fails to account for the real (non-ideal) situation encountered in the real world is doomed to failure! The problem isn't the limited model, nor is it the complex nature of reality! It is that your expectations are out of line!

And I will complicate things just a bit more! All of the talk of reflections has thus far treated them as ideal! The examples assume that the exact same amount of energy incident upon a surface will be 100 percent reflected at the incident angle with complete coherence! Really!?!?! If only! Doesnt this statement strike you as a little unrealistic? But all of the assumptions are based upon this! Where did you get this perfect reflector? And are you doing this experiment in a vacuum? How have you accounted for absorption, diffusion, the medium of air, temperature, and the frequency dependence of all the assorted variables? I hope you dont think that they are linear and effect all frequencies equally!

So the problem here is that we are mixing overly simplified ideal models with the complexities of the real world with its many assorted variable that have not been accounted for! And what are valid limited models and concepts are still valid! But, the real world environment, with all of its additional real world variables contained within, simply defines a much more complex environment!!!!!

But does that mean that it is impossible to accurately model and predict acoustic behavior to a level that bears close correlation to reality? NO! But it does require powerful tools!

One of my frustrations here is that we vacillate between overly simplistic models that are modeled in an ideal environment and designed to illustrate a very simple concept. And then we are all to quick to suddenly jump to the overly complex real world environment where we quickly declare that the concepts are not valid because they do not account for all of the real world variables! And then many declare acoustical analysis a failure because the real world is a much too scary place.

And the choice is not betwen 'mathematical' models and reality! It is between ideal and real scenarios. And by definition we deal with limited, defined models. Now many of the models scale very well. Others are too limited. But to discard them all is to simply return to the waiting for lightning to strike so that we can obtain a source of fire for the campfire! And I don't have the patience to sit around with the Luddites who fear dialectic process of science and reason!

And this is where I get to insert my gripe about some of the common tools that we WISH were sufficient to address the environment!, as many persist in running about with only their RTAs, EQs, and SPL meters! Now the SPL meters and the RTAs are fine instruments! But they do limited things! They are not the Holy Grail of acoustical tools! And far too many try to make these, and other tools do far more then they are designed to do. They cannot separate the superimposed signals into their constituent component signals! If one is focusing on electronics, few would maintain that the VOM is a not wonderful tool! But does it tell you as much as an oscilloscope? Does it tell you the same information? Would anyone suggest ignoring the information that an oscilloscope can provide?

I think the Chicken Little reaction to saying we have learned nothing is premature! We have learned allot! And recognizing the limits of presently used tools is critical!

But instead of simply declaring the task impossible, why are so few asking how or what can be done to move beyond these limitations!

Now I know that many of you have gotten in to the hobby as precisely that! A HOBBY! You did not get into this so that you could return to school and get a masters (nor even a bachelors degree!)in physics or acoustics!

But the fact is, the discipline has advanced more in the past 40 years then in the previous 2000 years! And it is still evolving at an incredible rate!

So the choice belongs to you folks out there! You can declare the subject too complex and return to debating, no- arguing, over which cables will solve the problem

OR, we can start exploring the new developments in acoustics that can account for the behavior mentioned! But the solutions are inherently complex. But basic principles can STILL be illustrated by simplified examples! AS LONG AS WE REMEMBER THE INHERANT LIMITATIONS OF THE IDEAL EXAMPLES AND UNDERSTAND THEIR LIMITATIONS WITH REGARDS TO THE REAL WORLD!

And while the basic frequency domain view is still valid, it is akin to the classical physics view that existed before the advent of quantum! And with that advent, there was required a fundamental shift in the paradigm (model). And in acoustics, the change that is equivalent to the quantum world is the pre-eminence of the world of the time domain!

So I guess the big question is, who is prepared to begin to explore and to understand it (and the weird characteristics that will challenge many heretofore held beliefs!) and who would rather ignore it and be doomed to relying on fundamentally flawed models that do not adequately account for the real world. The choice is yours. But I would ask a favor from those that choose to stay behind: please be content to ignore the new ideas around you and please dont simply keep jump up to yell burn the witch when these new ideas are presented!

We are so close to crossing that bridge, but we need to get a few more acknowledging that the bridge exists, and that there is something on the other side!

[sunnysal]

"strange women lying around in ponds distributing swords is no basis for a system of government, supreme executive power derives from a mandate from the masses, not from some farsical aquatic ceremony"

nuf'said?

tony

btw nice post dragon.

[D-MAN]

I have a supposition that a room of any given size would, like the speaker enclosure, behave just like one too, with the exception that the room has no exit for the soundwaves. Essentially we sit inside of an enclosure and listen to a smaller enclosure. Since the room is a sealed enclosure itself, the room must also have a low frequency resonance and also presumably, a low frequency Fc.

That is, every room has its initial resonant low frequency based on its internal volume and dimensions and also would have an inherent low frequency failure point (the point in freq. where it will not propagate without reflections and is therefore a distortion of the original frequency). The larger the space, the lower the Fz.

We are all aware that for a given listening space, there is an SPL level at which the sound turns into flying crap due to "room overload" or exceeding the absorbtion ability of the room. The higher the reflectivity of the room, the lower the SPL required to reach that point, etc. I suspect that there is also a low frequency point determined by the room dimensions below which the sound is distorted by intermixing different soundpaths from various reflection points.

The SPL it takes to capacitate the proposed room Fz resonance is another thing, but I haven't found anything that would contradict this theory.

The earphone thing: Yes, direct to ear removes ALL of the considerations of space. The introduction of space between the speaker and your ear IN A ROOM is the problem with bass. The ROOM is the problem with long waveform propagation using loudspeakers.

One-note-bass car audio is an example of Fz resonance in a compact space. Or is it that the subwoofer(s) are only capable of one-note? I have my suspicions.

DM

[sunnysal]

my room is anything but a sealed enclosure...my "little" (can I call k-horns little? lol) cabinet radiates into an irregular, relatively open space, so IMHO any attempts to draws paralells between what goes on inside a cab and inside a room are stretching it more than a little again IMHO. lastly, forget one note boom cars, forget cars altogether...I do not really believe you mean to suggest that 20hz cannot be reproduced and heard in a phone booth size room, much less in an ear size enclosure, that is just plain wrong. tony

[sfogg]

", like the speaker enclosure, behave just like one too, with the exception that the room has no exit for the soundwaves."

So when you put on bass and walk outside of your room you can't hear it?

I highly doubt that.

Most rooms are *very* leaky. Typical single stud drywalls let a very large amount of bass through them. Quite likely more bass 'escapes' the room then is reflected by the walls in a normal room.

My room is built on staggered studs (different studs on interior walls then the exterior drywall to reduce physical transmission) with double layers of drywall on the inside glued and screwed together. The walls are not connected to the house at all except on the poured concert basement floor. Ceiling is its own set of studs completely unconnected to the rest of the house with double drywall on it also glued and screwed. My door is *heavy* with Zero products acoustics seals and a hydraulic closer keeping it sealed against them.

Even with all this bass still gets out.

"The ROOM is the problem with long waveform propagation using loudspeakers."

The room is a problem.... period.

It isn't limited to bass. The bass range presents some special problems but the room influences all playback. Forget the length of the room. Look at the small path length difference from the direct sound and the first reflection point to the listener. That may be either from the floor or the side walls depending upon the speaker layout. Even in a 1000' long room that reflection will screw things up. The distance from the floor to the woofer will determine where the 'Allison Effect' kicks in which will alter the speakers power response pretty much throughout the room even without any other reflections.

Shawn

[D-MAN]

Agreed.

But I think that rooms tend to leak bass mostly due to the transfer of vibration, not through air leaks (hopefully). But the intent is that they are sealed to the "free" movement of air. The transfer of sound due to sympathetic vibration is another thing.

Granted some sound-energy is lost this way. But the highest percentage of sound energy is reflected around the interior until it either disapates and/or is absorbed.

I think that a solid (brick, concrete,etc.) surfaced room definitely sounds the best (with adequate absorption). Unfortunately, I don't have one.

DM