Wanted: Proof of multiple subs and sub EQ

[Ethan Winer]

Glad to! I have nothing to hide. It's too big to hide I tell ya'.

 

[Thomas savage]

Glad to! I have nothing to hide. It's too big to hide I tell ya'.

Now we know what the cats for...

 

[AJ Soundfield]

On your other assertion, that room treatment is more effective over a range of room locations than "active cancellation", I partially agree. No modification of the exciting source signal can remove a deep null, for example. Doing so without room treatment requires intelligent physical placement of multiple sources as well as DSP techniques.

Possibly for less $$, with much higher output/headroom, lower distortion, no gargantuan pillows eating up room space, etc, etc.
Hmmm, let's see now...

 

[NorthSky]

I also want to learn more from Nyal. I'll PM him and give him this thread's link.

I first PMed Nyal on March 22, 2016 (just over two weeks ago) to make him aware of this new science audio review site. I'm sure Nyal is a very busy man.
Today I PMed him again and with this thread's direct link, plus the crucial point (Wayne's post) @ where he/we asked ourselves the science behind multiple subwoofers @ different room's locations being able to reduce modal ringing. Is it truly possible and where are the measurements and graphs to show the possibility with certitude.

I am much interested on this, and first without using any EQ; just judicious multiple subwoofer's placement.
...Then with EQ to possibly further the modal ringing's reduction in that room (any room).
_______

If Alfred (Einstein) was still alive today, I would PM him too. ...But Nyal should do too.

 

[NorthSky]

Bumpit

• http://www.acousticfrontiers.com/20...ow-to-use-parametric-eq-to-flatten-your-html/

"The results of using multiple subs can be spectacular – near flat frequency response, little modal ringing and low seat-to-seat bass quality variability in multi-seat theaters."

• http://www.acousticfrontiers.com/20...improve-sound-quality-part-2-room-modes-html/

"The effect of a subwoofer on the level of a room mode depends upon where you put the subwoofer. If you put it in the center of the room at the null there would be no energy coupling between the subwoofer and the mode. The mode would not be excited and there would be no measureable peak in the frequency response or ringing in the time domain.

The other way to achieve the same effect is to use two subwoofers, each of which is positioned in a lobe of different acoustic polarity. This means that the positive sound wave created by the subwoofer in the left, positive lobe is met by a sound wave of equal level but negative polarity created by the subwoofer in the other lobe. If you have two sound waves that are identical in frequency and level but the polarities are opposite then there will be perfect cancellation. This means that there will again not be any measurable frequency response peak or time domain ringing.

There is so much that can be achieved by listening to a system to identify a sound quality issue, using measurements to find the cause and then using appropriate solutions. In this case I hope you can see how subwoofers can be used to effectively solve some room mode related problems."
________

♦ The first link above (Nyal's blog); Ethan, Wayne...care to comment? ...A subject that we we're all interested in.

 

[h.g.]

Great. Now apply that to the topic and question at hand and provide the answer so that we know what you mean by the word science. As I mentioned, unless you are an acoustic researcher, I like to see references to proper research in whatever you state.

What is missing from my replies in this thread? Why don't I have to give references where appropriate? Surely someone who works in the field is likely to provide clearer references? In this case there is no need for references because the physics/science of what is going on is easy to understand (see my post #127) even if you do not understand what a frequency response represents and it's relationship to the transient response and hence, presumably, to whatever is understood by "ringing". Is the concept of work perhaps an issue?

My forum and my rules? What rules?

A good question and one quite a few others are asking elsewhere.

You repeatedly criticized Ethan for not knowing the acoustic science involved in this topic.

Ethan stated he did not want to know the science, did not know the maths and just wanted a particular form of plot but not the conventional one which was provided by several people. No questions would seem to remain about whether he does or does not know the science. I am not sure he would dispute it although now he has degenerated to the level of banging on about ***** size we are unlikely to know.

I am giving you the full stage to school us on how it should be done according to your point of view of science.

Science is independent of a point of view. It is a body of tested knowledge that predicts the outcome of experiments as explained to you at school, in the wikipedia article referred to above and countless other articles.

I and some others have already answered the substance of Ethan's questions which is what is fascinating about this thread. Why can't simple school level science (which was presumably once understood?) break through the audiophile barriers of arrogance and ignorance. Despite some significant poking by myself neither you nor Ethan began to question what you believed by asking the simple question "why" that enabled you to work out what was going on as a child. Interesting stuff.

If you can't or unable to do so then I like to understand the motivation for the harsh criticism you have put forward.

There is no harsh criticism. Neither Ethan nor yourself think like an engineer or scientist. This is a simple neutral fact not a criticism. A criticism, though not a harsh one, would be how you reacted when you were poked with information that indicated you were wrong. The response of someone with a scientific interest would be to ask why rather than claim to have knowledge or make up stuff in the hope it fits.

The poking rather than being nice and sweet served as a small barrier to help check the interest was genuine, had it come, rather than politeness. Are you ready to be teased?

To repeat what I have stated before, my initial interest was in somewhere to possibly publish articles written for a home audio audience. It soon became clear that this is yet another audiophile forum rather than one with an interest in home audio in the way it used to exist as a technical hobby in the 70s with Wireless World, ETI and the like before the audiophile thing kicked off in the mainstream. No problem, it is what it is. While establishing this it became clear that some people such as yourself and Ethan had a rather odd view of science compared to those of us that work with it as part of the day job. This is interesting and again not a criticism. There is no reason you should reason like me and it would be a boring world if everybody did.

 

[amirm]

There is no harsh criticism. Neither Ethan nor yourself think like an engineer or scientist.

This is the third opportunity I am giving you to show us what thinking like "engineer or scientist" means. Because all I am seeing from you is bickering, not contributing in any manner consistent with those terms. You are spending considerable amount of time fighting with words with nary a technical contribution.

No problem, it is what it is. While establishing this it became clear that some people such as yourself and Ethan had a rather odd view of science compared to those of us that work with it as part of the day job.

So far that day job seems to be being argumentative on forums and unkind to boot. But by all means, point to what your work is in acoustic science/signal processing. Hopefully it won't take three tries and empty hands at the end with this request like the above.

 

[NorthSky]

Did you guys watch Star Wars: The Force Awakens recently?
@ the opening, after the crawl lettering, there is a huge spaceship crossing the silhouette of a planet in the background (Ice Planet?).
The spaceship's nose is pointed, like an arrow, and as it crosses the screen, you can hear (in space) its huge engines propelling it.
The low frequencies are unmistakable. That ship (Star Destroyer?) doesn't use the latest technologies with a silent engine drive, even flying very slow.
* I'm using two subs, equalized and both in phase. But it's a fart compared to say eighteen large subs that can go down to 10Hz (The Force Awakens has 13Hz content).

If you can get that low, and with high pressure decibels, not only your body should ring along with your couch, but the entire house too?
Or you can reduce the ringing by attaching a seat belt to anything that can move. ...With a two-tons rock attached to each object, including you. ...Way of speech, to make sure low frequencies are not moving many objects in your home.

You audio scientist people; do you measure for stuff like that...with ten to twenty subs (18 to 24" drivers in each), and with the volume control @ reference master level (140dB+ on peaks)? ...While wearing protective ear devices. ...Do you have microphones that can handle the job?
Also, do you measure similarly @ major movie theaters like IMAX? ...Or other state-of-the-art equipped Dolby Vision cinema theaters?
And if you do can you see any ringing from the graphs calculated by the mic(s) in that theater room?

Last, can we feel what cannot be seen on a graph? ...And not feel what can be seen?

Ok, let's take a room of a normal size here @ home. The laws of audio, of acoustics; do they apply/translate to all room's sizes equally?

I'm totally ignorant, I'm just asking few questions in order to push my knowledge further enough in real-life applications, home and cinema venues.

Say you have a 100-members orchestra playing in a top acoustically treated hall from Vienna. ...With the big drums in the right back.
And another non-treated hall. What differences can we expect in modal ringings?

Now, are the laws of physics applied equally to smaller rooms where you watch Star Wars: The Force Awakens with one, two or more subs?

This is free, you can ignore everything you've just read, and you can also start a discussion.
I'm ignorant, but interested in the science of audio physics.

 

[Thomas savage]

Space is a vacuum so ther should be no noise from the star ship..

 

[NorthSky]

You are right Thomas; in space sounds are invisible. ...But in movies with space scenes they don't follow the rules.

 

[Purité Audio]

Well it would be a very quiet film wouldn't it.
Keith

 

[NorthSky]

Let's take another example instead; like "Twister" the movie, on planet Earth. I've read somewhere that the sounds of a big twister, up-close-and-personal is tremendous. Like a gun shot or a grenade exploding @ ten inches from your ears, and echoing for a long long time. ...The force is so powerful that it can lift large semi trailer trucks and even houses up into the air. It's like a blasting wind of very high decibels and lashing @ all the bones in your body.
With that being more real than sci-fi flicks, how are the modal ringings behaving?

 

[h.g.]

This is the third opportunity I am giving you to show us what thinking like "engineer or scientist" means.

And for the third time you will get the same answer that it is already in the thread, for example, #127. Most people and particularly those with a scientific interest when they see a loop like this might go hmmm... perhaps I need to check I haven't got hold of the wrong end of the stick. Audiophiles of course have much more confidence. But don't worry three times is enough for me.

Is the problem with the science provided that it is simple school stuff that everyone knows without any references to status conferring sources such as people with impressive credentials or recognized technical publications. The science at school explaining how things worked and being able to predict answers for exam questions really was science. Recipes about how to setup multiple subwoofers is useful stuff but it is not science.

 

[Thomas savage]

You are right Thomas; in space sounds are invisible. ...But in movies with space scenes they don't follow the rules.

Wel Bob when ther designed the star cruiser I reckon they did not worry about how loud it was as its irrelevant in space but little did they know films were going to be made...

 

[Thomas savage]

And for the third time you will get the same answer that it is already in the thread, for example, #127. Most people and particularly those with a scientific interest when they see a loop like this might go hmmm... perhaps I need to check I haven't got hold of the wrong end of the stick. Audiophiles of course have much more confidence. But don't worry three times is enough for me.

Is the problem with the science provided that it is simple school stuff that everyone knows without any references to status conferring sources such as people with impressive credentials or recognized technical publications. The science at school explaining how things worked and being able to predict answers for exam questions really was science. Recipes about how to setup multiple subwoofers is useful stuff but it is not science.

 

[NorthSky]

And for the third time you will get the same answer that it is already in the thread, for example, #127. Most people and particularly those with a scientific interest when they see a loop like this might go hmmm... perhaps I need to check I haven't got hold of the wrong end of the stick. Audiophiles of course have much more confidence. But don't worry three times is enough for me.

Is the problem with the science provided that it is simple school stuff that everyone knows without any references to status conferring sources such as people with impressive credentials or recognized technical publications. The science at school explaining how things worked and being able to predict answers for exam questions really was science. Recipes about how to setup multiple subwoofers is useful stuff but it is not science.

{Ethan} "I can't for the life of me imagine that either can reduce ringing even half as much as a bunch of bass traps!" {End}

{#127=h.g}"Why not? You must have some familiarity with active noise cancellation and how effective it is at low frequencies. Passive devices at low frequencies are rarely viable because of the size.

The physics is simple and works just like timing the pushing or pulling of a child on a swing to slow them down rather than speed them up. When the subwoofer is surrounded by positive pressure it moves inwards to reduce the sound and when surrounded by negative pressure it moves outwards to boost it. From school physics recall that work is the product of force and the distance moved in the direction of the force and so by moving in the opposite direction of the force work is extracted. It removes the energy in the sound far more effectively at low frequencies than squeezing the relatively slow moving air through small spaces to use the product of viscosity and velocity gradients to dissipate the work as heat. Note the velocity gradients are relatively small at low frequencies."{End}

Some physic laws apply.

 

[NorthSky]

Wel Bob when ther designed the star cruiser I reckon they did not worry about how loud it was as its irrelevant in space but little did they know films were going to be made...

Tom, what would be one of your reference films for well balanced bass?

 

[Ethan Winer]

Ethan stated he did not want to know the science

I said nothing of the sort. I have a very good grasp of the principles even if I never got up to speed on the math.

And I certainly agree with Amir that your contribution to this thread has been all insults and no substance. Your Post #127 didn't even address the core question of my OP which was very clear: whether multiple subs can reduce ringing (not improve the response) and if so by how much. Your mention of active noise cancellation was therefore irrelevant.

--Ethan

 

[amirm]

And for the third time you will get the same answer that it is already in the thread, for example, #127.

OK, this is post #127:

Why not? You must have some familiarity with active noise cancellation and how effective it is at low frequencies. Passive devices at low frequencies are rarely viable because of the size.

As Ethan mentioned, that has no relevance to this topic. Assuming you mean active noise cancelling headphones, they have a microphone which "listens" to outside noise and generates an inverse waveform which is then used to cancel the external noise to varying degree. No such microphone exists when you use multiple-subs in your room. The subs cancel room modes on an entirely different principle. If a measurement mic is used to better optimize the location of each sub, it is only used during the measurement phase. It is never used to alter the sound that goes into each sub.

The physics is simple and works just like timing the pushing or pulling of a child on a swing to slow them down rather than speed them up. When the subwoofer is surrounded by positive pressure it moves inwards to reduce the sound and when surrounded by negative pressure it moves outwards to boost it. From school physics recall that work is the product of force and the distance moved in the direction of the force and so by moving in the opposite direction of the force work is extracted. It removes the energy in the sound far more effectively at low frequencies than squeezing the relatively slow moving air through small spaces to use the product of viscosity and velocity gradients to dissipate the work as heat. Note the velocity gradients are relatively small at low frequencies.

Sorry but this is lay logic and completely incorrect. Multiple subs work by being used in inverse polarity of each other (acoustically but not electrically although there is a version of that too).

This is what happens with a single sub:

The sub is on the left wall. Follow the line and see what happens when it hits the wall on the right. The wave reverses and perfectly so at certainly frequencies proportional to the room dimension. This inverted wave then comes back and either boosts or cancels the incoming waves using the principle of superposition (vector sum).

Before I get into multiple-subs, note a simple solution visible in that crutchfield graphics. Put yourself somewhere other than the null and you avoid that specific problem. This is why optimizing the location of subs and your seating position is a powerful technique that costs nothing but time.

Now, imagine what happens in words when we add a second sub and put it on the opposing wall. That sub's output is out of phase with the reflection of the other one. It starts out with a positive wave, not negative (the wall inverted the first sub's output). Borrowing a graphic form Dr. Toole's CEDIA presentation, we see this in action:

As you see in the top, in the one subwoofer example we had a null smack in the middle of the room at that frequency. The addition of the second sub in the middle cancelled that null because as I explained, its waveform is out of phase at the wall with the first one.

Another solution is the third instance where you put the sub where the null would have been. By definition then you no longer have a null there because the sub is there producing energy. That, combined with above phenomenon, give us two of the optimal solutions in a rectangular room: http://www.audiosciencereview.com/forum/index.php?threads/subwoofer-low-frequency-optimization.15/

Note that none of the subs are messing with each other's diaphragm as you seem to be saying. They still produce the sound they are told to produce. It is how they combine in the room that provides the magic.

This is physics of sound and simple principle of superposition at work. Stuff you are saying is some lay assumption of how it might work without actually studying it.

 

[h.g.]

As Ethan mentioned, that has no relevance to this topic. Assuming you mean active noise cancelling headphones,

No I meant what I said and provided a link to the manual of a subwoofer being used as an active absorber. I am curious what you think the device does if not what is says on the tin?

Sorry but this is lay logic and completely incorrect.

But you cannot refute any of it by saying this is wrong because... and that is wrong because... This doesn't ring any alarm bells for you or prompt a bit of interest in why you might be having these difficulties? Perhaps, banish the thought, to ask a question why?

The science stuff you learnt at school really does hold. Work really is the product of force and the direction moved in the direction of the force or more commonly in acoustics, the product of pressure (force/area) and velocity normal to a surface (rate of distance moved in the direction of the force). I don't know whether it is funny or slightly disturbing that you consider this lay stuff to be completely incorrect with such vehemence. I probably ought to tone down the teasing despite the paragraph at the top of the page because I don't think you are having fun in the way that I am.

Note that none of the subs are messing with each other's diaphragm as you seem to be saying. They still produce the sound they are told to produce. It is how they combine in the room that provides the magic.

I am curious about how you think mechanical energy is transferred from the speaker cone to the air in the form of sound if you consider the lay stuff be completely incorrect. Or is this irrelevant because you know the principle of superposition. Does this principle apply to everything pressure, particle velocity, sound intensity,...? Consider a dipole with sound radiating on both sides. Does superposition mean that it would radiate twice as much power into the room as a monopole with the same cone motion? If not, why not?

Stuff you are saying is some lay assumption of how it might work without actually studying it.

Where do you think these lay assumptions are coming from?