DIY Room Accoustics for Home-Theatre

[sdurani]

Toole and THX recommendation is for placing 2 sub-woofers and not 1 sub-woofer..

You miss the point: they both recommend placement at null locations (to cancel room modes), NOT inbetween null locations (as you recommend). ALL of Todd Welti's recommendations, irrespective of number of subs, are at null locations as well (to cancel room modes), never inbetween nulls.

 

[shelley]

Really..did i miss a point..??

You are completely lost my friend..

======================
While intelligent people can often simplify the complex, a fool is more likely to complicate the simple.
Gerald W. Grumet

 

[sdurani]

Really..did i miss a point..??

Yes, and a simple one at that: when it comes to using subs for mode cancelling, recommendations (even from the experts you cite) are for placement in nulls, not inbetween nulls.

I can't put it any simpler than that. By comparison, you're unnecessarily complicating things when they don't need to be.

While intelligent people can often simplify the complex, a fool is more likely to complicate the simple.
Gerald W. Grumet

 

[manoj.p]

Really Amazing...Great conclusion... is it quantum physics ??? LOL

Good it provided you some laughs. Although, I can't determine whether to laugh or cry at this comment. Anyways, that's moot. Its not quantum physics, but simple physics which is not hard to understand. If its not the right conclusion, then please enlighten me.

Follow your friend Sanjay

Funny you think all these are Sanjay's ideas. Actually, this is what he has learned from reading various material like technical papers, acoustics articles and experimenting with it. His advice has helped me and numerous other people here. He doesn't claim to be an expert (as you have accused) but himself says he is a learner. I don't have problem following him and won't have problem following you either IF you start making sense. No offense.

@manoj @sanjay
Place a single sub in the center and be happy ..Enjoy Life

I have 2 sub-woofers

I would do that too, if I can. But my room is challenging because it has a 6 ft opening in the back to living room which is open plan to kitchen as well. So I ended up trying to solve the 1st and 2nd width modes in my room by placing those at quarter points. Granted length modes are still present but by cancelling width modes, all the 3 seats in one row are consistent.

 

[manoj.p]

While intelligent people can often simplify the complex, a fool is more likely to complicate the simple.
Gerald W. Grumet

Now this I agree.

 

[shelley]

Yes, and a simple one at that: when it comes to using subs for mode canceling, recommendations (even from the experts you cite) are for placement in nulls, not inbetween nulls.

Refresh your maths and try to read and understand graphs and make comments after reading properly rather than jumping to conclusions....

In the graph shown above (one sub-woofer with antinode positions for all three harmonics) , in a 22ft room , is the sub-woofer placed at 11ft (the middle position) ?? The various positions are between 25% and 50% (4 sub-woofer positions are displayed) for smoothing out bass response.. Try to understand the scientific reason after viewing the graph displaying all 3 room modes..

I did not create this graph ..It is from an expert...

Please show this forum users where experts suggest that middle position is the best position for a sub-woofer to avoid stimulating any of the first three room modes or harmonics. I am challenging you....

Repeating again...all the information provided by me were from experts and you are telling that all of them are wrong..Please post your replies in the following forum and they will make you understand the reason you why you are wrong...
A Guide to Subwoofers (Part II): Standing Waves & Room Modes - Blu-ray Forum

Extract from above forum link:

The pressure zones are spread out and not pinpoint-sized. For all practical purposes, the subwoofer should be located at least 25 percent away from the end of the pipe/room to best avoid stimulating any of its first three harmonics. There is no location towards the middle of the pipe/room that suits a subwoofer position, as the pressure zones there are overlapping.

You are always talking only about first order modes in a room and cancelling it when in fact a closed room has multiple room modes at play..All the suggestions provided by experts point to the center of the room as the worst position for a single subwoofer with valid scientific explanations, and you are telling that it is wrong, just to conceal your wrong statements made earlier...

@sanjay, You are misleading users in this forum as a self proclaimed expert by telling facts without any scientific backing and you are trying to hijack this thread..
I was explaining my experiences in using healthy and cost effective alternatives for building a DIY Home Theater, after doing research about various possibilities and you Sanjay, right from the beginning was trying to hijack this thread. First you told that Glass Wool was not carcinogenic, then you are telling that middle position in a room is the best place for a sub-woofer, all contradicting statements with what experts suggest and without any scientific backing...

Shed your false ego and try to understand things...Let the forum users decide what is right after reading and understanding things.... Most of them would have understood the facts...

To all users of this forum....

If I am a misfit in this forum I will not post again nor visit this forum again..Does somebody have any opinion on this ????

 

[sdurani]

Refresh your maths and try to read graphs and make comments after reading properly rather than jumping to conclusions....

The conclusion is straightforward, no need for jumping: there are 2 modes nulling at the middle of that diagram. Placing one subwoofer there gets rid of both of them. Placing at a non-null doesn't get rid of any of them.

You are always talking only about first order modes in a room and cancelling it when in fact a closed room has multiple room modes at play..

OK, instead of talking only about first order modes I'll talk about multiple room modes. The diagram above shows multiple room modes (1st and 3rd) nulling at the middle. Placing a sub at the middle of the room makes multiple room modes (1st and 3rd, length & width) disappear, since it is at the null of both. With 2 of the first 3 modes gone, the frequency response is much improved.

all the information provided by me were from experts

Experts like Big Daddy? Do you even know his real name?

The rest of your post is personal comments about me (yet again) rather than the topic of this thread (acoustics), so no need for me to respond in kind. Bizarre that you're taking a discusion about acoustics so personally.

 

[shelley]

Amplitude is directly related to the intensity of a sound..Greater the intensity of a sound, the greater the amplitude. In a standing wave, greater the amplitude, higher the bass boom...

We need to find the position where the collective amplitude of all 3 room modes is the least, so that we get a smooth bass response.

Decide for yourselves which position has the least amplitude for standing waves, taking into consideration all 3 room modes
Your greatest mistake is that you consider only the first room mode while ignoring other modes...

100% amplitude for a room mode will have a bass boom for that frequency...The frequencies cannot be separated...While listening to music or movie all the frequencies are heard at the same time ...

The rest of your post is personal comments about me

I was telling facts and every user of this forum can view your earlier posts and decide...

 

[sdurani]

100% amplitude for a room mode will have a bass boom for that frequency...

It's a peak. And peak can be brought down by EQ, a null cannot be boosted by EQ. By getting rid of the nulls, the room correction in the receiver will take care of the peak. Your placement doesn't get rid of the nulls. And there is nothing the room correction can do to fix that.

 

[shelley]

It's a peak. And peak can be brought down by EQ, a null cannot be boosted by EQ

LOL ...
You are a cunning man and divert attention

Can you believe Dr. Floyd Toole ???? Here is the link to his paper (Loudspeakers and Rooms for Multichannel Audio Reproduction
by Floyd E. Toole, Vice President Acoustical Engineering, Harman International)
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/LoudspeakersandRoomsPt3.pdf

This is the article from which you copied the pictures (is it plagiarism??)

Part 3- Getting the Bass Right

Please read the second paragraph:

However, where we place the woofer with respect to the adjacent room boundaries does matter. The least effective location is in the middle of a room.

You have the article with you and you have not read the portion "The least effective location is in the middle of a room "....
Improve your reading skills..

is Dr. Floyd Toole wrong..????? Please provide your expert opinion, sir

 

[manoj.p]

Please show this forum users where experts suggest that middle position is the best position for a sub-woofer to avoid stimulating any of the first three room modes or harmonics. I am challenging you....

This is not directed at me, but look at the paper from Welti - from page 17 onwards.
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/multsubs.pdf

Also - as explained in above post by Sanjay, there is null of 1st and 3rd order at the mid point. What will happen if you put a sub there? 2nd order mode is already at 100% there and wont change if sub is put there. I don't think its that hard to understand.

 

[manoj.p]

LOL ...
You are a cunning man and divert attention by speaking unrelated jargon
I pity you....

This personal attack is just uncalled for. I hope none should report this post to mods because that really shows what kind of a person you are. :clapping:

 

[manoj.p]

LOL ...
You are a cunning man and divert attention

Can you believe Dr. Floyd Toole ???? Here is the link to his paper (Loudspeakers and Rooms for Multichannel Audio Reproduction
by Floyd E. Toole, Vice President Acoustical Engineering, Harman International)
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/LoudspeakersandRoomsPt3.pdf

This is the article from which you copied the pictures (is it plagiarism??)

Part 3- Getting the Bass Right

Please read the second paragraph:


is Dr. Floyd Toole wrong..????? Please provide your expert opinion

Things quoted in isolation make different meanings. Just read the paragraph before it and Dr. Toole is talking about place where the "woofer" is radiating the best. For that purpose, he finds center is least effective position and corner is best.

Read those two paragraphs again and try to understand before posting.

 

[shelley]

LOL

Things quoted in isolation make different meanings. Just read the paragraph before it and Dr. Toole is talking about place where the "woofer" is radiating the best

I read the whole article by Dr. Floyd Toole ...and this was the first paragraph:

So, we think that we know how to pick a good loudspeaker, and with some simple acoustical devices or smart design, we can avoid destructive reflections in a room. Now, what about low frequencies, the ones where the room is the dominant factor? The first task is to locate the subwoofer where it radiates most effectively. Closed box or reflex (ported) woofers are pressure sources. It matters not which way the diaphragm faces because all such loudspeakers are omni directional at low frequencies. Obviously, there needs to be breathing space if we choose to face the diaphragm against a wall. And, if there is a port, dont plug it!

@manoj
Why did you remove the extract I copied from the article in your quote above ("Please read the second paragraph:") ???
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/LoudspeakersandRoomsPt3.pdf

"However, where we place the woofer with respect to the adjacent room boundaries does matter. The least effective location is in the middle of a room."

This reveals your malicious intentions of confusing readers of this post....

Better you read it and try to understand it or else discuss it with some person if you are unable to comprehend it

Also - as explained in above post by Sanjay, there is null of 1st and 3rd order at the mid point. What will happen if you put a sub there? 2nd order mode is already at 100% there and wont change if sub is put there

LOL That was what I was telling right from the beginning...2nd order mode will be at 100%...

 

[manoj.p]

@shelley

Have you tried quoting someone's post? If there is any quoted post within that post, it is removed by the forum software. I did not remove it. Off all the people, a software engineer should realize that first. But this is what happens when a software professional is nothing but a google copy/paste coder.

Start thinking before calling people names.

 

[shelley]

If there is any quoted post within that post, it is removed by the forum software

Please all users read post 130 by me and post 133 by manoj...Judge for yourselves...Quote missing a valuable extract from Dr. Floyd Toole article...

"However, where we place the woofer with respect to the adjacent room boundaries does matter. The least effective location is in the middle of a room."

LOL..Okay I will inform vbulletin about the peculiar behavior of their forum software...Anybody can quote anything using QUOTE tags in a forum, even after removing important information

 

[sdurani]

You have the article with you and you have not read the portion "The least effective location is in the middle of a room "....
Improve your reading skills..

As Manoj correctly pointed out, you are quoting Toole in isolation to take his words out of context.

Here is the paragraph surrounding the part you quoted:

However, where we place the woofer with respect to the adjacent room boundaries does matter. The least effective location is in the middle of a room. It gets better on the floor, still better on the floor against a wall, and best in a corner. This is best in the sense of maximizing the quantity of bass radiated into the room.

So, the middle of a room is least effective when it comes to the amount of bass (volume level), not the quality of bass (smoother response). By comparison, corner placement is best. Again, best when it comes to amount of bass.

So you've taken a quote that has to do solely with bass quantity and tried to sneak it into a discussion about bass quality. Toole's comment has absolutely nothing (zero) with the mode cancelling we're discussing. Nice try, better luck next time.

And you call me cunning and question my reading skills. Remarkable.

 

[shelley]

Read the whole article before making comments..

The least effective location is in the middle of a room because of 100% second order room mode and overlapping room modes...Everybody knows that bass is highest at corners since as shown in the graph a subwoofer close to a wall is in the high pressure region of all the width modes and energizes all of them.

Did you calculate the effect of the standing waves in different subwoofer positions taking into consideration all room modes??? Then make your comments...

Quoting your friend Manoj

Also - as explained in above post by Sanjay, there is null of 1st and 3rd order at the mid point. What will happen if you put a sub there? 2nd order mode is already at 100% there and wont change if sub is put there

What is your explanation for "2nd order mode is already at 100%" at mid point (magenta) in the Graph. and how it correlates with smoother bass..sir

I challenged you in an earlier post...Why not take it up ??? Prove with reliable information that middle of the room is the best position for a sub-woofer..Not your opinions...But opinions from experts ....

Did you read the forum posts by users in this excellent forum where people do not display "false ego":
http://forum.blu-ray.com/showthread.php?t=48286

 

[shelley]

Another expert opinion from Acoustic Sciences Corporation
http://www.asc-home-theater.com/htvol3.htm

Arthur Noxon, physicist and state licensed acoustical engineer, also the inventor of the TubeTrap, continues still today as the owner, working president, and director of engineering of Acoustic Sciences Corporation.(USA)

The link above is knowledgeable for every user of this forum to understand sub-woofer placement. Clears all doubts..

Please view the first image for combined first, second and third harmonic modes..

It seems that no matter where a speaker might be located in a closed pipe, one resonant harmonic series or another will become stimulated. However, subwoofers are always rolled off just below the beginning of the vocal range, about 85 Hz. This means that the subwoofer cannot stimulate resonances above the roll off frequency. Now, if the first resonance is 25 Hz, the second will be 50 Hz, and the third 75 Hz. The fourth resonance will be at 100 Hz. The fourth resonance and all of those higher than it are above the 85 Hz roll off frequency of the subwoofer. This means that the speaker need only be positioned so that it doesn't stimulate the first, second, or third resonances. The speaker has to be located somewhere, but not at either end, not at the middle, and definitely not at the third waypoints.

Source:
@sanjay, read the article to clear your distorted ideas and notions: (Acoustic Sciences Corporation)
http://www.asc-home-theater.com/htvol3.htm


This is the crucial point to remember:

There is another factor that limits the remaining options for speaker placement. The pressure zone is not a pinpoint-sized space; it spreads out. If the speaker is located near enough to the center of the pressure zone, the resonance can still be stimulated. A pressure zone effectively extends about one quarter of the distance between adjacent pressure zones and the speaker should not be located inside the effective pressure zone space. For all practical purposes, the speaker should be located 25 percent away from the end of the pipe to best avoid stimulating any of its first three harmonics. There is no location towards the middle of the-pipe that suits a subwoofer position, as the pressure zones there are overlapping.

A pressure zone effectively extends about one quarter of the distance between adjacent pressure zones and the speaker should not be located inside the effective pressure zone space. That is how the pressure zones overlap...
Open your eyes widely ....Watch the pressure bands in the diagram above and sub-woofer positions

The sub has to be placed more than 25 percent away from the wall because of the first harmonic, but not in the central one-eighth width of the room due to the second harmonic. The sub can be located anywhere between three-quarters and 6-3/4 feet from the side wall. Lastly, the length of a room might easily be 21 feet long. The first resonance for this would be 1130/2x21 = 26.9 Hz. The second is 53.8 Hz and the third is 80.7 Hz. The fourth at 107.6 Hz md above are all well above the roll off frequency and can be ignored. For the length of the room, the sub position should be one-quarter of the room length or five feet off either end wall.

READ THIS IN THE ABOVE ARTICLE:

A listening room can be approximated as if composed of three intersecting pipes. These pipes would lie along the three room axes -- front to back, side to side, and floor to ceiling. This means that the subwoofer location for best, non-resonant playback will be about one-quarter of the ceiling height off the floor, one-quarter the width of the room off the side walls, and one-quarter the room length off the front or back wall.

Sanjay sir, what does one-quarter mean ??? is it 1/4th or 25% ??? OOOOH....maths again

Sir, is Acoustic Sciences Corporation and Arthur Noxon wrong ?? LOL...

=======================================
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is.
Winston Churchill

 

[rdksrk2013]

Hello,

I pondered a lot if I have to sneak in between but I would say both your arguments are enriching to all beginners like me.I was back in this blog after two days and seen all the correspondence.

In all these correspondences we forgot that Shelley is sharing his HT build and we would love to keep hearing his progress.

@sdurani: your advice and insight are enriching. I would first do the playing around with placement and then spend money on acoustics. Very good advice.

I think I should check if I can try both of your arguments(sanja's and shelley's). It does not cost money. With due respect to both of you.

Being from a technical background I can understand that both of you have a point to convey.

Only experts hold this long their point of argument. For people like us observing on the background you both are good in your understanding.:clapping:

Great going. Let us help shelley to realise his dreams. :yahoo: