Size of the Room?

[hiawatha]

Hi. I have a Room with low roof hight. It is just 207cm. With that low ceiling, for the best, fun sound with great bass, what Will you recommend for wide/lenghth wit low ceiling? Is gonna be a 5/7 channels with 4 subs. Speakers Will probably be the new Jbl hdi 3800 speaker om front.
Hope you people in here can hjelp me along the way with this, when I have no clue .
This Room is a dedicated Room for cinema/music/game, so its have no waf factor to decide how the Room acoustics Will be.
Best regards Hiawatha

 

[A J Womack]

Hello Hiawatha,
In your case forget room ratios as a design method, you will get nothing that is of any use to you!
Hold off buying your bass speakers until you have some idea of the lowest frequency your room will be able to reproduce!
Perfectionist is absolutely right in suggesting room modes as the way forward. Ideally first order modes, height, length and width should be evenly spaced but in the 'real world' this rarely happens so use what the calculator tells you as a gude for what low frequencies will need to be treated.
To be of any real use to you it would be helpful to know some more about your actual situation with regard to how far apart the existing walls are and what will be realistally possible with regard to cost and construction methods.
Come back to me iff you wish.
Regards Andrew

 

[Kakkadu]

Hello Hiawatha,
In your case forget room ratios as a design method, you will get nothing that is of any use to you!
Hold off buying your bass speakers until you have some idea of the lowest frequency your room will be able to reproduce!
Perfectionist is absolutely right in suggesting room modes as the way forward. Ideally first order modes, height, length and width should be evenly spaced but in the 'real world' this rarely happens so use what the calculator tells you as a gude for what low frequencies will need to be treated.
To be of any real use to you it would be helpful to know some more about your actual situation with regard to how far apart the existing walls are and what will be realistally possible with regard to cost and construction methods.
Come back to me iff you wish.
Regards Andrew

Wait, are you suggesting there is a limit to how low frequencies can be reproduced in a room?

To OP: If there is no WAF factor, invest heavy to acoustic treatment right on start. I would suggest calling Dennis Foley at Acoustic Fields for advice. I actually have a similar type of project going on with low ceiling height. I'm taking advantage of it by building a line source ESL panel from floor to ceiling...

 

[A J Womack]

Hello Kakkdu,
It's not a suggestion it's a fact. To reproduce or genrrate a note or tone with a frequency of 20Hz you need 22.5 feet of airspace in front of the generating element otherwise you are not hearing the sound at its full amplitude.
It is also worth bearing in mind that the "sweet spot" for monitoring, mixing bass frequencies etc. is around 33-35% down the length of the room, to avoid the antinode (dead spot) of the lowest note that your room can reproduce.
Subs positioned "toe in", so they have a bit more air in front of them may squeeze an extra hertz or so may help and make the antinode area a little less defined.
The only ESLs I have heard are British made Quads. The first time was fiftty years or so ago, great for classical but rock'n'roll felt lacking.
It would be interesting to hear how you get on.
Regards Andrew

 

[JStewart]

It's not a suggestion it's a fact. To reproduce or genrrate a note or tone with a frequency of 20Hz you need 22.5 feet of airspace in front of the generating element otherwise you are not hearing the sound at its full amplitude.

???? So we’re all wasting money on full range speakers or subs AND R.E.W. is not measuring correctly when it measures 15Hz in my 12.5” room? How is this possible?

 

[A J Womack]

I did not say that you are wasting your money, that is for yoj to decide. At such low frequencies you will find that the amplitude varies in different parts of the room along its axis at the same height. Vary the height in a fixed position and the level will also change. If you can, take the measurement mic out of the room with the door open and you should find the same thing occurs. If the door is on the main axis you will eventually find the peak point which will relate to the wave length of the frequency.
At frequencies of 20Hz and below you will probably be annoying your neighbours, who will might not only hear, but feel the sound wave if it is of suffcient amplitude.

 

[JStewart]

Hold off buying your bass speakers until you have some idea of the lowest frequency your room will be able to reproduce!

Wait, are you suggesting there is a limit to how low frequencies can be reproduced in a room?

It's not a suggestion it's a fact.

???? So we’re all wasting money on full range speakers or subs AND R.E.W. is not measuring correctly when it measures 15Hz in my 12.5” room? How is this possible?

I did not say that you are wasting your money, that is for yoj to decide. At such low frequencies you will find that the amplitude varies in different parts of the room along its axis at the same height. Vary the height in a fixed position and the level will also change. If you can, take the measurement mic out of the room with the door open and you should find the same thing occurs. If the door is on the main axis you will eventually find the peak point which will relate to the wave length of the frequency.
At frequencies of 20Hz and below you will probably be annoying your neighbours, who will might not only hear, but feel the sound wave if it is of suffcient amplitude.

Not answering the question. If you can't reproduce low frequencies in the room then how is R.E.W. measuring it in my room? You were asked if you were suggesting there was a limit to the low frequencies that can be produced in a room. You answered, "Its not a suggestion it's a fact". Is it?

 

[JStewart]

Hi. I have a Room with low roof hight. It is just 207cm. With that low ceiling, for the best, fun sound with great bass, what Will you recommend for wide/lenghth wit low ceiling? Is gonna be a 5/7 channels with 4 subs. Speakers Will probably be the new Jbl hdi 3800 speaker om front.
Hope you people in here can hjelp me along the way with this, when I have no clue .
This Room is a dedicated Room for cinema/music/game, so its have no waf factor to decide how the Room acoustics Will be.
Best regards Hiawatha

Welcome to the forum!

Ideal room dimensions are calculated so that "room mode" impact is minimized. Room modes can cause excessive peaks in low frequencies that mask other low frequencies. The phenomena can be described as "boomy" or "one note" bass. As a practical matter designing the room for ideal mode spacing is probably not of much use.

My suggestion is to design the room to fit your needs first. Avoid having the length, width or height of the room an even multiple of the other if possible. Try to allow for the main speakers being a few feet at least from the side walls.
Deal with low frequency uneven response by having two to four subwoofers in the room and the ability to adjust relative delays for each to get the best response from them.

If you would like to research the science and testing behind multiple subwoofers you can start here:

Todd Welti - Subwoofers: Optimum Number and Locations

https://www.harman.com/documents/multsubs_0.pdf

Floyd E. Toole, Ph.D. Getting the Bass Right Part 3

https://www.harman.com/documents/LoudspeakersandRoomsPt3_0.pdf

For info about room modes that multiple sub-woofers help overcome:

A Guide to Subwoofers (Part II): Standing Waves & Room Modes

A Guide to Subwoofers (Part II): Standing Waves & Room Modes - Blu-ray Forum

A Guide to Subwoofers (Part II): Standing Waves & Room Modes Subwoofers

forum.blu-ray.com

Listening Room Acoustics: Room Modes & Standing Waves Part I

Listening Room Acoustics: Room Modes & Standing Waves Part I

Dealing with standing waves in small room acoustics is a must for better bass. This can be done with bass traps or multi-sub or a combo of both.

www.audioholics.com

 

[A J Womack]

JStewart
A room has a bass cut-off point due to its physical size, hence the uneven bass response at very low frequencies in small rooms.
How low a freqency do you need to hear? The lowest note on a grand piano is bottom A, 27.5Hz.
Yes REW can measure 15Hz in your 12.5ft room but it only "seeing" part of the waveform hence the uneven bass response from a single woofer.
Extended bass response transports the bass beyond the room boundaries to varying degrees, by mechanical transmission through the structure, and through any "holes" in the structure unless it is hermetically sealed.
Doubling up or even more on subs just to try and beat the "laws of physics" and wring another octave of so out of system (and thag includes the room), seems a little pointless to me, the law of diminishing returns applies. Buy some "good" music instead and soak up the emotiom, and yes it might make you cry, but you pockets will not be empty, and you will be able to afford some tissues. Only joking!
After all this is Hiawatha any more enlightened, probably not!
H, follow the good advice you have been given on room modes and proportions. Forget "ideal" room sizes they rarely turn out as one hopes, and in your situation would be no good at all.
My case rests, enjoy the music or sound that "floats your boat".

 

[JStewart]

I believe the reason for nulls is due to reflections arriving at the measuring location out of phase with the direct signal. Either way the solution is the same. That is, multiple subwoofers for an even bass response in a domestic sized room as per Toole, Welti and Devantier.

 

[Kakkadu]

Hello Kakkdu,
It's not a suggestion it's a fact. To reproduce or genrrate a note or tone with a frequency of 20Hz you need 22.5 feet of airspace in front of the generating element otherwise you are not hearing the sound at its full amplitude.
It is also worth bearing in mind that the "sweet spot" for monitoring, mixing bass frequencies etc. is around 33-35% down the length of the room, to avoid the antinode (dead spot) of the lowest note that your room can reproduce.
Subs positioned "toe in", so they have a bit more air in front of them may squeeze an extra hertz or so may help and make the antinode area a little less defined.
The only ESLs I have heard are British made Quads. The first time was fiftty years or so ago, great for classical but rock'n'roll felt lacking.
It would be interesting to hear how you get on.
Regards Andrew

This is complete nonsense. Sorry I don't mean to be blunt but this is how I think. Below the Schroeder frequency the speaker driver starts to modulate the airspace directly and it boosts low frequencies actually. In a typical car direct modulation starts already around 100hz. This is where the 'room gain' comes from. That's why it's very easy to achieve extremely low frequencies in car audio where the air space is very small. The toe of subs means nothing because low frequencies are omnidirectional lol.

 

[Kakkadu]

I believe the reason for nulls is due to reflections arriving at the measuring location out of phase with the direct signal. Either way the solution is the same. That is, multiple subwoofers for an even bass response in a domestic sized room as per Toole, Welti and Devantier.

Dr. Earl Geddes made his Ph.D. with multiple subwoofers in a small room. He proved that it's possible to negate the standing waves in a room by placing multiple subwoofers at correct delays and amplitudes.

 

[JStewart]

Dr. Earl Geddes made his Ph.D. with multiple subwoofers in a small room. He proved that it's possible to negate the standing waves in a room by placing multiple subwoofers at correct delays and amplitudes.

You are, of course, correct. I should not have overlooked him.
Earl Geddes on Multiple Subwoofers in Small Rooms

 

[DanDan]

"To reproduce or genrrate a note or tone with a frequency of 20Hz you need 22.5 feet of airspace in front of the generating element otherwise you are not hearing the sound at its full amplitude."- AJ Womack

So how do headphones do 30Hz? How does 30Hz make it down the 3cm ear canal. The waveforms don't sound incomplete, nor do they look strange on screen. Andrew you are digging a hole. Stating nonsense and insisting is kinda palookaville bound here in a forum frequented by acoustically informed folk.

 

[Kakkadu]

"To reproduce or genrrate a note or tone with a frequency of 20Hz you need 22.5 feet of airspace in front of the generating element otherwise you are not hearing the sound at its full amplitude."- AJ Womack

So how do headphones do 30Hz? How does 30Hz make it down the 3cm ear canal. The waveforms don't sound incomplete, nor do they look strange on screen. Andrew you are digging a hole. Stating nonsense and insisting is kinda palookaville bound here in a forum frequented by acoustically informed folk.

I'm sure Andrew has a valid explanation for thinking how he does - even though being wrong. As Geddes said normal rooms are always so leaky that frequencies escape the room under the fundamental wavelength. If they didn't the same effect would happen like in car audio - even a small driver starts to modulate the airspace directly, increasing the efficiency of the driver by orders of magnitude. Distortion is minimised and sound linearity improved to near flawless levels.

 

[DanDan]

There are a few notions or phenomena. One, which has a rationale, is that it is best to not excite the lowest mode(s) in a small untreated room. Personally I think bigger speakers are just always better. They may excite lower LF but they also dominate the space more. There is also a thing about Sealed versus Ported speakers. The latter tend to be more efficient, louder, but LF drops off dramatically while sealed subs deliver to very much lower frequencies but less efficiently. Even the old studio pal the NS10 can deliver a clean 30Hz. Lastly most likely I guess, most LF in a room response is dominated by modes. But below the lowest mode the transmission from particularly a sealed sub becomes a direct pressure transfer. Similar to your car example. Although I would add, car boundaries are rather floppy, a Limp Bag as Newell describes them. The lack of destructive reflections allows great bass in cars and mobile recording trucks.

 

[Kakkadu]

There are a few notions or phenomena. One, which has a rationale, is that it is best to not excite the lowest mode(s) in a small untreated room. Personally I think bigger speakers are just always better. They may excite lower LF but they also dominate the space more. There is also a thing about Sealed versus Ported speakers. The latter tend to be more efficient, louder, but LF drops off dramatically while sealed subs deliver to very much lower frequencies but less efficiently. Even the old studio pal the NS10 can deliver a clean 30Hz. Lastly most likely I guess, most LF in a room response is dominated by modes. But below the lowest mode the transmission from particularly a sealed sub becomes a direct pressure transfer. Similar to your car example. Although I would add, car boundaries are rather floppy, a Limp Bag as Newell describes them. The lack of destructive reflections allows great bass in cars and mobile recording trucks.

Even though cars are floppy the displacement is so small that the amplification overcomes the leaks. A closed box bass driver tuned for 60-70hz will go completely flat to 20hz or even below inside a car. A feat impossible in a room let alone an open space.

Check out my idea of a subwoofer in the thread: https://www.avnirvana.com/threads/say-hello-to-my-little-friends.7015/

 

[DanDan]

I am not sure what you are saying. Cars are much smaller than rooms or the cosmos. I would assume that sub would have a similar response in any equal sized space with equally floppy boundaries. I suspect that a wooden shed or sheetrock on stud walled room would be of a similar order of floppiness to a car.
Steel is very friendly to sound, from the Modex Plate to the EMT 140 Reverberation Plate.

 

[Kakkadu]

I am not sure what you are saying. Cars are much smaller than rooms or the cosmos. I would assume that sub would have a similar response in any equal sized space with equally floppy boundaries. I suspect that a wooden shed or sheetrock on stud walled room would be of a similar order of floppiness to a car.
Steel is very friendly to sound, from the Modex Plate to the EMT 140 Reverberation Plate.

The difference in response inside a car can easily be measured and verified.The smaller the volume, the less sensitive to small leaks it gets.

 

[DanDan]

Sure cars are different to other spaces because they are smaller, but I am quite sure that they have plenty of air leaks to, well, not suffocate. BTW that is a massive pair of Woofers you have! Lordy. Speaking of which, I have been thinking about making some subs which are very shallow, in order to minimise SBIR in my concrete walled Control Room. Of course my search led to vehicle woofers around 3" deep. Some very good value from Pioneer etc, but some very expensive brands also. Any thoughts?

 

[Kakkadu]

Sure cars are different to other spaces because they are smaller, but I am quite sure that they have plenty of air leaks to, well, not suffocate. BTW that is a massive pair of Woofers you have! Lordy. Speaking of which, I have been thinking about making some subs which are very shallow, in order to minimise SBIR in my concrete walled Control Room. Of course my search led to vehicle woofers around 3" deep. Some very good value from Pioneer etc, but some very expensive brands also. Any thoughts?

Dayton audio has some extremely shallow woofers which are suitable for installations under the sofa etc. https://www.parts-express.com/dayton-audio-ls10-44-10-low-profile-subwoofer-dual-4-ohm--295-251

If you're looking for an OEM solution, there I can't recommend any as I have not tried them.

If you have any space left in the concrete walled space, I recommend building bass absorbing units with the instructions from Acoustic Fields. The plans are available for free if you look carefully - but don't cost much to buy with full assembly instructions.

 

[DanDan]

Ta, the Dayton is a tad deeper than most. The Acoustic Fields website is good. One of the best. However on a quick skim I see false statements about Rockwool. I see that Activated Carbon nonsense. I see a claim that their foam is superior and a blatantly faked absorption graph. But sure, many other of their products seem just fine. I approve acoustic treatment and if someone has the cajones to nicely remove excess wealth while making those people happy..... Good.

 

[Kakkadu]

Ta, the Dayton is a tad deeper than most. The Acoustic Fields website is good. One of the best. However on a quick skim I see false statements about Rockwool. I see that Activated Carbon nonsense. I see a claim that their foam is superior and a blatantly faked absorption graph. But sure, many other of their products seem just fine. I approve acoustic treatment and if someone has the cajones to nicely remove excess wealth while making those people happy..... Good.

I have had quite a few arguments with Dennis on several marketing statements but regardless of a few flaws, I find his site the best I know and obviously his customer testimonials tell that what he does also works.

The coolest thing about Acoustic Fields is that they support DIY. You can buy plans only, flatpaks or ready assemblies. This means you can get into acoustic treatments on a very tight budget.

Acoustic treatment is the best thing you can do to your music listening experience. Especially if your listening room is a concrete walled basement or a flat.

 

[Adhoc]

I would stay away from the site Acoustic Fileds and Dennis Foley. The site contains several incorrect statements and also some outright lies.

A much better one with sound advices (pun intended!) and no rubbish is: http://arqen.com/acoustics-101/room-setup-speaker-placement/ At first glance It may look like it is only for studios and control rooms but most of the info is directly applicable also for home theaters. -Like the advice of a starting point about 38% distance from the front wall where you have the screen. Just turn it around and use starting point for sweet spot as 38% of room lenght away from the wall behind you. (The advice comes down to the fact that in a non treated room theoretically the first 3-4 lowest length modes should be best balanced at that position. In a sealed concrete room that is. For a non concrete room with flexing drywalls, doors and windows, the best place might be somewhere along 30-40% of room length. -For length modes It doesn't matter if you are at a certain length away from the front or the backwall.)

Read through the "Tutorials a DIY resources", there is quite a bit of good advices.