MODE CALCULATORS - THE MATHS.... AND SOME OTHER STUFF !!!

Hi. I am new to the forum, so first of all i would like to say hi and congratulate you on an awesome little community. I have had a little look around to see if i can find the answer to my question but with no luck. I am a BA (Hons) student, studying Creative Music Production and Technology at Greenwich University... One of my modules is "Studio Design and Small Room Acoustics". It is in this module that i have decided to write my dissertation. My project is to help my friend turn his bedroom into a usable control room environment on a small budget. I plan to build my own bass traps to deal with any modal problems and to buy some acoustic panels to diffuse / absorb any higher frequencies that are causing problems. The project is coming along quite well and i have thus far calculated the RT60, cut-off frequency and critical frequency and carried out a spectrum analysis of the room. I have also figured out how to calculate the distance from the wall the panel resonators should be... The thing i cant figure out is the equations used to find out what the modes are in the room. I know there is various calculators online which will do this for you, but most of them are in imperial, and i need to work in metric... Also, for my dissertation, i really need to be able to explain the maths behind the equations and show that i understand them. I have the Howard and Angus book "Acoustics and Psychoacoustics", which explains them, but i still dont understand. I was wondering if there is anybody who could explain the calculations to me in more simplified terms?? Or point me to a an online resource or a previous thread on this forum that might help me. And once i have all the modes of the room, how do i know which ones i should build traps for? The dimensions of my room are as follows (in Metres): Length: 3.68 Width: 2.87 Height: 2.32 The cut-off frequency is 46.7 Hz The critical frequency is 271.2 Hz So the modal area of the room is between 46 and 271 Hz I done the RT60 using a Phonic PAA meter. This came back at 0.30 seconds at 1K, which i think is not bad for a control room?? I carried out a spectrum analysis using pink noise 3rd octave bands reference tones, at 80dB and 90dB, the results are here: https://files.me.com/djvinyljunkie/nc59rk Some other things as well... Could anyone possibly advise me on speaker placement for this room. My friend is using a set of KRK Rockit 6's... Or maybe you could advise on a better set of speakers for the room (working to a budget of £400)... And finally does anyone have a spec sheet for the Rockit KRK 6's which comes with a frequency analysis... Cant find one anywhere. Any other advice you could offer that may help with this project would be greatly appreciated. Thank you John VINYLJUNKIE

Reverberation doesn't exist in a small room so you might consider a change in terminology to something like "decay rate for indirect field pressure" for LF and "decay rate for indirect specular response" for HF or some such to more accurately depict it... that said, your best investment will be in a good self-powered PA speaker, a omnidirectional microphone (Behringer ECM 8000), a small preamp with phantom power (M-Audio Audio Buddy or similar), a boom mic stand, some audio i/o cables for mic and your laptop, and Room EQ Wizard (REW). armed with those tools you will be able to perform a significant number of accurate room measurements which will definitely aid you in your research and presentation. not to mention provide you with tools to begin your career.

Hi, have a look at my applet. There are some tabs with visualizations presented in some scientific papers. (Bolt, Bonello,...) References to those papers are also found on the left of the tabs. Some examples (your room) Since the importance of a particular mode is strongly dependent on the position of source and receiver...you could do a measurement with a speaker in one and a mic in the opposite corner of a room to excite all modes. I would be interested in such a recording or fft picture to compare it to the screenshot with the lines/modes (first picture)!! The applet is also capable of calculating the modes according to mic and speaker position, but I have just developed my own quick ideas here...don't know whether my algorithms are practical or crap. :)

Thanks for your replies... Much appreciated... Glenn, Why is there no reverb in a small room? Thats not what we have been taught in our acoustics lesson at Uni and our lecturer has a BSc in Acoustics, so i presume he knows what he is talking about. Also thanks for the advice on what kit to buy. Unfortunatley at the moment, living on a student grant.... I cant afford to buy them. :( Tried out your applet... Thanks for that, i will use that and i will try putting a speaker in one corner and an omni directional mic in the other corner as you suggested... With regard to the screenshots you sent me, i understand the first one... The graph showing all the modes. But the other two i am not familiar with. Can you tell me what they mean? Or point me to some web resource that explains? The bolt-area and the bonello graph. Thanks Guys John

true reverberation is composed of signals arriving at different times and levels as a diffusive field - which simply cannot happen in a small room. that said we all (me too) use RT60/RT30 to describe the time-balance in frequency attenuation within a room since its easier for most people to grasp as a metric even if it technically inaccurate.

Why is there no reverb in a small room? Thats not what we have been taught in our acoustics lesson at Uni and our lecturer has a BSc in Acoustics, so i presume he knows what he is talking about.

Like Glenn said: In order to speak about reverb in a room it has to be large enough for reverberation to occur, meaning that there has to be a direct field and diffuse field. The diffuse field is the zone beyond the critical distance. In a small room you cannot get far enough away from the speakers to have a diffuse field. ie, the walls are all closer than the critical distance. So technically, you can't speak about "reverberation" in a small room. Yeah, sound still builds up and dies away over time differently at different frequencies, even in small rooms, but in the strictest technical sense, that isn't "reverb", and measuring it isn't really measuring true RT60. Your uni lecturer is maybe just keeping it simple for you at present, not wanting to confuse you with the technicalities and the details. You'll probably get into that later.

Also thanks for the advice on what kit to buy. Unfortunatley at the moment, living on a student grant.... I cant afford to buy them.

You might want to look into that again! Some of the stuff Glenn mentioned is FREE! Such as REW for example: great acoustic tool, cost = zero. Can't argue with that! The other stuff you can compromise a bit, but you DO need the ability to measure the room accurately: You can predict some stuff with equations, but reality is not always the same as prediction, since there are so many unknown variables in your average room that the equations just cannot consider. You MUST actually measure it. REW is a wonderful way of doing that.

My project is to help my friend turn his bedroom into a usable control room environment on a small budget.

Define "small". If you can't afford the simple stuff that Glenn mentioned, then my guess is that you probably cannot afford the treatment either.

I plan to build my own bass traps to deal with any modal problems and to buy some acoustic panels to diffuse / absorb any higher frequencies that are causing problems.

This is a small room. Most diffusers do not work well in small rooms. I'd forget diffusion initially, and just go with lots of very large broadband bass traps, plus absorption for things like first reflection points and the back wall.

I was wondering if there is anybody who could explain the calculations to me in more simplified terms?? Or point me to a an online resource or a previous thread on this forum that might help me.

Try Bob Gold's calculator: It tells you practically everything you need to know about the room quality. http://www.bobgolds.com/Mode/RoomModes.htm It shows that the room you are talking about isn't too bad as it is.

The cut-off frequency is 46.7 Hz The critical frequency is 271.2 Hz So the modal area of the room is between 46 and 271 Hz

Actually, Bob Gold figures that your modal issues will be in the range 46hz to 150hz.

And once i have all the modes of the room, how do i know which ones i should build traps for?

You can't "have all of the modes"! There will be thousands of them! A modal analysis gives you a general idea of how the room will behave, but isn't really meant to tell you how to build hundreds of traps to deal with them. Just go for a broadband approach, to cover the areas where you have the most issues. (46-150). You do know that you cannot actually eliminate a room mode, right?

Some other things as well... Could anyone possibly advise me on speaker placement for this room.

Soffit mounted in the front corners, soffit surface area as large as possible, symmetric about the room center line, with the acoustic axes 1.2m above the floor and angled to intercept at roughly 60 degree angle, about 20cm behind the head, at about 38% of the room length (front to back). That's pretty much the best possible position for any small studio. If you can't quite make that work due to the room geometry, then you can adjust it. 38% is a guideline, not written in stone. 60° is a guideline, not written in stone. If you can't get them mounted at 1.2m, then put them higher and tilt them down so the axes still intersect at ear height, but do not angle them more than about 10° max, and preferably no more than 6°.

Any other advice you could offer that may help with this project would be greatly appreciated.

Standard advice: Keep the floor hard (concrete, wood, etc.) and the ceiling soft (703). Treat all of your first reflection points with 4" of 703 (or similar). Put large, deep, wide BIG superchunk bass traps in as many corners of the room as you can (there are 12 corners in a room, the two front verticals will be taken up by the soffits, leaving you with 10 possible corners). Tri-corners are the best place for bass traps. Oh, and make them BIG (it's a small room, so it will need lots of bass trapping). Cover some or all of them with plastic, thin wood, or something else, to avoid killing too much of the high end. Or better still, do John's usual slot walls. Did I mention that you need to make your bass traps big? Oh, and don't forget to make the bass traps big, and put lots of them in. That's about it. Ahh! I think I forget to say that your bass traps should be big, deep, wide, and plentiful. - Stuart - PS. Don't forget big bass traps! Lots of them.

Stuart... So small Bass traps and not too many of them!!!! :D No seriously though... Thanks for all that advice... Excellent. You da man.... I do have a budget to pay for materials for the treatment... wasn't planning on forking out on speakers and microphones just yet but i think the Uni will lend me some, so its all good... I have a couple more questions if you dont mind... ?? Regarding speaker placement... There seems to be 2 different schools of thought that i have found through my research... one saying that the speakers should be firing down the longest dimension in the room with the speakers symmetrical from each of the side walls. And another that says that you should fire your speakers down the shortest dimension in the room with the speakers different distances from the side walls (this is the one our uni lecturer recommends), ie your set up is not in the centre but to one side. What would you say about this?? Another thing i wanted to ask you is.... Our lecturer says that the frequency range of your speakers should not go below the cut-off frequency of the room. As this will mean that any frequencies in the room below the cut off will be attenuated by phase cancellation, meaning you wont be able to make accurate judgements on the level of the bass... He says there is not really any way to fix this.... Elsewhere i have read that this can be fixed by stopping all the reflections below the cut-off. What is your opinion on this matter?? Also... What is Soffit ?? And can you send me a link explaining Johns usual slot walls. Thanks once again for your help... I really appreciate it... John... BIG BASS TRAPS YEAH ???? LOTS OF THEM!! :lol:

Regarding speaker placement... There seems to be 2 different schools of thought that i have found through my research... one saying that the speakers should be firing down the longest dimension in the room with the speakers symmetrical from each of the side walls. And another that says that you should fire your speakers down the shortest dimension in the room with the speakers different distances from the side walls (this is the one our uni lecturer recommends), ie your set up is not in the centre but to one side. What would you say about this??

Absolutely you want your speakers firing down the room (long axis), and absolutely you want your room symmetrical. If the room is not symmetrical, then each ear is hearing something different, both in timing and in EQ, so it will be impossible to create a balanced mix where the instruments and vocals sit nicely on the sound stage and work together. If your left ear hears sound arriving a few milliseconds later than your right ear, and with a different resonance and EQ component (due to the different acoustics), then your brain will try to compensate for those differences in the mix: you'll end up adjusting the EQ, dynamics and panning to put things right again, so it sounds good in the room... but then when you take your finished song to any other place on the planet, it will NOT sound right any more. If there is a large distance between one speaker and its wall, but only a short distance between the other and its wall, then they will sound different, and have different responses, which you cannot fix with an equalizer, since they will be difference in both the time and frequency domains. An EQ can fix frequency domain issues, but it can do nothing at all about time domain issue: that is a function of room geometry. Plus, an equalizer will most likely screw up your phasing, too, unless you have lots of money for a phase-linear equalizer... In short, if your room is not symmetrical, then the only place where your mixes will sound good is in your room: everywhere else in the known universe they will sound ugly. Period. Unless you want to turn out garbage, you absolutely do need to have the room (or at least the front half of it) as symmetrical as you can possibly get it, with your speakers equidistant from the walls, from the centerline, from each other, and from your head. Anything else is an invitation to disaster, guaranteed. I've never seen any successful studio anywhere that isn't symmetrical. Not sure where your uni lecturer got that strange theory from! Maybe he can offer you examples of great studios where the speakers are at different distance from the walls, each other and the engineer? I'd love to see that!

Our lecturer says that the frequency range of your speakers should not go below the cut-off frequency of the room. As this will mean that any frequencies in the room below the cut off will be attenuated by phase cancellation, meaning you wont be able to make accurate judgements on the level of the bass... He says there is not really any way to fix this.... Elsewhere i have read that this can be fixed by stopping all the reflections below the cut-off. What is your opinion on this matter??

Simple: Your speakers need to cover the entire range that your music covers. If you are only mixing spoken voice (no music) then you don't need to cover anything below about 150 Hz, since there isn't much useful energy in the human voice down that low. But for everything else, you do need to hear it, so your speakers need to produce it. For example, if you went with your lecturer's "recommendation" and cut off everything below 50 Hz, then maybe YOU can't hear it in YOUR room, but someone else who listens to your music in another place (such as their car, living room, MP3 player, etc.) WILL be able to hear it. So they will hear stuff that you didn't mix.... BAD IDEA! Then you have the issue of roll-off. You can't go much better than 24 db/octave roll-off without getting into other serious issues (eg. major phase shifts). So let's say you set your system so that it rolls off -60dB at 50 Hz. That means you are -36dB at 100 Hz, and still a whopping -12dB at 200 Hz! You don't get back to flat until around 300 Hz!!! Wow! You just grossly distorted all of the lows and most of the low-mids, and you are still affecting a good chunk of the mid range. Your kick, toms and bass guitar are now out the window, and even the bottom half of your keyboards and guitars are blown away into muted mush. Maybe your sopranos and piccolos still sound OK, but everything else is crap. It simply isn't possible to do what this guy suggests. If you did, once again your mix will sound terrible everywhere else on the planet. This is called "translation". Ie, your mixes will not "translate" well to any other sound system ever built. In short, your speakers need to cover at least the entire "normal" spectrum, with reasonably flat response from 20 Hz to 20 kHz, and there is some reason to believe that they should go much higher than that to, up to maybe 40 kHz. (Yeah, your ears can't "hear" that high directly, but it seems that your brain can still sense when some of those extreme highs are not there. Not convinced on this one: jury still out, I think, but it kind of makes sense.) Anything less is not useful.

...this will mean that any frequencies in the room below the cut off will be attenuated by phase cancellation, meaning you wont be able to make accurate judgements on the level of the bass...

Wrong! In fact, it is exactly the opposite. You want flat response across the entire range (and maybe rolling off the highs, not the lows). Let me explain: ALL frequencies that bear some relation to the room dimensions (either axial, tangential or oblique) will suffer from phase cancellation, without question. This is NOT just about those below a certain frequency. Basic acoustics. The only question is WHERE in the room does the cancellation take place for each wave! That's what modal analysis is all about: figuring out what those frequencies are, and where the peaks and nulls will fall in the 3D space of the room. That's the whole point of the exercise. That's the reason why you should NEVER design a cube-shaped room, nor one whose dimensions are multiples of each other, nor put your head in the geometric center of any room. If you do, then you are amplifying some modes many times over, and placing your ears at the exact point where the modes have the greatest effect: ie, the maximum peaks and the minimum nulls always occur half way between parallel walls. You NEVER want your head in the center of a room. you NEVER want a round or cube shaped room. The whole point of modal analysis is to find dimensions for the room where the modes are spread around the spectrum evenly (not bunched up), and where the engineer's head is as far as possible from the major peaks and nulls in the room. You cannot fix modal problems in a room with EQ, or by trying to cut off the low end. It won't work. It cannot work. The physics of how sound waves interact with rooms does not allow it to work. (OK, there actually are a couple of exceptions to that: EQ can work for a limited set of conditions, but a several things have to line up for it to work, and the room has to already be extremely well treated.) Getting back to the point about your uni guy having things "barse akwards": the only frequencies that CANNOT POSSIBLY have modal nulls and peaks in a room, are those ones that fall BELOW the lowest frequency for which the room can support a standing wave. In your case, the longest path for resonance will only support modes down to about 46 Hz. It is therefore impossible to have a 30Hz tone set up standing waves in this room, and therefore impossible to have fixed peaks and nulls! So it makes no sense at all to cut off frequencies that actually cannot possibly exhibit the problem you are trying to prevent! That's like saying that you need to close the curtains at night to keep the sunlight out... :) The above is the reason why I gave you the 38% figure: that's the point (theoretically) of the room length where the modal activity is at the minimum, and therefore is the best place for your head. The worst places are 50%, 0%, and 100% of any dimension. 25% and 75% are also no fun. 62% is another good place, but you want your head closer to the front wall than the back wall, for other reasons, so 38% is the best point. Theoretically!!! But please do NOT take that as meaning this is ONLY place where you can put your ears! It is just a theoretical guideline. Lots of other things in your room can change that.

...meaning you wont be able to make accurate judgements on the level of the bass...

The only reason you won't be able to make accurate judgment of bass levels, EQ and placement is if you don't have enough bass trapping in your room! :) seriously, this is somewhat counter-intuitive, but it is the truth. You might think "Why do I want to TRAP bass in order to make the bass sound BETTER?" Truth is, its the only way. "Trapping" is not really what bass traps do, anyway. Bad name. In order to have good bass response in a small room, you need to "trap" it all, deeply and aggressively, without affecting the highs. You first need to feed the entire spectrum into your room, leaving out nothing (ie, you need full-range speakers that cover at least 20 Hz. to 20 kHz.), then you need to control the modal issues in the low end with major bass trapping, which helps in many ways that are rather complex to go into here.

He says there is not really any way to fix this.... Elsewhere i have read that this can be fixed by stopping all the reflections below the cut-off. What is your opinion on this matter??

You cannot stop reflections of low frequency sound with any reasonable method, just as you cannot eliminate the modes from a room. Think of it this way: a 20 Hz wave is about 17m long. Conventional acoustic wisdom says that you need absorption about one quarter wavelength deep to deal with a sound wave, or at the very least about 5% the depth of the wavelength placed about a quarter wavelength from the wall. You therefore need either insulation that is about 4.5 meters thick stuck to each wall, or at the very least insulation 85 cm thick placed about 4.5 m away from each wall.... (!) I think you get the picture: it can't be done in a small room, and in a room that is large enough where you COULD do it, it turns out that you don't need to do it that way any more... :) Ain't acoustics wonderful?

Also... What is Soffit ??

A "soffit" (more correctly called "flush mount") is just a large flat rigid massive panel around your speaker, which acts like an extension of the front panel. Technically, it is an infinite baffle. In other words, take the very largest piece of plywood or MDF that you can fit across the front corner of your room, cut a hole in the middle of it just big enough for the front of the speaker to poke through from behind, fill the gap behind it with insulation, and you have a soffit. (OK, its a bit more complex than that, but that's the basic idea.) It's just a really BIG front panel for your speaker, that covers the entire room corner, floor to ceiling, and as wide as you can make it. The theory behind it is related to the way sound waves react to objects that are smaller or larger than the dimension of the wave. A wave that is smaller than an object will bounce off it. A wave larger than the object will refract (bend) around it, as though it were not even there. So if you have a speaker producing waves at, say, 330 Hz (low mid range), those waves are about 1m long. Therefore those waves (and all ones longer) will bounce off things bigger than one meter, but bend around things that are smaller than 1 m. Your speakers are MUCH smaller than 1 m, so they will bend around behind it, right as they come out of it. All frequencies whose wavelength is appreciably larger than the size of the speaker itself will simply wrap around behind it, then get reflected off the front wall and come back at your head with a slight time delay and phase shift, causing comb filtering, phase cancellations, and other kinds of nasty stuff. An infinite baffle (or soffit) prevents that from happening. The soffit panel acts like an extension of the speaker, and prevents the waves from wrapping around behind it. In effect, as far as the sound waves are concerned, the speaker becomes infinitely big: No waves wrap around, and all waves are projected directly into the room, without the nasties happening. End result: excellent clear sound, great imaging, much improved frequency response. That's the theory. (It doesn't work exactly like that, but it gives you an idea.) So soffit mounting your speakers is a good great wonderful fantastic excellent nice advisable recommendable thing to do. It's also a good idea. It isn't easy to do right, but is well worth it. It also gives you a free boost in the bass response of your speakers (6 db), so you do need to have a speaker that is made for soffit mounting, and has an adjustment for rolling off the bass by 6 dB. You MUST roll off the bass if you soffit mount, since the soffit itself is providing that boost.

And can you send me a link explaining Johns usual slot walls.

Use the search feature of this forum, or just look around at any of John's designs. There are hundreds of examples here, probably thousands.... :) - Stuart -

Welcome back Stuart! :mrgreen: Please read up on John's recording manual since many of the questions you have will begin to be answered there and truly begin your quest.

Yes - welcome back Stuart - great to see you back. :thu:

Thanks guys! :) I had to take a break, and other stuff started happening that kept me away, but dammit I just couldn't resist the urge to pop back in, and now look what happened! :) :roll: :wink: - Stuart -

This is a small room. Most diffusers do not work well in small rooms.

Things change. For what it's worth, you might be interested in this Stuart. http://www.bozoel.com/hosted/myroom-aco ... _paper.pdf

yea, genus quadratical slatius diffusaurus

Wow gullfo. You're quick :mrgreen: Hey, your attachment is a read only. Dang. :twisted: :mrgreen:

once you download the skp file you should be able to edit as you want. it only includes the slatius diffusaurus components not the entire space as imagined...

I was just kidding gullfo. Already played around with it. And don't bother critiquing. It's only an exercise in Sketchup :mrgreen:

i figured you were kidding about the image but just in case... :wink:

Hey this is all great stuff guys... Thanks so much.... probably made my dissertation a lot more complicated but i will get a better grade if i can get my head round all this stuff!! HAHA I am going to be seeing my UNI lecturer tomorrow and will show him all this material, see what he has to say... and i may get back to you with a few more questions if you do not mind.... Better still i may even see if i can get him to join in the discussion. Thanks again John

Hey Soundman... :) First of all i would like to thank you again for all your advise... I've read through it quite a few times now and its really got me thinking and investigating other avenues that i probably would not have if it wasnt for some of the info you have given me... When i write my dissertation i would like to quote you if you don't mind?? I will of course give you a copy of the dissertation to read once it is done... (If you want it) Anyway.... A few more things i wanted to ask you...

Soundman2020 wrote:

Our lecturer says that the frequency range of your speakers should not go below the cut-off frequency of the room. As this will mean that any frequencies in the room below the cut off will be attenuated by phase cancellation, meaning you wont be able to make accurate judgements on the level of the bass... He says there is not really any way to fix this.... Elsewhere i have read that this can be fixed by stopping all the reflections below the cut-off. What is your opinion on this matter??

Simple: Your speakers need to cover the entire range that your music covers. If you are only mixing spoken voice (no music) then you don't need to cover anything below about 150 Hz, since there isn't much useful energy in the human voice down that low. But for everything else, you do need to hear it, so your speakers need to produce it. For example, if you went with your lecturer's "recommendation" and cut off everything below 50 Hz, then maybe YOU can't hear it in YOUR room, but someone else who listens to your music in another place (such as their car, living room, MP3 player, etc.) WILL be able to hear it. So they will hear stuff that you didn't mix.... BAD IDEA!

I spoke to my acoustics lecturer (Griff) today and showed him this thread... He said he agreed with most of it... I just wanted to clear something up that was my mistake... Above i said about sounds being attenuated below the cut-off frequency due to phase cancellation... That was wrong and probably a bit misleading and obviously influenced your answer... First of all my mistake was that the attenuation is not due to phase cancellation... it is due to air-loading (which i dont totally understand)... to quote howard and angus... "This is the region below the lowest resonance. In this region the room is smaller than half a wavelength in all directions. The environment will “load” any sources of sound below this frequency so that there is a reduced ability of the source to radiate sound into the room resulting at reduced sound levels at these frequencies" When i was talking about the cut-off frequency i meant the area below the lowest axial mode in the room (46Hz)... Griff thinks you got the wrong end of the stick (this is my fault as i did not word the question correctly) as you have talked about EQing the room, which obviously is no use at all unless the music is never going to be played anywhere else except in that room, Right?? I understand that, Griff said he would never advise EQing a room, unless it is a home cinema or something like that!! What i was actually trying to get at is... If you have a room and the lowest axial mode is 46Hz... and you have a set of speakers that have a Frequency response of 40Hz - 20KHz... Is there any point in this??? Griff says that if you put any frequencies into the room below 46Hz then they will be attenuated (due to air loading, not Phaze cancellation) meaning that the bass will seem quieter than it actually is, causing you to turn the bass up... so when you hear it elsewhere the bass will be too loud... I asked him what can be done about this and his answer was... put your speakers on ebay and find a set that are better suited to the room!!! I wondered if you would agree with this? Do you know what air loading is?? Can you enlighten me on it cos i am in the dark??

Soundman2020 wrote:

A "soffit" (more correctly called "flush mount") is just a large flat rigid massive panel around your speaker, which acts like an extension of the front panel. Technically, it is an infinite baffle. In other words, take the very largest piece of plywood or MDF that you can fit across the front corner of your room, cut a hole in the middle of it just big enough for the front of the speaker to poke through from behind, fill the gap behind it with insulation, and you have a soffit. (OK, its a bit more complex than that, but that's the basic idea.) It's just a really BIG front panel for your speaker, that covers the entire room corner, floor to ceiling, and as wide as you can make it.

I am not going to be able to go the "Soffit" route due to the fact that the bedroom studio is in a rented apartment and the landlord basically said no... this is a setback i know but its not the end of the world... so what is plan B ?? :) How far from the wall should i place the speakers and do i need to do any treatment on the wall behind them? They are front ported... Again, i cant thank you enough for spending the time to help with this John

the "loading" effect is (as stated) due to the inability of the room to support frequencies lower than its longest length so you get a pressure effect which can cause a number of issues. you could still soffit mount using portable components instead of built-in - John Sayer's has a components.skp which include all the details to build a set of components which provide a fully integrated environment.

When i write my dissertation i would like to quote you if you don't mind?? I will of course give you a copy of the dissertation to read once it is done... (If you want it)

:shock: Fine by me! PM me when you are ready. Love to see it!

it is due to air-loading (which i dont totally understand)...

Ahhh! Now we are getting somewhere! (Think of it kind of like impedance, except different: the speaker is sort of working against a "resistance" that shouldn't be there, and wouldn't be there if the room was bigger. Sort of.)

The environment will “load” any sources of sound below this frequency so that there is a reduced ability of the source to radiate sound into the room resulting at reduced sound levels at these frequencies"

Very true, but that still isn't a reason to try to eliminate frequencies below the lowest resonance. Yes, there will be issues with such low frequencies in the room, but that doesn't mean you cannot hear them! To my way of thinking, you do need to hear the entire spectrum in your room, from 20 Hz (or even lower) to 20 kHz (or even higher), for one basic reason. Like it or not, those frequencies WILL be in your mix. Therefore you DO need to hear them in order to get them right. If not, then your mix will go out the door and be played on other systems in other rooms, containing things that you never heard. So even though the room will have trouble with very low frequencies, you still do need to reproduce them.

as you have talked about EQing the room, which obviously is no use at all unless the music is never going to be played anywhere else except in that room, Right??

Exactly. EQ cannot fix room problems. At best it can disguise certain problems at certain exact locations in the room, but it cannot fix anything related to time, such as resonance and reverberation issues.

I understand that, Griff said he would never advise EQing a room, unless it is a home cinema or something like that!!

Yup! Totally agree. The time I usually EQ rooms is when I run sound for live events. Since I have zero control over the acoustics, and normally end up with a misc-mash of equipment with unknown and quirky characteristics, I do EQ everything then with a 1/3 octave analyzer and 1/3 octave graphic equalizer, just to take the edge off the most obvious issues. But I don't use EQ on a studio unless the place is acoustically treated to the extreme already, and a couple of important acoustic parameters happen to line up. If that happens, then you can get good results... but only at one point in the room. If you EQ for that location, you can get it good, but at the expense of other locations, which will end up bad. You also need a precision fully-parametric equalizer that is phase-linear with very fine adjustment... and a lot of patience...

What i was actually trying to get at is... If you have a room and the lowest axial mode is 46Hz... and you have a set of speakers that have a Frequency response of 40Hz - 20KHz... Is there any point in this???

In my opinion, yes, there is a point to it. Firstly, if the quoted spec for the speaker is response down to 40 Hz, then it is still putting out substantial energy at 20 Hz, and there is nothing you can do to prevent that, even if you wanted to.

that if you put any frequencies into the room below 46Hz then they will be attenuated (due to air loading, not Phaze cancellation) meaning that the bass will seem quieter than it actually is,

Very true, but I still don't see that as a reason to use speakers that do not give you the full picture. I don't want stuff going out the door that I didn't hear!

meaning that the bass will seem quieter than it actually is, causing you to turn the bass up... so when you hear it elsewhere the bass will be too loud...

Sure, but as a sound engineer you should be aware of the limitations of your room and equipment, and should compensate in your mix. But you can't compensate if you can't hear it! So if you know that your room has attenuation issues below 46 Hz., then you can just get your mix sounding good in the room, then roll off the lows below 46Hz by a few dB.

I asked him what can be done about this and his answer was... put your speakers on ebay and find a set that are better suited to the room!!! I wondered if you would agree with this?

Not really. I do like to hear the entire range, even the parts that I know my room is not doing justice to, precisely so that I can deal with those issues in the mix. To my way of thinking, replacing those hypothetical speakers with other hypothetical speakers that start rolling of at 100 Hz just makes the entire problem WORSE! In this case, your lows would be even quieter, so you would tend to compensate even more, by turning up the bass even louder! So by trying to solve the issue with reduced range speakers, you actually exacerbated the problem.

I am not going to be able to go the "Soffit" route due to the fact that the bedroom studio is in a rented apartment and the landlord basically said no... this is a setback i know but its not the end of the world... so what is plan B ??

Plan B is what Glenn suggested: make portable soffits, or ones that can be disassembled easily when you leave. A soffit is really just a big flat and massive piece of wood with a hole in the middle for your speaker to poke out of, but you can make up the panel from several smaller sections if necessary. Plan C is less attractive: Put the speakers right up against the front wall...

How far from the wall should i place the speakers

As close as you can get them.

and do i need to do any treatment on the wall behind them?

Yup! You always need treatment on reflection points.

Again, i cant thank you enough for spending the time to help with this

:) - Stuart -