Tekker
New member
Is it a good idea to have "studio foam" on the walls directly behind the monitors, if moving out into the room a few feet away from the walls isn't an option?
G
greyman
New member
If the monitors are not FLUSH MOUNTED ........''studio foam'' on the walls directly behind the monitors is a
''MUST'' ......to avoid out of phase frequencies.
''MUST'' ......to avoid out of phase frequencies.
John Sayers
Solar Power!!
Yup - ditto 
Tekker
New member
Thanx greyman, and John for the second opinion 
B
Brian Grey
New member
Tekker said:Thanx greyman, and John for the second opinion
If I had seen this thread earlier I would have shouted "Foam behind monitors!!!" but they beat me to it.
Later,
-Brian
sonusman
Banned
I need some explaining done here.
I understand how the BASS in the sound wraps around the box and how a wall behind the speaker could cause problems with this.
But studio foam? I suppose IF it has excellent absorbtion in the low frequencies then it is a great idea! But I have seen little of it that absorbs much below maybe 300Hz, and that is not the stuff that is going to wrap around the speaker and hit the wall, and come at you out of phase.
Am I missing something here guys?
Ed
I understand how the BASS in the sound wraps around the box and how a wall behind the speaker could cause problems with this.
But studio foam? I suppose IF it has excellent absorbtion in the low frequencies then it is a great idea! But I have seen little of it that absorbs much below maybe 300Hz, and that is not the stuff that is going to wrap around the speaker and hit the wall, and come at you out of phase.
Am I missing something here guys?
Ed
B
Brian Grey
New member
That's a very legit question. I'm not exactly sure on the specs of Auralex's 4" Wedgies foam, but they do suggest using that for the kind of use you're talking about.
Are your ear-level monitors getting down that low anyway? I can't remember what number you said now... They do suggest using 4" foam under your subwoofer to decrease the reflections off the floor. If they suggest using 4" foam under a subwoofer you'd think it would work fine for the monitors.
Are your ear-level monitors getting down that low anyway? I can't remember what number you said now... They do suggest using 4" foam under your subwoofer to decrease the reflections off the floor. If they suggest using 4" foam under a subwoofer you'd think it would work fine for the monitors.
vox
Member
You took the question right out of my mouth Ed.
Wow, brian beat my post by 30 seconds.
Wow, brian beat my post by 30 seconds.
sonusman
Banned
Brian, I have a hard time thinking ANY foam product could absorb freq's 100% any lower then MAYBE 125Hz, and that would be higher then the subwoofers crossover point.
I just installed rockwool at the club, 3" semi rigid. The coefficient is only .46 at 125Hz. I forgot the coefficient of 4", but if you do the math, it would only be like maybe .60 at 125Hz. It only gets worse as you go lower.
Flush mount enclosures enjoy a box that surrounds the speaker enclosure, and the absorbing materials in the box help, as well as the wall material in not letting sub content get out of the enclosure.
If you are going to put your speaker just a couple feet or less from a wall, I just don't think foam is going to help the most important part you want to absorb, which is low frequency content, like 125Hz and below. Now set those puppies in front of a rockwool lined cavity with absorbing hangers in it, then you have something! But you are going to need about what? 3' of depth to absorb that low? Might be worth it though for the improved imaging and lack of ANY phase problems from the wall behind the speakers.
I am still waiting for the resident expert (uh hmmmmmmmm...JS.....) to explain foam as being useful in the stated application. Thanks John in advance for clearing this up in my mind....
Ed
I just installed rockwool at the club, 3" semi rigid. The coefficient is only .46 at 125Hz. I forgot the coefficient of 4", but if you do the math, it would only be like maybe .60 at 125Hz. It only gets worse as you go lower.
Flush mount enclosures enjoy a box that surrounds the speaker enclosure, and the absorbing materials in the box help, as well as the wall material in not letting sub content get out of the enclosure.
If you are going to put your speaker just a couple feet or less from a wall, I just don't think foam is going to help the most important part you want to absorb, which is low frequency content, like 125Hz and below. Now set those puppies in front of a rockwool lined cavity with absorbing hangers in it, then you have something! But you are going to need about what? 3' of depth to absorb that low? Might be worth it though for the improved imaging and lack of ANY phase problems from the wall behind the speakers.
I am still waiting for the resident expert (uh hmmmmmmmm...JS.....) to explain foam as being useful in the stated application. Thanks John in advance for clearing this up in my mind....
Ed
John Sayers
Solar Power!!
Hi mate - yup I should..... ah clear this up. You are totally correct when you say that foam or rockwool won't absorb the frequencies that you refer to YET flush/soffit mounting does effect those frequencies which is why I continually suggest to flush/soffit mount. The difference really is incredible!! more of you should try it.
Now in this situation we have two speakers in a corner projecting forward in the upper mids and highs and also projecting back in the lower mids and lows BUT the area behind each speaker will also reflect the radiations from the opposite speaker as well.
For me the foam is more for the opposite speaker than for the frequencies radiated from the speaker itself. The foam creates a dead environment for the upper mids and the highs in the front projection area. It doesn't solve the low end problem as sonusman quite rightly says but it does create a dead environment for the highs and some mids which IMHO is better than none at all.
cheers
john
Now in this situation we have two speakers in a corner projecting forward in the upper mids and highs and also projecting back in the lower mids and lows BUT the area behind each speaker will also reflect the radiations from the opposite speaker as well.
For me the foam is more for the opposite speaker than for the frequencies radiated from the speaker itself. The foam creates a dead environment for the upper mids and the highs in the front projection area. It doesn't solve the low end problem as sonusman quite rightly says but it does create a dead environment for the highs and some mids which IMHO is better than none at all.
cheers
john
B
Brian Grey
New member
That totaly makes sense to me.
Recap:
1 - If you don't flush mount your monitors you're going to have low-end reflections... it's somthing you're just going to have to live with. It's a compromise between being able to get a different sized monitor some day, and not having AS good of sound.
2 - The best thing you can do for yourself is put some foam behind the monitors to at LEAST stop those pesky highs from bouncing around.
Thanks John... now if I can only get you to respond to my e-mails...
Recap:
1 - If you don't flush mount your monitors you're going to have low-end reflections... it's somthing you're just going to have to live with. It's a compromise between being able to get a different sized monitor some day, and not having AS good of sound.
2 - The best thing you can do for yourself is put some foam behind the monitors to at LEAST stop those pesky highs from bouncing around.
Thanks John... now if I can only get you to respond to my e-mails...
sonusman
Banned
Thanks John. I had a suspicion about all this....
By the way John, I had a little mix thing I did at the club yesterday. We still haven't removed the window right behind my mixing station, but I decided to throw up some rockwool in front of the window just for the day. I in fact put 2 layers of it directly behind me.
The monitors of course have no wall behind them (okay, they do, but that wall is over 50 feet away).
I cannot tell you how different this made mixing! I actually had to mix the stuff with a lot more bass then I am used to! Thing was, the bass translated almost EXACTLY to other playback systems! I found that I could have actually mixed with even a bit MORE bass!
So, next time any of you all are complaining about how when you mix in enough bass on your monitors but it translate to mushy and overbearing bass in other systems, your monitoring environment is more then likely at fault, NOT your monitors (I use Event 20/20's, so I can at least speak for them....).
Flush/soffit mount if you can (I can't at the club, but the big room behind the monitors is a big help here), and make sure to do treatments to the wall behind YOU!!!!
Oh, I did notice right away too that the imaging from the monitors was greatly improved!
By the way Joh,n (yes, another BTW), we decided that in those windows behind and above my mix position that we are going to take the window out, stuff the cavity with 6" or rockwool, and then just cover it with cloth. This will make the sound in the lobby a bit louder, but will make a huge difference at my mix position with the really low stuff below the .99 coefficient of the rockwool at 125Hz. I am thinking that the two layers will by design take care of everything going through the first time down to 125Hz, but it will still allow lower freq's pass too, but by the time the lower freq's get absorbed a bit passing through the first time, bounce around the lobby a bit, then pass back through the rockwool again, that everything below 125Hz should pretty much be taken care of too.
I am missing something? The lobby is about 9' deep, 25' wide, with 18' ceilings. I figure that is enough room for the low end to get messed up in before it hits the rockwool coming back.
Let me know.
Ed
By the way John, I had a little mix thing I did at the club yesterday. We still haven't removed the window right behind my mixing station, but I decided to throw up some rockwool in front of the window just for the day. I in fact put 2 layers of it directly behind me.
The monitors of course have no wall behind them (okay, they do, but that wall is over 50 feet away).
I cannot tell you how different this made mixing! I actually had to mix the stuff with a lot more bass then I am used to! Thing was, the bass translated almost EXACTLY to other playback systems! I found that I could have actually mixed with even a bit MORE bass!
So, next time any of you all are complaining about how when you mix in enough bass on your monitors but it translate to mushy and overbearing bass in other systems, your monitoring environment is more then likely at fault, NOT your monitors (I use Event 20/20's, so I can at least speak for them....
).Flush/soffit mount if you can (I can't at the club, but the big room behind the monitors is a big help here), and make sure to do treatments to the wall behind YOU!!!!
Oh, I did notice right away too that the imaging from the monitors was greatly improved!
By the way Joh,n (yes, another BTW), we decided that in those windows behind and above my mix position that we are going to take the window out, stuff the cavity with 6" or rockwool, and then just cover it with cloth. This will make the sound in the lobby a bit louder, but will make a huge difference at my mix position with the really low stuff below the .99 coefficient of the rockwool at 125Hz. I am thinking that the two layers will by design take care of everything going through the first time down to 125Hz, but it will still allow lower freq's pass too, but by the time the lower freq's get absorbed a bit passing through the first time, bounce around the lobby a bit, then pass back through the rockwool again, that everything below 125Hz should pretty much be taken care of too.
I am missing something? The lobby is about 9' deep, 25' wide, with 18' ceilings. I figure that is enough room for the low end to get messed up in before it hits the rockwool coming back.
Let me know.
Ed
John Sayers
Solar Power!!
yeah - that's a cool idea. It puts you in the middle of the room as opposed to "up against the back wall". If the club are happy with the extra sound in the lobby (which makes sense) then cool !
We flush mounted the events when we first set up here and they sounded fantastic!!
I gotta say it's so nice when you can mix with the bottom end you want rather than the one you know to be correct eh??
What ed's doing here is putting heavy absorption behind him to stop the reflections from the back wall. You can test your setup by putting your hands up to your ears which cuts out some of the rear reflections. If you hear a definite improvement in the imaging etc you have a rear wall problem.
cheers
John
We flush mounted the events when we first set up here and they sounded fantastic!!
I gotta say it's so nice when you can mix with the bottom end you want rather than the one you know to be correct eh??
What ed's doing here is putting heavy absorption behind him to stop the reflections from the back wall. You can test your setup by putting your hands up to your ears which cuts out some of the rear reflections. If you hear a definite improvement in the imaging etc you have a rear wall problem.
cheers
John
sonusman
Banned
Success!
Two layers of 3" rockwool right behind me. No backing to the rockwool, just the lobby. AMAZING difference at my mix position AND in the room overall!
Actually John, there was only a little bit of increase of low end, sounded like maybe below 100Hz in the lobby. The owners were both very pleased with how it sounded in the lobby, and agreed that the added low end made it sound better out there.....
I was standing on the stage with a very loud bass heavy CD playing. What amazed me standing there was that 95% of the sound I was hearing from the PA came from the SPEAKERS, and NOT the back wall! We still have a couple areas to treat, and of course, we will always have a bit or reflection from the mix position front wall, but that wall is about 1/20th of the total rear wall size, so I don't think it's reflections are going to hurt anything.
I am still hearing some hard refections from the side walls, mainly in the 200-1KHz region. If fact, now with the rear wall mostly dead, it is far more pronounced! I could really use those plans for the slot absorbers.... (hint hint....).
What is funny is that I am going to have to relearn mixing that room for the live stuff. I can't wait though to get the Events back in there now that I have the window out behind me and have the rockwool double thick where it used to be. I think about 10 hours of mixing will get my confidence back in my Events.
If that last statement didn't make sense to any of you, consider this. I spent over 3 1/2 years mixing in my old mobile recording studio, which was a converted motor home. The "room" itself had many built in features that made the sound in their very accurate (refer to John's recording manual for why cars are a great listening environment). So anyway, when me and my ex-girlfriend split, and I had to disassemble the mobile rig (long story, so don't ask..I just had to take it apart damnit!) . I have spent the last 6 months doing work in bedrooms, with all their problems. Mixing environments like that made me start to doubt whether I could actually get the job done. My confidence was starting to fade as an engineer. So, these new treatments at the club are a godsend because now I at least have a place to do some mixing that has an excellent acoustical environment like my mobile rig did. I am excited!
Anyway John, you KNOW you have been a big help in all this, and I thank you so much for that. Now, GET ME THOSE DAMN DRAWINGS FOR THE SLAT ABSORBERS!!! :d
Ed
Two layers of 3" rockwool right behind me. No backing to the rockwool, just the lobby. AMAZING difference at my mix position AND in the room overall!
Actually John, there was only a little bit of increase of low end, sounded like maybe below 100Hz in the lobby. The owners were both very pleased with how it sounded in the lobby, and agreed that the added low end made it sound better out there.....
I was standing on the stage with a very loud bass heavy CD playing. What amazed me standing there was that 95% of the sound I was hearing from the PA came from the SPEAKERS, and NOT the back wall! We still have a couple areas to treat, and of course, we will always have a bit or reflection from the mix position front wall, but that wall is about 1/20th of the total rear wall size, so I don't think it's reflections are going to hurt anything.
I am still hearing some hard refections from the side walls, mainly in the 200-1KHz region. If fact, now with the rear wall mostly dead, it is far more pronounced! I could really use those plans for the slot absorbers....
(hint hint....).What is funny is that I am going to have to relearn mixing that room for the live stuff. I can't wait though to get the Events back in there now that I have the window out behind me and have the rockwool double thick where it used to be. I think about 10 hours of mixing will get my confidence back in my Events.
If that last statement didn't make sense to any of you, consider this. I spent over 3 1/2 years mixing in my old mobile recording studio, which was a converted motor home. The "room" itself had many built in features that made the sound in their very accurate (refer to John's recording manual for why cars are a great listening environment). So anyway, when me and my ex-girlfriend split, and I had to disassemble the mobile rig (long story, so don't ask..I just had to take it apart damnit!) . I have spent the last 6 months doing work in bedrooms, with all their problems. Mixing environments like that made me start to doubt whether I could actually get the job done. My confidence was starting to fade as an engineer. So, these new treatments at the club are a godsend because now I at least have a place to do some mixing that has an excellent acoustical environment like my mobile rig did. I am excited!
Anyway John, you KNOW you have been a big help in all this, and I thank you so much for that. Now, GET ME THOSE DAMN DRAWINGS FOR THE SLAT ABSORBERS!!! :d
Ed
John Sayers
Solar Power!!
Yes ed they are coming.....just can't get myself away from the 4WD ....batteries, cookers, fridges etc etc but I'm cool now, had a good day today and have worked it all out for the time being.
So can relax tomorrow and get into your plans. Low mid absorption on the side walls will fix what you are refering to, plus break the reflections up and give the room some diffused sounds.
Mate - i really empathised with the rave about working around on different speakers etc etc. It can throw you out completely. I took an album I recorded 5 years ago and remastered it in the new control room. It was just EQ! The mix was fine, balance reverb etc etc. all was OK but the frequency response of the result was crook cos of the crook monitoring at the studio I was at. Your speakers are your mechanical ears and they have to be compatible with your physical ones. I'm glad your going to get back into your events with enthusiasm.....got your van back eh?.......cept BIGGER!!!!!!!
cheers
john
So can relax tomorrow and get into your plans. Low mid absorption on the side walls will fix what you are refering to, plus break the reflections up and give the room some diffused sounds.
Mate - i really empathised with the rave about working around on different speakers etc etc. It can throw you out completely. I took an album I recorded 5 years ago and remastered it in the new control room. It was just EQ! The mix was fine, balance reverb etc etc. all was OK but the frequency response of the result was crook cos of the crook monitoring at the studio I was at. Your speakers are your mechanical ears and they have to be compatible with your physical ones. I'm glad your going to get back into your events with enthusiasm.....got your van back eh?.......cept BIGGER!!!!!!!
cheers
john
sonusman
Banned
Sort of the rig back. I think better! The rig was just a tad bit too small, even though it did have a nice design. Great for tracking. Decent enough for mixing. NO WAY for mastering though.
I am excited. I have worked out of a few rooms that were "tuned" by pro's, but found them to be very bad sounding. Mixes didn't translate worth a shit! But when I did a quicky mix yesterday of a bands live tracks, I was amazed how the mixes on a regular old cheap car stereo sounded right in the same ball park as I was hearing. I was so used to not adding too much low end in mixes, and after reviewing the work on a few different system, found that I can very well add the kind of low end I would want in the monitors now and it would translate. That is of course a big plus!
I have become a VERY big fan now of "proper" acoustic treatments for a monitoring environment. Not the Aurlex shit, "PROPER" stuff. I am totally in agreement now with your thoughts on diffusion in a control room. Messes it all up. Full rear wall absorbtion (at least nothing getting back to the engineers position) and balancing the rooms RT is the WAY! I suppose it always has been, but hey, some of us learn in steps!
Yes! That was sonusman saying he has learned some valueable lessons in the last 6 months that any half baked engineer should just take as law! Let all who have doubts about competent advice take this as an example.
I just can't wait to work in depth on some stuff now at the club. I suspect that my work will take on a new level.
Thanks for the update on the plans John. No pressure. Certainly, your help in this is much appreciated, and NOBODY is expecting you to move fast on this. Actually, some of the delays have made me think through this stuff, and made it a lot more clear in my mind. So......
Ed
I am excited. I have worked out of a few rooms that were "tuned" by pro's, but found them to be very bad sounding. Mixes didn't translate worth a shit! But when I did a quicky mix yesterday of a bands live tracks, I was amazed how the mixes on a regular old cheap car stereo sounded right in the same ball park as I was hearing. I was so used to not adding too much low end in mixes, and after reviewing the work on a few different system, found that I can very well add the kind of low end I would want in the monitors now and it would translate. That is of course a big plus!
I have become a VERY big fan now of "proper" acoustic treatments for a monitoring environment. Not the Aurlex shit, "PROPER" stuff. I am totally in agreement now with your thoughts on diffusion in a control room. Messes it all up. Full rear wall absorbtion (at least nothing getting back to the engineers position) and balancing the rooms RT is the WAY! I suppose it always has been, but hey, some of us learn in steps!
Yes! That was sonusman saying he has learned some valueable lessons in the last 6 months that any half baked engineer should just take as law! Let all who have doubts about competent advice take this as an example.
I just can't wait to work in depth on some stuff now at the club. I suspect that my work will take on a new level.
Thanks for the update on the plans John. No pressure. Certainly, your help in this is much appreciated, and NOBODY is expecting you to move fast on this. Actually, some of the delays have made me think through this stuff, and made it a lot more clear in my mind. So......
Ed
sonusman
Banned
Oh! The damn stearing wheel is on the wrong side John! You better get that fixed....
Ed
Ed
Blue Bear Sound
New member
Oh no Ed.... that's not what I heard! I have it from a very reliable source (SmellyFuzz), that the one thing that will make more of a difference in response (especially in bass) is the cable! Forget the room, the monitors, their placement... it's all in the cable - especially if it's green-tipped! (ok, I added the part about the green tip!)sonusman said:So, next time any of you all are complaining about how when you mix in enough bass on your monitors but it translate to mushy and overbearing bass in other systems, your monitoring environment is more then likely at fault, NOT your monitors (I use Event 20/20's, so I can at least speak for them....
bwa-ha-ha!
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ola
Newbie
Well, according to Cathy, having monitors is a waste all together but she never said anything about studio foam behind her pioneer hifi speafkers. Maybe we should ask her
barefoot
barefootsound.com
Maybe this will clear things up a bit on what's going on when monitors are mounted close to a rear wall.
As you may know, the flat "anechoic" response curves given by manufacturers are a bit misleading. Most often the measurements are done using the standard IEC 60286-5 setup. The speaker is flush mounted in a large baffle and aims into an anechoic half space. The true full space anechoic response has a –6 dB step in the low end due to diffraction loss (wavelength getting large compared to the baffle). The anechoic response of an idealized monitor with a 25cm wide baffle, similar to the Mackies or 20/20s, would look something like this:
You can see the rolloff starts at the very top of the midrange. Even at 1kHz you have a noticeable amount of energy bleeding toward the back of the monitors.
Now lets look at a qualitative plot depicting what happens when you place the speaker directly in front of a wall. For this discussion we'll just assume it's a very large wall and we'll neglect the effect of the other walls, ceiling, and floor of the room:
The treble is unaffected since the wavelengths are small compared to the baffle dimensions, and all the sound radiates in the forward hemisphere. As frequency decreases energy starts wrapping around toward the back of the speaker. It travels the depth of the cabinet, reflects off the wall, travels forward again and, depending on it's wavelength, either positively or negatively interferes with the directly radiated sound. With lower frequency the ripple in the response gets larger as more and more energy bleeds towards the back. Moving even lower in frequency, however, the wavelength now starts to become large relative the to depth of the cabinet and the phase shift between the direct and reflected sound becomes correspondingly smaller. The response ripple then attenuates and the system once again approximates a speaker flush mounted in an infinite baffle.
If we cover the wall with foam the upper midrange response will look similar to the anechoic response since the foam effectively absorbs all the rearward energy. With lower frequency the absorption efficiency goes down, some of the ripple begins to appear and eventually the infinite baffle approximation holds true again. We can see the qualitative effect in this plot:
This midrange response dip is far from ideal, but it's certainly easier to "learn" this than the ugly response resulting with no foam.
This all illustrates why John's suggestion to flush mount your monitors is such an attractive solution - if you can do it. Apart from the room effects, you at least start out with a flat response.
barefoot
p.s. I didn't even discuss the high frequency ripples caused by diffraction from the cabinet edges which flush mounting also minimizes.
As you may know, the flat "anechoic" response curves given by manufacturers are a bit misleading. Most often the measurements are done using the standard IEC 60286-5 setup. The speaker is flush mounted in a large baffle and aims into an anechoic half space. The true full space anechoic response has a –6 dB step in the low end due to diffraction loss (wavelength getting large compared to the baffle). The anechoic response of an idealized monitor with a 25cm wide baffle, similar to the Mackies or 20/20s, would look something like this:
You can see the rolloff starts at the very top of the midrange. Even at 1kHz you have a noticeable amount of energy bleeding toward the back of the monitors.
Now lets look at a qualitative plot depicting what happens when you place the speaker directly in front of a wall. For this discussion we'll just assume it's a very large wall and we'll neglect the effect of the other walls, ceiling, and floor of the room:
The treble is unaffected since the wavelengths are small compared to the baffle dimensions, and all the sound radiates in the forward hemisphere. As frequency decreases energy starts wrapping around toward the back of the speaker. It travels the depth of the cabinet, reflects off the wall, travels forward again and, depending on it's wavelength, either positively or negatively interferes with the directly radiated sound. With lower frequency the ripple in the response gets larger as more and more energy bleeds towards the back. Moving even lower in frequency, however, the wavelength now starts to become large relative the to depth of the cabinet and the phase shift between the direct and reflected sound becomes correspondingly smaller. The response ripple then attenuates and the system once again approximates a speaker flush mounted in an infinite baffle.
If we cover the wall with foam the upper midrange response will look similar to the anechoic response since the foam effectively absorbs all the rearward energy. With lower frequency the absorption efficiency goes down, some of the ripple begins to appear and eventually the infinite baffle approximation holds true again. We can see the qualitative effect in this plot:
This midrange response dip is far from ideal, but it's certainly easier to "learn" this than the ugly response resulting with no foam.
This all illustrates why John's suggestion to flush mount your monitors is such an attractive solution - if you can do it. Apart from the room effects, you at least start out with a flat response.
barefoot
p.s. I didn't even discuss the high frequency ripples caused by diffraction from the cabinet edges which flush mounting also minimizes.
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