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PostPosted: Fri Apr 26, 2019 11:38 pm 
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I came across this forum and found the information very useful.

I have a question for my home studio.
I use this room predominantly for Tracking, and the overall room sound is good.
The bands are not excessively loud, and there are no isolation issues that I wish to address.

However, when we track, I find that the guide vocals which are tracked live in the room will bleed into the drum overhead mics.
The Bass, Guitars and Keys are all DI'd and all musicians are wearing headphones.

I would like to be able to control this, but hopefully without building an iso booth, since I don't really care about room bleed getting into the vocal track, since this will be redone later in the same room.

Is there any way to achieve this ?

I have sketched up the room, if this helps, since I am wondering whether using the foyer for the vocals, and adding some sort of absorber paneling between the foyer and the room would give me enough absorption of the vocals to stop them bleeding into the OH mics which are in the room..

Hopefully I have provi
Attachment:
IMG_2913.pdf
ded all the information required and followed the forum rules..

Regards Rob..


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PostPosted: Sun Apr 28, 2019 3:56 am 
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I think having the singer in the foyer would be best. That, or have the band play to a click and record guide tracks of the guitars, bass and vocals to that click. Then have the drummer record to the guides.

Greg

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PostPosted: Sun Apr 28, 2019 9:54 am 
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Thanks Greg. That is what I had in mind.. This is an existing room...
Would a gobo placed between the singer in the foyer and the rest of the band in the main room significantly reduce the vocal spill into the overhead drum mics?

I would like to maintain line of sight, so looking for an Abbey Road type of design, with a window.
Without building the gobo, is there any way of estimating the reduction in spill I could expect?
I assume because I want line of sight, the window will be the weak point?

I stumbled on this forum, and it’s got fantastic information..

Regards Rob


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PostPosted: Thu May 02, 2019 5:49 am 
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Quote:
Would a gobo placed between the singer in the foyer and the rest of the band in the main room significantly reduce the vocal spill into the overhead drum mics?

Not significantly. Slightly.

Quote:
Without building the gobo, is there any way of estimating the reduction in spill I could expect?

There are too many factors at play to give you an estimate, but if you have a loud singer, I would say that no gobo is going to be enough for your needs. Especially if you heavily compress your room mics. p

Quote:
I assume because I want line of sight, the window will be the weak point?

Acoustically for the vocal mic, the window will be the weak point. For isolation, the fact that it's not a sealed room is the weak point. Glass actually has WAY more surface density than wood/drywall/MDF.

Why don't you just record rough guide tracks of everything to a click WITHOUT the drummer. Then have the drummer track separately. This would make for easy and clean punch ins too.

Greg

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PostPosted: Fri May 03, 2019 7:26 am 
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+1 Unless this is a live gigging real band, there are loads of advantages to recording the drummer last. Including Musical/Production.
+1 Foyer best.
DD


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PostPosted: Fri May 03, 2019 8:03 am 
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I’d do guide tracks to click too, bit lifeless, then drums to click with guides quiet in case they’re not bang on, then record everything back over the drums with the swang it deserves :D
I’m a drummer.


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PostPosted: Sun May 05, 2019 12:27 pm 
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Thanks for all the advice. I do want to record live, since that’s the area I am most interested in.
I did a test, using a fold up table tennis table as the frame. I draped some Dooners and blankets over the table on one side, and then pumped pink noise and a dBx reference mic. Firstly took a reference point and the placed the gobo between speaker and mic.

I got a reduction of approx 10 dB at the high frequencies. The roll off started at approx 500 Hz.
Interestingly the dB levels at approx 120Hz were 3-4 dB higher than without the gobo, but I suspect that the accuracy of the measurements trail off at low frequencies.

If I could get a 10-20 dB reduction from 150Hz upwards, this could be worthwhile.
Any ideas on whether some proper high density Rockwool or fibreglass would get me in the ballpark, or is this something that I just need to buy a bag and try it out?

Regards Rob


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PostPosted: Sun May 05, 2019 3:28 pm 
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Quote:
I got a reduction of approx 10 dB at the high frequencies. The roll off started at approx 500 Hz. ... Interestingly the dB levels at approx 120Hz were 3-4 dB higher than without the gobo,
Yup. That sounds about right... It really does get louder in the low end, for complex acoustic reasons, and even in the high end you don't get usable reduction. That's typical of that type of solution, and frankly, there's nothing you can do about it.

A typical singer can sing at around 80 to 90 dBC, so your 10 dB drop in the high end would only bring that down to maybe 70 dB in the drum mics: still very loud. Plus you have the low frequency amplification issue, so the total isolation is lower.

A few years ago, Sound on Sound magazine ran a series of tests on several commercial products that attempt to do the same as you tried, for product with names such as "Reflection Filter" and " Portable Vocal Booth", and they came to the same conclusion you did: this solution does not work.

Here's a link to the article: https://www.soundonsound.com/reviews/ho ... cal-booths The test was done in part by one of the world's leading acousticians, very well respected author of many books and papers, Prof. Trevor Cox. You'll notice that you got the same results they did when they tested in a proper acoustical test laboratory. Take a close look at the response graphs in Figure 1... And the explanations are quite clear. Well worth reading that article.

Quote:
Any ideas on whether some proper high density Rockwool or fibreglass would get me in the ballpark, or is this something that I just need to buy a bag and try it out?
It is entirely predictable by acoustic theory, so save yourself the time and money, and DON'T buy that mineral wool! :) Contrary to popular belief, insulation does not stop sound. It damps resonance, and absorbs sound, but that's not the same as stopping sound. That's not intuitive, but it is reality. A lot of things in acoustics are not intuitive. You cannot use insulation to block sound, because the laws of physics don't allow it.

Quote:
If I could get a 10-20 dB reduction from 150Hz upwards, this could be worthwhile.


In order to stop sound, you need mass: heavy, thick, solid materials, such as wood, glass, brick, concrete, steel plate, etc. There's a simple equation in physics called "Mass Law", that describes exactly what you want. It goes like this:

TL(dB)= 20log(M) + 20log(f) -47.2

Where:
TL is the Transmission Loss (how much isolation you get)
M is the surface density of the panel (mass per unit area in kg/m² ), and
F is the center frequency of a one-third-octave measurement band.

You can plug in the numbers, and get the answers you want.

I did that for you, and to get 20 dB reduction at 150 Hz, you would need a panel that has a surface density of about 15.1 kilograms per square meter:

20log(15.1) + 20log(150) -47.2 = 20.001 dB

So, if you wanted to use plywood to do that, plywood has an absolute density of roughly 560 kg/m3, so your panel would need to be 15.1/560 = 26mm thick. That's a little more than one inch. Rather thick. If you wanted to use a thinner panel, it would need to be more dense. MDF is around 720 kg/m3, so an MDF panel would be 15.1/720=21mm thick. That's about 13/16", or a bit thicker than 3/4". If you wanted it thinner still, you could try glass, which is about 2500 kg/m3, so you could use glass just 6mm thick. That's about 1/4".

Those are all options that would give you 20 dB of isolation at 150 Hz. It always gets better as you go higher up in frequency. And you can predict that too: If you look closely at the equation, you'll see that isolation increases at the rate of 6 dB per octave, so you'd be fine for higher frequencies. However, that equation is theoretical for perfect materials in a perfect world: In reality, the rate is more like 4 to 5 dB per octave for real materials in the real world. Let's call it 5 dB/octave to make the math simple. Thus, at 300 Hz you would get 25 dB, at 600 Hz you'd get 30 dB, at 1.2 kHz = 35 dB, at 2.4 kHz, 40 dB, etc. Total overall isolation would be a bit more than 30 dB.

Acoustic theory is a wonderful thing! It saves you buying materials that won't work, since it can predict what would happen if you did. Based on this, to get isolation of 20 dB, from 150 Hz upwards, you just need to build a box from one inch thick plywood, and seal it air-tight all around. In fact, you could cut out a section of the 1" plywood on one of the sides and replace that with 1/4" thick glass so you can see inside. But since you need this for vocals, the box would have to be big enough to fit a person inside comfortably, along with a chair, mic, mic stand, and music stand, as well as having acoustic treatment inside to make it sound good, and a ventilation system, so the singer can breathe and stay comfortable during the session.... In other words, you need a vocal booth! :)

OK, so that's a rather round-about way to describe to you why recording studios have vocal booths: because it's the only way to do what you want. They already tried every possible alternative under the sun, just like you did, and they figured out in the end that the only way to get clean vocal tracks and clean drum tracks, is by putting the vocalist in an isolation booth.

There are no short-cuts, unfortunately! If there were, then somebody would have figured it out already, and put a product on the market... But the oly ones who tried that, failed. As you can see form the Sound on Sound article.

Sorry to be the bearer of bad news, but the only way to do what you want is to get the singer out of the live room, and into either the control room, or a vocal booth.


- Stuart -

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PostPosted: Sun May 05, 2019 4:40 pm 
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Thank you for the detailed response Stuart. I have read the article you linked and it was useful.

A final question before I give up..

Enclosed is a picture of the room looking at the foyer.. Would a moveable 100mm stud wall between the foyer and live room, give me the isolation inherent between the rooms?

I will try and measure the internal room isolation before I consider it...

Regards Rob


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PostPosted: Mon May 06, 2019 10:40 am 
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greenlounge wrote:
Thank you for the detailed response Stuart. I have read the article you linked and it was useful.

A final question before I give up..

Enclosed is a picture of the room looking at the foyer.. Would a moveable 100mm stud wall between the foyer and live room, give me the isolation inherent between the rooms?

I will try and measure the internal room isolation before I consider it...

Regards Rob


Hi Rob,

Is there a reason you want to do a movable wall and not just have some doors?
If you only need 20dB, you could do that with a single solid sliding door with automatic drop seals / a latch mechanism to pull it tight against some rubber seals.

Dan

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Stay up at night reading books on acoustics and studio design, learn Sketchup, bang your head against a wall, redesign your studio 15 times, curse the gods of HVAC silencers and door seals .... or hire a studio designer.


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PostPosted: Tue May 07, 2019 7:40 pm 
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Thanks for an alternative approach. Any idea of what sort of dB reduction I could expect, if it was sealed from the other room? Could I calculate the the door construction if I had a target dB reduction? I would like to see what it would take to match the dB reduction currently between rooms, so the doors aren’t the weak link, but not over engineered.

I have a question on how to measure the dB reduction between rooms. Pink noise in one room, ref mic against the wall and another measurement in the other room at the same point? RTA and then difference in dB between 2 measurement. Take into account wall thickness ?

Thanks again. Sorry for the silly questions.


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PostPosted: Tue May 07, 2019 11:51 pm 
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Quote:
Could I calculate the the door construction if I had a target dB reduction?
If you are just using a single solid door, then it's easy to calculate using a principle of physics called "Mass Law", which goes like this:

TL = 14.5 log (M * 0.205) + 23 dB

Where: M = Surface density in kg/m2

That gives you the general overall isolation that you can expect from any given "mass" (surface density). There's a more complete version of the same mass law where you can calculate the isolation for specific frequency bands:

TL(dB)= 20log(M) + 20log(f) -47.2

Where:
M is the surface density of the panel (mass per unit area (kg/m²) ), and
F is the center frequency of any one-third-octave measurement band

I already gave you the Mass Law equations before, but it looks like you missed them, because you asked again...

Both of those are for single-leaf barriers: eg, just one solid "thing", such as a door, or a brick wall, or something like that. You can also use them if the barrier is built up from several layers of "something". For example, three layers of drywall and one layer of OSB, all on top of each other with no air gaps. You just add up the individual surface densities of the the layers and use that total for "M" in the equations.

If you have two doors back-to-back with small air space between them, then it's a bit more complicated to calculate, but not too hard. You get a LOT more isolation like that, but because that's a resonant system, its a bit tougher to do the math.

Quote:
I have a question on how to measure the dB reduction between rooms. Pink noise in one room, ref mic against the wall and another measurement in the other room at the same point? RTA and then difference in dB between 2 measurement.
Pink noise is great for calibrating systems and checking levels, but not so good for testing isolation. The problem is that pink noise sounds just like random background noise, so when the levels are low, you can't really distinguish what is your pink noise and what is the background ambient noise.

The best way to check isolation levels in a studio, is just to play music. Very loud, on a full-range speaker system, and using music that has plenty of bass content. Play it inside the room at around 100 dBC SPL (wear hearing protection!) measuring the level inside with a hand-held sound level meter set to "C" weighting and "Slow" response, then go outside and measure the level again. The difference between the two is how much isolation you are getting. So for example if you played at 100 dBC inside and measured a level of 70 dBC outside, then you are getting 30 dB isolation. It's that simple.

If you need to know how much extra isolation you need, then turn off the music inside and go measure outside at the same spot you were before, at a very quite time of day (eg, 4:00 am) when there is no wind, and no other nearby sounds. The difference between that and the level you measured before at the same location, is how much EXTRA isolation you need, in order that your sound level there is reasonably quiet.

Quote:
Thanks again. Sorry for the silly questions.
Those are not silly questions at all! The only "silly" one, is the one you didn't ask because you were embarrassed! So ask away.... :) That's what the forum is meant for...

- Stuart -

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PostPosted: Wed May 08, 2019 10:15 pm 
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Thanks for a great reply Stuart. I will measure the current room isolation and then calculate an equivalent single mass structure for that same isolation...
I then have a starting point.
Thanks again


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PostPosted: Wed May 08, 2019 10:50 pm 
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The difficultly you will have, is that your rooms are not currently sealed due to the large opening between the room and the foyer. So you can't measure the isolation of your wall between those rooms.

Your best bet would be to find out what your wall is made up of, calculate the estimated isolation using either mass law (as above) in the case of a single leaf wall, or if it's plasterboard on studs (a coupled 2 leaf system) you'll need a new formula (I'm sure Stuart will provide that if you need it).
Then slightly exceed that figure with your door design, then in practice you will have similar isolation.

Dan

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Stay up at night reading books on acoustics and studio design, learn Sketchup, bang your head against a wall, redesign your studio 15 times, curse the gods of HVAC silencers and door seals .... or hire a studio designer.


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PostPosted: Thu May 09, 2019 8:29 am 
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Thanks Dan. I will measure the current isolation between the main room and another room next to it, with the same internal wall construction. Sorry I didn’t make that clear.


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