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Thread: Small Room Acoustics

  1. #1
    jhbrandt's Avatar
    jhbrandt is offline Acoustics design
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    Small Room Acoustics

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    Small Room Acoustics and appropriate treatment.

    It has been said that 'You'll never get a home studio room to the point where you can do professional mixes like they do in the big studios'.

    This is false.

    Today a great many commercial productions are done in small studios & home studios. You see production after production recorded and mixed 'at the private home studio of the producer'.

    The job of any Studio Designer is to create an acoustically accurate environment so that YOU, the artist, can work; faster & easier - Get the job done & enjoy it - Knock it out and do the next one - Make more money - Have an edge on your competition. This simple result is what my job in room acoustics and room treatment boils down to.

    Amazing productions have been done in the past in horrible rooms because of the talent of the musicians, engineers, & producers - and they continue to this day. I wouldn't tell any of my old friends in the business that they need to change their room because they are doing just fine in their environment.

    This may seem an odd thing to say coming from a design professional. But I follow the wise motto (modified for the music business): "If it's not Baroque, Don't FIX it!"

    That said, I'll move on to my recommendations for Treating your Space. I would expect and APPRECIATE your comments & questions.

    Room size and Ratios:

    If you cannot build or move a wall, room mode calculators will only tell you what you've got. Don't try to see if you have a good ratio. It is irrelevant.
    It is, however, important that you have good modal distribution, especially if you don't use enough bass trapping. (When I say enough, I mean A WHOLE LOT)

    Cubes are bad, as are room dimensions with common denominators. (When designing a studio from ground up I will most often use prime numbers for the room dimensions where possible.) For example; if you have a room that is 5 by 10 by 8, you have common denominators of 2 and 5, so 10 would need to change to 11. This works in feet or meters. It is simple mathematics. Of course, you should run it through a room mode calculator like the one on my publications page to be sure. (the link is on my signature) Again, this is only IF you can do anything about the dimensions. Most people can't, and if that's you, it's not the end of the world.

    The point of checking your room ratio or dimensions with a mode calculator is; it can tell you where you might have problem areas - plus information like: the lowest axial mode (if your room is concrete), the Schroeder frequency of the room, the ideal RT-60 (target), listening position, etc.

    Treatment & Trapping:

    I will always design for 'optimal' although, you can always do less. It is important that one knows and accepts the limitations that the real world imposes.
    For best results, I recommend a minimum treatment of 20% of 5 surfaces. The floor is excluded and since I am mentioning floors; All studio rooms should have hard floors, EXCEPT for Foley rooms which use thick padded carpet.
    Ok, so this means that 20% of four walls and the ceiling will be covered with treatment. Of primary importance are first reflection points (side walls and ceiling) and the back wall. The treatment of the back wall, or lack thereof, will greatly affect the perceived peaks and dips in the frequency response at the mix position, as will:

    Speaker position:

    The speakers that you use, be they M-Audio or ATCs, will always be the 'Elephant' in the room. In other words, compared to the technological advances of electronics and data storage these 'things' are ancient relics that color, distort, and literally screw-up the recorded sounds as they try to 'reproduce' them in your room. The physics of this energy transfer is complex, so I'm not going to bore you. We are stuck with these 'things' for the time being but I wanted you all to know that there are no perfect speakers. More expensive units are usually much better, but get what you can afford and work with it.
    SBIR or Speaker Boundary Interference Response is usually the cause of most monitoring anomalies. - I continue to see folks quoting online references that tell them to keep the speakers at least 'so far' away from the walls. Audiophiles are told to put speakers about 8 feet away from the front wall, etc. This is simply FALSE. I will explain:

    First, let me say that if you get the Low Frequency response in your room 'right', you have won 95% of the battle. Low frequency begins folding around objects at the top of the transition region and truly becomes omni-directional at the Schroeder frequency of the room. (Study the information just below the Bonello Distribution graph on the AllModes tab of my room mode calculator)
    So, the low frequencies produced by the speakers will fold around the cabinet and expand in a sphere in all directions until they hit an obstruction and reflect back. It is this REFLECTION that causes the problems. When the speaker is further from the room boundary the reflection will be delayed for a longer period of time. Sound travels at 343.54 m/sec @ 20° C or 1129.42 ft/sec. @ 70° F. If your speaker face is 1.22 meters or 4 feet from a boundary the delay will be 3.5 mS. This is half the length of a sound wave at 141 Hz., therefore full trapping is required at this frequency to eliminate the destructive reflection. NOW, push the speaker closer to the boundary so that it is half that distance or 61 cm / 2 feet. The resulting reflection will cause a delay (compared to the source) of 1.7 mS, corresponding to the half-wavelength of 282 Hz.

    Now that's quite a bit easier to trap. I'll explain with an example; At zero degrees incidence, a 1/4 wavelength trap is required to be as deep as the speaker is far from the boundary. 61 cm distance = 61 cm deep trap. 122 cm distance (4 feet) = the SAME distance filled with an absorptive trap. -- This is simply TOO MUCH to put in most home studios!

    Solution: Put the speakers/monitors as close to the front wall (boundary) as physically possible. This will result in a much higher interference frequency and therefore a much easier treatment solution.

    Treatment options & fabrics:

    When you build treatment panels, the density or GFR (Gas Flow Resistivity) should follow the thickness of the panels. For example, use higher density/GFR product for thin panels. As the panels go thicker, use lighter/lower GFR product. Rockwool & Fiberglass are made with the same process but with slightly different materials. Rockwool with Basalt and Fiberglass with Silica Sand. Rockwool tends to be crumbly while Fiberglass can be made more rigid and still have a low GFR. BOTH are equally suitable but not perfectly interchangeable. However, it is my opinion that there is too much 'splitting of hairs' over these minute differences. Bottom line: Get what is available to you in your area of the world and make it work. I have never recommended higher density than 60kg/m3 or 4lbs/ft3. (m3 = cubic meters and ft3 = cubic feet)

    The fabric that you choose should be breathable. In other words, you should be able to put it across your face and still be able to breathe comfortably. If not, the gas flow resistivity is too high and it will be acoustically reflective especially at glancing angles.

    If you are concerned with fibers escaping, you can use a 1/2" (12 mm) layer of Dacron. Dacron is used in dress making and furniture, pillows, etc.

    Foam acoustic treatment:

    Everything has a place. I have often used foam wedges on top of regular treatment panels that are placed at reflection points in critical listening environments since the fabric used can be (will be) somewhat reflective. If the treatment is very close to the operator, this could be a serious problem. Therefore highly absorbent foam can be used on top of the treatment panels to take care of the upper midrange frequencies that would otherwise be reflected into the sweet spot.

    Take care in using ONLY foam treatment in your room. It IS helpful, very useful, and has a place - especially in HOME studios, but it is NOT the Full solution to your room treatment needs. You will need much more trapping than can be obtained with a foam treatment plan. Now, I am not saying that you can't do it with foam. I am saying that proper treatment done with foam will be about 2 to 5 times the price of treatment that you can build with a little plywood, rock wool, glasswool, and fabric. These days, every penny counts and it will certainly add up when you build your home studio. For more information subscribe to my youtube channel.

    More to come.

    John H. Brandt - - SERVICES - CUSTOM PRODUCTS - PUBLICATIONS"Twenty thousand dollars worth of Snap-On tools does not make you a Professional Diesel Mechanic"

  2. #2
    mjbphotos's Avatar
    mjbphotos is offline Been Here, Posted That
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    Thanks for this. John. Someone should make this post into a sticky!

    I was always concerned that in my (very small) studio, I can't keep my monitors more than a foot from the front wall, but I can see from what you say that is probably much better for me than trying to move them out into the room further considering I now have full traps on the front wall.

    How abut an addendum for those with small rooms WITH carpet (sometimes its not a choice)?
    Last edited by mjbphotos; 12-28-2013 at 07:42.

  3. #3
    chronicle is offline Dedicated Member
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    Thanks for this. John. Someone should make this post into a sticky!
    Wow. Done deal. Sticky it is, and about time. John, I have to congratulate you for being the FIRST Pro Studio designer to post advice in a STICKY on HR! Fantastic. In that regard, I too am getting ready to start a series of Sketchup illustrations on various construction and treatment subjects, and have been offered a chance to make it a sticky as well. I have tons of illustrations I have modeled over the years, but frankly, if you don't mind, I may need you to "verify" the validity of each. But first, I have to organize them into a series of common sense sequences. And that will take me some time. In the meantime..Happy New Year!
    Chronicle Axiom-What’s the crime of robbing a bank, compared to the crime of starting one?

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    Chili's Avatar
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    Thanks for putting this up, John. It's a great benefit to have one post to refer our new members to.

    Quote Originally Posted by chronicle View Post
    In that regard, I too am getting ready to start a series of Sketchup illustrations on various construction and treatment subjects, and have been offered a chance to make it a sticky as well....
    In the meantime..Happy New Year!
    Looking forward to your post, Rick. Let me know when you're ready.

  5. #5
    grimtraveller's Avatar
    grimtraveller is offline If only for a moment.....
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    Man, that was heavy !
    But heavy good not heavy bad !

    I'm laying it down, but the mice ain't picking it up !

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    mixsit is offline Been Here, Posted That
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    I would like to add a thank you as well. This is going to be a good addition to the HR site!
    Placebo stomps 96k !

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    chronicle is offline Dedicated Member
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    Looking forward to your post, Rick. Let me know when you're ready.
    OK Chile, will do. Right now I'm helping my step daughter move...again. After 50 times over the years , this is it.
    Chronicle Axiom-What’s the crime of robbing a bank, compared to the crime of starting one?

  8. #8
    Dogbreath's Avatar
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    Mad props to ya John.
    good stuff here.

  9. #9
    joel77's Avatar
    joel77 is offline Studio 52
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    Thanks John! Looking forward to reading more.
    Joel, Studio 52
    In God We Trust

  10. #10
    DrewPeterson7's Avatar
    DrewPeterson7 is offline Sage of the Order
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    Awesome thread, and a very interesting (and sensible!) argument for getting your speakers close to the wall - that's the sort of very common-sense problem solving approach you don't often see applied to the home studio environment. I'll be reading this closely.
    "They can kill you, but the legalities of eating you are a little dicier." - David Foster Wallace (1962-2008)

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