Room Diffusers (part I)

September 22nd, 2008


 

Room diffusers are the answer for the dreaded “flutter echo”.  As discussed in earlier blogs, these evenly spaced repeating of sound waves greatly interferes with the listener’s ability to hear clean clear audio from a speaker, stereo or live performance.

If you have deep pockets; or a large budget, there are lots of commercial solutions to this major acoustic dilemma. As always, ask questions and do your research about products and the firms that sale those diffusers. For those who are willing to put in the sweat equity I will lay out some solutions that will greatly reduce flutter echo in any room no matter its size.

SHELVING

The simplest of all solution to flutter echo in a room is to put up shelves or shelving units. Shelves are not only a great storage solution, but they also work well for helping eliminate evenly spaced repeating waves of sound (flutter echo).   How?

The cause of this problem are hard parallel walls or parallel hard floor and ceiling, shelving helps change the profile of the rooms walls, eliminating the ability of the sound waves to form evenly space repeating of  themselves. When you put up the shelving (or whole units) make sure that each set of shelves are offset from other shelves (regardless if they share the same wall or on opposite walls from each other) a minimum of six inch offset (high or lower) will do the trick. The more objects place on the shelving, such as books, stereo equipment etc. will add to the irregularity of the wall(s), which in turn will improve the sound quality of the effected room.

CURTAINS

One of the other easy to do solutions is hanging curtains over one or more walls. The curtain material should be a heavy weave; some great materials are wool, wool blends or burlap. Both these materials have unique smells.  The “burlap odor” just as that of untreated wool, it is very noticeable,  but this will fade away over time. Or you can impregnate the material with any interior paint. When the fresh paint smell fades off in a few days, the burlap smell will be eliminated. Pleating the curtains helps greatly in giving the covered wall an irregular profile. The slowing of the sound waves as they travel through and back thought the material helps eliminate the sound waves ability to produce flutter echoes.

CARPETS  

Placing carpet on the wall will have the same effect as curtains. If you have a parallel ceiling to the floor, putting down carpet on the floor will change the floors profile, this will help to reduce the ability of sound waves bouncing off the ceiling and floor becoming evenly spaced. If possible, make sure to place carpet padding on the floor before laying down the carpet, this will add in slowing the sound waves. In this case, the thicker and deeper the carpet, the better. (Where is that funky old shag carpeting from the 70s when you need it?)

These measures are the easiest and the most cost effect measures to combat the dreaded flutter echo.

Next week’s blog: Building diffusers part II- How to build your own diffusing devices from scratch

Posted in acoustics | No Comments »

Room Speaker Placement

September 8th, 2008


NOTE TO READERS: The measures that I will discuss in this week’s blog are things that can be employed by anyone. Including those that consider themselves as the “non-do-it-yourself type.”

The great part is, that these room acoustic improving measures (excluding the purchase of speaker wire) are free of cost!

ROOM SPEAKER PLACEMENT

We have so far in the “Sound Advice” blog discussed the main acoustic problems rooms can suffer from, some corrective measure to solve these problems and how to test for acoustic problems.

A great but often overlooked way to improve the acoustic sound quality of your room is the placement and positioning of your speakers. The placement of speakers in your room greatly affects the tonal qualities and realistic sound reproduction of the audio your ears will perceive.

PLACEMENT OF TOWER (FLOOR) SPEAKERS

Tower speakers should be place at least a minimum of 12 inches out from the wall. This will allow the speakers to deliver optimal sound quality.

What happens if you place your speakers closer than the recommend minimum?

The closer to the wall you place your speakers the duller your middle and upper lower range sound tones become. With that said, if you have tower speakers in the lower price range category, that have small bass speakers, placing them closer to the wall will deliver a move powerful low range response.

If your towers have a two or three way speaker setup, they normally have separate controls on board for fine tuning your High-end, Mid-range and bass speaker. You will need to increase the level settings of your mid-range speaker to help compensate for the dullness created by you, when you ignore the minimum placement recommendation.

You will also want to be mindful of furniture placement. Avoid placing couches, love seats or chairs directly on the wall opposite your tower speakers. The wall apposing your speakers will reflect a lot of the speaker’s sound waves back into your ears from your rear, resulting in the delivery of over saturated bass response and poor overall sound quality to your ears. If you don’t have the space in your room to move your couch, love seat or chairs at least two feet from the wall, the placement of a wall hanging made out of thick fabric will help increase the quality of the sound your ears receive.

While shelving in your room serve help the overall acoustics, by acting as a natural sound diffuser, those really nice glass and glass top coffee tables can add unwanted reflection of the higher sound frequencies, especially when you crank up the volume on your sound system. To reduces this negative factor, you should cover the glass surfaces with a sham. My suggestion would be to use a sham made out of wool or a heavy cotton weave. You should also be aware, that windows pose an even greater problem of unwanted sound reflection, much more then glass tables and glass table tops, since they have a greater surface area. Heavy drapes or curtains are a very effective solution to this problem.

Another problem many people face, is the placement of their speakers next to their television, beside the power of the magnets from your speakers effecting the television’s picture. The sides of the television can cause and unwanted sound reflection effecting the room’s acoustics. The simple solution would be not to place your speakers next to your TV. If that is not an option for you due to your room’s layout, then the next best thing is to move your speakers forward, so they are no longer parallel with the sides of your TV.

SPEAKER ANGLING
Another great away that won’t cost you a penny to positively effect your rooms acoustics, is a technique called “Speaker Angling.”  I used this myself to help out my friends at the “911 Media Arts Center” in Seattle, Washington, using this simple technique improved the acoustic profile of their theater and greatly reduced the level of flutter echo.

Instead of placing your speakers so they face the apposing wall, you will be angling  the speaker toward each other. Using this technique can dramatically improve the sound quality that the speakers deliver to the listener’s ears, by reducing the area of initial sound reflections off parallel side walls or opposing wall ( which is the cause of flutter echo).

You will need an additional person beside yourself to employ this technique. First, sit yourself faces your speakers, then have the person helping you turn the speakers toward each other. You will hear the flutter echo decrease as the speakers are angled in toward each other. What you are listening for is, the “Magic position,” this is the point where there is the least amount of “flutter echo” and the best treble, mid-range and bass response.

There are is no set angle to set your speakers. Though, I find most people find their “magic point” some where between 5-45 degrees. It really depends on the speakers and size and dimension of your room as to how far in you will need to turn your speakers.

USING THE CORRECT SPEAKER WIRE

Another important factor in the delivery of good sound quality is using the proper gauge of speaker wire. In some cases, you just don’t have a choice in this matter, as some speaker manufacturers only sale pre-wired speakers. Then it becomes a matter of how far from the sound source you can place your speakers, based on the gauge of the speaker wire supplied by the manufacture.

I have seen wire as thin as 22 gauge used by some manufacturers of low price speakers. Most speaker wire world wide range from 20-12 gauge. The “gauge” is the thickness of the speaker wire. The lower the gauge number, the thicker the wire. The farther away from the sound source the speaker is drawing its signal from, the greater the loss of signal quality. To compensate for this loss you need to increase the thickness of the speaker wire you are using to deliver the signal to your speakers.

These are my recommend guidelines for the gauge of the speaker wire vs. distance from the source of the sound signal.

  • less than 10 feet-22 gauge
  • 10-20 feet-20 gauge
  • 20-40 feet-18 gauge
  • 40-80 feet-16 gauge
  • 80-160 feet-14 gauge
  • more than 180 feet -12 gauge

Next week’s blog will address the very serious problem of “FLUTTER ECHO” by giving “do-it-yourself” solutions to the reader in use of diffusing methods and materials.  

Posted in acoustics | No Comments »

How to test for acoustic problems in your room

September 2nd, 2008


TESTING FOR ACOUSTIC PROBLEMS
In previous blogs I have talked about the most common acoustic problems affecting rooms and how to take corrective measures. The only question left, is how you go about testing your room for these common acoustic problems? In this article we will cover some ways of testing for these problems.

The Hand Clap Test
If you have a good set of ears and some patience, there is a test you can employ that won’t cost you a penny, just some time. This test can help identify problematic sound reflections in your room.

The hand clap test: so named for obvious reasons. You will need to stand or sit as close the middle of your room as possible and clap your hands once, listening carefully to how the sound is affected. Do you hear a slow, even decay? Do you hear a single hard reflection? Or do you hear a multiple of closely spaced repeats? These faster echoes are known as flutter echoes and are created when sound bounces back and forth between two parallel walls or a parallel ceiling and floor. Flutter echo is something that you will definitely want to take measures to correct. One of the cheapest way to address the very serious problem is the use of diffusing methods. (this subject will be be covered in two weeks)

USING A SPL METER IN CONJUNCTION WITH A TEST-TONE CD

If you have a little money to spend, a very cost effective tool that you will want to pick up is a SPL meter. SPL meters are devices used to get an exact reading of your rooms sound levels. For most people the easiest way to effectively use this tool is to purchase a test-tone CD. To test your room, take your SPL meter and get as close to the middle of the room as you can, now start the test-tone CD, you will need to write down each number displayed by the meter. It will take around an hour or so to complete the room test. This test will give you a complete picture of your rooms acoustic responses. Now you know what problems your room has (if any) and what corrections to your room’s acoustics you will what to undertake.
If you have a big enough budget there are many high end testing devices and software on the market, just remember to do your research to find the best deal for your budget and needs.

In testing, one important point of information for all of you would be testers, is that each frequency has a different size wave length. How do you go about finding the size of the wave of a frequency? Here is a easy mathematically formula you can use to find the size of the wave of any given frequency: simply divide 1130 (sound travels at the speed of 1130 feet per second through air) by the frequency. As an example, a 100 Hz would be 11.3 feet and a 1000 Hz would be 1.13 feet. The rule of thumb: the higher the frequency the shorter the wave and the lower the frequency the longer the wave.

Next week’s blog: Room speaker placement. In order to deliver the best sound quality to the listener’s ear proper speaker placement is key. This is a no cost measure that even the non-do-it-yourself types can undertake to improve the listening quality of their room.

Posted in acoustics | No Comments »

BUILDING A BASS TRAP

August 25th, 2008

This week’s blog is all about Building Bass Traps.

A bass trap is a control measure for the dreaded “standing waves.” a build up of pressure in a room caused by low frequencies. This is a standard problem face by people who’s room wall are parallel. The “trap” is use to reduce the over abundance of 80-300Hz frequency sound waves (the bass range). They are most effective, when they are placed in corners of the room, which is where sound wave pressure is the highest .

There are 3 main types of bass traps are: The “cylinder,” the “panel” and the “corner” bass trap. In this article you will learn how to make the “cylinder” and “panel” types of bass traps.

The key filler ingredient is fiberglass or rock wool, use only materials rated with high R-values.

Materials for the trap’s frame can be made out of wood, metal and even chicken wire! The frame covering can be made from plywood, plastic or burlap.

THE CIRCULAR BASS TRAP

The easiest of all the trap to design is the circular bass trap. What you will need as far was materials is rock wool or fiberglass; chicken wire; burlap; 3/4 inch plywood, adhesive and staples.

Tools needed for this project: jig or skill saw, wire cutter, heavy duty scissors or sharp knife, staple gun, a roll of string, safety goggles and gloves.

First Step: Place on your safety glasses/gloves/mask (Note: Remember to wear safety gear throughout the whole process!), then roll the filler material(rock wool or fiberglass) tightly, the roll should be no smaller than 4 inches in diameter and I would suggest as a maximum no more then 12 inches, cut the remainder of the filler away with either a pair of heavy duty scissors or sharp knife.

Now Second Step: take the chicken wire and wrap it around the filler use the wire cutters to snip the wire to desired length and then firmly fasten the chicken wire unto itself.

The Third Step: cut the 3/4 inch plywood in to two circular disc to the same diameter as the top and bottom of the trap and attach the chicken wire with staples to the plywood discs.

Step Four: wrap the cylinder tightly with burlap (FYI- you can spray paint the burlap any desired color prior to added it to the cylinder) and fix the burlap to itself with adhesive.

The Final Step: take the roll of string and cut it at the minimum of 4 sections and tie them around the cylinder in several places to secure the burlap in place until the adhesive has a chance to cure (approx. 24 hrs). Once the adhesive is dried remove the string. Congratulations, you now the owner of your own cylinder bass trap.

You can now place the cylinders in the corners which will reduce the low-end wave pressure in the effected room.

THE PANEL BASS TRAP

The materials you will need as a filler is rock wool or fiberglass. You will need pine studs (2″-4″ in width) to build your frame, you will also need a sheet of 1/4 inch plywood, burlap, 2″ & 1″ nails, adhesive and staples.

The equipment you will need for this project are safety gloves & glasses, a saw, hammer, staple gun, heavy duty scissors or sharp knife.

The First Step: is to decide and design a plan as to how wide and long you would like the frame of the panel trap to be.

Step 2. place on your safety glasses/gloves/mask (Note:Remember to wear safety gear throughout the whole process!), before using a saw to cut the studs to desired sizes for your panel trap’s frame, then use a hammer (or optional nail gun) to fasten the frame together with 2″ nails.

Step 3. Use a saw to cut the 1/4″plywood to fit the frame you have made, then tack the plywood to the frame with the 1″ nails.

Step 4. Now cut the filler to a size where it fit snuggly inside the frame, and cover the plywood bottom located inside the frame with a strong adhesive. Then press and place the filler inside the structure.

Step 5.Take the burlap and use the heavy duty scissors to cut it, make sure you cut it large enough to overlap the frame of the panel trap. Overlap the top of the frame for the panel trap with the burlap, then stretch and tack it to the sides of the trap with staples and staple gun.

You now have the option: to add coasters or wheels to the bottom of the panel trap to make it easy to move or re-position; or to use toggle bolts to permanently fix the panel trap in position on a wall or covering a corner. For those of you that would like to build a trap for underneath your speaker or sub woofer. make sure to build the trap a little larger than the base of the speaker or sub-woofer you are going to rest on the trap. Make sure to flip the trap over and use the plywood side to rest your speaker on.

Please note, that using the plywood side of the trap will work to effectively to reduce the the low end frequencies of 80Hz-140Hz (by facing out the burlap side you help reduce low frequencies from above 140Hz to 300Hz). By placing a panel traps on the wall behind where you have your speakers (plywood side facing out), you can reduce a lot of the “low-end frequency bleed through” to the neighbors living directly below you and behind the wall where your speakers are set.

For the non-do-it-yourself-types, (who have the budget) you will be able to find manufacturer’s produced Bass traps, the most popular design being the corner units. Be a smart consumer and shop around for the best prices.

Now you know what measures to use to reduce “standing waves” in poorly acoustically designed rooms. If you don’t already know how, you will want to know a few ways to tests and figure out what and where the problem areas might be in your room, next week’s blog will cover that issue.

Next week’s blog’s tittle: “How to test for acoustic problems in your room.”

Posted in acoustics | No Comments »

COMMON ACOUSTIC PROBLEMS IN ROOMS

August 16th, 2008

COMMON ACOUSTIC PROBLEMS IN ROOMS

What is one of the most common acoustical problems in many rooms? “Flutter echo”. What is flutter echo? First let’s start off by giving those of you who don’t have a background in acoustics the definition of an “echo”, an “echo” is sound being reflected off of a surface and returning to you ears. Like what you experience when shout hello in a canyon. A flutter echo is equally spaced in time repetitive and successive sound reflections. This to varying degrees can make speech difficult to understand or in some cases totally unintelligible in rooms. It can also effect your perception of music’s tonal qualities by adding a negative pitch or timbre coloration. This problem can be greatly amplified by speakers and their placement in the room. What are the main causes of this Problem? Those perfectly designed parallel walls and the ceiling and the floor of a room being parallel. So when you design your room, keep this in mind.

For those of you whose room has already been built, there are some measures I can suggest that can greatly reduce or eliminate this problem completely. The first is the use of sound absorption materials on one or more walls and or on the ceiling. There are many high-end products on the market designed to help you address this problem, if you have a big enough budget. For those who don’t have a big budget, you can use egg cartons, office ceiling & wall tiles. The general idea is to keep the sound waves from reflecting back at you in an equally time spaced repetitive rate. The second suggestion would be the use of sound diffusers unlike absorption materials diffusers redirect and or scatter sound waves, thus prevent the sound waves from being able to reflect back at you in a uniformed rate. Again, if you have the budget there are lots of high-end products to meet your needs. If your budget is tight, you can also make your own diffusers. Wood make a great diffuser so does Masonite. The idea is to make sure the surface is curved, angled or slotted. Strategically placed book shelving will also work well as room diffuser.

Another common acoustical anomaly - that of “standing waves.”
Here we are describing a type of low frequency reflection, caused by dimensional relationships within the room. Low frequency standing waves can be predicted mathematically when the dimensions of the room are known. Standing waves build up in the listening environment and conspire to sabotage the low-end performance of stereo systems and can greatly affect the recording qualities of a studio’s “live room”. A low frequency standing wave is likely to “bloat” the character of the bass, causing severe peaks at points throughout the range. The only cost-effective method available on the open market for the treatment of standing waves is the use of ASC Tube Traps (AKA bass traps). These units, placed in the corners (The point of maximum pressure) can dramatically improve the quality of low frequency sound in a space plagued by standing waves.

For those with do-it-yourself abilities, good news, in next week’s blog, I will give you step-by-step instructions on low cost ways to make your own room bass trap.

Posted in acoustics | No Comments »