DIY Subwoofer Risers

[Big Daddy]

BUILDING SUBWOOFER RISERS

Many people report better bass response by raising their subwoofers. One of the most popular products for this purpose is the Auralex Isolation Risers Gramma & Great Gramma, Subdude, and SubdudeHD. According to Auralex, Gramma stands for Gig and Recording, Amp and Monitor, Modulation Attenuator. I have no idea what that name means.

Gramma Specifications:
23" long x 15" wide x 2.75" high
Weight Limit: 300lbs.
Market Price: $50

Great Gramma Specifications:
30" long x 19" wide x 2.75" high
Weight Limit: 300lbs.
Market Price: $80

Subdude:
15” x 15” x 2 3/4”
Market Price: $50

Subdude HD:
15" x 15" x 2.5"
Market Price: $60

Where to Buy
http://store.audioholics.com/section/66443/1/auralex
http://www.sweetwater.com/store/detail/GRAMMA
http://www.sweetwater.com/store/detail/GreatGRAMMA/
http://www.sweetwater.com/store/detail/SubDude
http://www.sweetwater.com/store/detail/SubDudeHD/


Isolation Pads from Elemental Designs (4" Height, from $55 to $85):

http://www.edesignaudio.com/index.php?cPath=2_126


Auralex Mopad, $39.95:
http://www.sweetwater.com/store/detail/MoPAD

Auralex SpeakerDudes, $40:
http://www.sweetwater.com/store/detail/SpeakDudeHD

Low cost alternatives:

http://shop.mapleshadestore.com/products.asp?dept=1
http://meniscusaudio.com/bvd-feet-p-744.html


Reviews:
http://www.hometheaterhifi.com/volum...ma-4-2004.html
http://namm.harmony-central.com/WNAM...at-GRAMMA.html
http://www.amazon.com/Auralex-GRAMMA...owViewpoints=1
http://www.sweetwater.com/store/detail/GRAMMA/reviews/
http://www.zzounds.com/productreview--AURGRAMMA


I decided to make my own subwoofer isolation risers for two of my box-type front-firing subwoofers. In the spirit of the B.S. from Auralex, I decided to call them Grampa (Gyration Rhapsody Ass Moped Physical Amplifier).

According to Houghton Mifflin Dictionary:

Gyration: Circular or spiral motion. An oscillation or varying between states.
Rhapsody: Exalted or excessively enthusiastic expression of feeling in speech or writing. In music, a usually instrumental composition of irregular form that often incorporates improvisation.
Ass: Any of several hoofed mammals, resembling and closely related to the horses but having a smaller build and longer ears, and including the domesticated donkey. A vain, self-important, silly, or aggressively stupid person. The buttocks.
Moped: A lightweight motorized bicycle that can be pedaled as well as driven by a low-powered gasoline engine.
Physical: Of or relating to the body as distinguished from the mind or spirit. Of or relating to matter and energy or the sciences dealing with them, especially physics.
Amplifier: A device, especially one using transistors or electron tubes, that produces amplification of an electrical signal.


For the top, I used high quality Birch 3/4" plywood and for the legs, I used standard 2x4 wood. The size of each subwoofer riser is 20" by 20". Instead of plywood, you can use 3/4" MDF wood.

I drilled holes about 2.5" apart and attached the top to the legs with long screws.

Next, I cut the carpet to size and used 3M heavy duty spray glue to attach the carpet to the top.

For the bottom, I used staples to attach the carpet to the board.

It is a good idea to fill the space between the the two legs with 1/2" Acoustic Foam or 1" Acoustic Foam. Regular foam is not effective in absorbing the lower frequencies. If you want your riser to also act as a sub trap, build a 2 feet riser and fill the inside with rigid fiberglass or mineral wool. Wrap the surrounding of the riser with carpet or grill fabric.

You can also buy much cheaper solid foam from fabric stores, craft stores, mattress stores, or Wal-Mart. The one from Wal-Mart is 15" x17" with a thickness of 2". It looks like the following picture, but smaller.

This is a picture of the finished risers.

This is one of the risers under the Acoustic Audio 12" subwoofer.

After the risers were finished, I added new legs to them and increased their height by 6". I also added more dampening foam to the bottom. Now, I have to paint the legs and cover everything with carpet.

Additionally, you can add rubber vibration isolation pads or spikes to the bottom of the legs.

http://www.av-outlet.com/index.html?...tml&lang=en-us
http://stores.ebay.com/South-Florida...=p4634.c0.m322
http://stores.ebay.com/PARTSPIPE/Flo...=p4634.c0.m322
http://www.soundproofcow.com/sound-i...n-control.html
http://www.drillspot.com/tag/vibration-isolator/
http://www.fullcompass.com/product/316672.html
http://www.fullcompass.com/product/239266.html
http://www.fullcompass.com/product/239265.html
http://www.fullcompass.com/product/239264.html
http://shop.ebay.com/items/?_nkw=spe...ikes&_osacat=0
http://www.parts-express.com/wizards...hFilter=spikes

If you get desparate, you can go to a sporting goods store and buy a few hockey pucks.

HockeyPuck.jpg

ROUND SUBWOOFER RISERS

I was so happy with the results of the square risers described above that I decided to build two round subwoofer risers for my two cylindrical Hsu subwoofers. I am sure you realize that building a round riser is a much more difficult task. I decided to call them the Round Great Grampa Subwoofer Risers. Here is a pictorial summary:

These are the wooden tops. The diameter of each one is 24" to accommodate the 23.5" diameter of the Hsu subs.

These are the attached legs. The length of each leg is 6".

After the legs were fully attached, I covered the tops and the legs with carpet and attached dampening foam to the bottom. I used the 3M spray glue to attach the carpet to the top and used staples to attach the carpet to the bottom of the wooden top and the legs.

I then attached 4" legs to the subwoofers. The subs already had metallic spikes. I was not very happy with them as they were two short and I was worried about scratching the wood floor.

I bought 16 Buttkicker RI-K28-4 Small Vibration Isolators from AV Outlet for the four subwoofers/risers in my HT room. The cost was $7.99 per package of 4 for a total cost $31.96 + Free shipping.

Go to AV Outlet, on the left hand side, click on Seat Shaker & Amplifiers, and then click on Rubber Vibration Isolators for Chair and Platforms.

This is a picture of the back of the isolators.

I attached the isolators to the legs of the risers with wood screws.

I then carried the heavy subs and put them on top of the round risers.

The final step was to run test signals and calibrate them again. With my old and reliable SPL meter in hand, I turned the receiver’s test tones. As soon as I heard the test tones through the 4 subwoofers, I jumped about 6 feet into the air. It was so much louder than before. Even my wife noticed it in the next room. Wow....just wow!!!

I am not exaggerating. It was almost 10db’s higher than before. Immediately, I had to run and turn the volume of all the subwoofers down. After I completed the calibration, I played some CD’s and could not believe that such a simple and inexpensive (about $20 to $30) riser can make such a huge difference. I HIGHLY RECOMMEND THEM TO EVERYBODY.

Did I notice a change in the bass response because of the rubber isolators? Well, I tried to measure the perfromance before and after with my SPL meter. There may have been a difference of 1 or 2 dB, but that can be due to error. I felt that there was a very small amount of tightness, but it could be due to placebo.

For $8 per subwoofer I bought peace of mind and hopefully I managed to silence the naysayers who have been complaining that the DIY risers do not decouple the subwoofers effectively from the floor. Personally, I think decoupling from the floor is over-rated. Raising the subwoofer and dealing with vertical axial mode is far more important.

How High a Riser?

Theoretically, if your ceiling is 8ft high, you can go up to 2 feet. However, when you raise it that high, you should really fill the gap under the riser with dense material. Take a look at these SubTraps from ASC.

SubTrap1.jpg

SubTrap2.jpg SubTrap3.jpg

18” SubTrap (50 Hz) Standard, most Subwoofers: $469
22” SubTrap (30 Hz) Large Subwoofer: $586
http://www.asc-home-theater.com/subtrap.htm

Once you hear the difference, you’ll never go back. The SubTrap is more than a simple isolation stand. In addition to isolation, it absorbs excess bass and decouples your sub-woofer from room mode. The end result is a unique product available only from ASC. Raise your subwoofer up to its full performance potential. Just slip the ASC-SubTrap underneath your subwoofer and you’ll create the powerful “SubStack.” Instantly improve bass detail, changing “muddy” low frequency playback into a richly detailed picture. Not only does the SubTrap increase bass extension and punch, it also gets rid of "one note bass.

By raising the sub off the floor and putting a SubTrap under it, the subwoofer is effectively decoupled from the vertical room mode. Excess bass buildup is reduced and the playback volume of the subwoofer can be cranked up much higher than before.

Reviews:
http://hometheaterhifi.com/volume_12...ap-6-2005.html
http://www.stereophile.com/musicinth...ic/index1.html

A LOW COST TWEAK FOR SPEAKERS

Here is another tweak for your speakers that does not send you to the poor house.

I have been thinking about putting something under my vintage Polk speakers. I have searched the internet and found crazy things for $300 or $400 each. I finally gave up and went to my favorite high-end audio/video tweak shop, Home Depot.

I went to the crown moulding department of Home Depot and bought these wooden mouldings. They come in different sizes. I bought 8 of the 2" x 2" mouldings for $1.10 each. They were on sale. I put them under the speakers for additional stability and decoupling from the floor. You can paint them if you want. I believe I noticed a slight improvement in midrange, but it could be placebo. For less than $5 per speaker, I am not going to worry about it.

[Big Daddy]

THEORETICAL FOUNDATION BEHIND RISERS/STANDS/ISOLATION FEET

Risers, stands, and isolation feet can have three effects:

1. Raising the tweeters of bookshelf speakers and bringing them up to ear level. It is recommended that the tweeters of the front speakers should be at ear level.
2. Isolation and decoupling from the floor and reduction in the energy transfer and vibrations between the floor and speakers/subwoofers. Hearing this benefit may be a bit difficult and hard to quantify.
3. Changing the nature of the interaction between the waves and the room boundaries. This effect is usually more pronouced, particularly in the case of subwoofers and their effect on vertical room modes.
4. A fourth benefit of a subwoofer riser is to use it as a bass trap. For the riser to act as a bass trap, it needs to be tall enough (≈ 2 feet) and the inside has to be filled with rigid fiberglass or mineral wool. The surrounding of the riser/bass trap should be covered with speaker carpet or grill fabric.

ISOLATION EFFECT

The waves from all speakers/subwoofers in a small home theater ineteract with the room boundaries. The effect of lower frequencies generated by subwoofers are more noticeable because they have longer wavelengths. Moving speakers/subwoofers horizontally across the room has a significant effect because of the inetraction with the side boundaries. Moving speakers/subwoofers up or down can also have a significant effect because of the change in the position of the speakers/subwoofers with respect to floor and ceiling.

Some people use sand in their stand. It is important to remember that stands and sand do not contain magic particles. The reasons you may receive a benefit are explained above. Sand makes the speaker stand heavier and more stable and reduces the transfer of energy. As I said before, this effect is more noticeable for lower frequencies and subwoofers.

Normally, the best solution to achieve better bass response in a room is optimal subwoofer placement or using multiple subwoofers. Unfortunately, there may be another problem. The other objects in the room may vibrate due to secondary resonances. This problem may require a different type of solution to absorb vibrations and reduce secondary resonances.

A secondary resonance occurs when lower frequencies cause other objects in the room such as furniture, walls, pictures, and even other speakers, to vibrate. An isolation pad/stand is designed to isolate the speakers/subwoofers and prevent vibrations from transmitting to other objects. It allows the listener to hear the source by reducing vibrations from other objects.

In the case of a subwoofer, the frequencies that cause secondary vibrations are harmonic frequencies above 100Hz, up to about 250Hz. By controlling these vibrations and harmonic frequencies, the fundamental frequencies below the crossover point (80Hz to 120Hz) will be reproduced with no interference, resulting in better definition and greater clarity of bass frequencies.

The following article from Audioholics disputes the benefits of spikes and cones under speakers.

http://www.audioholics.com/education...019s-the-point

EXPLANATION OF ROOM MODES

The bass waves coming out of all subwoofers interact with the room boundaries (side walls, floor, & ceiling) and create standing waves or room modes. Because of this, the location of the subwoofer in the room and the place that you normally sit play an important influence on whether you hear good bass output or almost no bass output. That is why placing a subwoofer is much more difficult than the other speakers and requires experimentation. When you move the subwoofer around in the room, you are in effect dealing with horizontal interaction of bass waves with the side walls. The only way we can deal with the effect of the low frequency wave interactions with the ceiling or the floor is to move it off the floor by putting the subwoofer on a riser or hang it from the ceiling, but that is much more difficult.

A more detailed explanation of standing waves and room modes can be found in A Guide to Subwoofers (Part II): Standing Waves & Room Modes.

The low frequency waves interact with the room boundaries (side walls, floor, and ceiling) and create standing waves or room modes. The standing waves are different between floor and ceiling, side walls, and end walls, unless any of these dimensions are the same (the worst kind of room is a perfect cube). There are three basic types of modes: axial, tangential, and oblique. Examples of these modes are shown in the following diagrams:

Source: Marktaw.com

The formula to calculate all room modes is as follows:

F = S/2 * SQRT((a^2)/(L^2) + (b^2)/(W^2) + (c^2)/(H^2))

Where:
F= Frequency in Hertz
S = Speed of Sound (1130 feet per second or 344 meters per second)
SQRT = Square Root
^2 = squared
L = Length of Room
W = Width of Room
H = Height of Room
a, b, and c are coefficients representing the modes we are interested in.

For the first axial mode for the room length, a =1, b = 0, c = 0.
For the second axial mode, a = 2, b = 0, c = 0.

To find the first tangential mode, we have to give two of the cofficients a value of 1
For the first tangential mode of room length and width, a = 1, b = 1, c = 0.
For the first tangential mode of room length and height, a =1, b = 0, c = 1.

Axial Modes are the strongest and the most important, and the easiest to compute. Tangential Modes are about half as loud, and Oblique Modes are about a quarter as loud. They tend to be the least important, but if an oblique room mode occurs near another mode, that frequency may still be a problem. Generally, as we go higher into the multiples (harmonics) of the modes, they become less intense, but because the frequencies will have smaller wavelengths, they occur at more places in the room.

If you look at the diagrams, you will notice that there are basically two types of axial modes: horizontal and vertical. Almost every person who owns a subwoofer discovers that room placement plays an important role. In reality, by moving the subwoofer around, you are dealing with the horizontal axial mode. Unfortunately, subwoofers do not understand horizontal or vertical. These classifications are in our heads. As far as subwoofers are concerned, waves are waves. We need to deal with vertical axial modes exactly the same way we dealt with horizontal axial mode, but how can we do that as Sir Isaac Newton and gravity work against us. There are two options: put the subwoofer on a riser or hang it from the ceiling and get shot by the wife in the process.


Rule of Thumb:

• An average home in the U.S. has a ceiling about 8ft high.
• Rule of 25: It is normally a good idea to put the sub approximately up to 25% away from the boundaries. For a riser, it means ceiling & floor.
• 8ft x 0.25 = 2ft.
• Raise your subwoofer approximately 2ft. You can also try to hang it 2ft away from the ceiling, but do it at your own risk. The WAF is waiting.

Rule of 25:

The low frequency sound waves generated by subwoofers interact with room boundaries and create standing waves (pressure zones). These ressure zones are spread out and not pinpoint-sized. For all practical purposes, the subwoofer should be located at least 25 percent away from the room boundaries to best avoid stimulating any of its first three harmonics. There is no location towards the middle of the room that suits a subwoofer position, as the pressure zones there are overlapping.

Many people have done years of research at the National Research Council of Canada and at Harman International under the guidance of Dr. Floyd Toole (currently, a Vice President at Harmon).

The 25% Subwoofer Positioning: This solution is suggested by Todd Welti at Harman International:

You shrink the whole room by 25% and put the subwoofers at the corners of that virtual room. Of course you get incredible performance, but that is not practical for most people. But if you use two or four subwoofers in the corners or the wall midpoints, you can get pretty good performance.

References & Additional Information:
A Guide to Subwoofers (Part II) : Standing Waves & Room Modes
http://www.gikacoustics.com/news_040109.html

[Big Daddy]

http://www.asc-hifi.com/articles.htm

Feedback Control: The Science Behind The SubTrap
Arthur Noxon, President Of ASC/Inventor Of The TubeTrap

Feedback can happen in most any type of audio system, adding a howl or whistling tones to the program material. It happens when sound loops back into the electronics and generates some version of the original signal within the electronics. Feedback loops must be controlled to achieve accurate reproduction of the program material.

The most common form of feedback is electroacoustic. A good example of this is the howl of an open microphone on stage. It can be fixed by moving the microphone, changing its pick-up pattern or applying equalization (EQ). Mechanical-acoustic feedback (microphonics) is similar except that it occurs when vibration from a loudspeaker buzzes the electronic circuits or the transport of a record, CD, or DVD. A rumble or ragged tone is heard. Platform isolators can decouple the vibration conduction path.

Room-acoustic feedback occurs when loudspeakers couple with room modes. The subwoofer is particularly vulnerable to room-acoustic feedback, especially the vertical room mode. It colors the playback and blurs the articulation. Room-acoustic feedback control is essential in all quality audio playback environments.

Without room acoustic feedback control, the subwoofer couples to one or more room modes and gets so loud at those frequencies that the overall bass volume has to be turned down. But that also turns down the volume of the program material. The result is the “one note bass” effect, and it is the common shortfall in subwoofer performance.

To reduce mode coupling, the subwoofer can be moved around the room, but the basic problem, the vertical room mode, remains. For an 8-foot ceiling, the feedback resonance is at 70 Hz, right in the middle of the subwoofer response curve. EQ can be applied, but that only quiets the loudness of the mode coupling. The inarticulate slurring, the failure to present a fast tracking dynamic bass line, remains inadequate. The ASCSubTrap is a pre-engineered broadband acoustic feedback control system that directly addresses vertical mode coupling, regardless of ceiling height. It reduces the excessive loudness (one note bass) and improves the articulation (mud) normally associated with subwoofer placement on the floor.

The setup is almost too simple. Lift the subwoofer up and slip the SubTrap underneath.
1) This raises the subwoofer up off the floor, out of the vertical mode pressure zone and decouples the subwoofer from being able to contact a pressure mode and pump energy into the mode.
2) In addition, a bass trap has been located on the floor, right in the middle of the vertical mode pressure zone. Any vertical mode action that might be stimulated by the subwoofer is rapidly damped out.
3) Finally, the SubTrap acts as an iso-deck, a floating platform to mechanically decouple the subwoofer vibration from the floor, electronic gear, video equipment and the rest of the house.

When vertical mode buildup is eliminated, the EQ can be turned off, and the subwoofer volume can be turned back up to match the main listening level. The subwoofer can finally do its job, which is to complete the full bandwidth presentation of dialogue, musical detail, and explosive program material.

[Driver_King]

Very nice Big Daddy! Are you going to build some isolators for your speakers too?

[Big Daddy]

Originally Posted by Driver_King

Very nice Big Daddy! Are you going to build some isolators for your speakers too?

Did you read my mind? I have been thinking about putting something under those big and heavy Def Tech Super Towers.

[Driver_King]

Hey, you never know. I was thinking of putting all of my speakers on some isolators to see how that worked.

[crazyBLUE]

Does raising the sub really help
I at this point have my sub on 2" blocks of wood





I did this because the bass port is on the btm. & in the carpet ! Would making stand that raised it & put something solid under it be better with the bass port on btm., as far as sound goes!!

[Big Daddy]

Originally Posted by crazyBLUE

Does raising the sub really help
I at this point have my sub on 2" blocks of wood





I did this because the bass port is on the btm. & in the carpet ! Would making stand that raised it & put something solid under it be better with the bass port on btm., as far as sound goes!!

You will get better performance and the cost is very little. I know you are very good with wood. This should be a good project for you over the weekend. It should not take you more that a few hours.

[crazyBLUE]

Originally Posted by Big Daddy

You will get better performance and the cost is very little. I know you are very good with wood. This should be a good project for you over the weekend. It should not take you more that a few hours.

First ~ Does It need to be covered with something (carpet or material) .
You're subs are now 4 5/8 higher than they were , is that A good level or is a little taller OK !
FOAM : I plan on using small blocks rather than 2x4's , this will leave underneath totally open ~ is some type of foam a must for underneath the stand !!
IDEAS ~ IDEAS ~ IDEAS !!!!

[Big Daddy]

Originally Posted by crazyBLUE

First ~ Does It need to be covered with something (carpet or material) .
You're subs are now 4 5/8 higher than they were , is that A good level or is a little taller OK !
FOAM : I plan on using small blocks rather than 2x4's , this will leave underneath totally open ~ is some type of foam a must for underneath the stand !!
IDEAS ~ IDEAS ~ IDEAS !!!!

Yes, cover them with carpet.

Considering that I was thinking about hanging my subwoofers from the ceiling, four inches is nothing.

The Auralex raises the subwoofers around 3".

For the foam, go to Walmart craft department and buy square foam poly-fill that people use for pillows and cushions. Attach them with glue. Since nobody can see them, you don't need to cover them.

[crazyBLUE]

Originally Posted by Big Daddy

Yes, cover them with carpet.

Considering that I was thinking about hanging my subwoofers from the ceiling, four inches is nothing.

The Auralex raises the subwoofers around 3".

For the foam, go to Walmart craft department and buy square foam poly-fill that people use for pillows and cushions. Attach them with glue. Since nobody can see them, you don't need to cover them.

WOW ! From the ceiling ~ that would be A different thing to experience I'll bet !
So carpet & as high as I want to go
I've allready taken all my measurements off the sub so I'll see what I can come up with !!

[crazyBLUE]

I got started on my sub stand today at work , Big Daddy ! Made the legs , Bought the carpet & foam. All I need to buy is matterial to cover foam! so far I have spent $15.00 , So this stand will cost less than $20.00 , Not bad !

[Big Daddy]

Originally Posted by crazyBLUE

I got started on my sub stand today at work , Big Daddy ! Made the legs , Bought the carpet & foam. All I need to buy is matterial to cover foam! so far I have spent $15.00 , So this stand will cost less than $20.00 , Not bad !

Did you buy solid foam or loose foam? For solid foam, you don't need a cover.

[crazyBLUE]

Originally Posted by Big Daddy

Did you buy solid foam or loose foam? For solid foam, you don't need a cover.

It is solid foam ! & I need to cover it because you will see it ! Remember I like making thing's that are original (1 of A kind) Thats just the way I am !!!

[Big Daddy]

In the craft department of Wal-Mart, they have solid foam. It is 15" x17" with a thickness of 2". Looks like the following picture, but smaller.

[Big Daddy]

Originally Posted by crazyBLUE

It is solid foam ! & I need to cover it because you will see it ! Remember I like making thing's that are original (1 of A kind) That just the way I am !!!

Ok, Mr. perfectionist. Cover it with carpet.

[crazyBLUE]

Originally Posted by Big Daddy

Ok, Mr. perfectionist. Cover it with carpet.

I just want it to look good ! I hope it will !

[Johnny Vinyl]

Originally Posted by crazyBLUE

I just want it to look good ! I hope it will !

Then don't go and spend time over at the DRUNK thread!

John

[Slec]

:goes looking for the thread in question:

[crazyBLUE]

Originally Posted by John72953

Then don't go and spend time over at the DRUNK thread!

John

WHO ME !!! NEVER !!