DIY Subwoofer Risers

[PurpleJesus74]

Originally Posted by de Rookie

Oh, very nice. Good to know

Sounding great with it in place. Ran Audyssey after I placed the Legend on top of it and the results were immediately noticeable. It's also nice that some things that were rattling in the immediate area are now happy

Glad I needed new drumsticks

Nice setup you have,glad it helped with the sound.What kind of drumsticks,Vic Firth,Pro Mark?Just curious i used to play a little,but only air drumming these days.

[Istoc]

So I finally made an impromptu riser out of some wood and scraps I had around from other speaker builds, re-ran my Calibration and it is immediately apparent the difference it made, its truly noticeable. I doubted the difference it would make until I did it...

[PurpleJesus74]

Originally Posted by Istoc

So I finally made an impromptu riser out of some wood and scraps I had around from other speaker builds, re-ran my Calibration and it is immediately apparent the difference it made, its truly noticeable. I doubted the difference it would make until I did it...

Very nice ! And the best part is you didnt have to spend any extra money .

[KickItUpANotch]

Originally Posted by PurpleJesus74

Here are some pics. of my risers,i was able to build both for under $25,the most expensive part was the foam from Hobby Lobby.I later discovered a 40% off coupon i could've used,but it was too late dangit,lol oh well,still not complaining.I've also got some more pics. in my gallery.Big shout out to Aerodude73 for giving me the inspiration,i know they won't win any style points,but they get the job done and i didnt want to spend the $ on the subdudes.Thanks alot !

...

How did the results sound? Very economical looking

[de Rookie]

Originally Posted by PurpleJesus74

Nice setup you have,glad it helped with the sound.What kind of drumsticks,Vic Firth,Pro Mark?Just curious i used to play a little,but only air drumming these days.

I use Vic Firths

[PurpleJesus74]

Originally Posted by KickItUpANotch

How did the results sound? Very economical looking

Well i'm not gonna say they work miracles or anything,but they definitely improve the sound as well as reducing items rattling in the room,windows included .

[nathan_393]

Question for everybody regarding the foam:
I have access to foam underpadding - the sort of stuff that they put beneath carpet over top of concrete. My parents are ripping out their new house's basement carpet and that'll be what I use for my riser. Do you think I'll need additional foam if I have foam underpadding?

Thanks a lot!

[Test4echo101]

Hi everyone,

Like all of you, I built riser's for my 2 subs.
My subs reside over basement concrete and thick carpet.
So, I didn't build them for DE-coupling issues. I built them to address vertical room modes.
No knowing much about the technical details I relied on my ears to tell me if a difference was heard. (Never admit in a forum you used you ears to decern a difference....lol)

Well, to me it made a significant difference for the better. Placebo? Maybe, but placing them on the floor, then moving back to risers, then back...lol I can hear and notice quite easily a difference. Why? I don't know.

So, i posted my experience in another forum to get some feedback and ask other's to try as well.

I am getting hammered. Basically they say I'm hearing things (maybe I am) and that Big Daddy's posts on vertical modes are wrong.
As an example, one poster said this:

He's incorrect. The lowest frequency vertical mode in a room is half way up and for an 8' ceiling, that's 71Hz or so. I plotted modes using the Harman calculator and 500' w and d to keep them out of range. As you can see (in the attachment), moving your sub's acoustic centre from within 2" or so of the floor to 7" or so will at best bring you close(r) to the node at 283Hz, well outside the sub's operating bandwidth. Your Klipsch sub even has a 24dB/oct low pass at 120Hz max so it's ouptu will be 30dB down there.

I haven't found an answer for that. What does the above say about the usefulness of addressing vertical modes?

They all want REW measurements, graphs....So instead of raising their subs and trying it out for themselves they want me to spend $200 bucks on equipment to measure the differences.

Besides the de-coupling aspect, how do you prove vertical axial modes can be addressed by using risers and then produce tangible data to show those who are basically saying its bogus that "something" is happening.
Or, Is it just a fairy tale?

Thanks,

[comp1demon]

About to start a few DIY risers and Subtraps myself.

Would I better off making SUB traps and Custom Tower Risers? Or could I build a Giant Riser pack it with foam and dense material and put both my SUB and Tower speaker on it?

When building a sub trap am I better off having all sides closed with dense material inside or is it better to have open ports (with a material cover) on a few sides?

[Big Daddy]

Originally Posted by comp1demon

About to start a few DIY risers and Subtraps myself.

Would I better off making SUB traps and Custom Tower Risers? Or could I build a Giant Riser pack it with foam and dense material and put both my SUB and Tower speaker on it?

When building a sub trap am I better off having all sides closed with dense material inside or is it better to have open ports (with a material cover) on a few sides?

Individual risers will give you more flexibility in placement.

If you decide to build a subtrap, make sure it is closed on all sides, brace it internally, and pack it with dense material. You can cover the outside with any material that you prefer. Also, you can attach rubber feet or spikes to its bottom.

EDIT: If you want to build a subtrap that acts like a bass trap and plan to fill the inside with Mineral wool or Fiberglass, then it is perhaps better to keep the sides of the subtrap open and cover them with speaker grill fabric . You can buy FiberGlass or Mineral Wool from ATS Acoustics.

http://www.atsacoustics.com/cat--Fib...ards--106.html

[comp1demon]

BIG DADDY - you confused me.

I've been reading through the thread. and then your edit threw me off.

What is better? Sub trap? or Sub Trap that acts as a Bass trap?

I want my subs off the floor and I want them TIGHTER in sound and I want to be able to up the bass on them without distortion. Ny room is pretty large but they will be near the corners but I might swap the towers and the subs and move the subs in to the TV more and put the towers on the outside a bit more. I eventually will build acoustic panels for behind the towers - but I want the towers up about 12-18Inches first (hence I will build risers for them with the sub traps).

[Big Daddy]

Originally Posted by comp1demon

BIG DADDY - you confused me.

I've been reading through the thread. and then your edit threw me off.

What is better? Sub trap? or Sub Trap that acts as a Bass trap?

I want my subs off the floor and I want them TIGHTER in sound and I want to be able to up the bass on them without distortion. Ny room is pretty large but they will be near the corners but I might swap the towers and the subs and move the subs in to the TV more and put the towers on the outside a bit more. I eventually will build acoustic panels for behind the towers - but I want the towers up about 12-18Inches first (hence I will build risers for them with the sub traps).

Sorry about the confusion.

Raising the subwoofer and decoupling it from the floor has some benefits, including dealing with axial modes. However, a subtrap is a different animal. It deals with absorbing and controlling the lower frequencies to improve the bass in the room. They also absorb the mid and higher frequencies.

Check the following links to learn about bass traps and tube traps.

http://www.gikacoustics.com/gik_elite_pillar.html
http://www.asc-home-theater.com/tubetrap-flyer.pdf
http://www.asc-home-theater.com/cube-tw.htm
http://www.realtraps.com/products.htm

[Test4echo101]

Hi everyone,

So, I did some measurements in REW using a riser design from this thread.
2 of them because I have 2 subs.

If i could, I'd like to share the data that I collected.

I would first like to say I'm only after the truth. Nothing more. I'm not an expert nor am I even at the skill level of many in this thread.

I present this data as is and I may have overlooked something significant.
If I have, please feel free to correct me or point me to another measurement that I could perform.

Let me qualify the following by saying that I DID perceive better SQ in my listening position after the subs were on risers.
The data however tells the story.











I don't see any significant differences between On and OFF risers (In my case)

I'm sorry the Waterfall graphs scale is slightly different. One is a 10hz start the other is a 20Hz start. But if you take that into consideration there's not much a difference.

So, if you say these measurements don't reflect whats really going between risers and no risers, then what measurement would?

Using REW how would I define or "capture" the perceived improvement?

Thanks,

Test,

[Big Daddy]

The best subwoofer riser is one that has a height of approximately two feet and is filled with fiber glass or mineral wool to act as a sub trap at the same time.

I also noticed that when I put four subwoofers on four risers that are 1.5 to 2 feet tall, there was a significant change in the total output. This change in output was not only noticeable in the sweet spot, but also in different locations in the room.

Important Facts About Subwoofers, Listeners, and Standing Waves

• Subwoofers are sound pressure generators. They will reinforce the room modes when they are located in high pressure regions of the standing waves.
• Ears respond to sound pressure. When our heads are located in the high pressure regions of the standing waves, the room modes will be most audible.
• If the subwoofer is placed in the null areas, the corresponding modes will disappear.
• If you move your head to the null areas, you will not hear a lot of deep bass.
• Room dimensions and subwoofer location create room modes.

There is another factor that limits the remaining options for speaker placement. The pressure zones are spread out and not pinpoint-sized. For all practical purposes, the subwoofer should be located at least 25 percent away from the 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.

Calculating the Resonance Modes of a Home Theater Room and Subwoofer Placement
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. It is best to calculate all room modes to see where any overlap may be.

For most rectangular home theater rooms, it may be sufficient to calculate only the axial modes of the room.

Since a room can enforce a wave twice as long as it is, the first fundamental frequency can be calculated by using the formula: Standing Wave Frequency = Speed of Sound / 2*Distance Between Boundaries. If we multiply this frequency by 2, we will get the second harmonic frequency and so on. Usually it is necessary only to look at the first three or four modes because the crossover frequency for most home theater rooms are set around 80Hz-100Hz. Let us now calculate the axial modes for a 15ft W x 20ft L x 8ft H room.

Width
The first resonance frequency: 1130ftps / 2x15ft = 37.7Hz.
The second resonance frequency: 37.7 x 2 = 75.4HZ.
The third resonance frequency: 37.7 x 3 = 113.1HZ, ignore, because it is above the croosover frequency of 85Hz. However, the LFE channel has frequencies up to 120Hz. So even this resonance frequency may play a role.

The subwoofer has to be placed at least 25 percent away from the wall (15x0.25=3.75ft) because of the first harmonic, but that is the point of minimum of the second harmonic. Therefore, the subwoofer can be placed anywhere between 3.75ft (minimum of the second harmonic) and 7.5ft (minimum of the first harmonic) away from either wall.

Length
The first resonance frequency: 1130ftps / 2x20ft = 28.3Hz.
The second resonance frequency: 28.3 x 2 = 56.6HZ.
The third resonance frequency: 28.3 x 3 = 84.9HZ.
Since all three harmonics are below the crossover frequency of 85Hz, we should place the subwoofer in a position that avoids the maximum and minimum of the three waves – at least 25% (20 x0.25=5ft) from either end walls.

Height
The first resonance frequency: 1130ftps / 2x8ft = 70.6Hz.
The second resonance frequency: 70.6 x 2 = 141.2HZ, ignore, because it is above the crossover frequency of 85Hz.
The third resonance frequency: 70.6 x 3 = 211.8HZ, ignore, because it is above the crossover frequency of 85Hz.
The vertical position for a subwoofer is anywhere in the middle half of the room, keeping it at least 25% (two) feet away from either the floor or ceiling.

If we raise the height of the ceiling to 10ft, the first resonance frequency drops to 56.5Hz and the second resonance frequency will be 113Hz. For a ceiling height of 12 ft, the first and second resonance frequencies will be 47Hz and 94Hz. Many people use their living rooms as their primary home theater. The ceiling height of some of these living rooms may be much higher than 8 feet. For example, if the ceiling height is 15ft, the first, second, and third resonance frequencies will be 38Hz, 75Hz, and 113Hz.

So, a 15ft W x 20ft L x 8ft H room will have the smoothest bass if the subwoofer is located 2ft from the floor or 2ft from the ceiling (6ft from the floor), between 3.75ft and 7.5ft from the side walls, and five feet from the end walls. This is done to avoid the coupling of the subwoofer to room modes.


The following is written by Art Noxon at ASC:

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.

[Test4echo101]

Originally Posted by Big Daddy

The best subwoofer riser is one that has a height of approximately two feet and is filled with fiber glass or mineral wool to act as a sub trap at the same time.

Thank you so much for responding Big Daddy.

The quote you made above is why I think I'm having some issues.
You did say in your original front page post that "2 feet or less" would be sufficient.

"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 or less. You can also try to hang it 2ft away from the ceiling, but do it at your own risk. The WAF is waiting. "

Now for me, my subs are on risers 7" inches off the ground. Does that not fall within the "Raise your subwoofer approximately 2ft or less." rule?

I will try my subs at 2 feet (or more) and post my results using every measurement REW will allow.

I would really like to encourage all you guys here to post some before/after graphs as well.

I think it would only help to have the data support the perception.
I've only seen ONE graph in this thread regarding the issue.

I DO "think" I perceive a difference (good or bad that's yet to be determined) while subs are 7" up On a below grade concrete floor with thick carpet over top.

Again, I'm just suggesting we post some before and after measurements using whatever flavor you like, REW, True RTA...etc...

Thats reasonable isn't it?

Test,

[Big Daddy]

I have the Velodyne SMS-1 equalizer. It draws the subwoofer's frequency response graph on the TV screen with the touch of the button on its remote.

When I built four risers for my four very big subwoofers, there was a significant difference between the on and off frequency graphs. I also realize that each room is different and even identical subwoofers behave differently in different rooms. There is no one-size-fits-all solution as far as subwoofers are concerned.

A subwoofer riser can have three benefits:

1. Isolation and decoupling.
2. Dealing with vertical axial modes.
3. Acting as a subtrap.

I am not a carpenter and have limited skills and tools. The risers that I built are not exactly the most professional looking risers. In addition, my intention was to come up with ideas that are simple to build and cheaper than $20. For a riser to effectively deal with the vertical axial modes, it needs to be around 2 feet, depending on the ceiling height. When it is shorter, it may only act as a decoupling tool. For the riser to act as a sub trap, it needs to be built like a subwoofer cabinet and filled with rigid fiberglass or mineral wool. Unfortunately, once you start building a riser that is tall and acts as a sub trap, the cost will go way up.

The best type of risers are the SubTraps from ASC, but they are very expensive.

SubTrap1.jpg


SubTrap2.jpg SubTrap3.jpg

[Test4echo101]

Thanks Big Daddy,

Higher UP we go!

Test,

[crazyBLUE]

Originally Posted by Test4echo101

Thanks Big Daddy,

Higher UP we go!

Test,

Higher is better Test

Mine are 14" & 30 " & 32" off the ground

[Aerodude73]

Originally Posted by crazyBLUE

Higher is better Test

Mine are 14" & 30" & 32" off the ground

So you're saying your ceilings are almost 12' Tall then? (32" = approx. 1/4 of 12')

[crazyBLUE]

Originally Posted by Aerodude73

So you're saying your ceilings are almost 12' Tall then? (32" = approx. 1/4 of 12')

Yes I am crazy Steve. The two back ones are at ear level to match having the 4 surrounds 2 feet above ear level