Homemade Subwoofer Risers

[derrickdj1]

After reading info on standing wave, I found out that axial room modes were the most important. A subwoofer riser wood decrease the modes and improve the quality of the bass and midrange.

Supplies:

20 in. X 20 in. plywood (2)

Four 2 X 4 cut 18 in.

Cheap carpert

Liquid Nail

Screws 3/4 in. (20)

Spay Glue

Staple Gun

Acoustic Foam 1 in.

Cost -$31.62

[derrickdj1]

Simple construction of the riser: Acoustic foam placed between riser legs and secured with a staple gun.

[derrickdj1]

Finished riser: Epik Legend and PA 150 subs with saw dust[]

[derrickdj1]

Before the risers the 3 standing wave measurements from MCACC were 121 Hz, 149 Hz and 201 HZ all attenuated 3.5 db with a xo of 80.

After the risers the 3 standing waves were 149,110, and 193 attenuated 2.5, 1.5 and 3.5 respectively with a xo of 100 set by MCACC.

The bass and midrange are more detailed. The subs gains are around 10 O'clock which they were before the riser and the avr SW level was -2.0. The new SW level is -5.5 in the avr.

[derrickdj1]

The standing wave mesuremets indicate reflections for the room. The level change is due to placement and / or slight movement of the gain control during the moving around process. The Legend and PA 150 subs have a small gain control and slight movement between 10-2 O'clock can yeild the noted increase. When level matching the sub on a .1 avr, I only adjust the phase on one of the subs for optimal results. I deally, to drastically change standing waves between the floor and ceiling, the riser should be around 2 ft. tall with acoustic foam in the middle. For me, decoupling the subs from the wood flooring was the goal. One sub is next to an RF 7 and the other several ft. away form the RF 7. Subs are located on the front wall.: this allows for better integration of the subs with the main speakers and the use of a xo of 100. The difference between a xo of 80-100 is nothing to loose sleep over. It can improve midrange imaging.

[CECAA850]

I'm not quite sure how these would change axial room modes any more than moving the sub would. I understand the changes made by decoupling the sub from the floor.

[Chris A]

I'm not quite sure how these would change axial room modes any more than moving the sub would.

Here is a way to eliminate the problem of axial modes: the double bass array technique.

Here is a thread where different techniques are discussed to reduce or eliminate room mode issues: bottom line is to either use arrays of subs or put the subs in the corners of the room. Decoupling them from the room boundaries is a much less effective approach, since it results in decreased lf performance by way of poorer low frequency FR smoothness, among other issues.

Chris

[derrickdj1]

First, thanks Cask05 and CECAA for responding to the post, I was hoping to get a little discussion and learn something from others that work a lot with subs. I agree that standing waves especially greater than 100 Hz are the most problematic in the HT. Room modes can't be eliminated in a typical HT due to the small size compared to a theater. I also consider the suggestion of adding weight to the subwoofers. A lot of us do not have a dedicated HT room and have to make the most of what we have to work with.

Adding weigth to the subs works similar to risers: Isolation and decoupling from the floor and reduction in the energy transfer and
vibrations between the floor and speakers/subwoofers. This is hard to quantify, but hearing was my best measurement tool.

Corner loading will get the most performance or SPL from the subs but not necessarily the clean bass . This favors Addyseey systems, since the EQ is done at the last stage where peaks are tamed, this can also decrease the LF respones and sub output. MCACC address the bass management from a different perspective focusing on standing wave before any EQ and phase issues. MCACC is not as slanted toward corner placement, I am not saying one is better than the other, I am just speaking on how they approach bass management.

Changing the nature of the interaction between the waves and the room
boundaries can change the qutality of the bass in the room . This effect is usually more pronouced, particularly in the case of
subwoofers and their effect on vertical room modes. horizontal and longitudinal modes are also present.

Secondary vibrations occur in the HT with standing waves greater than 100 Hz and can cause other objects in the room to vibrate such as, other speakers, pictures, walls and furnishings. An isolation device can help eliminate the secondary vibrations and clean up the sound in the room. Four subs are ideal, 2 subs will get you 75-85% the benefits of four subs. All of this is easier to do with identical subs but, good results are possible with non-identical subs of similar output and careful setup.

MCACC does a great job with phase issues which is one of the reasons that this works in my HT. Setting the xo at 100 Hz and setting the other speakers to small also helps with standing waves and other bass problems in the room. Also, since I use a Y connector, is the reason I adjust only one subs phase control since they are acting as one. The phase control on a sub only addresse one frequency and not others that may also be problematic. Risers are just another tool to tweak the system and this project was fun since I do not do this this kind of thing, and it was cheap. I hope this post was not to long, wrong or boring.[8-|] Bass management is the most difficult part of a good HT.

[CECAA850]

Adding weigth to the subs works similar to risers: Isolation and decoupling from the floor and reduction in the energy transfer and vibrations between the floor and speakers/subwoofers. This is hard to quantify, but hearing was my best measurement tool.

I would think that they work just the opposite. Adding weight helps to couple the sub to the floor and allows more energy to be transmitted from the sub by reducing the energy being wasted through cabinet movement. A riser de-couples the sub from it's surroundings and does nothing to stop cabinet vibration.

The phase control on a sub only addresse one frequency and not others that may also be problematic.

Not quite sure I understand this either. To me, using the phase knob is more like adjusting the timing of the sub in relation to the mains (or other sub). Adjustable phase allows you to get the sound from the sub to your ears the same time the sound from your mains hit your ears. Bass from subs out of phase sounds smeary and undefined. If your sub only has a 0-180 switch, you can use the sub distance setting in your receivers bass management menu to accomplish the fine tuning that a phase knob would normally be used for.

[Chris A]

Adding weigth to the subs works similar to risers: Isolation and decoupling from the floor and reduction in the energy transfer and vibrations between the floor and speakers/subwoofers. This is hard to quantify, but hearing was my best measurement tool.

I would think that they work just the opposite. Adding weight helps to couple the sub to the floor and allows more energy to be transmitted from the sub by reducing the energy being wasted through cabinet movement. A riser de-couples the sub from it's surroundings and does nothing to stop cabinet vibration.

This is the principle on which the Khorn works - coupling to boundary walls, in its case, a room corner. It works the same way for subwoofers, since they are also covering the same bands that the Khorn bass bin covers.

PWK was one of the first to recognize that putting a speaker into a room corner actually helps lf performance and FR smoothness (thus avoiding diffaction or comb filtering issues due to speakers located away from the walls and floor). He recognized that, by using the corner, lower amplitudes of woofer motion are required, which in turn leads to much lower levels of modulation distortion (i.e., "anything that moves--distorts, anything that reduces movement, reduces distortion"). Other JAES papers have been written by audio practitioners and researchers that have recognized this advantage: put the speaker in the corner then EQ its resulting FR until relatively flat, and much smoother FR and lower modulation distortion results - for free.

If you are having problems with floor vibration, then I'd recommend thicker carpet, more heavy furniture in the room to lower the floor resonant frequency (-ies), and putting the speaker (sub) in a corner to gain floor stiffness due to increased structural stiffness at the room corners.

Chris

[derrickdj1]

The subs are tight, they are less than a year old. The risers cut down vibrations upstairs and cleanup the bass a little.[]