Cheap Tweaks Part V: Acoustics: Sonex Classic 2

Before telling you more about Sonex, you need to know the basic principles of acoustics if you ever want to achieve any good sound with your hard earned system. First basic rule of acoustics is getting the proper speaker location. This can be a challenge, a real good one.

In order to guide you the basics, the famous golden rule ratio will normally get you in the ballpark. The distance from the center of the woofer face to the side wall is room width x 0.276. The distance from the center of the woofer face to the wall behind the speakers is room width x 0.447. This gives you numbers that will help reduce unison or near unison room nodes. In plain English: having the least probability to interfere (augment or subtract) on volume depending on frequency.

Golden Ratio

You should experiment with this placement. First backing the speakers will give you more bass but the soundstage shrinks, bringing them forward will reduce bass but will image better.

Second, vary the distance between sidewalls and speakers. The further apart the speakers are, the wider the soundstage until the first reflections problem rear it’s ugly head (it’s going to blurry images if too close to sidewalls). You should get a wider soundstage with less center fill, probably a bit more bass too. You should keep a good center focus; try a folk signer to correct it.

Third on the list is toe-in. This means the angle of the face of the speaker. This will affect soundstage a lot. If you never try this at home, you’ll be surprised by the results.


As you toe-in, the center stage will be more stable and signer will almost appear in your room (sadly, it’s also a bit in relation with the money spent in the system, we don’t yet live in a perfect world…). When you toe-out the soundstage will physically widen up to a point. Be careful with this thin balance, it’s hard to achieve the best compromise between center fill (no sound anchored in the middle) and soundstage, play a lot of different music to test it. Beware of the widest soundstage, it’s great to impress most people but you’ll give up a lot of emotion content from the music.

The fourth fundamental placement trick is tilt angle. This will vary depending on speaker design. Before beginning, you should have the correct speaker height, especially if it’s on stand (the designer of the speaker should always look to have the tweeter level at hear height unless they have a trick of their own). From this point you can play with tilt angle. This will mainly change two parameters: the balance of the treble and the height of the soundstage.

Tilt angle

As you give more angle, the tweeter will move from a direct line to your ears to a line that pass over your head. The more angle you give, the higher the soundstage will reach and the tweeter will seems sweeter (less direct energy). In correct doses this will help cure a hot, nasty or harsh tweeter. Always check for correct tonal balance, inadequate treble level will dull performances. Too much treble can cause headaches and you’ll lose interest for hi-fi in the long run. One of the most common mistakes is to associate detail with prominent treble, it does seem like you get more information but it’s not the case and manufacturer (and retailers) knows this. I’ve spoken to a very high end speaker manufacturer and one store owner distributing them and what I’ve heard was almost shocking. When a customer comes in and asks for speakers in the 20000$ plus, they have 2 models: one exaggerated treble and the other one with ‘neutral’ response. If they play the one with exaggerated treble then the neutral one, the later seems to be dull. But if they do the opposite, the neutral won almost each time…

As soon as you change one parameter, repeat each step in the order. It’s a long and painful experience but you will learn a good deal about your room and set-up. Also try to make everything symmetrical between speakers (in some rooms with irregular shape it will be impossible but try the best you can). Also your preferences in music and hearing can differ with others. Personally, I love detail but emotion and tonal balance prevails.

A good tip to help you pinpoint toe and tilt is to work with a laser pointer (about 20$ at hardware store). The best way to do it is to cut a carton or a piece of wood (at least 24’’ by 24’’) and fix it at the same place your head is when you listen to your system. To further help you, trace a line at your ears height and another dividing your left and right side. Doing that, you’ll have a target for the laser beam. Be sure to do this when you’re alone (don’t blame me if your significant other thinks you’re crazy…). The only no-trespassing rule here is to get symmetrical laser points at the target. Experiment, have fun. This will fine tune your system and you will be ready to take care of the infamous first reflection.

Sorry for the long introduction, I taught this was necessary to understand the very basic acoustic speaker placement before going further. So I was supposed to tell you more about Sonex acoustic materials. This stuff is used to absorb mostly mid to high frequencies. It is use to great efficiency in recording studio, I was one of them, to reduce reflecting sound and obtain the purest sound (especially to be tweaked with good reverb effects). What interest us here is absorbing the dreaded first reflection.


  • Open cell polyester urethane
  • Density: 2lbs per cubic foot
  • Flame spread <75 ASTM E84 class 2
  • Acoustic absorption coefficients
  • Frequency (Hz) 125 250 500 1000 2000 4000 NRL Absorption 0.09 0.29 0.64 0.97 1.05 0.97 0.75
  • 8 pieces box (2’x 4’): 211$ (available separately at some stores)

Acoustic is the most important aspect of a good system (I heard so many nasty sounding system costing more than I earn each year), this is where your audiophile skills can crush a rich buddy with the latest most expensive components. Slap echo from parallel non-absorbing walls is one of the most annoying problems you can encounter in your audiophile journey. This is normally the byproduct of uncontrolled first reflection: the sound reaching your ears just after the direct sound hit your head. This first reflection concept come from the notion that below 2kHz, the brain detect time delay between signal reaching your ear: no delay, the sound is coming directly in front, a delay front either side you will know it’s origin. Only after this recognition that the brain enjoys tonality.

First reflection

You are aware that this is a simplified version because there is more than one wavelength reflection but the first one is the most offensive. It creates a ghost image (delay) with direct sound, decreasing intelligibility and adds harshness especially in the treble. It’s almost impossible to kill it but reducing it pays big dividends.

At home, I do this in part with carpet over wooden floor (first reflection from floor), Sonex 2’x 4’ constructed panels (on each sidewall) and looking to put damping on the ceiling (my wife thinks it’s not a good idea but this is another story). The important rule here is to 1) not abuse damping as it kills the life and dynamics of your system and 2) use different materials in order to avoid specific frequencies suck outs.

Sonex makes a number of different panels for most application. A good approach is to have different densities and/ or different thicknesses to make sure that the suck-out effect is minimized. On the Sonex website, they have the acoustic absorption coefficients for most options. A general rule is the thicker, the better: as the frequencies go lower, a thick and/or denser material will trap them better.

The Sonex I use is the Classic line with a wedge pattern that gives a studio like effect and, to my eyes, is very stylish. Another good point: the material is fire retardant urethane. Available in a range of colors (charcoal, beige or brown) and in a melamine composite that can be painted the color you want (not tested here but beware closing up small pores with paint that absorbs frequencies).

Constructed panel picture

The panels I’ve made takes a Sonex 2’x 4’ Classic 2’’ thick glued to a 1/8’’ wood panel and finished around with stained wood molding (glued and nailed). This gives a mobile acoustic panels, it’s great, especially if you move in a new house or room. The Sonex was brought at a music instrument store as they could sell them individually. This helped me clean up the sound a lot and it’s great if you’re on a budget.

Another trick that can help or replace Sonex is furniture; a big heavy couch help lower reverberation time and absorb more frequencies. I know some audiophile who hangs carpet about a foot from wall to trap reflections (it’s more efficient than directly on walls as reflections will be trapped from both sides). Anyway try to kill that first reflection; you’ll be glad when you’ll hear the results. Better intelligibility, less headaches and more relaxing music. But never forget that each change in acoustic space can have an impact on your sound. Each time it does, go back at the beginning of this article and adjust speaker placement.

from affordableaudio, By Charles Painchaud