August 24, 2012


This one is for Earle Weston of Weston Acoustics ...

Melbourne music spotlight: Stewart Kohinga

Ever noticed how much mediocre music lives on the radio, regardless of the channel? Well, in the interests of promoting musis that is actually worth hearing, that you might not hear on the radio, let me introduce some local talent. Stewart Kohinga is Melbourne singer and songwriter who recently performed live as part of the Live at Baker street series.

I would describe his music in poetic terms, but you can hear it for yourself on youtube >

Stewart Kohinga online:

Facebook page

Live at Baker Street series >

August 15, 2012

Melbourne event : live music to CD

This is a rare treat. A studio in Melbourne this Saturday are offering a live music experience where you then get to hear the recording on a $150k system.

Read more on StereoNET >

There is also a session on Thursday 30th.

August 14, 2012

RSA HE2 almost there

HE2 progress - the box is almost complete.


This first version will be my demo speaker.  Since various aspects of this build proved to be very labour intensive, I will be making a simpler version based on CNC machined panels. This one includes bitumin rubber damping, which is very labour intensive to apply, and quite expensive. It will be an upgrade option added to the standard model. 

Coming up:
  • clear finish
  • directivity measurements
  • passive crossover
Once complete, it will be available for demos with a Weston Valve amp, with various upgrade options. I'm currently considering the choice of finishes, where I may build future versions out of MDF with a choice of veneer.

Loudness perception and bass

We've all seen the equal loudness contour:

It tells us quite a few things, many of them missed in casual observation. The first thing we might notice, is that our hearing is most sensitive to midrange from about 200 Hz - 14 kHz. Bass is subjectively "turned down" indicating that it's actually not very important in the functional sense. Bass doesn't tend to occur in nature in isolation of much higher frequency content. We also note that our ears are especially sensitive around 3.5 kHz.

This was made clear to me when as a teenager, I measured my first system. I found a huge peak around 3.5k and playing test tones and measuring with an SPL meter outside the science lab in high school, those 107 dB peaks were just plain nasty! No doubt that was a big part of what made little 15W speakers sound loud to my teenage ears.

This 3.5k peak in sensitivity does have implications. Many midrange drivers have cone breakup around this region, and many crossovers are not far removed from this point. A very large part of our internal hearing mechanism is dedicated to 1 - 7 kHz primarily, this region is critical.

SPL and tonal balance

Notice how things change with level. At a typical quiet background noise level of about 26 dB, we need over 90 dB at 20 Hz before we perceive the bass as simply matching in loudness. Many subwoofers fail to even register as a quiet background noise level! Now if we listen at a moderate level of 60 dB, we need 110 dB @ 20 Hz or about 94 dB @ 40 Hz. We probably need about 25 - 30 dB increase in bass level to get it to sound about the same in level across the bass spectrum.

If we boost the level to 80 dB, we need about 20 dB increase in bass level. The bass is starting to sound a bit more solid. If we increase the level to 100 dB, we are now in the very loud range, and the bass only needs about 12 dB boost to match the level.

So why don't we all boost our bass by these crazy amounts? These effects are partially allowed for in the recording process, so you don't want to invert these curves and use them for EQ. But these curves reveal that the tonal balance changes with level and in this regard, it is the bass that changes the most.

I had previously thought that the equal loudness contours explained the harshness of some speakers when turned up loud. The contours don't support that view. Perception of treble stays about the same at high levels. In reality this might be explained in terms of system stress where distortion causes the treble to sound louder, especially where the amp is clipping.

What do we learn?

  • 10 dB in the midrange sounds twice as loud
  • 6 dB in the bass range sounds twice as loud - this number decreases at high SPL levels
  • Maximum sensitivity - 200 - 7k
  • Peak sensitivity 3.5k
  • A dip in sensitivity occurs around 10k

Waveguide damping

This is how I add damping to plastic waveguides to improve their performance. I use bitumin rubber which is mainly used for waterproofing applications. It has mass, adhesion and flexibility which make it work here also. 

Raw plastic waveguide:

To ensure good adhesion, the plastic surface is scratched up with coarse sand paper:

Then the bitumin rubber is diluted and applied as a primer:

When it dries, the surface is slightly rough and has the kind of texture that easily bonds to successive layers. Masking tape is applied.

After a few hours, a thick first layer is applied with a metal paint scraper and a brush.

Then a second layer includes fine screenings, which add greater mass. The screenings are cheaper than the bitumin rubber, ensuring that it goes further, but they also improve the performance. 

A third layer seals up the mix of screenings and bitumin rubber. This locks them in the middle. Without a layer underneath, they can tend to lack adhestion. Without a layer on top, they can tend to come off.

August 13, 2012

Custom Acoustic Treatment

This is a placeholder right now for the acoustic treatment I'm using in my room, which is a work in progress. Who wants their room to look like a stack of stock panels have been thrown up into their room? Even if you have a dedicated room, you really don't want that look and sometimes you need to go for custom work to get the look you want. The scheme I'm working on includes:

1. Large corner bass traps (floor to ceiling and 1.1m wide) which serves as a baffle for horns and also hides my active woofers.

These are made and waiting for my S3 point source horns. They include a pegboard membrane on the front and are wrapped in black cloth and use rigid fibreglass.

The baffle will allow me to have an ideal mouth termination on the horn. It will also visually integrate the horns into the room. Basically they will disappear, I'm going for the invisible built-in look.

2. Rug on the bare timber floor (probably).

3. Soffit bass traps at the ceiling/wall junction over the listening position.

This location is the most "out of sight" and in a small room this is important.

4. Rear corner bass trap.

This could either be a large broadband trap, which I've used here previously, or an arrangement of L shaped pressure traps or helmholz resonators. The broadband trap works, but will conflict a little with the surrounds on the side walls. It's a good excuse to go to the extra effort to experiment with narrow band low profile traps.

5. Diffusers.

In my room which is small, the focus is firstly on treating the bass and then on improving the overall sonic signature of the room. Horns can change the game a little, because it eliminates first reflection points. There are less reflections to deal with, so room reflections take on a longer path and are less dominant. Being a small room, the focus shifts to retaining some of that energy and diffusers tend to have a more natural sound than a bare wall.

You may recall this reverb time chart posted recently:

The orange line is my S2 and you can see the even reverb that is quite a bit lower than the other two rooms. The blue line is a room at the Australian hifi show. The red is a large and open room with some Linkwitz Orion speakers. Apart from the unexpected anomaly in the midrange, the orange line shows close to ideal performance in a small room.

Custom treatment and room analysis

In combination with my room meaurement service, I also now offer custom room treatment. No longer can you say "yes but my wife won't approve!" This service is available in Melbourne.

Not in Melbourne? I'm now introducing a remote room consultation service, whereby you take your own measurements, following instructions provided, and I will then analyse the results and make sense of them for you. In many cases, online help in this area on forums is a case of the blind leading the blind, and many people  don't have time for a wild goose chase. You need to know what tools to buy, exactly how to measure, what to measure and then how to interpret the results and then what to do with them. I can help with all of these aspects, and in the end, if you make further changes in your system, or even move house, you will still have the tools.

Request room measurement service >

August 9, 2012

Remote room measurement service

Do you want to have your room measured? I provide a service in Melbourne, but if you aren't in Melbourne there is another option. There are a couple of challenges and I can help with all of them:

1. Knowing what to buy

It's very easy to buy equipment that doesn't work. Rather than go through a trial and error process, I can save you the hassle and expense, pointing to the lowest cost effective options.

2. Knowing what to measure

I can provide instructions. Online threads with different individuals of varying experience often means going through a wild goose chase. When you know what to measure, you can do it in one sweep. If you are waiting for a time slot with the kids away, this matters!

3. Understanding the results

Very important!

4. Knowing what to do with them

This is critical - the point in measuring is then being able to use those measurements to improve your system.

One of the benefits of this service is that you can repeat your measurements later as you make changes in your system.

Enquire about this service >

Read more about room measurement >

August 7, 2012

Lexicon outside, Oppo inside

This term has always annoyed me:

"You get what you pay for!"

It's the line that people use when justifying spending more where it's not really clear what extra you are getting. Sometimes we fall for the price quality illusion. We instinctively feel that the more expensive product must be better. In many cases, it may have more to do with what the manufacturer knows they can charge.

Today I stumbled across a story I had heard before. One high end manufacturer got caught out when they packaged up a much cheaper Bluray player into a new case, then jacked up the price. The Oppo original cost US $500. Lexicon added $3000 to the price without changing the internals. Whilst this is a blatant example, I'm sure there is a lot more of this going on.

Why does it happen? I believe the main reason is that they can get away with it. The reason they can get away with it is that the performance differences between a $500 and $3500 player are often more imagined than real. If manufacturers were expected to produce a product that is easily recognised as superior and if this were really evaluated properly, this kind of thing would not happen. A manufacturer who tried something like this would get a bad name. I believe modern manufacturing and engineering means that decently transparent devices can be made affordable. Lexicon know that people will pay for their name and their better case.

So in this case, what are you paying for? You're paying for a nice case. You're paying for their marketing. You're paying for the perception that their name confers better performance. You're paying for staff to think up ways to charge more without actually offering real performance.  

Yep, you get what you pay for ... but that doesn't make it a good buy!

Read about it on Audioholics >

August 6, 2012

JV60 crossover upgrade

Pre-assembled crossover for JV60.

This is a 2.5 way crossover for the following drivers in a Vifa driver floorstander:

2 x Vifa P17 6.5" poly midbass 
1 x Vifa D25AG aluminium dome

Normally  this crossover would include an Lpad for tweeter attenuation, but it was omitted in this one by request.

Components are fixed with adhesive and cable ties to ensure long term reliability and to avoid vibration issues. 

Further upgrade options:
  • Jantzen Superior caps 
  • Solen AWG 14 inductors
Available on a made to order basis. Enquire >

August 1, 2012

JV60 crossover

JV60 crossover upgrade

This is an upgraded crossover to the Jaycar JV60 kit. It uses good quality Jantzen audio components.

This works well with the transmission line design shown elsewhere.

Available for purchase on a made to order basis. Enquire >

Butt join samples

Painting over butt joins can be a challenge. Previously I've shown some samples where I've tried different methods of achieving a seamless butt join with a paint finish over, using automotive paint. They are now complete:

This one illustrates the problem. Ply also has issues:

A cheat solution (shown in ply) is grooves:


A better solution uses fibreglass reinforced filler, with two part filler over

You can see the end grain has started to show through.

The best result was achieved with MDF:

It turns out that MDF is actually easier to work with than ply, where the entire surface must also get some attention.