March 12, 2012

Linkwitz Orion system measurement

The Linkwizt Orion needs little introduction amongst DIY enthusiasts. This project uses the Linkwitz crossover but the baffles are a DIY project that have been well executed. Greg is a graphic designer and the his feel for design is evident in his home as well as in how this speaker has been put together. I prefer this version to the original in terms of its form. 

The Orion is quite interesting regarding its placement. Linkwitz recommends an unusual placement out into the room further than one might typically consider viable. We experimented with various placements and noted their impact on the imaging and sound stage. 

The room has a high ceiling (sloped) and a mezzanine above. It also has many windows and openings onto other spaces. Acoustically it is a relatively complex space.

Various Pass labs power amps:

All of them remain hot even when not powered up.

Temporary acoustic treatment on the rear wall is also seen.


In running sweeps, high levels of reverb were evident. In this regard a swept sine wave can be surprisingly revealing, even more so than music. 

To give some perspective, a relatively dead sounding room would have a RT of 0.2s. This would be typical in a home cinema system. As you can see here, the RT is low in the lower midrange, but above 200 Hz it is 0.5s and in high frequencies it almost reaches 0.7s which is quite high. There is some reduction above 5k but it still remains quite high. A reverb time of around 0.4s might be considered a good ballpark figure for a two channel system. 

Frequency response in the listening position - farfield including room effects:

The bass typically runs about 10 dB higher than the midrange and the treble is slightly reduced.

Bass range only:

You can see a relatively broad suck out centred around 40 Hz. This results in the bass being slightly thin and lacking body and fullness. Later we included the subwoofer and worked on reducing this effect. The fullness of the bass was then improved.

Waterfall response. 

In this case the decay plot turns out to be more revealing:

The red line represents the frequency response, while the purple line shows the decayed version 150 ms later. In my bass integration guide, I use this as an indicator of bass buildup in a room. A well damped room will see the response decay at all frequencies by around 20 dB or more. So the line has been drawn on to show the decay that meets that target. The regions where the rule is not met are highlighted in magenta. You will note that I'm not concerned with below 40 Hz. The area that needs the most work is about 48 - 75 Hz. Above this region the target is barely missed.

Immediately this points to pressure traps as a good solution. They are lower in profile and can easily cover this narrow range without taking up much space.

Over the course of the day, many other measurements were taken. Various sub positions were measured, along with various settings on the crossover and we also tested the EQ system. The crossover on the Orion was also tested to confirm things were as they should be, along with channel balances. For the sake of brevity, these won't be shown.

We also experimented with a little treatment on the front wall. I suggested to the owner the use of narrow band pressure traps in addition to a mix of diffusion and absorption on the front wall, with experimentation to determine the desired amount. Absorption in particular tends to dial back the characteristic open baffle sound and there is some personal taste involved. Our quick trial indicated that with a little absorption, it was desirable to have the speakers closer to the wall.

This system sounded very good indeed. When the JL audio Fathom sub was added, the bass had more weight and fullness and added what was missing. Running test tones down to 10 Hz either with or without the high pass filter in place resulted in extreme excursions on the woofers. The high pass appears to be set around 28 Hz but in my view it should be set higher, more like 40 Hz, allowing for augmentation from a subwoofer. Otherwise, the maximum output is restricted.

I can be a little critical of the lack of focus in the image from dipole speakers - all suffer from this problem, especially in home cinema applications where human vocals are stretched artifically. However, this aspect can be dialed back with treatment. There is a trade off between the sense of sound stage depth, and the sharpness of the image. This will be a matter for the owner to decide where he will set the balance.

The sound as it stands at the moment is very detailed and refined. Clearly, this is an exceptional speaker. The JL subs were clean and articulate and added to the Orions very well.

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