Australian Hi-Fi

Laboratory Test Report

- Steve Holding

Readers interested in a full technical appraisal of the performanc­e of the March Audio Sointuva WG speakers should continue on and read the LABORATORY TEST REPORT published on the following pages. Readers should note that the results mentioned in the report, tabulated in performanc­e charts and/ or displayed using graphs and/or photograph­s should be construed as applying only to the specific sample tested.

The first graph I’m showing is one that Newport Test Labs prepared at the conclusion of all its tests and measuremen­ts. Graph 1 shows a composite response, where the lab has spliced the in-room low-frequency response (measured using a pink noise test signal) to the highfreque­ncy response the lab measured using a test signal that delivers the response that would be obtained if the speaker were measured in an anechoic chamber.

You can see that the frequency response is not only very, very flat but also spectrally balanced, so that no one group of frequencie­s dominates at the expense of others — and in particular that the response is not ‘tilted’ to favour either the bass or the treble. You can see that the majority of the response, from around 70Hz up to 17kHz is within a 2.5dB envelope — albeit with a tiny suck-out at around 13kHz that falls slightly outside it. However, this suck-out is so narrow in bandwidth and has such a small drop in level that it would never be audible, even with a test signal specifical­ly structured to identify it.

Below 70Hz, the response rolls o‹ very smoothly — there is not the precipice one would expect to see from a cabinet with a reflex port, and the response is only 5dB down at 55Hz and

10dB down at 30Hz. This is an impressive performanc­e — not least so because Newport Test Labs measured it with the Sointuva WG located well away from any boundaries, so the level of bass will be much higher and the low-frequency response more extended if the speaker is operated close to one (or two) walls, as is shown in Graph 6, where the low-frequency response is shown with boundary reinforcem­ent.

Above 17kHz the response rolls o‹ quite sharply, which is consistent with the frequency response published by SB Acoustics for the Satori TW29BNWG tweeter in its specificat­ion sheet. This should be of no concern because there are no musical fundamenta­ls at or above this frequency and no-one over the age of 30 can hear frequencie­s above 16kHz when other, lower frequency sounds are present.

Graph 2 shows the high-frequency response of the March Audio Sointuva WG in more detail by ‘stretching’ the graph by the expedient of dispensing with the low frequencie­s. The particular measuremen­t method used by Newport Test Labs allows extremely precise measuremen­ts of both level and frequency, with frequency resolution of better than 1Hz (far better than is possible with impulse response analysis, which is the method used by most other test and measuremen­t facilities), yet you can see that the Sointuva WG’s frequency response is still almost completely flat and linear.

From the low measuremen­t limit of 600Hz up to 9.5kHz you can see that it almost tracks the calibratio­n line at 82.5dB. You can also see that the tweeter’s response rises in level after initially falling from 17kHz to be only 5dB down at 24kHz, at which level it remains out to 35kHz before rolling o‹ again. In musical terms the bandwidth between 17kHz and 24kHz is C10 to F10, so it’s only four notes in an octave that’s a full two octaves higher than the highest note possible to play on a piano.

Graph 3 shows the near-field performanc­e of the March Audio Sointuva WG’s bass/midrange driver (the black trace) and that of the two rearfiring passive radiators (the olive and maroon traces). You can see that the bass driver’s lowfrequen­cy response holds up very well down to 60Hz, after which it rolls o‹ to a minima at 35Hz, which means that you can expect very little from it below this frequency. However, you can also see on this graph that the two passive radiators are kicking in to make up for the shortfall, with excellent output from around 25Hz up to 60Hz. Response is particular­ly flat and right up at reference level between 30Hz and 45Hz and if the section between 35Hz and 60Hz had been summed, rather than measured and graphed individual­ly, the overall low-frequency response would have extended flat right down to 30Hz.

The impedance of the March Audio Sointuva WG is shown in Graph 4 and you can see that although March Audio specifies a minimum impedance of 3.4Ω at 168Hz (exactly as measured by Newport Test Labs), it seems that it means for this minimum to apply only for frequencie­s within the audio band because, as you can see, the impedance dips below 3Ω at 26kHz and continues to fall to be 2.6Ω at 40kHz. This could possibly — and I emphasise ‘possibly’ — trip the protection circuitry in some amplifiers, particular­ly poorly designed Class-D amplifiers (though not Purifi Class-D amplifiers, obviously!).

The in-room response, using pink noise, is shown in Graph 5: It’s as impressive­ly flat as the anechoic response.

Graph 6 shows the in-room free-standing low frequency response that has been used for all the previous graphs as the brown

shows exactly the same measuremen­t, the only difference being that the speaker has been moved close to a rear wall. You can see that at the expense of a very small suck-out centred at 100Hz, the low-frequency response has been extended such that it’s only 2.5dB below reference at 27Hz, 5dB below at 23Hz, and 10dB below at 20Hz. You can see why it’s important to position your loudspeake­rs correctly in the room!

Newport Test Labs measured the sensitivit­y of the March Audio Sointuva WG speaker at a distance of one metre as being 82.6dBSPL with an input of 2.83Veq. This was close enough to March Audio’s specificat­ion of 83dBSPL that the difference could be attributed to different measuremen­t techniques, but even a result of 83dBSPL means that the Sointuva WG is an extremely low-efficiency design — indeed, I think this is the lowest figure ever measured by Newport Test Labs for any loudspeake­r!

This efficiency result means you’ll need 4W of power just to deliver the same volume most speakers can deliver with just 1W of power. It also means that you’ll need a moderately powered amplifier to achieve good in-room volume levels without amplifier clipping, and also that you’ll have to give considerat­ion to not overdrivin­g the speakers by accidental­ly applying too much power from a high-powered amplifier.

Notwithsta­nding their low efficiency, which to its credit is made very clear by the manufactur­er in its specificat­ions, March Audio’s Sointuva WG speakers delivered outstandin­gly good performanc­e in all areas measured by Newport Test Labs.

... you’ll need 4W of power just to deliver the same volume most speakers can deliver with just 1W of power

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 ?? ?? trace: its appearance is different because it has been smoothed to one-third octave via post-processing to ‘average’ the trace to what the human ear would perceive. The blue trace
trace: its appearance is different because it has been smoothed to one-third octave via post-processing to ‘average’ the trace to what the human ear would perceive. The blue trace

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