‘Absolute Phase Correct’ and Naim amplifiers

[AlexP]

When looking up specifications of the 155XS (noting it too is 2 ohm stable) I noticed that both it and the matching NAC are referred to as ‘Absolute Phase Correct’ in the XS brochure. See the screen shot below. Interestingly, the XS integrated is not referred to as phase correct in the same brochure.

I also noticed this being referred to in a review of the 5si when it was measured (possibly by John Atkinson). This led me to wonder if being phase correct is a feature of all Naim amps?

I’m well aware of the potential impact of phase shifts as a feature of passive crossover slopes in loudspeakers so does the same apply to amplifiers? If so, and assuming that Naim amps are all ‘Phase Correct’ (non-inverting) does this help explain their timing abilities and also their ability to present instruments as a cohesive whole within the soundstage?

Just curious as to the technical side of this.

[Christopher_M]

One for @110dB perhaps. (But the staff need a weekend too.)

[AlexP]

Yes, you are most likely correct and certainly they deserve a weekend off.

From memory I think John Atkinson (Stereophile) always measures whether an amplifier preserves phase or inverts it. Perhaps there is potential for a degree of phase shift within an amplifier that Naim are very careful to avoid.

Chris, as an owner of a 202 with 155XS, how do you find the combination? Which pre-amp (if any) did you have before the 202?

[Christopher_M]

Hi, I had a NAC152XS. (It’s still languishing at the back of a cupboard). Very good with the NAP155XS (unsurprisingly). The NAC202 offers more though, in terms of weight and scale, while still retaining the speed. My aspirations are 202/200.

At the risk of contradicting myself, fifteen years ago, I found my Nait XS wonderful. It has a very complete, balanced sound even without a Flatcap XS. It was my pleasure in the XS that encouraged me towards the XS separates.

Chris

[110dB]

Hi @AlexP and @Christopher_M ,

All Naim sources, pre-amps, power amps, etc., are absolute phase correct — i.e., they do not invert phase.

When a positive sound pressure wave is recorded (e.g., from a kick drum), the entire system will reproduce a positive pressure wave, rather than a rarefaction (negative pressure).

Rooms, acoustic instruments, and ear canals are not perfectly symmetrical in their response to positive and negative pressure waves. Some listeners are sensitive to this asymmetry; others are not.

If you’re curious, it’s easy to test: choose a live recording (not synthesised), listen normally, then reverse the polarity of both speakers — red to black, black to red. This will cause the speaker cones to move inward instead of outward, and vice versa.

Other subtle effects may also influence the sound, such as even-order harmonic distortion from the speaker interacting with the amplifier’s distortion phase — potentially cancelling or reinforcing.

A small minority manufacturers have absolute phase inversion, possibly due to circuit simplicity. i.e. their circuit may inherently phase invert. Rather than adding a second stage to correct phase, they leave it inverted. Some reverse speaker terminal colours to compensate. About 30 years ago, phase buttons were common on DACs.

Note: absolute phase is distinct from phase shift with frequency (caused by filters). Absolute phase refers to a full 180° flip — not a gradual shift.

Cheers
Steve

[AlexP]

Neil, many thanks for taking your time to answer over the weekend - your very detailed response is much appreciated. It all makes sense and answers the questions I had. It certainly makes sense that phase shifts within electronics would be 180 degrees rather than the gradual shift that occurs with certain order passive crossovers.

For better or worse I think I’m one of those ‘afflicted’ by differences in phase within speakers/room interactions. Thus I’ve found that the continuously variable phase adjustments on my 4 subwoofers in the main system an absolute boon rather than the simple 180 degree switch on RELs etc. A little trick I learned was to play a test tone at the specified crossover frequency and then listen between each subwoofer and its corresponding speaker then adjust phase on the subwoofer until perceived bass response at that frequency was strongest - interestingly, being in 2 stacks of 2, they were all slightly different.

Ref your suggested experiment, I once tried wiring the 0.5 woofers of my biwire 2.5way Tannoys in the sunroom system out of phase (top +ve to woofer -ve and vice versa) and the negative impact on bass response was very noticeable indeed.

Many thanks
Alex.

[AlexP]

Thanks Chris very useful.

I have an XS3 with a Flatcap XS in the main system - I like the XS3 on its own but, to my ears, it sometimes felt a bit ‘aggressive’. Adding the FCXS made a huge difference to my ears - not only did the ‘forwardness’ disappear, the soundstage opened up, the HF sounded cleaner but, most noticeable, instruments (particularly in the bass) took on a more real and palpable sense of being in the room.

The reason I asked yourself is I know that you have experience of NACs and NAPs at this end of the Naim catalog. I recently bought a DAC V1 for the sunroom system which I’m using as a pre-amp into an Arcam A28 (AV bypass mode) into either my DIY OB system or my older Tannoys (the Arcam has A/B speaker outputs).

I will happily keep the A28 with the OB system (it is all very carefully dialled in) but I would like a Naim amp/power amp with the Tannoys. I keep toying with a Nait 50 but something like a NAP 200 or 155XS with the V1 as a pre could be just the ticket. There is currently a relatively late 155XS on eBay at the moment which looks quite appealing.

[110dB]

Hi @AlexP

Adjusting the phase of subwoofers and its effect on sound quality is subtly different from ‘absolute phase’. Absolute phase inverts all frequencies, and the frequency response remains unchanged.

Subwoofer phase, when adjusted relative to the main speakers, affects how their outputs blend around the crossover frequency—this does impact the frequency response. Your test method is a great way to dial it in.

Also worth noting: swapping just one set of bi-wire terminals per speaker can cause a dip in response at the crossover point.

Have you tried the ‘subwoofer crawl’?
It’s a simple, fun (looks crazy) but effective technique:

• Place the subwoofer in your listening seat - a cheap long lead is fine for the experiment.
• Play bass-heavy music
• Crawl around the room where you’d like to place the sub
• Listen for smooth, even bass with minimal peaks
• Place the sub where it sounded best
• Adjust phase
• Repeat if needed

Cheers
Steve

[AlexP]

Thanks again Steve for your reply. Sorry, for some reason I clocked your name as Neil - apologies for that.

Yes I think the dip in response at the CO frequency when polarity is reversed makes sense, especially when combined FR plots for drivers in speakers are studied.

I once tried the subwoofer crawl using my then Tannoy subwoofer that weighed 35KG + it had spikes - it was a bit hard work! It was a ported design that I could never seem to get to sound right. A low FR but ‘slow’ and timing/integration was not strong no matter how I set it up - I would get it right for one recording only for it to sound unbalanced with the next.

My much smaller sealed BKs (connected at high level as per REL) work so much better there is, IMO, no comparison - set using the method above, a few small tweaks to each unit’s gain that was all that has been required. The lowest 2 left and right are set circa speaker’s F6 point. The higher pair are set circa 70hz and it all seems to have a downward ‘cascade effect’ bearing in mind the even good sized subwoofers are not flat down to 20hz, though room gain can help.

Regards
Alex

[Innocent_Bystander]

Some devices offer optional phase inversion - my DAC does - so if something else inverts it can be switched to correct for it.

[Ebor]

@110dB

If you’re curious, it’s easy to test: choose a live recording (not synthesised), listen normally, then reverse the polarity of both speakers — red to black, black to red. This will cause the speaker cones to move inward instead of outward, and vice versa.

This is an interesting idea, but doesn’t it rely on the assumption that everything (microphones, mixing desk, recording device) that was used to make the live recording is similarly phase correct?

Is this a reasonable assumption? Off the top of my head, I have no idea.

Mark

[Richard.Dane]

I’d say that’s reasonable in that on my main system if I sit on the sofa absolutely equidistant between the speakers and facing them it’s very comfortable and there’s a definite solid stereo effect of being able to close your eyes and picture the musicians in the recording space (whether actual or artificial). However, there’s one particular studio whose half-speed mastered LP output in the past decade or so has become almost impossible for me to listen to in this way. In doing so I get a sort of weird pressure discomfort between the ears and I have to sit slightly off to one side or other, or just listen completely off centre or on another sofa in another part of the room. You don’t get the solid stereo effect, but it does mean the pressure discomfort is not there either. I only get this effect with this studio’s half-speed vinyl releases so I would guess that this may indicate a phase issue somewhere in their vinyl mastering or cutting chain, and my system is accurately replaying this in my music room.

[robert_h]

The original release of Skylarking by XTC is out of phase. Originally released in 1986, it wasn’t noticed until 2010, and the “corrected polarity” version was released on CD in 2014.

[AlexP]

Having not knowingly heard either, does the phase-corrected version sound any different?

[feeling_zen]

It seems obvious that phase would be retained but anyone who’s owned A Linn Karin will remember it was a phase inverting preamp which meant you had to connect the speakers out of phase to be in phase.

Why didn’t they just wire the pre-oits on the Karin in reverse? I dunno. I suspect because the negative phase was active and positive went to chassis ground and it was more important to retain that up until the speaker connections than anything else. But who knows.