Naim’s advice, back in the day when they made a sub (and speakers) was,
“It is impossible to predict which option will sound best in a particular system and installation, however the speaker level option, by virtue of higher signal levels being more robust over long lead lengths, is potentially superior.”
The increased capacitance of the load will reduce the margin of stability of the power amp (and can sometimes even cause instability). The resistors limit the deleterious effect of this.
To understand why this is, look at the Bode plot (or Nyquist diagram) for an amplifier, and vary the capacitative load.
Using the high level connection has the disadvantages that
1 The sub is affected by the back emf caused by the movement of the main speakers.
2 The sub is subject to the LF group delay of the power amp as well as it’s own group delay.
I am not saying you are wrong or your idea does not have any merit but I have never read a manual from a subwoofer manufacturer where they have suggested using a resistor on the high level connection.
Naim recommend a resistor (and fit a 100R on their own sub lead) on the low level (pre-amp level) connection. The resistor is there because the pre-out (usually through the pre-amp’s power supply) was never designed to drive a long interconnect. So the resistor helps prevent possible instability. A better bet though is to use a high level connection, but as Naim power amps use the speaker cable to provide the necessary inductance, the addition of a high level lead to the subwoofer can upset this, so Naim recommend taking the reference signal from the speaker terminals (where they are effectively not seen by the power amp) rather than from the amp terminals.
Hi Richard I checked with Naim support and they said it was ok to take the high level signal from the Uniitilite speaker outlets on the amplifier itself.
Is this ok
With a Unitilite you may be OK. However, I do recall one or two reported issues doing it this way with a NAIT 5i. In particular, sound quality was reported to improve markedly when the signal was taken from the loudspeaker’s terminals rather than from the output terminals on the NAIT 5i. If only for peace of mind, I would definitely do it this way instead.
Richard, as the topic of this post is about supernait sub out rca connections would you know if a resistor would still be required in this case?
I know that the sub out is another pre out but would assume that there would already be something in the circuit to keep the preamp stable. There is nothing at all in the manual about this matter and it doesn’t tell you to use the naim cable.
I know chord and other manufacturers make sub cables up to 10m in length and don’t believe they have a resistor. There also doesn’t appear to be anyone bringing up the subject elsewhere on the internet which leads me to think that it’s not a big problem.
I get that the high capacitance could have a detrimental effect on the old pre’s but again would think that the issue would’ve been designed out by now on a sub out connection.
My cable is actually only 2m long so it probably doesn’t effect me either way but I find the subject interesting.
Thanks Adam, sorry to be a pain in the ass but I would assume that also be true for the SN2 which I use?
My afternoon today consisted of butchering my high level cable as it was was designed to be connected to the amp speaker connections. I had to cut all the insulation off it so it’d reach the speaker terminals then it took me two bloody hours to wrap PVC tape back up the cores for each speaker. My idea was that if it was preferential then it would stay in place.
My sub allows me to connect both high and low signal cables at the same time so I was able to try both by switching between them on my sub’s menu.
It took a bit of time to match the levels but when this was done I got the following results:
The high level connection gave a slightly fuller bass but at the expense of speed a clarity compared to the low level one. There was also a very slight increase in noise coming from my speakers with the high level connection in place. At first I thought I could be imagining this but when I removed the cable the nose floor dropped again.
So in my system I’ve came to the conclusion that the low level connection is preferential although I must add that it was not a night and day difference. I currently use a twin run of mogami 2549 cable so I might have gotten different results with a different cable or different sub for that matter.
I’ve also come to the conclusion that I’m an idiot as had to shell out £37 to order another high level cable as I’d have to include one if I ever sold the sub. At least I now know which connection works for me.
In terms of the fuller / loose / slower bass, that is likely to be the interaction of the back EMF from the speakers combined with the increased LF group delay from the power amp.
So, no you’re not imagining it - that’s exactly the expected effect!
Hi Xanthe,
Thanks for they reply and explanation of what’s going on.
The bit I thought I might be imagining was the increase in the noise floor. I didn’t spend anytime investigating so am unsure whether it was noise coming through the speakers or a slight increase in transformer hum.
Good to have that reassurance from Naim, as this subject keeps on coming up! I have stuck to the traditional Naim advice in the past, and connected at the speaker end - it seems logical given Naim’s advice on speaker cable matching in general. BUT I have discussed this with my dealer a couple of times, and on both occasions he has insisted that connecting at the amp end is fine, and that’s on separate Naim power amps as well as Unitis. He’s a well established Naim and REL dealer, so he should know his stuff - but I suspect the debate will continue to rumble on here.
Everyone please note I only talked to Naim support regarding my Unitilite subwoofer connection it may well be a different situation for other Naim amplifiers.
Prior to me upgrading my front AV speakers (which doubled up as Hi-Fi speakers) I used the small front pair from the 5.1 AV set-up - ProAc Hexa Satellite - but as these provided little/no bass my (Naim) dealer sourced and sold to me the following, using the SuperNait speaker connections to the SubWoofer Hi-Level input:
InterQuake 5m (Neutrik) Interconnect
It worked … but as I subsequently replaced said small speakers with ProAc TriTowers (lovely!) I dispensed with the interconnect … which resides with the numerous interconnects, no longer required, in my garage (anyone for a SCART?)