Subwoofer crossover possible on Naim preamp?

Hi-Fi Corner
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I’m considering adding a subwoofer to my system. I am running a Naim NAC 152xs preamp and NAP 155xs power amp.

I am also using a NADC658 as a source (Streamer/DAC). The NAD unit does have the ability to set the subwoofer crossover inside the unit and the NAD also has a subwoofer output.

Is there a way to utilize the NAD subwoofer crossover feature and still keep the Naim preamp in the chain?

I assume using the NAD subwoofer output while running the higher frequencies from the NAD to the Naim preamp would cause odd issues with timing.

Thank you for any ideas.

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Putting a high pass filter on the main signal makes a lot of sense to me. It’s all very well putting a low pass filter on a sub, but if all those low frequencies are also fed to your main speakers too, that’s putting a considerable burden on them, and I imagine they would be happier without it. It’s a pity you can’t adjust the high pass frequency to suit your own speakers and sub, but still, I like the idea. The only other example of this that I’m aware of is a rather expensive standalone crossover from JL Audio, but I’ve never heard it in action.
You could be right about the delay issue using a separate amp, but it might not be an issue. I guess the only way to find out is to hook up a sub and try it.

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Your main issue here will be that levels will be very hard to keep matched up unless volume is totally controlled from the source.

I think you’re probably best letting the sub do the crossover.

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The NAD still sends a full range signal to the sub on the assumption that it has the usual low pass filter. It just applies a high pass filter to the main signal to relieve the speakers of the burden of the lowest frequencies, which on the face of it seems like a good idea to me.
How well it works in practice is another matter, especially with a separate amp.

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I’m not familiar with the 152, but could you add a Flatcap to it, and then take the feeds to the power amp and subwoofer from the Flatcap?

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The 152 has a dedicated sub out, but the OP is asking if he can use the high pass filter in his NAD to better separate the main and LF signals

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Yes, thank you ChrisSU. That is exactly what I am trying to determine a way to accomplish.

I didn’t consider the volume concern until I read Richard’s comment although I guess I could control the volume via the source.

I can’t figure our a way to make this work and still keep the Naim preamp in the chain.

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I presume you already have a sub and a suitable lead? In which case you should be able to just connect it up to the NAD and try it.
Strictly speaking you don’t need the Naim preamp, as the NAD puts the signal through its own preamp and volume control, but there’s nothing to lose by trying it. You could also try just connecting the power amp. There is a view that a Naim pre and power amp are best used together, but the power amp will still work without it so I think you just need to see what actually works by trying it.

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It is very likely that a much better result will be obtained by connecting the sub to the sub out connections of the NAC-152 via something like a miniDSP2x4 or a DSpeaker Antimode 8033 SII

These little boxes can be used to accurately control a sub so that it integrates well with the main speakers and, most importantly, with the room, so as not to excessively excite the resonant behaviour of the room. In my experience putting high pass filters in the feed to the main speakers degrades the musical performance of the whole system; note this is from real experience of trying it!

To set up a sub correctly isn’t just a matter of putting it near to the main speakers and setting the crossover frequency to about the lower frequency of the main speakers then adjusting the volume by ear; that may work if you’re exceptionally lucky. In practice a much better solution is to get a calibrated mike (such as a miniDSP UMIK-1) and a copy of REW, then use these to align the sub, including moving it closer to the listening position to dramatically reduce the timing issues associated with the delay in the sub’s internal amplifier. This delay is typically between 2 and 4mS, so the sub needs to be somewhere 0.7 to 1.4m closer to the listener than are the main speakers (and definitely NOT in the corner of the room). REW can also show you the resonant peaks in the room response, so you can programme the miniDSP 2x4 to reduce the sub’s output at these particular frequencies.

Incidentally you haven’t told us what your main speakers are or what the size of the room is, and both these substantially affect the integration of a sub.

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You don’t need to the 152 has ‘sub out’ RCAs.

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I’m sure the OP can speak for himself, but he was asking how he could use the Naim amp with his NAD while still using the high pass filter it has on the main speaker signal. To do this he would need to use the sub out on the NAD, not the 152.

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To answer jmtennapel’s question, and I might be wrong, but I think that the ‘subwoofer’ output on most Naim equipment is actually full range and therefore really just a pre-amp out. If so, given that the NAD has high pass filtering on its subwoofer out, the OP is looking to limit the lower frequencies going to the main speakers by application of said filter. The problem will arise when the OP wants to adjust the volume as both the NAD and the Naim will have different gain structures etc.

Regarding Naim and HPF on the sub out, I am aware that the UnitiQute and the Uniti had it, but the Unitilite and Superuniti didn’t - I have no idea why this was the case. On the units mentioned that have it, I think it was set at 100hz (possibly higher) which for many larger speakers is simply too high in my book. As mentioned before, perhaps someone with detailed knowledge of Naim preamps can tell us if any equipped with a subwoofer out actually have any form of HPF. If they have, is the frequency adjustable?

Interesting comment about subwoofer positioning made above. After a lot of research I have found that the large (15 inch driver) Tannoy subwoofer I use in my main system has finally integrated properly when repositioned from on-axis between the speakers on the same wall to halfway between my main speakers and my listening position along the side wall. The sub ‘fires’ across the room from the left and ‘intercepts’ the main speaker output (large floorstanders running full range) about where my feet are. The continuously variable phase is set at about 15-20 degrees. Doing this has made a considerable difference.

In car audio circle HPF is common place - I use it on the fully active system in my MGB. How you set it depends upon which crossover slope you use as it can result in a boost, cancellation or smooth frequency transition depending on the slope - a useful video on YouTube explained it all. The head unit in the car has an extensive range of DSP and EQ adjustments including adjustable crossover slopes - 6db/12bd and 18db - I think I went 18db in the end to avoid cancellations. The unit also allows programming of the exact distance of each speaker from the listening position, the size of each speaker, the type of vehicle and stage height to be adjusted electronically.

The office system I have runs a BK Gemini II and the Mission speakers are full range, with no adverse effects - the speakers have never shown signs of suffering. Conversely the AV system is set up with an HPF as the glass Celestions I use as stereo fronts really benefitted from having an HPF applied by the AV amp and the lower frequencies routed to the Active sub.

Finally, I do have an Arcam Solo Movie 2.1 that has the ability to set an adjustable HPF/LPF crossover point. Ironically I do not run a sub in that system but I keep meaning to engage the HPF to see if it will make any difference to the performance of the little Piega speakers that I use with it. It would mean that it would divert the lowest frequencies to a non-existent sub but it could be worth trying.

Overall, smaller speakers may well benefit from HPF but it needs to be properly implemented, otherwise run full range on the stereo pair and take care to position/set up the subwoofer properly. Obviously, if you hear the mains ‘strain’ at very low frequencies then HPF is a good idea but I would be surprised if most HiFi speakers really need it.

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I’m pretty sure there are no high or low pass filters on any Naim amp. All subs that I’m aware of have a low pass filter, usually adjustable, so that they can deal with the full range signal from the amp.
The reason for putting a high pass filter on the main speaker signal is to relieve the main speakers of the burden of the lowest frequencies which they struggle to cope with, so that they are better able to deal with the higher frequencies.

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Why would properly designed speakers struggle to cope with frequencies within the audio spectrum?

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In reality, how many people have speakers that cope well, or even cope at all, with lower bass frequencies for which a sub with a big LF driver is optimised. The OP’s Dynaudio Focus 160s are not so unusual in having small cabinets with a 17cm drivers which are going to be much happier if they do not get fed the lowest frequencies that are, in any case, going to the sub which is designed to deal with them.

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16V into 8Ω @ 1Khz = 32W
16V into 8Ω @ 50hz = 32W
16V into 8Ω @ 20hz = 32W

On a linear system, these are the same SPL.
The only practical difference for real speakers is that below the lower turnover frequency the elastic properties of the spider of the LF drive unit limits the movement of the cone rather than it being limited by a combination of air movement and the elastic properties of the spider. Consequently below the lowest frequencies that the speaker can reproduce linearly, the excursion of the cone doesn’t increase with reducing frequency.

Well designed modern speakers do not struggle to cope with low frequencies - that’s an audio myth (it was correct in the 1950s, but in better speakers, those problems were well sorted by the 70s).

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Yes I think there is a (considerable) difference between the lowest frequencies of a speaker being augmented by a subwoofer and a speaker struggling to reproduce those frequencies and therefore audible distortion being produced. Clearly, many good quality speakers don’t produce the lowest frequencies but they don’t distort: instead they roll-off the lowest frequencies and the frequency they start to roll-off at depends on the speaker design, the room itself and the speaker’s placement in the room. There is an argument that bass frequencies require more amplifier power and therefore, not requiring the amplifier to produce those frequencies reduces the demand on the amp and thus enables it to play louder and clearer at higher volumes. IME it’s certainly the case that higher power amplifiers tend to ‘grip’ a speaker better and therefore produce a ‘better’ bass. Speaker load is not linear across the frequency range, with impedance dips of particular speakers potentially causing issues for amplifiers. However, I am not sure that these impedance dips are always in the lowest frequencies.

As I mentioned above, HPF is common in car systems. I don’t know for certain but is suspect this is because most cars speakers are not really ‘speakers’ as much as drivers that end up being placed in a very wide variety of different-sized enclosures (read doors/parcel shelves etc.) with wildly different characteristics. The speaker designer cannot therefore control the ‘cabinet’ of the speaker and thus HPF can be used to make the speaker play within its specified frequency range - this will help reduce the chances of audible distortion by not asking too much of a driver placed in a sub-optimal cabinet.

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