There’s a lot of confusion about how to select the correct crossover for your speakers in a multi-channel setup, so I thought I’d write a quick article to cover all the bases.
THX & Audyssey Recommendation
Both THX and Audyssey recommend an 80Hz crossover. In an ideal world, this crossover is the correct setting. This is because:
1. Generally speaking, for most listeners, frequencies above 80Hz are localisable and directional. That is they are able to say where the sound originated from. However, anything below 80Hz is generally not directional. This means playing them back from a subwoofer or a couple of subwoofers does not make a difference from a steering perspective.
2. Lower frequencies below 80Hz are difficult to control in rooms. However, it is generally easier to control them from a single source rather than from multiple sources where they can interact. Subwoofer systems (multiple subs) can be configured to act as a single source even from multiple locations and cover a seating area with less problems (peaks and dips) when configured correctly.
3. Audyssey’s recommendation is 80Hz because of the above two points. With this in mind, they designed XT32 to have more resolution (corrective power) for the subwoofers as opposed to the main speakers below 80Hz. This could make the bass smoother just purely due to how the EQ implementation works on the subs. (Please note that other Audyssey versions don’t have a higher resolution on the subs.)
The Real World
What about the real world then?
Let’s tackle the obvious things first. Speaker ratings and in-room response can and will differ. This is due to speaker dispersion characteristics and how sound waves interact with the room and with themselves. Therefore we need to establish some common sense rules:
1. If your speakers are not designed to go below a certain frequency, you should ensure the crossover is not set below that. For example, if your smaller satellite speakers are rated down to 100Hz (+\- 3dB) then you have no business setting them to 80Hz even if the AVR detected the crossover as 80Hz. This is because the speakers may distort when pushed that hard below 100Hz.
2. However, if your speakers are rated below 80Hz (e.g. 60Hz) and the AVR detected them to be 60Hz, you can set the crossover to anything between 60Hz and 80Hz dependent on what your goals are, how high-quality your subs are, etc.
3. If your speakers are rated down to 80Hz but the AVR detected the crossover above 80Hz (e.g. 100Hz), it means the speaker positioning or room is limiting performance at the seating positions so lowering the crossover to 80Hz might result in some content not being heard properly. In this case, it is important to re-do positioning. I cover a lot of speaker positioning (and de-coupling guidance) in Secrets of Audyssey, YPAO – The Lost Manual and Dirac Live Perfection.
So in summary: you can always up the crossover, but you should generally never lower it.
Let’s tackle the issue of localization next. If you haven’t sufficiently de-coupled your subs from the floor or sub-floor, energy will get transferred into your floor, walls and furniture which means the frequencies will create harmonics that are localizable.
In addition, even if there is no direct energy transfer, anything that’s not secure in the room: furniture, nicknacks, pictures, etc can still resonate in the high pressure areas such as corners and wall boundaries. This again can create localizable harmonics and noise.
For more on subwoofer decoupling, you may want to read our review of the SVS Soundpath Subwoofer Isolation System which goes into this in a bit more detail.
If your subs produce any mechanical noise, distortion or port noise, that can also make them localizable so it is important to choose high-quality subwoofers for your setup that are appropriately sized (have ample output) for your particular room or space.
In terms of control of frequencies from multiple sources, this generally will depend on the room and speaker / listening positions. If the sub or subs are not in an ideal position and they haven’t been set up with care, some of the main speakers (such as the Left / Right / Centre speakers) might be able to deliver bass more consistently.
Therefore, it isn’t so clear cut!
Ultimately, if you are able to put the time in to set up your subwoofer(s) well, and their in-room response is smooth at the listening positions, then an 80Hz crossover is certainly ideal. It provides you with a less difficult setup than having to worry about bass frequencies and room modes from multiple sources.
If you have multiple subwoofers, I would highly recommend you use Multi-Sub Optimiser and and external DSP to pre-equalize your subs before running room correction such as Audyssey or YPAO.
However, if your subs are not set up well, you may find that the main speakers will deliver better bass when their crossover is lower.
Ultimately, the recommendation is to set up speakers with an 80Hz crossover initially and ensure subwoofer performance is optimised fully. Then if required, try lower crossovers for the front speakers for example – if the AVR detected a lower crossover point. Listen for which setup sounds more linear and even across the listening space.
When lowering the crossovers or setting speakers as large, it may be required to provide external amplification for the affected speakers dependent on the load. This is not normally required with an 80Hz crossover as amps within high-end AVRs can normally take the load without breaking a sweat as long as the load is matched correctly. But asking an AVR’s internal amps to drive 4ohm speakers under 80Hz at high volumes is asking for trouble: at the very least you may be listening to a lot of distortion in addition to the program material. See my article on whether you need an external amp for your AVR.
Let’s talk about how bass is routed by default in most AVRs.
- When you select a lower crossover frequency for a speaker, only the bass from that channel is played on that speaker. The LFE is still routed to the subwoofer.
- When all speakers have a crossover set, bass below the crossovers is redirected to the subwoofer, in addition to the LFE.
- When you select a speaker pair to be large without a crossover, it means that the AVR may route the bass from the other speakers to the large speakers as opposed to the subwoofer. Again, LFE will still be played by the subwoofer(s).
- The only time the large speaker pair would play the LFE signal is when there are no subwoofers connected.
Now the above is only the default behaviour. AVRs nowadays come with more and more sophisticated bass management, which means you really need to consult your user manual, as LFE can now be routed to large speakers and with directional bass, bass routing to subwoofers can also be more complex.
The Issue with Bass Summing
There is one last issue we need to address: bass summing.
There are some mixes where the same bass information is in the main speakers and in the LFE signal. In this instance, the impact might be somewhat different with bass management on (small speakers with crossovers set) versus bass management not being on.
This is because the bass from the main speakers is summed with the LFE signal to create the signal for the subwoofer(s). This can create a larger impact than if the mix was played without summing the bass.
Good mixing engineers understand this and will monitor the mix for such an issue as they are mixing to minimize it. Unfortunately, some engineers will altogether remove the bass information below 80Hz from the main channels in the mix and route everything under that to the LFE channel. While this ensures consistent playback across systems, it isn’t necessarily ideal for larger playback systems with full-range speakers. This is especially true for the centre channel where male voices have harmonics below 80Hz. Some users may wish to have full-range LCR speakers for this very reason, so as not to route male voices to the subs and they have purpose-built rooms to ensure even coverage from the front speakers across the listening space.
As you can see, there are numerous issues to contend with. It isn’t as clear-cut as looking at the speakers specifications sheet or running your AVR’s automatic setup routine / room correction.
We have really just scratched the surface with this article, but I hope it has helped you understand and correct for the main issues.