Speaker “Toe” - What’s It All About?

Posted on 28th October, 2014

Speaker “Toe” - What’s It All About?

In this article we discuss one very important aspect of loudspeaker placement. This is an easy to implement tweak that requires nothing more than the ability to listen for particular changes and then decide what you like better.

Does one size fit all?

There isn’t a single solution that best fits all. The ideal amount of toe in depends on:

  • Speaker placement
  • Location of the listening position
  • Width of the listening area
  • The sound radiation pattern of your speakers
  • Acoustics of your room
  • Design guidelines of the speaker manufacturer
  • Your personal preferences

All these factors are interrelated. Many guides on this topic assume that you have conventional box speakers, but what if you have electrostatics or horns? Every system is unique and requires its own solution.

The interdependence factor

It’s important to realise from the outset that many statements are made here that are generally true with the condition that all other factors are disregarded. Many statements here apply when all else is equal. In any particular system, many interdependent factors come into play. All else is never equal! This explains why in principle many will have a different experience to what is described here. Don’t be surprised if your experience is the exact opposite regarding aspects described here. It usually means another interdependent factor is at play.

Listening is the key

The most important advice offered in this article is simple – change just one thing at a time and then listen for the difference. If you change multiple things at a time, you may miss the best solution. Some factors may cancel others out, so you need to be patient enough to be quite focused in your approach. Other factors will work at the same time and you end up with misconceptions about what actually made the difference.

Critical listening is the skill required here. It works best when you listen in a deliberate and more disciplined way than you would choose for enjoyment. Listen to one aspect at a time – this is arguably the biggest secret understood by critical listeners. When listening in this way, your listening acuity increases dramatically. Listen for specific aspects. This is part of helping you to learn the art of critical listening.

No toe in

The configuration below represents speaker set up with no toe in.

Fig 1 – Speakers set up in a 4 x 6m room with no toe in. The speakers fire in a direction parallel to the side walls.

Setting speakers up with no toe in at all is recommended by some manufacturers who have designed their speakers to be set up this way. This creates a wider sound stage due to illuminating stronger sidewall reflections. A mirror image is created shown as speaker with a lighter shade of red. The extra sound source is faint because it is subject to the reflectivity of the wall, the extra path distance and the radiation pattern of the speaker. Generally speaking, having no toe in will create a different spatial impression, one that tends to be wider but less precise. It’s often more critical to sit dead centre with this arrangement.

This setup means that one is also listening off axis. It leads to greater treble attenuation – the altered tonal balance may enhance or degrade the performance of your speakers. Bright speakers may be tamed slightly. Conversely, speakers designed for zero toe in may become slightly bright if toed in.

Fig 2 – Conventional toe-in. A triangle is created where the listening distance is greater than the spacing of the speakers. Speaker axes cross behind the listening chair. This configuration will suit many with conventional stand mount or floorstanders with dome tweeters and cone drivers.

The setup shown in fig 2 is the one that will suit most audiophiles and it’s a good starting point.

In comparison to no toe in, the stereo image should become sharper and more precisely defined. The tonal balance in the treble region should be slightly more forward. The apparent width of the sound stage may be altered.

Speaker placement

Speaker placement is closely connected to toe in. A couple of things to note:

Distance to the sidewall affects the strength of side wall reflections. As the speakers move away from the side walls, the reflections occur later in time and they are lower in level.
Distance to the front wall (behind the speakers) affects sound stage depth. Near wall placement results in a shallow sound stage. Toe in also affects this aspect to the degree that it affects the energy radiated to the front wall. Moving speakers well out from the front wall and using a fair amount of toe in is expected to create a deeper sound stage than no toe in at all and speakers right up against the front wall.

Location of the listening position

The location of the listening chair is equally as important as the speakers. Close proximity to the speakers approaches a nearfield listening arrangement which increases the direct field (sound from the speaker alone) relative to the reverberant field (sound reflected around the room). Sitting near the rear wall with speakers close to the front and side walls creates the opposite situation where the reverberant field dominates. The right balance normally lies in between the two.

If your room is acoustically appealing, then it tends to lead to a greater degree of reverberant energy being desirable. You will enjoy the sound and sonic signature of the room interacting with the speakers. If your room is sonically poor, with unpleasant colorations that have not been resolved, this tends to lead to an arrangement that seeks to minimize the room sound by approaching a nearfield arrangement. Both speakers and listening chair come out from the walls. This would also tend to lead to a more aggressive toe in. In an acoustically good room, the need for toe in may also become less.

Width of the listening area

The arrangement shown in fig 1 with no toe in tends to restrict the listening area to one chair. Moving as little as one seat to either side of the listening chair results in a loss of the centre image, the sound becomes localised to the nearer speaker and immersion within a realistic sound stage is lost. Toe in increases the effective listening area so that side seats can still maintain the centre image, although this effect is strongly related to the radiation pattern of the speakers. Conventional cone and dome box speakers experience this effect but it can be optimized further with open baffle and some horn speakers with greater dispersion control characteristics.

 

 

Fig 3 – With no toe in, the centre image is lost in side seats

In the arrangement above, the left side seat will hear sound mostly localised to the left nearer speaker, both due to proximity and the off axis response of the right speaker.

To the degree that the speakers control dispersion off axis, the solution in fig 4 provides a solution to maintaining a good centre image in side seats, where a larger listening area is important.

Fig 4 – The speakers are aggressively toed in so that the further speaker fires directly towards the side seat. The right speaker fires on axis, whilst the nearer speaker is now off axis.

This unconventional arrangement is shown as an option, but of course choosing the best toe in should factor in other considerations. The arrangement above tends to best suit speakers with a greater level of dispersion control, using compression drivers loaded with waveguides. Many of my own loudspeaker designs have greater than typical. I consider this a neglected aspect of loudspeaker design which is a consequence of designing loudspeakers to be very compact.

The sound radiation pattern of your speakers

In the context of this topic, speakers can be divided into various classes according to their sound radiation characteristics:

  • Omni directional – sound is radiated evenly in all directions
  • Conventional monopole – omni directional low frequency radiation transitions to a forward focused beam at high frequencies
  • Constant directivity designs – off axis response is flat but attenuated in level
  • Bipole – sound is radiated to the rear as with dipoles but without the null at the sides.
  • Dipole – this category has three varieties, all of them with approximately equal front and rear radiation with a null perpendicular to the baffle.

Dipole speakers:

  • Electrostatic – extremely narrow vertical beam with a very narrow horizontal beam that fires with almost equal energy to the rear.
  • Planar dipole – similar to electrostatics but the horizontal dispersion is wider.
  • Open baffle – sound is radiated to the rear and front with a dipole null in line with the baffle.

Covering all these types of speakers is beyond the scope of this article, but it should be noted that dipoles tend to have unique requirements. Dipoles differ to the extent that they deserve their own article and separate treatment.

True Omni loudspeakers obviously can’t benefit from toe in whilst constant directivity designs will benefit from well-considered toe even more than conventional designs.

General room acoustics

The general acoustic characteristics of your room will affect toe in choices. In a very bright and highly reflective room, more toe in can tame room reflections slightly. This is where constant directivity designs benefit from toe in to a greater degree, since their off axis response is attenuated, resulting in toe in having a greater impact on the sound that is radiated into the room. These designs can serve to tame the room where room treatment isn’t an option one is willing to consider. In the ideal case, however, treatment should be used to achieve the best possible sound in your room.

Design guidelines of the speaker manufacturer

Loudspeaker manufacturers who provide recommendations on speaker placement will tend to offer general suggestions combined with some that relate to how they have designed their speakers. A designer may have intended that their speaker will be placed close to the front wall, meaning the crossover anticipates some bass loading from this wall. They may also design their speakers to sound balanced with no toe in at all.

Things to listen for

The key to getting the best sound here is changing one thing and listening for specific changes. Some of the changes you should notice include:

  • Tonal balance shift – the treble is the most likely change.
  • Width of the sound stage – how far do sounds appear to be placed outside the speakers?
  • Stability of the centre image in side seats (if this is a priority)
  • Depth of the sound stage
  • Sharpness of the stereo image (can you locate individual sounds)
  • The balance of direct and reflected sound
  • Vocal clarity
  • Perceived smoothness of female vocals

The solution that works best for you may take some time to discover, but don’t be averse  to trying things that seem wrong, even if just to experience something that may clarify your preference. The process can take some patience, as there are so many things you can adjust. It’s not simply a matter of angling the speakers. The time consuming part is the combination of changes. You may shift the listening position and then repeat previous changes.

In the end, it’s important to realize that there isn’t a single best solution but many possibilities. The best configuration is the one that caters to your preferences. When you sit in your listening chair, you should feel engaged by the music, immersed in a sound stage where individual sounds come from precise locations. The tonal balance should feel right and everything should converge into a whole such that the room and speakers disappear and the music emerges. If this isn’t your listening experience, try the suggestions here before reaching for your wallet.

Learn more about speaker placement and room acoustics in the Discussion Forums.


About the Author

Paul Spencer is a StereoNET Technical Contributor. Paul is a long time StereoNET member, and owner of Red Spade Audio, specialising in Room Analysis and Custom Audio Design.
For more information visit http://www.redspade.com.au/audio/

      Paul Spencer's avatar

      Paul Spencer

      Paul Spencer is a StereoNET Technical Contributor. Paul is a long time StereoNET member, and owner of Red Spade Audio, specialising in Room Analysis and Custom Audio Design.

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      Posted in: Hi-Fi Home Theatre
      Tags: speaker placement  room acoustics 

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