What is meant by “axis”?

[Good4it]

What is on axis and off axis of a speaker? What controls it? Is one better than the other? Is it measured both horizontal and vertical? Why do some speakers do some do better?

 

[j_garcia]

 

[shadyJ]

What is on axis and off axis of a speaker? What controls it? Is one better than the other? Is it measured both horizontal and vertical? Why do some speakers do some do better?

Lol, wow, that is a lot of question on some deep subjects in speaker design. I can only give surface answers here, because I don't have time to write a multi-volume book, lol.

Axis is the angle at which the listener is at with respect to the speaker. If you are standing dead ahead in front of the speaker, that is zero degrees which is called 'on-axis' or the 'direct axis'. If you are standing to the side of the speaker at some angle, that is 'off-axis'. Here is a picture which illustrates the concept:

Looks like the guy in that pic is standing about 45 degrees to the left and right of the direct axis, btw.

What controls the axis response is the design of the speaker. We call the axis response the 'directivity' of the speaker. Speakers that are highly directive do not shoot sound of of a wide frequency spectrum out at a wide angle; they have a very narrow angle at which they project sound, and consequently, they have a small listening area at which they sound good. Low directivity speakers project a wide frequency band of sound out at a very wide angle, so they can sound good at a very broad listening area in front of them.

Neither low nor high directivity speakers are better than the other, it depends on the situation requirements. There are things to consider like the acoustics of the room and the width of the listening area when thinking about the directivity of a speaker.

One thing to keep in mind that while most speakers are designed to be listened on the direct axis, many speakers are designed to be listened at an off-axis angle. If you want to know the best angle to listen to a speaker at, look for manufacture recommendations or off-axis dispersion measurements.

The axis can be measured by both vertical and horizontal, but people mostly mean horizontal in conversation, at least if they don't specify vertical. If you read a comment where someone says, "these speakers have a great off-axis response", they will mean horizontal.

Regarding how well a speaker handles off-axis response, the best design approach is to have a smooth off-axis response that mirrors the on-axis response. The reason for this is that a lot of what people hear in-room is actually acoustic reflections from the room surfaces rather than the direct sound of the speaker. So if a speaker had a perfect direct-axis response but a very erratic and uneven off-axis response, that speaker can still sound terrible.

Here are some examples of good and bad off-axis response. Here is a good on and off axis response, that shows direct axis, 15 degrees, and 30 degrees; they are all beautifully uniform:

Here is a miserable on and off axis response:

Look at that big suckout from 2 kHz to 5kHz at 30 degrees, this speaker is going to have a veiled sound in-room because of that.

 

[Good4it]

Very good response. If a manufacturer doesn’t give a axis recommendation does that mean anything? Is on axis always “the best”and off as little as needed?

Just trying to learn. My education is in cars not audio.

 

[TLS Guy]

Very good response. If a manufacturer doesn’t give a axis recommendation does that mean anything? Is on axis always “the best”and off as little as needed?

Just trying to learn. My education is in cars not audio.

When it comes to specs most speaker manufacturers are morons. They give incomplete and misleading specs, as a rule. There are precious few speaker manufacturers whose specs are even useful and can be trusted.

 

[shadyJ]

Very good response. If a manufacturer doesn’t give a axis recommendation does that mean anything? Is on axis always “the best”and off as little as needed?

Just trying to learn. My education is in cars not audio.

Some engineering departments will make speakers to be used at a certain angle, but the marketing departments will not get the memo on and so do not say "intended to be used at X angle." The best thing to do, if possible, is try to get in touch with the engineers of your speaker and ask them. Just today I measured a speaker that looks very much like it was intended to be used at an unconventional angle, but you would never know that from the product page or user manual.

On-axis is not always the best axis. It depends on the speaker and also on listener preference. Here is a graph from a speaker that was intended to be used about a 15 to 25 degree toe-out:

This graph compares the direct axis response with the 20 degree off-axis response. The 20 degree response is a lot flatter and better sounding. The direct axis response makes this speaker quite sibilant because of that treble spikiness. This speaker was designed to face straightforward and not to be toe'd in to the listener. Some people just want parallel positioning in their speakers and these cater to that need.

If you want to know how to determine the best angle, look at dispersion measurements in reviews. Stereophile has some good dispersion measurements however they zero out the off-axis measurements with respect to the direct response, so you have to make an effort to understand what you are looking at with Stereophile's off-axis measurements. Soundstage has more intuitive measurements for understanding off-axis behavior. At the risk of sounding like boasting, Audioholics does very good too.

 

[Good4it]

Thanks that makes it clear as mud. Sounds like there’s more to it than I’m equipped for.

Isn’t there a easier way? I just want to hear good sound.

 

[shadyJ]

Another way to look at it is that most speakers lose high-frequency energy more rapidly at off-axis angles, so if a speaker has treble that sounds too bright on its direct axis for your tastes, you can just angle the speakers inward or outward until the treble sounds more tolerable. Here is an example, this is a measurement of a a speakers response from 0 degrees out to 90 degrees in 10 degree increments:

The highest lines will be the direct axis response and as the lines fall off, that is responses of the speaker's angles going outward so the lowest curve is 90 degrees (or perpendicular to the speaker's direct axis). Here is a 3D view of that same graph:

Anyway, note that spikiness at around 6 kHz on the direct axis measurement; that could end up sounding a bit sibilant where the 'T' and 'S' sounds from vocals are unusually pronounced. What we can see is that at from 20 to 30 degrees (count down the curve lines from the top, each being a 10 degree angle), that peak at 6 kHz gets greatly reduced while not losing much response at lower frequencies. At the 20 to 30 degree angle, the response does roll off rapidly above 13 kHz or so, but that is not such a big deal because there isn't really a lot of content in that range. So you could 'tame' the treble in these speakers by listening to them at a 20 to 30 degree toe-in or toe-out (if you want more precise center imaging, use a toe-in, but if you want a wider, more spacious soundstage, use a toe'd-out angle).

This stuff is not really that complicated, I could explain it a lot better in person, but it is more difficult to convey in text explanations and abstract graphs.

Anyway, you can explore the phenomenon yourself and get a more practical understanding of it: using a single speaker, only play a music track that has lots of treble content throughout. With your ears at tweeter height, move around the speaker from directly in front of it to different angles off of the direct axis (while keeping the same distance from the speaker). Note how when you move off to the side, the high frequencies get attenuated the most, from higher to lower. If you work your way to the back of the speaker, all you will hear from the speaker itself is bass (you may still hear high frequencies, but they will be acoustic reflections from your room). This effect is especially pronounced if you do this outside in an open area. However it should be said that not all speakers behave this way, and the ones that defy this sort of behavior are odd designs, like flat-panel dipole speakers.

 

[MrBoat]

Of course then, there is the SEOS waveguide, to where your life, and everything in it becomes the speaker.

 

[Good4it]

I appreciate your time trying to help me understand. It’s complicated.

Thanks

 

[Swerd]

I appreciate your time trying to help me understand. It’s complicated.

It helps to think of speakers dispersing sound like a car's headlights spread light. Low beams disperse the light broadly and high beams keep the light in a narrow pattern. Similar to flood lamps vs. spot lights.

I like speakers that disperse sound as broadly and as evenly as possible.

What makes it complicated is the range of wavelengths involved with sound. In a typical 2-way speaker, low sound wavelengths range from about 25 to 0.5 feet, and a tweeters sounds range from 0.5 to 0.05 feet. Long wavelengths tend to disperse more broadly than short wavelengths. As a result, the amount of dispersion changes with the wavelength.

In contrast, visible light wavelengths are quite a lot shorter.

 

[Good4it]

Any way to know without expensive measureing equipment?

 

[shadyJ]

Any way to know without expensive measureing equipment?

Well there is no way to tell that is speaker has good off-axis performance without measuring it, unless you have a reliable way of actually hearing that.

As far as looking for narrow dispersion speakers vs wide dispersion speakers, you can kind of get an idea by just looking at a speaker. If the speaker has large drivers playing midrange frequencies or a narrow wave-guide, that is going to be a narrow dispersion tweeter (think live-sound pro stuff). Small speakers or speakers that use smaller drivers to play low frequencies will inevitably have a wide dispersion (think a tower speaker with dome tweeter using a bunch of 4" drivers for the bass).

 

[Swerd]

Any way to know without expensive measureing equipment?

Find a test CD that has pink or white noise, such as Behringer's audio test disc. Track 83 is a recording of pink noise. Play that track, on only one speaker at a time. Walk around the room, in a semicircle, while keeping the same distance from the speaker. Listen to a speaker's mid range and higher frequencies as you go from directly in front of the speaker (on-axis) to off to the side (off-axis). You will notice a shift in the overall tone of the pink noise, from bright to less bright. By this method, you can easily compare two different speakers while in a store.

Generally, I like wide dispersion better than narrow dispersion. With music, in stereo, wide dispersion creates a more realistic "out-of-the-box sound image" where the music tends to sound like it is coming from outside the speaker cabinets. Narrow dispersion (beaming) tends to make the music sound like its coming from within the speaker cabinets.

 

[Good4it]

Does one sound better or is it a matter of personal preference?

 

[MR.MAGOO]

Finally, on September 27, 1940, Germany, Italy, and Japan signed the Tripartite Pact, which became known as the Axis alliance. Even before the Tripartite Pact, two of the three Axis powers had initiated conflicts that would become theaters of war in World War II.


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oops! sorry, wrong forum.

 

[ski2xblack]

Does one sound better or is it a matter of personal preference?

Your preferences, along with the desired illusion you're after, within your specific acoustic environment, will determine which is best. Each has strenths, e.g. wide dispersion can do envelopment trickery very well, while narrow dispersion, provided the speakers are oriented correctly, can provide image stability in a way that wide dispersion just cannot pull off. In either case, smooth off axis response is critical.

 

[highfigh]

Does one sound better or is it a matter of personal preference?

When data is used to choose speakers that meet the needed criteria, one of the specifications is dispersion because they're trying to cover a specific area with sound, at a particular SPL, frequency response and without bleeding into other areas. Off-axis response can also be used when a room's acoustics could badly affect the sound- you don't want wide dispersion if the walls adjacent to the speakers are hard and reflective with no possibility of using treatment to tame the reflections. If you'll be sitting in one place and nobody else needs to hear the sound equally well, narrower dispersion is OK, but if you move while the music is playing, sit in more than one place or want everyone to hear things equally, wide dispersion is better.

 

[Good4it]

Very good info all, THANKS.

 

[Art Vandelay]

Here is a miserable on and off axis response:

Look at that big suckout from 2 kHz to 5kHz at 30 degrees, this speaker is going to have a veiled sound in-room because of that.

There are quite a few good sounding 2-way monitors that exhibit a similar polar response - with a suck-out near the crossover region off axis. If the speaker is designed to be listened to at close range, as is the case with many mini monitors, then it's not a problem at all. in a large room that speaker may not sound great but "veiled' is the wrong word IMO. Lacking in presence, perhaps, but not "veiled"unless there are problems with the design.