joz Posted December 22, 2015 Posted December 22, 2015 Ok I've heard the term thrown around a bit. Usually heard about it being associated with big drivers playing to high up? But can someone explain to me exactly what it is and what does it sound like. And where and how would someone be able to experience it. Why is it bad? Is it bad?
Anthony John Colbert Posted December 22, 2015 Posted December 22, 2015 afaik it means that the higher frequencies will radiate in a narrower beam so if you are off axis you will loose the higher frequencies from that driver. So on axis things will sound normal but if you go say 30 degrees off axis you will lose a lot of the higher frequencies. IOW you end up with a narrower sweet spot 1
Telecine Posted December 22, 2015 Posted December 22, 2015 (edited) There's a well known speaker in these parts that nicely illustrates the problem. It is generally a crossover and driver integration issue where a driver is asked to play frequencies outside of the optimal range. In the case of the speaker that comes to mind, I believe that the tweeter is asked to play too low. The result in that case is that certain frequencies fall out of the image and appear to come directly from the driver. In other words they beam at you. It is aggravating if you are sensitive to it but my observation is that few are. Edited December 22, 2015 by Telecine
Zaphod Beeblebrox Posted December 22, 2015 Posted December 22, 2015 (edited) Ok I've heard the term thrown around a bit. Usually heard about it being associated with big drivers playing to high up? But can someone explain to me exactly what it is and what does it sound like. And where and how would someone be able to experience it. Why is it bad? Is it bad? Is it bad? Depends. Hopefully, all will become clear soon. An audio frequency may be expressed in two ways: 1) Frequency. 2) Wavelength. The relationship is as follows: Frequency (in Hz) = speed of sound/lambda Speed of sound is usually rated as 343.2 metres/sec Lambda is wavelength From this equation, we can work out the wavelength of any frequency. Let's take 1,000Hz. Wavelength is 343.2/1000 = 343.2mm VERY close to the diameter of a 30cm bass driver. At 1000Hz a 30cm bass driver operates with maximum efficiency, as the dimensions of the cone are close to one wavelength of the input signal. It is also a frequency where the driver tends to cease operating as an omnidirectional source. IE: It 'beams'. Since a driver operating at or near cone resonance is operating at very high efficiency, this may be desirable for some applications. Many pro systems operate like this. Trouble is, once a driver is operated beyond it's 'piston range' various other, undesirable artefacts may manifest themselves. [EDIT] This is a short description, by someone who is not expert enough to explain it properly. Hopefully, others, who have more knowledge can chime in and tidy up what I am attempting to say. Edited December 22, 2015 by Zaphod Beeblebrox 4
almikel Posted December 23, 2015 Posted December 23, 2015 In the case of the speaker that comes to mind, I believe that the tweeter is asked to play too low. The result in that case is that certain frequencies fall out of the image and appear to come directly from the driver. In other words they beam at you. this is not an example of beaming - getting the tweeter to play too low is asking for too much excursion (bad), but nothing to do with the narrowing of the radiation pattern, which is what beaming refers to. As Zaphod says, beaming relates to a drivers radiation pattern as it operates as a piston, and is directly related to the diameter of the driver. The beam width goes from omni-directional to pointing forwards with side lobes as the frequency rises. The lobing effects are easily determined, based on driver size. A parameter k.a or ka is defined ka = 2pi a/wavelength and a = radius Attached is a picture of lobing vs ka for any driver Somewhere between ka = 2 and ka = 5, lobes develop With multi way speakers, keeping ka <=2 will prevent any lobing. Geddes has a good paper on directivity that's worth a read: http://www.gedlee.com/downloads/directivity.pdf Note that the lobing has nothing to do with cone breakup - that's a different mechanism entirely cheers Mike 1
joz Posted December 23, 2015 Author Posted December 23, 2015 So is keeping drivers omni directional difficult or is bad speaker design responsible for beaming? At the recent DEQX demo Alan was trying to explain beaming to me but I'm afraid I wasn't a good student on the day.
Volunteer sir sanders zingmore Posted December 23, 2015 Volunteer Posted December 23, 2015 My lay understanding is that speakers that beam do not have a consistent frequency response off axis. This is supposedly bad for a couple of reasons. 1. The reflected sounds that reach your ears have a different "signature" to the direct sound. This messes up /confuses the direct sound and so the speakers don't sound as good 2. The sweet spot is much smaller. Having said that, it's not all bad. Some speakers (like mine) are designed deliberately to beam. The fact that they are dipoles confuses things a bit because of the back wave.
almikel Posted December 23, 2015 Posted December 23, 2015 It all comes down to the design goals. Geddes deliberately chooses larger mid woofers where the pattern has begun to narrow to match the directivity of the waveguide he's crossing to. I can't imagine why any designer would run a woofer up to the point of lobing (eg k.a >= 5). Crossing a narrowing woofer to a tweeter with a wide pattern is not ideal, hence the "controlled directivity" designs such as Geddes and the PSE. Full range designs would suffer significant lobing, but it can't be avoided. cheers Mike
Darren69 Posted December 23, 2015 Posted December 23, 2015 So is keeping drivers omni directional difficult or is bad speaker design responsible for beaming? At the recent DEQX demo Alan was trying to explain beaming to me but I'm afraid I wasn't a good student on the day. The social lubricant at the time may have been responsible for your own beaming mate. Cue can tan.
joz Posted December 23, 2015 Author Posted December 23, 2015 The social lubricant at the time may have been responsible for your own beaming mate. Cue can tan. You mean my beaming smile? 1
Darren69 Posted December 23, 2015 Posted December 23, 2015 You mean my beaming smile? Coupled with the aura, of course.
ZEN MISTER Posted December 23, 2015 Posted December 23, 2015 Beaming with a perfect square wave. . Beaming with a 'Moir ' pattern. Beaming with a single point dispersion. Oops, sorry I always confuse planking and beaming. Billy. 10
rollo Posted December 23, 2015 Posted December 23, 2015 Beaming Occurs when the tweeters are not linear to the frequencies. treble will arrive at ones ear first beating the rest. Using reflective and diffusive surfaces can and will eliminate the beaming. Not easy but doable. charles
Newman Posted December 23, 2015 Posted December 23, 2015 Some of the answers above are only partly right. (You have probably figured this out already, since they can't all be right). The natural tendency of a driver, bass, mid or treble, is to beam as frequencies rise above a certain frequency that depends on the driver's dimensions. 'Beaming' means that the driver's beamwidth is getting narrower. 'Beamwidth' means double the number of degrees you can move off-axis before the loudness drops by 3 dB. See diagram. Other words that mean much the same thing but measured differently, are directivity and dispersion. Let's say a speaker is really good on-axis, but is strongly beaming. If you are sitting outdoors and in line with the speaker's axis, it will make no difference. But if you move to adjacent seats, or tilt the speakers away from you, the sound will change. So, 'beaming' contributes to 'hot seat' listening positions where only one person in the audience gets good sound. What it 'sounds like' will depend entirely on how the speakers behave when they beam, and where the crossover frequencies lie. But there's more. Let's move the above outdoors setup into a home audio listening room. Even the person in the hot seat now hears not only direct sound, but also reflected sound off of all four walls and floor and ceiling. When a speaker is 'beaming' badly, the reflected sounds have a very different frequency response or 'tone' to the direct sound. This inconsistency between direct and reflected sound has been proven in blind tests to sound 'wrong', or to use the experimenter's terminology, it is 'less preferred'. Where or how to experience it? Nearly all speakers exhibit it to varying degrees. Probably yours do. Electrostatics and full-range single-driver speakers usually beam strongly. Easiest way to exaggerate it is to listen to your speakers rotated a long way off-axis, say 60 degrees. 3
legend Posted January 20, 2016 Posted January 20, 2016 (edited) The reason beaming occurs is destructive interference of the waves that occurs when they are out of phase I.e. when one is upside down relative to another the two waves will cancel and this will occur when the waves are shifted by half a wavelength. So when the diameter of a driver becomes about half the wavelength then waves generated on opposite sides of the driver can start to destructively cancel when you go off-axis where the path lengths from the opposite sides of the driver to the ears are different. For a mid-bass driver of around 15 cm this destructive interference and so beaming starts to occur around 1000 Hz where the wavelength is around 30 cm. However beaming only becomes really important at about twice this frequency i.e 2000 Hz and above. As described by Newman and others this beaming can have deleterious effects on the indirect sound reaching the ears through reflection off walls by affecting the overall tonal balance. However there are times when it may help. Most 15 cm drivers also tend to breakup above about 1000 Hz which causes gross distortion so turning down the perceived volume can effectively reduce this distortion, particularly because ears are most sensitive in the 2-4 kHz region. Note however that the breakup of the driver cones is a mechanical failure unrelated to destructive interference and it is a coincidence that they occur at much the same frequency for many drivers. However very rigid drivers such as Legend uses in its high-end speakers and as Alan at DEQX uses do not breakup until well above the frequencies at which beaming would occur if it were not for the multiple drivers and very steep crossovers. Edited January 20, 2016 by legend
Nada Posted January 21, 2016 Posted January 21, 2016 My impression is that "beaming" in audio is a term with negative connotations. It relates to the PA problem of providing consistent sound to a large audience dispersed spatially. If the PA system beams audience members at the sides will hear more bass while those at the back middle will hear more treble. Home listening for a solitary aging male as the target audience is the opposite situation. Here the term beaming is misleading. Instead lets call it directivity. A system with very tight directivity across most frequencies can deliver unsurpassed clarity of imaging and microdynamics. When your in the precise sweet spot of large ESL's and are captivated part of the magic is coming from the high directivity. Other benefits of this tight sweet spot behavior are: new girl friends who want to listen to music have to sit on your lap allowing both parties to enjoy a hopefully tight sweet spot old girlfriends who would normal demand the volume be turned down can sit in the same room in a different spot and hear markedly less volume neighbours dont hear so much 6
davewantsmoore Posted January 21, 2016 Posted January 21, 2016 My lay understanding is that speakers that beam do not have a consistent frequency response off axis. That's correct. A typical speaker, will radiate 20 Hz everywhere.... the same amount of sound goes forwards backward, up down, everywhere. A typical speaker, radiated 20 kHz over a very narrow area .... (like a laser beam) As you go up in frequency, the coverage pattern changes (and typically radiates over a narrower and narrower areas .... until it is like a "laser beam") If it has a changing coverage pattern ..... This means that sound firing from your speaker at different angles, have different balances of bass, mid and treble.... which means the reflections are processed differently by our hearing Ideally the coverage pattern should be the same at all frequencies..... ie. for a certain listening angle, the high, mid and low frequency balance should be the same as other listening angles) If the coverage pattern is going to change ..... it should change evenly with frequency (ie. no sudden changes) 1
legend Posted January 21, 2016 Posted January 21, 2016 (edited) I think you have to distinguish between a single driver and a loudspeaker which usually has more than one driver. For say a small two driver speaker consisting of a 15cm mid-bass driver and a 25 mm tweeter then the mid-bass driver will tend to start beaming (response off axis decrease) above around 1kHz and increasingly so up until the crossover to the tweeter typically around 3 kHz where the sound wavelength is approximately 100 mm. So the tweeter does not beam when it comes on at this frequency causing a sudden change in on- to off-axis response and perceived tonal balance. The perceived brightness in treble is often caused by this sudden change and one way of ameliorating it is to use a wave guide that narrows the tweeter output to more closely match the beaming of the mid- bass driver at Xover. Above about 10 kHz where the half the sound wavelength is about 15 mm then the tweeter's response itself tends to narrow I.e beam increasingly so as the frequency increases to become laser like as Dave points out. The ratio of off to on axis response (beaming) is important but only one of the factors that a speaker designer must consider. Others are the overall on-axis frequency linearity or otherwise (frequency distortion), linear distortion such as cone breakup & non-linear distortion due to driver suspensions and motors - and how these vary with frequency. In the end all loudspeakers are a compromise between all these factors and how a designer balances them. Edited January 21, 2016 by legend
rowuk Posted January 22, 2016 Posted January 22, 2016 (edited) It is impossible to say how "beaming" sounds. The term just means that the loudspeaker elements produces a very narrow beam of sound - like a flashlight only illuminates a narrow area. If the sound is still good, we point the speaker towards our ears and get great, balanced sound. Many times however, beaming is accompanied with distortion (that has nothing to do with the beaming). If we are not talking about horns, the frequencies that beam generally also distort. That is simple driver design. A great example of good sounding beaming would be most top electrostatic speakers that have very low distortion at those frequencies that beam. An example of "distorted beaming" would be from so called 4" full range drivers. They do not necessarily sound bad, but the distortion measurements tell a very important story (if we are willing to listen). Edited January 24, 2016 by rowuk
rowuk Posted February 2, 2016 Posted February 2, 2016 I will disagree with the notion that speaker directivity "should" be the same for all frequencies. I believe this to be a very popular DIY fantasy. Rooms do not behave evenly at all frequencies, our ears do not behave evenly at all frequencies, microphones that record our music do not behave evenly at all frequencies and musical instruments do not behave evenly at all frequencies. Even the question of changes of directivity vs frequency have no absolute rule. In a concert hall, much of the violin, viola and flute sound is reflected off of the ceiling. In real life, they are much more diffuse than say a trumpet. Recording engineers use a mix of directional and omnidirectional microphones for most acoustic events. What matters most is what gets to your ears and how. Recording engineers speak of "early" and "late" reflections. The early reflections seem to do the most damage as our brain cannot separate them from the original sound. They make localisation and interpretation of timbre more difficult. Speaker choice for the room used requires some research and experimentation for best results. In fact, many arguments can be made for wide, medium or low directivity. They all have a bit of truth behind them, but none of them provide a universal solution. If you follow the rule, play before you pay, you should never be disappointed. The assumption that a "beaming horn" is bad is rubbish. If we use a "conventional" horn in its optimal frequency range (generally a decade or about 3.5 octaves), we have no "beaming". We have the desired radiation pattern. I will maintain that there is no best architecture, only intelligent people that get the most out of what they choose for themselves. 1
Happy Posted February 2, 2016 Posted February 2, 2016 @@rowuk but apparently in DBTs the majority favours CDs. What do you say about that? Sent from my iPad using Tapatalk
rowuk Posted February 2, 2016 Posted February 2, 2016 (edited) @@rowuk but apparently in DBTs the majority favours CDs. What do you say about that? Sent from my iPad using Tapatalk Majority? What does that mean? Who did the "majority" of Australians vote for? If we talk about "audio" majority, then we are at mini systems with no-fi sound. I think the majority of professional musicians own Bose speakers - and they get the real thing with far more regularity than the typical audiophile. That does not mean that Bose is better, it means that musicians buy them - probably not for the same reasons that audiophiles use. I am sure that constant directivity speakers (well it is a nice name even if the "majority" of so called CDs don't do justice to the name) can sound very good. Whether or not the usual 2 way implementations can be considered superior is VERY subjective. I insist that no architecture can make claims to superiority. It ALWAYS depends on the complete system and audio hygiene of they that assembled and integrated the system. I will also insist that the sound of a CD dependent on many factors, the directivity not being the primary cause, rather the driver and the frequency band that it is supposed to deliver. I remember when the "Econowave" speaker made its debut and offered exceptional performance for a very low price by combining a big woofer and a CD horn. This effort alone raised the bar of "inexpensive" audio quality and certainly got many that thought that horns were only for PA turned into believers. This closely followed the efforts of Earl Geddes and others. If we follow those hobbyists, we do see that many upgraded to more complex systems including Tom Danleys Unity and Synergy horns. Others moved on to other types of multi way horn speakers. I sincerely doubt that many of them have "better" sound as that is less dependent on hardware than many want to believe. My only point is that there is no reason for dogmatic arguments. The results are a function of focussed efforts and we do not all end up with the same solution. Edited February 2, 2016 by rowuk 1
Happy Posted February 2, 2016 Posted February 2, 2016 Just read the first two lines and I said the majority in DBTs, not the general public. Sent from my iPhone using Tapatalk 1
Slartibartfast Posted February 2, 2016 Posted February 2, 2016 Some of the answers above are only partly right. (You have probably figured this out already, since they can't all be right). The natural tendency of a driver, bass, mid or treble, is to beam as frequencies rise above a certain frequency that depends on the driver's dimensions. 'Beaming' means that the driver's beamwidth is getting narrower. 'Beamwidth' means double the number of degrees you can move off-axis before the loudness drops by 3 dB. See diagram. Other words that mean much the same thing but measured differently, are directivity and dispersion. Let's say a speaker is really good on-axis, but is strongly beaming. If you are sitting outdoors and in line with the speaker's axis, it will make no difference. But if you move to adjacent seats, or tilt the speakers away from you, the sound will change. So, 'beaming' contributes to 'hot seat' listening positions where only one person in the audience gets good sound. What it 'sounds like' will depend entirely on how the speakers behave when they beam, and where the crossover frequencies lie. But there's more. Let's move the above outdoors setup into a home audio listening room. Even the person in the hot seat now hears not only direct sound, but also reflected sound off of all four walls and floor and ceiling. When a speaker is 'beaming' badly, the reflected sounds have a very different frequency response or 'tone' to the direct sound. This inconsistency between direct and reflected sound has been proven in blind tests to sound 'wrong', or to use the experimenter's terminology, it is 'less preferred'. Where or how to experience it? Nearly all speakers exhibit it to varying degrees. Probably yours do. Electrostatics and full-range single-driver speakers usually beam strongly. Easiest way to exaggerate it is to listen to your speakers rotated a long way off-axis, say 60 degrees. What about the forgotten vertical plane? Beaming is very much a three dimensional phenomenon. And, in the vertical plane, crossovers and design will also impact the polar response. At a crossover frequency, you have two drivers working in parallel, so beamwidth is approximately halved (dependent on driver distance), and depending on the slope of the filters used, interference effects can exist at up to several octaves above and below the crossover points. Also, if a speaker is configure in a d'appolito array the vertical beamwidth is going to be reduced, and the tendency to beam with frequency will be exaggerated.
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