À propos to this discussion, I have a story in the October Stereophile about some new speaker design effort from B&O which addresses this very topic. In print now. Dunno if/when it will get to the web.
Early Reflections 101
- Thread starter Nyal Mellor
- Start date
Looking forward to that.
It's an important discussion because which ever way one's opinion falls, one should select the speaker design consistent with that opinion. As we know, there are many different speaker design philosophies.
It's an important discussion because which ever way one's opinion falls, one should select the speaker design consistent with that opinion. As we know, there are many different speaker design philosophies.
I hesitate to mention it considering all the more active approaches listed here; but my experience with simple fabric over walls to deal with reflections is the best result from any acoustics treatment I've ever heard. and since it does not deaden, change tonality, or remove energy it's 'just right' for lots of situations.
this is different from fabric drapery; which will act like an anechoic room.
if all you need is to knock down the high frequency reflection and harshness simple fabric has been transformative in my room.
it is laughingly cheap and super easy to try, and then easy to remove if you don't like it.
all this talk about trying different types of diffusion combined with absorption and not finding 'just the right thing'....I think I've done that.
this is different from fabric drapery; which will act like an anechoic room.
if all you need is to knock down the high frequency reflection and harshness simple fabric has been transformative in my room.
it is laughingly cheap and super easy to try, and then easy to remove if you don't like it.
all this talk about trying different types of diffusion combined with absorption and not finding 'just the right thing'....I think I've done that.
I read your account from the B&O tour. That sounds like a very cool speaker technology. It sounds very similar to the Kiiaudio approach to controlling directivity with DSP. The measurements look like B&O is definiteley not interested in omni-directional speakers. The pattern control looks like it's pretty consistent up to very high frequencies. I am not sure whether the Kiiaudio can control directivity up to such high frequencies. So this sounds like a very cool new speaker. You must have had a great time.
That is one setting. Since the directivity is determined by the programming of the drivers, other options including omni-directional are possible.
I didn't catch that part about adjustable directivity from your write up. It sounds like a very special technology. I hope there's more to come about the new B&O speaker.
Kiiaudio Three directivity in the highest frequencies is limited by the large tweeter they are using. You can see this in the measurements published in the german magazine.
I found Kal's report on the B&O speaker prototype most interesting as well. And, the measurements he provided are quite interesting, particularly in light of the discussions of Toole's views in other threads here. The B&O prototype seems to offer directional response consistent with that. And, it also hints that DSP will be a growing trend, as more and more applications for it are developed, beyond just room EQ. Many interesting new speaker designs are appearing that utilize DSP in creative ways.
Anyway, I hope you enjoyed Denmark, Kal. The first time I was there my reaction was I had never seen so many beautiful blonde women before in my life.
I have never been convinced about the desirability of omni response. I did not especially care for Radialstrahlers, for example. It strikes me that they might excite too many room reflections above the deep bass region.
Also, in TAS, there is a review of the newest Carver ribbon hybrid, which has some angled, side firing midrange and bass drivers for dispersion. Unfortunately, and typical of TAS, there are no measurements.
I used to work in Denmark and I visited a B&O store in Arhus, wasn't impressed... but I did enjoy Denmark a lot, it's a beautiful country with lots of beautiful people, good food and drink... not cheap though, so it was nice to have someone else's credit card to use while I was there. 
Danes party like nobody else, I was in Copenhagen for summer solstice and in Viberg during a town festival. Things are only getting started by midnight.
Danes party like nobody else, I was in Copenhagen for summer solstice and in Viberg during a town festival. Things are only getting started by midnight. It might be advantageous. I have had worse bass standing wave problems in some rooms doing that, however. I have avoided it ever since.
Hi Nyal,
I thought I’d add my 2 cents to this -
To the best of my knowledge there is no evidence whatsover that early reflections in small rooms with with music played over 2-channel loudspeakers have detrimental effects as a matter of principle.
There are a few studies where music was indeed used:
Schubert, “Detectability of single reflections for music”, Technische Mitteilungen RFZ 1966, vol. 10, no. 3, p.124
Detection threshold for a single lateral reflection for music was between -18 and -25 dB, depending on music motive. Setup was one loudspeaker as direct source, one loudspeaker as reflection, the whole in an anechoic chamber. No data for complete sound field with 2-channel and all of the reflections + reverberation.
Dietsch et al. (1986), “An objective criterion for the measurement of echo disturbance during presentation of music and speech” (Ein objektives Kriterium zur Erfassung von Echostörungen bei Musik- und Sprachdarbietungen), Acustica, vol. 60, p.205
Wagener, "Spatial distributions of hearing directions in synthetic sound fields” (Räumliche Verteilung der Hörrichtungen in synthetischen Schallfeldern), Acustica 1971, vol. 25, no. 4 , p.203
Echo thresholds were between 50 and 150 ms, depending on music motive. Setup was synthetic sould field (multichannel speaker system) in anechoic chamber, coincident reflection.
Naqvi et al. (2005), “The active listening room- a novel approach to early reflection manipulation in critical listening rooms”, Journal of the Audio Engineering Society, p.385
In a room according to ITU-R. BS.1116 a reflection free zone was created by using panels to direct the early reflections away from the listening zone. Due to the dimensions of the panels the low-frequency cutoff was at about 500 Hz. Omnidirectional bending wave panel loudspeakers from NXT were used as panels. In addition to re-directing the early reflections created by the main loudspeakers they were used to generate artificial early reflections.
As stimuli anechoic recordings of cornet, trumpet, and acoustic guitar were used. During the experiments these recordings were fed as direct sound to a single center loudspeaker (mono source). A Lexicon processor generated early reflections and reverberation which were fed equally to right and left front loudspeakers. Variation of the relative gains allowed creating different perceived source distances (very close, intermediate, and very distant)
It was investigated (ABX-method) whether the artificial early reflections had a perceivable effect. 12 reflections with a delay of 1.5 to 12.5 ms and a level of -7 to
-12 dB below the level of the direct sound were generated. In all cases the addition of the artificial reflections could be perceived (>75% correct answers), where the percentage of correct answers was different for the different stimuli.
The cues used for detection of the presence of the artificial reflections were source width or focus, environment width, timbre and loudness, which cues are similar or identical to those used in previous detection threshold experiments. It has to be noted, though, that also Naqvi’s configuration does not represent the usual 2-channel stereo setup with centred phantom source, which is different in timbre and in spatial impression when compared to a single source, and has lower interaural cross-correlation than the single source.
Toole’s image shift experiments were done with speech, not music.
There are absolutely no perceptual data for music played over a 2-channel stereo in a complete sound field, so what data are your predictions based upon?
As far as the work of D. Griesinger is concerned, to the best of my knowledge it’s exclusively related to large rooms such as concert halls, hence very different in acoustic and psychoacoustic aspects, so that the results can not be applied to small rooms.
Obviously a key parameter when talking early reflections is the off-axis behaviour of the loudspeakers, and here data are needed which loudspeaker manufacturers simply don’t provide, even on request, which for me merely means that they either don’t measure at all or that the data are that bad that they better not be shown.
Klaus
I attach my writeup on early reflections.
I thought I’d add my 2 cents to this -
To the best of my knowledge there is no evidence whatsover that early reflections in small rooms with with music played over 2-channel loudspeakers have detrimental effects as a matter of principle.
There are a few studies where music was indeed used:
Schubert, “Detectability of single reflections for music”, Technische Mitteilungen RFZ 1966, vol. 10, no. 3, p.124
Detection threshold for a single lateral reflection for music was between -18 and -25 dB, depending on music motive. Setup was one loudspeaker as direct source, one loudspeaker as reflection, the whole in an anechoic chamber. No data for complete sound field with 2-channel and all of the reflections + reverberation.
Dietsch et al. (1986), “An objective criterion for the measurement of echo disturbance during presentation of music and speech” (Ein objektives Kriterium zur Erfassung von Echostörungen bei Musik- und Sprachdarbietungen), Acustica, vol. 60, p.205
Wagener, "Spatial distributions of hearing directions in synthetic sound fields” (Räumliche Verteilung der Hörrichtungen in synthetischen Schallfeldern), Acustica 1971, vol. 25, no. 4 , p.203
Echo thresholds were between 50 and 150 ms, depending on music motive. Setup was synthetic sould field (multichannel speaker system) in anechoic chamber, coincident reflection.
Naqvi et al. (2005), “The active listening room- a novel approach to early reflection manipulation in critical listening rooms”, Journal of the Audio Engineering Society, p.385
In a room according to ITU-R. BS.1116 a reflection free zone was created by using panels to direct the early reflections away from the listening zone. Due to the dimensions of the panels the low-frequency cutoff was at about 500 Hz. Omnidirectional bending wave panel loudspeakers from NXT were used as panels. In addition to re-directing the early reflections created by the main loudspeakers they were used to generate artificial early reflections.
As stimuli anechoic recordings of cornet, trumpet, and acoustic guitar were used. During the experiments these recordings were fed as direct sound to a single center loudspeaker (mono source). A Lexicon processor generated early reflections and reverberation which were fed equally to right and left front loudspeakers. Variation of the relative gains allowed creating different perceived source distances (very close, intermediate, and very distant)
It was investigated (ABX-method) whether the artificial early reflections had a perceivable effect. 12 reflections with a delay of 1.5 to 12.5 ms and a level of -7 to
-12 dB below the level of the direct sound were generated. In all cases the addition of the artificial reflections could be perceived (>75% correct answers), where the percentage of correct answers was different for the different stimuli.
The cues used for detection of the presence of the artificial reflections were source width or focus, environment width, timbre and loudness, which cues are similar or identical to those used in previous detection threshold experiments. It has to be noted, though, that also Naqvi’s configuration does not represent the usual 2-channel stereo setup with centred phantom source, which is different in timbre and in spatial impression when compared to a single source, and has lower interaural cross-correlation than the single source.
Toole’s image shift experiments were done with speech, not music.
There are absolutely no perceptual data for music played over a 2-channel stereo in a complete sound field, so what data are your predictions based upon?
As far as the work of D. Griesinger is concerned, to the best of my knowledge it’s exclusively related to large rooms such as concert halls, hence very different in acoustic and psychoacoustic aspects, so that the results can not be applied to small rooms.
Obviously a key parameter when talking early reflections is the off-axis behaviour of the loudspeakers, and here data are needed which loudspeaker manufacturers simply don’t provide, even on request, which for me merely means that they either don’t measure at all or that the data are that bad that they better not be shown.
Klaus
I attach my writeup on early reflections.
That B&O speaker is the schnizz.. on paper.. read their manual/white paper and be amazed...
Ugly tho ...
http://www.bang-olufsen.com/en/sound/loudspeakers/beolab-90
http://az498215.vo.msecnd.net/static/files/productsheets/BeoLab90_Technical_Sound Guide_1510[1].pdf
Ugly tho ...
http://www.bang-olufsen.com/en/sound/loudspeakers/beolab-90
http://az498215.vo.msecnd.net/static/files/productsheets/BeoLab90_Technical_Sound Guide_1510[1].pdf
Warning - this is a three year old thread!
I had previously allowed side wall reflections but when I introduced an absorbent panel, not on the walls but next to the outside of the speaker, catching both first and second reflections, I found that the higher frequencies became 'crisper'. I liked that.
I've just been reading Toole's Sound Reproduction Third Edition. I had the first edition but there seems a lot of new information in the latest book and for me is well worth buying.
Chapter 7 describes the flaws in the phantom image generated by the two stereo speakers, namely a dip around 2kHz of something like 6dB. He calls it 'interaural crosstalk' and says it's cause is an 'acoustical interference comb filter' resulting from the slight delay of the arrival at your left ear of the sound from your right speaker compared to the sound from the left speaker, and of course the same at your right ear. That delay is caused by the slight increase in the distance of travel to get round your head.
It makes sense and I think I can hear one of the symptoms of this that Toole describes, namely if I lean my head to the left, say, the sound is a bit brighter. I get the same effect if I direct my head towards the floor.
This 2kHz dip is often partly filled in by side wall reflections.
This idea suggests one reason why side wall reflections are preferred by some.
I had previously allowed side wall reflections but when I introduced an absorbent panel, not on the walls but next to the outside of the speaker, catching both first and second reflections, I found that the higher frequencies became 'crisper'. I liked that.
I've just been reading Toole's Sound Reproduction Third Edition. I had the first edition but there seems a lot of new information in the latest book and for me is well worth buying.
Chapter 7 describes the flaws in the phantom image generated by the two stereo speakers, namely a dip around 2kHz of something like 6dB. He calls it 'interaural crosstalk' and says it's cause is an 'acoustical interference comb filter' resulting from the slight delay of the arrival at your left ear of the sound from your right speaker compared to the sound from the left speaker, and of course the same at your right ear. That delay is caused by the slight increase in the distance of travel to get round your head.
It makes sense and I think I can hear one of the symptoms of this that Toole describes, namely if I lean my head to the left, say, the sound is a bit brighter. I get the same effect if I direct my head towards the floor.
This 2kHz dip is often partly filled in by side wall reflections.
This idea suggests one reason why side wall reflections are preferred by some.
From the link:
Quote:
The level and time delay of the reflection. The relationship of the reflection to the direct sound in terms of level and time delay changes the way we perceive reflected sounds. Higher level reflections can cause image shifts whereas lower level reflections are generally perceived as improvements in spaciousness.
End Quote.
To clarify, "height" as in actual tape measurement kind?
Would the transition height level be at mid-height or more like the lower 1/3 of the wall?
I ask because wainscot could be part of one's room design.
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