What is the ideal directivity pattern for stereo speakers?

[Pano]

Come on, you've been here longer than I have. You should know better.

 

[Elias]

BTW, I have made several conclusions already


- Elias

 

[graaf]

the amount of small detail from the recording was so enormous it could be perceived at once by every unbiased listener.

bigger ammount than in case of good ear phones? with all due respect I seriously doubt

I just do not have this fetish

Good Oliver ! Finally someone who understands !

yeah! Oliver is smart!

Yes the challenge is there when using the room as an integral part of the reproduction, however it is not too great of a challenge since leaving ceiling and side walls reflective is enough ! Do not try to absorb early reflections.

true! it is not a real challenge

Yes I have got ideas !

Now this journey has got me to the crossroads: Stereolith vs. Beveridge on wall line array ?

Beveridge was the inspiration of the placement.

The purpose of such an array, as I said, is to mimic the stereolithic side wall reflections with real sound sources.

Place the Beveridge at the point of first ipsilateral reflection from a Stereolith. Of course it is not identical, but the pattern is the same, only that Stereolith creates wider stage than Beveridge.

yes, my comments (with some underlines added):

not all "normal stereo" give "contradictory localisation cues"
this is not inevitable
...
when we integrate "the speakers as early reflections" into the room walls - "left reflection" into the left wall, right into the right we have completely different story

this is what Harold Beveridge has done

on stereolith in this connection:

precisely speaking the device is right, only recordings are crappy

but what can we do?

fortunately - yes we can do something

...

I realized that Harold Beveridge proposed such a different solution – an alternative method of achieving the same result

in his recommended speaker positioning (low directivity speakers against the opposite side walls facing each other I front of the listener) the speakers are acoustically integrated with the side walls – they are perceived as a reflection off the wall

in fact for our hearing the speakers ARE reflection off the side wall and for our brain the room itself is playing the music and not the speakers

so:

in a sense, for me both back-to-back and Beveridge sidewall placement are method of "acoustically hiding speakers in the room"
this is what back-to-back with sufficient directivity and/or with direct sound additionally blocked does – because of its "bipolar" directivity our hearing is unable to locate the speakers themselves as a distinct sources of sound
...
Harold Beveridge proposed just a different solution – an alternative method of achieving the same result

most of the above comments of mine are from 2008...

we had such discussions then:

So from reflections only we cannot define the space and so we don't know the location the initial sound event took place.
We will define the space in our brain by hearing the direct sound AND reflections alltogether, but cannot do with either alone.

no - absolutely not, the first two coherent lateral reflections are sufficient

sometimes it just takes a long time and - of course - it is essential to be unbiased and to try it Yourself

 

[DBMandrake]

Isn't that what this thread is for?

If there were a simple answer that we could establish with a few weeks discussion in this diy thread, I think the last 40+ years of research would have already found it.

More realistically I think there is no straightforward answer, and that many people myself included have a lot more food for thought to chew on than they did before...and that is a good thing.

 

[Elias]

it is essential to be unbiased and to try it Yourself

This is the core of learning something new !

P.S. I'm still a bit thrilled about the picture Markus will draw

 

[graaf]

do not expect miracles!

ps.

Let's make the beveridge as a sparse floor-ceiling line array and it mimics the side wall reflections of a stereolithic projection.

but how can exactly such an array achieve the ideal directivity pattern of directional <1 kHz, stereolitic >1 kHz?

pps. I mean of both directional <1 kHz, stereolitic >1 kHz, and in particular the directional <1 kHz part of it?

 

[markus76]

Markus, now you take pen and paper and draw some lines, maybe with the help of a ruler

Here's the direct sound and first side wall reflections for Beveridge:

An externally hosted image should be here but it was not working when we last tested it.

... and Stereolith:

An externally hosted image should be here but it was not working when we last tested it.

Fundamentally different.

 

[Pano]

And fundamentally, like, where's the speakers?

 

[markus76]

And fundamentally, like, where's the speakers?

Where the arrows emanate from. Green is the direct sound. Blue is the first side wall reflection for the left speaker, green for the right speaker.

 

[Radugazon]

markus, I respect and envy somehow your strictness (true, it's the only way to go), but I suppose that Elias was thinking of the beveridge taking the exact place of the virtual speaker created by a side firing, without considering immediately their own reflection paths.

When listening a side firing in a reflective room, don't have to draw something so much it's the evidence.

 

[keyser]

38 pages of the thread at 40 posts per page; any conclusions yet?

You are actually expecting conclusions?

Isn't that what this thread is for?

Come on, you've been here longer than I have. You should know better.

When I started this thread, I hoped we would get several conclusions, i.e. different directivity patterns and room lay-outs for different well-defined tastes in sound quality.

It's of course difficult to have these online discussions in a structured way. There are many different people with just as many different views and anybody can say whatever they want whenever they want. There is no chairman to keep the discussion on track - which would moreover be an impossible task because this thread runs 24/7. There have been many very good contributions, though. However, they tend to increasingly get snowed under in off-topic chatter. In my opinion all the stuff about flooders, stereolith and all those other controversial topologies don't belong in this thread. I am getting a bit annoyed by having to read several pages each time I check this topic and seeing the same few posters repeating themselves. And I know I'm not the only one who feels this way!

I was hoping to get to some kind of consensus here. Then putting forward controversial ideas and ideologies all the time isn't helping. I'm not saying those issues aren't worth discussing, but please do that in a different thread.

 

[a_tewinkel]

I guess you mean to say that this thread is about conventional stereo, so we should stick to that? I agree.

 

[Radugazon]

You are really dreaming of a uniform static world ?

 

[a_tewinkel]

This quote is not exactly correct (nor is your interpretation of it). For slow moving symphonic music it is generally considered that sound within the first 50ms increases perceived level without degrading musical clarity. For speech the window must be dropped to 30 ms otherwise inteligibility suffers. That is, increasing the direct sound and early reflections before 30 ms will increase speech level without degrading inteligibility. If we are talking about precedence effect and masking (whereby later sounds will be hidden by preceeding sounds but can add to their level) most studies show integration times of about 20msec with gradually falling levels after that.

Now if we are talking about perceived frequency responses of loudspeakers, Salmi, Kates, Queen, Bech and others show that the ear effectively uses a variable time window, short at high frequencies and long at low frequencies. The time window is so short at high frequencies to only let in the direct sound and some nearby cabinet reflections. By the midrange the nearest boundary bounces, such as the floor bounce, will be perceived wile later bounces are excluded. At low frequencies the window is fairly long and most of the room response is perceived.

At least for upper frequencies, the direct sound is very much a reality.

David S.

David,

I was reading your interesting post again and I noticed that you speak of "precedence effect and masking". If you mean by "masking" the perception of multiple reflections as a single source, then isn't the term "masking" inappropriate strictly speaking, since these reflections are heard (as you already pointed out correctly) as adding loudness, although not as a different auditory event?

The most interesting question of course, which has been debated here over and over, is to what extent early reflections degrade sound/intelligibility. I've read some parts of Floyd Toole's recommendations again. His opinion is that it's often better to have first reflections than applying absorption that does not work across a very wide frequency band. I could agree there, depending on how bad your absorption is.

He states that notions about degraded sound quality have been shown to be false. If I'm not mistaken he even quotes research showing that (early?) reflections add "body and richness" and enhance the timbre perception.

Of course, without hard numbers this is a rather difficult case to debate. Linkwitz for example states that 6-8 ms is the minimal delay for first reflections, Geddes says 10 ms (so they're more or less in agreement I guess). Looking at detection and image shift thresholds, this seems perfectly reasonable, although the threshold itself does not say anything about perceived degradation of the sound beyond it. I'm wondering on which research Toole has based his conclusions and which hard numbers for early reflections were mentioned there.

I suspect more can be found in the AES papers you mentioned, so keyser and me will probably be visiting the university's AES archives soon

 

[el`Ol]

Sounds a bit pricey?

It is not known yet, to me, what is the ideal vertical directivity pattern of a stereolithic projection. I could guess, that some second order ipsilateral reflections from ceiling and floor are beneficial, however this is not confirmed yet? Then if we assume this, vertical directivity should be wide. However, that kind of line source could work if arranged horisontally and aimed sideways towards the first ipsilateral reflection point to prevent direct sound from reaching the listener. Maybe better make a prototype with a cheaper unit first

- Elias

It's 140 € and got an excellent test result in a DIY magazine.
What about such a setup, where you would try to avoid the problem with treble localization and work conventional in the less critical region?

 

[graaf]

...
Linkwitz for example states that 6-8 ms is the minimal delay for first reflections, Geddes says 10 ms (so they're more or less in agreement I guess).

where did You find this "6-8 ms"?

It looks that He rather consistently states "6 ms", try google search for:
>>"6 ms" site:www.linkwitzlab.com<<

so it seems that they are not in agreement on that

the difference between 6 ms and 10 ms makes huge practical difference from perspective of room lay-outs

 

[a_tewinkel]

where did You find this "6-8 ms"?

It looks that He rather consistently states "6 ms", try google search for:
>>"6 ms" site:www.linkwitzlab.com<<

so it seems that they are not in agreement on that

the difference between 6 ms and 10 ms makes huge practical difference from perspective of room lay-outs

I'm pretty sure he mentioned 6-8 ms some time ago, maybe he only uses 6 ms nowadays. It's probably not a very hard number. The difference in time between 6 and 10 ms is large, but I'm not sure if the difference in detection threshold is that large.

 

[graaf]

I could guess, that some second order ipsilateral reflections from ceiling and floor are beneficial, however this is not confirmed yet? Then if we assume this, vertical directivity should be wide.

I believe that it is rather majority opinion, corroborated by some studies also referred somewhere in this thread, that floor reflection is detrimental in every case except special design that specifically rely on it - like Keele's CBT array

What about such a setup, where you would try to avoid the problem with treble localization and work conventional in the less critical region?

and how about making the center midtweeter channel >1 kHz just mono - just like Schupbach does? ...more directional or less? perhaps back-firing?

this plus OB-arrays <1 kHz more like Beveridge that is closer to side walls for wider angles than conventional 30º?

 

[markus76]

markus, I respect and envy somehow your strictness (true, it's the only way to go), but I suppose that Elias was thinking of the beveridge taking the exact place of the virtual speaker created by a side firing, without considering immediately their own reflection paths.

When listening a side firing in a reflective room, don't have to draw something so much it's the evidence.

Sorry but I don't understand what you're trying to say.

 

[keyser]

I respect Your point of view, however don't You agree that Your qualification of the topic is a bit... er... late?
now when we are beyond post #1500 You would like to ask some users to leave the thread??

now it just is ideal directivity pattern for stereo speakers thread
it's too late to change it - I am sorry

please start a new thread - this time more explicitly titled for example: "ideal directivity pattern and room lay-outs for conventional forward firing stereo speakers" - and for my part I promise I will not interfere as I am not interested in this kind of stuff anymore

I understand and respect your point of view too. However, I have before hinted to please not push your controversial views too much, because I would like to try and come to some kind of general consensus. You have a strong way of expressing yourself and it sometimes seems as if you discard anything but your own point of view. Also you are the prime contributor of this thread with respect to the number of posts, so the thread drifts more and more off the original topic. Some other contributors now seem to to have left this thread and I regret that.