graaf said:
No there is nothing wrong with that, but did you consider ALL rays in ALL directions impinging on ALL surfaces? I looked at what you had done and it seemed to me that you were ignoring a few key ones. Draw a map of the sources and listeners and show the rays and the distances traveled. That will tell you (and me) what we need to know. Don't forget about the floor, ceiling and back walls. Just because the source is CLOSE to the wall does not mean that it won't refelct off of the wall. Only if it is flush with the wall surface can you assume that.
gedlee said:
yes, as I have said:
I drew the maps although I didn't post them. I had to draw them to be able to calculate the path lenghts and delays.
I didn't forget about the floor, ceiling and back walls:
It seems that apart from those earliest reflections <1 ms all other reflections are delayed more than 8 ms
all of this assuming that the room
my room is small and hence the delays are in the range of 8-9 ms
in a bigger room they would be easily above 10 ms
if those earliest reflections < 1 ms are problematic, I don't know, then they probably can be absorbed with Carlsson style wall absorbers (images attached earlier in the thread)
these reflections are very specific
are we sure that they are problematic? I don't know
they come from almost exactly the same direction as the direct sound, very early <1 ms (the speaker axis is <13 cm from the wall), they are low pass filtered because of the directivity of the speaker and their contribution to the overall SPL is very small
(in case of Etienne88 setup they are absorbed by the couches)
tell me - are You sure that they are audible and detrimental to the sound?
I understand that in the light of Your research we can say that they probably can be detrimental to the sound but the real question is - are they?
what if not?
best,
graaf
Graaf, now that I read both Beveridge's and Carlsson's papers, I can say that your loudspeaker set up is much more closer to Carlsson than Beveridge. Beveridge idea seems great in theory put in the practice, I don't know...
In our case, with a unique driver firing upward, we get an omnidirectional speaker at the low frequencies. Then, the higher it gets, the closer to a thin cone you get. I don't see any line source in that. Could you explain where you see a line source?
What I will remember from both papers is first, the importance of having a reflected sound with almost the same frequency response as the direct sound (omni or dipole being possible solutions). Second, to take into account the time delay.
I did some delay calculations with the speakers at the armrest level (driver at 60cm above the floor). By the way, it is better like this than with the lower positioning, I get more medium-highs. But then the delay calculation showed that the roof reflection arrives at 4,5ms which is not very nice since it is a difficult one to damp (WAF oblige...).
Some readings (from Olive and Toole) I did told me that: depending on the level and the delay of the reflected sound, the reflection can be perceived as an echo, a broadening of the image, spaciousness or not perceived at all. This means that if you can sufficiently damp a reflection in an undesirable time domain, it will be perceived as spaciousness or not be perceived at all!
Back to delay calculations: I have a short delay from the wall close to the LS at 0,5ms. If this reflexion is 10dB lower than direct sound it will be heard as spaciousness, if it is 20dB down, it will be inaudible. I now get why Carlsson had acoustic foam on the wall side of its speakers. I did the same!
The second short reflection is at 1,1ms from the floor. I have a sofa on both sides so that I guess that these reflections are well damped.
I already talk about the roof...
Then we've got the front one (the one hitting the wall you look at when you listen, ok!). The delay is 7,5ms. If the reflection is at least 3dB below the direct sound it is heard as spaciousness, if it is 15dB below, it is not heard at all. I put cushions in front of the window!
The reflexion from the right speaker coming on the left is at 8,6ms. I did not do anything.
I also calculated the secondary reflections, they are really hard to describe with my "poor" English level... 2 are are below 5ms, 5 are between 5 and 10 ms, the rest is above. Since they hit 2 surfaces their level is most probably lower than the direct sound (how much is another question...). Some more damping of the side walls as well as of the roof would be needed. 2 secondary reflections involving the floor are around 8 ms, the sofas are there to tame them!
Going back to Briggs, non directional and natural results are the advantages he named of upward firing units. Remember that it was the beginning of stereo and that most of the book consider mono reproduction. Nevertheless, at the end he writes about column speakers giving good results (subjectively) for stereo listening. Both type have upward firing drivers and a diffusing cone is added above the drivers. The cone can be improved to a circular parabolic diffuser which is turned from hard wood and coated with hard cellulose or shellac. The diffuser might be looking like this.
The last link, shows very nice looking LS which principle remove the need of treating the roof reflections. From that I fully understand how Earl went into horns! But I think that it is a mistake (I am young and foolish so that I can do mistakes by myself! ) since you don't get any direct reflections from the back wall and less from the side walls, floor and roof.
Regards,
Etienne
In our case, with a unique driver firing upward, we get an omnidirectional speaker at the low frequencies. Then, the higher it gets, the closer to a thin cone you get. I don't see any line source in that. Could you explain where you see a line source?
What I will remember from both papers is first, the importance of having a reflected sound with almost the same frequency response as the direct sound (omni or dipole being possible solutions). Second, to take into account the time delay.
I did some delay calculations with the speakers at the armrest level (driver at 60cm above the floor). By the way, it is better like this than with the lower positioning, I get more medium-highs. But then the delay calculation showed that the roof reflection arrives at 4,5ms which is not very nice since it is a difficult one to damp (WAF oblige...).
Some readings (from Olive and Toole) I did told me that: depending on the level and the delay of the reflected sound, the reflection can be perceived as an echo, a broadening of the image, spaciousness or not perceived at all. This means that if you can sufficiently damp a reflection in an undesirable time domain, it will be perceived as spaciousness or not be perceived at all!
Back to delay calculations: I have a short delay from the wall close to the LS at 0,5ms. If this reflexion is 10dB lower than direct sound it will be heard as spaciousness, if it is 20dB down, it will be inaudible. I now get why Carlsson had acoustic foam on the wall side of its speakers. I did the same!
The second short reflection is at 1,1ms from the floor. I have a sofa on both sides so that I guess that these reflections are well damped.
I already talk about the roof...
Then we've got the front one (the one hitting the wall you look at when you listen, ok!). The delay is 7,5ms. If the reflection is at least 3dB below the direct sound it is heard as spaciousness, if it is 15dB below, it is not heard at all. I put cushions in front of the window!
The reflexion from the right speaker coming on the left is at 8,6ms. I did not do anything.
I also calculated the secondary reflections, they are really hard to describe with my "poor" English level... 2 are are below 5ms, 5 are between 5 and 10 ms, the rest is above. Since they hit 2 surfaces their level is most probably lower than the direct sound (how much is another question...). Some more damping of the side walls as well as of the roof would be needed. 2 secondary reflections involving the floor are around 8 ms, the sofas are there to tame them!
Going back to Briggs, non directional and natural results are the advantages he named of upward firing units. Remember that it was the beginning of stereo and that most of the book consider mono reproduction. Nevertheless, at the end he writes about column speakers giving good results (subjectively) for stereo listening. Both type have upward firing drivers and a diffusing cone is added above the drivers. The cone can be improved to a circular parabolic diffuser which is turned from hard wood and coated with hard cellulose or shellac. The diffuser might be looking like this.
The last link, shows very nice looking LS which principle remove the need of treating the roof reflections. From that I fully understand how Earl went into horns!
But I think that it is a mistake (I am young and foolish so that I can do mistakes by myself! ) since you don't get any direct reflections from the back wall and less from the side walls, floor and roof.Regards,
Etienne
Etienne88 said:
not a line source but I see the beneficial effects of a line source, as I have said my aim was to "emulate" Beveridge setup with conventional cone driver
first - wide and even dispersion in horizontal plane
second - with positioning just above the floor - the problem of floor and ceiling reflection is pratically gone
my loudspeakers are closer to Carlsson but setup is very specific and invented by Beveridge
nowhere in Carlsson paper You can read about speaker positioning against opposite walls - and this is most important in the setup I proposed
only with positioning against opposite walls You can get this much better reflection pattern and longer delays
that's rightEtienne88 said:
well, theoretically it should be worst because You get worst reflectionsEtienne88 said:
why not trying some frequency equalization instead of elevating the speakers?
can You hear any difference with or without those absorbers?Etienne88 said:
I now get why Carlsson had acoustic foam on the wall side of its speakers. I did the same!
Etienne88 said:
move the stereo triangle back a little and it will shift beyond 8 ms
Etienne88 said:
which of them are below 5 ms?
there seem to be three time limits separating "very bad" early reflections from "just bad" and then from "not so bad" and "the good" in the end
these time limits seem to be: 5 ms, 10 ms and 20 ms
this is probably why for some the most important is to delay the reflections above 6 ms, such is for example Linkwitz's minimum recommendation
those below 5 ms are really bad
Etienne88 said:
I don't know - diffusing cone means a lot of frequency dependent VER
presumably something "not right"
Etienne88 said:
But I think that it is a mistake (I am young and foolish so that I can do mistakes by myself!
sorry I don't understand this last senstence - what is a mistake?
a waveguide approach?
best,
graaf
graaf said:
I don't know of any such calculator but fortunately the calculations are not overly complicated
just Pythagorean theorem
best,
graaf
But it is about orthogonal triangle, isn't it? Tens of them. I am not convinced of practical usefulness of it. Even worse for hand calculation when two borders are included. Grafical solution could be more suitable.
Etienne88 said:
This is an incorrect conclusion from what Toole said. You NEVER get a spaciousness perception from reflections below 20 ms. So you must either get rid of them below about 20 dB or they will have a negative effect.
I highly doubt that!
As I said before this is not correct, at only 3 dB down you will get a bad coloration effect. And cusions will not decrease this reflection very much at all. You need to do actual measurements and not just guess at the effects.
From that I fully understand how Earl went into horns!
BUT I DON'T WANT side wall, floor or roof refelections thats just the point!! I DO GET backwall reflections and plenty of them since the rear of the room is highly reflective. This sets up exactly the situation that I want. No significant early reflections, with lots of delayed reflections coming mostly from the sides and rear. You aren't thinking this through.
graaf said:
The equalisation I have on my amplifier do not correct the right frequency.
I will make a try and I tell you what I feel. (measuring would be better)
I cannot, I have a big shelve along the wall right behind the right sofa...
Take the right wall as a mirror, it will give you an image of the right speaker. Then mirror this speaker up and down with the floor and ceiling, these 2 images are below 5ms.
It feels to me like a slot aperture in a line source...
And, yes the waveguides feels like a mistake.
Regards,
Etienne
gedlee said:
I don't have the papers at hands, I just have a book with a nice graph... The book is Master Handbook of acoustics (4th edition, page 77, if you have it...). It gives references to:
- Olive and Toole, The Detection of Reflections in Typical Rooms JAES 37 1989 539-553
- Toole, Loudspeakers and rooms for stereophonic sound reproduction AES Int. Conf. 3-6 May 1990
At the end, you say something, the book says something else. You are obviously much more experienced than I am, so does the book writer... I see myself as a student her, I'm trying to learn! Could you give some scientific facts about your sayings, please?
No offense, but why? The absorption coefficients of a sofa are around 0,3 between 125Hz and 4kHz...
Cushions will certainly be better than the window, even if they don't do that much.
I more than agree about the measurement part. I actually purchased a microphone and hope that I will get it running in a near future...My mistake here! I wrote back wall meaning front wall... The front wall (the one you look at when listening to music) is well at the back of the speakers!
Regards,
Etienne
Etienne88 said:
I see - this is because You lifted the speakers
I think that what is needed in Your situation is dedicated equalization - passive RLC or active
but unfortunately it means soldering or buying a professional parametric equalizer which is either very expensive or not of very "audiophile" quality (Behringer)
but I seriously believe that this is better option then lifting the speakers
You can correct the frequency domain but time domain cannot be corrected (at least practically)
Etienne88 said:
well, I respectfully disagree
for me gedlee's approach is a reasonable alternative, especially when one needs full frequency spectrum 20-20k Hz and higher SPL
with our fullrangers we cannot have that I suppose
of course this opens separate discussion on "who needs it?", the SPL targets and how much bass and highs is in our music and so on
anyway, when one needs good "room-speaker interface" and high SPLs and 20-20k Hz then I cannot see, frankly speaking, any alternative to Dr Geddes' designs
too bad that their availability (and market impact) is so limited
best,
graaf
graaf said:
But you see, the high SPL capability is simply a convenient collateral benefit. If you want a loudspeaker system that is "room compatible" then a waveguide is required no matter what SPL you use. Nothing is less "room compatible" than an omni loudspeaker which sees all of the rooms flaws. The high SPL is just a nice added benefit of getting the directivity right.
About Omni vs controlled directivity, I read that on the web:
When listening to extremely focussing loudspeakers which therefore produces few indirect sound, the listener hears the direct- and indirect sound of the recording in a spot beam from one direction. This is, however, a completely unnatural sound situation
It comes from a paper found on Duevel website. The guy makes argument to sell his product, which is natural! But he makes an interesting point.
I guess that in Earl's case, reflections come from the back making it more "natural" sounding. But still, it is only indirect sounds from the front (from the recording) and the back (from the room) only...
I am not trying to convince anybody with all these arguments, I just want to learn something and opposing ideas seems to be a good way of getting the truth out of it all.
Earl design seems to be a well developed LS with promising possibilities, I don't doubt about it. I just never add the chance to listen to it. Then I would like to believe that it is not the only way to achieve good sounding LS. The future might prove me wrong. Or not...
Regards,
Etienne
When listening to extremely focussing loudspeakers which therefore produces few indirect sound, the listener hears the direct- and indirect sound of the recording in a spot beam from one direction. This is, however, a completely unnatural sound situation
It comes from a paper found on Duevel website. The guy makes argument to sell his product, which is natural! But he makes an interesting point.
I guess that in Earl's case, reflections come from the back making it more "natural" sounding. But still, it is only indirect sounds from the front (from the recording) and the back (from the room) only...
I am not trying to convince anybody with all these arguments, I just want to learn something and opposing ideas seems to be a good way of getting the truth out of it all.
Earl design seems to be a well developed LS with promising possibilities, I don't doubt about it. I just never add the chance to listen to it. Then I would like to believe that it is not the only way to achieve good sounding LS. The future might prove me wrong. Or not...
Regards,
Etienne
gedlee said:
well, once again let me
You told me to "consider ALL rays in ALL directions impinging on ALL surfaces" because it seemed to You that I was "ignoring a few key ones"
I think that I explained above that I have not ignored them.
In a room slightly bigger than mine all early reflections from every direction can be delayed by 10 ms or even more.
Or am I wrong?
I just did simple calculations
Of course there are those VER <1 ms off the adjacent wall. They can easily be absorbed, they are already low pass filtered in case of directional speaker like my Fostex
But let me say and ask again:
best,
graaf
gedlee said:
burden of proof?
but these are simple calculations. Anyone can do them.
Shall I really do them for You?
they are simply obvious, I can't imagine how can anyone put those simple calculations into question?
it is beyond me
they are like "2+2=4"
shall I also prove that?
but do I have to have it all absorbed? reducing their level by 10 dB wouldn't suffice?
after all in case of Your CD speaker there still are reflections, they are only reduced in level
I can do the same in case of those VER's in my case
There are very effective acoustic materials with 90% absorption >500 Hz
why not?
well, but what exactly have You found?
in another thread I asked:
You answered then:
ok!
in the set up I have proposed those VERs above 1 kHz can be minimized quite effectively
first of all they are minimized because of the directivity of the loudspeakers themselves - my loudspeakers are about -8<10 dB at 1 kHz at 75-90 degrees (the angle of reflection)
most of it can be easily absorbed, no problem with effective absorption of fequencies above 1 kHz
so why are You telling me "it is a disaster" "it cannot work" and so on?
I don't understand
best,
graaf