Earl, there are 100's of people here that are reading and interrupting every word you say, without argument. Questioning what you are saying is natural but, sometimes difficult for you. That is not the majority of the followers intentions. 
Earl, there are 100's of people here that are reading and interrupting every word you say, without argument. Questioning what you are saying is natural but, sometimes difficult for you. That is not the majority of the followers intentions.
I like a good argument, I abhor shooting from the hip. Thanks though.
To attempt to argue with me about the acoustics of small rooms at LFs simply shows a fairly high level of naiveté.
It's clear that high frequencies are dominating when you're "watching" sound stage images. That is proven by research and individual experiences. No problem so far.
But if clarity/resolution is clearly weighted to high frequencies, sound reproduction is not balanced, relaxed and natural. Bling-blings and other HF nuances of instrument sound will be pronounced and forwarded, hiding lower frequency information. I call this kind of sound reproduction as "quasi resolution". It's easily attracting and easy to sell by using cheap trick; directive HF radiator with single monopole bass...lower midrange.
Clarity/resolution spectrum can be estimated by using MTI results of STI measurement. Result of WG + monopole in lively environment is very unequal aka bad.
I know that having directivity at low frequencies is not pointless. Research and experience is available, but somehow it's ignored here.
'Earth is flat' was also a fact some years ago. Same story with 'directive bass is pointless'. Research was probably weak and ended few decades too early, ears and other listening sensors are closed and forum discussion switched to repeat mode.
Damn! I thought that the heavy membranes with their inability to stop were to blame 🙄😉
When you think you know something, that is the most perfect barrier against learning (Frank Herbert).
Makes sense. However, from 200 to 700 there are almost 2 octaves. Thus, it is not irrelevant how that transition curve looks like.
Correct, but as I pointed out above the "somewhere" is more important that you would like to admit. Your opinion is 700Hz, but...
...it turns out Griesinger, did, in fact, deal with loudspeakers in rooms. The more I read through is papers, the less convinced I become of your opinion. Let me give you a few examples:
http://www.davidgriesinger.com/spatialization_and_loc.doc
Turned out, things are not as "logical" as they might seem at LF:
"The spaciousness experiments and some calculations of the effects of room modes on localization suggested that low frequencies should be difficult or impossible to localize in a room. Localization would be determined by high frequencies, and localization of these frequencies would be reasonably independent of speaker position. A set of localization experiments using pan pots was devised to test this, and the data showed both hypotheses to be wrong.
"It is the lateral sound energy which creates pressure differences between the two ears of a front-facing listener at frequencies below 700Hz. The easiest way to measure or think about lateral sound is in terms of the lateral or Y axis sound velocity, which one can measure with a sideways facing figure of eight microphone. See Fassbender."
LF separation is quite important (and higher directivity at LF should help with that):
"Rooms do the opposite of what recording engineers would like. They decrease the LF separation and sometimes increase HF separation. FOr coincident or pan potted recordings you would like them to increase separation at LF (for spaciousness) and reduce it (or leave it alone) at HF."
The parts on frequency-dependent image shift in stereo (LF tends to go towards center, HF to spread apart) is also very interesting:
"In fact, we may be using our two channel room equalizers in the wrong way. When we equalize a room we should separately equalize the L+R and the L-R response, not the L and R response individually. The equalization of the difference signal should be adjusted so that the localization of high and low frequencies coincide, preferably following a cosine law. Doing this would allow more precise imaging and more convincing stereo from most systems."
Mind you, the man even tested dipoles:
"E. A test of dipole speaker systems was made with 2 pairs of identical small speaker systems was arranged in position B of room 1, with the two speakers in each pair pointing away from each other with a 2'x3' plywood baffle between them. They were wired so the backwards facing speakers were either (1) out of phase with the front speakers, (2) in phase, or (3) off. This system showed that when the back speakers were out of phase with the front (dipole radiation) the sound was always either the same or more spacious than with a standard direct radiator."
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Interesting reading, but not conclusive. Here he is talking about LF spaciousness more than "image". I agree with him about LF spaciousness which I achieve with multiple subs widely spaced about the room. This yields the random sound character that he talks about in several papers. The L+R and L-R EQ is interesting - I had not read that before.
I agree that dipoles sound better at LFs than stereo/mono monopoles, but to me, they sound the same as multiple spaced subs. I have stated this many times over.
I agree that dipoles sound better at LFs than stereo/mono monopoles, but to me, they sound the same as multiple spaced subs. I have stated this many times over.
On localization:
"Initial results with 1/3 octave filtered noise as a source showed it was indeed hard to localize low-frequency sounds. Hbwever, after some experimentation it was found that filtered speech --in this case a monaural recording of Alistair Cooke filtered with the adjustable band-pass filter shown in figure 3-- gave consistent data and frequently very sharp localization, even at frequencies below 400Hz. The requirement for localization was speech and adequate bandwidth. For low frequencies one to two octaves of bandwidth seemed to be necessary."
"Rooms at low frequencies:
The results for rooms were quite surprising. Speech in the 180-400Hz band localized in ways which were highly dependent on the room and the speaker- listener position."
I still don't see where any of this says that < 700 Hz is MORE important than > 700 Hz. Of course at the extreme there is SOME imaging < 700 Hz, but you have to consider the relative importance and weigh that against the design.
It does not say it's more important. It also does not say is less important. It says it could be equally important and - even more important 🙂 - that, for convincing imaging, LF localization cues should be in alignment with those at HF. In a room, that would mean more separation at LF than HF (the L-R eq part) and a higher DI (and consequently a higher D/R ratio) would favor that.
That is why i said that individual has to think for themselves and read between the lines.
Of course that Dr Geddes is saying that under 700Hz is not all that important. That may well be because it really isn't important or he is biased because he doesn't make loudspeakers that do this (and reasons for it could be because making loudspeaker like that for a manufacturer gets far more complicated, time consuming and the price of the loudspeakers go sky-high).
There are no papers which proves that imaging bellow 700Hz is important but there are no papers that excludes its importance. In cases like that i choose to form my oppinion based on the worst case scenario - it is important like hell and try to make it and then listen. If it is not worth the trouble, no problem - it can hardly ruin the sound of the loudspeaker right ? I am not a manufacturer and i do not have to worry if material for a pair of loudspeakers will cost me few hundred euros more but for someone who makes a living out of it is very important.
I'm not trying to be disrespectful in any way to Dr Geddes or BzfCocon. I'm just trying to look at things objectively and to take everything into consideration.
That being said, i am not 100% convinced that difference between the loudspeakers that have controlled directivity down to 250Hz will definitely sound better but it doesn't hurt to try.
As was said many times before - question everything 😉
Of course that Dr Geddes is saying that under 700Hz is not all that important. That may well be because it really isn't important or he is biased because he doesn't make loudspeakers that do this (and reasons for it could be because making loudspeaker like that for a manufacturer gets far more complicated, time consuming and the price of the loudspeakers go sky-high).
There are no papers which proves that imaging bellow 700Hz is important but there are no papers that excludes its importance. In cases like that i choose to form my oppinion based on the worst case scenario - it is important like hell and try to make it and then listen. If it is not worth the trouble, no problem - it can hardly ruin the sound of the loudspeaker right ? I am not a manufacturer and i do not have to worry if material for a pair of loudspeakers will cost me few hundred euros more but for someone who makes a living out of it is very important.
I'm not trying to be disrespectful in any way to Dr Geddes or BzfCocon. I'm just trying to look at things objectively and to take everything into consideration.
That being said, i am not 100% convinced that difference between the loudspeakers that have controlled directivity down to 250Hz will definitely sound better but it doesn't hurt to try.
As was said many times before - question everything 😉
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I will never accept that directivity control has any importance in the modal region. A region where the whole concept of directivity is erroneous. Hence its importance MUST go to zero as the frequency declines unless one believes that there is somehow a step function from very important, or "most" important, down to zero at some frequency. This just does not make any sense and is the kind of thing that virtually never happens in physics. Certainly not in psychophysics.
If one imagines that the "importance function" of directivity to imaging goes from zero at LFs to some value at 700 Hz and then is flat above there, that would make the integrated importance of < 700 Hz rather small. Even if the values of importance for any frequency were all equal, the integrated value for frequencies < 700 Hz would be small. It would take an extremely high value < 700 Hz for the integrated importance < 700 Hz to equal that > 700 Hz. This goes against all that I know about hearing.
In my image model the "importance function" of directivity to imaging curve goes smoothly from zero at LF to some value at 700 Hz and then rises slightly to peak at about 2000 Hz and falls again slowly to about 8 kHz and then drops after that to almost nothing at 15 kHz. Integrate this curve for values below 700 Hz and you will get a value of somewhere between 10 and 15% or maybe less.
I will remain with my stated opinion that < 700 Hz is simply not as significant as > 700 Hz. It takes a real stretch of the imagination and the data to believe otherwise.
PS. I have tried for directivity < 700 Hz, but the problem is that one cannot isolate the directivity problem from other problems that ensue and, in my case, the other problems were the greater, creating a situation where the tradeoff was negative even if the effect of the directivity aspect was positive. Electronic cardioid is the only way that I can see doing this without tradeoffs that are unacceptable to me. I showed the theory of this technique in my book, but I have not tried it in practice owing to the cost implications. As was correctly pointed out, I do not develop ideas that have no product potential because of cost and/or complexity. I have know how to do this for along time - my 13 year old book shows that - but it just has never been attractive enough to enlist my attention. Others claim great results, the problem is that everyone makes that claim. So without some solid evidence, and I see none at this time, I am not going to pursue these ideas.
If one imagines that the "importance function" of directivity to imaging goes from zero at LFs to some value at 700 Hz and then is flat above there, that would make the integrated importance of < 700 Hz rather small. Even if the values of importance for any frequency were all equal, the integrated value for frequencies < 700 Hz would be small. It would take an extremely high value < 700 Hz for the integrated importance < 700 Hz to equal that > 700 Hz. This goes against all that I know about hearing.
In my image model the "importance function" of directivity to imaging curve goes smoothly from zero at LF to some value at 700 Hz and then rises slightly to peak at about 2000 Hz and falls again slowly to about 8 kHz and then drops after that to almost nothing at 15 kHz. Integrate this curve for values below 700 Hz and you will get a value of somewhere between 10 and 15% or maybe less.
I will remain with my stated opinion that < 700 Hz is simply not as significant as > 700 Hz. It takes a real stretch of the imagination and the data to believe otherwise.
PS. I have tried for directivity < 700 Hz, but the problem is that one cannot isolate the directivity problem from other problems that ensue and, in my case, the other problems were the greater, creating a situation where the tradeoff was negative even if the effect of the directivity aspect was positive. Electronic cardioid is the only way that I can see doing this without tradeoffs that are unacceptable to me. I showed the theory of this technique in my book, but I have not tried it in practice owing to the cost implications. As was correctly pointed out, I do not develop ideas that have no product potential because of cost and/or complexity. I have know how to do this for along time - my 13 year old book shows that - but it just has never been attractive enough to enlist my attention. Others claim great results, the problem is that everyone makes that claim. So without some solid evidence, and I see none at this time, I am not going to pursue these ideas.
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Are you talking here about image localization only? If yes, I'm very sorry about my previous posts.
I had no intention to interfere discussion about image localization because it's not primary design parameter for me. Just "as is" after room and speakers are designed to their (usually easily measurable) primary targets, and listening setup/geometry carefully tuned.
But it's hard for that point to transfer as anything more than subjective opinion and to translate it technically as a mathematical principal is impossible because of the near infinite configurations of rooms.
I recently tied to explain some principles of bass propogation in a very non technical forum in a very non technical way. Fluid dynamics and wave propogation were the only method I could come up with so I asked people to liken their room to a closed body of water. Let surface waves represent sound waves. If a strong directional wind blows in one direction, you wind up with a large continuous slow swell. If you liken the peak and trough of the wave to amplitude, you can see or translate to audibly this being not desired. But if you generate waves from multiple points in multiple directions, the resulting collisions( read cancellations) result in much smaller, faster or more frequent waves which would translate to sound as less peaks and nulls but a more even in room response. They got it, thanked me for it and have the multi sub principle a try. This would have never worked with thick headed audiophiles otherwise.
This did occur to me when I was lying in bed last night 😉 Certainly using methods to control directivity in the LF region can have good results at improving the LF performance, but not in terms of improving imaging, which is what most of this has been about.
I agree as well. A reflection could influence the frequency response at the listening position, but not the imaging. However, if you look at the effect of a reflection below 700 Hz it is not very large. Not at all like it is above 700 Hz. This all depends on room size, of course, but I am pretty consistent in talking about home listening rooms because that's all I do. Some have been on the large side and I've had to think about that a little - its clearly NOT the same. But then again, very large listening rooms are not very common either.
Clearly, the larger the room the lower in frequency all of this happens to the point where in a concert hall its ALL important and directivity down as low as possible is always an advantage - for different reasons however.
Clearly, the larger the room the lower in frequency all of this happens to the point where in a concert hall its ALL important and directivity down as low as possible is always an advantage - for different reasons however.
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