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Hi Will, thank you for the dispersion diagram. Because of my room irregular boundaries (no right sidewall on the right speaker I have put bass traps 3 ft behind speakers and improved low level detail greatly. My room have has resonances at 33 and 39Hz which does wonders for the sound of the tympany.
I do have some concerns about the dispersion diagram accuracy. I have attached a polar frequency response graph for the Quad 57 speakers which has a fair amount of detail. The column width of the 745 is about 5″ which is the wavelength of 2700Hz. The adjacent column angle of the 745 is 7.5° while the Quad plotting angles are 10° each. I don’t understand the positioning of the -6dB point or how it is derived.The pictures of your system I assume are taken at your home in Japan.
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Hi Slide, I think your text is directed to me (I’m Chris in Japan – and yes the photos are from my various rooms in Japan).
Yes, actually all the column widths are about 5″ in width (in all models).
I’m not sure I can explain the -6db point well or not…I’ll try to explain what I have understood. I believe it is understood that if a wave length is shorter than the width of the radiating plane, the sound wave will ‘beam’ directly off the membrane (and not have any radiating angle). And yes, a 2700 hz sound wave is basically 5″ as you wrote. If you take one cell for example, the mylar at the center of the cell will radiate an amount of energy and moving out to the sides of the cell the mylar will move less than at the center and therefore radiate less energy. Roger has this calculated to be a reduction of -6db if you were to compare the center to the side and this is for 20khz. As you can imagine, beaming and ‘not-beaming’ is progressive – it is not just an ‘on-or-off’ situation. If what I have described above is true for 20khz, frequencies less than 20khz will have more and more tendency to radiate with more angle. But let’s go back to 20khz and say there is a 6db drop in energy between the center and the sides of the cell. So at one side of a cell and the next adjoining cell there is a mergining of two points which are radiating at -6db which in essence are merging and providing the same energy as from the center of any one cell. This is what Roger explains is actually ‘over-kill’ to make sure that there is no ‘picket-fence’ effect if you were to move around in front of the speaker (it is built to sound as there is no drop in frequency energy between cells from 20khz and lower…)
I am interested to know if you can follow my explanation, and if anyone disagrees or has any comment, that is most welcome too of course.
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Sliderule, a mentor of mine taught me the “Rule of Thirds” for speaker placement. Position them both laterally and longitudinally in the room at a third of the distance.
Empirically, I found the smoothest response in the Schroeder frequencies worked out to almost exactly that position in my 25′ x 16′ room – about 8′ from front wall. I use a number of tubular bass traps and employ a range of diffusion solutions (Skylines and Troy Studio panels) behind and use fake plants to the sides.
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Hi All, I finally received my Majestic 745’s a couple of weeks ago. I have been experimenting with position and toe-in. Using REW software and measuring the speakers at 1′ (near field) and 4′ the early reflections show up at phase reversals between 100Hz and approx 220Hz. My listening room is essentially node free so sub 100Hz resonances are not an issue. Looking suggestions on back wave solutions.
-david
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Hi David,
I’ll try to make some comments and hope they might help.
First thing is (I guess you might know) is to be flexible and to try anything…little position changes make huge changes to sound stage, depth of imaging, perceived volume etc.
Anything I say is just a suggestion…. and the bottom line, even more bottom than a ‘measurement’ , is how it sounds to you.The right speaker in the photo may be pointing to the open hallway behind… and I’m not sure why the TV is not centered (maybe you are concerned about the left wall?) Or I may be misunderstanding that you have 1 speaker in near field and the other back?
Putting that aside for a moment, I just want to make sure you know how the sound converges at a point behind the speaker – and knowing this will help you starting thinking about what is going on. (sorry if you already know) If you can, please try standing behind the speaker and you will definitely notice sudden focus of sound energy at the convergence. The speaker as you know has 45 degree dispersion, that means there is a ‘phantom’ location behind the speaker from where the sound appears to originate.Keeping that in mind, if the wall is exactly where all the sound converges, you will have a strong refection of sound from one point. If the speaker is closer to the wall or farther away, you can deduce that the back wave is spreading or converging and depending on what’s behind the speaker (absorbing material, irregular objects, or flat wall) will help absorb or diffuse the sound.
If you toe in the speaker and it is pointing towards the right hallway (for example), the convergence point might all be going into the hall and create unbalance with left speaker which has a wall that is reflective.
If I have really missed what you wanted to hear, please let me know!
Note: putting absorbing material at the point of convergence is a useful way to control the back wave – it doesn’t have to be a huge wide absorbing panel, because it is all at one point and easy to ‘catch’. How much you want to catch or leave ‘open’ is again up to everyone’s preference.
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I see a unit between the speakers and don’t know what it is. Can you tell us all of your components in your system.
Are you running the woofer pannels parallel with the main speaker as Dr. West has done with most of the other Speakers and Sub panels?
Dr. West always said if you are using the 4 panels take the efficiency of the main speaker and add 6db to the sensitivity number. You should be getting I would guess about 95 DB now. With the berning amplifier, does it drive to great levels or is it limited. Does it have the follow through bass with that power of the Berning compared to a big unit with hundreds of watts?
Your speaker curver reading of the speaker looks fine. I noticed it even has a “BBC” Dip.
More well recorded YouTube videos would be greatly appreciated as very few ever get to hear a Soundlab with subs and especially in an open room.-
Just to follow up…I posted some photos on Face Book group:
‘Electrostatic Speakers’and also trying to make an effort to update my FB page
Sound Lab Electrostats
https://www.facebook.com/profile.php?id=61553919383032Cheers,
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Hi Earl,
I am not sure if I answered all your questions fully – please comment. I also tried to start a new topic showing the delivery to Nagano with a link to youtube video with sound sample.. but I don’t see it here. I am not sure of how the backyard of this group works. Any comments/advice – perhaps this is not the correct place for me to post.
This is one video link:
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Hello Earl,
Thank you for asking the questions. I’ll respond briefly here now (more in 48 hrs) as I am actually in deep Japan cottage country with poor internet (actually delivery of a Sound Lab pair to customer)
Between the speakers is the newest (in Beta release) DEQX Pre-8. Extraordinary advances with this machine.
Yes, running in parallel with Berning but option to by-pass all controls (bass panels have freq cut-off, damping, level controls) with separate set of post.
Berning amp only 60w/channel but over 95db SPL easily achieved and that is more than enough for me. But describing sensitivity for line source is never so simple and to say speakers have increased sensitivity from 90 to 95 is dependent on many factors. I also use Benchmarks (use 2 in mono) which is a LOT of watts, but almost no difference in ‘volume’ and the Bernings are just incredibly ‘alive’ and engaging – describe more on that later. videos coming soon!
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Thank you all for your comments. The original setup with the speakers with them far from the back and sidewalls leads me to the conclusion that early reflections do reduce details. I have calculated that the focal point of the back sound waves is ~35″ behind the 745 speakers. As I cannot move the speakers further out from the back wall, I will need to use treatment on the back wall.
I have REW software and calibrated test gear for measuring speakers in my room. I have attached a screenshot of the speaker response – left, right and both. Red trace is both and right is blue and left is green. The right speaker is far from the sidewall while the left is only a couple of feet away. The 80-90 Hz dip is due to the Allison “effect”. These measurements were made with the microphone vertical at the listening position (and using the vertical calibration file). Measurement is with 1/3 octave smoothing. Note that when the speakers are in phase the combined level is approximately +5dB and when the speakers are out of phase -4dB about 1300Hz.
The Sallie’s info says they are effective at 250Hz and up. I have not found any technical info on the Apperature IIs – onlu subjective revierws.
One interesting note is one els manufacturer claims the the sound stage width is widest with the speakers parallel to the back wall and the width decreases and the stage depth increases as the speakers are toed in. -
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Hi Sliderule768,
I do not own Sallies or Stillpoint Aperature II’s but have experimented extensively with room treatments with my SoundLabs, so thought my experience/thoughts might be useful/helpful.I found that pulling the speakers out 5-6feet from the front wall behind them worked best which amounts to about a 9-10ms delay of the rear firing sound. This amount of delay falls just shy of calling attention to its self as a discrete reflection which maybe why when you have them 12 feet out polarity changes are more audible as separate reflections. More than 10ms and the precedence effect starts to break down. Three feet from the front wall would harm soundstage depth and the rear firing sound reflections are just over 5ms making them nearly indiscernible from the front firing soundwaves, hence your challenge/inability to hear polarity changes.
When my speakers were 5-6ft from the front wall, it sounded best as an untreated surface meaning no diffusion and no bass traps on the front wall behind the speakers. I focused the treatments on the rear parts of the sidewalls behind my MLP and back wall.
Are you able to take acoustical measurements of frequency response and decay times? These would serve you well if they were available and could help with finding positions where treatments were most effective.
If you are “stuck” with a 3foot distance to the front wall, you can try 6″ or deeper QRD diffusers that when positioned with their wells vertically will scatter/diffuse horizontally which aids in soundstage width.
Besides acoustic treatments and acoustic measurements, digital room correction via FIR convolution files is very effective as is multiple subwoofers, but you may already be aware of all this . . .
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Hello Slide, I have not used Sallies myself, but I know how they are intended to work with Sound Lab and if you have more specific question I am happy to explain. I am not exactly sure what your goal is. Your ears should be the best solution to your specific room. Understanding how the sound emanates from the front of Sound Lab (45degree) dispersion and then how the sound then exits the back of the panel is also helpful to think of positions (there is a conversion point behind the speakers where sound will focus at one point)
The photo shows what I use – not exactly a Sallie, but a cylinder diffuser with a layer of absorbing material (I plan to improve on this, but mostly it these are hidden from view) They are positioned where the conversion of sound meets strongest behind the speaker. -
I have very irregular shape listening room. Does anyone on SLOG have experience using Soundlab Sallies or Stillpoint Aperature II diffusers. I am looking for a problem descriptions and if the treatment resolved it or not.
When I had my current speakers setup 1/2 way between the front and backs (24′ total distance) reversing the speaker polarity via my preamp was very obvious.
Now setup 3′ from the back wall in my listening room I can no longer tell any polarity difference.
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