Room Acoustic Problems

[Sliderule768]

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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[ChrisSoundLab]

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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[Earlinarizona]

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.

[ChrisSoundLab]

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=61553919383032

Cheers,
Chris

[ChrisSoundLab]

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:

[ChrisSoundLab]

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!

[Sliderule768]

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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[ChrisSoundLab]

Yes, they are both ‘9’ series (tallest model)
Outside are full range. Inside ‘flat’ panels are bass panels – not quite as wide as regular panels – they are custom built. They are used together now in the system.
You can see a bit more in this video link if interested:

[Earlinarizona]

I noticed two panels per channel in the picture. The tall speaker looks like a 9 series. Are the second panels Bass panels or what model. Are they both used together or for display?.

[kevinzoe]

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 . . .

[ChrisSoundLab]

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.

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[Sliderule768]

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.

[Author]

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