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Old 16th January 2014, 09:08 PM   #21
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Quote:
Originally Posted by beanbag View Post
1. That seems to be Sander's approach in going back to flat panels. But if directional is what you want, why not have a smaller panel, but put some kind of sound absorbing aperture or baffles in front of the speaker to aim the sound right at your ears?

1a. And why would Martin Logan suggest you to toe out the speakers slightly instead of aiming right at your ears?

2. If less room reflections is the goal, then for a panel of the same width, a taller panel would be worse because it sprays sound at your knees, in addition to your ears. That extra sound will bounce around.
You could go with a smaller speaker and use waveguides to limit dispersion. Horns are basically doing that. At low frequencies the horn would need to be rather large.

Martin Logan's recommendation would bring into play more room acoustics, which would add a sense of spaciousness, but that sense of spaciousness would be the same for every recording, and is a step away from actual fidelity. David Griesinger, formerly of Lexicon, talked about that in one of his papers. I'd hesitate to over do that. It will blur imaging if that matters.

It seems counter-intuitive to say this, but less room reflections is not necessarily the goal. If you had only one reflective surface in a room causing comb filter effects, the cancellations might be 12dB deep (typical of my measurements), and less but still substantial at all the integral multiples of the fundamental cancellation frequency. If you then add another reflective surface to the environment randomly, it's probable that where in frequency one comb filter mechanism causes a 12 dB cancellation, the other comb filter mech won't have it's cancellation, so it somewhat fills in the cancellation from the first mechanism at the listening position. In real world typical listening rooms, there will be many reflective surfaces, some much more dominant than others.

I set up my stereo in a room with no carpeting one time, in an old victorian house, expecting it to sound awful. The room was very "live" with reflections. Much to my surprise it actually sounded very good. Significantly better than the carpeted room I had previously been in. There were so many reflections in this room that virtually all cancellations were largely filled in.

Down around 100HZ - 200HZ (the Shroeder frequency area), where half wavelengths fit between room boundaries, most rooms get into trouble. You'll only have one or two paths so maybe no real fill in potential. Bass gets "boomy". Although I haven't done it, I suspect that having two woofer towers may combat this pretty good. To illuminate the room on all 3 axis with bass frequencies. I notice that several high-end speaker companies are doing this (Infinity, McIntosh, etc.)

A separate issue is room ringing from the presence of parallel walls. The victorian had a bay window that lessened the amount of parallel wall surface area. Ringing didn't seem to be a big problem.
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Old 16th January 2014, 09:48 PM   #22
tyu is offline tyu  United States
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I have a lot of fun with the logans...have 4 pr here know...but horns or voice can sound real big....i can get the sound of the sound.... too be greate with some mods to the panel........ when i use flat ESL panels..... just sounds realer.......
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Old 18th January 2014, 10:17 AM   #23
beanbag is offline beanbag  United States
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Quote:
Originally Posted by geraldfryjr View Post

I have had better luck with not ruining the sound quality by using reflectors directly behind the diaphragm than I have had trying to dampen the backwave with some sort of absorbing material that is close the the diaphragm.

The back pressures created from anything within about 10"-12" from the diaphragm would reduce all of the finest details in sound that ESL's are so well known for, in my earlier experiments.
How did you implement the back wave reflectors?

I have mdf boards behind my Martin Logans angled at 45 degrees so it shoots the sound upwards. It makes the wall behind the speakers much less sensitive to rear wave stuff, i.e. putting acoustic foam there only makes a minor difference.

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Originally Posted by Bob Richards View Post
[stuff]
Thanks for explaining.
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Old 18th January 2014, 03:21 PM   #24
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Quote:
Originally Posted by Bazukaz View Post
Simulation of segmented ESL of the same size. As it can be seen sensitivity is more or less of similar level and even higher at lower frequencies not taking resonance into account. Perhaps it won't accept the same levels of input power like 8x dynamic drivers output can still be quite adequate, even for larger rooms.
Keep in mind that the segmented ESL simulation includes LF boost from the proximity effect. Based on the curves I would guess you simulated at 1m. The array of 8 dynamic dipoles would experience a similar boost but it doesn't look like it was included in their SPL estimate.

Quote:
Max. combined displacement of a) case seems to be around 1.6 litters, compared to 1.2 litters in case of b). So there is no reason for ESL not to reach similar or even higher max.
I agree that at LF the main factor limiting SPL for dipoles is volume displacement(area x excursion). If the 8 dynamic drivers were spaced along the height of the ESL and their baffle was the same size as the ESL they would produce similar LF max SPL for for similar volume displacement limits. However, the dynamic driver array would not be required to produce high quality midrange sound. This frees up the option to include extended baffles edges(H-baffle, U-baffle...etc) which would boost LF output capability significantly.
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Old 18th January 2014, 11:32 PM   #25
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The pictures of the panels in this link is the basic setup I used,

Acoustat panel angles? 8" vs 9" panels?

I had also built up a top barrier using a bunch of stacked up heavy books and sealed the edges with some tape.
This worked well.

Then I tried to dampen the back wave even more by using some very thick (8" or so) fiberglass insulation but and it did help somewhat but if the insulation was within less than 10" from the diaphragm it decrease the fine detail and high end finesse that they have.

The setup became much bigger than it was worth for what I was trying to do, and logic told me that normal proper wall treatment is the only feasible choice for a larger panel.

You can put foam up on the walls behind them and this will help but it won't do anything for the lower midbass to bass frequency's depending an the type of foam you are using.

Here is a picture of the foam wall I once had and a crappy picture of one of my Apogee Duete's later positioned in front of it were the Piano was.

jer
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Old 19th January 2014, 01:58 PM   #26
Calvin is offline Calvin  Germany
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Hi,

the dynamic dipole bass also profits from the inherently higher force/area it can put out.
It also profits from a cabinet (folded dipole), while a ESL-panel is best without wings or supporting cabinet structure (increase active panel area instead of fudging with wings et al).
Example:
A MartinLogan CLX and my smaller esl share a similar-sized-in-width mid-high panel.
But while the ML pairs a double membrane ESL bass panel, my esl features a dynamic dipol tower with 6pcs. of 6.5" drivers.
The outer dimensions of the CLX are ~180x65x37cm (over all), the esl measures 130x54x31, of which the bass tower takes up a footprint of just 22x15cm.
Due to active filtering the tower is equed either down to 35Hz wo. subwoofer, or 50-60Hz w. subwoofer.
Already with the 35Hz setting the dynamic capabilities exceed those of the CLX, not to talk about the higher precision and better definition around Fs due to much lower Q.
Set to 60Hz -which is the CLX´s lower bandwidth limit- the bass tower is close to its Fequal - the frequency where a dipole offers same SPL as a monopole.
Here, just 2-3 drivers would suffice to keep up with the Logan.
Don´t know about the THD, but that will probabely be worse with the CLX below 200Hz too.
Summed up, the dynamic dipole is smaller/more compact, more efficient and more precise.


jauu
Calvin
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Old 19th January 2014, 03:11 PM   #27
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by bentoronto View Post
Maybe for the same reason some folks like tubes and vinyl records: less treble.

Ben
Huh .....

I agree with Calvin , if doing a panel speaker best to go hybrid if seeking SOTA sound , boomy bass is from bad application/design, radiating output has to be similar so if using sealed bass , best to use bipolar setup or if vented, rear firing ports , linesource application is good too , if panel cutoff is too high it will interfere with bass integration and lead to boomy bass also , you have to balance panel cutoff with xover and woofers acoustic center , if not integration will be poor and boomy ..

Last edited by a.wayne; 19th January 2014 at 03:19 PM.
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Old 19th January 2014, 03:23 PM   #28
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by geraldfryjr View Post
The pictures of the panels in this link is the basic setup I used,

Acoustat panel angles? 8" vs 9" panels?

I had also built up a top barrier using a bunch of stacked up heavy books and sealed the edges with some tape.
This worked well.

Then I tried to dampen the back wave even more by using some very thick (8" or so) fiberglass insulation but and it did help somewhat but if the insulation was within less than 10" from the diaphragm it decrease the fine detail and high end finesse that they have.

The setup became much bigger than it was worth for what I was trying to do, and logic told me that normal proper wall treatment is the only feasible choice for a larger panel.

You can put foam up on the walls behind them and this will help but it won't do anything for the lower midbass to bass frequency's depending an the type of foam you are using.

Here is a picture of the foam wall I once had and a crappy picture of one of my Apogee Duete's later positioned in front of it were the Piano was.

jer
Interesting Gerald, i have found foam kills the sound of dipoles fast , finding best to diffuse and leave rear wall live , if apply foam to problem areas i use very sparingly ...

Last edited by a.wayne; 19th January 2014 at 03:44 PM.
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Old 19th January 2014, 05:23 PM   #29
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There's no such thing as a feasible dipole bass unless you have no interest in strong bass below 40 Hz - unless you are trafficking in lucky-spaced room resonances or piggy-backing on driver resonance for a one-note boost (as I do). Do the numbers.

Yes, you can design UNFEASIBLE subs with 3-inch excursions and 16 drivers and 60dB Linkwitz boosts at 20 Hz.

I wish all this loose talk about direct and reflected sound would start being coherent. The main issue is straightforward to anyone who has taken the time to read Toole (and if you haven't read Toole you should the decency and modesty to keep quiet).

The vicissitudes of the front sound are well known if not exactly as simple as they appeared before Gedlee's time.

The "rear" sound connects to the parameter of satisfaction known as ambiance. While that single word doesn't "explain" what is happening in all respects, it does provide a coherent framework for discussing the effects of rear propagation and control of absorption.

Ben

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Old 19th January 2014, 06:13 PM   #30
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by geraldfryjr View Post
I have taken the approach of building narrower panels instead of wide ones.
I like their horizontal dispersion characteristics better.

I also have started to employ electrical segmentation in my latest build as well, I just haven't gotten the needed resistors yet.

I also use a bit more D/S than most, 1.85mm is what my new panel is set and may need to be increased a little, as this will allow for more output at the lowest frequency's than your typical panel made just for the midrange and higher with a typical D/S of 1/16".

I can get really good performance down to the 150hz to 250hz range just at the edge of diaphragm\stator clipping with a D/S of 2mm (3/32") and a width of 3.25" (and a 9.75" length) or so, and it is quite loud at this point (est. about >105db at 1 meter).

To compensate for this I use a much higher Bias voltage as well.
And higher transformation ratios (1:150-250) as well are possible increasing the overall efficiency using smaller area panels.

When the panels width equals one wavelength or greater than the frequency being produced, Then the dispersion starts to transition form a figure 8 pattern in to a narrow beam and keeps getting narrower as the frequency rises.
It also produces main smaller lobes off to the sides as well.

I have no issues of getting a high output from my little panels even down to the 200hz to 300hz range, providing that the stator coatings are up to the task of with holding such high voltages and there is plenty of D/S spacing.

At the lowest Frequency's the output level is directly related to diaphragm displacement and of course the dipole cancelling effect otherwise it would have a circular horzontal dispersion because the diaphragms width is much much less than one wavelength of the frequency being produced.

Wings can help with this and in a small setup I have found that it can increase the low end output by as much as 3db.

I have had better luck with not ruining the sound quality by using reflectors directly behind the diaphragm than I have had trying to dampen the backwave with some sort of absorbing material that is close the the diaphragm.

The back pressures created from anything within about 10"-12" from the diaphragm would reduce all of the finest details in sound that ESL's are so well known for, in my earlier experiments.

Using wings will help with the low end roll off as per dipole action, But the width of the diaphragm itself will determine the horizontal dispersion effects (beaming) for the higher freqeuncys.
And the more the displacement, This helps with the low end.

It is obvious as to why ML suggests to toe out there speakers!!
Its due to the delays and refraction issues of using a curved panel.

When using a taller panel in a line source arrangement the top and bottom reflections from the ceiling and the floor give the impression of having a larger room such as mirrors would do using light waves.
Giving an extension to a virtual room, If you will.

At least that is the way I understand it from reading a lot material on the subject.

Having any space from the ends of the driver to the ceiling and floor is when the reflections are refracted differently and unequally.

FWIW

jer
I would prefer flat panel no more than 14 inch wide with wings and hybrid woofer design ...
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