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Old 11th August 2011, 07:09 PM   #101
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Originally Posted by gedlee View Post
Its not really that expensive, but it does take a bit of room. More than feasible here in North America, but not Europe. But the question of the thread is "How do I get good imaging?" not "How do I get good imaging when I have to compromise everything?" I can answer the first, but not the second.
Well, that's the real crux of engineering, isn't it? How do you do it at reasonable cost and with what ever other constraints are required?
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Old 11th August 2011, 07:49 PM   #102
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Originally Posted by dirkwright View Post
Since the room apparently plays a role in imaging, how does this arrangement look? The two triangular objects in the corners would be loudspeakers designed for corner placement, and the rectangular box in the third corner is a subwoofer. I'm thinking of changing my living room to this arrangement by adding a wall so that I get two good corners.
This setup is very similar to how I had my Yorkville U15s set up, and IMHO can be a successful approach, although not without it's compromises.

The main shortomings are
a) depth. Late/diffuse reflections from the front do seem to influence soundstage depth.
b) spaciousness. this depends a lot on how you treat your first reflection points. In my case, the room was so narrow that I had to put heavy absorption on the first reflection points, making for a very dead room overall, and spaciousness suffered.

Aside from that, my setup was very successful and satisfying - 'imaging' in the sense of left-right placement and speakers disappearing was fantastic. Compared to the best setups I've heard, it was only that last element of 3-D-ness related to the sense of space that was lacking. It did require a fair bit of acoustic treatment though, and the U15's have a very tight 60-degree dispersion pattern which I believe helped.

So, I wouldn't necessarily advocate this as preferable to a more conventional approach, but if it's what you have to deal with it can work.
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Old 11th August 2011, 08:28 PM   #103
gedlee is offline gedlee  United States
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Originally Posted by dirkwright View Post
Well, that's the real crux of engineering, isn't it? How do you do it at reasonable cost and with what ever other constraints are required?
Yes, of course, but I'm still waiting on the car that's as fast as a Ferrari, quiet as a Roles and priced like a Ford Focus. It's just engineering with some contraints right?
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Old 11th August 2011, 08:54 PM   #104
tinitus is offline tinitus  Europe
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right now, I got back the good imaging I'm used to

on my diy supertweeter ribbon I changed a 2.2uf series cap to 1.5uf, and a 1R5 series resistor to 1R8

that did the trick, and my diy 4way transformed into a different speaker
very simple, yet tricky
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Old 11th August 2011, 11:27 PM   #105
terry j is offline terry j  Australia
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Forget the stuff between the speakers I reckon, in most cases it won't make a whit of difference. For sure, we get the audiophile who puts a blanket on it for critical listening and claims it makes big differences...in most cases rubbish it does.

Because, again in most cases, it is just one of these audiophile 'tricks' he has read about on the net, does it, reports back how good it is. Typical stuff usually associated with cables et al.

Pan the camera shot back of his room and see (again usually) NO treatment, often nice looking glass walls, bare wooden floors (looks nice tho! the wife loves it) etc.

In that morass of early and late reflections, boominess etc etc think a blanket on a tv screen will make a difference??

Note the use of 'usual' and 'mostly'...I am not talking about the proper set ups.
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Old 12th August 2011, 05:35 AM   #106
Pano is offline Pano  United States
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Which a number of us here have, BTW.
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Old 15th August 2011, 09:17 PM   #107
boris81 is offline boris81  United States
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Default A guide to better imaging

Hi, I'm putting together a small guide and I'd like to post it here for review before making it more public. I'm sorry for repeating topics that have been discussed already.
---------------------------


I would like to present a simple strategy that has helped me achieve better imaging. Equal distances of the left and right speaker to the sidewalls improve the accuracy of the stereo image. If one speaker is closer to the sidewall than the other, a smearing in the image occurs towards that side. When the speakers are properly positioned in the room, the listener can move left and right and the image will shift sideways while losing some clarity.


The underlying concept is not new and has been discussed in numerous publications. A presentation of the basic principles can be found on Singfried Linkwitz's web site. My contribution expands on how one can verify the distance of the left and right acoustic paths by using measuring equipment. I do not understand the underlying psychoacoustic mechanisms that govern this process but the benefits of this approach are readily audible. Everyone is encouraged to try this out and comment on the perceived effects.


Please verify that you meet the following requirements before continuing:
- You have access to measuring equipment.
- Your speakers have an even power response. Omni, Constant Directivity, Fullrange designs as well as some small bookshelf implementations should be the best candidates. Implementations with uneven off-axis response may not be suited for this arrangement.
- Your listening position should bound by two large, acoustically similar, parallel surfaces on your left and right side.(walls)


Good tonal balance takes priority over imaging and is therefore out of the scope of this article. Room modes and early reflections are the primary concern of proper speaker positioning. It's assumed that the reader is aware of their room's limitations. Objects with sharp discontinuities should not be in the way of the direct acoustic path and at least 2ft away from the tweeter and midrange.

img.PNG
We may begin by positioning the measuring microphone close to the preferred listening spot, equally spaced between the left and right wall. Use a tape measure and try to get to about an inch accuracy. In my far from acoustically perfect room there is a huge panoramic window on my left. I understand that the majority of sound reflections on my left will be coming from the window so I treat the glass surface as my left boundary. I have discovered through experimentation that crude acoustic treatments such as blankets and curtains have negligible effects in this application and should not be considered.


Next, using a tape measure let's place the speakers at equal distances to the sidewalls. 2ft or greater clearance is recommended from the side walls. The clearance from the back wall should be at 3ft minimum. Please do not undermine the effect of room modes when selecting the speaker position. When you have the speakers at a satisfactory position run a MLS sweep and have a look at the recorded Impulse Response. For this guide I used a blue plot for the right speaker and red for left.
ardor-align-bad.PNG

In the plot the highest amplitude signal is the initial pulse coming directly from the speaker to the microphone. Subsequently at around 1.7ms there's a little bump in the right channel. Judging from the intensity and timing this is most likely a diffraction from furniture in the signal path. Diffractions can be easily identified by covering the suspected sources with a pillow and running another sweep to see if the acoustic signature of the diffraction has changed. Another strategy is to turn the speakers to an angle at which they illuminate the offending object with less intensity while maintaining full energy radiation towards the listening spot.


The second largest disturbance in the plot at 3ms is without doubt the reflection from the side wall. The later reflection at 3.5ms is most likely from the ceiling. Linkwitz recommends that there are no wall reflections for the first 6ms but I ruled that impossible to accomplish with the size of my living room. Yet I get a very sharp stereophonic image which prompts me to believe that although a wider room might be beneficial it may not be necessary.


The most important factor for the focus of the stereophonic image I found to be the equal distance of the speakers to the sidewalls. When centering the speakers one must be careful to align not only the distance to the wall but also the angle at which the speakers face the listening position. It is clear from the initial plot that reflections from the right channel arrive faster than those from the left. In practical terms that translates to the stereophonic image smearing towards the right side. The effects are audibly obvious when one is auditioning image test tones.


Audio measuring equipment can help align the reflections timing very precisely. It can also detect and help neutralize diffractions in the signal path. I think it's important to encourage a culture beyond measuring speaker performance and towards using these tools to properly integrate audio equipment and the listening space.
ardor-l-r-align.png
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Old 15th August 2011, 09:32 PM   #108
Pano is offline Pano  United States
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That's a good guide and I use this technique myself. However, I do lock the time in HOLM so that I can better see any offsets. Even without locking time, different reflection paths can be seen as you point out so well.
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Old 18th April 2012, 03:02 PM   #109
jim1961 is offline jim1961  United States
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This is a great subject. For me, imaging / soundstage is what makes me feel part of the process. Lends the illusion of being there. Without it (poor imaging) the sound is flat, barren and lifeless.

Room treatment is critical to this end, imo. Dealing with first reflection points and creating a RFZ (reflection free zone) around the listener. By RFZ, i mean early reflections. I target those up to 25ms-30ms. By free, and I dont mean -40db in the 0-30ms range, but rather I use the Haas curve for reference.

Click the image to open in full size.

Referring to this curve, I try to keep the first 20ms reflections to -15db. Between 30ms and 80ms, I aim for reflections in that zone referred to as "spacious"

Using ETC tests, one can get a graph like this:

Click the image to open in full size.
The green and orange lines I added from the haas data. These illustrate the "inaudable" and "spacious" boundaries, just to help me see visually how things look.

Certainly, what people like in regards to reflections varies. This is just an intro to my approach, and nothing more.

Last edited by jim1961; 18th April 2012 at 03:05 PM. Reason: syntax
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Old 18th April 2012, 03:56 PM   #110
gedlee is offline gedlee  United States
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To me its what is going on below 10 ms that is the most important. The curves are obviously much more complex and things change rapidly in this time region. So I would want to see your green and yellow line and the impulse response (not some time averaged ETC curve) from 0-10 ms. Out to 100 ms is simply a waste of paper. 0-20 ms. maybe (I am assuming that we are talking about a small room like we find in a home where there are lots of reflection < 10 ms.)
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