designing for imaging, soundstage

anyone care to share thoughts on baffle design/crossover points/etc. with regard to imaging and soundstage? haven't read much discussion on this topic here.

wayne j. has some ideas from the eros design a few yrs ago;
"The front baffle is 9.5" wide with an outer edge rounded with a 1 1/2" roundover router bit and the inner edge rounded with a 3/4" bit. This was done in combination with offsetting the woofers drivers 5/8" to the inside of the baffle's vertical centerline to improve imaging. The tweeter is offset 1 1/8" from the centerline toward the inner edge of the front baffle. The center to center distance between each woofer and the tweeter is 6.75" for reasons that will be more fully explained in the crossover design section. Don't be surprised that this number is somewhat larger than the center to center distance recommended by other designers, as my experience has found that this approach provides a taller, deeper soundstage with less compression in front of the speaker at the expensive of a slight amount of imaging that can be regained with a good quality amplifier and proper speaker placement in the listening room."

this sounds like a low crossover point is good but keeping c-c distance as far apart as possible with that crossover.? right, wrong? any differing or more complete views on how to obtain great imaging? how do these theories differ from MTM to TM? lots of of offset tweeters but haven't seen many offset mid/woofers.
searching for answers
david
 
I've heard a good thing to do to improve imaging is to slightly boost the response from 2-4khz by about 2dB, which is very slight. But sure enough if you read reviews of speakers that are said to have "great imaging," many of them tend to have this slight bump from 2-4khz.
 

tomtom

Member
2006-12-18 10:33 am
planet10 said:
Good phase response (preferably no XOs in the critical region) and a low diffraction signiture help alot,

dave


I hear so many opinions about where critical region is.

50-1500
300-3000
700-3000
1500-7000

So where it is?

Is there some well documented and accepted consensus?

Imaging and stage is on top on my priority list too.
 
All of the above. Lobing and polar pattern are everything. Take a look at the waterfall displays that Stereophile shows to indicate off axis response. Speakers with good imaging that isn't insanely room-critical tend to have very consistent polar patterns without serious lobes. When you see responses with rollercoaster humps and dips off axis, you know that either the imaging and soundstage will be poor or that the ignoramus reviewer will comment on how great the speaker is because the setup and placement is so critical.

I would have to disagree with planet 10 regarding phase response; the phase response of an LS3/5a, for example, is a horror show, it has a crossover right in the upper midrange, a steep one at that, yet it's an imaging/soundstage champ. But the designers took great care about diffraction, lobing, and horizontal polar pattern.
 
I think this is purely subjective unless you have the same speakers and room that were used for the final mix of the recording. Even then what were they listening to/for? probably not 'imaging' or 'soundstaging' - more like tone and wholesomeness of the event - or the intent - of the final production.
 
sdclc126 said:
I'm not a big believer in imaging/soundstage etc. - you rarely if ever hear any of the popular designers talk about it. Speaker placement/listening position are probably the real contributors here - build a properly designed speaker with quality drivers and the rest will fall into place.

Dunno about that... my BG line array dipoles produce a rock solid, you are there image as long as the source was marginally well recorded. Female solo guitar work has incredible "in your home" presence, as does solo piano.

Sometimes I actually jump startle if I'm doing something while listening, and a well recorded piece comes on... it's like there's someone else in the listening space all of a sudden.

I've grown especially sensitive to soundstage/imaging deficiencies, as the quality of my repro gear has improved through the decades. I believe dipoles / line sources are the way to go if you have the room to use them.

John L.
 
Yes good points -

I should clarify - the issue can be addressed in speaker design (and placement) rather than in individual driver performance, which was what I had on my mind at the moment rather than what the question was really about.

I certainly believe in the dipole concept and intend to build such when I have the space for it, as soundstage & imaging are what they are designed to realistically recreate.

What I really should have said was that these things matter little with lousy drivers - you're not going to enjoy it regardless.
 
SY said:
I would have to disagree with planet 10 regarding phase response; the phase response of an LS3/5a, for example, is a horror show, it has a crossover right in the upper midrange, a steep one at that, yet it's an imaging/soundstage champ. But the designers took great care about diffraction, lobing, and horizontal polar pattern.

I just had a pair of LS3/5As thru here, and while they may have seemed like imaging/soundstaging champs in their day, these were actually quite boxy & the soundstage was but a shadow of the Fonkens we were comparing them to. To further check this out i have a set of Spendor BC-1s to be auditioned soon.

dave
 
I concur with the views that the polar response and power response are everything. Imaging has got a lot to do with localization of sound sources, which the brain does by analyzing reflections that are heard. No reflections (as in an acoustically dead room) will kill the soundstage, too much reflections will result in a less sharply defined soundstage. The localizations of sound sources will be easier when the reflections have the same spectral content as the direct sound. Therefore a flat power response is very important.

By the way, I find this to be a very interesting text about stereo and imaging.
 
All intended imaging and soundstaging in audio is embedded in the recording itself.

Good imaging is due to the accumulation of optimized factors in an audio chain. Minimizing distortion and non linearity is critical.

Distortion meaning anything that is being output, that was not input to begin with.

Starting from the speakers, driver performance is an important factor. You can learn a lot about how a driver will sound based on it's measured performance. Frequency response graph's, distortion plots, and spectral decays will tell you a lot.

Driver's that have ringing, stored energy issues that have not been properly addressed will be detrimental to faithful audio playback, as they are playing back sound that was not input into the speaker.

Critical crossover area's are in the 2.8 Khz region, as human hearing is very sensitive to that region. If the crossover from the tweeter to the mid-range is in that area, and not very carefully done, then the speaker can sound terribly "off".

Low crossover points from tweeter to midrange are best. The lower, the better (assuming the tweeter is properly capable). Simple physics. Tweeter's have much less mass, and are quicker responding to high frequencies than even the best midrange drivers.

Ambient reflections which we use to localize sounds are in the higher frequencies.

Cabinet resonances are another critical area. You cannot make a cabinet too stiff. Ideally, it would not resonate at all. Internal control of backwaves coming back to the driver need to be minimized.

Coupling and mass loading speaker enclosures is a benefit as well.

Diffraction off the baffle itself can be minimized by rounding over vertical edges, adding felt surrounds to the tweeter area.

Gains can be had in crossover components as well. Detail retrieval is critical in getting proper imaging and soundstage. Bypassing caps has become a norm over the last little while, as a simple and effective way of increasing detail retrieval. Capacitors themselves have a great impact on speaker (and source components) performance.

And finally, room acoustics. Room acoustics are a critical factor in system performance. Especially critical in smaller rooms. The largest gains in audio are in properly treating your listening room.

The best room, is no room at all. But since that is highly impractical, room acoustics need to be carefully addressed.

The most important factors are, treating first reflection points, treating corners with bass traps, and properly diffusion and/or absorption. Lowering noisefloor, by lowering STC will aid in system performance as well.

Cheers
 
Coupling is achieved with using spiked feet.

Mass loading is done by building the speaker enclosure out of heavier materials, or adding ballast in the form of sand, or lead shot to any unused volumetric portion of the speaker.

I should also add that properly bracing the walls of the speaker, and adding damping to enclosure walls is a very important feature of a good speaker as well, and simple to do if you are building the speakers yourself.

Cheers
 
All intended imaging and soundstaging in audio is embedded in the recording itself.
Nice to hear such a truth. :angel:
Simple physics. Tweeter's have much less mass, and are quicker responding to high frequencies than even the best midrange drivers.
Wrong statement. Very hard to remove such an idea from the brain of even well-known speaker builders. :dead:
 

ttan98

Member
2006-04-04 11:24 am
Melb
Daygloworange said:
Coupling is achieved with using spiked feet.

I should also add that properly bracing the walls of the speaker, and adding damping to enclosure walls is a very important feature of a good speaker as well, and simple to do if you are building the speakers yourself.

Cheers

I have read a no. of reports on bracing and damping, I am now experimenting with them.

In your opinion as a cabinet maker what is your approach that is effective, if you have written a report/article I don't mind a copy. You can post here it or email me.

Cheers.