Dispersion characteristics' effect on overall sound

Defo

Member
2008-11-06 9:15 pm
I'm curious about different dispersion characteristics typical effect on the overall sound of the speaker in-room.

Say you have a 3-way with wide dispersion all the way up to the top octave like this:

ECGJ8kf.jpg


And compare that to a 2-way with more narrow but even dispersion pattern like this:

pO2GMhN.png


Obviously the 3-way radiates more treble energy into the room compared to the controlled directivity 2-way.
How does this manifest in perceived tonal balance of the speaker?
 
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It depends to a large degree on the room size. While wide dispersion is generally preferable in large rooms, the opposite is generally true for small rooms.

In small rooms it also depends on where the speakers are located relative to the front and side walls, as well as the location of the listening position.

This excellent paper by Richard Taylor explains the precedence effect and related issues in detail:

http://faculty.tru.ca/rtaylor/publications/reflectgeometry.pdf

He concludes that for speakers with wide dispersion the room should be at least 17' wide by 14.2' long.
 
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Defo

Member
2008-11-06 9:15 pm
It depends to a large degree on the room size. While wide dispersion is generally preferable in large rooms, the opposite is generally true for small rooms.

In small rooms it also depends on where the speakers are located relative to the front and side walls, as well as the location of the listening position.

This excellent paper by Richard Taylor explains the precedence effect and related issues in detail:

http://faculty.tru.ca/rtaylor/publications/reflectgeometry.pdf

He concludes that for speakers with wide dispersion the room should be at least 17' wide by 14.2' long.

Thanks for the insight and resource! From what I've gathered it relates mostly to stereo imaging.

In Stereophiles B&W 802 review, they state the following:

the large-diameter midrange unit does drop off at the top of its passband more than 45° to the speaker's sides, which might make it sound a little polite.

Is there any similar "rule of thumbs" to how a speaker sounds given a certain dispersion pattern?

Given a regularly sized listening room of something like 4x5 meters, what would the typical listening impression be between omni, wide and narrow dispersion speakers?
 
Hej Defo,


I might offer some personal experience gathered over all the years, but please keep in mind it´s just this: personal, no proofs, questionable and so on:


- the wider the dispersion, the further distance from reflective surfaces (walls) is needed. A CD (horn, waveguide, synergy) speaker may be close to the frontwall or corners, but of course this involves other problems. An omni speaker should be wide away from walls.
- In audiophool lingua: controlled (narrow) dispersion gives you the "i am there" illusion. You will notice more of the original recording acoustics.
The wide dispersion (OB, dipole, bipole, omni) speaker gives you the "they are here" illusion. You will notice more of your own room acoustics.
- I have a feeling that a narrow dispersion speaker might be better suited for large orchestra (although I personally would never attempt to try to create the orchestra illusion in a "small" room of 20 m²)
- The wide dispersion speaker, well implemented, might do a better illusion of small (jazz, chamber music, girl/guitar) musical events in a relatively small room.
- The narrower dispersion speaker might be better in precise phantom source localisation (but that depends on many other design criteria as well).
- The wider dispersion speaker might be better in creation of a large "soundstage" (but that depends on many other design criteria as well).
- Any sudden changes and discontinouities of dispersion along the speaker´s passband are not good.


My personal compromise out of this is an OB (but not dipole over the whole passband) system, which can give best of both worlds, but I´m not listening to large orchestra symphonics at all. Instead I like european, especially scandinavian modern jazz. The illusion works, Karl, Tord, Tore and others are here every evening in a 4x6 m room...


All the best


Mattes
 

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To me, narrow dispersion does create a good illusion with precise imaging. But it can seem like the illusion is in some place that **I** don't happen to be present in, too different from my actual surrounding and at odds with what I know is there. Kind of like through an opening in a wall to some other room. A better option to me is to have narrow dispersion from midrange and up, along with effectively wide dispersion via other drivers (perhaps behind the speaker cabinet) electronically delayed by 10 or 20 msec, to reflect off of side walls and ceiling. That gives both the locating precision and the illusion that you also happen to be in the room where the music is playing. It works even with things recorded in a huge room, listened to in my tiny room. Sounds big but plausible.
 
Hej Defo,


I might offer some personal experience gathered over all the years, but please keep in mind it´s just this: personal, no proofs, questionable and so on:


- the wider the dispersion, the further distance from reflective surfaces (walls) is needed. A CD (horn, waveguide, synergy) speaker may be close to the frontwall or corners, but of course this involves other problems. An omni speaker should be wide away from walls.
- In audiophool lingua: controlled (narrow) dispersion gives you the "i am there" illusion. You will notice more of the original recording acoustics.
The wide dispersion (OB, dipole, bipole, omni) speaker gives you the "they are here" illusion. You will notice more of your own room acoustics.
- I have a feeling that a narrow dispersion speaker might be better suited for large orchestra (although I personally would never attempt to try to create the orchestra illusion in a "small" room of 20 m²)
- The wide dispersion speaker, well implemented, might do a better illusion of small (jazz, chamber music, girl/guitar) musical events in a relatively small room.
- The narrower dispersion speaker might be better in precise phantom source localisation (but that depends on many other design criteria as well).
- The wider dispersion speaker might be better in creation of a large "soundstage" (but that depends on many other design criteria as well).
- Any sudden changes and discontinouities of dispersion along the speaker´s passband are not good.


My personal compromise out of this is an OB (but not dipole over the whole passband) system, which can give best of both worlds, but I´m not listening to large orchestra symphonics at all. Instead I like european, especially scandinavian modern jazz. The illusion works, Karl, Tord, Tore and others are here every evening in a 4x6 m room...


All the best


Mattes

So what is the best answer for listening to orchestral music in a small room?

The room I plan to use is only 12 sq. meters. Worse yet, it's almost square in shape.

But that's my only option at the moment and all I listen to is classical music and opera. Need to find the best answer, even if it's not ideal.
 
After looking at many different DIY options I'm now thinking of trying the new Magnepan LRS planar OB speakers instead.

At only $650 for the pair the cost is comparable to building something on my own. Plus they have a generous 60 day full refund return policy, so there really is no financial risk.

I've listened to them in a store, but that was in a room with about 4 times the area and 8 times the volume of mine. And the orchestra was enormous. It completely filled the large front wall. Not sure how that will sound though in my room.

Plan to try it, but need to get a new amplifier first. Maggies take a lot more current than my existing amp can deliver properly.
 
So what is the best answer for listening to orchestral music in a small room?

The room I plan to use is only 12 sq. meters. Worse yet, it's almost square in shape.

[FONT=Fira Sans, sans-serif]James Heddle[/FONT][FONT=Fira Sans, sans-serif] has developed an Excel-spreadsheet[/FONT] [FONT=Fira Sans, sans-serif]which computes early reflection data for omnipoles and dipoles in rooms of a given size. You can download it at http://www.linkwitzlab.com/LX521/Dipole First Room Reflections SL rev4-b.xls
[/FONT]
[FONT=Fira Sans, sans-serif]The results for a room of 3,7 x 3,5 m are promising, especially if the dipole is toed in at 45°:[/FONT]
[FONT=Fira Sans, sans-serif]
attachment.php
[/FONT]


attachment.php
[FONT=Fira Sans, sans-serif]
[/FONT]
[FONT=Fira Sans, sans-serif]A comparison for an omnipole and dipoles at 0° and 45° shows the advantage of the toed in dipole. All seven first reflections (except floor) stay below -15 dB and above 5 ms delay.[/FONT]

attachment.php


[FONT=Fira Sans, sans-serif]Next figure is an example of a bigger room in which some of the first reflections are demonstrated: closest sidewall (light blue), front wall (yellow), front corner (dark blue), furthest sidewall (red). It is helpful to damp the front wall and corner reflections. The side wall reflections don‘t need attenuation.[/FONT]

attachment.php



Keep in mind that this is valid for a real dipole-8 only. You will need a 3-way system for that. A single fullrange driver above a big woofer won't do the job.
 

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Lots of smart info given. Sounds like you are on the right track, just thought I'd mention that in a smaller squarish room, placing the listening position facing a corner works best for me. No side wall reflections.

I've seen this suggested before, but don't understand exactly how to implement it. What are the guidelines for locating the speakers relative to the corner itself?
 
Speakers are the typical 7' apart or so in a small room, putting each of them maybe 5' on either side of a corner. Listening position is equilateral triangle (or closer for near field listening, which can be great), with your back and front both facing a corner. This arrangement also seems more tolerant of speaker placement closer to the walls than you otherwise would be able to.
 
Speakers are the typical 7' apart or so in a small room, putting each of them maybe 5' on either side of a corner. Listening position is equilateral triangle (or closer for near field listening, which can be great), with your back and front both facing a corner. This arrangement also seems more tolerant of speaker placement closer to the walls than you otherwise would be able to.

So if you draw a line 7' long connecting the two speakers together, how far out from the actual corner of the room would you locate the midpoint of that line?
 
You'll have to go through the tweaking process to dial it in, but i start with the speakers maybe a foot from the sidewall. With small dipole panel speakers you'll probably want to be farther from the walls though. That line would be probably 5.5 feet from the corner, just spit balling. It will depend a lot on how big the room is, i can't recall if you said exactly. I think Magnepans make a lot of sense for you. I almost bought a pair of 3.7s. They're remarkable. Nice combination of controlled dispersion with the energy from the back of the speaker energizing the room for a more natural, open sound than you get with horns.
 
Hi classical,


if you like the Maggies (and there´s a lot to like, had active 1.6 myself for a long time...), try it in your room and try different variants, keeping the speaker clear from the walls.
As your situation in a small room will end up with your goodselve pretty close to the speakers, you might also try a well-balanced fullrange driver which "integrates" well over short distances. This don´t need to be expensive - have a look at the Fast-5 thread.


All the best


Mattes
 

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