Loudspeaker Positioning for 2-Channel Listening

Draft – writing in progress… 

 

 

 

 

 


 

The physical location of loudspeakers in a listening room is crucial in achieving high performance from a sound system; much more so than the quality of the gear used. Unfortunately this is not very well understood and often overlooked, resulting in severely compromised performance. This article summarizes how loudspeakers interact with the room and aims to provide a quick but complete “how-to” guide to achieve an optimal positioning.

Background – Room Acoustics

Loudspeakers are designed to have a virtually flat frequency response in anechoic conditions, i.e. without influence of a room on the response. During development, loudspeakers are measured in anechioc chambers, or outside in large open spaces, with the typical goal of a ruler flat frequency response. Once the loudspeaker is placed in a room, the response at 150Hz and below, which is highly room dependent (referred to as the Schroeder frequency), can deviate wildly from this ideal response. This is illustrated below, comparing a free field response (red) to an in-room response (blue) of a typical loudspeaker.

(Source: hunecke.de)

The cause of this skewed response are standing waves that are generated between the parallel surfaces of the walls, floor and ceiling. The standing waves consist anti-nodes where the amplitude is the loudest, and nodes where the sound is completely cancelled. At low frequencies the location (distance) between the anti-nodes and the nodes are the greatest which becomes problematic as chances are the loudspeaker or listener are positioned near these peaks and nulls. More accurately; the location of the loudspeakers and the listener in relation to these standing wave patterns determines to what degree the ‘excitement’ of the nodes by the speakers effects the frequency response at the listening position. Below a standing wave pattern involving all 3 parallel wall surfaces (1x 2y 1z) is visualized.

 

Goal

The overall goal of optimized loudspeaker positioning is to minimize unwanted influence of the room on the frequency response. To summarize, the goals are:

  • Achieve the flattest response possible at  listening location
  • Maintain ‘equilateral triangle’ configuration for ideal stereo imaging
  • Minimum distance of listener to loudspeakers > x m

Loudspeaker Implementations

full range vs monitors with subs
full range = 20-20k hz
Limited Low-Frequency Extension = 40-20kHz
LLFE + sub – sub operating range 15-40Hz

http://www.stereophile.com/content/fifth-element-46-size-matters
In my view, the real tipping point comes at E = 41Hz, which is the upper reach of the bottom octave (20–40Hz). If a speaker is nearly flat at 41Hz, which is the frequency of the lowest string on an electric bass guitar, and has well-controlled, non-lumpy bass rolling off below that, that speaker is likely to be sufficient for most purposes, coming up short only for pipe-organ pedals and large symphonic works.

Approach

0 room treatment (if possible)
1 loudspeaker positioning
sub positioning (if applicable)
3 digital eq – final tuning

Tools

  • Predictive calculator
  • Measurement microphone
  • SPL meter for calibration

Rectangular room – mapping of modes

www.hifizine.com/2011/09/prototyping-dipole-bass-system/
other methods
ethan – THE 38 PERCENT RULE
cardas golden
trail and error –

Common Methods

  • Summary of method
  • Resulting position in my listening room
  • Resulting response in my listening room
  • Comments

Cardas Golden Rule Method

Mathematical relationship between speaker (bass driver) and width of back wall (behind speakers).

  • Distance of bass driver from side walls = 0.276 x length of back wall
  • Distance of bass driver from back wall = 0.447 x length of back wall

Listening position = Tip of the equilateral triangle formed using the tweeters as the triangle corners.

Ethan Winer – The ‘38% rule’

Mathematical relationship between speaker (bass driver) and the width and length of the room.

Room Mode Calculator

Mathematical relationship between speaker (bass driver) and the width and length of the room (positioning relative to room modes).

  • Distance of bass driver from side walls = width / 1.6184 or width / 1.6183.
  • Distance of bass driver from back wall = length / 1. 6184 or width / 1.6183.

Nordost Method 1 – ‘Audio Arithmetic”

Mathematical relationship between speaker (bass driver) and nearest room boundaries.

  •  Positioning relationship of Y2 = XZ.

Where:

  • X = distances from center of bass driver to nearest boundary
  • Y = distances from center of bass driver to 2nd nearest boundary
  • Z = distances from center of bass driver to 3rd nearest boundary

The height of the bass driver is often fixed, and a second variable can often be fixed (either sonically or domestically).

Example: A standmount speaker has a woofer 75cm from the floor, and the furthest practical distance from the back wall is 60cm. The sidewall distance could then either be (taking X as the unknown, X=x, Y=60, Z=75) 48cm or (taking Z as the unknown, X=60, Y=75, Z=x) 93.75cm.

Nordost Method 2 – “Voicing the Room”

Based on Wilson Audio method. In short, this method is based on walking away from the walls and assessing at which point your voice sounds most natural and balanced. The method aims to optimize for room gain/boundary reinforcement optimization only.

Nordost Method 3 – “Rule of Thirds”  – Applicable to dipoles only

  • Listening position at 1/3 of room length, speakers at the 2/3 position.
  • Or, front of baffle to rear wall = height x 0.618
  • Front of baffle to side wall = width x 5/18

TAS System Set Up Guide

Other Room Geometries

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