All posts by Nyal Mellor

Using multiple subwoofers to improve bass: The Welti / Devantier and Geddes approaches

This article continues the theme of the last two blog postings in whic we outlined some ways in which subwoofers can be used to improve sound quality. Last week’s installment ‘Using Subwoofers to Improve Sound Quality: Part 2 Room Modes‘ outlined a technique whereby two subwoofers are positioned within a room to destructively drive a particular room mode, nullifying its frequency response peak and time domain ringing. This week we introduce the Welti / Devantier and Geddes multi-sub methodologies. Both involve using multiple subwoofers as a way to smooth bass response and reduce the impact of modal resonances.

Using subwoofers to improve sound quality: Part 2 – Room Modes

Room modes are caused by perfect constructive interference between a sound wave traveling between two boundaries. This article provides a high level overview of room modes and their impact on sound quality. Two examples of how to use subwoofers to reduce the impact of these modes on sound quality are explained – placing the subwoofer in a pressure null and destructively driving a mode with two subwoofers.

Using subwoofers to improve sound quality: Part 1 – Speaker Boundary Interference

Deep nulls in the frequency response in the bass region can be caused by phase cancellation between the direct sound wave from a sound producing device and the indirect sound wave that has reflected from a nearby boundary such as the floor, ceiling or walls. This phenomenon is called speaker boundary interference or SBIR for short. This article introduces SBIR and explains how these deep nulls can be ameliorated through use of a subwoofer.

A survey of Room Correction devices – Meridian, TacT, Lyngdorf

In the next couple of articles I’m going to create a comprehensive directory of the room correction products available on the market and assess them against the functional criteria that have been explained in the last two articles (here and here). Today I’m covering Meridian (the 861 and G68 surround processors), TacT (including the 2.2XP) and Lyngdorf. Future articles will examine Audyssey, Velodyne and DSPeaker.

Room correction – why the needless analog to digital conversion?

Last week I talked about the importance of letting any end user choose the frequency range to which room correction is applied and allowing them to specify a target frequency response. In this weeks article I cover the last two functional criteria for a room correction product. Whilst these are less important than the first two, they are still important, and just make good sense! This week I cover the importance of not performing needless analog to digital conversions and providing measurement and filter generation capabilities.

Two things a room correction product must do

My research has led me the conclusion that there are a number of basic functional elements that ALL room correction devices should possess. These conclusions derive from a room acoustics viewpoint rather than a sound quality perspective. It is interesting that there are many devices on the market that do not meet these two basic criteria…