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Category Archives: Acoustics

Hard proof that equalization kills room modes

In recent years there has been much debate about how effective equalization is in reducing the negative impact of room modes. Room modes are characterized by a peak in the frequency response and extended ringing in the time domain. They create low frequency coloration and lack of articulation and are perhaps one of the most prevalent acoustical problems, since they exist in all small rooms. This article provides measured evidence of the efficacy of equalization in reducing both the peak and ringing associated with room modes.

Impulse Response measurement showing reduction in ringing from EQ

Two channel amplifiers with bass management and room correction!

Recently I have become aware of a new class of product: two channel amplifiers WITH bass management AND room correction. Why is this cool? Well until this new class of products came out the only way to do this type of thing was with a home theater receiver or a separate preamplifier such as a DEQX or TacT and a power amplifier. Two channel systems benefit just as much from subwoofers and equalization as home theater systems. Many two channel speakers, even high end ones, cannot reproduce low bass below say 30-40Hz with low distortion. A JL Audio F112 can play down to 19Hz at a -3dB point! Using subwoofers also allows for cunning room mode cancellation and avoidance of speaker boundary interference.

Classe CP-800

Free Apple iOS acoustic measurement app created by Studio Six Digital for JL Audio

Studio Six Digital, makers of the AudioTools acoustic measurement software for Apple iOS, have created a free acoustic measurement app for JL Audio called, rather creatively, “JL Audio Tools”. In this blog post I’m going to walk you through the main features of the app. Once you’ve downloaded the app and launched it the first screen you see is the menu screen. The JL Audio Tools app does not have all the features of the paid-for Studio Six Digital Audio Tools app but does have many of them. The JL Audio app offers a Sound Pressure Level (SPL) meter, a Real Time Analyzer (RTA), a speaker polarity test and some handy audio calculators.

    

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.