Charlie Hughes

Loudspeaker Maximum Input Voltage Test Results

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Impedance Measurement

Some methods and caveats in characterizing the load seen by the amplifier

By Charlie Hughes

To determine the input impedance of a device both the voltage across the device and the current flowing into the device must be known. The impedance is simply the voltage across the device, E, divided by the current flowing into it, I. This is given by the following equation

It should be understood that since the voltage, E and the current, I, are complex quantities the impedance, Z, is also complex. That is to say impedance has a magnitude and an angle associated with it.

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Understanding Horn Directivity Control

By Charlie Hughes

Horns are often used in loudspeaker systems for a variety of reasons. One may be to provide increased acoustical loading to the driver attached to the horn. This helps to increase the sensitivity/efficiency. Another may be to provide some control over the radiation pattern of the driver attached to the horn. It is this directivity control aspect upon which we will focus our attention for this article.
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Using Limiters to Help Protect Loudspeakers

By Charlie Hughes

Using limiters to protect loudspeakers is nothing new. In many applications a limiter is placed immediately in front of a power amplifier to keep it from clipping. While this is certainly a good use, there is more that can be accomplished with a limiter to squeeze a bit more low frequency performance out of a loudspeaker while keeping it within is safe operating area. Read more »

Target SPL and Required Amplifier Size

By Charles Hughes

In a previous article1 I examined the topic of loudspeaker sensitivity and how it may or may not relate to the overall Sound Pressure Level (SPL) produced by a loudspeaker. One of the conclusions of that article is that the SPL produced will be dependent on the spectral content of the signal driving the loudspeaker. Thus, having knowledge of the driving signal (i.e. program material) or being able to make an educated assumption about it may aid in the design of a loudspeaker or sound reinforcement system so that the required bandwidth and SPL is delivered to the audience. The output capability of the amplifier driving the loudspeaker is of equal importance to achieving the target SPL from the direct field of a loudspeaker. This can also be related to the driving signal or the intended program material. Read more »

Using All Pass Filters to Improve Directivity Response

By Charlie Hughes

All pass filters are perhaps one of the most overlooked and poorly understood tools for the general audio practitioner. John Murray has written about their use to yield more linear phase response through the majority of a loudspeakers pass band. Their application can also be used to optimize the directivity and magnitude response of a loudspeaker system. Perhaps we should first look at just exactly what an all pass filter is. Read more »


By Charlie Hughes

EASERA SysTune™ is a relatively new, patent pending audio measurement program from the Ahnert Feistel Media Group (AFMG). It is designed for real-time analysis of acoustic signals and aimed at those doing system alignment, tuning and live sound applications. SysTune is not a replacement or upgrade for the EASERA measurement program. Rather, it has its own unique features that allow it to perform measurement tasks not currently available in other measurement programs. More in-depth acoustical analysis of the measurements made with SysTune can be done with EASERA. SysTune runs under Windows 2000, XP and Vista operating systems. It is a multi-threaded application that is capable of taking advantage of multiple processors within a computer. Read more »

Phase Response and Receive Delay

Some time-of-flight compensation guidelines for proper viewing of the loudspeaker’s phase response

By Charlie Hughes

At the recent EQ07 workshop, and on the SAC email discussion group afterwords, there were some questions about the “correct” phase response when measuring a loudspeaker or some other band pass device. I thought it might be informative to review setting the receive delay within a measurement system so that the displayed phase response is the “correct” one. Read more »

Square Waves and DC Content

By Charlie Hughes

A recent thread on the SAC listserv “Looking for a new DMM” generated a lot of good discussion about transients, clipping, square waves and DC. I thought it might be useful to expound on this a bit. First let’s look at a square wave and see what causes it to have its square shape. A complex waveform can be constructed from, or decomposed into, sine (and cosine) waves of various amplitude and phase relationships. This is the basis of Fourier analysis. A square wave consists of a fundamental sine wave (of the same frequency as the square wave) and odd harmonics of the fundamental. The amplitude of the harmonics is equal to 1/N where N is the harmonic (1, 3, 5, 7…). Each harmonic has the same phase relationship to the fundamental. Read more »

Subwoofer Alignment with Full Range System

By Charlie Hughes

I have heard the question “How do I align a subwoofer with a full range loudspeaker system?” asked many times. I thought it might be interesting to delve into this to see if I could come up with an answer. The task of adding a subwoofer to a loudspeaker system to increase the low frequency bandwidth should typically entail three primary items.

  • • The relative bandwidth of the subwoofer and the full range system (crossover)
  • • The relative output level of the subwoofer and the full range system (gain)
  • • The relative arrival time of the signal from the subwoofer and the full range system (delay)

It is this last item that is perhaps the most challenging. This is the one that we will primarily investigate. We will also look at the first item briefly. With these taken care of item two should not be too much of a problem. Read more »

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