Home Entertainment Show 2007
Listening & Measurement Workshops Workshop #1
How are amplifier measurements done, what do they mean, and do they have any real value? This amplifier measurement clinic will show attendees how audio power amplifiers are measured and which measurements are important. Power amplifiers will be measured in a fashion similar to those published in Stereophile equipment reviews. This clinic will be conducted by Bob Cordell, who is an amplifier designer experienced in tube, bipolar and MOSFET amplifier designs. Bob has also worked in the forefront of developing new and more sensitive distortion tests for amplifiers. These include Multitone Intermodulation (MIM) and Phase Intermodulation (PIM) tests, as well as distortion magnifier techniques for measuring ultra-low levels of THD, crossover and TIM distortions. Measurements on actual amplifiers will be made and differences in measurements and design will be discussed. Bob will share his views on why amplifier measurements are not always a good predictor of sonic differences. Vendors will be invited to take advantage of this opportunity for measurement of their amplifiers, either in a public setting or in private.
Few audiophiles have ever been able to participate in a real-time, level-matched comparison of two power amplifiers driving the same speaker system in the identical acoustic environment. Amplifiers will be auditioned in real-time listening comparisons using a line-level matching scheme that does not degrade audio quality or introduce impedance-dependent colorations (e.g., as opposed to the use of L-pads that kill the damping factor). This is an interactive presentation, as component comparisons are a hot topic on most of the Internet boards. Some people will come away from this presentation amazed at how hard it is to hear variances in obviously different components, while others will relish the ease with which they can perceive subtle audible differences. The highlight of this presentation will be a listening comparison of a 35 wpc vacuum tube amplifier against a solid state amplifier rated at more than 200 wpc.
Loudspeaker auditioning is always a hot topic, but few have ever been able to participate in a real-time, level-matched comparison of two speaker systems driven by the same power amplifier. Level matching is critical to a proper listening test where different speakers are being compared. Unfortunately, simple level matching schemes employing L-pads introduce impedance-dependent colorations because they kill the amplifier damping factor. A line-level matching scheme will be used in these listening tests that does not introduce those degradations. This listening comparison will demonstrate how hard it is to determine what sounds "right", and will illustrate how one speaker can make the other sound "wrong". This workshop will include a short presentation on audition music with discussion on what to listen for and what kind of music works. Peter Smith, a longtime speaker designer, will present this workshop. Peter recently wrote an article describing his "NeoNoir" loudspeaker in AudioXpress.
A live demonstration of speaker MLS testing will be presented and many of the challenges in speaker design will be discussed. Modern speaker building software and measurement techniques will be demonstrated. Much of this PC-based technology is available to the DIY community at a very affordable price. This workshop will be presented by Darren Kuzma. As speaker component systems manager at Parts Express, Inc., Darren was largely responsible for their very popular Reference components. This workshop is a MUST for any attendee who is contemplating building his own speaker system.
This attention-getting demonstration may make you think twice about how much amplifier power you need. You will be able to see in real time the very high peak-to-average power ratio (crest factor) of music while you are listening to it. The high crest factor of well-recorded music can place very high peak-power demands on a power amplifier even at modest listening levels. This will demonstrate why high-power amplifiers sometimes sound better. Amplifiers may clip more often than we think. You are welcome to bring your own music. Examples of MP3 and off-air f.m. broadcast material will also be available for comparison.
Active loudspeakers tend to have an unfair advantage over their conventional cousins. In these speakers the amplifiers, crossovers and loudspeaker drivers are mated together to form a complete synergistic system. Such speaker systems have been very popular in the pro-sound arena for quite some time, but have yet to make a significant impact in the audiophile community. This will begin to change as more compact and efficient power amplifier technologies capable of high sonic quality emerge. The Athena active loudspeaker developed by Bob Cordell will be described and be available for audition. This speaker integrates four 125-Watt conventional Class-AB MOSFET power amplifiers into each cabinet, and demonstrates what can be accomplished in an audiophile active speaker system. The active configuration allows the Athena to use a special form of vented box active equalization, called EQSS™, to achieve good bass extension and SPL in a small footprint. The 3-1/2-way Athena mini-tower is only 39 inches high and 9 inches wide.