Home  |  Audio Reviews  Show Reports   Partner Mags News 


 

April 2014
Enjoy the Music.com Review Magazine
Headphone Amplifiers
Specifications are only part of the story.
Article By Benchmark Media Systems

 

Benchmark Media Systems  A couple years ago, some of us at Benchmark noticed a weird discrepancy between our HPA2 headphone amp (built into our DAC1 and DAC2) and some comparably-priced headphone amps. The advertised specifications of all the amps were basically the same, but they sounded noticeably different. Benchmark launched a detailed investigation to identify the differences. The results were surprising and are detailed in a white paper by John Siau.

If you care to read the whole white paper, you can do so here. Otherwise, please continue reading the summary presented in this blog post. Either way, our findings were the same:

We tested three high-quality pro-audio headphone amplifiers with built-in D/A converters. All three had similar published specifications. All units are priced between $1000 and $2000. We verified that the manufacturer's specifications were accurate, but we have shown that these published specifications are not sufficient to tell the whole story. In this case, the published specifications were not a good representation of typical operating conditions.

The key to the riddle is that all of the published measurements were made with an ideal resistive load. Performance changed dramatically when headphones were connected in place of the resistor loads. With actual headphones loading the amplifiers, the specifications mirrored what we had experienced in listening tests. There were significant differences in the measured performance of the three units when driving headphones, but not when driving resistive loads. We found that our subjective listening tests were validated by the measurements when the tests accurately reflected real-world conditions.

It would be nice if we could build headphones that would behave like an ideal resistor. This would make a headphone amplifier's job easy.  Unfortunately, electro-mechanical transducers are far from ideal. The burden falls squarely on the headphone amplifier. As it turns out, headphone amplifiers are not created equal:

In order to make a fair test, we compared the HPA2 (again, included with our DAC1 and DAC2) to comparably spec'd headphone amps costing between $1000 to $2000 -- not inexpensive models you'd expect to be deficient. All these amplifiers had similar “ideal” specs, but how would they hold up in real-world tests? We wanted to find out.

1.gif (46176 bytes)
Click here for larger image.

You can see in the graph above, the ideal test, everything is basically even. None of the three amps show much distortion. Without actually running the signal into a load, the Total Harmonic Distortion + Noise (THD+N) is comparable. While the HPA2 measure slightly better than the others, you probably wouldn't hear a difference between these amplifiers in this ideal world. These are the measurements/specifications that manufacturers show consumers.

 

2.gif (45170 bytes)
Click here for larger image.

In our second test we added a 60-Ohm resistive load to simulate headphone loading. Notice that distortion begins to increase in the non-HPA2 amplifiers (green and magenta curves). In contrast, the performance of the HPA2 is nearly unchanged when driving a 60-Ohm resistor (blue curve).

 

3.gif (45284 bytes)
Click here for larger image.

In our third test, we replaced the 60-Ohm resistor (ideal load) with a pair of 60-Ohm headphones.  Distortion rose significantly in the non-Benchmark headphone amplifiers. The 60-Ohm headphones do not behave like 60-Ohm resistors. Clearly the other two amplifiers were having difficulty controlling the headphone transducers. In contrast, the HPA2 measured almost the same as it did in the unloaded conditions (1st test).

This third graph shows the THD+N for the three amplifiers while driving a pair of Sony MDR-V6. The Sony headphones aren't extremely hard to drive, but they do tax the performance of the non-Benchmark amplifiers.

All three headphone amplifiers have enough power to drive the MDR-V6 headphones at their 500 mW rated power. Nevertheless, units 2 and 3 were unable to fully damp the mechanical resonances of these popular headphones. Consequently, units 2 and 3 show significant distortion at low frequencies.

Units 2 and 3 produce audible levels of distortion when driving the popular Sony MDR-V6 headphones. Clearly these two amps are not able to maintain control over the headphone drivers.  Distortion can color the voicing of the headphones and cause listener fatigue. This correlated with the original listening tests that prompted this investigation.

In conclusion, all three of these headphone amps have the same specifications under ideal loads, but they don't perform the same when driving headphones.

If you'd like to learn more, please feel free to read the white paper. Or, get in touch with someone at Benchmark, and we'd be happy to answer your questions.  We work hard to develop products that perform and measure well under all real-world conditions -- not just selected ideal conditions.

 

See Part 2 of this article at this link.

 


www.BenchMarkmedia.com 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     
Quick Links


Audiophile Review Magazine
High-End Audio Equipment Reviews

Equipment Review Archives
Turntables, Cartridges, Etc
Digital Source
Do It Yourself (DIY)
Preamplifiers
Amplifiers
Cables, Wires, Etc
Loudspeakers/ Monitors
Headphones, IEMs, Tweaks, Etc

Superior Audio Archives
Ultra High-End Audio Reviews

Videos
Enjoy the Music.TV

Columns
Editorials By Tom Lyle
Viewpoint By Roger Skoff
Viewpoint By Steven R. Rochlin
Various Think Pieces
Manufacturer Articles


Show Reports
New York Audio Show 2018 Report
Capital Audiofest 2018 Report
Copenhagen HighEnd 2018 Show Report
Australian Hi-Fi & AV Show 2018
Rocky Mountain Audio Fest RMAF 2018
CanJam 2018 Denver RMAF
KL International AV 2018 Show Report
High End Munich 2018 Show Report
AXPONA 2018 Show Report
CanJam SoCal 2018 Show Report
CanJam NYC 2018 Show Report
Click here for previous shows.

Other
Audiophile Contests
Cool Free Stuff For You
Tweaks For Your System
Vinyl Logos For LP Lovers
Lust Pages Visual Beauty

Resources And Information
Music Definitions
Hi-Fi Definitions
High-End Audio Manufacture Links

 


Daily Industry News

High-End Audio News & Information

Partner Magazines
Australian Hi-Fi Magazine
NOVO (CANADA HiFi)
hi-fi+ Magazine
HIFICRITIC
HiFi Media
Hi-Fi World
Sound Practices
VALVE Magazine

For The Press & Industry
About Us
Press Releases
Official Site Graphics

Contests & Join Our Mailing List

Our free newsletter for monthly updates & enter our contests!

Our Social Media & Video Channel
      

 

 

       

Home  |  Sitemap  |  Industry News  |  Equipment / Music Reviews  |  Press Releases  |  About Us  |  Contact Us

 

All contents copyright©  1995 - 2018  Enjoy the Music.com®
May not be copied or reproduced without permission.  All rights reserved.