Acoustics for Communications

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Conference Phones and Speakerphones

*  Audio Testing and evaluation of both Digital and Analog designs.

*  Electroacoustic testing to industry standards and our specialized tests.

*  We’ll debug your buzz, rattle, feedback and howling speakerphone problems.

*  We can help smooth out problems with component vendors and incoming inspection.

*  Specification writing for system or audio components.


Conference Phone with Bruel & Kjaer 4227 Artificial Mouth

Terminal and 4227 Artificial Mouth

Speakerphone Testing

We can assist you with most aspects of speakerphone work including acoustic testing, writing specifications, dealing with vendor and manufacturing problems, or “bailing out” problematic designs.

*   Frequency Response

*   Electroacoustic Testing

*   Terminal Coupling Loss (Echo)

*   Buzz, Rattle, Instability, Resonances

*   Send and Receive Loudness Rating

*   Switching problems on half-duplex



Speakerphone Send and Receive Setup (Free Field Microphone)

Send and Receive Test Setup


Graph: Loudness Directionality around a Telephone

Loudness Directionality


Graph: Speakerphone Instability in Dial Tone Area

Instability in the Dial Tone Area

About Speakerphones - Handsfree

Speakerphones (called Hands-Free Terminals by many standards) are a challenge to a design team. Dozens of interacting variables electric, acoustic and psychoacoustic require a delicate balancing act.  What seems like a simple concept can be beset with buzzing plastics, voice cutouts, acoustic feedback, echo, and unstable calls. 


Some customers prefer a “rich, bassy“ low end while others like a clear intelligible sound. Since these can be conflicting goals, the frequency response must be adjusted carefully in order to satisfy each group. 


Stability is essential. The system must handle voice, music and call-progress tones without self-interruption or oscillation.  Switching should be smooth and unobtrusive – especially at the onset of an interruption.


Loudspeaker selection is critical. Cost, efficiency, resonant frequency and unit-to-unit consistency are some considerations in loudspeaker selection.


Microphone sensitivity, manufacturing consistency, and proper mounting into the housing are important factors. 


The plastics design affects transducer performance of both microphone and loudspeaker and is critical to a successful project. 


 Owner, Ron Magnuson, has made extensive contributions to North American speakerphone
 standards.  He chaired the TIA working group that created the original speakerphone
 standards for narrowband and wideband digital terminals (TIA-810, TIA-810A and TIA-920)
 and is a major contributor to IEEE handsfree and acoustic standards.

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© Ron Magnuson,
Acoustics for Communications

Austin, Texas