Category: Bang & Olufsen

B&O Tech: Loudspeaker Enclosures

#105 in a series of articles about the technology behind Bang & Olufsen loudspeakers

I’ve started working with a number of my colleagues on a series of videos for internal training at Bang & Olufsen. They were kind enough to make some of these videos publicly available.

This video explains why loudspeaker drivers are typically put in enclosures (boxes), the three types of enclosures that we use (sealed, ported, and passive radiators), and the differences in impact that these enclosure types have on the loudspeaker’s behaviour.

B&O Tech: Beamforming

#103 in a series of articles about the technology behind Bang & Olufsen loudspeakers

I’ve started working with a number of my colleagues on a series of videos for internal training at Bang & Olufsen. They were kind enough to make some of these videos publicly available.

This one explains why loudspeaker drivers produce a narrower “beam” of sound at higher frequencies and how multiple loudspeaker drivers can be used to control both the direction and the width of an acoustic beam.

B&O Tech: Phantom imaging in two-channel stereo

#102 in a series of articles about the technology behind Bang & Olufsen loudspeakers

I’ve started working with a number of my colleagues on a series of videos for internal training at Bang & Olufsen. They were kind enough to make some of these videos publicly available.

This video explains (and demonstrates) how recording engineers are able to control the perceived location of different sound sources in a two-channel stereo recording using different techniques.

B&O Tech: Sound Source Localisation

#101 in a series of articles about the technology behind Bang & Olufsen loudspeakers

I’ve started working with a number of my colleagues on a series of videos for internal training at Bang & Olufsen. They were kind enough to make some of these videos publicly available.

This video explains how we are able to localise the direction of and the distance to a sound source in the real world.

B&O Tech: Human Hearing

#100 in a series of articles about the technology behind Bang & Olufsen loudspeakers

I’ve started working with a number of my colleagues on a series of videos for internal training at Bang & Olufsen. They were kind enough to make some of these videos publicly available.

This one explains some basic concepts of human hearing in the frequency domain, including how our hearing changes with level, the reason we use “loudness” processing in loudspeakers, and psychoacoustic masking.

B&O Tech: Frequency vs. Time

#99 in a series of articles about the technology behind Bang & Olufsen loudspeakers

I’ve started working with a number of my colleagues on a series of videos for internal training at Bang & Olufsen. They were kind enough to make some of these videos publicly available.

This one is an explanation of the relationship between the frequency and the time domains, and why we often do “impulse response” measurements.

B&O Tech: Basics of Sound and Acoustics

#98 in a series of articles about the technology behind Bang & Olufsen loudspeakers

I’ve started working with a number of my colleagues on a series of videos for internal training at Bang & Olufsen. They were kind enough to make some of these videos publicly available.

This first one explains the basics: how sound is produced, how it travels through air, and some of its basic measures like the speeds of sound, frequency, wavelength, amplitude, and why sound gets quieter with distance.

B&O Tech: A little history

#98 in a series of articles about the technology behind Bang & Olufsen loudspeakers

Okay… this posting has nothing to do with technology, or B&O loudspeakers…

One part of my job these days is to dig into the history of B&O, looking into some of the technologies that are “under the hood” of our older products, as well as the people and processes behind them.

Once in a while, I stumble across something that doesn’t fit into any category other than something that I find interesting. This is one example.

Once-upon-a-time, Bang & Olufsen had a bakelite press. I’ll probably talk about this sometime in the future, but the short version is that bakelite was an early kind of plastic that gave people a whole new way of making products with new shapes (do a search for Beolit 39 for example).

B&O used its bakelite press to make items other than radios and parts for their audio products. One example of this is the ashtrays you see in the photos below. One thing to notice is the B&O logo up on the underside of the cigar/cigarette rest.

Reading Specs – Part 3

#97 in a series of articles about the technology behind Bang & Olufsen loudspeakers

This week, a question came in from a B&O customer about their Beovox Cona subwoofer, starting with this photograph:

The question (as it was forwarded to me, at least…) was “what does ‘Long term max power 125w’ and ‘Max noise power 60w’ mean?”

This caused me to head to our internal library here in Struer and look at an ancient kind of document called a ‘book’ that contained the information for the answer.

The first clue is at the top of the photo where it says “IEC 268-5”, which is a reference to a document from the International Electrotechnical Commission in Switzerland called

CEI/IEC 268-5 International Standard
Sound System Equipment
Part 5: Loudspeakers

As you can see there, we happen to have two copies in our library: the second edition from 1989 and 3.1 from 2007, so I took a look at the 1989 edition.

Long Term Max Power

This term is defined in part 18.2 of that document, where it says that it’s the “electrical power corresponding to the long term maximum input voltage.” In order to convert voltage to power, you need to know the loudspeaker’s rated impedance, which is 6 Ω, as is shown in the photograph above.

Power = Voltage2 / R

So, in order to find the Long Term Maximum Power rating of the loudspeaker, we have to do a Long Term Maximum Input Voltage test, and then a little math to convert the result to power.

The Long Term Maximum Input Voltage is defined in section 17.3 as:

“… the maximum voltage which the loudspeaker drive-unit or system can handle, without causing permanent damage, for a period of 1 min when the signal is a noise signal simulating normal programme material (according to IEC 268-1).”

“The test shall be repeated 10 times with intervals of 2 min between the application of the signal.”

So, if I do the math backwards, I can calculate that the Cona was subjected to that special noise signal with an input voltage of 27.39 V with a pattern of

  • 1 minute of continuous noise
  • 2 minutes of silence
  • repeated 10 times

After this was done, the Cona was tested again to make sure that it worked. It did.

How I did the math to figure this out:

  • P = V2/R
  • therefore sqrt(P * R) = V
  • sqrt(125 * 6) = 27.39 V

To do the test, the loudspeaker is placed in a room of not less than 8 m3 with controlled temperature and humidity requirements. An amplifier droves the noise signal into the loudspeaker for 100 h

Max Noise Power

The Maximum Noise Power is tested in a similar way, however, instead of delivering the signal in 1 minute bursts with 2 minute rest periods, the speaker has to play the noise continuously for 100 hours. After the 100 hours are over, then the speaker is put in a room to recover for 24 hours. After this:

“The loudspeaker may be considered to have fulfilled the requirements of this test if, at the end of the storage period, there is no significant change in the electrical, mechanical or acoustical characteristics of the loudspeaker itself compared to those stated in the data sheet for the loudspeaker type, other than a change in the resonance frequency. The acceptability of this change is subject to negotiation; it shall therefore be stated when presenting the results.”

The reason the Maximum Noise Power is lower than the Long Term Maximum Power is the 2 minute rest time in the test. It’s important to remember that a loudspeaker driver is very inefficient when it comes to converting electrical power to acoustical power, and so most of the electrical power that goes into it is just lost as heat caused by inefficiency. The 2 minute rest time allows the loudspeaker to cool down a little before the signal starts heating it up again, and therefore it can handle more power (a little more than 3 dB more – which is the same as 2 x the power) than when it’s playing continuously.