Wednesday, November 22nd, 2017

Neumann : fundamental engineering principles within monitor loudspeaker design

By editorApril 30, 2012

TECHNOLOGY

Andrew Goldberg, Neumann Product Manager - Studio Monitor Systems

Born in 1968 in Portsmouth, UK, Andrew Goldberg has had a varied and international career, in which a hobby has turned into a profession.  He has moved from cutting-edge defence avionics, through the stark realities of a fast-paced commercial product manufacturing, to leading the field in audio reproduction.  A Bachelor’s degree in Audio Technology from Salford University in the UK was followed by a Master’s degree in Acoustics and Audio Signal Processing from Helsinki University of Technology.  Almost ten years with Genelec led to a move to Klein and Hummel in Germany in 2006 to become the Product Manager for their Studio Systems.  In 2010, as part of a corporate reorganisation, he was transferred to Neumann to continue in the role of Product Manager – Studio Monitor Systems.  As well as defining the studio monitoring product range, Andrew conducts research in low frequency reproduction.  He has also been measuring listening rooms of all types and lecturing to industry professionals for about 15 years.

Many of our readers will be familiar with the common audio performance parameters such as frequency response, distortion and colouration but there’s quite a bit of confusion about what are the really important performance issues with regard to monitor loudspeaker performance. What do you consider these to be, and how have they influenced your design philosophy?

“Neumann is making measurement tools.  The electrical input signal is measured and converted to an acoustical output at the listening position.  Oscilloscopes do a similar thing: converting an electrical input to a visual output on a screen. From there, the user of the equipment can make appropriate decisions.

“The only way to make the best tool for these tasks is to correctly use fundamental engineering principles in all parts of the design.  This is what drives the working methods of our development team.

“What does this mean to the customer?  In the designs, Neumann tries to achieve the best in these parameters: on-axis response (as flat as possible), off-axis response (as smooth as possible), group delay (as low as possible), noise (as low as possible), distortion (as low as possible).  Additionally there are practical factors that should be considered such as interfacing (analogue, digital, etc), control (remote controls for volume and other functions), and installation (mounting hardware).”

Do you favour designing professional monitoring speakers for a listening environment which is fairly dead or for a more ‘natural’ listening environment (assuming for this point that the listening room has been treated to diffuse standing wave responses). Please explain the reasoning behind your preference.

O 410 Active Studio Monitor

“Neumann designs monitors with waveguides so that a smooth off-axis response is achieved. This means that the interface with the room environment is well-controlled, and so the quality of the room acoustics is less important than for loudspeakers without a waveguide.  Having said that, poor room acoustics will make any loudspeaker sound bad, so the better the room the better the sound at the listening position.  Typically stereo rooms have a dead end and a live end because the sound should mostly travel from one end of the room to the other, and not back again.  With the move towards surround systems such as 5.1 and 7.1, the concentration of acoustical damping at one end of room is no long appropriate so one sees a much more even distribution of the acoustical treatment.  Neumann’s designs must cope with all types of acoustics so this why front panels with waveguides and back panels with acoustical controls are designed into the products.”

Is there a significant difference in design approaches for nearfield loudspeakers as opposed to for ‘whole room’ monitoring?

“Yes.  Nearfield monitors are used at shorter listening distances than midfield monitors or main monitors. In a nearfield monitor, the waveguide needs to be wider to give the same wide listening area as a midfield monitor or main monitor used at a longer listening distance. Also the longer listening distances demand a higher max SPL from the monitor itself. This leads to the need for larger/more drivers, larger/more amplifiers, larger power supplies, and a larger cabinet.”

KH 120 D - Active Studio Monitor with Digital Inputs

How important are the frequency sensitive directional properties of speaker systems and are there other important issues to consider when designing monitor speakers to offer a stable stereo image?

“Good directivity control reduces the influence of the room on the sound at the listening position. This will reduce differences in the perceived sound from the left and right monitors at the listening position. However, before the room has any effect, there is the monitor itself. Differences between serial numbers will reduce the quality of the stereo image. These differences are function of the design, the tolerances in the parts, and quality control of the production line. Neumann Studio Monitors are well-known for have an excellent stereo image for these reasons.”

Coming back to listening environments, a reality seems to be that many people are trying to monitor in less than ideal acoustic environments. They may make an attempt to deal with the worst of the room’s standing waves and may sometimes over deaden the listening environment. Is there anything which can be done within the monitor speaker design to lessen the effects of poorer listen environments? Can DSP processing play a useful part?

“Room acoustics are a three-dimensional problem whereas filtering inside a studio monitor is a one dimensional solution.  So as a general rule, one should tackle the room acoustics FIRST and use filtering LAST.  The problem with room acoustic treatment is that people do not want to spend lots of money on something that is structurally fixed to a specific location.  Conversely, filtering in a monitor is portable and included with the product that has already been purchased.  Ignoring the room acoustics and going straight for the backpanel switches is like sticking a plaster on a broken leg!

“Here is an example, a room mode typically has quite a high Q factor.  If you use a filter with a high Q factor to fix it (“notch it out”) one ends up with a combined Q factor that is even higher.  High Q filters are audible when they exceed a value of about 16 (which occurs very easily in this scenario).  There have been controlled blind listening tests to prove this.  So you can see that it would better to not have a room mode that does not need to be fixed than to have a room mode than does need to be “fixed”.”

“Onto wideband damping, these days it is typical to see over-damped high frequencies (thin foam panels on the walls) and under-damped low frequencies (no thick damping or panel resonators anywhere).  The result is that the spectral balance will be wrong (the mix sounds too bright), reverb effects are inappropriately chosen (too much added due to the perceived dryness of the room), and the bass is mixed out (the room is adding bass that is not actually in the mix).

Remember that every creative artistic decision taken by the sound engineer is based on the objective presentation of the audio signal to the ears by the combination of the room and the monitoring system. Saving money on the room, the acoustics, and monitoring is a false economy.”

Are there significant advantages in designing monitor speakers and their power amplifiers as a ‘matching pair’?

“Yes.  The interface between the amplifier and driver is known.  The designers know what they are connecting in terms of the complex load that is a loudspeaker driver, its power handling, its frequency response, its sensitivity, etc.  Because the system is closed, a protection system can be designed to monitor the output and then protect the drivers and amplifiers from damage.  This is not easy to do, or maybe impossible, in a “separates” system.  Also as all the parts are designed as one “system” everything can be tuned to operate perfectly with the other parts.  This helps to reduce noise and distortion, and improve the frequency response linearity and extension.”

Neumann kh810 subwoofer

“The one disadvantage is that an active monitor appears to be more expensive, however this is not the case as a passive loudspeaker, low-level crossover, and separate power amplifiers are actually much more expensive in total, and also take up a lot more space too.

“Finally, in the new age of efficiency in power consumption, modern active systems with switched mode power supplies and class-D amplifiers are clear winners against traditional passive systems with large class-A amplifiers.”

What advice would you give to readers in respect of selecting and installing monitor speakers (and power amps) for their studios.

“Read the ‘Product Selection Guide’ and ‘Questions and Answers’ section on our website before purchasing.  Then read the Operating Manuals during installation of the products.  It is much easier to get the most from a product when one knows how it works ”

Our thanks to Andrew for the clarity of his views and insights into the design of professional studio monitor loudspeakers.  For more information on the whole Neumann product range, have a look to www.neumann.com

 

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