Lambda Labs professional acoustics


General questions General technical questions TX-1A TX-2A TX-3A CX-1A & CX-1B CX-2A CX-3A MF-15A DH-18

What does the sensitivity of speaker systems indicate?

Sensitivity measured in dB/1W/1m states the achieved sound pressure level of a speaker system for a defined reference input voltage (e.g. 2,83V for a nominal impedance of 8Ω). The actual input power thereby fluctuates frequency-dependent with the given impedance curve of the loudspeaker system.

On high directivity or bigger arrays it is proper to measure the sensitivity at a larger distance and to rescale it to 1m.

Why is the stated sensitivity value of Lambda Labs’ products seemingly low?

We are comitted providing realistic and honest product details to our customers. The lower frequency range of a loudspeaker system is ordinarily that one with the inferior sensitivity. This is given by the physics of the acoustic radiation impedance. The value of the lowest sensitivity in the transmission range defines the maximum useful sound pressure level on an equalized system.

Our data derived from the median of the lower frequency range and makes our products especially comparable among themselves. Based on these values, the user will be able to estimate real sound pressure levels taking power compression into account as well. For the practical usage, sugar-coated or sheer mathematical calculated measured values are worthless.

A helpful hint for the comparison of sensitivity values: It is easy to push the figure upwards technically. Lambda Labs expressly dissociates itself from regretfully frequent practices like:

  • 2,83V as reference voltage for lower nominal impedances than 8Ω
  • Averaging over the complete and unequalised system response
  • Declaring the maximum point of sensitivity
  • Ground plane based measurements of compact boxes for the high-mid frequency range

How does Lambda Labs determine the sensitivity?

It is reasonable to determine the sensitivity with a method closely related to the real purpose. Therefore, calibrated measurements of fullrange boxes take place in free field (fullspace). Subwoofers are measured on the ground (groundplane). In the case of optionally flown subwoofers we indicate the sensitivity of both, ground- and free-field based measurements.

What is the sensitivity of fullrange loudspeaker systems in floor monitor application?

Stage monitors obtain an increased sensitivity in the lower frequency range, when placed on the floor. The gain is up to 6dB for the very low frequencies, and is depending from diaphragm size and shape of the monitor followed by a weak but destructive interference with the reflected sound from the ground for slightly higher frequencies. At higher frequencies the directivity becomes greater and the radiation do not suffer from floor reflections any more. This effect is considered and correctet in the floor monitor setups.

The sensitivity by itself is difficult to define with a single number with our usual method. The sensitivity is considerably higher than in free space operation, but is strongly dependent from frequency and the choosen hearing position.

What does performance data mean, and how can I assess their significance?

The thermal power handling of a loudspeaker system can be compared by different standards (e.g. AES2-1984). How much specific stress a speaker can handle depends on many complex factors. Besides the thermal power handling further factors, such as mechanical capabilities, linear and non-linear distortion play a significant role.

Each of this topics can be devided into further subareas. The thermal power handling depends on several state variables. For example one of these is the frequency-dependent impedance curve, which varies with the actual temperature of the voice coil. For a given amplifier voltage, the applied power differs by large depending on frequency. Furthermore the heat dissipation, which is enlarged by mechanical movement of the voice coil, is also frequency-dependent. If you are interested to learn more about this complex topic we are looking forward to welcome you on one of our workshops.

How is AES power defined and why doesn’t Lambda Labs use this as a comparative value?

The AES data is a standard to compare the thermal power rating of speakers. The procedure includes a test run over a period of two hours. During that time pink noise with a bandwidth of one decade and a crest factor of 6dB is applied as test signal. The calculation is made on the minimal impedance, however this won’t give a conclusion about the frequency-dependent effective power handling, which would be decisive for music applications.

How does Lambda Labs define power handling (RMS amping power)?

The indication of the power handling refers to the power capability of the amplifier. To max out the full potential of loudspeaker systems, it is advisable to use an amplifier with the same or higher power capability. To ensure a safe operation up to the power limit, one should set up a limiter carefully to avoid overpowering.

To reproduce dynamic peaks correctly, the peak power has to surpass the power recommendation of the amplifier by a factor of two. This is already considered by indicating the maximum amping power as a RMS figure. An amplifier which is capable to deliver a sinus burst of 2000W RMS, indeed manages to deliver 4000W Peak power per definition.

What’s the idea behind the technical term of power compression?

Powercompression is a synonym for the decrease of the theoretical sound pressure level during the practical operation close to the maximum system capacity. The power compression can be divided in three crucial subareas such as: acoustical, mechanical and thermal compression.

Lambda Labs speakers are engineered, that the acoustical and mechanical powercompression in a first approximation could be neglected, even when driven with the full specified amplifier power. The thermal power compression is caused by the heating of the voice coil. Due to the resulting higher impedance of the system, less electrical power is applied to the speaker and therefore less sound pressure level is achieved.

The true power compression is frequency-dependent and is influenced by the crest factor of the music signal. As a practically relevant figure the presumption of 3dB powercompression has been proved. This is the value that should be subtracted in case of long-term high power operation from the maximum achievable sound pressure level, to get a realistic figure. We are looking forward to welcome you to one of our future workshops if you are interested to learn more about this complex topic.

How should I adjust my limiters?

The peak limiter should be adjusted in the value so, that limiting happens at the nominal impedance with either a RMS voltage, which should correspond to the suggested RMS amplifier power, or a peak voltage corresponding to the double of the RMS amping power.

Is the system operated at heavy load conditions and the peak limiters are often triggered, the crest factor of the music signal will decrease. We strictly recommend the additional use of RMS limiters.

The thermal RMS limiter should limit the output to a RMS voltage that corresponds approximately to one third of the recommended RMS amping power. This limiter is conservatively setted up as a protective function and not necessarily mandatory to play music. The limiter will trigger, if the signal reaches prohibited low crest factors. Too low crest factors can be a result of constant and massive peak limitation. More detailed information can be gathered in the FAQs of the specific speaker.

How can I determine the maximum sound pressure level of a Lambda Labs speaker system?

The maximum level is calculated as: SPLmax = 10 * log(power handling) + sensitivity.

The calculated value of the sound pressure level is an effective value (RMS) for short-term sine bursts. The often usual SPLmaxpeak is 3dB higher given by maths. To get a realistic view it is essential to use the correct calculated sensitivity as it is described above. Otherwise the calculated values will result in too high figures and can’t be verified anymore by measurements or have little validity for music playback.

The above calculated figure of the maximum achievable sound pressure level at the weaker point of the lower transmission range of the loudspeaker system is a valueable information for playback of music and makes the loudspeakers of Lambda Labs compareable especially among themselves.

For measurements it is necessary to use amplifiers which can effectively deliver the required sine bursts. The duration of the burst has to be adapted to the power capabilities of the given frequency range. Bursts with a duration of 0,1 to 1 seconds have proven themselves very well in practice. It has to be considered that the voice coil should reach the ambient temperature between measurements. Maximum levels calculated or measured in this way, distinguish themselves fundamentally from the usual sugar-coated values in often encountered brochures.

The calculability of the reasonably useable value of maximum level shows the technical and the practical attitude of Lambda Labs. Is the output power of the amplifier limited by a peaklimiter one has: SPLmax = 10 * log(Urms²/Znominal) + sensitivity

Why is a relatively higher bass level preferable?

The sensitivity threshold of the ear, decreases at low frequencies especially for low sound pressure levels. Depending on the hearing habit, music style and given sound pressure level, a boost of 6dB to 20dB in the very low frequencies with a smooth transition range at 80-160Hz is felt as pleasant. A recommended higher level of 10dB for the subwoofer finds wide approval.

The human ear is able to adapt to a dynamic range of one to a million. To handle very high sound pressure levels without distortion, the tympanic muscles are decreasing the sound transmission into the inner ear and reduce the sensitivity of the ears thereby.

Loud sonic impulses and frequencies above 1kHz are particularly harmful to the inner ear, due to the retarded onset of the cochleostapedial reflex after 50ms. Very low frequency sound waves are of little strain for the inner ear, but trigger the cochleostapedial reflex. The hereby triggered self protection mechanism saves the ear against overstress to a certain degree.