Measurements and compare

About the measurements
The present measurements are performed using MLS (Maximum Length Sequence) technology that allowed to perform the speaker driver measurements from 125Hz up to higher frequencies without a parasitic influence of reflected signals with no need of using an acoustic anechoic chamber. With the aim of getting the maximum reliable and high resolution measurements, especially when measuring harmonic distortion, we use metrologically tested professional equipment of Brüel & Kjær (Denmark) and RFT (Germany) companies. The applying of the acoustic pressure calibrator is allowed to measure the absolute sensitivity of speaker drivers.

Because a considerable part of measurements had being performed during many years and were not determined yet the final approach to their format and content some types and modes are absent in the early measurements.

Measurement setup specification

Test baffle size – 1650x1150 mm
Measuring equipment:
- measuring microphone Brüel & Kjær 4133
- microphone preamplifier Brüel & Kjær 2639
- preamplifier power supply Brüel & Kjær 2804
- sound levek calibrator MMF 05000 (94 dB/1kHz)
- sound card EMU-0202USB with upgraded op amps to OPA1612 
- DSP Xilica  XM2040
- second-order analog ultralinear high-pass filters with switched cutoff frequencies from 20 to 2000 Hz based on the OPA1612 op amps
- ultralinear power amplifier PURIFI 1ET400A

About compare feature

On the website is realized mechanism that allow to compare visually all of parameters and characteristics of two or three drivers. Compare feature is available for registered users only. Choose the drivers of interest and press “Compare” button in the compare block (this block is located in the right side bar on desktop monitors or under the speaker drivers table on tablet and smartphone displays). After that the compare page will be open and atop of page there will be the speaker drivers tabs. Choose one or another tab and you will see the page of chosen driver parameters and characteristics. You can choose the measurement mode of interest by pressing one of buttons above diagram. These modes will be saved after switching to other tab. All measurements are given at different test voltages for a user be able to choose measurement modes that close by the sound pressure for more correct compare. You can delete any driver from compare block by pressing red X next to the driver model name.

Types and purpose of the measurements

Technical data – the speaker driver parameters from manufacturer official datasheets are listed here

Axial magnitude frequency response – absolute magnitude frequency response on the main acoustic driver axis measured at different test voltages. The measurements are performed  at 315 mm distance from the baffle and the results are recalculated to 1000 mm distance.  Measuring at 315 mm distance allow  to reduce parasitic diffraction effects from the test baffle ends, to increase direct signal to reflected signal ratio and to increase “anechoic measurement window” width. It can be considered that reliable frequency response is displayed  from  200Hz and higher up. Under 200Hz frequency response falling is started due non-endless test baffle size and acoustic short circuit between sound wave radiation from front and back sides of a driver membrane.  Because the same reason it can be viewed a small hump, up to 1,5-2dB, in the 140-280Hz range for majority woofer and midwoofer drivers. This hump is due in-phase summing front and back waves. This effect should be taken in consideration during the data analysis. The smoothing 1/12 oct is used for all measurements if there is no other stated like “no_smoothing” words.

Off axis magnitude response – the family off-axis frequency responses  measured at different angles at tested voltage 2,83V at 315mm distance  from intersection point  between the  main acoustic axis and test baffle plain.

Near field FR response (20 mm) normalized to 200 Hz – relative magnitude frequency response measured at tested voltage 2,83V at distance 20 mm from membrane and normalized to sound pressure level at 200 Hz. This kind of measurement allow  o analyze speaker driver frequency response in the piston range and detect the problem regions outside the piston range that are caused by the membrane and surround parasitic resonances. In the case of absence any defects the driver frequency response in the piston range is defined by the Qts parameter only and the normalized frequency level at the main resonance frequency Fs is approximately equals 20*log10(Qts). The parasitic and reflected signals level is so low that we can suppose the measurements is performed in the free field. Moreover, the meaning of this response is the correction that should be added to the frequency response meaning at 200 Hz from Axial magnitude frequency response at the same test voltage level to get the wanted sound pressure level at the frequency up to 200 Hz. For example, you know the Axial magnitude frequency response is reliable down to 200 Hz but you need to know what the sound pressure speaker driver  develops at 40 Hz at 5,6V voltage level. For this purpose you should choose 5,6V test voltage mode in the Axial magnitude frequency response, then to determine sound pressure level at 200 Hz and to add to it the value in dB at 40 Hz frequency from the diagram Near field FR response (20 mm) normalized to 200 Hz.

For the Accuton S280-6-282 driver the sound pressure level at voltage 5,6V at 200 Hz is 98 dB. The correction at 40 Hz is approximately 6,5 dB. So, the sound pressure level at 40 Hz equal =98dB+(-6,5dB)=91,5dB.

HD frequency response (315 mm distance) – harmonic distortion frequency response measured at different test voltages at the distance 315 mm and having 1/12 oct smoothing. We recommend use this kind of measurement from 150 Hz and higher up because decreasing of the useful signal level and increasing the measurement error.

HD frequency response (20  mm distance) – harmonic distortion frequency response measured at different test voltages at the distance 20 mm and having 1/12 oct smoothing. This kind of measurement gives a good precision at harmonic distortion measurement of woofers and midwoofers in frequency range up to 300 Hz.

Near field HD spectrum (20 mm distance) – the alternative method of measurement and displaying of harmonic distortion in the frequency range up to 300 Hz. The measurement distance is 20 mm, the smoothing is off. The measurement is performed at different test voltage levels and discrete frequencies. The main advantages of tis method are high signal to noise ratio and the displaying of more harmonic distortion components quantity. This kind of measurement gives a very good precision at harmonic distortion measurement of woofers and midwoofers in frequency range up to 300 Hz.

Impedance frequency response – frequency dependence of speaker driver impedance module. It is performed at some mA current level and is displayed in different scales for the purpose of more detail analysis of the problematic regions.

How to use the speaker driver models table?
You can use a sorting by the each column except the model name column. Just click on the column header and the data in the table will be sorted. On the next such click on the same header the data will be sorted in the opposite order.  Choose the speaker driver model of interest and click his name – you will go on this driver measurements page. You can add or delete this driver to the compare block if you click the red or blue cross symbol in the end of the string respectively.

To avoid incorrect  website functionality we strongly recommend to back return from a speaker driver measurement page and a compare page by means of buttons “Back to table” instead of the web browser  “Back” button.