Hello, DIY community.
A very short list of magazines / reviewers use maximum SPL measurements, such as compression and/or distortion limited SPL, to evaluate speakers. The most prominent is the German magazine Production Partner, and its sister magazines Fidelity Online and Sound & Recording, with Prof. Dr. Anselm Goertz at the helm.
A few years ago, I started to replicate their testing methods & compared my results, with the aim to gain the opportunity to directly compare the performance of my own speakers, or third party speakers I'm interested in and could get a hold of and measure, to the wide variety of speakers that those magazines had already tested.
For those interested in the topic, here's documentation of the process.
Specific Requirements:
Types of Max. SPL measurements:
- Max. SPL @ THD: sine bursts that increase in level until a pre-determined total harmonic distortion limit (THD) is reached; then switching to the next higher frequency (in 1/3 to 1/12 oct steps) and repeating the process. Usual THD limits are 1% (for HiFi speakers), 3%, or 10% (subwoofers, PA speakers). Here's a demo of mine that shows the process on a subwoofer (note: low frequency = large wavelengths only, no flat surface required) -> ARTA / STEPS distortion limited SPL measurement - THAM 15 w/ 15LB075-UW4
- multitone distortion: full range multi sine signal that is increased in level until a pre-determined total distortion limit (intermodular distortion (IMD) & harmonic distortion (HD)) is reached
Comparisons on commercial speakers both the Production Partner and I have tested:
TW Audio T24N:
Frequency response 1m 4pi; Production Partner orange curve, me black curve:
Max. SPL @ 3% THD; Production Partner blue curve, me black curve (note: my measurement intentionally limited @ ~130 dB):
QSC CP8:
Frequency response 1m 4pi; Production Partner red curve, me black curve:
Max. SPL @ 10% THD:
Multitone distortion, 6 tones / oct, EIA-426B output filter, 110 dB RMS; left Production Partner, right me:
The congruence turned out as best as can be expected from commercial speakers with at least a minor amount of series deviation & difference in break-in, difference in environment variables (temperature, pressure, humidity), and known calibration tolerance of the hardware. A 100% match isn't possible - but, as we can see, a ~80-90% match was accomplished, which is more than good enough for most comparisons, where major, not minor differences, are the decider.
That's it. I hope the documentation proved interesting.
Regards
Stoneeh
A very short list of magazines / reviewers use maximum SPL measurements, such as compression and/or distortion limited SPL, to evaluate speakers. The most prominent is the German magazine Production Partner, and its sister magazines Fidelity Online and Sound & Recording, with Prof. Dr. Anselm Goertz at the helm.
A few years ago, I started to replicate their testing methods & compared my results, with the aim to gain the opportunity to directly compare the performance of my own speakers, or third party speakers I'm interested in and could get a hold of and measure, to the wide variety of speakers that those magazines had already tested.
For those interested in the topic, here's documentation of the process.
Specific Requirements:
- frequency calibrated microphone w/ low distortion at high SPL; my choice: Isemcon EMX-7150 (135 dB @ 1% THD)
- SPL Calibrator; my choice: Isemcon SC-1 (Class 2, temperature & supply-voltage compensated; Accuracy +/- 0,5 dB)
- software with Max. SPL measurement routines; my choice: ARTA, STEPS
- reflexion free, low noise measurement environment; my choice: GPM (ref.: Gander, AES; Erin) on smooth concrete strip in rural outdoor environment on wind free days
Types of Max. SPL measurements:
- Max. SPL @ THD: sine bursts that increase in level until a pre-determined total harmonic distortion limit (THD) is reached; then switching to the next higher frequency (in 1/3 to 1/12 oct steps) and repeating the process. Usual THD limits are 1% (for HiFi speakers), 3%, or 10% (subwoofers, PA speakers). Here's a demo of mine that shows the process on a subwoofer (note: low frequency = large wavelengths only, no flat surface required) -> ARTA / STEPS distortion limited SPL measurement - THAM 15 w/ 15LB075-UW4
- multitone distortion: full range multi sine signal that is increased in level until a pre-determined total distortion limit (intermodular distortion (IMD) & harmonic distortion (HD)) is reached
Comparisons on commercial speakers both the Production Partner and I have tested:
TW Audio T24N:
Frequency response 1m 4pi; Production Partner orange curve, me black curve:
Max. SPL @ 3% THD; Production Partner blue curve, me black curve (note: my measurement intentionally limited @ ~130 dB):
QSC CP8:
Frequency response 1m 4pi; Production Partner red curve, me black curve:
Max. SPL @ 10% THD:
Multitone distortion, 6 tones / oct, EIA-426B output filter, 110 dB RMS; left Production Partner, right me:
The congruence turned out as best as can be expected from commercial speakers with at least a minor amount of series deviation & difference in break-in, difference in environment variables (temperature, pressure, humidity), and known calibration tolerance of the hardware. A 100% match isn't possible - but, as we can see, a ~80-90% match was accomplished, which is more than good enough for most comparisons, where major, not minor differences, are the decider.
That's it. I hope the documentation proved interesting.
Regards
Stoneeh
Last edited:
Using a using a perceptual based weighting in your distortion measurement, for example as in CEA 2010, can be a useful extension of this.
CEA-2010 & its modernisations, up to CTA-2010C, is probably the most meaningful max. SPL routine for subwoofers - but, for subwoofers only.
Only perception weighted routine used for full frequency spectrum I'm aware of is the GedLee Metric, which, warranted or not, has not been widely adopted. My view is that multitone distortion testing performed by the Production Partner & replicated by me, which is at least output filtered to represent a music signal, is probably fine for that purpose.
Only perception weighted routine used for full frequency spectrum I'm aware of is the GedLee Metric, which, warranted or not, has not been widely adopted. My view is that multitone distortion testing performed by the Production Partner & replicated by me, which is at least output filtered to represent a music signal, is probably fine for that purpose.