Frequently Asked Questions – FAQ
FAQ 01 – Besides quality rankings of new equipment considered for purchase or checking stuff we already own – what else can I measure with TestHiFi?
- test before you buy used equipment
- adjust optimum listening axis of your loudspeakers (there will be more information about this soon)
- compare different listening environments, such as: at home, in the car, at a store and at your friends’ places
FAQ 02 – Why can the same item measure differently at repeated tests? Or “how to tease your buddy by measuring his valued audio system RED (even if it qualifies to be possibly HiFi)”
We put a lot of effort into eliminating room influence from TestHiFi measurements. But of course you can override our intentions … or just ignore the instructions where to place your phone while measuring.
If you move your test object inbetween measurements this will change the room influence on its reproduction. A worst case example for such a difference would be to place a small speaker directly into a room corner. Then compare this to a relatively far-out placement. Corner positions augment low frequency SPL over free field levels. Manufacturers usually design their products to sound good in average positions, with a small low frequency room-gain included. But they (mostly) do not design them for corner positions.
We use a sophisticated 3-position room average concept to improve TestHiFi’s sensibility to various influences, but can not eliminate extreme contrasts as indicated above. You may expect to achieve slightly different results between similar, but not equal test situations.
Another typical example of very position-dependent results is caused by frequency dependent directivity of loudspeakers. Imagine a simple two-way system (one woofer, one tweeter), mounted on a common vertical axis, tweeter above woofer. There is a spectral region where both diaphragms radiate in parallel, the so-called crossover frequency. Around this frequency many two-way loudspeakers have a wildly varying response in diverse vertical directions. Usually they work best on tweeter axis. If all of your 3 measurement positions are above or below tweeter axis, the crossover region will be under-represented. TestHifi probably reports a frequency response amplitude drop around 1-3 kHz.
So put your buddies loudspeaker in one room corner and avoid the tweeter axis while measuring to achieve a severly distorted quality report …
FAQ 03 – What if I do not measure close to the loudspeaker but at a distant listening position?
You may want to evaluate the performance in different listening positions: This will tell you more about the environment and less about the sound-source. To find out the influence of different loudspeaker or listening positions, you can use TestHifi as usual. But you can also repeat the 3 individual test-runs at the same position. To cheat our averaging concept. In very reverberant or small rooms (in your car, or a small kitchen) very small geometric changes produce large response variations. But our hearing mechanism adjusts to environmental changes like our visual sense does for different lighting conditions. Our averaging concept reflects this behaviour to achieve a more “human” test result.
FAQ 04 – What does dBSPL mean?
SPL stands for sound pressure level. dB for decibel, a logarithmic scale used for SPL. dB SPL is referenced to the weakest sounds our hearing can detect, corresponding to 1 pW (one picowatt, or 10 ^ -12 watt). To expand the dynamic range of our hearing it expands the scale towards lower levels and compresses it towards higher levels: from 0 dB SPL, our threshold of hearing, up to 130 dB SPL (this hurts!). The logarithmic scale reflects this perception. Every 10 dB step up in SPL is equivalent to ten times higher acoustic energy. A quiet live concert will be around 80 dB, loud music may reach 110 dB. I measured short duration forte-fortissimo levels of large orchestras around 120 dB.
To reproduce music at low concert levels we want our hifi to at least achieve 86 – 90 dB SPL without significant distortion. TestHiFi asks you to perform measurements at this level in the “level” procedure.