This page does not review anything 7Hz makes. It counts one thing: how much of what this database says about their products came out of their own documents, and how much had to be worked out or left blank.
| Model | Impedance | Sensitivity | Source of the figure |
|---|---|---|---|
| Legato | 26 Ω | 92.1 dB/mW | Converted from per volt from a shop listing |
| Salnotes Zero | 32 Ω | 93.1 dB/mW | Converted from per volt from a shop listing |
| Sonus | 30 Ω | 93.8 dB/mW | Converted from per volt from a shop listing |
| Timeless AE | 14.8 Ω | 104.0 dB | Unit not stated from a shop listing |
| Zero:2 | 32 Ω | 97.0 dB | Not published |
Impedance is almost always printed. Sensitivity is the one that goes wrong, because a decibel figure means two very different things depending on whether it is per milliwatt or per volt — about five decibels apart at 300 Ω and eighteen at 16 Ω. The conversion is here.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| Legato | 10Hz-20Khz | not printed | not printed |
| Salnotes Zero | 10-20000Hz | not printed | not printed |
| Sonus | 10-20KHZ | not printed | not printed |
| Timeless AE | 5-40000hz | not printed | not printed |
| Zero:2 | 10HZ-20KHz | not printed | not printed |
7Hz prints a frequency range for all 5 models here whose sheets have been read.
Not one of those ranges comes with a tolerance in decibels. Without a ±dB figure a range says nothing about how loud the headphone is at either end of it, which puts 7Hz with the majority: of the 490 models across this database whose maker prints a range, 58 print the tolerance.
The rows are not even called the same thing twice: 2 different headings across 5 models (“Frequency response”, “Frequency response range”).
5 of these figures stand on a shop listing rather than on anything 7Hz published; those model pages name the shop.
No measurement is published here — only what was printed. The whole count, maker by maker, is in the frequency response audit.
The hardest of the 5 to drive is the 7Hz Legato: 6.2 mW and 0.40 V for a 100 dB SPL peak. Their impedances run from 14.8 to 32 Ω, which matters because the voltage a headphone wants rises with impedance while the power falls.
280 of the 280 sources here reach 100 dB on all 5, and the cheapest of them is the Apple USB-C dongle (EU) at $9. “Reaches” means the maker’s own published power figure is enough at that load; it is not a judgement of how it sounds.
On hiss the count is smaller, because most of the industry does not publish a noise figure at all: of the 83 sources here that do, 80 stay under the threshold of hearing on all 5 of their in-ears. The one to watch is the 7Hz Timeless AE at 122 dB/V — the more sensitive the in-ear, the more of the amplifier’s own noise you hear.
Their lowest impedance is the 7Hz Timeless AE at 14.8 Ω, so a source wants an output impedance at or below 1.9 Ω to satisfy the one-eighth rule on everything they make. 131 of the 169 sources that publish an output impedance manage that.
These counts use figures the source makers published themselves. A product that publishes nothing is not counted as a pass anywhere above, which is why the three numbers differ so much. The collection matcher runs the same arithmetic over whatever you actually own.
Very little of what this site says about 7Hz came from them. That is not an accusation about how their products sound — it is a statement about their paperwork, and it is the reason those pages carry so many qualifiers.
The rule used here is the same for every maker and is described on the manufacturer index. Every figure behind it can be opened on the product page it came from, with the document it came from linked.