Frequently Asked Questions

70% minimum impedance value & 5.6 ohm value (detailed)

We cannot comment on the kind of consideration that went into the design of this device. Though given the numbers, it should really come with a dedicated amplifier supplied by the manufacturer, as few commercial amplifiers, headphone amplifier chips or indeed discrete designs can tolerate such a load. Only amplifiers designed for speakers come to mind - which would usually be unusable due to excessive noise.

Questio: May we learn more about how R&D came to the 70% minimum impedance value, as well as the 5.6 ohm value?

Answer: International standards (voluntary in most countries - arguably) state that a transducer (Speaker/Headphone/Microphone) impedance rating shall represent the average impedance across the whole 20Hz-20kHz frequency range, however the minimum impedance of the transducer shall be no lower than 70% of the rated impedance, or the rated must be adjusted according to the minimum impedance. This is found in standards and recommendations as far back as the IHF/IEE and the German DIN 45500 standard from the 1960's and is retained in current recommendations.

Thus a transducer that has a minimum impedance of 4 ohm anywhere between 20Hz & 20kHz can only be rated as having 5.7 Ohm nominal impedance (e.g. 4Ohm are 70% of 5.7Ohm), even if its average impedance may be 100Ohm.

Rating impedance at one specific frequency only, especially if this rating varies greatly from that obtained using the standard method is not covered by standards and in itself neither wrong or correct, however it can be misleading if anyone would mistake this rated impedance as one that is comparable to ratings applied according to the standards.

The reason for these strictures is to make sure a reasonable equipment matching is retained. For example, most Headphone amplifiers are designed for headphone impedances between 16 Ohm & 600 Ohm. Higher impedances generally present no problem, but impedance much lower than the intended design target may degrade the objective or subjective performance severely, or indeed may damage connected equipment as excessive current is drawn, beyond design limits. Hence it is important that such specifications are realistic.

While designing the iEMatch we applied the same 16 Ohm-600 Ohm target range as reasonable. However we also looked at some of the more extreme common designs (e.g. some from Shure) that have considerably lower minimum impedances than 11.2 Ohm and thus should not be rated as 16 Ohm or higher and actually had one of our researchers comb the entire library of headphone measurements at innerfidelity.com to make sure that we would cover the largest possible range of headphones and IEMs.

The manufacturer’s site specifies the IEM in question as 12.8 Ohm, which seems in disagreement with the graph included with the comments. With a 12.8 Ohm impedance specification the minimum impedance should be no lower than 9 Ohm according to the standards. Such a specification would be at the absolute extreme of the range the iEMatch is intended to handle and will already be a load few headphone amplifiers can handle well.

As it appears the headphone in question is of a much lower impedance (indeed one that is low by the standards of Loudspeakers), it cannot be recommended for use with the iEMatch (though it is unlikely to cause damage), simply because it is far outside the range of impedance the iEMatch is intended to deal with.

Furthermore, it would likely be a good idea to make sure that any headphone amplifier it is used with should be explicitly rated for permanent operation into 4 Ohm loads and it should only be used to evaluate headphone amplifiers explicitly stated to be designed for correct operation into 4 Ohm loads. Otherwise the findings made using such an IEM are likely to be very much at divergence with those made making more common and more generally compatible headphones & IEMs.

Of course, none of the prior comments should be seen as explicit or implicit criticism of either product or manufacturer. It is up to every manufacturer to decide how they specify their devices and how they design them, even if they decide to not apply best practice or common standards in deriving specifications and if they decide to produce designs that offer poor compatibility with the majority of equipment, well that is their choice. However, it is unreasonable to expect such an extreme product to be compatible with any device that is designed to cover the 99% instead of the 1% and is designed and priced accordingly.

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