Well, let me tell you that high impedance HPs are designed for professional use, where they have different amplifiers that allow 4 or 8 (or more) headphones to be plugged at the same time.
Which leads to the following text:
Quote:
Higher impedances, such as 600 ohms, are more useful in studio installations where many units may be wired in parallel for studio monitoring applications. [...] To produce 200 mW in a 600-ohm load a signal of 11 V is needed. This shows that the advantage of high impedance headphones is that they can be used with almost any amplifier output without any risk of being damaged by overload, and you can connect up to 10 or more pairs to the same output. However, they may be not loud enough with some portable recording devices.
Low impedance headphones will sound louder with devices with low output voltages such as portable MD recorders etc., you cannot use more than one pair of headphones at the same output simultaneously. |
You should read this too:
Quote:
Headphones, like loudspeakers, also present a load impedance to the driving amplifier. However, there are three main classes of headphone design — and I'm talking just about impedances here, not the arguments over closed-backed, open-backed, or in-ear designs. The impedance of a headphone is determined by the design of its voice coils — the length and size of wire used, the number of turns around the former, and so on. Consequently, the impedance will affect the volume produced by the headphone — but so too will the strength of the magnet, and several other aspects of the design. The best guide is the quoted sensitivity of the headphone in terms of decibels per milliwatt (dB/mW). The design of the amplifier used to drive the headphones will also have a significant bearing on the output volume.
Broadly, headphones can be categorised into three groups by their impedance: broadcast, professional or portable. The 'broadcast' group have a relatively high impedance, typically of between 1.5k(omega) and 2k(omega). The idea behind this relatively high impedance is so that the headphones can be plugged into a patch bay to monitor a signal source without loading it unduly and causing a drop in the level. The ubiquitous Beyer DT100 can be specified with a 2k(omega) impedance, for example.
The next group are the 'professional' designs which typically range from 150(omega) to 600(omega). Within this group it is often the case that the lower the impedance the higher the volume. It is an obvious marketing ploy, but, given two otherwise similar designs, the one with the lower impedance will sound louder when plugged into the same amplifier — and, of course, some purchasers may be swayed into purchasing one pair of headphones over another simply because of the extra volume. The Sennheiser HD250 is available with a 150(omega) impedance, for example.
The third group are the designs intended for use with portable CD players and the like. Power is the product of voltage and current, but, since the supply voltage to the amplifiers is limited (because you're using batteries), more power requires more current. That can only be achieved if the headphones have a low impedance. Typical designs provide impedances in the 8-32(omega) region — the Sony MDR7509 is specified with a 24(omega) impedance, for example.
Increasingly, people tend to use high-quality 'professional'-impedance headphones with portable equipment, and this is rarely a problem, except that the maximum volume will be reduced compared to a lower-impedance design — which is no bad thing in most cases and could potentially increase the battery life of the player. It is worth noting that most manufacturers offer a variety of impedance options with many of their headphone models — Beyerdynamic are particularly comprehensive in this respect, but it is often worth asking the question if a favoured model appears not to be of a suitable impedance for your application. |
With all of that there you should know that the HPs you have need an amp if you want to hear them loud enough. Your PMP might give them "juice", but most likely not the necessary.
Next time, as you are going to use your HPs at your house, buy lower impedance cans. And don't worry about giving an overload to your HPs. You would turn deaf long before
EDIT: Forgot to add. You can buy a portable amp to use those HPs, and the volume can be increased, but bare in mind that portable amps most likely won't be designed for such a high impedance. So you can either spend some of your money in a portable amp that might not give you a good result, or buy another set of HPs with lower impedance that will not need a portable headphone amp as well as having another pair of HPs... You choose.
Hope this makes things clear
EDIT: For how loud it will sound you also have to take SPL in account.
