Grado HP 1 headphones
The name Joseph Grado is certainly not new to the transducer field, but the HP 1 is his first entry into the headphone market. The HP 1s are billed as "Professional Recording Monitor Headphones," and Grado is clearly targeting professional recording engineers and equipment designers in need of an accurate monitoring tool. Joe's designs, whether they be phono cartridges or tonearms, have never been ho-hum also-rans when compared to their competition. His products have invariably shown unique design ingenuity, often radically departing from accepted practice. His Signature Tonearm (the last such product he made, now discontinued), which I still use as a reference, is a case in point. The HP 1 headphones are no exception, being rather unusual in design, physical appearance, and construction.
While most high-end phono cartridges have been based on moving-coil principles, Grado has continued to develop and improve his moving-iron designs. Similarly, he has not chosen an electrostatic design for his new headphones, instead refining dynamic moving-coil principles. Each earpiece of the HP 1s contains a small dome-shaped diaphragm approximately 5/8" in diameter. The diaphragm is made of a low-mass plastic with high internal damping in an attempt to control high-frequency resonances which often lend an artificially bright tonal balance to headphones. Joe wasn't interested in extending the high-frequency bandwidth to daylight or beyond. The diaphragm was designed to offer rigidity, and consequently low distortion, within the audible bandwidth, and at high volume levels.
The voice-coil is attached to the perimeter of the diaphragm, in a manner similar to a dome tweeter. Surrounding the voice-coil is the suspension, which is made of the same material as the diaphragm. The suspension is approximately 5/16" wide, larger than on many headphones, but allowing sufficient compliance for accurate low-frequency reproduction. The suspension is said to radiate some energy at low frequencies. Special attention has been paid to the wire in the voice-coil, using slow drawing and annealing to produce a wire with an extremely smooth surface.
The HP 1s are constructed unlike any other headphone I've encountered. Grado's design goal was to minimize and control the resonance problems which plague so many headphones with plastic housings. You won't find a single piece of plastic anywhere on the HP 1s, each earpiece assembly being constructed from machined aluminum alloy parts, brushed for an attractive appearance. During processing, some of the alloy is removed, resulting in a somewhat porous metal. Final treatment of the metal fills in the porosity with a nonresonant material.
The headband connecting the two earphones is a solid, curved, stainless-steel spring rod padded with genuine leather. Grado claims that the diameter of the spring rod is critical; if changed by only 0.001", the sound will also change. Similarly, substitution of a material other than leather for the pad will have a detrimental sonic effect. Straight, solid, stainless-steel rods project from each earpiece, and two solid aluminum blocks containing thumbscrews, at either end of the headband, allow individual height adjustment of the left and right sides.
In common with most current headphones, the diaphragms of the HP 1s are not mounted in a sealed housing. The back of each earpiece is fitted with a stainless-steel screen, eliminating the colorations associated with sealed enclosures. The rear of each diaphragm doesn't radiate completely freely, however. It is resistively damped in order to equalize pressure on both sides of the diaphragm when the headphones are in use. A polarity switch is mounted on each screen, allowing the user to correct for errors in absolute polarity on recordings. Each earpiece is fitted with a soft foam cushion. The HP 1s fall into the supraaural rather than the circumaural category of headphones since the cushions rest against the ears' pinnae rather than surrounding them.
The HP 1s are supplied with a premium-quality interconnect cable made to Joe Grado's specifications. A gold-plated phone plug is molded to the end of the cable, but the plug may be the weak link in the wiring. The gold plating is not particularly heavy, and mine was already showing signs of wear as a result of use during my listening evaluations. Unlike most audio interconnect cables, which can remain plugged in for months at a time, a headphone, particularly in a professional recording environment, will be subject to constant insertion and removal. There is a definite need for a gold-plated ¼" phone plug which can stand up to heavy use. So far, I haven't seen any. Of course, another limitation in the connection will be the ¼" jack into which the headset is plugged. No one, to the best of my knowledge, makes a high-quality, gold-plated, chassis-mount ¼" jackall are plated with nickel, a sonically mediocre conductor.
Anyone who has ever repaired a headphone (I've unfortunately fixed dozens of them) will appreciate the Grado's all-metal construction. The majority of headsets are made of molded plastic parts, which are either fused or glued together. Sooner or later, most headphones subject to heavy use will require some type of repair. This usually involves replacing the cable assembly due to a broken internal wire. In order to replace a headphone cable, the plastic pieces must be literally broken apart. After connecting the new cable, the now-broken plastic pieces must be glued back together. Needless to say, this is an extremely irritating process.
The HP 1s can be disassembled in minutes. Each earpiece contains seven Allen screws which hold the driver assembly in place. Removing the Allen screws frees the assembly for removal from the aluminum housing, allowing easy rewiring. This should make the Grado headphones extremely attractive to music libraries and other institutions. I realize that $600 is more than most libraries normally spend on headphones, but the ability to rewire the HP 1s, again and again if necessary, without the destruction of the headset, makes them an excellent long-term investment.
Quality control is essential to the performance of the HP 1s, and every headset is hand-assembled and tested by Joe Grado. Parts which are not quite up to spec, but still within the bounds of acceptability, are not thrown away, however. These parts are used in the HP 3 headphones, which sell for $395. In addition, Grado offers the model $495 HP 2, which is identical to the HP 1 but lacks the polarity-reversal switches.
Evaluating headphones can be a difficult task, particularly when it comes to selecting a suitable amplifier. A high-current, high-powered amplifier capable of driving low-impedance reactive loads with minimal sonic coloration will probably perform well with any loudspeaker it drives. In my opinion, this is not the case with headphone amplifiers. Dynamic headsets have widely varying impedances, from 8 ohms to 600 ohms and beyond. The impedance of a dynamic headset is determined primarily by the DC resistance of the wire in the voice-coil and the inductive reactance of the coil. Electrostatic headsets present an entirely different type of load, and the best of them require an external power supply for the polarizing voltage.
As I see it, at least three distinctly different types of headphone amplifiers are needed for the wide variety of headphone designs currently available. An 8 ohm dynamic headset is best driven by a small power amplifier. Paul Klipsch once said that what the world needs is a good 5W amplifier; in this particular case, I agree. Many dynamic headsets have impedances in the 30 to 40 ohm region. For these headphones, a power amplifier designed for very-low-impedance loads is overkill, and invariably requires the use of some type of resistive attenuation between the amplifier and the loudspeaker. For these headsets, the amplifier should more closely resemble a preamp line-level stage, having a voltage gain of around 10, with a low-impedance buffered output. 500mW of power into 40 ohms is more than sufficient, and this type of amplifier will work equally well with 600 ohm headsets.
Electrostatics normally require a small power amplifier, but in this case the amplifier must be able to drive a small capacitive load without instability and must also provide the necessary polarizing voltage, if required. Some electrostatics, such as the Stax Lambda Pro headphones, are normally powered by the manufacturer's own amplifier. I agree with such custom tailoring in a electrostatic headphone amplifier, rather than simply using an adaptor box containing the polarizing supply. Most adaptor boxes contain a matching transformer which provides an 8 ohm load for the power amplifier, but a transformer will deliver poorer sonic performance than an amplifier direct-coupled to the electrostatic elements.