Hard disk drives have been a staple of computing for decades. As technology has advanced, hard drives have gotten faster, gained more capacity, and decreased in physical size. However, one thing has remained constant: hard drives are noisy mechanical devices.
Quick Answers
Hard drives make noise for a few key reasons:
- Spinning platters at high speeds cause air turbulence
- The drive head moves rapidly back and forth to read data
- Motors spin the platters and move the heads
- Vibrations from internal components
While solid state drives have no moving parts and are silent, traditional hard disk drives must physically move parts to operate. This inherent mechanical nature results in audible noise. However, steps can be taken to reduce hard drive noise via dampening and insulation techniques.
How Hard Drives Work
Before diving into the specific sources of noise, it’s important to understand how hard drives work on a basic level. A hard disk drive consists of one or more circular platters coated in a magnetic material which are stacked on top of each other and rotated at very high speeds by a spindle motor. The surface of each platter is divided into billions of tiny regions representing individual bits for data storage.
A read-write arm with a head at its tip is positioned just above or below each platter. As the platters spin, the heads can detect changes in magnetization to read data, or change magnetization to write data. The arms move in and out so the heads can access different regions of the platters as needed to read or write data.
An actuator motor controls the movement of the arms. Hard drives also contain logic boards and controllers to coordinate all these mechanical components. Connectors provide the interface to the rest of the computer system.
Key Components That Cause Noise
With this basic operational overview in mind, we can look at the main hard drive components and functions that contribute to the various noises hard drives make:
- Spindle motor – This motor spins the platters at speeds ranging from 5,400 RPM to 15,000 RPM in modern drives. Faster spin rates allow for lower data access times. The high rate of rotation causes turbulence in the air that results in a steady background whirring noise. Variations in platter spin speed also cause modulations in the sound.
- Heads moving – The read-write heads are positioned just microns above the platter surfaces. As they rapidly move in and out to access data across the radius of the platters, they displace air which causes an oscillating swooshing sound that is especially noticeable when drives first spin up after being powered on. The sound varies as heads speed up, slow down, and change directions.
- Actuator arm – To move the heads, the actuator uses a coil and magnet structure. As current passes through the coil, it generates a magnetic field that interacts with the fixed magnets to rotate the structure. This occurs thousands of times per second, resulting in a steady tone across a range of frequencies as the current and field strength vary.
- Vibration – All the mechanical components generate vibration as they move and interact with each other. The spinning platters, moving arms, motors, and airflow all create resonant vibrations that are transmitted through the structures of the hard drive and radiated as audible noise. Careful damping and isolation of components helps reduce this vibration noise.
Air Turbulence from Spinning Platters
One of the most constant sources of hard drive noise is the turbulence generated by air moving past the rapidly spinning magnetic platters. Consumer hard drive platters typically spin at 5400 or 7200 RPM, though high performance drives can reach 15,000 RPM speeds.
Regardless of the exact speed, the circumferential velocity at the outer edge of the 2.5″ or 3.5″ diameter platters approaches over 30 meters per second! As the platters continuously spin, they are essentially pumping air around their circumference at high speed. This creates air turbulence and eddies that cause pressure variations that we hear as noise.
The noise has a broadband nature with most energy in middle frequencies around 500 Hz to 2 kHz. The frequencies change over time as the airflow turbulence randomly varies and the platters speed up or slow down. Out of all the hard drive noises, the steady airflow hum is often the most noticeable and continuous.
Effects of Spin Speed
Faster platter spin speeds result in even higher air velocities and more turbulence, increasing the broadband noise level. Testing has shown that total noise is roughly proportional to the 5th power of spin speed due to the complex fluid dynamics involved.
For example, increasing spin rate from 5400 RPM to 7200 RPM, which is about 33% faster, actually increases the sound power by over 2x (1.33^5 = 2.3). So higher RPM hard drives are inherently noisier – a tradeoff for their better performance.
Acoustic Management Techniques
Manufacturers use advanced fluid dynamic and acoustic simulations to optimize hard drive enclosure, platter, and head designs to minimize turbulence and noise. Small geometry variations can make measurable differences. Careful structural design to prevent and dampen vibration also reduces platter noise.
Some drives use “acoustic management” features to physically slow down platters when workloads permit. For example, GreenPower technology from Western Digital varies platter speeds between 5400 and 7200 RPM depending on workload. Slower spin means less noise during quiet periods, though full noise returns when heavy access requires full speed.
Sound from Read/Write Head Movement
The next major source of audible noise comes from the rapid movement of the read-write heads. As the heads move in and out radially across the platters to access different data tracks, they cause several types of noise:
- Swooshing noise – The heads flying just above the platter surface push air as they move, causing turbulence and pressure variations. This creates a distinctive oscillating swooshing sound that varies with head acceleration and velocity.
- Windage – Similar to the platters, the head motion causes steady wind noise due to air impacting the slider surface at an angle to the movement direction. Larger heads create more windage noise.
- Vibration – Any sudden head movement or change in direction transmits vibration through the arm structure which radiates as sound.
This head noise is most noticeable when a drive first spins up after idle, as the heads move out to their parked position. But it occurs anytime heads change tracks to read or write data. Faster, more random accesses cause more frequent swooshing sounds.
Effect of Data Location
Because heads move radially, the relative position of accessed data matters. If data accessed sequentially is located all over the disk, the heads have to seek long distances. But if data is grouped closely together in tracks, shorter seeks are required.
File system optimization to place related data in proximity helps limit long seeks and reduces overall noise. Short stroking, where only the outer tracks are utilized, also makes seeks shorter and quieter on average.
Voice Coil Actuators
Most hard drives today use rotary voice coil actuator designs. These consist of magnets attached to the drive body, with a coil of wire on the actuator arm. Running current through the coil in the magnetic field generates torque that rotates the arm.
The actuator driver circuitry modulates the current to accelerate, decelerate, and position the heads with speed and precision. However, this creates magnetostriction effects that cause the coil and structure to vibrate at various resonant frequencies, adding tonal components to the sound.
Careful design is required to prevent and dampen these vibrations. Shock mounts isolate the actuator assembly from the rest of the structure. Firmware optimization of drive currents also helps reduce noise by avoiding unnecessary movements.
Noise from Spinning Motors
Motors are another key source of noise due to their rotating nature and vibrations. Hard drives have two types of motors:
- Spindle motor – Rotates the disk stack
- Actuator motor – Moves the read-write arms
Both generate electromagnetic vibrations, in addition to any physical bearing noise or imbalance. They also transmit vibrations into the drive structure.
Spindle Motor Acoustics
The spindle motor rotates the platters at a constant, precise speed 24/7 while the drive operates. Any deviation from the target speed would disrupt the heads’ ability to reliably access data from the tracks.
Hard drive motors spin at very high speeds – up to 15,000 RPM for high performance drives. Just like other rotational components, the motor and attached platters have resonant frequencies that can amplify vibrations and noise if not properly damped.
Careful design of the bearings, drive electronics, and rotational balancing helps reduce harmonic noise from the spindle motor. Acoustic noise masks can also hide remaining motor tones within other drive noises to prevent specific frequencies from standing out.
Actuator Motor Noise
The actuator motor also generates electromagnetic noise and vibration as it rapidly repositions the arms. However, since actuator motion is limited to less than a full rotation, its effect is less continuous.
The driver voltages and currents energizing the coil also induce vibration in the motor laminations and surrounding support structure. Isolation mounts, bearings, and lubricants reduce transmission of these vibrations.
Resonance and Vibration Transmission
All the moving hard drive components – platters, arms, heads, and motors – contribute structure-borne vibration in addition to their airflow noises. These vibrations inevitably generate audible noise as they transfer through the drive frame to the external case.
Certain resonant frequencies inherent to the materials and structural designs can amplify vibrations. The frame, fasteners, circuit board, and even screws act as transmission paths, radiating vibration as sound.
Careful design is required to isolate, dampen, and reduce vibration inside the hard drive. External mounting and insulation techniques also prevent vibration transmission to the outside case.
Reducing Internal Vibration
Engineers use many techniques to deal with hard drive vibration, including:
- Isolating components with rubber gaskets and screws
- Using damping coatings and films
- Designing flexible suspension structures
- Balancing rotating components
- Avoiding resonances through modeling
The spindle motor and platters make up a precisely balanced rotating system. Any tiny imbalance can cause significant vibration. Likewise, the actuator arm assembly must be balanced.
External Acoustic Management
Insulating external drive mounts and enclosures prevents noise transmission beyond the drive itself. Enterprise storage arrays use specialized drive sleds and carriers engineered for quiet operation.
Some consumer external drive enclosures even sandwich the hard drive between noise damping pads. Careful mounting of the circuit board, connectors, and cables limits their coupling to the frame.
High-end home NAS units also come with noise-optimized drive bays and insulation to maintain quiet operation even with multiple hard drives installed.
Electronics Noise
While not a direct acoustic noise source itself, the drive’s internal electronics and external interfaces can couple to and transmit sounds generated by components:
- Board circuitry vibrations
- Currents in flexible cabling
- Electromagnetic coupling to read heads
Careful circuit board mounting and shielding helps prevent electronics noise pickup. Short, stiff cabling reduces coupling opportunities. Proper grounding and power conditioning is important too.
Fan Noise
One electronic-generated noise that can be noticeable comes from any small cooling fans inside the drive enclosure. While high performance hard drives rarely need active cooling, lower-end consumer drives often have 40mm fans to extend component life.
Like other air moving devices, these small fans generate a turbulence hum. Bearing noises, rotor imbalances, and electromagnetic motor noise can also occur. Vibration damping and isolation mounts reduce fan noise.
Acoustic Testing and Validation
With so many factors influencing hard drive sounds, extensive testing is required to achieve quiet operation. Engineers measure noise levels at various stages – from individual components to fully assembled drives.
Different test conditions like idle, seek, and vibration are evaluated. Microphones placed around the drive allow engineers to identify problem areas. They can then make design tweaks to reduce noise.
Sound Power and Sound Pressure Measurements
Key drive measurements include:
- Sound power – Total noise emitted by the drive across frequencies
- Sound pressure – Noise level at a location near the drive
Sound power indicates how much total noise is generated, while sound pressure measures the audible effect external to the drive. Both help characterize noise, with sound power providing an overall drive noise target.
Meeting Acoustic Requirements
Hard drives are designed to meet certain acoustic requirements based on factors like:
- Target market and applications
- Expected operating environments
- Required reliability levels
For example, drives for home theater PCs need quieter operation than enterprise datacenter drives. Engineers tailor designs to limit noise while still meeting other criteria like capacity, performance, and reliability under the expected workloads.
Optimizing Hard Drives for Quiet Use
While hard drive physics make some noise inevitable, there are ways to choose, configure, and use drives to minimize disturbance:
- Select lower RPM drives – The lower spindle speeds generate less air turbulence and vibration noise.
- Choose drives with acoustic management features – This allows variable RPM and head positioning optimizations.
- Prioritize seek time and locality – The file system should reduce long seeks and random head movements.
- Isolate and dampen mounts – Prevent transfer of vibration and noise to chassis.
- Place in insulated enclosures – Hard drive docks, DAS/NAS units, etc can mask noise.
- Use sound dampening materials – Sound dampening pads in PC cases absorb noise.
- Utilize SSDs forsilence – If maximum quiet is required, solid state drives have no moving parts.
With careful drive selection and configuration, hard drive noise can be reduced to an acceptable level without sacrificing too much performance.
Conclusion
Hard disk drives make various sounds due to their fundamental mechanical nature and spinning parts. Airflow turbulence from platters, head seeks, motor vibrations, and structural resonances all contribute to noise levels. Engineers use advanced design and testing methods to minimize acoustics, but some audible noise remains unavoidable.
Understanding the sources of hard drive noise provides insight into why these devices are often the noisiest PC component. This also allows users to make informed choices to configure drives for quieter operation when needed. While solid state drives are silent, hard drives continue improving while remaining a cost-effective bulk storage solution.