QRD Diffuser

105.00 0% tax

Ozone disinfection. Virus-free acoustic panels!

Properties of QRD 7 Diffuser :

If you buy with bank transfer you will give 10% discount from the total price.

Size: 120x60x10cm  Weight  15kg

Size: 104cmx60x10cm  Weight:15kg



QRD Diffuser

7 lamellae

qrd diffuser

  • natur, real wood (pine) 104x64x10cm, 120x64x10cm size
  • dark, laminated board 104x64x10cm size
  • light, laminated board 104x64x10cm size
  • white, laminated board 104x64x10cm size
  • black, laminated board 104x64x10cm size

The distortion which is caused by slap echo and comb filtering in musical detail, vocal clarity and response cancellations can be controlled with Diffusion Products, which diffuse sound, and are particularly good for acoustic diffusion as a home studio diffuser.

QRD Diffuser (or wood “diffusor”) gives your recording studio or listening environment a sense of spaciousness in your music by addressing the above issues without deadening the room too much.

PERFECT ACOUSTIC is proud of our attractive line of sound diffuser products. Our QRD Diffuser panel or sound diffusion panels are a proven, cost-effective solution for recording studios, 2-channel listening rooms, home theaters, and many more applications.

Warsaw hifi show Exhibition of Core Audio and Perfect Acoustic

Warsaw hifi show
Exhibition of Core Audio and Perfect Acoustic

Improve Sound Quality

Sound diffusers scatter sound across two planes: horizontal (left & right) and vertical (up & down), which is called acoustic diffusion. This two-dimensional scattering broadens the soundscape and makes a room sound larger.

Look Good

Our QRD Diffuser and our new combination absorber/diffuser products give your room and your audio some extra texture that looks and sounds incredible.

Quality Materials

PERFECT ACOUSTIC’ sound diffusers use hardwood plywood that won’t shrink, swell or warp as much as lumber.

QRD7 Diffuser


The QRD diffuser is a high-performance quadratic residue diffuser (QRD*) based on a primitive root sequence that employs a grated array of 7 precisely calculated wells to break up and scatter acoustic energy to create a diffuse sound field.

Originally developed by Schroeder, QRDs have long been considered to be one of the most effective forms of diffusion. A series of wells are mathematically arranged in such a fashion that sound waves entering the device reflect back into the room at different times, thus shifting their relative phase. This produces both spatial dispersion (left and right) and temporal dispersion (time shift) which effectively eliminates flutter echoes, breaks up strong first order reflections and reduces standing waves without overly deadening the space.

Unlike light-weight plastics that are unable to control powerful low frequencies, the QRD diffuser combines heavy, MDF slats with a furniture grade solid wood laminate surround for added mass and rigidity. The grated  array is made up with a series of 7 deep, narrow wells that will effectively diffuse acoustic energy from 224Hz to over 5.5kHz with excellent scattering down to 200Hz. This makes the QRD diffuser particularly effective in varients of the LEDE (live-end, dead-end) studio control room designs where several units are typically clustered across the rear wall, spanning the width of the work surface.

Once in place, the QRD diffuser creates a sense of air and space, giving the impression of being in a much larger room. This creates a more natural and comfortable working environment. The QRD diffuser is ideally suited for studio installations, soft seat theatres, high-end home theatres and performance venues.


The Science Behind The QRD diffuser

  • Not all diffusers are created equal!
  • Predicting the low frequency performance
  • Calculating the high frequency cut-off point
  • Maximizing the bandwidth and effect
  • Mass and resonance

A quadratic residue diffuser such as the QRD diffuser is a device designed to break up directional sound waves and reduce powerful first order reflections, standing waves and flutter echo. It is an excellent complement to sound adsorption because it does not remove energy like acoustic panels.

Diffusers reflect the energy back into the room. But unlike flat reflective surfaces that mirror energy, the QRD diffuser radiates the energy in a hemi-disc pattern to create a more diffuse acoustic space. This eliminates acoustic glare and gives the impression of being in a larger, more natural environment.

Although diffusion has been around since Roman times, in recent years advanced mathematics have spawned new designs in recent years that deliver predictable results. Pioneered by Physicist M. Schroeder, quadratic residue diffusers or (QRDs) employ a series of mathematically calculated wells of varying depths. These are set in a sequence based on prime root numbers in effort to diffuse energy in an equal fashion.

Sound arrives as a wave front and enters the diffuser’s phase grid where it will be reflected back into the room. Since the wells are of varying depths, the energy exits at different times relative to each other. This both shifts their relative phase or temporal mode (time shift) and spreads the energy across the grid creating a spatial shift (width in space).


Sound arrives as a wave-front (blue). Without diffusion, the wall’s flat, hard surface reflects energy back (red) like a mirror causing echo. This can be in the form of first-order reflections, flutter echo or room modes.


The wave-front enters – energy strikes the shallow wells first & reflects back into the room while the remainder continues into deeper wells. A ‘temporal shift’ occurs ‘over time’ as it enters, reflects and exits the diffuser.



When identical frequencies enter and exit identical wells at the same time, they will be in phase and reinforce each other. If they exit at different times phase cancellation occurs relative to the frequency & well depth. modes.

A. The well width determines the upper frequency limit of diffusion. The narrower the well, the higher the frequency it will diffuse.
B. The deepest well in the sequence determines the diffuser’s lower limit. The QRD diffuser’s deep well design is effective down to 400Hz.
C. The higher the prime number sequence, the more even and smooth diffusion will be throughout the audio spectrum.

Predicting the Low Frequency Performance

Sound is made up of various air molecule compressions commonly called sound waves that vary in length depending on the frequency. Lower frequencies have longer wavelengths. Given the same amplitude, these contain more energy than shorter high-frequency wavelengths which make them all the more difficult to control. Furthermore, it is generally accepted that sound begins to beam or become directional above the 300Hz to 400Hz region. If a diffuser’s primary function is to break up directional sound energy, it follows that the optimal diffuser should reach down into this lower frequency range. These criteria set the low frequency performance target for the QRD diffuser

When designing a quadratic residue diffuser, the deepest well determines the lowest the frequency that it will effectively diffuse. It is also important that the device be rigid enough that the bass will not cause it to unduly resonate and contain sufficient mass so that the energy does not merely pass right through.

To predict the low frequency performance of a diffuser, one applies a quarter-wavelength calculation: For example, one can estimate that the low frequency cut-off point of a diffuser will be approximately 1130Hz. It is generally accepted that sound will continue to scatter by as much as an octave below this point which will yield a low frequency limit at around 565Hz.

Although the QRD diffuser can be ‘calculated’ to perform down to 424Hz, it will in fact continue to scatter energy down as low as 212Hz thus the reason the extra octave is identified in the table above.

The QRD diffuser’s deepest well measures 18cm). Quarter-wavelength calculations dictate a low frequency cut-off at 425Hz. This prediction was substantiated by Dr. Bouhioui who performed advanced computer modeling on the Razorblade employing what is known as the ‘Finite Element Method”. While working for Boeing, he developed a proprietary algorithm that breaks down the wave, transmission medium and resulting vibrations to predict the noise caused by air flow of the airplane windows. A similar approach was employed using quadrangles to predict the Razorblade’s performance.

It is of interest to note that many acousticians predict the low frequency diffusion will further extend down an octave* below the measured quarter-wave. The belief is that sound continues to scatter below the cut-off point producing audible benefits. Based on this, one can predict the effective low frequency range of the Razorblade will extend down to 212Hz.

This has more to do with the scattering effect of the diffuser which will not stop at a specific frequency, but instead have less and less effect as the frequency goes down. There is documentation on the web that points to diffuser authority T.J. Cox from Stanford University, whereby he suggests that the practical low frequency range can be approximated by multiplying the well depth by a factor of 11. This would suggest the QRD diffuser will work down to 150Hz. But since most agree that sound tends to beam above the 300Hz~400Hz region, we have chosen to ‘specify’ the QRD diffuser’s diffusion start point at approximately 400Hz with sound scattering providing positive benefits down one octave below.

Calculating the high frequency cut-off point

For fun, clap your hands in an empty room and you will likely hear a series of echoes as sound ricochets off the walls, ceiling and floor. This is known as flutter echo or room chatter and is very pronounced in rectangular shaped rooms with hard surfaces. What you are hearing is the high frequency waves bouncing off these surfaces causing what are known as specular reflections or a mirror-like effect. High frequencies are more directional than low frequencies and therefore act like beaming light vectors. Compared to bass, given the same amplitude, these quickly loose their energy as they travel though mediums such as air, liquid or solids.

In a Schroeder diffuser, the width of the well mouth determines the highest cut off frequency. The narrower the width, the higher the frequency the device will diffuse. But if the well width is too narrow in relation to the depth, the device begins to resonate which reduces the effectiveness of the diffuser as it exceeds its viscous limit. On the other hand, if the well is too wide, high frequencies will simply reflect back into the room with very little effect. Schroeder proposed that the maximum high frequency limit will be ½ the wavelength of the well width. The following table shows predicted high-frequency limits of a QRD depending on well width.”

Maximizing the bandwidth and effect

As described above, increasing the diffuser’s well depth lowers the effective frequency, while narrowing the well width increases the effective bandwidth within the practical limit posed by the self-resonance (viscous effect) that can occur inside the wells if too narrow. The greater the number of wells or the higher primitive root sequence; the more even the dispersion will be. This is because each well depth will have an effect on the given frequency and harmonics. For instance a device with 3 wells will not be as effective at diffusing energy as one with 7 wells. The down side is that as you increase the depth and well count, you increase the complexity which makes the device more difficult to build… and therefore more expensive.

The QRD diffuser design delivers balanced spectral diffusion across the bandwidth while also producing excellent temporal behaviour. Graph (A) shows a powerful first order reflection as one would encounter before diffusion is applied. In the second (graph) you can clearly see how the peak energy has been shifted over time.

Typical Studio Control Room

QRD diffusers are ideally suited to be positioned at a distance between six to eight feet behind the listening space. (2 ~ 2.5 meters) These normally span the width of the work area whereby if your workstation or console is 6 feet wide (1.8 meters), then three QRD diffuser would be employed. Placement in the critical sweet-spot helps eliminate trouble some first order reflections while retaining a sense of air and space in the room.


 Wide Wall Spaces

In rooms that have a very wide wall space behind the listening position, adding Bass Traps to the array can both reduce costs while providing added bass absorption. This is particularly important for improving the acoustics at the sweet-spot or primary listing position. The FullTraps are the same size as the Razorblades  (60cm x 120cm). This makes lining them up together in an array simple and attractive. It is best to cluster the QRD diffuser together as this will provide even diffusion.


Building a control room or studio? You can flush mount your QRD diffuser array as easily as installing a window. Flush mounting does not affect the diffusion performance of the QRD diffuser but can enhance the aesthetics of your room design if you are willing to do the framing. If your control room or studio is already finished, you can build a false wall to flush mount the array. This could also be an excellent opportunity to add acoustic isolation between rooms or incorporate a large built-in bass trap.


Audiophile Listening Space

Probably the most demanding listeners of all are audiophiles. Adding QRD diffuser to this type of listening space eliminates troublesome reflections while retaining a sense of air and space. This is particularly important when listening to jazz or classical ensembles that have been recording in an acoustically vibrant space as these recordings benefit from natural room ambiance. Placement is usually behind the listening position however some enjoy breaking up sound energy at the source end of the room.

razorblade-audiophile-plan (1)






As waves exit the various wells, they interact causing energy to disperse across the phase grid resulting in a horizontal ‘spatial shift’. This spreads sound in a hemi-disc, resulting in a greater sense of space.


QRD Diffuser



További információk

Tömeg 20 kg
Méretek 140 × 60 × 10 cm


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