high frequency sizing screens

high frequency sizing screens

Widely used in fine wet screening applications, these high frequency screening machines comprise of up to five individual screen decks positioned one above the other operating in parallel. The stacked design allows for high-capacity units in a small footprint. The flow distributor splits the feed stream evenly to the individual polyurethane screen decks (openings down to 45 pm) where feeders distribute the stream across the entire width (up to 6 m) of each screen. Dual vibratory motors provide uniform linear motion to all screen decks. The undersize and oversize streams are individually combined and exit toward the bottom of the Stacked Sizer. Repulp sprays and trays arc an optional addition in between screen sections, which allow for increased screen efficiency.

By classifying by size-only, screens compared to hydrocyclones, give a sharper separation with multi-density feeds (for example, in PbZn operations), and reduce overgrinding of the dense minerals. Operations that replaced hydrocyclones with stackedhigh frequency screening machines in closing ball mill circuits can result in a decrease in the circulating load from 260% to 100% and 10 to 20% increase in circuit throughput.

The high capacity Stacked Sizing/screening machine consists of up to five decks positioned one above the other and all operating in parallel. Its use together with urethane screen surfaces as fine as 75 microns (200 mesh) has made fine wet screening a practical reality in mineral processing operations worldwide. The application of this technology in closed circuit grinding is demonstrated with specific application examples.

Screening is the process of separating particles by size and fine screening typically refers to separations in therange of 10 mm (3/8) to 38 microns (400 mesh). Fine screening, wet or dry, is normally accomplished with highfrequency, low amplitude, vibrating screening machines with either elliptical or straight-line motion. Various types ofwet and dry fine screening machines and the factors affecting their operation have been discussed previously.In fine particle wet screening, the undersize particles arc transported through the screen openings by the fluid andthe fraction of fluid in the slurry will therefore affect the efficiency of the separation. From a practical standpoint, the feed slurry to a fine screen should be around 20% solids by volume to achieve reasonable separation efficiency. Asmost of the fluid passes through the screen openings rather quickly, the fine screening process can be completed in ashort screen length. Therefore screen width, rather than screen area, is an important design consideration for fine wet screening.

Recognition of this concept led to the development of multiple feed point fine wet screening machines, or example, the Multifeed screen consists of three screen panels mounted within a rectangular vibrating frame and is actually three short screens operating in parallel. Each screen panel has its own feed box and the oversize from each panel flows into a common launder and then to the oversize chute. Similarly, the undersize from each of the three panels flows into the undersize hopper. The popular 1.2 m (4 ft) wide by 2.4 m (8 fl) long version has a total effective width of 3.0 m (10 fl) In general, multiple feed point machines have been shown to have 1.5 to 2 times more capacity than a single feed point machine of equivalent size and screen area.

Expanding further on this concept, the Stacked screening machine was introduced in 2001. With a capacity considerably greater than any other type of fine wet screening machine previously available, the Stack Sizer has up to five vibrating screen decks operating in parallel for a total effective width of 5.1 m (17 ft). The decks are positioned one above the other and each deck has its own feed box. A custom-engineered single or multiple-stage flow distribution system is normally included in the scope of supply to representatively split the feed slurry to each Stacked screen and then to the decks on each machine. Ample space is provided between each of the screen decks for clear observation during operation and easy access for maintenance and replacement of screen surfaces. Each screen deck, consisting of two screen panels in series, is equipped with an undersize collection pan which discharges into a common launder with a single outlet. Similarly, the oversize from each of the screen decks collects in a single hopper with a common outlet large vibrating motors rated at 1.9 kW (2 5 HP) each and rotating in opposite directions produce a uniform high frequency linear motion throughout the entire length and width of all screen decks for superior oversize conveyance.

As mentioned above, the fluid passing through the openings carries the undersize particles through the screen openings. The screening process is essentially complete when most of the fluid has passed through the openings. Any remaining undersize particles adhere to the coarse particles and are misdirected to the oversize product An optional repulping system is available for the Stack Sizer in which spray water is directed into a rubber-lined trough located between the two panels on each deck With this feature, oversize from the first panel is reslurried and screened again on the second panel. This repulping action maximizes the correct placement of undersize particles and its use will depend upon the particular objective of the screening machine.

To date, 1000s of screening machines are in operation at mineral processing plants worldwide. Dry mass flow capacity typically ranges from 100 to 350 t/h. This is roughly equivalent to 3 or 4 of the older style Multi-feed screens discussed above Like all screening machines, capacity depends upon many factors such as screen panel opening, weight recovery to oversize, the amount of near-size particles, particle shape, and slurry viscosity.

Sizers are for high capacity in a short compact machine. Generally you can make good cuts or separations with high efficiency. If you need near absolute 99.9% precision cuts, then a sizer cannot do that, and most inclined screeners also cannot. So that is why it is very important to understand what the separation goal is before selecting a screener. You cannot have high capacity and high accuracy + 99.9 in the same machine! This machine does not exist! A sizer generally can accomplish a similar separation of a single inclined screen in 2 or 3 screens, and 1/3 the length. of course a lot depends on the PSD, and how close the remaining particles are on each side of the desired cut.

mev screener - midwestern industries, inc

mev screener - midwestern industries, inc

The high-frequency screens manufactured by Midwestern can be utilized in many screening applications from rugged quarry and rock sizing to sand and gravel processing and high volume fine mesh screening. With a variety of sizes and screening decks, the versatile MEV Screener can fit numerous applications.

The MEV High-Frequency Screener is a rectangular screener that utilizes an elliptical motion to convey material across itsscreening surface. Available in sizes three-foot by five-foot (3 x 5), four-foot by eight-foot (4 x 8), and five-foot by ten-foot (5 x 10) with the availability of one to five screening decks gives the MEV Screener the versatility to meet your screening needs.

The MEV Screener is designed to retain material at the feed end for a longer period of time and then gently slops the material near the discharge end, assisting itoff the screening deck and into production. This is achieved by the screeners unique parallel-arc configuration. Crossbars support the end-tensioned screens tocreate a flat screening surface, thus maximizing the screening area.

The end-tensioned screens used in the high-frequency screener simplify changing screen panels. End-tensioning permits the use of square-opening and slotted screens and is accurately maintained by a spring-loaded drawbar. Users can make screen changes in 1015 minutes.

Midwesterns commitment to providing our customers with outstanding screening products continues with our full line of replacement rectangular screens. Our screens are manufactured to fit all makes and models of screeners.

acoustics 101-absorbers, diffusers, reflections, room dimensions and subs - from vinyl to plastic

acoustics 101-absorbers, diffusers, reflections, room dimensions and subs - from vinyl to plastic

Lets apply a little of your new found sound knowledge from the first post in this series. Remember, we are not designing a room to build, just gathering information that will help with that and most importantly the treatment of an existing room.

Lets get this one out of the way first. As we have seen sound is absorbed as heat. Either directly by causing minute movements within a material or indirectly by causing the resonance and flexing of panels or some form of air resonator. For many of us the simplest type of absorber is just a wad of porous material, but not just any material. Two commonly used porous material in home theaters are Roxsul RW40 and Dow Corning 701/703, typically 4 thick.

No materials or designs of absorbers absorb all frequencies uniformly. A materials absorption coefficient measures how much of the incident sound energy is absorbed. An absorption coefficient of 1 means that all incident sound is absorbed. A coefficient of 0 means no incident sound is absorbed totally reflective. It is possible to have coefficients greater than one for some measurements as the edges of the material also absorb sound together with its frontal area.

Clearly porous absorbers even 4 deep, do not perform well at low frequencies, even though they are often used to create bass traps. Their physical installation and design has to be looked at if they are to perform well at absorbing the lower axial modes. Bass trap/absorber design and installation will be reviewed later.

A materials flow resistance or impedance, is a measure of how easily a sound pressure wave can penetrate the material. In simple terms easy penetration high absorption, low penetration low absorption. It is measured in pascal second per cubic metre (Pas/m3) or the rayls per square metre (rayl/m2).

Unfortunately nothing is quiet as simple as it looks with acoustics, and a materials acoustic absorption is actually a function of its flow resistance, density and how the fibers intermesh. Never the less, large depths of high resistivity materials are not conducive to good bass absorption.

Another important parameter of sound absorption, besides the absorbers design, is its AREA. Presenting high surface areas to the incident sound wave provides rapid absorption of the wavefront. Take a look at every anechoic chamber in the world. They do not have their walls lined with many feet of solid absorber they use deep pointed absorbers that present huge surface areas and great depth.

In small rooms there is generally insufficient wall area, or space for enough large bass traps. So you need to get creative by using all the rooms corners, and selecting correctly designed and placed bass traps. In addition, using multiple subs will make a huge difference to a rooms bass performance. More on this later.

For the sake of simplicity, we shall only consider closed rectangular rooms and axial modes. Irregular shaped rooms, angled walls, vaulted ceilings and open rooms create other acoustic issues that are unique to them and cannot be reviewed here. (If you ever build a room from scratch make it rectangular, its acoustic performance is far easier to predict.)

Comparing the two standing wave diagrams the cube clearly shows that the axial standing waves are all the same frequency and occur at the same points in space. My A/V room dimensions were deliberately chosen to try to spread out ALL modes in the most uniform possible way. While at the same time meeting a number of preferred acoustic requirements.

Mode bunching can clearly be seen in the following two tables. Table 1 for the cube shows a low count of all modes in vertical straight lines with significant bunching between 100Hz and 200Hz. Table 2 shows a much higher count of modes fairly well distributed all the way up to 350Hz.

When selecting room dimensions they should be chosen to ensure the most uniform spread of modes in order to reduce room colorations and provide easier room acoustic treatment. These dimensions also effect other acoustics critera that need to be taken into account when designing the room. An excellent tool for selecting a rooms optimum dimensions (my favorite) is Griggs Calculator found here. There are also numerous golden ratios, some of which are shown below and the research carried out by Professor Cox from Salford University here.

The location of the main listening position or MLP is quite important. This position can be considered to be the money seat for those of you, who like me, are a little selfish and want your position to sound the best. In larger home theaters it is much more about getting an even sound for all seats rather than the best sound for just one.

Looking at the above standing wave plots you ideally do not want to locate the MLP at either a pressure maximum or minimum on any room dimension. However, there are practical limits to just what can be achieved. Assuming that the screen is on the wall of the longest dimension, then you can adjust your MLP from the screen so that it is neither at a maximum or minimum, the same for the height for many of the modes. However, as most MLPs are in the center of the width of the room you are stuck with what the width dimension presents you, and you can only improve the standing waves on this dimension by absorption and/or diffusion. Ultimately using EQ to trim the response.My MLP is 46 from the rear wall and 34 from the floor. Which is clear of any mode or antinode location except as described earlier, the width modes.

A single measurement at an antinode may result in excessive level reduction at that particular frequency when electronically equalized, adversely impacting other seats. A single measurement at a node can easily result in signal clipping and speakers being overdriven when attempting to bring these low levels up to match the average room level. This is why when equalizing a listening location it is better to average many readings around the MLP seat rather than at one specific location. Both our ears are never in the same location as the mic!

Optimizing the rooms response for multiple seats above 300Hz is generally straight forward and only requires the addition of relatively small absorbers and diffusers to control and diffuse reflections plus a good equalization system.

Stereo, ambisonics and multi-channel sound were created to provide the listener with the illusion to perceive the physical locations of all the sounds and instruments. In the case of multi-channel movie sound these effects are more directed to following the movies action. For music we try to create an image of the performance that shows the physical locations both between and outside the speakers and their relative depth and height positions. This illusion is very much part of both the microphone technique used and the way the reflections in your room interfere with the direct sound from the speakers. You do not need your eyes to see the musicians, your ears and brain are quite capable of creating this spatial illusion. Just close your eyes at a live concert. For recording, once the engineer deploys more than one stereo mic it all becomes more complex to maintain the illusion. Each mic picks up multiple paths of the instruments sound reflections and starts to smear their timing information which is what your ears need to be able to create the spatial illusion.

In modern day multi-track recording creating a well-defined left/right image is relatively easy (panned stereo), creating the illusion of depth AND relative height is far more challenging. I have no modern multitrack recordings that can compare to the depth and relative height placement of Sheffield Lab recordings. Many of which were accomplished with just one stereo microphone and a fill for the kick drum and double bass. Mixing and level control was then at the discretion of the band leader not somebody sat at a console adjusting numerous spot mics to balance the mix.

So why have I just spent two paragraphs explaining what happens during the recording? When we are talking about reflections in our rooms. What we are trying to accomplish is to create an aural illusion of the original soundstage. So anything that interferes with that creation should be dealt with.

The ear/brain is quite sensitive to how it interprets room reflections relative to the original direct sound. It is these reflections that can make or break the stereo, or multi-channel image illusion. So lets look at some of the effects and what we should be thinking of when controlling these reflections.

In short, when two identical sounds from different sources arrive at the ear with only a small time difference, the ear will localize the sound as coming from the earlier source only. Our ears determine the position of a sound based upon which ear receives it first and then its successive reflections. This arriving sound information, will also give us the perception of depth and spaciousness. Pretty simple!

Much work has been done by many researchers to show that in order to provide a stereo image with precise imaging and good depth perspective there is an optimal initial time window of up to 35mS, after which, room reflections are heard as discrete echoes. This effect is often referred to as the Precedence Effect. When a sound is followed by another sound separated by a sufficiently short time delay, listeners perceive a single auditory event; its perceived spatial location is dominated by the location of the first-arriving sound. The lagging sound reflections can affect the perceived location. However, their effects are suppressed by the relative level of the first-arriving sound.

A special application of the Precedence Effect is the Haas Effect. Haas showed that the precedence effect appears even if the level of the delayed sound is up to 10 dB higher than the level of the direct sound. In this case, the range of delays, where the precedence effect works, is reduced to delays between 10 and 30 ms.

Significant reflections within the first 2-5mS can create an effect called comb filtering. It is like a whooshing effect sometimes called phasing as you move your head left to right. These reflections will come from furniture and acoustical paths that are typically just a foot or so longer than the direct path to the MLP and very often come from seat reflections especially if they are made of leather. You can see some early seat reflections in the following graph at 2mS. These can be reduced/prevented by using cloth seats or covering the tops and rears of leather seats with blanket absorbers.

The initial time delay gap (ITD) is the time interval between the arrival of the direct sound and the first significant reflection from the surfaces of the room. It corresponds with the impression of clarity and intimacy for the listener. If a space has a relatively short ITD gap, it is said to be more intimate; a longer ITD gap indicates less intimacy.

During the ITD no reflections should ever exceed the level of the original sound. The length of the ITD is really a function of how big your room is and how well you can suppress early reflections. The ITD length and what happens to reflections during it is a very important parameter in the design of control and listening rooms.

These control rooms were very popular for many years but have recently fallen out of favor as newer diffusion designs have appeared. However, in their hay day LEDE research provided a lot of valuable information as to how a listening environment should behave with regard to a rooms reflections. See here for a review of the LEDE technique by Don Davis. (My A/V Room is loosely based upon this design concept). The concept relies on a totally none reflective room front in order to prevent reflections arriving at the MLP within the reflection free time zone, and an ITD that is terminated with an added burst of reverb created by a Hass Kicker. This effect is controlled by the design of the reflective back half of the room.

You might ask why is all this done? You perceive a rooms size and acoustics by the length of the ITD and subsequent reflections. So if the mixing engineer, and you the listener, what to hear the space and reverb effects that were recorded you do not want to mask the recorded ITD with your rooms ITD. If yours in much shorter than the one recorded you will not hear the recorded acoustics as they were intended.

Excessive treatment of all primary reflections with large enough porous absorbers can result in the room becoming too dead. This is compensated for by the addition of diffusion at the rear of the room like that of a LEDE room. However, the timing of the reflections from these diffusers needs to be reviewed if they are close to the MLP.

Creating a Hass Kicker is not an essential part of many room acoustic designs, can be difficult in a none dedicated room, and will not be reviewed here. However, achieving the reflection free zone as described above is really a must.

While solution one will certainly prevent the negative interference effects of early arriving reflections, in my experience it tends to produce an uncomfortable acoustic hole behind the listener unless the treated surface is immediately (a foot or two) behind the MLP.

NOTE 1: When placing ANY porous absorption it is essential that the bandwidth of the absorber is wide; ideally at 300Hz to 20KHz. Why? If you only absorb a small range of reflected sound frequencies the rooms acoustic performance will become colored and unbalanced as the absorbers will leave an unbalanced amount of reflected energy. So a reflection path of typically 8 is required. In my experience this generally requires absorbers that are at least 4 deep and often up to 8 depending upon the incident angle of the sound.

NOTE 2.The deployment of too many absorbers can quickly cause small rooms to become too dead and unpleasant acoustically. Reflection problems in many rooms can often be better dealt with using diffusers. These breakup the incident sound wave in to many wavefronts that vary in direction and time for 2D diffusers. This removes the strong single point refection while at the same time keeping the room reverberant.

When deploying solution 2, the diffused sounds should arrive at the MLP at least 20dB lower than the direct sound within the first 8-10mS. This ensures that they will not interefer with stereo imaging or depth perspective but will enhance the openeness of the perceived sound field. An acoustic delay of approximately 10mS means that the rear diffuser needs an acoustic return path length of at approximately 10 feet to the MLP. When using QRDs to diffuse sound this distance is also critical to stopping a condition called lobbing where the QRD acts like an acoustic lens concentrating their reflected energy into narrow beams (see Diffusers below). QRD design and deployment will be briefly reviewed in the next post.

The terms velocity and pressure doesnt describe their inner workings, but instead describe their optimum placement in a room. Pressure based treatments are most effective at areas of high sound pressure in the room, whereas velocity based treatments are most effective at areas of high particle velocity.

The most common and popular bass absorbers are nothing more than a specific application of porous absorbers that are placed at points of high particle velocity. Specific problematic room modes can be dealt with using tuned, resonant sealed panels, that are placed at points of high pressure.

For any room the biggest challenge is bass absorption and there is no one simple solution for this. Unless of course you have lots of available unused space. Absorption at bass frequencies is generally achieved using large porous absorbers and/or resonate panels for specific problematic frequencies. Diffusers are rarely practical. Bass piles up at room boundaries and corners so installing the correct type of absorbers in these locations will provide the largest amount of effective bass absorption.

The depth (D) of all the above bass traps determines the lowest frequency (wavelength) that can be efficiently absorbed. In the ideal world (D) would be equal to 1/4 the wavelength of the lowest frequency that you need to absorb. In practice this is rarely practical as a 40Hz signal has a 1/4 wavelength of over 7 feet. However, even depths shorter than 1/8 or less of the wavelength can significantly help control low frequency modes.

Understanding that the peak absorption occurs at the peak particle velocity for a porous absorber, we see in the following diagram how the peak absorption will change based upon the wavelength/frequency of the signal, air space depth and absorber thickness.

All these porous absorbers are wide band, absorbing the entire frequency range and if extensively deployed without due consideration to mid band and high frequency absorption can cause a room to have too low a reverb time at mid band and higher frequencies.

The other common bass absorber is the panelresonant absorber. These rely on the mass/compliance of a panel or air mass in conjunction with a sealed air chamber to resonate and absorb energy over a band of frequencies. They are placed at points of high sound pressure, typically on walls or in corners.Rooms that only have one or two problematic bass standing waves can use resonant devices that are tuned to those problem frequencies.

Membrane panels have a resonance frequency that depends upon the depth of the trap (D) and the mass of the panel (M). Although quite large for bass absorption the Helmholtz resonator is another popular resonant pressure absorber.

The perforated panel Helmholtz resonator has a resonant frequency that depends upon the depth of the chamber (D), the diameter of the openings (d), the panel thickness (PT) and the panel % perforation.

It is essential that in all resonant designs that the enclosures are completely air tight or they will not resonate at the designed frequency and it will not absorb very well. Also the damping behind the membrane must not touch it or it will significantly reduce the absorption and alter the absorbers bandwidth. If the membrane is not rigid like drywall or plywood and is self damping like Revac or roofing materials (a limp membrane absorber) you can often omit the damping immediately behind the membrane and place it at the rear of the box.

There are many ways to scatter, diffuse or breakup a sound wavefront. The technique used can vary from a simple domed geometrical structure to complex two and three dimensional structures. Like absorbers, diffusers have a diffusion coefficient between 0 and 1, indicating the degree of sound diffusion, 0=no diffusion, 1=100% diffusion. This coefficient, just like that for absorption, will vary with frequency.

All diffusers have a low and high cut-off frequency beyond which they no longer diffuse the incident sound energy, but either reflect it and/or provide some degree of absorption. They all also have a minimum seating distances in order for the diffusion to be effective. Badly designed QRD diffusers or sitting too close to one can result in lobbing. A condition where by the diffusers act as a lens concentrating certain bands of frequencies into areas radiating from its surface called lobes. See below:

In the above diagram the thin lines are for a single panels and the thicker lines are for multiple panels and preferred panel sequences. Note the reduction in discrete lobbing for multiple panels using the correct panel sequence. Also the need to sit a sufficient distance away from the panels in order to be in a uniformly diffused region.

In small rooms and even sometimes large ones getting enough low frequency absorption installed can be very challenging. Equalization at these low frequencies can flatten the rooms frequency response but frequency response alone DOES NOT make a room sound good. One of the major measurements that really impacts a rooms bass performance is its decay time. If it takes too long for a sound to decay the room will become colored and sounds will become muddled and muddy despite the rooms apparently flat frequency response. These two parameters, flat frequency response and fast decay time are not directly linked. You can have a flat frequency response with very long decays, just as you can have a very lumpy frequency response with fast decays. How do you achieve both? Lots of bass absorption, multiple subs with optimum placement and a good equalization system.

The above graph shows the sub decay response of my room. Note how all room modes above 10Hz have decayed by at least 30dB within the first 300mS. The preferred LF decay is generally taken as being at least -20dB in the first 160mS across all bass frequencies; which this graph shows. The long decay at 15Hz is the resonance (ringing) of the room walls and ceiling construction. Not a decaying room mode. (This floating room within a room is a separate isolated structure and is not attached to the main house structure.)

Many automated room equalization programs cannot optimize decay time while at the same time optimizing frequency response..well none that I have used. See here for my experiences equalizing four subs using Audyssey XT32.

The addition and placement of additional subs in a room can significantly improve both axial modes and overall bass uniformity, but bass absorbers are still a pre-requisit for a good low frequency acoustical performance. Multiple subs are NOT a replacement for the lack of bass absorption, although they will help smooth out the rooms frequency response making electronic equalization easier.

NOTE: Almost everybody places sub(s) on the floor, so using subs to improve height axial modes doesnt work unless you raise them off the floor to the appropriate height. Something that is generally not required and is highly impractical for most of us, even with a dedicated and purpose built room.

Single subs are frequently placed in room corners. This is because a corner restricts the area of the subs wavefront providing it with effectively more acoustical output as the sound pressure is not radiating into a sphere. This is particularly true at its lowest frequency range, where the room gainor the boundary effect takes hold. Depending upon the room geometry and seating positions one corner may be better than another. Experimentation is required here.

A common way to determine a single subs best placement is to do the bass crawl. Put the sub where you sit, play some bass heavy music and crawl around your room on your hands and knees in order to determine the smoothest and cleanest sounding bass location. This is where you put your sub. Yes, I know it sounds ridiculous but it does work. Unfortunately you may end up with a location that is just not practical or acceptable to your better half!! So that corner maybe looking really good at the end of the crawl.

Remember, and this is VERY important. When using more than one sub all the subs technical performances must be the same. DO NOT mix different designs of subs like sealed and vented and do not mix different sized subs. Ideally do not mix manufactures and models at all. Why? There are several reasons:

Equalizing a room for best acoustic peformance is more than just getting a flat frequency response. The rooms decay must also be uniform and meet certain preferred criteria as discussed earlier. Achieving a flat frequency response while technically correct has been shown to be less pleasing to many HT listeners than a gradual 10dB fall from 20Hz to 20KHz. See below.

However, flat is flat, and that sets your reference point giving you somewhere to start from and return to. Preference is a whole different issue and is simply what the user prefers to hear, which may or may not be close to what was heard in the studio control room.

Equalizing for both frequency and time (decay) issues is complex, particularly at low frequencies. In a simplistic world a rooms low frequency response can be shown to be composed of a number of resonant frequencies having nodes and antinodes. This is the area below Schroeders critical frequency where the rooms acoustic performance is dominated by standing waves. These discontinuities cause the irregular frequency and time (decay) responses. If we can create exactly the opposite nodes and antinodes for the rooms low frequency response, that is dominated by these room modes (standing waves), both the frequency and time responses will be optimized. The LF waterfall response that you see above was created by doing exactly that.

With modern laptops and software this process is quite simple using free programs like Room Acoustic Wizard (REW). Some automated equalization programs also claim to be able to equalize both frequency and time anomalies. I am yet to be convinced by this; Audyssey XT32, in my experience, certainly doesnt!

There are literally hundreds of free acoustics programs available on line. Many are very basic just calculating room modes and predicted required room absorption, others are are very sophisticated in that they can provide optimized room sizes according to a number of acoustic criteria that you select. Below are a small selection of acoustics programs and further reading:

So now we know how to choose materials, where to place the different types of absorber design and where to place additional subs. In the third and final part we will see how to determine primary reflection points and examine how to build several different types of absorber and QRD diffuser.

vibrating screen, multi deck high frequency screen | h-screening

vibrating screen, multi deck high frequency screen | h-screening

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Vibrating screensare the most important screening machines primarily utilised in the mineral processing industry. They are used to separate slurry feeds containing solid and crushed ores down to approximately 200m in size, and are applicable to both perfectly wetted and dried feed. H-Screening offers high frequency fine screen stakck sizer, linear vibrating screens for fine screening and wet processing, dewatering screens, PLC controlled electromagnetic vibrating fine screen.

7 series products | jbl professional loudspeakers

7 series products | jbl professional loudspeakers

The JBL 7 Series provides a powerful and flexible monitoring solution for music, post and broadcast production. Now available in four modelsthe install 705i and 708i and the powered 705P and 708Pthese monitors deliver exceptional output, stunning detail, an expansive soundstage and impressive accuracy. 7 Series speakers achieve this

outstanding performance by leveraging patent-pending driver technologies and the renowned JBL Image Control Waveguide. All models integrate with the Intonato 24 Monitor Management Tuning System, which provides intuitive remote control and calibration. 7 Series monitors are equally at home in stereo, surround, and immersive-audio production rooms.

Our patent-pending JBL Image Control Waveguide brings exceptional clarity and detail to all 7 Series models. First introduced in our flagship M2 Master Reference Monitor, the waveguide ensures an acoustically seamless transition between the low- and high-frequency transducers, and provides a wide soundstage and precise imaging. Smooth on- and off-axis frequency response allows the JBL 7 Series to deliver neutral reproduction across an expansive listening area in a broad range of rooms.

7 Series monitors leverage JBL patents and our latest driver technologies to provide unparalleled output with greater dynamic range and extended frequency response in demanding production applications. Custom low-frequency transducers utilize patented JBL Differential Drive technology to reduce power compression for more sustained output and extended linear low-frequency performance. Our low-frequency port design works in concert with the low-frequency transducer to produce an accurate bass response at all playback levels.

Each 7 Series monitor is equipped with a proprietary JBL 2409H high-frequency compression driver, which features an innovative low-mass annular diaphragm. This driver delivers extraordinary output, a wide dynamic range and very low distortion even at high SPLs. Competitive monitors utilize radiating dome tweeters, rather than compression drivers, that require amplifier limiter circuitry to prevent failure at higher SPLs which also negatively affects the speakers stereo imaging and dynamic range. 7 Series innovative compression design does not need limiting circuitry and iscapable of reproducing frequencies with a smooth response beyond 36 kHz.

JBL 7 Series monitors provide construction and mounting features that make installation simple. Constructed from rugged birch plywood, the cabinets are specially braced and reinforced to allow safe mounting. Top and bottom mounting points in a two-hole mounting pattern facilitate effortless wall and ceiling installations using readily available brackets. Both vertical and horizontal orientations are supported. Integrated handles aid in speaker positioning.

The 705i (5-inch) and 708i (8-inch) install monitors bring next-generation technology to multichannel monitoring setups in post rooms, broadcast facilities and trucks. Delivering detailed imaging, extended frequency response and remarkable output from compact enclosures, theyre centrally amplified and tuned, and easily installed. 7 Series install monitors form the heart of an elegant, scalable system for broadcast and post facilities working in immersive audio formats.

The 705P (5-inch) and 708P (8-inch) are self-powered reference monitors built with the modern control room in mind. A compact two-way design minimizes interference with video displays and sight lines while providing output comparable to larger speakers. The powered 7 Series monitors feature built-in DSP allowing for integrated EQ and delay controls. You also get an AES/EBU digital input, and an RJ-45 network connection for HARMAN HiQnet connectivity.

7 Series monitors are designed to easily integrate with the JBL M2 Master Reference Monitor to create a modular and scalable system that can be custom configured for the number of channels and the room size. Compact enclosures and integrated mounting points allow versatile mounting options

The JBL Intonato 24 Studio Monitor Management Tuning System is a perfect complement to any 7 Series-based monitoring system. It simplifies setup while offering precise automated calibration and complete control of monitors in stereo, surround and immersive-audio-production rooms. Intonato 24 includes a calibration microphone and innovative Automated Speaker Calibration process that tunes each speaker to compensate for speaker placement and room acoustics, delivering a neutral response to the mix positioneven in less-than-ideal workspaces.

china high frequency screen, high frequency screen manufacturers, suppliers, price

china high frequency screen, high frequency screen manufacturers, suppliers, price

China manufacturing industries are full of strong and consistent exporters. We are here to bring together China factories that supply manufacturing systems and machinery that are used by processing industries including but not limited to: vibrating screen, vibrating sieve, screening machine. Here we are going to show you some of the process equipments for sale that featured by our reliable suppliers and manufacturers, such as High Frequency Screen. We will do everything we can just to keep every buyer updated with this highly competitive industry & factory and its latest trends. Whether you are for group or individual sourcing, we will provide you with the latest technology and the comprehensive data of Chinese suppliers like High Frequency Screen factory list to enhance your sourcing performance in the business line of manufacturing & processing machinery.

high frequency screens and flickering laurent's choice

high frequency screens and flickering laurent's choice

A high frequency monitor means more image rendered on your screen per second. Example in hand, if you have a 60 Hertz screen, your screen will refresh its rendered image 60 times per second. If you have a 100 Hertz refresh rate, then your screen will run at 100 Frames Per Second (FPS).

The only problem is that an abnormal amount of people report having issues with high refreshing rate monitors. No matter the monitor or video card monitor brand, thousands upon thousands of otherwise happy gamer are reporting the very same issue: Flickering (or black screens).

The epileptic nightmare. Imagine going on with your daily business, or playing your favorite video game, and suddenly, your screen goes black.. then comes back.. and then black again, doing so at irregular interval and without obvious reasons.

Your first reflect is to check that your display cable is securely in pace both on your monitor and your video screen, you may even reinstall your video card drivers, or try to OC your GPU. Every one seems to have the same approach.

Before going on to forums and start endless threads, which of some are a decade old with posting of a this very week, make sure to have what it takes to run a high frequency game and high frequency monitor.

Here is the funny thing. To take full advantage of a high refreshing rate, you need a game to output the same or greater Frames Per Second. For example, if you have your screen refresh rate set at 100 Hertz, and your game output only up to 60 FPS, then obviously, you will only see experience a 60 FPS game. You will need enough memory, CPU process, GPU horse power to match or over perform the monitor refreshing rate.

NVIDIA did try (somewhat successfully) to address this with its G-SYNC chip-set which it installs in both its newer GPUs and high performing monitors. This allows the GPU and the monitor to sync both the GPU performances and the monitor refreshing rate to have a matching FPS and refreshing rate as much as possible.

It seems almost trivial to say so, but make sure that your video card can handle such refreshing rates (if produced after 2011, they usually do) and that they are DisplayPort 1.2 compliant at the very least.

To run a high refresh rate monitor, ONLY the Display Port can do so! The HDMI (even 2.0) will lock your frequency at 60 Hertz or below. Any attempt to run your config at a higher refresh rate, will result in an out of range message on your screen.

Display Ports cable ARE confusing. Unlike USB plug, they do not have any color codes, or marking to identify which generation they belong to. Even their boxing seems to purposely not report what gen they are from.

The flickering effect that you so dread is due to the fact that you are using a 1.0 or 1.1 Display Port cable. These cables do not provide enough bandwidth to convey, say, 144 frames per second of 2k resolution. And when you do try, of course, your cable cannot keep up with the massive GPU output and what the monitor needs, to keep a steady flow of video output.

IIf you are going with a high-en gaming monitor, I would go straight to a 1.4 HBR3 cable. They are more expensive (about 35 USD), but you are set for generations of monitors and video cards to come. This new standard can not only deliver 240 Hertz refresh rates to a 4k panel, but it can cater to 5k and 8k panels as well! In short it is future proof!

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high frequency screening: from piles to profit - quarry

high frequency screening: from piles to profit - quarry

The underlaying features of high frequency screens have remained constant, that is, their highly efficient ability to separate particles from around 25mm down to 0.425mm and the capability to handle wetter, stickier materials. What has now developed is the means at which this capability is deployed.

Astec has now produced three track-mounted systems, to be used for a variety of applications. The FT2618VM is the system with the most runs on the board, as it typically runs in-line with Astecs FT2650 tracked jaw crusher and FT300 tracked cone crusher as a final screen for producers wanting to screen for a specific manufactured sand profile. Recently, the high frequency range has increased to include the GT205 multi-frequency tracked screen and the GT165 multi-frequency tracked screen.

{{image2-a:r-w:300}}The GT205 is a direct feed screen with a conventional top deck to screen off top size overs but also includes high frequency technology on the second and third decks to allow a more efficient product cut.

Recent use cases have seen the GT205 being fed recycled gypsum, recycled glass and topsoil. The most intriguing use case has been the processing of otherwise waste material to produce low grade road base that meets local council specifications.

Astec has recently launched the GT165. In this configuration, the multi-frequency screen with its mix of conventional screening on top deck and high frequency lower deck has been arranged for scalping. The benefits of using the multi-frequency configuration in the scalping function is that raw feed (larger rock) can be handled on the top side deck, while the second deck can run a much finer screen cloth that can handle a stickier type of materials often found in scalping applications.

Apart from mobile track-mounted applications, Astec has also sold different sized high frequency screens that have been mounted in a modular frame. With minimal dynamic loading, the structures are modest, robust and can be used for a wide variety of applications. The most common use cases for high frequency screens in static applications include operations processing crusher run of dust into manufactured sand.

To accommodate unique site requirements, static applications of high frequency screens can be configured with multiple decks and differing lengths and widths. One of the strengths of running the high frequency screen is the ability to change the screen angle, frequency and stroke of the individual screen decks. This control allows tuning of the screen to the properties and size of the material being screened, giving precise stratification and optimal screening outcomes.

To date the high frequency screen has been successfully used in manufactured sand, concrete stone, agricultural lime, recycled materials and topsoil. To assist producers in scoping the high frequency screen for their application, Astec offers a complimentary material testing service where customers can test their specific materials on a demo screen at the Astec head office in Brisbane, Queensland.

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