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Chapter 13 Loudspeaker Cabinets
Published in Douglas Self, Audio Engineering Explained, 2012
Also known as ported enclosures, vented boxes or phase inverters, reflex enclosures use openings, or ports, to tune the cabinet resonance to a desired frequency. Effectively, the air in the port, which maybe a simple hole or a tube, acts as a mass which resonates with the spring created by the air inside the cabinet. In Figure 13.5 , a mass is shown suspended below a spring. Almost everybody will intuitively know what would happen if they were to pull down on the weight and then let go—the weight would spring back and the system would go into oscillation until the energy was finally dissipated. Adding more weight would cause the oscillation to slow down, as would using a weaker spring. Therefore:
Acoustics and acoustic devices
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2012
Instead of attempting to lose the backwards radiated sound energy by fitting a large baffle or a closed box to the loudspeaker, several designs actually redirect this energy so that it contributes to the total sound reaching the listener. The trick is to reverse the phase of the back wave before sending it on its way, and this will then add to the forward wave (at least at low frequencies) instead of cancelling it. This can provide greater efficiency and bass extension than the closed-box system. In the most usual type of bass reflex enclosure (Figure 2.63(b)) there is a vent or port, generally let into the front panel and having an associated outlet tunnel or pipe. The dimensions of the vent are carefully calculated so that vibrations of the mass of air contained in it will resonate at the same frequency as the main cone–enclosure system. In this condition the air in the vent will move back and forth in step with the main cone at low frequencies and thus reinforce it. Vented enclosures are relatively large, when wellextended bass is required. It may be noted that, whereas the typical bass drive unit has a much increased load impedance at resonance due to the generation of a high `back-e.m.f.', reflex loading restricts cone movement at resonance. This produces a dip in the impedance curve at resonance with smaller peaks at either side. Further tuning (broadening) of the response can be effected by introducing acoustic resistance or air friction to the vent in the form of wool padding or other porous material. As an alternative to the open vent, some designs employ an auxiliary bass radiator (ABR) which consists of a passive non-driven cone assembly of about the same dimensions as the main driver
Acoustics and acoustic devices
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2013
Bob Walker, Talbot-Smith Michael, Chris Woolf, John Borwick, Francis Rumsey, John L. Andrews, Peter Baxandall, Alan Tutton
In the most usual type of bass reflex enclosure (Figure 2.63(b)) there is a vent or port, generally let into the front panel and having an associated outlet tunnel or pipe. The dimensions of the vent are carefully calculated so that vibrations of the mass of air contained in it will resonate at the same frequency as the main cone-enclosure system. In this condition the air in the vent will move back and forth in step with the main cone at low frequencies and thus reinforce it.
Use of gaming technology to bring bridge inspection to the office
Published in Structure and Infrastructure Engineering, 2019
Muhammad Omer, Lee Margetts, Mojgan Hadi Mosleh, Sam Hewitt, Muhammad Parwaiz
The research presented herein proposes the combined use of VR and LIDAR as a novel tool for the inspection of bridges and demonstrates its use for a typical masonry bridge. Terrestrial LIDAR is used to digitise the geometry of a selected masonry bridge. This results in a point cloud where each point has x, y, and z coordinates together with an RGB intensity value. The point cloud is rendered to produce surfaces, using post-processing software, which is then ported to a VR environment which depicts a real-world scenario. The vision is that engineers could perform Principal Inspection in VR, overcoming the drawbacks discussed earlier that are associated with conventional techniques, thus, improving the overall standard of Principal Inspection. It is intended that the proposed methodology will contribute to a revision of the industrial standards of Principal Inspection. Instead of the office going to bridges, the bridges come to the office.