University of Liverpool Rotblat Lecture Theatre

University of Liverpool Rotblat Lecture Theatre

 

1.0 Project Brief

 

PDA Ltd was commissioned by the University of Liverpool to undertake the acoustic design and coordination of the five month fast-track project to remodel and refurbish the Rotblat and Barkla lecture theatres within the Chadwick Lecture Building at the University of Liverpool.  Work was carried out during the summer on the old Rotblat and Barkla lecture theatres, transforming them into the new 400 seat Rotblat Lecture Theatre. The project also included a full mechanical and electrical refurbishment including a new plant room structure, refurbishment of the toilet facilities, plus the creation of accessible toilets and a Changing Places facility, the first on the University’s campus. The PDA Ltd brief was to undertake the full acoustic design of the building for the University including the following:

 

• Conceptual design input
• Room acoustic design
• Envelope sound insulation
• Internal sound insulation between sensitive spaces
• Mechanical services noise control to the interior and exterior
• Assessing Contractor and sub-contractor proposals
• Design team meetings
• Site inspections

 

In addition to meeting industry standard requirements the brief was to interpret and achieve the SKA requirements for the building in terms of D25 Plant Noise Assessment, and also for planning requirements in terms of plant noise break-out.

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1:  The Finished Lecture Theatre

 

2.0 Acoustic Challenges

 

The main challenges for this project were in terms of spatial constraint as follows:

 

• There were ceiling height limitations as the existing roof soffit height and projection of down-stand beams below this reduced the available depth for ventilation and air conditioning ductwork. This was not a problem in the previous lecture theatre as it was served via ductwork routed through the walls and wall mounted vents.  However, the new lecture theatre needed a distributed ventilation system with ceiling mounted supply and access diffusers to achieve the required thermal comfort.  A number of 90-degree bends were required on the supply and extract routes to navigate to and from the roof-top AHUs from the extract grilles and diffusers.  Both the limited duct cross-sectional areas available and the contorted nature of the duct routes, in addition with the diffuser configurations required to give adequate throw, led to challenges in suppressing airflow regenerated noise from the supply and extract systems, a common problem in this type of refurbishment.

 

 

Figure 2:  Supply Duct from roof top AHU (from below) showing bends required to clear down-stand beams in Lecture Theatre (Air flow direction in green)

 

• Ceiling height limitations further caused challenges due to the existing building envelope and down-stand beams. This led to challenges with configuring the ceiling reflectors to optimise the room acoustic design.

 

• Access requirements for the ceiling mounted supply and extract ducting was a potential issue. This required at least 600mm spacing between ceiling reflectors, thus adding further challenges in getting even coverage of reflections from the lectern position across the seating rake, and in achieving a doubling up of reflections at the rear of the rake.

 

• The openings to the ceiling void between the reflectors increased the potential for regenerated noise break-out to the auditorium from ducts, and also regenerated noise from the extract grilles which are normally protected by a full ceiling working as a plenum.

 

3.0 Acoustic Design and Site Support

 

The technical challenges were overcome in the design process as follows:

 

• Design software was developed to allow optimisation of the reflectors for maximum speech intelligibility (see Figure 3 below).

 

 

Figure 3: Vertical section showing throw of sound via overhead reflectors from lectern

 

 

• CATT Acoustic ray tracing modelling was used to verify the optimised reflector design and to design the lecture theatre to University standards in terms of reverberation and speech intelligibility (see Figure 4 below).

 

 

 

Figure4: CATT® Ray Tracing Model of Proposed Lecture Theatre

 

• The mechanical services systems to the interior were carefully assessed and secondary silencers were applied to supply and extract systems to reduce airflow regenerated noise emission from the ventilation system which necessarily had a contorted route within the existing building.

 

• Lagging was applied to the closely spaced duct bends where increased regenerated noise to the interior was predicted due to airflow turbulence.

 

• Primary attenuators to the interior and exterior were designed based on standard attenuation models.

 

Site visits were undertaken to ensure that the mechanical services mitigation (including smooth routing of ductwork and connections to reduce airflow regenerated noise) and reflector geometries were correctly implemented along with the other acoustic finishes in the building.  In addition the PDA Ltd sound insulation design in terms of lobbies and party structures to plant room and circulation spaces were correctly carried out.

 

4.0 The Building in Use

 

Commissioning showed that the building performed exactly to the required standards in terms of internal noise levels and room acoustics.

 

The University are extremely pleased with the building and are using the specification and design as a template for all further lecture theatre refurbishments as shown in the University Press Release (https://news.liverpool.ac.uk/2019/11/15/chadwick-building-lecture-theatres-refurbished/).

 

In addition PDA Ltd have been commissioned to oversee the acoustic design of four further lecture theatre refurbishments since this date, the first being the Hele Shaw lecture theatre in the Engineering Department, this having been completed in August 2022.