Acoustic Door Seals FAQs (Courtesy: Norsound Ltd.)

Can I stop an acoustic seal at the ironmongery points?

No, absolutely not! Any weakness in the seal such as a break or void for the latch to pass will allow sound to literally stream through. Tests have shown that doors where acoustic seals have been fitted but stopped and started at ironmongery positions simply cannot reach either their desired performance but in many cases base Building Regulation required performance.

Do I need to specify a ‘specialist acoustic door blank‘ for standard Document ‘E‘ 29db ratings?

No, the Norsound range of seals offers the specifier a simple, low cost solution to the problem. Put simply the normal GDC or solid timber cores are excellent acoustic barriers and when used correctly with the seals offered in this website you can easily reach 29dB and more. Obviously if you are looking for more than the normal decibel reduction for a specific application you may be forced to look at the expensive alternatives but as a general rule this can be avoided in most applications at a very significant saving for the client.

Do I need to put a seal at the base threshold?

Yes, as sound has no up nor down the top, sides or base carry equal penetration opportunities for it, we must ensure a proprietary seal has been fitted ALL ROUND THE DOOR LEAF to create the performance specified in this, or any other for that matter, publication.

Would the perimeter seal have lower opening and closing forces than standard smoke seals?

Yes, quite possibly, the Norsound 710 is positioned next to the door stop and as such is not affected by door growth to the same degree as a centrally fitted seal. To understand door growth look at the diagram below and you will see the door is at its biggest at the point smoke seals are fitted, the perimeter seal sees the door reducing in length as it closes easily over its location.

As you can see the arrow labelled door growth line dictates the two points at which the door leaf is at its longest, as the door closes we call this ‘door growth‘ and it is at it‘s worst when it passes over the typical intumescent smoke seal position.

Do I need smoke seals with the Norsound range of acoustic seals?

Not in the vast majority of cases, all seals that have an acoustic capability resist ‘airborne sound‘ and as such will resist the passage of air. Norsound have carried out a full smoke sealing test regime in accordance to BS 476 Part 31:1.

Why detail a ‘specific acoustic seal‘ over an intumescent based ‘acoustic seal‘?

Primarily the problem of ironmongery stops most of the centrally situated intumescent seals offering a complete perimeter seal. Tests have shown that seals with breaks for ironmongery simply fail to perform. The seals themselves will work if uninterrupted but latches typically throw 6mm between the stop and break, simply not enough to continue the seal blade.

What have I to be wary of when specifying acoustic seals?

Test evidence! Always ensure that seals you are specifying are suitable for the application you intend to use them in. This may seem an obvious point however in acoustics many companies simply will omit to tell you that their seals have no evidence if certain ironmongery is used, if the doors are latched, if the seals are set as normal or do they need moving etc. This is an area where specification is advised to be thorough, it is indeed ‘buyer beware‘. The Norsound range offers clear and tested evidence in single or double leaf applications where the leaves are latched or unlatched, we believe this is a major move forward in the acoustic seal industry.

Can I glaze an acoustic door?

Yes, glazing offers excellent acoustic performance.

What is meant by a decibel reduction?

Decibel reduction is a term that states desired / tested performance in regards to the acoustic performance of a structure. It is typical that Building Regulations Document ‘E‘ a 29 ‘decibel reduction‘ from a doorset will be requested, by this we mean sound will be reduced by 29 decibels when passing through the doorset.

How are door values calculated?

Airborne sound transmission is determined from the difference in sound pressure levels measured across a test sample installed between two reverberant rooms. The sound pressure level in Decibels is measured under the following calculation:

Difference = sound pressure in source room - sound pressure in receiving room

All calculations are carried out under the relevant sections of BS EN ISO 717-1: 1997

Will a simple smoke seal give any acoustic performance?

Yes, but this performance is normally under the 29dB rating stipulated by Document ‘E‘ together with the seal being normally broken for ironmongery due to its intumescent (fire rating) location. Any seal that restricts the passage of airborne sound will effectively give an acoustic seal however these must have values that are of use to the specifier, in general brush smoke seals do not reach minimum performance levels.

What are the basic differences between an acoustic door and a non acoustic fire door?

Not as much as you might think! Standard fire doors can be used as ‘acoustic‘ doors should the correct combination of seals be used to ensure the performance is optimised. Acoustic doors which are intended to perform over the Document ‘E‘ levels will invariably be of specific construction and in essence completely different products, these cores can achieve over 40dB reduction, they come to order and at a price!

How are acoustic door seals tested?

Norsounds range has been tested within the UK in accordance with BS EN ISO 140-3: 1995. The basic laboratory consists of two rooms, a ‘source room‘ and a ‘receiving room‘. To give an idea of the scale of this test the source room in one of our tests was 115 cubic metres and the receiving room 300 cubic metres. A broad band of noise is generated via an electronic generator, powered through an amplifier and loudspeaker. The receiving room has a microphone mounted on an oscillating boom which in turn is connected to a real time analyser.