Welcome to Acoustic Frontiers Blog

Creating a system you love shouldn't be difficult. The Acoustic Frontiers blog is here to help.

THX reference level explained

by ct_acoustic_frontier July 06, 2022

What is 'THX Reference Level'?

Reference level is a calibrated volume setting used for both movie production (in dubbing stages and post production houses) and reproduction (in screening rooms and theaters). The human hearing system is non-linear, especially in the bass, so having a consistent playback level - a reference - is critical if the mix is to translate from one production house to another and audiences are to hear the director's intent in terms of the balance in the soundtrack between dialog, effects and ambiance. />



Reference level for all channels except low frequency effects is calibrated by adjusting the audio chain such that a pink noise signal recorded at -20dB relative to full scale (0dB) creates 85dB sound pressure level as measured with a C weighted SPL meter at the seating locations. Volume levels are adjusted for each channel individually until they read 85dB. The master volume control setting associated with this playback level is then set to a nominal 0dB, or <strong>reference level</strong>. The history behind this is that sound engineers and producers generally work so that the average recording level for dialog in movie soundtrack is -20dB. This allows for 20dB of dynamic range in the soundtrack. The low frequency effects channel is calibrated higher, so that a -20dB signal reaches 95dBC at the seating locations.<img class=theaters and consumer gear.  

What does 'Reference Level' mean for home theater design?

Reference level means two things for home theater design:   1. Speakers and amplifiers must be capable of 105dB peaks If the playback chain is calibrated to produce 85dB for a -20dB signal at the listening position then the speakers and amplifiers could be asked to produce 105dB for a 0dB signal. It is a challenging proposition for an audio system to reproduce this level cleanly, without dynamic compression and to be able to do so reliably. Most standard consumer technologies such as soft dome tweeters are not up to scratch in any reasonably sized room. Speakers should have high sensitivity and high power handling, such as the Procella Audio speakers we recommend and use.   2. Subwoofers must be capable of 115dB peaks The low frequency effects channel is handled slightly differently and has a 10dB boost relative to the other channels. The maximum SPL that subwoofers could be asked to reproduce from the low frequency effects track is therefore 115dB at the listening position. In reality the situation is nearly always worse because the subwoofer must additionally reproduce bass managed* content from other channels. These challenges mean that multiple large subwoofers are typically needed to be able to properly reproduce the soundtrack as the director intended. * Bass managed content is that from other speaker channels that has been diverted to the subwoofer. In home audio video receivers (AVRs) and pre-processors this is done by setting the speakers to small in the bass management menu and specifying a crossover frequency. With surround speakers, for example, an 80Hz crossover is typically used. This means that any content in the surround channels under 80Hz is essentially diverted to the subwoofer. For 5 bass managed speakers an additional 6dB and for 7 bass managed speakers an additional 8dB of output may be required from the subwoofer channel.  

Is your audio system capable of 'Reference Level'?

We have written two calculators that allow you to determine if your speaker/amplifier system and subwoofer systems [forthcoming blog article] are capable of achieving reference level.  

Acoustic Frontiers Demo Room case study

In our demo room we use the Procella Audio P610 speakers. The 'head unit' of these speakers is a P6 with 90dB sensitivity and 300W peak power handling. The listening distance is 11ft maximum in our room. Plugging these numbers into our calculator shows that this speaker is cable of reference level since peak amplifier watts is less than the maximum power handling.  />


<a href=eBook_banner_WO3  



Also in Blog Articles

Room Correction: A Primer

by Nyal Mellor July 28, 2022 0 Comments

Much confusion still exists about what a room correction product does, what problems it can (and cannot) solve and therefore its 'place' in a modern high quality sound reproduction system. Part of the challenge of understanding room correction is that it requires a reasonable level of understanding of sound quality, acoustic science, acoustic measurement and psychoacoustics (how humans perceive sound). The majority of the articles I have read online or in print magazines do not cover the fundamentals in enough depth to allow the curious and committed reader a chance to understand room correction on anything more than a cursory level. By the end of this article I hope that you will have learnt enough to judge for yourself what room correction can and cannot do and how best to apply it in the context of a world class music or home theater system.

Continue Reading

Acoustic Frontiers Blog

by Shopify API July 19, 2022 0 Comments

Continue Reading

We are giving away $1800 in free services!

by ct_acoustic_frontier July 06, 2022 0 Comments

Continue Reading

Contact Us About This Product


Nyal Mellor, Founder, Acoustic Frontiers

  • (415) 524-8741
  • Serving USA & Canada
  • Fairfax, Northern California, USA

ask us a question about this product