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Loudspeaker Measurement Test Chambers

For far too long loudspeakers have been the poor man of audio, largely out of control and terribly variable. We should ask why?

 

Simply we have not been able to measure loudspeakers consistently!

 

Hill Acoustics introduce the Tetrahedral Test Chambers consistently stable and affordable loudspeaker measurements

 

Making stable, consistent and accurate loudspeaker measurements

What's the Advantage?

The tetrahedral test chamber (TTC) ensures a precisely defined, stable and modally minimised environment. Completely free from set-up variations.

 

This gives precision along with highly accurate and repeatable measurements in a small volume at greatly reduced cost compared to an anechoic chamber. An IEC Baffle, shown above with a TTC350.

Another advantage is that a TTC can measure to much lower frequencies than a conventional anechoic chamber. But a  TTC is not an anechoic chamber.

An anechoic chamber attempts to absorb all reflected energy at all frequencies. In contrast a Tetrahedral Test Chamber is designed with absorption sufficient to clean up high frequencies only.

The theory has been published and is readily available see the technical page.

An equalisation curve is supplied with each tetrahedral test chamber.

Physical Design

The physical design of a Tetrahedral Test Chamber, is based upon the triangle amongst the strongest known structures; it differs from test boxes, by minimising parallel surfaces, which in turn reduces modal effects that seriously interfere with most measurement chambers.

The measurement microphone is fitted inside the chamber at a known and easily set distance. The loudspeaker to be tested is placed so that it's sound is directed into the chamber - towards the microphone, not out of it like a normal loudspeaker enclosure.

Individual sub baffles are then used to adapt individual loudspeaker drive units to the test chambers allowing rapid and very accurate physical location which equates to more stable measurements.

We have experience integrating TTC's into production environments.

50#7 and 68#2to#7.JPG
How Accurate and How Consistent is a TTC?

The top graph shows the response of a single SEAS loudspeaker drive unit #7 measured fifty times with the chamber equalisation applied in a TTC900. The one-third octave curve is the error level at 95% confidence, is less than 0.2dB from 20Hz to 10kHz, even at the loudspeaker drivers resonance, up until 20kHz where the SPL drops off.

The lower graph shows the results of  a seriers of these loudspeaker drive units #2 to #7 but measured sixty eight times. This shows greater variation as would be expected from different loudspeakers. Note: The minimum variance shown in the mid band is 0.25dB, is in agreement with the first graph, so these are genuine loudspeaker response variations.

These graphs demonstrates the control and stability of the measurements that a tetrahedral test chamber can provide, wherever they are used. R&D, QC, production, goods in or repair and refurbishment all can benefit equally.

 
 

ABOUT

ABOUT

Hill Acoustics was formed in 2013, to promote loudspeaker test chambers based upon the Tetrahedral Test Chamber principle expounded by our Chief Technical Officer - Geoff Hill.

 

Loudspeaker measurements have long been a source of excessive variability with typical tolerances of +/- 3dB being the norm, whilst a tolerance of +/-0.1dB is typical for  virtually all the rest of the equipment chain.

 

Long frustrated by the state of loudspeaker measurements Geoff set out to provide a better alternative. Launched in 2013 we built various sizes of chambers whilst refining the theory & design. And understanding that international standardisation was a necessity we pursued this through publication of the principles with: The Audio Engineering Society, ALMA, ISEAT and working with the International Electrotechnical Committee (IEC-TC100), on updates to IEC 60268-5, 60268-21 & 22 and working with the AES SC-04-03 on the Loudspeaker Measurement Chambers, Information Document, AES73id-2019.

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This was achieved in 2018, with the inclusion of the technique as an alternative in IEC60268-21 section 13.1(d) "A test cabinet not in accordance with annex A.1.2 (type-A or type-B), generating a defined air load and radiation condition at the front of the transducer may be used for end-of-line testing and relative measurements (see [15])."

 

Loudspeaker Test Chambers

SOME USERS

CONTACT

Hill Acoustics TTC's are manufactured in the UK by Spectral Measurement under license from Hill Acoustics.

Please contact us now for pricing and availability or for advice on which size to choose!

Spectral Measurement Limited,

Unit 1A, Grovemere House

Lancaster Way Business Park,Ely, Cambridgeshire,CB6 3NW, UK

Inquiries

For any inquiries, questions or comments , please call: +44-(0)1353 648 888 or click the following link TTC enquiry form

Geoff Hill

If you are interested in Consultancy on Loudspeaker Design and or Measurements?

Please send an e-mail to: geoff@geoff-hill.com

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