Acoustic product development, troubleshooting and R&D

The result came back below target. What now?

A failed test is almost never a mystery. In our experience the number is lost in a small number of predictable places, and most of them are cheaper to fix than the manufacturer expects.

• Seals, thresholds and perimeter detailing — on doors and windows this is the single most common cause, and it is usually the cheapest to correct
• Flanking and mounting conditions rather than the element itself
• A cavity that is the wrong depth for the frequency range that governs the rating
• A coincidence dip sitting inside the band that determines the single-number result
• Panel mass distributed inefficiently — more weight in the wrong place, no gain in the rating
• Missing or misplaced damping, so the panel radiates energy the material was supposed to absorb
• An absorber with the right high-frequency performance and almost nothing below 500 Hz, where the specification is actually decided
• A specimen built for the test that does not represent the production product — or the reverse

What we do

• Acoustic product development — new products where acoustic performance is part of the specification: absorbers, acoustic panels, doors, windows, partitions, floors, barriers, enclosures, silencers, ducting, machinery and HVAC equipment. Concept, prototype, measurement, improvement, validation.
• Product acoustic troubleshooting — you have a product that does not reach the performance it was designed for. We investigate why, quantify each contribution, and give you a ranked list of changes with expected gain.
• Acoustic design optimisation — material, geometry, thickness, cavity depth, damping, decoupling, seals, perforation ratio, facing and backing. The objective is not simply more performance, it is more performance without unnecessary weight, thickness or manufacturing cost.
• Prototype testing and development cycles — test A, analyse, modify, test B, verify. Each round is designed to answer a specific question, rather than testing variants and hoping.
• Competitive benchmarking — you give us your product and two competitors. We measure all three under the same conditions and show you where you lose, in which frequency bands, and what it would take to close the gap.
• Design for target performance — you need NRC ≥ 0.80, or Rw 50, or a sound power level below a contractual limit. We develop toward the target rather than testing to discover you missed it.

The numbers that decide your rating

Most products that miss their target miss it for reasons that are predictable from first principles. These are the mechanisms we look at first.

• A small gap dominates everything. An open area of roughly 1% of a partition caps its transmission loss at around 20 dB, no matter what the element itself is capable of. This is why door seals, thresholds and service penetrations decide so many results — a leaf tested at Rw 40 sealed can lose several decibels through a gap of a few millimetres.
• Mass has diminishing returns. Doubling the mass of a single leaf buys about 6 dB in theory, and commonly 4–5 dB in practice. Adding a second leaf with a cavity buys far more for the same total weight — provided the mass-spring-mass resonance sits below the range that matters.
• Below that resonance, a double wall is worse than a single one. A cavity tuned wrongly does not merely fail to help; it actively costs performance at low frequency.
• The coincidence dip is where the single number is usually lost. 12.5 mm plasterboard dips around 2.5–3 kHz; 6 mm glass around 2 kHz. Stiffer and thicker panels move the dip lower, straight into the bands that govern the rating.
• A porous absorber needs depth. Effective absorption requires material thickness approaching a quarter of the wavelength. At 250 Hz that is around 340 mm; at 125 Hz around 690 mm. This is why a 50 mm panel with excellent high-frequency figures collapses at low frequency — commonly α above 0.9 at 1 kHz and in the region of 0.2 at 125 Hz.
• An air gap behind the panel is nearly free performance. Moving a 50 mm absorber 50 mm off the wall shifts useful absorption down in frequency without adding a single millimetre of material or a gram of weight.
• NRC does not include 125 Hz at all. NRC is the average of the absorption coefficients at 250, 500, 1000 and 2000 Hz, rounded to the nearest 0.05. A product can carry NRC 0.80 and do almost nothing at 125 Hz — which is exactly where the complaint that sent your customer looking usually sits. ISO 11654 αw behaves similarly.
• Perforated facings have a limit. Below roughly 15–20% open area, the facing itself begins to restrict the absorption of the material behind it.

These are the mechanisms, not your result

The figures above are physics, not a prediction for your product. Which mechanism is costing you performance, and what it is worth correcting, comes out of measurement on your actual product.

Products we work on

• Acoustic panels, baffles, ceiling systems and wall absorbers
• Acoustic doors, door sets, seals and hardware
• Windows, glazing units and façade elements
• Partitions, drywall systems, floating floors and floor build-ups
• Noise barriers, screens and cladding systems
• Machine enclosures, acoustic housings and cabinets
• Silencers, attenuators, louvres and ducted systems
• Industrial machinery, pumps, compressors and generator sets
• HVAC equipment, air handling units, chillers and cooling towers
• Consumer products and appliances where perceived sound quality matters
• Automotive and rail components, trim and insulation packages
• New and recycled materials being developed for acoustic use

How a development cycle runs

Each round is designed to answer one question. Testing five variants at once tells you which was best; it does not tell you why, and it does not help you with the next product.

• Establish the baseline — measure the current product and identify which frequency bands actually determine the single-number rating you are chasing
• Diagnose — separate the contributions: element, seals, flanking, mounting, radiation. Intensity mapping, near-field scanning and component-level measurement as required
• Model the change — predict what each candidate modification will deliver, before anyone builds anything
• Build and test the variant — a targeted prototype, tested under laboratory conditions
• Compare against prediction — where measurement and prediction diverge, that divergence is itself information about the product
• Iterate or verify — once the governing mechanism is identified, the direction of the fix becomes far clearer
• Final accredited test — carried out by the laboratory, under its accreditation, for the certificate you present to your customer

Improving performance without adding cost

Adding mass, thickness or layers will almost always improve an acoustic result. It will also make the product heavier, larger, more expensive to ship and harder to install — and it frequently prices the product out of the market it was designed for. The engineering question we are actually paid to answer is the constrained one: reach the target within the weight, thickness, cost and manufacturing envelope the product has to live in. That usually means moving material rather than adding it, changing where a cavity or a damping layer sits, or correcting a detail that is quietly costing several decibels for no benefit at all.

Competitive benchmarking

A specification sheet tells you a competitor's single-number rating. It does not tell you how they achieved it, where their performance falls away, or whether their number was obtained under conditions your product would also enjoy. Measuring your product and your competitors' side by side, under identical conditions, in third-octave bands, answers a different set of questions: where you genuinely lose, where you are already ahead and are failing to say so, and whether the gap is a fundamental design difference or a detail worth two days of work.

Independent consulting, independent testing

Geonoise is a consulting company. We are not a testing laboratory, we hold no testing accreditation, and we issue no test certificates. Accredited testing is performed by a laboratory under its own accreditation and its own impartiality controls. The result it issues is not ours to influence, and we would not want it to be — a certificate that could be influenced by the consultant is worth nothing to the customer you are trying to sell to. We work with test data from any accredited laboratory, including reports you already hold. Our advice does not change depending on where the testing was done.

Standards & method

ISO 354 · ISO 10534-2 · ISO 11654 · ASTM C423 · ISO 10140 series · ISO 717-1 · ISO 717-2 · ASTM E90 · ASTM E413 · ASTM E492 · ISO 3741 · ISO 3744 · ISO 9614 · ISO 11201 · ISO 11546 · ISO 11691 · ISO 7235 · ISO 15665 · EN 1793

FAQ