The Best Bass Traps

Here is the whole page in one paragraph, so you can stop reading if it is enough.

NRC is the average of the absorption coefficients at 250, 500, 1,000 and 2,000 Hz, rounded to the nearest 0.05. It does not include 125 Hz. A bass trap exists to absorb energy at and below 125 Hz. So an NRC figure on a bass trap is a number that structurally cannot describe the product’s purpose — and of the products on this page, only one publishes a 125 Hz coefficient for a corner trap.

The 125 Hz table, which is the only table that matters

The Auralex LENRD’s 250 Hz figure is 1.55 and the ATS flat panel’s is 0.67; the full published curves for both are in the spec tables further down this page.

Read the first and last rows together. The ATS flat panel has a higher 500 Hz coefficient and an NRC of 1.00, and it absorbs 0.12 at 125 Hz. The Auralex corner trap absorbs 1.30. That is roughly a tenfold difference in the band that defines the category, and it is completely invisible in the NRC column.

Even better: compare the LENRD to Auralex’s own 2-inch Studiofoam Wedges, which the same company measured in the same lab under the same standard, and which absorb 0.11 at 125 Hz. Same material, same maker, same test. The difference is the shape and where it sits — and it is a factor of about twelve.

Why coefficients above 1.00 are not a mistake

The LENRD publishes 1.30, 1.55 and 1.53. An absorption coefficient of 1.00 means all incident energy absorbed. So what is 1.55?

It is an artifact of how ASTM C-423 works. The test measures the change in a reverberation chamber’s decay time when a sample is introduced, and calculates absorption from the sample’s stated surface area. A thick sample with exposed edges absorbs energy arriving from the sides too, so it removes more energy than its face area alone accounts for. Divide by the smaller number and you get a coefficient above one.

It is not a claim of 155% absorption and it is not a marketing invention — it is a well-understood property of the standard, and it appears in genuine lab reports throughout the industry. What it does mean is that you should not treat 1.55 as “1.55× better than 1.00”, and that comparing figures across differently-shaped products carries a margin of error the raw numbers do not show.

Why ATS ranks second despite publishing nothing

The ATS Tri-Corner trap publishes one number: an NRC of 0.95 for the 2-inch fiberglass core. No per-frequency curve at all. For a product sold as a bass trap, publishing only the metric that excludes 125 Hz is a real gap and we have said so.

It ranks second anyway because of what it is made of and how it is shaped. It publishes a rigid fiberglass core at 6 lb per cubic foot with 35° mitered edges for corner mounting, and an ASTM E84 Class A fire rating. Density and depth are the two physical properties that determine low-frequency absorption, and a 6 lb/ft³ rigid fiberglass corner section is, on physics, a more capable low-frequency absorber than foam of the same dimensions.

We are telling you our reasoning is physical rather than documentary, because that is exactly the kind of inference this site usually refuses to make silently. If you want a trap whose low-frequency performance is published, buy the Auralex. If you want the material that theory favors and are willing to take the gap on trust, the ATS.

The Primacoustic caveat, and why it drops to third

Primacoustic publishes the whole curve instead of an NRC, which is better practice than anyone else on this page. But read the footnotes.

The kit’s main panels are the 1.5-inch Control Columns, and that row is marked “typical performance based on quarter wavelength calculations” — calculated, not measured. Only the 1-inch Scatter Blocks row is lab-tested, by Riverbank Acoustical Laboratories under ASTM C423-02a and E795-05.

So the kit’s headline low-frequency numbers are theoretical. We publish the measured row in our table above (0.17 at 125 Hz) rather than the calculated one, because presenting a calculated figure as measured is exactly the quiet fabrication this site exists against. It is a well-made kit that does its job at first reflection points; it is not a bass trap.

What a bass trap can and cannot do

A trap absorbs energy. It cannot boost a frequency the room is canceling. Room modes produce both peaks and nulls, and a null — where two reflections arrive out of phase — is a subtraction. Absorption reduces the peak and reduces the reflection that causes the null, which flattens the response overall, but nothing fixes a null by adding material.

That is also the honest limit of the room correction in an AV receiver: boosting a frequency the room is actively canceling just burns amplifier power. Physical treatment and DSP address different halves of the same problem, and below about 200 Hz the physical half does the heavy lifting.

Where to put them, and how many

Corners, and specifically the vertical wall-wall corners behind and beside the speakers first. Pressure is highest at boundaries and highest of all where boundaries meet, so a given volume of absorber does the most work there. Wall-ceiling corners are next.

The LENRD is a 1 ft × 1 ft × 2 ft triangular section, so a floor-to-ceiling treatment of one corner in an eight-foot room is four units. Four corners is sixteen. That is a real cost, and it is why the packs are sold in multiples. Our treatment-quantity guide works through what a room actually needs before you buy sixteen of anything.

What we would buy

The Auralex LENRD, for one reason that outweighs everything else on this page: it is the only corner trap here whose maker publishes a 125 Hz coefficient, and that coefficient is 1.30. You can check the claim. Nowhere else in this category can you.

If you would rather have rigid fiberglass than foam and can accept an undocumented low-frequency response, the ATS Tri-Corner. And if you have not yet treated your first reflection points, do that before any of this — it is cheaper, easier, and changes more.