Primacoustic - Acoustical Solutions

The impulse response chart maps how a room responds to a burst of sound. The vertical axis is amplitude or loudness the horizontal axis is time. For small rooms the test can be as short as 100ms.

A Theoretical impulse wave animated in two dimensions. In the real world wave propagation is very complex.

GREEN= Impulse wave from speaker.

A loudspeaker excites the air space, then abruptly shuts off.

RED= Early reflections.

Reflections off the side walls, floor and ceiling are almost as powerful as the direct impulse wave and can interfere with speech intelligibility and stereo imaging.

PURPLE= Secondary reflections.

Weaker because they have traveled further, secondary reflection arrive at the mic behind the early reflections. Secondary reflections helps the brian to sense the size of the space.

YELLOW= Diffuse reflections.

Having reflected off of two or more surfaces, diffuse reflections create the what is perceived as reverb. The brain uses this data to sense what the walls of a room are made of.

The impulse response test is well suited to determine the effectiveness of acoustic diffusion treatments like the Primacoustic Razorblades.

The impulse response test charts the way reflected sound waves behave within a room. The test uses an short duration sound burst to excite the air space with a loudspeaker. The rooms response to the burst is captured for analysis.

Think of clapping your hands in a parking garage. Your clap is the impulse wave and the test starts the moment after the clap. The resulting sound waves form the impulse response as they bounce around the garage.

In room acoustic, where a loudspeaker is the sound sound source, the first three room reflections form a critical acoustic fingerprint for the listener. They are:

Early reflections
Secondary reflections
Diffuse field reflections

The brain processes the information from these reflections to sense the size of the acoustic space and what its made of.

Early reflections are the first reflections of the impulse wave to arrive at the test microphone. Our animated room graphic shows what typically happens in small rooms. The first and loudest early reflections come from the side walls because that is the shortest reflected path between the loudspeaker and the listener. On the response chart the first loud spike represent these early reflections. Many more early reflections follow in decreasing amplitude reflected from other room surfaces and transverse angles.

Secondary reflections arrive behind the early reflections. The second large spike on the chart represents secondary reflections from the rear and side walls.

The brain uses information provided by secondary reflections to gauge the size of a space. The longer the delay between the impulse wave and secondary reflections the larger the room.

The brain knows that, having traveled further, secondary reflections are naturally weaker. This poses an acoustic problem for studios and home theaters. The close proximity of the rear wall can set up a situation where the secondary reflections arrive with as much or more energy than the early reflections. The brain tries to deal with the unnatural acoustic but eventual ear fatigue results.

Diffuse field reflections are a complex propagation of the acoustic energy between many room surfaces. The time interval between reflections is overlapping and the ear hears the multitude of reflection as a single wash of reverb. This is shown on the chart as a dense field of low amplitude spikes. They are much weaker now, having bounced off of two or more surfaces, and eventually fade away altogether.

These diffuse reflections also carry information about the acoustic space to the brain. There is a natural attenuation of very high frequencies in the diffuse field time region because of the directional characteristic of high frequencies and their nature to be absorbed by soft materials. Since diffuse reflections have bounced off of more surfaces there is more opportunity for high frequencies to be absorbed.

Think back to the parking garage and the sound after the hand clap. The concrete surfaces and nearly 100% reflective and the diffuse field will return a high portion of high frequencies. The resulting diffuse field will sound bright compare to the same clap test done in a log cabin. Wood absorbs high frequencies and the diffuse field in a log cabin would sound darker because less high frequencies are being returned as reflections.

Interpreting the Razorblade Result Charts

The impulse response test is conducted twice in the test room. The first test is done in an empty room with no acoustic treatments (red chart). The second test is performed with the Razorblade mounted on the receiving wall or rear wall(blue chart). Comparing the charts side by side reveals the diffusion effect.

The red chart shows us the test room has a very strong secondary reflection that is louder than the early reflections. This is common in rooms where a set of loudspeakers are pointed directly at the rear wall. The blue chart shows the effect the Razorblade has made. The secondary reflections are lower in amplitude, the reflections are denser and spread out over a longer period of time. The same can be seen by analyzing the reverb decay portion of each chart. In the room treated with the Razorblade the reverb decay is denser showing more amplitude spikes packed in tighter.

Although this test was performed with the Razorblade mounted on the receiving wall the same effect is possible to apply to the early reflections by employing diffusion on the side walls to break up the first early reflection.

Here's a tip: Invest in books! A full height bookcase across the rear wall is an excellent diffuser for home theaters. The spines of the books will reflect some high frequencies and the randomness of the book sizes will act like the wells of the Razorblade, breaking up the reflections, slowing them down and returning them to the space. Books have excellent mass for their size and can have significant low frequency resonance to absorb bass frequencies.



	Back To Last Page Impulse Response Test Results What is it and what does it test for How is it tested Interpreting the results graph The impulse response chart maps how a room responds to a burst of sound. The vertical axis is amplitude or loudness the horizontal axis is time. For small rooms the test can be as short as 100ms. A Theoretical impulse wave animated in two dimensions. In the real world wave propagation is very complex. GREEN= Impulse wave from speaker. A loudspeaker excites the air space, then abruptly shuts off. RED= Early reflections. Reflections off the side walls, floor and ceiling are almost as powerful as the direct impulse wave and can interfere with speech intelligibility and stereo imaging. PURPLE= Secondary reflections. Weaker because they have traveled further, secondary reflection arrive at the mic behind the early reflections. Secondary reflections helps the brian to sense the size of the space. YELLOW= Diffuse reflections. Having reflected off of two or more surfaces, diffuse reflections create the what is perceived as reverb. The brain uses this data to sense what the walls of a room are made of. The impulse response test is well suited to determine the effectiveness of acoustic diffusion treatments like the Primacoustic Razorblades. The impulse response test charts the way reflected sound waves behave within a room. The test uses an short duration sound burst to excite the air space with a loudspeaker. The rooms response to the burst is captured for analysis. Think of clapping your hands in a parking garage. Your clap is the impulse wave and the test starts the moment after the clap. The resulting sound waves form the impulse response as they bounce around the garage. In room acoustic, where a loudspeaker is the sound sound source, the first three room reflections form a critical acoustic fingerprint for the listener. They are: Early reflections Secondary reflections Diffuse field reflections The brain processes the information from these reflections to sense the size of the acoustic space and what its made of. Early reflections are the first reflections of the impulse wave to arrive at the test microphone. Our animated room graphic shows what typically happens in small rooms. The first and loudest early reflections come from the side walls because that is the shortest reflected path between the loudspeaker and the listener. On the response chart the first loud spike represent these early reflections. Many more early reflections follow in decreasing amplitude reflected from other room surfaces and transverse angles. Secondary reflections arrive behind the early reflections. The second large spike on the chart represents secondary reflections from the rear and side walls. The brain uses information provided by secondary reflections to gauge the size of a space. The longer the delay between the impulse wave and secondary reflections the larger the room. The brain knows that, having traveled further, secondary reflections are naturally weaker. This poses an acoustic problem for studios and home theaters. The close proximity of the rear wall can set up a situation where the secondary reflections arrive with as much or more energy than the early reflections. The brain tries to deal with the unnatural acoustic but eventual ear fatigue results. Diffuse field reflections are a complex propagation of the acoustic energy between many room surfaces. The time interval between reflections is overlapping and the ear hears the multitude of reflection as a single wash of reverb. This is shown on the chart as a dense field of low amplitude spikes. They are much weaker now, having bounced off of two or more surfaces, and eventually fade away altogether. These diffuse reflections also carry information about the acoustic space to the brain. There is a natural attenuation of very high frequencies in the diffuse field time region because of the directional characteristic of high frequencies and their nature to be absorbed by soft materials. Since diffuse reflections have bounced off of more surfaces there is more opportunity for high frequencies to be absorbed. Think back to the parking garage and the sound after the hand clap. The concrete surfaces and nearly 100% reflective and the diffuse field will return a high portion of high frequencies. The resulting diffuse field will sound bright compare to the same clap test done in a log cabin. Wood absorbs high frequencies and the diffuse field in a log cabin would sound darker because less high frequencies are being returned as reflections. Interpreting the Razorblade Result Charts The impulse response test is conducted twice in the test room. The first test is done in an empty room with no acoustic treatments (red chart). The second test is performed with the Razorblade mounted on the receiving wall or rear wall(blue chart). Comparing the charts side by side reveals the diffusion effect. The red chart shows us the test room has a very strong secondary reflection that is louder than the early reflections. This is common in rooms where a set of loudspeakers are pointed directly at the rear wall. The blue chart shows the effect the Razorblade has made. The secondary reflections are lower in amplitude, the reflections are denser and spread out over a longer period of time. The same can be seen by analyzing the reverb decay portion of each chart. In the room treated with the Razorblade the reverb decay is denser showing more amplitude spikes packed in tighter. Although this test was performed with the Razorblade mounted on the receiving wall the same effect is possible to apply to the early reflections by employing diffusion on the side walls to break up the first early reflection. Here's a tip: Invest in books! A full height bookcase across the rear wall is an excellent diffuser for home theaters. The spines of the books will reflect some high frequencies and the randomness of the book sizes will act like the wells of the Razorblade, breaking up the reflections, slowing them down and returning them to the space. Books have excellent mass for their size and can have significant low frequency resonance to absorb bass frequencies.

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