Physics of frequency response irregularity around 500-600hz?

[reza]

I'm going through measurements of two way monitors (with crossover frequencies of around 2kHz), and so many of them exhibit this anomalous behavior (usually either a dip or a peak, but sometimes a full somersault) around 500-600Hz. I thought maybe the driver size and the wavelength at that frequency are similar and somehow that causes interference or something. But they're not, wavelength of a sine wave at 500 Hz is around half a meter, not 5-7 inches.

This is present to varying degrees in even well measuring speakers. I have pasted a few links here, but there are a lot more.

Is this a known phenomenon? What causes it? Their prevalence makes me think that some wave mechanical effect is involved, but I have no idea what.

SoundStageNetwork.com | SoundStage.com - NRC Measurements: Dynaudio Special Forty Loudspeakers

www.soundstagenetwork.com

SoundStage! Measurements - Ascend Acoustics Sierra-1 Loudspeakers (9/2007)

SoundStageNetwork.com | SoundStage.com - NRC Measurements: KEF LS50 Loudspeakers

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SoundStage! Measurements - Revel Concerta M12 Loudspeakers (2/2006)

SoundStageNetwork.com | SoundStage.com - NRC Measurements: Focal Electra 1008 Be 2 Loudspeakers

www.soundstagenetwork.com

 

[Deleted member 46664]

I'm going through measurements of two way monitors (with crossover frequencies of around 2kHz), and so many of them exhibit this anomalous behavior (usually either a dip or a peak, but sometimes a full somersault) around 500-600Hz. I thought maybe the driver size and the wavelength at that frequency are similar and somehow that causes interference or something. But they're not, wavelength of a sine wave at 500 Hz is around half a meter, not 5-7 inches.

This is present to varying degrees in even well measuring speakers. I have pasted a few links here, but there are a lot more.

Is this a known phenomenon? What causes it? Their prevalence makes me think that some wave mechanical effect is involved, but I have no idea what.

You can have a resonant reaction at 1/2 wavelength which at 550hz is about 12 inches.
Might be a box resonance... ?

 

[alex-z]

Baffle edge diffraction would be my first guess, followed by a port resonance. Hard to say without more detailed data, like testing the same speaker with a plugged port, and a full CEA-2034 sweep.

 

[reza]

You can have a resonant reaction at 1/2 wavelength which at 550hz is about 12 inches.
Might be a box resonance... ?

I suppose it could be a box size resonance together with a quarter wavelength resonance. I hadn’t thought about that.

Although it still looks suspicious that some of those speakers have a step function at that frequency, and some others have a delta function. Could resonance manifest in the form of step or its derivative?

 

[reza]

Baffle edge diffraction would be my first guess, followed by a port resonance. Hard to say without more detailed data, like testing the same speaker with a plugged port, and a full CEA-2034 sweep.

Do those tend to happen around 500 Hz?

 

[alex-z]

Do those tend to happen around 500 Hz?

Depends on the dimensions of the baffle, sizing of port, placement of port, design of the port, etc.

But yes, 500-600Hz is a common range for port resonance issues. Even good designs like the LS50 Meta for example have a 600Hz port resonance, albeit suppressed by 15-20dB.

 

[reza]

Depends on the dimensions of the baffle, sizing of port, placement of port, design of the port, etc.

But yes, 500-600Hz is a common range for port resonance issues. Even good designs like the LS50 Meta for example have a 600Hz port resonance, albeit suppressed by 15-20dB.

That makes sense. Thank you.

 

[Deleted member 46664]

I suppose it could be a box size resonance together with a quarter wavelength resonance. I hadn’t thought about that.

Although it still looks suspicious that some of those speakers have a step function at that frequency, and some others have a delta function. Could resonance manifest in the form of step or its derivative?

Resonance, in terms of an exaggerated response to moderate stimulation, can happen almost anywhere.

I'm thinking @alex-z is probably closest to right at this point... box or port are the two most likely culprits.

 

[fineMen]

...

SoundStageNetwork.com | SoundStage.com - NRC Measurements: Focal Electra 1008 Be 2 Loudspeakers

www.soundstagenetwork.com

Are You a speaker designer? If You do not like the graphs as a customer, see it as a feature, and simply avoid models that show the undesirable effect.

Why do You bother with design decisions made by a professional? Choose by data to Your liking.

 

[reza]

Are You a speaker designer? If You do not like the graphs as a customer, see it as a feature, and simply avoid models that show the undesirable effect.

Why do You bother with design decisions made by a professional? Choose by data to Your liking.

No, not a designer. Just curious.

 

[fineMen]

No, not a designer. Just curious.

O/k, from the examples You gave I cannot derive any regular irregularity.

The human mind is trained to identify regularities. Sometimes one is subject to the error of bias confirmation. This seems to be the case here.

Regarding curiosity, are you affected by these suspected disadvantages? Already before, or only after the assumption?