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[Pierre Olivier]

Measurement mics are omni.

A "Directional mic" will introduce all sorts of "distortions to the response" of its own.

The only thing a directional mic could be good for is comparative measurements.  NOT absolute.

The IMPORTANT thing when comparing 2 products is to make SURE there is only 1 variable (the product) and not some thing else.  Like reflections-electronics etc

Would you care to elaborate on this?
Why exactly are measurement microphones omnidirectional?
I don't quite understand how a directional mic would introduce "distortions to the response"...
I used a Sennheiser MKH40, which is known for its ruler-flat response.
I am aware that I'm very far from beign able to claim absolute results. Relative results will satisfy me!

[Ivan Beaver]

Would you care to elaborate on this?
Why exactly are measurement microphones omnidirectional?
I don't quite understand how a directional mic would introduce "distortions to the response"...
I used a Sennheiser MKH40, which is known for its ruler-flat response.
I am aware that I'm very far from beign able to claim absolute results. Relative results will satisfy me!

I don't know about that mic, but the very action that produces a cardioid (or other pattern) is CANCELLATION, which means response "distortion".

Distortion is NOT just THD, but anything that changes the original signal.

When measuring (for other than comparative results), you want was little as possible to enter into the measurements.

That is one reason the mic capsules are very small.  Large diaphragm mics will alter the signal being received-simply due to their physical size.

[Helge A. Bentsen]

Would you care to elaborate on this?
Why exactly are measurement microphones omnidirectional?
I don't quite understand how a directional mic would introduce "distortions to the response"...
I used a Sennheiser MKH40, which is known for its ruler-flat response.
I am aware that I'm very far from beign able to claim absolute results. Relative results will satisfy me!

Measurement mics are omni mostly because all directional mics have proximity effect, with means that directional mics are LESS sensitive to low frequencies on a distance.

This means that your MKH-40, wich is an excellent sounding microphone for a lot of applications, is tilting your measurement considerably off in the low end of the spectrum.






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[Merlijn van Veen]

Omnis, like the word implies, are "immune" to rotation. The same evidently can't be said for directional mics. So mic positioning and orientation becomes much more critical. Another variable complicating things.

Also D/R values are different for directional mics compared to omnis. Angle of incidence for direct sound is the same but not for ER and the "homogeneous" distributed reverberation field.


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[Keith Broughton]

While the comments made about test mics are true, in Pierre's case, he is testing relative not actual frequency response.
He wants to see if 2 different speakers exhibit similar response patterns given the terst method and equipment are the same.
Should be fine with the mic he has.

[Pierre Olivier]

Hey, I've got another mystery for you!

I was going over the documentation of the M-1A and B-2A, and now I'm puzzled as ever!

Says in the m-1A operation manual:
Lo Cut Switch. This switch introduces a 6dB/octave high pass filter at 160Hz. It is designed to provide an alternative crossover slope when using Meyer Sound subwoofers, but can also be used to compensate for the proximity effect of cardioid microphones. This filter is automatically inserted when the Sub Input is used.

Then I read the Operation manual of the B-2A, and the crossover frequency is stated as 95 Hz.

Knowing that I should connect the "high" ouput of the B-2A (that contain 95Hz up) into the "sub in" of the M-1A (which implements a lo-cut of 160Hz), WTF happens to our clients 95 to 160 Hz?

(of course, that is all theoretical, as I don't have a B-2A. I DO have however a crossover and subs).

In other words, what frequency the crossover between the subs and the tops should be??? I assumed it was 160 Hz, but now I'm confused.

[John Sulek]

Knowing that I should connect the "high" ouput of the B-2A (that contain 95Hz up) into the "sub in" of the M-1A (which implements a lo-cut of 160Hz), WTF happens to our clients 95 to 160 Hz?

My understanding would be that they are gently rolling off from 160Hz towards 80Hz where they will be 6db down from the corner freq of 160hz. Probably to help the acoustical summing of the UPA and sub be flatter and have a better phase response. Neither of these speakers are going to fall off a cliff response wise at 95Hz.
Apologies for my less than technical musings.

[Keith Broughton]

My understanding would be that they are gently rolling off from 160Hz towards 80Hz where they will be 6db down from the corner freq of 160hz. Probably to help the acoustical summing of the UPA and sub be flatter and have a better phase response. Neither of these speakers are going to fall off a cliff response wise at 95Hz.
Apologies for my less than technical musings.

I agree with John about the acoustical summing.
65 Hz is not really al that much and the slopes of the crossovers are probably not all that steep.
As I recall from listening to Meyer 650s, the low pass slope is rather shallow.

[Ivan Beaver]

Hey, I've got another mystery for you!

I was going over the documentation of the M-1A and B-2A, and now I'm puzzled as ever!

Says in the m-1A operation manual:
Lo Cut Switch. This switch introduces a 6dB/octave high pass filter at 160Hz. It is designed to provide an alternative crossover slope when using Meyer Sound subwoofers, but can also be used to compensate for the proximity effect of cardioid microphones. This filter is automatically inserted when the Sub Input is used.

Then I read the Operation manual of the B-2A, and the crossover frequency is stated as 95 Hz.

Knowing that I should connect the "high" ouput of the B-2A (that contain 95Hz up) into the "sub in" of the M-1A (which implements a lo-cut of 160Hz), WTF happens to our clients 95 to 160 Hz?

(of course, that is all theoretical, as I don't have a B-2A. I DO have however a crossover and subs).

In other words, what frequency the crossover between the subs and the tops should be??? I assumed it was 160 Hz, but now I'm confused.

In almost every case, the ACOUSTICAL and ELECTRICAL crossovers are NOT the same.

This is due to a couple of factors.

One is the fact that very very few speakers are actually flat-around crossover point.

Full range products tend to be a bit low in level and subs tend to be a bit high in level.

Also consider that subs are typically run higher in level, means that the electrical crossover point for the subs will be a lot lower than the acoustical crossover to the full range speaker.

So while it may "appear" to be a hole in the response-there is not and in many cases there is actually a HUMP in the area you "think" there is a hole.

[Keith Broughton]

The biggest thing between me and great sound is the exchange rate on the US to CDN $$    KILLING ME!

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