Speakers in a null - Why is this bad?

[SouthSIDE Glen]

A guitar string is like a room with many modes. A pick is a speaker, putting energy of a broad spectrum of frequencies into the string.
...
This might be a crappy explanation.

No, actually that is - for me, anyway - and excellent analogy and explanation which helps me out quite a bit. Thanks!

G.

 

[apl]

I put this afterthought into the wrong thread...

You can't make an open A string sound a B even if you try to mechanically excite it with an electromagnetic driver.

 

[Ethan Winer]

treatment doesn't move the peaks and dips (in the low end of course) or change the frequencies, but only makes them less deep or tall yes?

Yes.

Also, the text below from a recent post I made elsewhere is relevant here.

--Ethan

There are three separate factors that determine the response at any given location in a room.

First is the room's natural resonances, or modes. These are independent of speaker and listener placement, and the frequencies are determined entirely by the wall-wall and floor-ceiling spacings. If you stand in an empty stairwell and clap your hands, you'll hear a "boing" sound whose pitch is usually determined by the spacing between the walls. Whether you stand near to one wall or the other, or crouch down low or clap your hands high above your head, the pitch of the "boing" remains the same. That is the mode frequency.

The other two factors are SBIR and LBIR - Speaker-Boundary Interference Response and Listener-Boundary Interference Response. These are the classic 1/4 wavelength related peaks and nulls whose frequencies are based on the distance between each speaker and each boundary, and from the listener and each boundary.

The response at any given cubic inch in a room is the sum of all three of these factors, and that's a lot of variables given two speakers, one listener, and six boundaries. There are programs like RPG's RoomSizer that attempt to calculate the response based on all of these variables, but I've never tried them. People I trust say they're somewhat useful as a starting point, but they never give the same results as actually measuring with a microphone and meter etc.

 

[SouthSIDE Glen]

The other two factors are SBIR and LBIR - Speaker-Boundary Interference Response and Listener-Boundary Interference Response. These are the classic 1/4 wavelength related peaks and nulls whose frequencies are based on the distance between each speaker and each boundary, and from the listener and each boundary.

The response at any given cubic inch in a room is the sum of all three of these factors, and that's a lot of variables given two speakers, one listener, and six boundaries. There are programs like RPG's RoomSizer that attempt to calculate the response based on all of these variables, but I've never tried them. People I trust say they're somewhat useful as a starting point, but they never give the same results as actually measuring with a microphone and meter etc.

THANK YOU! I was hoping you'd chime in on this Ethan, you usually manage to get ideas through my thick skull pretty well

While I knew I did not - until halfway through this thread - have the right mental handle on mode resonances, I knew there was more to the situation it than just that; that placement did make a difference (except just not with the simple mode map, which is where I made one of my mistakes), and that maps like what are shown in the Nightfly thread were far too simplified and idealized to bear much real realtion to what's happening in a real room. Which was my main concern.

G.