driver baffle placement

[lilun]

hi,

I am confused about the problem I am having with the driver placement of the woofer and tweeter. I am crossing over at 2khz, so that means the wavelength of 2khz is about 17cm. So why am I finding that the the front to back distance of the tweeter relative to the woofer makes such a critical difference even if I move it 1cm?


also currently the tweeter is not completely flush on the baffle because I am still in the process of experimenting, So the faceplate sits on top of the hole. Does this kind of thing, affect the sound much? The baffle edges are also very sharp and ragged, not rounded.

thanks
bye

 

[wintermute]

Hi Lilun, just thinking about this, there are 360 degrees in that 17cm so 1/17th of 360 degrees is about 21 degrees.

So shifting the tweeter in or out by 1cm changes the phase by around + or - 21 degrees (or 42 deg total phase shift from -1cm to + 1cm) . Depending on what the initial phase relationship is that 21 degrees may be enough to make a positive or a negative effect on the sound when it comes to the drivers summing at crossover.

With respect to the tweeter not being flush mounted, this will almost certainly cause aberrations in the frequency response up high. Not huge ones but they will be noticeable when measured.

Tony.

 

[lilun]

So what is happening is that the soundwaves from the tweeter are not adding up with the woofer waves properly. some are cancelling and some are just not in phase. Is this correct? because the stereo images are not being formed properly.

As a temporary measure, can I use a bit of cardboard to make the tweeter flush and also round the edges by bending the card around the cabinet edges? would 3mm thick cardboard be usable?

 

[Greebster]

So what is happening is that the soundwaves from the tweeter are not adding up with the woofer waves properly. some are cancelling and some are just not in phase. Is this correct? because the stereo images are not being formed properly.

Yes

As a temporary measure, can I use a bit of cardboard to make the tweeter flush and also round the edges by bending the card around the cabinet edges? would 3mm thick cardboard be usable?

Flush is flush. Also the Z axis needs to be shifted back to time align correctly. The choice of crossover used will also affect this. When done correct, the phase alignment tracks for at least an octave above and below X point.

 

[lilun]

so is cardboard ok to use as a temporary 'baffle' for the tweeter? will it reflect the highs?

For example I read that a sphere would be the best shape for a cabinet. So is it possible to take any typical rectangular speaker and then cover a sphere over the baffle? you could again use cardboard or maybe a plastic mould.

and also does the diffraction issue affect the waves from the 6 inch woofer or is it just a tweeter issue? How do I know whether what I am hearing is a baffle step issue or diffraction issues or improper summation of the tweeter/woofer?

 

[Greebster]

so is cardboard ok to use as a temporary 'baffle' for the tweeter? will it reflect the highs?

For example I read that a sphere would be the best shape for a cabinet. So is it possible to take any typical rectangular speaker and then cover a sphere over the baffle? you could again use cardboard or maybe a plastic mould.

and also does the diffraction issue affect the waves from the 6 inch woofer or is it just a tweeter issue? How do I know whether what I am hearing is a baffle step issue or diffraction issues or improper summation of the tweeter/woofer?

Tested AMT's recently using coroplast. Made the baffle the same width as what the real example would have ~8" and rolled the edges into a 2" roundover. The coroplast is as thick as the tweeter bezel so was flush. This worked quite well for testing purposes.

Diffraction is a function of frequency. Example above adversely affects sound below ~1750Hz. The tweeter tested was operating above 2.2k