What happens to sub impedence curve when a board is placed close to front?

[eRiCdWoNg]

Just curious what happens to the impedence curve of a sub if say a board is placed infront of it, or if the sub cone is fired into the wall or floor at close range. Reason I ask, my latest fabrication is for my car, and its a subwoofer that is in the rear firing up. My car has a removeable targa top and it stows in the rear. The woofer fires directly into the targa top with maybe 1" or so of clearance. This was the only way I could have the woofer setup and still have space to stow the top.

I noticed tonite though that I had the top stowed in the back that my headlights were dimming a good amount. Then later on, I was driving with the top back on the roof and playing the same music at the same volume and there wasnt near as much headlight dimming.

While there might be other variables, I'm sure that board was changing some of the electro-mechanical characteristics of the woofer. Any thoughts on this?

[hunter audio]

hi

the impedance is the result of a coil moving in a motor structure

if you feel the cones movement in turn - the v c movement will be damped or restricted by placing a board in front of it

its simlar to a load as seen by the loudspeaker

this load can be good and bad

a loudspeaker is loaded by its - spiders and surrounds - mechanical term - compliance

a loudspeaker (as in hi fi to pro audio) is designd to perform with an addittional load to it - that is the air mass in its enclosure
for max efficiency and SOAR charecteristics

to determine the over all total load - we have t/s parameters
that is the air loading required for the particular driver

in a poor design or where t/s parameters have not been taken into account very carefully

- you are in terms loading the v c poorly

now for - poor loads ,

form my measurement s on poor loads

with a long voice coil - as in a car audio spk

(i have had problem with short coils when not loaded well )

with a 2.8 ohms (re) long coil in a 12 inch woofer through various poor loading conditions the impedance never went to critical levels to spoil a car amp - or blow its fuses , or output

(i am not exactly measuring the impedance here as car amps are designd for upto 2 ohms load)

i suggest if you have obtructions in front of the driver cone (as long as it doesnt touch the cone and for all practical purposes if a bit away for the cone)

go in for a long throw sub , and there may be a fall in responces - this will lead you to turn up the bass amps more , there fore increase the capacity of your batteries / alternator

Suranjan

Transducer design engineer

[eRiCdWoNg]

Hmmm, interesting. Makes sense about the load. I gotta run more tests to see how much its affecting the performance. What I will probably wind up doing is making a "recessing ring" that will drop the woofer down an inch or so for more clearance and a more flush look. While this might not make a huge difference its also additional bracing for the baffling as well as get the driver's surround further away from my fingers possibly puncturing it when i put the top in/out. Only trouble is im not sure how I'll get that flush ring down in there. Probbly cut a slit to send it through then either make a design to that or patch it.