BillFitzmaurice.info

Been thinking a little bit about SLA surrounds so knocked these up in AutoCAD. Interested in comments and opinions...

I definitely need more than one speaker in a box for the surrounds because of my receivers "all speaker stereo" mode for music.

This first one is my favorite so far.

You might wanna consider impedance, as 3 paralleled is 2.66ohm.. 4 is needed for 8ohm

D'oh, school boy error

Edit: Back home now.

3 woofers in parallel is 4.66 ohms because the impedance at 4kHz is 14 ohms for the GW-4028's

= 1/ (1/14 + 1/14 + 1/14)

= 4.6667 Ohms!

I would think 2 woof, 2 or 4 tweets would be plenty for the surrounds.

2 of Each works. That comes out at 4 Ohms for the tweeters and 7 Ohms for the woofers.... which complies with Bills "try to keep the ratio of impedance's within 2:3" rule.

That 4.66 ohms is not the nominal impedance, only the resistance at 4k.

Yep, that's (14 Ohms) what you use to work out the cross over values.

Ian Westwood wrote:Yep, that's (14 Ohms) what you use to work out the cross over values.

I don't think you're getting what we're saying.. The impedance at 4khz is for figuring out your filter.. The woofers are still 8ohm nominally and that's 2.66 when you parallel 3..

I get that... I'm looking at using 2 of each right now.

The other thing is that the speaker line (lenght of the contiguous midwoofers)
needs to be at least 3 ft. (or thereabouts) in order to take advantage of an
arrayed configuration. If it's shorter than that and/or with the impedance
problems everyone is pointing out ...you may be better off building 2-ways
or MTMs for your surrounds.

I've been thinking about this too, and I was considering 4 of each driver. Placing two in parallel in a having those in a series. This would create an 8-ohm nominal impedance across four drivers. I suppose if I were to use the 2/3 rule, which I don't quite recall, but I'm assuming it's that the tweeters impedance is 2/3 of the woofer impedance, then maybe 6 tweeters with three in each parallel and wired into a series. I know 14-ohms is the "dead" (no signal/power) impedance but I think if 8-ohms is the nominal, then once power is going to the speaker that would end up closer to 8-ohms.

All of this is pointless. All there is in the surround channels is "ambient sound" which is not a lot of sound. There is no need to put anything more than a woofer and a tweeter on your surrounds. Point them at a wall to remove some "directionality". I point mine at the joint of a wall and ceiling.

DJPhatman wrote:All of this is pointless. All there is in the surround channels is "ambient sound" which is not a lot of sound. There is no need to put anything more than a woofer and a tweeter on your surrounds. Point them at a wall to remove some "directionality". I point mine at the joint of a wall and ceiling.

Not necessarily. Some DVDs are now mixed with specific content that can benefit from directionality and high output capability. I think MKtheater is now using DR200s over T39s for his surrounds.
But he's seriously nuts.

Bill Fitzmaurice wrote:I think MKtheater is now using DR200s over T39s for his surrounds.
But he's seriously nuts.

Yeah but in the best possible way...