[paulspencer]

I've started a surround speaker build. This will be a low profile box.


Midwoofer: B&C 8PS21

CD: B&C DE250


I'm planning a custom waveguide, probably oblate spheroid with 90 - 110 degrees dispersion. Considering a 10" waveguide to allow wider dispersion.


To get started, here is my test box:

This will let me measure it for directivity and experiment with knock up waveguides, before building the final thing, and also experiment with placement a little.


More about it here:
http://redspade-audio.blogspot.com/2...surrounds.html


I know there are some good waveguides out there, but I'm aiming for a "cast in one piece" look.

 

[Looneybomber]

"At 3m, the output is reduced by ~4.5 dB,"


This is what you measured in your room at that speaker's location or are you using someone else's data? I ask because that coincides with a nearfield attenuation of 3db/doubling of distance as opposed to the standard farfield attenuation of 6db/doubling.


If you do only lose 4.5db, what kind of room treatments do you have?

 

[A9X-308]

Just go wth the Ewave.


Your attenuation calc is a bit low, OTTOMH I get 9dBish.

 

[paulspencer]

That is an estimate based on Toole.

 

[noah katz]

Why not get one of the Autotech WG's?

 

[coctostan]

I would watch for vertical null spacing when using round WG's for surrounds. I obviously don't know how you are placing them in the room or what your seating is like, but you can get a pretty narrow vertical window with an axisymmetric wg.

 

[A9X-308]



Quote:
Originally Posted by paulspencer /forum/post/20876880


That is an estimate based on Toole.

I calculated it (in my head) but plenty of calculators out there.

 

[noah katz]



Quote:
Originally Posted by coctostan /forum/post/20877384


I would watch for vertical null spacing when using round WG's for surrounds. I obviously don't know how you are placing them in the room or what your seating is like, but you can get a pretty narrow vertical window with an axisymmetric wg.

Good point.


Makes one of the 8" B&C coaxes seem like an obvious alternative.

 

[paulspencer]

Will be mounted horizontal wg next to mid and there is one row of seats, so that will affect the off axis more. Autotech I might consider but I'm thinking of a one piece construction and having some fun with fibreglass as well.

 

[paulspencer]

I used one online calculator and it indicated higher SPL than my estimate, more attenuation based on distance, but more boost from other factors. Average listening distance is actually closer to 2m. Not too worried about the estimate, point is it looks like I'll get THX levels.


This will be powered by MiniDSP + 4 amp channels, IIRC 50 + 250w.
http://redspade-audio.blogspot.com/2...crossover.html


The coax drivers are an interesting way to do it, especially for multiple rows. In my case, I already had the compression drivers (picked them up second hand cheap). I was buying some Synergy horn mids and I saved $65 on shipping by ordering the midwoofers for this at the same time.


I'm thinking I'd like to build some fibreglass waveguides (been looking for an excuse to do something in fibreglass for years). Fury has offered a loan of some DDS waveguides to make a mould and then fibreglass version. I'd like to give it a try and I might also knock up some quick n dirty fibreglass ones to try wider dispersion.

 

[GRBoomer]

So how low did you get the boxes to go? Did you hit 80Hz?

 

[paulspencer]

It's been a while since I looked at it but as I recall they had trouble getting to 80 Hz and it was more like 90 - 100. They will be wall mounted high up on side walls near a corner. That is likely to help.


Just had a look at previous comments regarding attenuation due to distance. Around about 4 db loss by the listening position actually corresponds to what I've noticed with the SPL meter in this room. My prediction has turned out to be true. I'm certainly not getting 6db attenuation per double distance.