Help for 3 or 4 way loudspeaker

[tinitus]

be cautious with porting and lots of bracing
may not work well together
woofer and port must not be too far apart from each other

 

[jReave]

That's interesting. Do you think merlin needs to make some changes to his design?

Certainly B&W uses probably twice that amount of bracing and still ports the cab out the bottom.

 

[jReave]

Listening position is 88cm

How to add a high pass filter to mids?

Thanks.

The simulation will figure out the LP and HP filters at the same time.

 

[tinitus]

Certainly B&W uses probably twice that amount of bracing and still ports the cab out the bottom.

study the B&W matrix bracing closer
with this 'issue' in mind, you will notice that there are free air passages between woofer and port

 

[jReave]

Will do.

 

[merlin el mago]

My 2 way cabinet uses B&W matrix bracing, sounds wonderful...

 

[jReave]

merlin,

I'm running into some nasty baffle diffraction effects with your tweeter. In the graph below the blue line shows these effects on your current baffle for your 2-way. Peaks and suck-outs are rather large.

The purple line is the same baffle but with a 3/4" (19mm) chamfer around all its edges. Much flatter. I would highly recommend this if you are able to do it. Make the chamfers as large as driver locations permit. It doesn't really need to be done for the lower cab, but you can do it there too if you like the look better.

I might also suggest a change to your lower cabinet bracing. I think the piece that is running vertically and is parallel to the front baffle should be changed, especially where it's right behind the driver. There's too much reflecting surface sending sound back at the driver there. Change it to something more similar to B&W's matrix, where the vertical braces are running perpendicular to the front baffle. It could be 1 brace in the middle or 2 pieces like B&W. This may improve the air flow to the port too and/or you can also probably increase the size of some of those holes to do that too. Or change some of them to squares. (Thanks tinitus)

B&W matrix info:
http://www.bowers-wilkins.com/Downloads/Product/Brochure/ENG_FP29483_805-Diamond_brochure.pdf
Bowers & Wilkins - Matrix

Also, can you tell me what the distance will be from the front baffle to the back wall and the distance from the driver centers to the side wall?

 

[merlin el mago]

jReave,

Both tweeter & mid-woofer are chamfered.

Baffle to back wall 80cm (left loudspeaker) 3meters (right loudspeaker).

 

[tinitus]

my latest bass box with modest matrix bracing, and 'light stuffing'

 

[merlin el mago]

Cool, thanks to share your work tinitus

 

[merlin el mago]

tinitus that's my matrix work for 2 way cab

tweeter

An externally hosted image should be here but it was not working when we last tested it.

mid-woofer

An externally hosted image should be here but it was not working when we last tested it.

 

[jReave]

ok, here is what my sims show so far.

Graph 1 is your 2-way with your current xo. Not bad but it looks like BSC hasn't been factored in (slightly weak bass), it could be flatter and I would consider 2000Hz just a little low for that tweeter (3rd and 5th harmonic distortion start to rise below 3000Hz - last graph). Phase at the xo is perfect.

Graph 2 is exactly the same except now the edges have been chamfered by 19mm. Much smoother above the xo.

Graph 3 is not a bad result using most of your present values, the chamfered baffle 2-way and adding in the woofer with a 3rd order LP. It's fairly flat, phase is close in the xo regions, sensitivity has increased and the mid/tweeter xo has moved up to about 2500Hz. Woofer/mid xo is at 250Hz. What I don't like is that I have no HP filter on the mid - this sim is running it wide open. Also, the impedance ends up closer to 4ohm so your amp is going to have to be happy with that. Give me some more time, I'm going to keep working on it.

If you're curious, woofer LP values at present are:
L1 6mH .4ohm
C1 135uF
L2 2mH (.4ohm)
plus 10ohm in parallel,
but these could change so don't do any ordering yet.

 

[merlin el mago]

thks for the sims, I calculate aprox. for the final volume cab:

1L for the woofer
1L for the BR port
3L for the bracing 10mm (or I need 10mm plywood)

Do you believe is aprox OK?

 

[merlin el mago]

About bracing 10mm or 20mm of plywood?

 

[tinitus]

depends on bracing 'type', but some will be fine even with 6mm MDF, if you like

btw, other than a nice girl with a cell phone, I can't see anything in your pic 'upload'
(which is why I cannot comment)

 

[merlin el mago]

Sorry tinitus I see the bracing, are you kiding?

 

[tinitus]

Sorry tinitus I see the bracing, are you kiding?

if you mean about the picture links ? .... no, I see an advert for a microsoft account, and the same on both links, thats all

btw, it says 'Outlook.com for your cell phone'

please use forum attachment
its much better, for all
though I noticed you tried twice, but had problems with your photo resizer

 

[jReave]

thks for the sims, I calculate aprox. for the final volume cab:

1L for the woofer
1L for the BR port
3L for the bracing 10mm (or I need 10mm plywood)

Do you believe is aprox OK?

For the port, you're a little low:

outside diam = 89mm, so
r = 4.45cm
port length inside cab= 27.4 - 4 cm (port length - front baffle thickness) = 23.4cm
so,
V = (4.45 * 4.45 * 3.14 * 23.4)/1000
V = 1455.01/1000
V = 1.45L

See my previous post about your bracing - you should consider a re-design. I believe in a little overkill in cabinet building, so I think 20mm plywood bracing is best. However, 10mm MDF may do just fine. I can't accurately calculate bracing volume without knowing the exact dimensions of your circular cut-outs. If I assume the diameter of the holes is 10cm and bracing thickness is 10mm, then 3L is about correct. If you use 20mm, it'll be 6L.

Do you also plan to include the xo's in the bass cab?

Those bracing links do nothing for me either.

 

[merlin el mago]

Now you can see the images?

xo will be in external boxes.

 

[jReave]

Yup.