Just wanted to know if I should be adding volume to offset bracing.? I’m hoping the answer is yes because I’ve somehow ended up with 2.4lt of additional volume lol.!
17.1 to 19.4, subsequently the internal height is now 20mm shorter and the internal depth is 40mm deeper..!!! I at least got the width correct..!! It’s a ported enclosure using Markaudio 10p
My question is, would the above shape changes have any impact? The original design was 369mm internal height so would I need to place the driver and port a little higher to compensate?
Thanks in advance, it’s my first build so hopefully someone can help..!! It’s not really an issue to cut more ply to the right size but I prefer the look of this cab being a tad shorter and deeper.
Cheers
🔫
17.1 to 19.4, subsequently the internal height is now 20mm shorter and the internal depth is 40mm deeper..!!! I at least got the width correct..!! It’s a ported enclosure using Markaudio 10p
My question is, would the above shape changes have any impact? The original design was 369mm internal height so would I need to place the driver and port a little higher to compensate?
Thanks in advance, it’s my first build so hopefully someone can help..!! It’s not really an issue to cut more ply to the right size but I prefer the look of this cab being a tad shorter and deeper.
Cheers
🔫
Yes.
17-18 litres is close to optimum.
Not much on the lf but the shape can affect internal resonances and external diffraction effects.
In a reflex the driver placement should not affect LF.
dave
Thanks Dave, this is exactly what I needed to confirm.
With this OV9 design the drawing I have doesn’t indicate a port height? I’ve scaled the drawing and it appears as the driver centre is approximately 1/3rd, top of port 2/3rds and 3/3rds would be the bottom edge of cabinet.
I have calculated 1.4lt of bracing so my silly mistake has paid off..!!! Lol I think I read somewhere that bracing should have about 40% of the mass material removed..?? All edges rounded and attempt to make contact with at least 3 of the inner surfaces..?? Bracing to hug driver and be off centre..??
With this OV9 design the drawing I have doesn’t indicate a port height? I’ve scaled the drawing and it appears as the driver centre is approximately 1/3rd, top of port 2/3rds and 3/3rds would be the bottom edge of cabinet.
I have calculated 1.4lt of bracing so my silly mistake has paid off..!!! Lol I think I read somewhere that bracing should have about 40% of the mass material removed..?? All edges rounded and attempt to make contact with at least 3 of the inner surfaces..?? Bracing to hug driver and be off centre..??
What box? What drawing?
I typically target 30-40% holes. Then i can calculate teh volume of bracing by using 2/3rds the brace thickness. So if i put a brace in, say 18mm, front-to-back, volume is easily maintained by pushing the width out 12mm (18*0.6666….)
dave
@waterpistol is it this one? https://wodendesign.com/downloads/simpleReflex-103-10p-plan-100214.pdf
jeff
jeff
Thanks Dave.
I can see the 50mm port ID, sorry I should have said port height/location on the baffle measured from the bottom front internal corner.
I can see the 50mm port ID, sorry I should have said port height/location on the baffle measured from the bottom front internal corner.
If there's sufficient clearance (depends on the duct design), centreline 56mm up from the base on the front or rear baffle would be my choice.
Hi Scott, is there any interdependency between the port and driver to maintain the same vertical axis?
In regard to the internal damping material and design instructions noting “all surfaces lagged” would this also apply to the bracing? I understand it would be difficult with conventional materials however a rubberised or bituminised rubber paint could easily be applied.?
Thank you for your input and advice with this.
In regard to the internal damping material and design instructions noting “all surfaces lagged” would this also apply to the bracing? I understand it would be difficult with conventional materials however a rubberised or bituminised rubber paint could easily be applied.?
Thank you for your input and advice with this.
Depends on the design so there's no specific answer to the first. Re the damping, bitumen / rubber is mass-damping to lower the frequency of vibrational modes in the structure; acoustic damping (e.g. fibreglass, BAF etc.) serves a different purpose. You shouldn't need any on the brace however, and unless indicated in a given design, I wouldn't use mass-damping for panels. When you're bracing a box, you're generally aiming to raise panel Fs (and Q) above its operating BW to a point where little energy is available to excite it. Adding mass to a well-braced cabinet tends to simply lower the panel modes back down toward the operating range once again. It does have its uses, but usually you're best applied sparingly, targeting specific remaining modes etc.
Thanks again Scott. Unfortunately we (Aussies) have limited retail access to good quality damping procured locally and only large quantities available via online with a rather large shipping cost. I have looked for alternatives and stumbled across vehicle underlay that is a non woven 900gsm polyester, other options are acoustic open cell foam, Monacor MDM30 low expansion foam 300kg/m3, pure wool felt (from a fabric store) and the two offerings from Mundorf.
If you add damping to the brace it should be lower density and covering the holes is more important than covering the solid bits.
Given the just off centre brace, damping placed on the centreline side has damping right wher eit will be maximally effective at killing any standing wave side-to-side.
dave