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Folded Horn/Bandpass 15" Design Pics.

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    Posted: 22 July 2019 at 12:44am
Anyone suggest if this box has too much bracing. I don't decrease the rear chamber volume. 

Also the Output only produces 97 ish db around 40hz. I want the lowest frequencies possible but with a chart like this, Is this cab worth building? I'm planning on building it in birch ply but hope someone with some experience could advise if it's worth it before I commit.
Cheers
:)





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Post Options Post Options   Thanks (1) Thanks(1)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2019 at 8:00am
That's a nice innovative design, 10 points for that!

Some pointers:

  • I would go with a lot more bracing inside the vented chamber. I doubt that small triangle at the top panel is going to do anything effective. Personally I like large single bracings, along the middle line of the cabinet, that connect to multiple (at least two) walls.
  • The output at 40 Hz and lower doesn't look like it's optimal. At this point I can't say for sure if it's due to the chamber size or the particular driver used.
  • Hornresp doesn't take the directivity of the horn into account in this simulation. If you approximate the horn as a single segment and simulate directivity you'll see a lot of rising output above 60 Hz-ish.
  • Also the port looks kinda small (surface area).
Can you post the Hornresp input parameters?






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Post Options Post Options   Thanks (0) Thanks(0)   Quote ARR_PG Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2019 at 9:21am
Thanks. I love the design. The parameters are very sensitive. Small changes make big differences. The volume in the rear chamber has been calculated and is 109.9 ltr without the bracing. 

The port should be correct. I just wanted this cab to go down as low as possible and as loud as possible. Why I chose rear vented chamber.  



 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ARR_PG Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2019 at 9:28am
Port: I did "Ap" 75.50 /25 = 3.02

Height - 3.02 , Width - 25 cm    although its cm2. Hope I havent made a mistake. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2019 at 12:24pm
75sq cm of port area is almost certainly too small for a 15" driver tuned that low. Ordinary vented boxes covering that kind of frequency range will use vents of between 1/3 and 1/2 of the driver's SD. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ARR_PG Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2019 at 1:35pm
OK. Problem is when I increase Port Area "Ap" and the length "Lpt", the power has a sharp peak. I wanted to keep a smooth curve around 40-90hz . Unless you suggest otherwise?

Here is the Acoustical Power for the Port as 75.5cm2 (Area) 


Here is the port scaled up for an example. The only way to smooth out the curve is increasing the Lpt to an impractical size to match the larger Port Area.


Here is a larger port but the output is the same as the original 75.5cm2 Area. So the small port achieves the same results as the larger port in this case. It seems. See "Ap" and "Lpt" differences in the images.




First image and last image are the same output power but the last has a larger port. It seems that practically I would choose the small port option to build to fit in the rear chamber.  The rear chamber is the recommended size for the driver. A happy accident lol.

Thoughts? all comments mean a lot to me and are really appreciated. Thanks guys for your time.

Main question is though. Is this worth building you think or is the box and driver too weak to really sound , well like a beast? :)
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Mikkel Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2019 at 3:33pm
Hi mate. Yea youve just found an unfortunate truth with speaker design. Its always a compromise. You need the higher cross sectional area in the port to stop port noise, but that raises the port tuning, so you would need to make the port longer, which takes more rear chamber volume, and so on. LOL

What i find easiest is, once you have everything in hornresp, raise the voltage untill it hits xmax, then look at the ports particle velocity, if it is higher than 30m/s then you know to increase the port area/tweak accordingly.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ARR_PG Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2019 at 4:46pm
Ahh I see. Yeah seems like that's the case. Awesome advise mate, Ill get busy with that. :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ARR_PG Quote  Post ReplyReply Direct Link To This Post Posted: 22 July 2019 at 7:09pm

Quick Fix: 156 litres is still in the driver's cabinet size range and I could maybe fold the port. I used the rule DMorrison said of 3rd of the Sd.  Im liking the results. If this reduces noise. Then all should be good.
  
Will look into Mikkels method in the Max SPL though too. 

Here's the AccPower now with new port dimensions. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ARR_PG Quote  Post ReplyReply Direct Link To This Post Posted: 23 July 2019 at 12:48am
Originally posted by Mikkel Mikkel wrote:


What i find easiest is, once you have everything in hornresp, raise the voltage untill it hits xmax, then look at the ports particle velocity, if it is higher than 30m/s then you know to increase the port area/tweak accordingly.


Mikkel I did a Maxium SPL with 200 volts and the xmax at 6.5. Some frequencies are limited by driver displacement. Is that what you mean by reaching the xmax?  

Or do you mean raise the "Eg" in the Loudspeaker Wizard. I tried your method and expected to see The Particle Velocity to be above 30ms. This is result is the small chamber and small port dimensions. 

Port Outlet and Inlet are the same. Does this mean the small port is OK?  75.5cm2 Area 27.70 Port Length. 




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Post Options Post Options   Thanks (0) Thanks(0)   Quote ARR_PG Quote  Post ReplyReply Direct Link To This Post Posted: 23 July 2019 at 11:34am
With a few tweaks I am happy with the results. Now have a 105db peak at 40hz and a large enough port area. 






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Post Options Post Options   Thanks (1) Thanks(1)   Quote Mikkel Quote  Post ReplyReply Direct Link To This Post Posted: 23 July 2019 at 3:08pm
I assume you mean 200watt as 200 volt would be 5000watt @ 8ohm. 

Also i mean using the excursion graph at xmax not using the max spl function. What youve posted doesnt look right at all. Using the 'clean' data when looking at the port velocity will give you a better idea of whats happening. Hope that makes sense.

It looks good now anyways.
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