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Droogne

Skramlike sub: some design questions.

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8 minutes ago, peniku8 said:

It was +75% of the shorter dimension in my case, since the port opens to the side of the longer dimension in my cab.

It's a guess, but the tuning of yours will probably come in between +50% and +75%.

Allright.

What are you trying to achieve with the filling?

Honestly no clue, thats why I wanted to ask. You only used minimal I see.

 

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I staple gunned foam to the sides to reduce distortion, especially out of band distortion when running at high output levels. Any sort of filling will reduce maximum output capabilities.

PA subs usually don't use filling for that reason. If you have a very nasty resonance resulting in a bad waterfall plot, using some (lots of) filling will enhance SQ, but reduce sensitivity and efficiency. I'd line the sides with foam and only add some actual filling if I notice anything problematic when measuring/listening.

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Yup yup, all "non-essential" stores will be closed from tomorrow on. So I will not be able to buy the wood I need. Will have to shelve the project. I'll finish up the design, focus on tweaking my mains (of which I will be starting a large thread on AVS/diyAudio/both), study, and hope I have the time to build the subs before my event in june. 

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39 minutes ago, Droogne said:

Yup yup, all "non-essential" stores will be closed from tomorrow on. So I will not be able to buy the wood I need. Will have to shelve the project. I'll finish up the design, focus on tweaking my mains (of which I will be starting a large thread on AVS/diyAudio/both), study, and hope I have the time to build the subs before my event in june. 

That's what I have an emergency stock for..!

SP0Zqck.jpg

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12 hours ago, peniku8 said:

That's what I have an emergency stock for..!

SP0Zqck.jpg

I build my speakers in my living room 😛 I would never be able to store, let alone bring up, huge pannels like that. I might find some pannels on the second hand market, but I would have to cut them myself.. something which is something I rather not do as I do make mistakes (I dont have have a decent cutting table.. just a very small one for small cuts.) The store I normally go to is pretty cheap, has wood I really like (maybe not the best structural strength, but it has a nice look) and they cut it for free as long as the cuts are straigt. So for me there are no good alternatives. Oh well.. We all have to make compromises these days I guess.

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Yep...

This is a 6th order BP type design. You don't want stuffing, just line the walls with some 1.5 or 2" / 50mm thick foam and staple gun it in there. Do the ported section only. All you are trying to do is knock down some of the high frequency reflections outside of the sub bandwidth. Try sticking your head inside of the unlined cab and snapping your fingers...There will be a lot of HF's and reflection. Repeat after lining and it's much much deader. Also it keeps the wire from rattling if they end up touching the cabinet wall. Keep the port entry clear though. A good 6" / 150mm clearance or so should be fine. See pics below. 

For a particularly nasty resonance you could put a pillow in there somewhere but it'll cut some efficiency and you must keep it away from the motor vents and the ports both. 

For calculating port tune I never include any extra length past the front plane of the port exit. 

When the exit is close to internal walls it will result in an apparent lengthening / deeper tune. This is where the extra apparent length comes from. See the line through the middle of the port section in the sketch below. Sometimes I use a radius in the corner in place of the straight angle, but this way is slightly more conservative. This is how I calculate them in cases like this. No extra length beyond the external exit. There is an extra few cm beyond the internal exit due to the back panel. A 45deg angle seems to approximate this length well based on measurements. 

 

425271478_BottomFireFoldBentPort.thumb.png.eb4ab040b19146f71362d8d6b2c543e9.png

 

 

20170225_143411.thumb.jpg.8d761b30d61be05b6c547fd42491e2e1.jpg

20170225_150433.thumb.jpg.c821fdbeba0f36a9118d7299d782f751.jpg

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On 3/18/2020 at 3:04 PM, Ricci said:

Yep...

This is a 6th order BP type design. You don't want stuffing, just line the walls with some 1.5 or 2" / 50mm thick foam and staple gun it in there. Do the ported section only. All you are trying to do is knock down some of the high frequency reflections outside of the sub bandwidth. Try sticking your head inside of the unlined cab and snapping your fingers...There will be a lot of HF's and reflection. Repeat after lining and it's much much deader. Also it keeps the wire from rattling if they end up touching the cabinet wall. Keep the port entry clear though. A good 6" / 150mm clearance or so should be fine. See pics below. 

For a particularly nasty resonance you could put a pillow in there somewhere but it'll cut some efficiency and you must keep it away from the motor vents and the ports both. 

What do you mean by 'only do the ported section'; Only my first box, or more in general? Because the IPAL seems to have it on all walls; except the ports.

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Don't put anything in the horn/slot section. The front phase of the driver. Sorry I worded that badly. 

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14 minutes ago, Ricci said:

Don't put anything in the horn/slot section. The front phase of the driver. Sorry I worded that badly. 

All right, so eerything except the walls adjacent to the port opening (including a part of the walls cornering it).

 

EDIT: sorry, you worded it correctly. Everywhere except in front of the driver (and in the ports themselves I guess). I do however see you also didnt line the parts around the port opening. Because you counted this parts as part of the port?

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Been thinkering again, got a week of now till I start again with work (in the COVID19 wards; so will not have a lot of free time as you can imagine). 

The models with the NLW9600 make me appreciate a higher tuning some more.

 

Xmax limited

                         130dB point               lowest level                      effective 0dB FR

31hz tune        32.5hz                        129.8dB

32hz tune        33.0hz (+0.5hz)        130.6dB (+0.8dB)

33hz tune        33.8hz (+1.3hz)        131.3dB (+1.3dB)            34-.. hz 131.3dB +-0dB

34hz tune        34.3hz (+1.9hz)        131.9dB (+1.9dB)            35-.. hz 131.9dB +-0dB

(I have to admit I didnt incorporate the increase in size by reducing port size)

FR between 34 and 31hz for reference

image.png.a30f071d9914e7e2e22492f86a45eeb1.png

 

So for these drivers a somewhat higher tuning might increase the output while sacrificing 1-2hz cutoff. Maybe just tune them at 34hz (or even higher), and use a single specific port divider to allow tuning between 31 and 34hz. 

Yes I like low frequency output, also for PA (as it suits my music), so I'm not eager to give up the LF output for some more output in general. But it does look like shifting the tuning a little bit might be beneficial in general. 

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