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design help on small 6th order BP welcomed


MomoTon
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I´m working with two friends on a high end sound reprudaction system, and although this is our first project, we are about to aim for the highest.
The main Speakers use an Mundorf Pro AMT with two Beyma 12MC700ND in closed boxes, in MTM config., driven by a FP10k. Under the mains, we use two skrams, loaded with the 21ipal + Mod, another two are hopefully coming soon. 

Now we are designing a smaller Setup for monitoring or to use in smaller rooms. For the heights we use again a Mundorf AMT (for half the price as seen in the link, but still crazy expensive, but they are worth all the Money), and one 10MC700ND in a closed Box, which we choosed for it´s extremely low distortion. Hopefully a Hypex Fusion FA503 Amp will provide enough pover to come down to a crossover point at 100Hz, maybe 80Hz, when not driven too hard. 

So there are missing one or two small, compact subs, and as we couldn´t find a design which was promising enough, we desided to design our own 6th order bandpass. We found design recommendations on B&C, (S12BP) and 18sound (12in BP subwoofer), but both of them just doesn´t seem right.

So I started to design my first 6th order BP from there, calculated the volumes and port dim. of the two designs, threw it into Hornresp, looked at the response and was not really satisfied. So I searched for other similar drivers and found the 12P1000ND but also the SICA  12 S 4 PL, both for around 320€. I threw them both into the sim. and they looked pretty good, much better than the orignial drivers. As the new drivers have much more powerhandling than the originals, I would tend to use the B&C design, as it uses 220cm² Ports (rect.), instead of 157cm² (round), also the tuning of those seem to make more sense.

A first big question is about the different alignmet of driver and the vents between the two designs as seen below. Intuitively I would say the 18sound has an advantage here, as the B&C let one part of the driver look directly into the vent, which I would guess makes it easier to hear distortion? It seems they did this as an tradeoff for the longer rear Chamber vent.

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I would try to do a mix of these designes, mainly like the 18s., but with bigger, rect. Vents like the B&C.

Which of those (four) designes would you recommend? Or is there another smart possibility? I would go for my left one, if I can fit the vent lenght inside, alternatively for the right one.

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My other quastions are basicly about how to use hornresp:

-LC1/LC2: is here the longest path for a standing wave requested, or the nearest parallel wall of the driver?

-should I always click on the "Lossy Le" button in the Wizard schematic window?

-I tried to hold the Port velocity at ~ the rated RMS Power under 25m/s, is that ok or still too high? the tradeoff for bigger Vents are it´s lenght and port resonance, right? How much over the crossover of ~100Hz I should hold that one?

-Does it even make sense to go for a 100L cab, or would it then be better to use something like a 14in or 15in driver?

-maybe one could look at my hornresp input to see if it makes any sense at all?

-any other advice/ design suggestions are very welcomed, as this is my first try on designing a 6th o. BP, I would appreciate any comment/ suggestion/ idea or other help.

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On my way through the forum I came across a sketch Ricci put in another thread which looks pretty similar to my sketches, except the front chamber being a horn like in the skram design (and its for a 21" chassi).

What are the advantages/ differences using a horn instead of a volume + vent? I would tip on more output due the compression, but because it´s physics, there must be some tradeoffs?
Can anyone help me understand how to splice this design into sections to put it into hornresp, and with what kind of compression ratio I should start messing around with?

Alternatively, are there good papers/ explanations on this subject to find?

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Welcome to the forum.


I have not looked at these designs in detail, but my 2cents. If you're using a high sens. pro style driver, I don't really see how the system benefits from putting that kind of driver into a 6th order bandpass because the bottle neck is still the low end and its not lacking in mid-bass punch. Using the same size box, you can make the simple 4th order with a larger port with more headroom. I would be interested to see if anyone has experimented with 6th order and compared it to standard ported boxes (same size) with these type of drivers.

 

 

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I think for a small box you would be better off looking at reflex as high excursion 12" drivers are usually capable of overloading most practical port designs.  The main limitation to SPL is port compression and 'cuffing' due to the high air velocity near tuning.  To this end what I think you need to look at more complex port designs that incorporate flares rather than designs using more ports that take away volume that could be used for your fundamental tuning.  Here are some guidelines on ports:

https://www.subwoofer-builder.com/flare-testing.htm

Saying that tapped horns are series 6th order bandpass boxes with huge ports so it might be worth looking into a tapped horn design if you want a bandpass response.  You're using DSP so attenuating out of band issues (which are never as bad as Hornresp predicts due to losses) should be trivial.

 

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Thank you two for your comments! 

I will look for different drivers in BR designs and also 4th Order BP. 

I did only a little research on them, but wasn't able to get a 12" in a 4th o. near to the response of the 6th o. design. So I tried to use a 15" instead, and with a little more modeling here,  in the same nett volume, a B&C15Sw100 or 15ds100/115 sems to be the better option over the 12", especially as the price is the same as for the beyma 12p1000

 

hope to have some time at the weekend to model some 4th o. and compare them to the BR design

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  • 1 month later...

Through recommendations on other forums, I came to the conclusio to try a closed box first, if the output doesn´t hit my expectations, I will change to a BR design

External dim. should stay less than 150L
if going for sealed, I would make one duoal opposed box, a second would be added later
in a BR design, I think 2 drivers should already hit my expectet SPL so this one would be cheaper obviusely
Drivers that came in my mind:

15DS100 (~250€)   120L Vb recommendet for 40Hz tuning
15DS115 (~300€)   80L Vb recommendet for 40Hz tuning

18DS100 (~264€)   rec. encl. size 200L 😕 (for 35Hz Tuning) In 150 L ext., I don´t think it will get much more than the half of it...
18DS115 (~322€)   100L Vb recommendet for 40Hz tuning

So although I would prefer the 18DS100 for it´s price/ output, I think the 50€ upward for the DS115 would pay off for the smaller enclosure size?

 

Any other driver suggestions/ good enclosure recommendetions for those drivers?

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High power closed box doesn't work well for PA the air inside the box gets hot so after an hour or so you will get noticeable reduction in output, I have tried it and changed to a design closer to ported.  Some reduction in box size should be possible by accepting a non flat un-equalised response.

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  • 4 months later...

Screenshot_20210911_205800.thumb.jpg.50b9b52e71161c3129cd6beb93fabf65.jpgI've finally built my first self- designed subwoofer. 

I decided to go for the 15DS115, ~90L net Volume and big ports with 3D adapted flares. 

 

The difficult part was actually to make the front small enough that the ports fit within the depth of the speaker, while trying to get as much flare area as possible. A simple 40mm flare radius would have made the front much larger. 

 

Tuning was more or less a blind shot. The vents were removable and I tryed 3 different lenghts before they and the back panel were glued. As I ran out of time,  I measured just some short sweeps in REW, trying to tell the tuning frequency from the SPL and phase graph and then cut some cm off the vent pipe

Tuning should be somewhere at 38 Hz now, but that's just what I can tell from the Rew measurements.

 

I put more than 90 hours into the design, but therefore it is a n enjoyment to put all the parts together and see how perfectly all of it fits. 

I havn't really tested them to their limit, they are way to overpowered as monitor subwoofer, but I'm looking forward to hear and mwasure what they are capable of. 

 

https://www.dropbox.com/sh/frit8jmum8ptds3/AADfJ97ODnKO5Y4Gz1iBtawva?dl=0

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Outer dimensions are 43x58x65,5cm so ~164L.

I think I could have lowered the net volume (~90-95L, B&C suggest 80L), also at the cornes I loose a little volume, but as mentioned, the limiting factor was the port lenght and to fit it inside the cab without to bend it while letting the front big enough for driver and vent flares.

Some other facts about the cab:
The "main" front is 30mm, plus 15mm added under the driver cutout to have enough depth for the 40mm Flare, and another 15mm at the backside of the front, as reinforcement for the driver (30mm-20mm would have left just 10mm for screws) and as pipe-holder. (this one was meant to be 12mm, I just didn´t think about it and used 15mm instead).
So at the thickest part, the finished front is 60mm or 2,36" thick, yet it wasn´t that heavy, obiusely because the front is mainly just three holes rather than remained material.
All the other parts were made of 15mm MPX, but as you can see, i didn´t skimp on brazings, so the cab should still be pretty stiff....
I hadn´t time to put it on a scale yet, and this one isn´t a lightweight for sure, but at least, a single person is able to lift it up and put it on a wheel board.

 

I will post measurements as soon as i have time to make some. The ones I did to test tuning frequency were really dirty (no fix mesaurement distances and even bader, a back panel that was hold together with clamps, as I had to be able to remove the pipes through it to make them shorter).
Actually, I always made a ~2m ground plane measurement and another one at the outlet of the port. With the second one it was pretty easy to determine a tuning frequency, although I have no idea how close this one comes to an impedance measurement.
Honestly, I don´t even know why it´s important to know the exact tuning, or how I can find the optimum, but the measurements showed some dB more around 40Hz with the shorter port, still there was enough low end in the listening test.
The great thing is that the ports are so big, that it should be ok to close one of them for small gigs or a home theatre show at home, tuning drops down to ~25Hz with one port closed.

 

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Impressive ports.  The 15DS should be one of the very best 15" drivers.  The best way to find tuning is to measure the impedance of the box W.R.T frequency where it will be at the minimum value between the two peaks.  If you only have a microphone you could also try looking for a notch in the near field of the woofer response and peak in the port response but this may be complicated by their close proximity.

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