Sub build! Beyma 15" driver, help needed :)

[Blaser]

sparky77 wrote:

It's really for the most part just a guess, without actually hearing the woofer in action, but judging by the xmax and xmech, the travel is going to be quite nonlinear bemuch more than 2 mm beyond the xmax and the distortion might become audibly noticeable.

Thank you for your clarification. Indeed, there is only one sure thing: you cannot know unless something like Ilkka's test is performed. There is no program that I know will tell you anything about distortion (and that's why I asked).
I have no time for now to enter deeply into details, but I will quickly make allusion to my DIY subs (let the commercial apart). I am feeding them with 2 KW each and according to modeling programs I am exceeding Xmax by about 12 mm. 2KW should send them to Xmech (40mm). Let me inform the subs clip the amps on Master and Commander and I can't really hear much distortion until the amps clip. I believe THD isn't meaningful below 10% (but when does it happen? ).

That tells us few things:
- On program material the subs are certainly not close to Xmech
- On program material the driver can handle more than the conservatively stated 1000 W (don't do it with SIN waves).
- Modeling is conservative and only accurate if you will be listening to SIN Waves.
- I can't know how much distortion there is when the driver's doing its Xmax

So I can't imagine why I would recommend only 40 W while manufacturer says 150 W.
I also don't think the best utilization for this woofer would be to limit the power input to the point there is still 7.25 more times excursion till Xmec regardless of Xmax.

Here you go for the graph

[Blaser]

A much more realistic representation would be the RMS value of cone excursion (and port velocity by the way). If you see below graph, you will note that the same 2000 W are now only pushing the sub to Xmas (there is still 1.46 times more excursion to reach Xmech and that still sounds acceptable for me). Actually this is more in line with what truly happens with Master and Commander cannon scenes when the amps clip.

IMO, you best use the driver when you give him some work to do, and this won't be unless it is pushed to at least 2/3 Xmech (IF YOU NEED TO)

Here's the RMS excursion graph

[Blaser]

Am I sounding crazy in this thread??

[sparky77]

I'm not saying that it has to be limited to 40 watts, you can most certainly get better performance using 150 or 300 watt amp, but you won't need the full power of the amp to get the necessary outpout from the sub. What is often left out of a speakers t/s parameters is the frequency range and amount of different harmonics used when testing the speakers power handling ability. Often times movies have less audio bandwidth being used at a single time versus the broader range of simultaneous sounds produced in music, which is why so many subs can sound equally well with music and HT, and the sub can seem to handle much more power than it was rated without damage. The point of this is that the amp the op already has will power 2 of these quite well, enough to nearly push the woofer to its limit, and get quite satisfying results and doing so on a low budget since he already has the woofers and the amp.

[fidomuh]

Guys, thanks for all the input - lots of good stuff in here

Now we all agree that Sparky has come with the most "optimal" solution, tuning of 25hz and a 307 liters box?

#sparky

Size limits are a matter of "how much better will it get" - no Wife, no GF, only me :P
My living room is rather small, but I have ( now ) a corner ( semi corner ) spot for at that yields a 70 x 70 cm ground area and roughly 1.8meters upwards.
If the output is "great", I have no problem with having such a monster in my living room

Sonotubes are lovely, but I have no idea where to get the stuff in Denmark - haven't seen it being sold anywhere :/
If anyone knows of such a place here in Denmark, please share

Like you said, my plan is to build 2 of these badboys and power them with the same amp.. My Surround amp limits at 80hz I think ( Thx Ultra 2 spec ), so a high pass should not be needed..
With the tune at 25hz, would I need a lowpass to clip it at, say, 22hz ?

Also, for me this is mainly an experimental build.. Just want to keep it for 2-3 years tops, before I build something more "awesome" :P
[Add]
Not that I would boot it out, just that I would replace them as my "living room subs" :P
I would probably put these in my ( hopefully ) office or something

[Mike P.]

Not much difference in output between 8 cu. ft. 23 hz tune and 10.8 cu. ft 25 hz tune. The advantage of the 10.8 cu. ft. box would be in the future should you wish to replace the sub drivers. Lots of 15 inch subs will work in that size enclosure. Make sure you post some build pics when you get started on this build!

[fidomuh]

Mike P.

Of course, I'll show off my woodworking skills

But I'm a simple man, a simple rectangle with cut corners will do me over just fine.. Though I'd like to see if I can get it to match the fronts of my Dali Ikon 8s


And without the front lining:


Will probably take some trial and error to make something that matches :P

[Blaser]

fidomuh wrote:

Now we all agree that Sparky has come with the most "optimal" solution, tuning of 25hz and a 307 liters box?

I agree with both Mike or Sparky, either solution will do fine. But I do not agree with the 25 Hz tune. Too high. You need to tune it max 23 Hz, that will help hearing your music without much involvement of port anomalies. For that, you'll need a 20 cm diameter, 45 cm long port (assuming 307 liters).

[fidomuh]

Blaser wrote:

I agree with both Mike or Sparky, either solution will do fine. But I do not agree with the 25 Hz tune. Too high. You need to tune it max 23 Hz, that will help hearing your music without much involvement of port anomalies. For that, you'll need a 20 cm diameter, 45 cm long port (assuming 307 liters).

23hz it is.
If the tune is too low, I'll tune higher in the same box.. Should be very simple

Any comments on the low-cut? Is it needed with the 23hz tune?

[Blaser]

If you're a smart user, you may do without. But in order not to start a war here, yes you'll need a high pass at around 20-21 Hz

[fidomuh]

Hehe, I'll find my notes on butterworth filters then :P

Better to have it all planned out before starting

[fidomuh]

Okay, so I've come up with a plan of making a footprint of 60x60 cm, 1 meters high, with 18mm mdf ( double front ) should yield ~313 liters.

With bracing and the likes inside, that should bring me down to ~307 liters..

Wouldn't you agree?

[Mike P.]

The internal volume of the box you describe is 286 liters. Subtract one cubic foot for the sub woofer, port, and adequate bracing. The net volume would be 258 liters, or a little over 9 cubic feet.

[fidomuh]

Huh?
Is my math broken, or is work just pushing too hard on my brain today...?

60 by 60 by 100, yields an equation of:
~56*56*96, yes?
Which gives roughly 307.000 cm3, divided by 1000 = 307 liters internally..
But I see that it needs to be tad higher, like 1.10 meters..

That should net 340liters, internally - without taking bracing etc into account..

[Mike P.]

I re did my math. 568mm x 550 mm (double front) x 968mm = 301 liters. You can build that size cabinet and subtract the volume of the sub, port and bracing, or build a bigger cabinet to include the sub, port and bracing. Either way there won't be a noticeable difference in output.

[fidomuh]

Ah, sorry, I was unclear on the double front thing, I will have the second layer of "front baffle" on the outside, yielding a footprint of 600 by 618mm

But the difference in size could be good if I simply wanted to swap the driver at some point, no?

[Mike P.]

Glad we got the math straight! Your box size will make a good candidate for a future sub down the road.

[Blaser]

Hey, are you guys familiar with SI units over there?

[fidomuh]

Blaser, yeah?

Why ? :P

Also, do you guys think a 3rd order Butterworth provides enough slope for the cut-off?

[Blaser]

Did,

Since you're from Denmark, it should be OK

I think a third order high pass is enough, even a second order is.

[SQCherokee]

that beyma looks alot like a peavey pro woofer

[hifijev]

Hi, I have not read all replies. But has an Isobaric subwoofer yet been mentioned? Saves a lot of space. Use WinISD Beta to determine the box properties...