My first Diy System

[farcasmihai91]

Hello !
I recently found an old Monacor (Monarch) SP260HT 200W 8 OHm just sitting around! I want to build my first Diy System with it. Nothing fancy, just a cheap 2.1 system. I want to use the SP260HT for the subwoofer.

This is what i could find about it:
Thiele Small Paramater (TSP) SP260HT

fs: 25Hz
spl: 93db
cms: 0,78
mms: 48gr
qms: 11,43
qes: 0,21
qts: 0,20
vas: 130L
rdc: 6,1OHM
le: 0,8mH
Schwingspulendurchmesser 65mm
Bbelastbarkeit 200w
Luftspalthöhe 10mm
Bl: 15,9
Sd: 343cm²
Kaptonschwingspulenträger
Hub lin xmax 9mm
Hub abs xmax 12mm


I did some calculations in WinISD. It recomended me a vented box 13l in volume: dimensions 30x45x20 (cm) including .25cm width pannels (woodwork). Here is where it gets tricky: it recomended me a vent of 10cm in diameter and 1.5m in LENGTH !!! WTF !?

Also i want to tune the box to 35Hz ... how do i do that ?
And I would also like some sugestions for the main speakers. I want some decent cheap mids and tweeters, that would balance well with the sub.

Any recommendations are welcome. Thanks!

[ßart West-VL.]

Hello,

I'll try to help some, as I'm busy simming all weekend anyway, lol.

What diameter tubes can you get your hands on? (inside diam.)
A box with an internal volume of 45l (net volume to the driver!) and a tuning at 35hz would need a tube of 75mm with a length of 185mm.
At 100W you get a maximum air speed of 33m/s at 32,5hz, but I think it's acceptable¿
If you can high pass it at 30hz 4th order, you can give it 100W all week and there will also only 21,5m/s airspeed maximum at 37hz.

hope I could help someone else for a change

[ßart West-VL.]

O yeah...
It has a -3dB point at 56hz
and -6dB at 40hz

Better upload a screen shot...

[ßart West-VL.]

So...100W, simulated coil induction, a 20°C temp rise and a high pass at 30hz 4th order slope.
SPL at 100W, 35hz would be 102dB, this is at the -10dB point.

[farcasmihai91]

Thanks for the quick response.
I can get a tube of 75mm with a length of 185mm. I can get virtually any size tubes, that won't be a problem. I just need to know exactly what kind of tube i need.
And just so i understand correctly: net volume to the driver is the volume inside the box - volume of the driver - volume of the tube ?

You gave me the example with the 45l box. Does this driver really need a 45l box or was that just for refference. Because the calculation i made (probably wrong) told me i need a ~13l box for this driver.

So if i understood correctly: tuning a box is just a matter of choosing the right size of tube?

Sorry about all the questions, but i have virtually no experience


Correction:
I see the graphs now. So i really do need a net voulume 45l box, and a 75mm inner diameter vent wit a length of 185.5mm.

So the box should be something like 41x63x27cm. Is that about right ?

[farcasmihai91]

Oh sorry, i see the graphs now. So i do need a 45 net liter box, and a vent with 75mm inner diameter and 185.5mm length. So the box should be something like: 31x63x27cm?

[farcasmihai91]

I also found a tube: http://www.audioalchemy.ro/accesorii...x/BRKAH505.jpg
It has an inner diameter of 76mm and 250mm length (adjustable).

[ßart West-VL.]

You can use a smaller box but the vent tube will get longer.
the vent may sit on the outside too, but most of the time this is unwanted.
The volume has to be calculated without bracing, driver volume, panels and vent(s), so a large vent in the box would increase box size considerably.
Your dimensions of the box ends up with 70 litre volume but now you subtract the thickness of the panels, the vent, the braces and the volume the driver occupies.
The tube can be anything stiff enough to not deform, like thick cardboard, PVC, even metal but you might want to dampen metal tubes against ringing. (experiment)

Play around in WinISD with the tuning and box volume untill you see somthing you like in the graph.

[farcasmihai91]

Is putting the drive in water for measuring its volume safe ?

the tube volume is easy to calculate. The wall thickness of the box is included in the calculations WinSID does.

Thanks alot for the help!

[ßart West-VL.]

Heheh, better not drown your nice driver.
Don't bother about the 0,1l difference a rough estimate could make, the result of the build will not be that accurate anyway.
If you can pack the driver 100% airtight, you can slowly lower the magnet in a large bucket I guess, don't submerge it, it's the backside you want to know. But anyway, the result will give you a volume that's too large, the plastic bag won't go deep enough under the basket.
You can add a cm or so to the tube lenght and measure the resonance of the system afterwards and cut the tube bit by bit until satisfied with the result.