Eminence Alpha 10

Hi all

I was wondering if anyone could help - I have an eminence alpha 10
(see http://www.maplin.co.uk/module.aspx?ITAG=SPEC&ModuleNo=21377&doy=26m2#spec
for specs)

so I would like to make a subwoofer capable of 30Hz - 100Hz will no ill effects (distortion etc). I can get a maximum of 50 watts into it (amplifier could be better)

Anyways... I was wondering about the size of the box - please try to keep it small ish as I am limited for space if you have any ideas - would 30Litres be any good???

Thanks
Chris
 
Sorry but I don't think it will work very well. The fs is too high for any conventional boxes to get down to 30Hz. You could try a horn (or a tapped horn) but the Q is a bit high. Maybe one of the horn experts here could model it for you. Theoretically I suppose you could do it in a 10 cubic foot BR but I have my doubts.

The only other option I see is a Ripole as it lowers the resonance a little. Still have my doubts though.

This driver is a nice driver for it's intended application but it is not really a subwoofer driver. So how about it ladies and gentleman? Could he do it in a tapped horn?

mike
 
equalisation

Hi again.

suppose i could equalise it to play the low notes - you can buy/make bits of clever circuitry which increase the amplifier's output as the notes go lower...

Wouldn't the room resonance also help the low notes (people think they start helping around 40Hz)

I'm only doing this because the subwoofer i have is a 20W 5 inch driver in a tiny box which distorts with anything below 60Hz - so anything would be an improvement...

Thanks for the quick reply
Chris
 

ejohanne

Member
2005-08-22 3:28 am
You can make any high fs driver work in a small box and have a low f3 just by increasing the actual or apparent mass of the cone. Horn loading is one way but takes allot of volume, the other was is slot loading. By firing the woofer into a panel that forms a slot where the air escapes out the side you increase the mass and lower the fs. The basic physics are a cone is a weight and the air in the enclosure is the spring. Now imagine the mass is pulled and let go, it will start to oscillate at a frequency that is dependent on the softness of the spring and the weight. To have a lower resonance you can a) lower the spring force (bigger box/softer suspension) or b) increase mass (heavier cone). Some have experimented with adding weights to the cone but this is very dangerous as you can unbalance the cone or create breakup modes. Slot loading works well the only trade off is that the q will go up and efficiency will go down but thats acceptable to get a woofer that will play down to 20Hz. The reason that we have small subwoofers is because manufactures are willing to trade of efficiency for size. Power is getting cheaper so its not as much a problem as it once was. Car audio is the extreme with subwoofers that can work in tiny boxes and have 20mm+ xmax and low f3 but they need 1000w to get the same output that a pro audio 18" woofer with a light cone and a 8ft^3 box will produce with 50W. I have taken a similar situation and put a passive radiator right on it as if it was a isobaric box and then you can mass load the crap out of it and get 10hz f3s. Have fun.
 

ejohanne

Member
2005-08-22 3:28 am
I just remembered another good technique, You can add glue to where the dust cap meets the cone. There is glue there already but if you add a thick uniform bead you might be able to get enough mass to drop the fs by 15 or 20 hz. Then put it in a sealed box. If you have access to the woofer tester or other low cost methods (function generator, resistor, meter.....) of measuring the vas, qts and fs then you can model it to see what enclosure size would work best.
 
Remember the Alpha 10 is not a Subwoofer Driver, it´s more an entry-level Midbass Driver with a fairly low xmax and a small VC (compared to most other PA-Drivers). Using a linkwitz transform puts quite a lot of stress on the driver and uses a lot of Watts. The method is good for small enclosures and a very accurate, tight sound, yes. But you can´t get very loud, expecially with this driver and 50 watts.
The Qts is fairly high, so a small vented enclosure that tunes very low is not that recommendable, a sealed enclosure should give a smoother response. You could try a Volume of 120 Liters, tuned to 50 Hz which gives you around 45Hz (-3dB), but it should be quite "boomy" in sound and it´s not very small.
Try a Bandpass enclosure, there you might get enough low end in a not too big a box, if you have two drivers, the already mentioned isobarik approach is very recommendable. (it´s mounting two drivers face to face so they create a new driver - accuracy is improved and box-volumen can be reduced).
For playing around, try winisd which is free and good to start with.
 

ejohanne

Member
2005-08-22 3:28 am
Actually this driver is a good mach for 50W because of the low xmax. You shouldnt have a problem with bottoming out with low power and part of the reason that it is so efficient is because of the low xmax. It would sound better that a driver with a 15mm xmax and a 87db efficiency. Use it, you might be surprised.