Which drivers for my next open baffles?

[SimontY]

I calculated it using pie (mmm) ARRRR squared . My "C" grade at GCSE maths came in handy

Obviously I didn't account for what was and wasn't radiating area. Anyway, it's still more area than 4 x 7", as I will have got Sd wrong for those too

 

[SimontY]

So are you in favour of the Skytronics ahead of Beta 12LTA then Graham?

I can always change them later if it's not good enough - a couple on my parcel shelf with T-bass appeals...

Simon

 

[SimontY]

I've been X-Baffling myself!

Here are 4 relevant drivers (just one of each, so not a reflection of a final system):

 

[SimontY]

This shows that the Alpha 15 is, as we already knew, a kick **** OB woofer! It clearly has the flattest response, so needs the least EQ. It also has big volume displacement.

Of the 12" drivers the Eminence 12LTA is clearly going to play a lot louder than the Skytronic plastic coner, but is not quite as flat, so is maybe harder to get "right" with a passive crossover. The 12LTA is also twice the price of the Skytronic and has a whizzer cone, which might contribute to more filtering of the HF being required. Le is not specified for the Skytronic woofer but a wild guess says it's higher and being plastic I'd not expect any big breakup problems.

So on balance I think I favour (only slightly) the Skytronic 12" woofers.

The 7" looks ok - like a much smaller, lower output version of the 12LTA - but any of the big woofers will be a significant step-up in displacement.

Simon

 

[SimontY]

I think, on balance, 15" woofers are not required for my application. I do not intend to use much equalisation, and due to my small room, it may be a daft idea attempting to reach extension lower than about 40hz.... it has been suggested that it's not possible to go low in a small room with OB anyway.

I've gone ahead and ordered 4x 12" Skytronic 902-222. £65 posted for FOUR 12" woofers is stupidly cheap and little to pay if it doesn't work out as intended.

I was almost tempted to get a couple of their 8" Kevlar woofers to try as mids, but I think I'll try the Beta 8 first

I just seem to like the sound of Kevlar mids.

Simon

 

[bigwill]

SimonTY

Congrats on your purchase, I am very curious as to how these woofers will work out. Be sure to post plenty of pictures!

Sims aside, my intuition says they will work decently

 

[SimontY]

Thanks Will,

I will be sure to document the entire project fully! I will begin a new thread for it as this one's getting a bit long and was just for the driver selection.

I'm now on the hunt for suitable T-bass transformers...

RS do the following spec:
Transformer,toroidal,300VA,0-230V pri,50/60Hz,2x0-30V sec

..for £25 each

Simon

 

[Graham Maynard]

Hi Simon,

As you can see from XLBaffle the Alphas was much more efficient.

A 300W transformer would have been okay for 2x Alpha, but not 2x Skytronic.

I can recommend Farnell-InOne part number 433-5429 @ £31.10 with free ordinary post when I last purchased. 500VA 40-0-40V.

This with the Skytronic 12s will please you no end, as long as your amp has the drive.

Cheers ...... Graham.

PS. I would not choose Eminence 12"ers for OB, they all roll off at too high a frequency.

 

[SimontY]

Graham,

I don't understand your transformer rating selection so I will just trust you on this! The last thing I want is for the performance to be limited by such a part.

8mH choke ok for this one?

My amps are good for 125w/8 or 180w/4. Not huge current delivery then but quite powerful!

Thanks,
Simon

 

[Graham Maynard]

Those drivers are 6dB down on anything I have so you need more drive.
The larger trafo has lower winding resistance/dynamic loss and you will hear the difference with those lower Fs drivers.

Going from 7" to 12" will be an excellent upgrade for you, so I'm just waiting now to hear how much more broad your smile will be.

Cheers ......... Graham.

 

[SimontY]

Excellent, I'm looking forward to hearing all the new drivers

Sadly that transformer at Farnell is discontinued! The other 500VA toroids seem to start at over £40, which is a bit much.

I'll look at 400VA next... edit: can't see any of those!

I'm not really happy paying £80+ for two transformers.

Might I "get away with" 330VA?

If so the saving is huge:
http://uk.farnell.com/avel-lindberg/fd330-30/transformer-330va-2x-30v/dp/177942

Those "limited stock - we ordered too many" are only £18.23 each!! I feel I could do worse than try these

It's a good step up from the 100VA I'm currently using, if not totally perfect.

Simon

 

[Pano]

Good job, then! Glad you pulled the trigger.
Those 4 12s should really rock.
My guess is that you'll need about 5 or 6 mH on those woofers (drivers in parallel). Get a large gauge iron core type, don't bother with air core for this application.

You may also want to play with a shunt cap, if the woofers reach up too much into the midrange (likely). The shunt cap won't change the crossover point much, it will just make it roll off faster - the bigger the cap, the faster the roll off.

I like Graham's T-Bass circuit, but you don't have to go there right away. Build your rig 1st, then add refinements like the T-Bass later. You'll have enough on your hands just getting the crossover tuned and the speaker voiced.

As you can see from XLBaffle the Alphas was much more efficient.

Yeah, I must have done something wrong in my sim of the Alpha. Gotta have a look at that.

 

[ShinOBIWAN]

Excellent, I'm looking forward to hearing all the new drivers

Sadly that transformer at Farnell is discontinued! The other 500VA toroids seem to start at over £40, which is a bit much.

I'll look at 400VA next... edit: can't see any of those!

I'm not really happy paying £80+ for two transformers.

Might I "get away with" 330VA?

If so the saving is huge:
http://uk.farnell.com/avel-lindberg/fd330-30/transformer-330va-2x-30v/dp/177942

Those "limited stock - we ordered too many" are only £18.23 each!! I feel I could do worse than try these

It's a good step up from the 100VA I'm currently using, if not totally perfect.

Simon

Hey Simon,

The price of toroids has gone up in recent years as raw materials become more expensive. Farnell has always been expensive but now I think they priced themselves out of most DIY pockets.

A short while ago I was looking for 500VA toroids and used Airlink. I paid around £30 each. Quality is really nice too, even better than the Farnell ones which are great too.

http://www.airlinktransformers.com/

EDIT:

Also have you seen these:

http://cgi.ebay.co.uk/Fane-1-Pair-1...634741&_trksid=p3911.c0.m14&_trkparms=72:1301|66%3A2|65%3A12|39%3A1|240%3A1318

I imagine them to be suited for OB but with less bass extension than some drivers due to the high FS. The same ebay seller occasionally has the 12 and 15 inch versions of this driver which are more desirable with lower Fs and higher sensitivity. They only a fiver more for the larger sizes too.

For the price I think there's no risk whatsoever.

 

[pacificblue]

As you said, this will not be the last speakers you will ever build. So here is another not too expensive 12-er to consider. SP-302C for 31 € here in Germany or ~26 £

 

[bigwill]

As you said, this will not be the last speakers you will ever build. So here is another not too expensive 12-er to consider. SP-302C for 31 € here in Germany or ~26 £

CPC Sell these, if anyone in the UK is interested

 

[SimontY]

Good job, then! Glad you pulled the trigger.
Those 4 12s should really rock.
My guess is that you'll need about 5 or 6 mH on those woofers (drivers in parallel). Get a large gauge iron core type, don't bother with air core for this application.

You may also want to play with a shunt cap, if the woofers reach up too much into the midrange (likely). The shunt cap won't change the crossover point much, it will just make it roll off faster - the bigger the cap, the faster the roll off.

I like Graham's T-Bass circuit, but you don't have to go there right away. Build your rig 1st, then add refinements like the T-Bass later. You'll have enough on your hands just getting the crossover tuned and the speaker voiced.

Thanks for the tips Michael. This will be my second open baffle project so much of what you say fits nicely into my established ideas. I am still not 100% happy with the balance of bass in those speakers - perhaps having better drivers to start with this time will help.

Simon

 

[SimontY]

Shin/Ant,

Hey, how's it going with your setup??

I've ordered my 4 x 12" woofers now so I'm not getting any others...yet! Cheers for thinking of me though. And I notice that seller has an RS SPL meter for a good price too.

And thanks for the Airlink tip. It's still £30 for a 500VA toroid, but that price is ex. delivery and VAT. It's still on a par with Farnell's prices and following your tip on quality and Graham's insistence on monster transformers I went ahead and ordered 2 x 500VA 40-0 40-0 toroids!

I have T-bass on my current speakers and now can't wait to hear what it can do for bigger woofers.

Simon

 

[SimontY]

Pacific, those Monacor car sub-woofer drivers look like they have really great OB specs! They're astonishingly ugly though

It seems there are various affordable OB woofer choices around.

Simon

 

[pacificblue]

They're astonishingly ugly though

What are you saying? The eighties look is all the hype again with people here in Germany.

 

[SimontY]

Hehehe. I may order some Beta 8 and APT-80 today, I just need to go over the old finances lol