This design look OK?

[garymck]

Hi,
I'm looking to DIY a cheap sub. I've come across this driver, a 15" low cost unit - $99 here in Australia

SPECIFICATIONS
Nominal impedance: 4 Ohms
Power rating: 250WRMS
Sensitivity at 1W@1m: 88.48dB
Voice coil resistance (Re): 3.5
Resonant frequency (Fs): 25.65
Mechanical Q factor (Qms): 3.552
Electrical Q factor (Qms): 0.578
Total Q factor (Qts): 0.497
Equivalent volume (Vas): 150.7Lt
Voice coil diameter: 65.5mm
X max: 15mm
Magnet diameter: 156mm
Magnet height: 40mm

It models very well. In a 100 liter sealed box (28liter =1 cu foot) it is 12 db down at 20hz. With some room reinforcement, lets say 6-8 db at 20 hz, it would only be a few db down. Thinking of a sealed enclosure because due to WAF it will probably have to be placed in a corner. I have also designed the box so I can add a port later (in the 100l box tuned to 18hz its 9db down at 20 hz, with group delay less than 12msec at every frequency over 20hz.)

Can someone check my design or pass any comments? Suggest better designs for it? Wondering if a cheap driver can really perform this well.

cheers
Gary

[Danny]

The problem with the cheap drivers is they normally produce muddy bass and at $99 for a 15inch driver this will probably be the case - I bought a 12inch sub recently with a RRP of $495 for just the driver and after listening to it, I can say that it produces a clean, tight bass end. My thinking is that if you want to add a port later you might be better off to just design the sealed enclosure now for just low bass without consideration for adding ports, then if you want to add a port in the future you design a ported box and put the driver in that, MDF is cheap and it won't cost you much more to do this, that said it's possible that you won't hear much change doing this, all I can say is have a look at the design chart and find out if it will make a notable difference. Where are you getting this driver from, it looks to me like it comes from Jaycar or Wow. General rule is probably the more you pay the better it will sound.

Regards
Dan

[garymck]

Hi Dan,

yes, its a Jaycar.

I was also looking at a 15" shiva at $264, but after looking at the specs it seemed no different to the Jaycar. It was a paper cone, had a smaller voice coil (50mm versus 65mm) and a pressed steel frame - so I figured why pay the extra $???

Can't afford to import from the US at the moment, and our driver choice here is so very restrictive. The only other driver I've seen is a 10" Peerless 850146 at $135. Seems to produce a reasonable performance.

Any Ideas at the low end?

cheers
gary

[Danny]

I'd say don't try and get anything below 20Hz. Have you got an amp to drive it with? If not you might be better off just buying a prebuilt unit with an amp built in. The size of the cone is unimportant to a point, I believe that it's more important to have clear bass as your first priority. - might get a 12inch cheaper as well so you may be able to spend a bit more. Jaycar has a few good drivers, watch the sensitivity higher numbers are better. If you do go with a driver and DIY a box for it, price an amp that will drive it before you go out and buy it, amps don't come cheap. I assume you know all about how to build a box?

Dan

[garymck]

Dan,

I'll be driving it with the power amp section of my NAD 3155 - a solid 150watts in bridged mono mode, using the sub output of my Yamaha RX-V657 to crossover. Looked at some of the other Jaycar drivers, but they all seemed to have a very limited Xmax (like 5mm) . Building enclosures is not a problem. In my early incarnation as a HiFi enthusiast I used to line my boxes with 1" of concrete (shoulda heard the bass.......But I'd need a crane to move a 100l concrete lined box :-).

cheers
gary

[Danny]

If you're using the amp in bridged mode make sure it can handle the impedance of the sub - eg if it puts out two 4Ohm channels the in bridged it will be one 8Ohm Channel. I'm a bit worried about the amp only putting out
150Watts when the sub can handle 250, be very careful in setting your level and make SURE that the amp is not clipping, an occassional clip is alright but sustained clipping destroys the driver. It's a lot harder to destroy a driver with a larger amp than with a smaller one, my sub is rated at 300Watt but I'm putting 600 through without problems because the signal is free from clipping. 5mm X-max isn't too bad - if you give me the catalog number i'll try and find you a response curve for the driver you're looking at and you can compare it to one with a 5mm X-max.

[garymck]

Dan,

the amp is switch selectable for impedance - so the 4 ohm load is no problem. In bridged mode the 150 watts is a genuine contiinuous power. It can double that for transients so I think it'll be ok - I'm not a super high volume listener anyway.

One other driver possibility is the Jaycar CAT. NO. CW2145 12" carbon fibre woofer.

12inch Carbon Fibre Woofer

This 300mm driver has a black woven carbon fibre cone and rubber surround a high temperature Kapton voice coil and a huge magnet weighing 1.412 kilograms.

It is suitable for both vented and sealed enclosures, however the vented box provides best bass extension.Specifications:-

Nom impedance: 8ohms-
Power handling 200watts RMS-
Frequency range: 25Hz - 3500Hz-
Sensitivity: 93dB 1watt 1metre-
Voice Coil Resistance
(Re): 6.9ohms -
Resonant frequency (fs): 21.3Hz-
Mechanical Q factor (Qms): 8.709 -
Electrical Q factor (Qes): 0.364-
Total Q factor (Qts): 0.350 -
Equivalent Volume (Vas): 230Lt-
Cone Area (square meters): 0.0494

believe the Xmx is 5mm (not certain.)

cheers Gary

[Danny]

CAT. NO. CW2145 12" carbon fibre woofer. - Response.jpg

Venom 15inch - CAT NO - CS2345 - Response venom.jpg

[garymck]

Dan, 15" doesn't look too shabby????

Gary

[Danny]

The Response certainly looks alright, its just the clarity/quality that I was thinking might be lacking. Even so if you're not listening at Extreme SPL's and driving the speaker to it's limits, it should turn out alright.

Dan

[garymck]

Dan,

I guess we'll see! I'm going out to buy the mdf to build it today.......Will post results when it's built good or bad..Probably in a week or so

Gary

[Danny]

Good Luck Mate
Would like to see how that turns out

Dan

[Exocer]

garymck, it looks like you found a bargain! Good luck with your project.

If you find that you aren't thrilled with it's performance however (which I hope doesn't happen), the next best cheapest step forward would be the Dayton DVC 15". It models very well (85liter sealed enclosure) with just a modest 240-250 watts of nominal input power and costs about $130.