[TrophyJem]

I'm planning on building myself a DIY passive subwoofer.

I have a spare Arcam SA200 amp that I'm intending on using to power it, so plenty of power available.

Now to my question.

I have two Vifa drivers that I acquired many moons ago with a spec as below and I'm trying to decide if they are even remotely suitable to build a subwoofer with, or if I should purchase somthing more suited for this application?

• Vifa P21WO-20-08, 8" cast frame woofer.
  • Cast magnesium basket
  • Mineral filled polypropylene cone
  • Rubber surround
  • 80 watts RMS/115 watts peak
  • Voice coil diameter: 1-1/2"
  • Inductance (L) = 0.90 mH
  • Impedance (Z) = 8.0 ohms
  • DC resistance (Re) = 5.7 ohms
  • Frequency response: 28 - 4,000 Hz
  • Magnet weight: 24.6 oz.
  • Fs = 28 Hz
  • SPL = 91 dB @ 1W/1M
  • Vas = 3.99 cubic feet or 113.1L
  • Qms = 1.60
  • Qes = 0.41
  • Qts = 0.33
  • Xmax = 4.0 mm
  • Dimensions: 8-1/2" across with 7-3/8" cutout

I have the neccassary experience of woodworking etc, so that does not phase me in the slightest. It's the calculations and choosing a suitable driver that I'm finding tricky.

[swift1]

Hi TrophyJem,

have you tried contacting the manufacturer about this..... I've made loads of car sub boxes for JBL subs long time ago and all I did was contact JBL tel them what I was doing then they would fax the size of the box including what size mdf i should use etc.

[dj-dulux]

The first thing you need to decide is what type of box, sealed, IB, ported, bandpass 4th order etc. They all have pros and cons. Once you know what space you have and what box type you want you can design a box. Plenty of programs on the internet for calculating box sizes, also books like the Loudspeaker Design Handbook (1-882580-10-9) and Loudspeaker and Headphone Handbook (0-240-51371-1) are worth looking at.

Depends how much of the design you are comfortable with, if you have done electronics and understand analogues then its fairly easy to get your head into the design (LL Beranek, Acoustics, Acoustical Society of America, 1993, is a good place to start).

Word of warning: the small signal parameters quoted by manufactures are not that accurate, often >20% out. Therefore you need to measure them yourself or do lots of trial and error. I know commercial designers who use both methods so neither is better than the other!

Dupe...

[TrophyJem]

I thought the sealed box would be a good starting point. Size isn't a major issue to me as its going in a dedicated cinema room.

The problem is with the calculations I've done (spreadsheet from The Subwoofer DIY Page), I've come up with a 32.32 litre enclosure for one of these Vifa drivers (or double for both) that will only give me a -3db cut-off of 60Hz. This just didn't seem a low enough frequency to me for film use.

So I'm guessing that purchase of a different driver may be the way to go.

[IronGiant]

-3dB at 60Hz doesn't sound too promising, what main speakers are you using?, because you may find they go lower than that.

Dave

[Sawdust]

Have a look at WinISD: LinearTeam

It's free, easy to use and will do all the calcs you need and help you design a box.

I think you will struggle to get low enough with a sealed box and will probably end up needing to build a ported cabinet. As far as I know, most sealed subs use additional equalisation to boost the bottom end.

One thing that would worry me about the drivers you have is the X-max figure of 4mm. An 8inch driver with an X-max of 4mm isn't going to move much air and is likely to keep bottoming out at anything other than very low volume.

I guess it depends how big your room is and how loud you like it. I built my sub based on the BK monolith - same drive unit and port and same cabinet volume. I do have a big room but it's not unusual for it to bottom out on the really loud bits.

Cheers
Mike

[TrophyJem]

Hi Sawdust,

Thanks for the link. I'll have a good look at that.

Yes I wondered about the Xmax figure, as all the examples had about 7 or 8mm.

I think a ported box maybe the best option and I'll search for a better (bigger) driver at a sensible price.

I'm after plenty of bass, as I do like my action movies!

[TrophyJem]

Originally Posted by IronGiant

-3dB at 60Hz doesn't sound too promising, what main speakers are you using?, because you may find they go lower than that.

Dave

Arcam Two's

[TrophyJem]

Can anybody recommend drivers worth looking at for sensible money?

[bigmacx]

The Peerless XLS range are well thought of and don't require massive boxes and amps to get the best out of them. There's also a lot of DIY projects using them that you can follow on the web.

Most importantly they're available in the UK, a lot of the decent stuff is only available in the US unless you want to spend a fortune importing it (they obviously weigh quite a bit).

Available here for example:
Peerless XLS10
https://secure.wilmslow-audio.co.uk/...4?osCsid=57583

Regards,
Mac.

[tony brazao]

Originally Posted by TrophyJem

Can anybody recommend drivers worth looking at for sensible money?

How long is a bit of string?

This USA based firm makes one of, if not the most potent and capable home cinema subs in the world (test results here).

They also sell the parts (amps and selection of drivers) for those wanting to do custom/diy builds and export to the UK. Before any one asked, I am not a sales rep and I have never heard one of the above firm's products.

[TrophyJem]

My piece of string is around the £40 mark.

What's the likely hood of me finding a suitable driver at this sort of price that would be suitable for a DIY sub?

Any recommendations / suggestions?