Bastani Prometheus w/dipole sub

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Here are some pictures of my latest project.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

To see the buildingprocess se HERE

The sound is VERY nice.

The subs are active trough a behringer DCX. The top is fullrange trough a tiny EL84 tubeamp.

Thanks Nuuk

It's the Peerless SW315. They are connected in parallell. To increase the Qts I have connected a 2 ohm resistor in series. Actually I have disabled the eq. Not really needed at this point. But I live in a concrete flat, and the bass can get quite exaggerated if there is too much level. So I just fill in the good signature of the prometheus. In another room maybee more eq is needed.

Well I have always thought that the Prometheus deserved dipole bass and your design fits in so well with the main baffle!

I like my TL woofers but they are so large and I am growing tired of having to lean over them to reach my CD rack. So you have rekindled my desire to do something very similar! ;)
Very cool!

I looked for the SW315 on the peerless (tymphany) website and could not find it. The closest I could find was the 315 SWR (831857). Is that it?

Also, do I understand you to be saying you aren't using any eq? Are you doing anything to integrate the subs to the mains?

I'd like to build a dipole using the CSS FR125S and a woofer, but I figured I'd need to go active to do the crossover (which I can't afford at the moment :( ).


Paul Ebert
Thanks for the kind words.

It's the SWR yes. Did not remember the last letter :)
I am using the Behringer dcx2496. It's a digital 3 way crossover. I could apply eq if I want. It's a feature in the crossover. I have tried, and used it for a while, but for the moment it's turned off. The resistor in series increases the Qts, which is a natural EQ for the elements. I would recommend that you try EQ if you build a pair. If I move to a larger room, or a room with wooden walls, I most certanly would apply EQ.
Now I integrate the sub by trying out different X-over freq. and levels.
The woofers com in at 82 hz/ 48 dB. The prometheus goes fullrange, no filter, bur rolls of around 80 hz.

If you go for any speaker with seperate woofer, I would recommend a separat amp yes. Active setups have advantages there.


Very, very nice. Dipole bass is Where It's At with open baflfe systems, no doubt. I was wondering which EL84 amp you are using. One thing I love about high sensitivity wide rangers is that they can extract unreal sonics out of a couple of sweet SE watts. Right now I am using the Bottlehead SEX amp, and a Korneff 45 for my Visaton OB.
Hi Icebear

Very nice speakers you have there. And they're inspiring: I was planning to go for an H-frame for sub, but your W-frame solution is much more appealing, because the frame doesn't get that high, allowing to build the midrange woofer and tweeter (or fullrange) at about ear level.

So I'm going to build dipoles to, with sub's in a W-frame and a B200 from Visaton in an open baffle - crosssed at about 100Hz. For the subs I looked at the Toxic CBL-300 (available at conrad for 30 euro's), which is 12" with Fs of 21Hz, but Qts is about 0,4, a bit too small. And actually I wanted at least a 15". So i starter searching at and found some 15" speakers for less than 20 euro each, but no data, absolutely no data available. I let them for what they are when I found this little one

It's sensitive, it has a Fs of ~30Hz, a Qts of 0,62 and lots of Sd. I think this one will manage the task (two per side). Yesterday I bought four (actually I bought one for 39,95 euros and send them a e-mail I want four). Now I see they are asking 49,95, let's see what they'll charge from me.

Hum, actually this post has not much to do with your speakers - to get back to the thread, once more, many thanks for the inspiring thoughts.

Hi Erik

The Visaton looks good. Are you planning to cut them of at 100hz, or just let them roll of naturaly in the OB?
When it comes to Ob bass, it's strange how many different drivers actually works ok. You can look at the specs and shake you head, but works ok when you try them out. Ofcourse it depends om the soundlevels you are aiming for, but at normal to loud levels, many 12" and 15" wold work ok.
If the basses have FS at 30hz, you may have a peak at these freq. It may be an issue, or not. If you set the elements in a Linkwitz dipole or a Ripol, you will lower the FS some. I have tried them both, and found the Ripole satisfying. You migth try it. It does not make a big footprint either. The Qts of 0,6 is good. Try the resistor in series to get it even higher.

This is taken from the site (
Fs can only be altered by mechanical modification of the woofer, but Qts may be altered to suit your needs by application of a calculated series resistor. The formulas used for this are:
Rs = Re*(Qes'-Qes)/Qes

If we for example want to alter the Qts in the Peerless 831857 driver from 0.46 to a more suitable 0.6 the figures are (Qms = 3.90, Re = 5.5):
Qes' = 0.6 x 3.90 / (3.90 - 0.6) = 0.68
Rs = 5.5 x (0.68 - 0.46) / 0.46 = 2.6 ohm

Best regards
Hi Bjørn

Thanks for your reply! So I bought 4 units of those 18" subs. I thought about a H-frame, but they are too big, they wouldn't fit my room, so I decided to go for a W-frame.

At first I will run the B200 fullrange, but later on I plan to add a HP crossover at 100Hz, I believe both the valve amp and the speaker will like not having to play the lower octaves.

As the last step I plan to add a ribbon, see if the sound gets better. It will be driven by its own active crossover (at 10kHz) and amplifier.

I am going to build the sub crossover now :)

Nuuk said:
Thinking about the arrangement of the woofers in Icebear's speakers, I wondered whether having them in that position is likely to cause any damage. They are neither vertically nor horizonatally mounted so is that likely to be a problem for the suspension?

I have four Visaton W250 drivers working in the same W-arrangement for about one year now. No signs of sag or voice coil rubbing whatsoever.
Only some VERY sloppy suspensions or VERY heavy cones should be at risk in this configuration. The dynamic loads on the moving parts of a driver are so much stronger than the static gravitational "load" that any quality driver suitable for dipoles should have no problem with a 45° position IMHO.
Now I have a question - wouldn't it be possible to use an arrangement just like the dipole subwoofer used with the Phoenix speaker from linkwitzlab? I mean, build that sub (should be no higher than 50cm) and but the main baffle above it?!

I don't see why not! I think that the Phoenix uses 10 inch woofers so you can get them in vertically. But for larger woofers, a fold is required to keep them under the main baffle. :smash:
Hi Icebear.. and all the rest of you, too!

Dipole or OB bass has not really interested me before, but I have been looking into this for quite some time now..having read all the posistive comments on the reproduction of mid/highs. The mid /high section is quite understandable, but moving down the bass is quite something else..
Finding your thread , it occured to me that I have access to one pair SWRs for free... and possibly another pair at a very low price....

there are some info to find , but not very much conclusive....
KYWs OB spreadsheat do tell part of the story, but still there's a lot left....

Icebear- since you say you don't use EQ, - other than the 2 ohm resistor,- would it then be possible to integrate the bass section passivly to a mid/high setup of suitable sensitivity..????
I would prefer to go without bi-ampingand active XO, if possible....

other comments/ ideas ????
Hi AuroraB

It's possible to go passive, but the inductors will not be cheap, and it will kill the dynamics in the system. Another problem will be level matching against the rest of the system as you pointed out.
The basses is also putting out a fair amount of inducted returncurrent to your amplifier. It may mess up the rest of the system when it goes in to the feedbackloop in you amplifier.
I would defenetly go active. It can be done very easy. Rigth now im using a passive linefilter. 2 RC filters and a volumepot. This gives me a 12dB/oct filter at 70 hz, with a levelcontrol at the end. Works nice for now (the behringer needs repair :))

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