Hi all,

I have a pair of BeoVox S55 (type 6426) woofers in for restoration.

At some point in the past, the owner tells me that the foam surrounds decayed, and the "repairer" didn't know how to repair them, so he just put in a convenient pair of atrocious Sansui woofers, which sound like one is listening though a thick curtain - positively anaemic, with no bass at all.

I A-B'd with my S45's (type 6302), and my S45's blow the S55's away.

The mission now is to replace the S55 woofers with units as close to the original as possible.

1. Does anybody have the original model number of the B&O woofers (perhaps made by SEAS or Peerless)?

2. Does anybody know which current SEAS or Peerless model would be an excellent sounding woofer unit for the S55?

http://www.tymphany.com  Peerless

http://www.seas.no SEAS

Menahem

In short, none.

The original S55 woofers are 6.4 Ohms, no modern replacement will fit correctly.
I have a pair of original refoam'ed woofers but unfortunately shipping to your
country from Denmark seems to be a problem. 

Martin

Hi Martin,

Thanks for your offer.

As far as I remember, the original S55 woofers were very bass-deficient anyway. I much prefer the S45's.

From all the current Seas and Peerless 8" woofer products, I could not find a single one which physically fits in the S55's weird rear-mounting hole.

But I have found a pair of Monacor SPH-200KE woofers, which fit exactly. I entered the Thiele-Small numbers into my speaker software, and in the S55 enclosure, they appear (on paper at least) to give a very flat response with excellent bass.

These woofers are rated at 80W RMS, and have a DC Resistance of 6.2 ohms, so from all points physical, they are a very good substitute.

When I have them delivered and installed, I will let you all know.

In the meantime, I have rebuilt the crossovers with Solen 400V Polypropylene caps.

Menahem

If you are talking about the early S45 model (type 63xx), I agree.
If not, I don't. The Beovox S55 are classes above the later S45 (type 64xx),
also when it comes to bass response, but that's just my opinion.

A DC resistance of about 6 Ohms points to an impedance around 8 Ohms.
Those parameters are not the same.
The original S55 woofers are odd with an impedance of 6.4 ohms so mounting
8 ohm drivers instead may provide a weaker bass response but do let us know
what you find out.

Martin

Yes, these S45's are the Type 6302's, with me since 1977. The older, the better!

The nominal impedance is not that critical, when attempting to minimize deficient bass response.

What is more important, is at which frequency(s), the peak impedances occur - sometimes as high as 48 ohms.

The impedance of a given speaker will vary between the DC Resistance (in this case 6.4 ohms) to its peak of 48 ohms, according to the graph below.

The designer can influence the position of the peak impedance by altering the size of the box, or the vents (if a ported design). Generally, the larger the box, the lower the frequency at which the peak will occur. The optimum solution is to use crossovers to move the audio signal to another driver of higher or lower frequency, at a frequency before the peak impedance occurs.

Here in this hypothetical example (impedance vs frequency) of a vented SPH-200KE in a box of 40 litres, you can see that the nominal impedance of about 7.8 ohms occurs at only 29Hz, and there are 2 peaks of about 48 ohms, one at 18Hz - which we would not bother about, because it is below normal hearing range, and the other critical peak at 48 Hz, definitely limiting perceived bass response.

The box designer would have to experiment to minimize this impedance peak at 48Hz - beyond my current abilities!

Not shown here is the graph of impedance phase, which B&O partially solved with the Uni-Phase design of these speakers.

If anyone wants to learn more about these factors, the software at http://www.linearteam.dk/ is a great tool. 

I used this software to design my subwoofer, about 200 litres, 2 ports, an ED 1300W amplifier (with B&O's ICE components), and a TC-2000 15" driver.

Yes, I know.

So why are the Sansui ones mounted bad then, did you check their specs ?
If impedance is not important, which basically is what you tell us, maybe some other parameter
in the Sansui woofer specs will tell the reason for the lack of bass.

Unfortunately, the specs of the original woofers are not disclosed and they don't bear a brand name or type number, but
it's my experience (and opinion) that nothing does it quite as good as the originals. And I have tried quite a few.
Since they are custom made for B&O, I suppose they would have changed something, like mounting off-the-shelf 8 ohm woofers,
if that would have made them sound better. Clearly, they didn't choose to have 6.4 ohm woofers custom made because it was the
cheapest solution.
But there has been a development in speaker drivers (though the physical laws and T/S formulaes are still the same) and I could be
wrong and am very excited to hear about your results.

Martin

OK, Martin,

Get excited!

Oh, WOW, Oh WOW!!!!!

For me, the best passive speakers I've ever heard are my restored S45's with rebuilt Audience crossovers - I covered that in a post long ago...

I've taken those S45's to a local real HiFi dealer, and A-B'd them with nearly every highly-acclaimed big-name speaker around (large-bookshelf-size), and they all pale in comparison, except for 2 offerings from Totem Acoustics - a Mani-2 and to a slightly lesser degree, the Model 1.

So, anything which is coming up against these S45's is in for a real tough ride.

These Monacors are REALLY good. Firstly they fit PERFECTLY, which was asking a lot, in that weird B&O mounting setup.

I left the BM3400's LEFT channel connected to my S45, and connected the redone S55 to the RIGHT channel. I put on Bob Marley - great clear tight bass, and listened. I moved the balance slider from L to R to get a good comparison.

Oh man, this is GOOD.... The S45's have a slight edge on the bass response - they definitely go lower than the Monacors, but the S55 now has a stunning "presence". It is definitely good to listen. That woofer dances with Bob Marley - you can see the excursions.

The Monacor SPH-200KE - A definite recommendation for 8" replacements - from this chap in Belgium - the lowest prices I could find in Europe.

http://www.diyparadiso.com/

I'm not sure how much the rebuilt crossovers contribute to this win, but after about 100 hours, I'm definitely expecting a further improvement, as the Solen caps loosen up.

What a pleasure to deliver a real piece of listening enjoyment to my customer!