Vintage KEF PR SP1042 - anyone have TS parameters? Or ideas how to model them?

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morbo

Member
Joined 2004
#1
Hi folks;

I have here a set of the old racetrack PRs from kef - model SP1042. I have been able to find lots of information about the history of these and the products they were used in, the best here:

https://us.kef.com/pub/media/pdf/A_History_of_Kef_Drive_Units_issue_3.pdf

However, I haven't been able to find TS parameters for them. I wonder if anyone has these? I'd like to model them in vituixcad or bassboxpro but don't know where to start.
 
#2
Oh that's super easy.
Start by researching what the Thiele Small parameters encompass.
Then research what a Passive Radiator is.
This should take less than ten minutes to find the basics.
Then you can tell us why you can't find any T/S parameters for your passive radiators.

I could tell you the answer.
But it will be better for you to learn for yourself.

Teach a man to fish and all that..........
 
#4
Seems I really am clueless, thanks for the education gentlemen.

Interestingly, both Bassbox Pro and Vituixcad have parameters listed for a variety of PRs, and require them to model a tuned PR enclosure.

m1iInEH.png


And manufacturers or PRs are in the habit of providing them as well:

http://www.madisound.com/pdf/SB29NRX-00.pdf

As much as I appreciate the lesson, it doesn't help me model an enclosure using these PRs. If anyone can help with that, I'd appreciate it.
 
#5
It is intended that a PR have mass added to tune it, so none of the data (other than size & xmax) would stay the same. You use the extra mass to tune it in the same way that you change the length of a pipe to change the tuning. And that is very dependent on the box size.

You would tune it by building the box, measuring the impedance, then adding mass until the impedance minimum is where you want it.

I am not a big fan of PRs.

dave
 
#6
planet10 said:
It is intended that a PR have mass added to tune it, so none of the data (other than size & xmax) would stay the same. You use the extra mass to tune it in the same way that you change the length of a pipe to change the tuning. And that is very dependent on the box size.

You would tune it by building the box, measuring the impedance, then adding mass until the impedance minimum is where you want it.
Click to expand...

Indeed, that is one way to design a PR enclosure, in much the same way one might build an oversized box for an unidentified woofer, and add bricks to reduce volume until reaching a desired tuning.

Fortunately if we have the parameters, the modelling software allows us to adjust this added mass, saving some of this trial and error and getting us closer to a final alignment faster, just as it does for other alignments. Hence my original question. I and many others have done this before to design PR enclosures with other PRs, with reliable results.

planet10 said:
I am not a big fan of PRs.
dave
Click to expand...

I appreciate that you're not a fan of the alignment, and I certainly won't compel you to use it.
 
#7
morbo said:
...in much the same way one might build an oversized box for an unidentified woofer, and add bricks to reduce volume until reaching a desired tuning.
Click to expand...

Bad analogy. You have modeled the driver and you know the volume and where you want to tune it. It is like startin gwith a too long a tube and shortenin guntil it is right.

Often had to be done in tower BR that were actually ML-TLs. Now we can model those.

dave
 
#8
Again; I appreciate the attempt at education. But also again, regardless of what you think of my analogy, we can and do model PR alignments as well. Perhaps you were unaware of this, perhaps you don't think the modelling works; whatever the case, it's frankly immaterial to my original request for information.

To reiterate; I am looking for help with the parameters, or a way to determine them. If you have them I'm all ears. Otherwise I'll wait until someone who can help comes along.
 
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#10
Richard Small didn't publish the TS back then I guess. I don't recall the CS kits had those specs and data of individual drivers only were available from third parties.

But Cms and Sd are measurable with a known weight and a ruler for starters. Fs is somewhat harder to get. I'd try recording the unit's response on tapping the cone and recording the response with a scope app on my smartphone. Or build a test enclosure and determine Fc. With Cms and Fs you have Mms, Cms and Sd give Vas. Acquiring Rms is a real challenge, though it's probably not that important.
 
#12
Thanks to you both - those are useful suggestions. I will do some digging to see to what extent the soft parts between the b139 and the PR, certainly the SD should be the same and possibly the useable throw if the surround is the same. I'll also check out how to do the CMS measurement with the ruler and weight.
 
#13
Sorry to reply to an old thread, but I thought it may be useful to have this info in a relevant thread.

The only info I have or have recently found, pertaining to the B139 shaped KEF passive radiator, are the following three models. Hope it helps somebody in the future.

BD139 SP1042 passive radiator (to match B139 SP1044 speaker)
------------------------------------------------------------
Sd = 354 cm^2
Vas = 163.2 litres
Cms = 9.3e-4 m/N
Cas = 1.1654e-6 m^5/N
Qms = 5.5
Xlin = 6.0 mm
Xmax = 12.0 mm
Mmd = 30.97 gms
Mms = 34.41 gms
Rms = 1.11 Ns/m
Fs = 28.0 Hz

BD139 SP1037 passive radiator
-----------------------------
Fs = 28.0 Hz
Qms = 5.5
Cms = 9.3e-4 m/N
Sd = 354 cm^2
Mms = 37.5 gms
Xlin = 6.0 mm
Xmax = 12.0 mm


BD139B SP1082 passive radiator
------------------------------
Fs = 13 Hz
Qms = 0.71
Cms = 1.66e-3 m/N
Sd = 354 cm^2
Mms = 90.5 gms
Xlin = 12 mm
Xmax = 20 mm
 
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