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Measuring Tannoy drivers

C

Cesare

pfm Member
I've been playing around with measurements from my Tannoy cabinets + drivers, and so far the measurements haven't looked anything like the model, and this has made me realise that i'm actually guessing quite a bit about the T/S parameters for my drivers.

The history of these drivers is that they were 15 inch HPDs, but have been re-coned as Golds, so they have the light weight cones, solid edges/string but I presume the HPD horn and magnets. I've also got HPD crossovers for them, again no idea if they would need modifying for Gold use, or whether they have in fact had modifications made to them.

So lots of unknowns, and hence lots of DIY fun to explore exactly what is going on.

The T/S parameters I used for modelling were taken from http://www.44bx.com/tannoy/Tannoy_ts.html

Having decided these were probably suspect, i've invested in a DATS V3 setup, and made some test measurements, and it looks to me like these drivers have a totally different F(s) than the above web site suggested, Q is totally different, as is V(as). I used the 'add mass' technique to measure V(as) and it's rather dependent on the size of the driver, and i'm not totally sure what size is right for these, i've gone with 340mm as the cone diameter certainly isn't 15 inches.

Anyhow, here's a link to the DATS image with the calculated numbers:

Driver by Cesare Ferrari, on Flickr

Of course it could totally be operator error, that i've got something daft going on when measuring, and that these are misleading. So, has anyone put some 15 inch golds through a DATS type analysis and got numbers to compare these against?

I guess the first question is really, is F(s) of 57Hz reasonable (certainly higher than i'd expected)? BTW, the second driver measures give or take the same
 
Just to check you are measuring these in free air, not in an enclosure?

The Qms seems quite high, even for a vintage driver but the Qes seems very high, as you say, as does the fs.
 
This is a free air measurement on my table, with connections straight to the driver terminals (so no crossover). I'm actually wondering if i've got a known driver I can test to ensure the system is calibrated. I think i've got an old pair of celestions in the loft which might do the job...
 
Mms is 68g(typo fixed!), Mmd is 90g, there is no such thing as a lighter Gold cone.
I've had Golds measure even worse Fs at 70 hz!
Put the driver on a pile of books as reflections from table top will mess up the free air measurement. Have you calibrated the V3 with the supplied resistor?
Are the cones new, surrounds still tacky/ shiny?
They can stiffen up depending on the life they've had.
 
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In case you don't know - piston diameter only usually includes half of the surround.
As Cooky says, make sure you run the calibrations, test lead calibration and resistor calibration. You have to do this for any new USB port used (at least you used too).
Give the driver a good blast of low frequency test tones or sweeps to warm it up, then let it cool for 5 minutes or so.
I'd adjust the weight of the added mass, and then measure, repeat, measure, repeat, until you achieve an MMS of 62g. You usually want to use as little weight as you can get away with.
Also make sure the scales you use to weigh the added mass are correct. I check with coins because they are a known weight, but I use Blue Tack because I worry that something like a coin could vibrate or jump a little and mess-up the measurement.
 
cooky1257 said:
Mms is 62g, Mmd is 90g, there is no such thing as a lighter Gold cone.
I've had Golds measure even worse Fs at 70 hz!
Put the driver on a pile of books as reflections from table top will mess up the free air measurement. Have you calibrated the V3 with the supplied resistor?
Are the cones new, surrounds still tacky/ shiny?
They can stiffen up depending on the life they've had.
Click to expand...

Ok, so the Fs isn't a total surprise then? I'll try measuring the drivers on a stool which will give me plenty of room between the drivers and the floor to avoid any mess up. Yes, the instrument calibrated correctly, and i've compared it's measurements for some capacitors and resistors with a meter I trust, so I think i'm using the instrument right.

The cones aren't new and shiny, they are somewhat old, but they look to be in pretty good condition. Of course I have no idea of their history, or for that matter, what they should really look like!

The other question is what diameter to use in the software when measuring with mass - i've gone with 340mm, the distance between the metal edge which I presume is gripping the driver cone to the basket, as being a hard edged driver i'm not totally sure where you should measure from (no equivalent of a rubber surround to stop at).

I reattempted the V(as) measurement, and got varying values for mass and volume, with the mass if anything going down. I've a feeling i'm not attaching mass reliably to the cone, and so would appreciate help with what the best method is... Obviously the Fs and Q aren't affected by this mass as they are from the free air calculations, but given Fs is in the 50s, and the table I checked gave Fs in the mid 20s, and that's what i'd used to design the cabinet and ports, it's not surprising i'm getting totally different results!

Other question, the bit of string around the edge, is it supposed to sit alongside the metal clamp that holds the cone in place, or underneath it as a sort of string sandwich? It's come loose in a number of places, so i'm not sure if it's supposed to be stuck back on at the paper meeting metal edge, or if the metal clamp needs to be loosened to push the string slightly underneath. Also, what string is best to use as a replacement? This stuff is old and nasty looking, so could probably do with replacing.

PXL_20210317_153221772 by Cesare Ferrari, on Flickr

PXL_20210317_153230319 by Cesare Ferrari, on Flickr

PXL_20210317_153236534 by Cesare Ferrari, on Flickr
 
Hmm, those edges look dry as a bone, any plasticiser has long departed by the looks of it, cones themselves look in great nick, though stiff surround means higher Fs.
I'd contact Nick Potter at Lockwood Audio or maybe some of the fishies holding recone kits can comment what's in the box regarding doping liquid/string etc.
Mike P reconed a pair not too long ago too(I haven't reconed Golds for 20 years).
Think long and hard about removing the edge clamps as the edge can stick to them and possibly tear.
VAS is notoriously difficult to measure and often best calculated from other data.
For diameter as Matt says I'd use mid way between the edge fold and the edge clamp.
The cones are clamped to the frame, the string is attached to the surround and forms a kind of fillet between the HE to the clamps and is usually coated in the HE doping.
There's a seller on eBay who sells bottles of dope but I have no idea if it can re-plasticizes the edge of old units-the ad says 'stiffens paper' so it's a bit confusing.

If all else fails you can always recone them back to HPD's..
PS please note the Mms is 68g.
 
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Ok, thanks for the comments. I'll see what Lockwood say. Given these were re-coned, is it possible that it was a partial job, and not all of the steps with doping etc were followed? Anyhow, i'll see what they have to say!

Yes, re-coning them to be HPDs would be a definite option too, if the kits were available at a sensible price, sort of returning them to factory, but I think i'll see what can be done with these cones first I guess.
 
Ok, an update. I've had a bit of a dig around on the web looking at other tannoy drivers, and i've a feeling what has gone on here is that this pair of drivers have replacement gold cones, but the person who has installed them has not doped the cones correctly - it looks to me like a minimal amount of doping has been applied around the edges, but not to the fold between the cone and the outer rim. Also, the inside of the drivers looks to not have been doped.

I removed the wool/string thing, and we see doping underneath, and the metal retaining bits appear to have some dope under them, enough to mean removing the drivers cleanly would be a fiddle:

PXL_20210319_045207585 by Cesare Ferrari, on Flickr

Looking at the back of the cones we also see a distinct lack of dope:

PXL_20210319_060655121 by Cesare Ferrari, on Flickr

I'm not sure how much dope gets applied, but if it's anything like 20-30ml per driver, then that would account for the light weight of the cone in it's current form, and hence the higher than expected Fs. So, I reckon the first thing to try is to get some dope for the tannoys, and see what happens as I apply it. I'm most bothered by the lack of dope on the inner surface - is this from seepage from the front through the material, or should some be applied to the inside as well? And if it should be applied to the inside, is this done before or after assembling the driver?

Oh, and if all else fails, getting some HPD cones would be the right thing to do, it might actually be the right thing anyway, but since i've got these with gold cones, i'll experiment with them as is first.
 
With the high Qes and low VAS you measured, that's a sign of stiff suspension. Perhaps doping the surround will loosen it? I'd be surprised if the spider went stiff with age - if anything I'd have thought it would loosen up.
 
The link below is how I'd expect the edges to look, he has 3 ( pretty rough looking)cones for sale with one showing a bit of damage to the outer edge caused by removal:
I follow your logic but I wouldnt assume that the fs has increased due to loss of dope mass it's lost its, or never had it in the first place, compliance , i.e. It doesn't matter what the spider( which provides most of the control)wants to do, the stiffened edge is stopping it.

https://www.ebay.co.uk/itm/TANNOY-1...d=link&campid=5338728743&toolid=20001&mkevt=1
 
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cooky1257 said:
The link below is how I'd expect the edges to look, he has 3 ( pretty rough looking)cones for sale with one showing a bit of damage to the outer edge caused by removal:
I follow your logic but I wouldnt assume that the fs has increased due to loss of dope mass, it's lost or never had it in the first place, compliance , i.e. It doesn't matter what the spider( which provides most of the control)wants to do, the stiffened edge is stopping it.

https://www.ebay.co.uk/itm/TANNOY-1...d=link&campid=5338728743&toolid=20001&mkevt=1
Click to expand...

Yes, i'm speculating (that's half the fun), but i'm pretty sure that the design has the doping for a reason, and hence it needs to be added. Fingers crossed it will alter the parameters in a positive way - I can't imagine it can hurt unless I make a total hash of applying the dope.

I need to find a guide to installing Gold cones to check what the procedure is, specifically if I should remove the cones and apply dope on the back before assembly, or working with them assembled is the right course.

And I like the idea of actually reconing them back to HPDs, as the sort of hybrid nature of the current setup doesn't appeal to me as much as having them 'original'. I imagine the surrounds failed on this pair, and the owner decided to replace them with Gold style to avoid an ongoing cost, or maybe they believed golds were superior and a perfectly good pair of HPD cones were removed.
 
This site contains affiliate links for which pink fish media may be compensated.
Fatmarley said:
With the high Qes and low VAS you measured, that's a sign of stiff suspension. Perhaps doping the surround will loosen it? I'd be surprised if the spider went stiff with age - if anything I'd have thought it would loosen up.
Click to expand...

Yeah, and as I think I mentioned, I believe these were re-coned within the last 10 years
 
@cooky1257 , I'd have to unpack my cones again to take photos. Will this pic (from Lockwood) do in the meantime?:

1512491-dc6416b3-tannoy-15-gold-and-hpd-recone-kits.jpg
 
Fatmarley said:
With the high Qes and low VAS you measured, that's a sign of stiff suspension. Perhaps doping the surround will loosen it? I'd be surprised if the spider went stiff with age - if anything I'd have thought it would loosen up.
Click to expand...
The Fs of my rubber surround MGs has dropped to 20Hz (from 27-28) with age.
BTW, if you play with Tannoy crossovers, measure the inductors for yourself. Many of the published Monitor Gold circuit diagrams give 1.2mH for the bass inductor. My original one measures 3.3mH!
 
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