Speaker questions

Hello. I would be grateful for any answers to my following questions.

1) Doping of drivers - what effects does doping a driver have on it's T&S parameters ? I thought it lowered resonant frequency and efficiency and increased Qts but i would appreciate confirmation of that and any other effects it has.

Many thanks.
 

academia50

Member
2013-01-16 2:52 pm
Beyond the variations caused in the T / S parameters, the correct application of "doping"
- done seriously and with measurements -, is done to eliminate certain unwanted frequencies in the cone. They can be peaks or valleys. This doping can be partial in the form of rings (usually near the wing) or total, covering all of it, usually mixing certain compounds in the cone material.

Recently I had to extract the midwoofer from an Infinity SM-65, quite vintage by the way.

I thought it was "only" a polypropylene cone, judging by its exterior appearance , great was my surprise to observe it from the inner side and discover that it has a layer of fabric attached to it. Maybe we can't call that "doping," but the concept I think applies.
I was surprised by the good performance of that transducer in the voices, seeing that I realized!
It does not have the sound to "tuperware" so characteristic of poly.
 
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I was surprised by the good performance of that transducer in the voices, seeing that I realized!
It does not have the sound to "tuperware" so characteristic of poly.

Right, most quality wide range drivers are layered 'sandwiches' of differing materials, compositions with the 'right' bonding material between them and sometimes a bit of actual doping.

For instance, my ancient Altecs started 'life' as a very 'snappish' lead guitar diaphragm, then worked 'backwards' to get the desired Fs, frequency response, 'tone'.

GM
 

academia50

Member
2013-01-16 2:52 pm
For instance, my ancient Altecs started 'life' as a very 'snappish' lead guitar diaphragm, then worked 'backwards' to get the desired Fs, frequency response, 'tone'.

GM

And what treatment did you use for them? It's a secret ?
I ask why the Eminence that I use in my subwoofers are 100% paper, and maybe at some point I can load them to increase Mms and lower the Fs ....

Thank you ! ( see attached here ;) )
 

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Not DIY; it's my understanding the Altec/GPA 416, 515, etc., drivers starts with a 15" musical instrument [MI] diaphragm and did/do whatever to make the others; and yes, it's not common knowledge AFAIK, for sure I don't.

Most point source driver diaphragms are made from paper pulp [hemp originally] and normally us DIYers add a massive ring to the front of the diaphragm since it's easiest, and ideally close to the VC under the dust cap [DC] or ~1/3rd out from it.

Of course if you have the patience to cover ~ the whole diaphragm to both stiffen/mass load it, then this is preferable for 'sub' woofer duties if the XO is fairly low.

GM
 
Ah, I understand, something similar to Aquaplas from JBL but obviously not in white.

What is Aquaplas

I had to be very careful when replacing the foam wings of JBL speakers with that treatment (LE14C, LE14A, etc.), the MEK softens and degrades it!

Anyway, applying coatings on the back of a paper cone of a tiny thickness like Eminence of 18 inches, would be a heresy. It was just an occurrence, like that of the GM logo, it won't happen again.