Great Plains Audio 515-16G T/S Parameters and cone number

[rubjel]

Hi,

I recently aquired a pair of GPA 515-16G woofers.
They measure close between the two, but wildly different compared to factory T/S specs..
These are labeled on the back as "horn loudspeakers", but my Qts measurements from both are 0,4, way too high for horn loading.
This is double the value they are supposed to be at 0,21. Fs is also much higher at 48hz vs 37hz factory spec.

All this has made me wonder if the cones are original. They have P/N's GPA-10494 on the first line and 10 236 below, can anyone verify if this is correct please?

[RMC]

Have you given the drivers a "break in" period before measurements? New woofers do need a good workout before their parameters settlle to normal values.

"The stifness of surrounds and spiders may tend to vary to some degree, causing the Vas and Qts parameters to shift." (John Eargle, Loudspeaker Handbook, 2nd ed,. p. 365)

So perfect compliance with factory numbers may be hard to get, but should not be way out of line.

Also with new manufacturing methods and materials i'm not sure if GPA's drivers are exact clones of the originals.

Richard

[rubjel]

Have you given the drivers a "break in" period before measurements? New woofers do need a good workout before their parameters settlle to normal values.

"The stifness of surrounds and spiders may tend to vary to some degree, causing the Vas and Qts parameters to shift." (John Eargle, Loudspeaker Handbook, 2nd ed,. p. 365)

So perfect compliance with factory numbers may be hard to get, but should not be way out of line.

Also with new manufacturing methods and materials i'm not sure if GPA's drivers are exact clones of the originals.

Richard

Hi Richard,

yes the drivers have been used since 2015. However parameters will never shift this much with break in, in my experience maybe max 10%. Almost 100% is ridiculous.
These were measured several times with DATS V2 and V3 as I have both.
These are not the first GPA woofers I have had with parameters way out of spec, but never this bad. Suffice to say, I will never buy another driver/woofer from GPA.

[RMC]

Well, based on your experience and measurements then GPA woofers should be considered as new and different versions vs the originals. I haven't compared their TS parameters (older vs new) but i guess someone looking for GPA replacement drivers should compare carefully data available before purchase, even when its same model number.

If GPA shows the same TS than older models and the newer ones don't measure similar then it would seem like a red flag for the intended application.

As for horn loading you mention , yes traditionally drivers with low Qts were preferred for such application. Low cone mass and high BL product are also attributes indicated by Eargle.

Richard

[rubjel]

Well, based on your experience and measurements then GPA woofers should be considered as new and different versions vs the originals. I haven't compared their TS parameters (older vs new) but i guess someone looking for GPA replacement drivers should compare carefully data available before purchase, even when its same model number.

If GPA shows the same TS than older models and the newer ones don't measure similar then it would seem like a red flag for the intended application.

As for horn loading you mention , yes traditionally drivers with low Qts were preferred for such application. Low cone mass and high BL product are also attributes indicated by Eargle.

Richard

Richard,

regardless of whether new and different versions vs Altec originals, they should nonetheless conform to the published T/S specs (by GPA) don't you agree?
I have not referred to any Altec specs here, only to those published by GPA.

I'm not sure why you are discussing "old vs new" as that is not really relevant to my post. I am discussing GPA 515-16G measured vs published specs.

[Earl K]

In the past when Speaker Exchange sold authentic GPA kits, this is the cone number that appeared on the cone ( this was used on all the available kits > 604, 515, 416 ).


90427


I think GPA ( a good ten years back ) was experimenting with cone and coil combos ( as well as dust-caps ) before settling into whatever they're using now.

:)

[rubjel]

In the past when Speaker Exchange sold authentic GPA kits, this is the cone number that appeared on the cone ( this was used on all the available kits > 604, 515, 416 ).


90427


I think GPA ( a good ten years back ) was experimenting with cone and coil combos ( as well as dust-caps ) before settling into whatever they're using now.

:)

Thank you very much Earl, this is good info :)

Isn't that kit supposed to be for all 515G models? I think I have seen the number 35400 mentioned before..
I have never come across the number stamped on mine, which is why I am asking for advice.

If what you say about GPA experimenting is right, that is terrible practice imo. They should experiment first and then settle on a set of parameters before selling prototypes to the public.

[RMC]

Sorry for my misunderstanding, i do agree they should conform to specs, within the tolerances provided if any.

I was referring to old vs new since GPA is re-issueing former Altec models, i.e.continuing the legacy.

When GPA you measured vs GPA published specs don't agree by a wide margin as you have shown, then it looks like GPA has a quality control issue or a curious way of indicating specs.

If asked why such spec differences from your own data I think that GPA might say your measurement method may be wrong or different than the one they use...

Richard

[rubjel]

Sorry for my misunderstanding, i do agree they should conform to specs, within the tolerances provided if any.

I was referring to old vs new since GPA is re-issueing former Altec models, i.e.continuing the legacy.

When GPA you measured vs GPA published specs don't agree by a wide margin as you have shown, then it looks like GPA has a quality control issue or a curious way of indicating specs.

If asked why such spec differences from your own data I think that GPA might say your measurement method may be wrong or different than the one they use...

Richard

No problem Richard.

I think you are probably right about your assumptions wrt GPA response.. I have sent several emails about this, but sadly their reputation of never replying to emails is true.

[Earl K]

All this has made me wonder if the cones are original. They have P/N's GPA-10494 on the first line and 10 236 below, can anyone verify if this is correct please?

Here's an internet pic of a GPA 515-8G . Looks like your cone number is correct.

90428

The pic came from HERE! (http://srsystemaudio.blogspot.com/2011/04/great-plains-audio-gpa-515-8c-vs-gpa.html)

The one person that I'm aware of ( who's had more GPA woofers filter through his hands > over in the EU ) is Stephane Rame ( the author of the Blog I just linked you to ) .

(BTW ) He's had a few threads here at LHF.

Here's a short thread about some changes ( he's observed ) to the GPA 515-8G. See GPA 515-8G ( cosmetic differences ) (http://www.audioheritage.org/vbulletin/showthread.php?30463-GREAT-PLAINS-AUDIO-GPA-515-8G-Difference-manufacturing)

Here's a good thread ( that includes Stephane ) over at melaudio ( in french ) (https://forums.melaudia.net/showthread.php?tid=1604) My Chrome browser is set to auto-translate most languages.

If you could get his attention, he might be a good resource to shed some light on your funky TS parameters .

:)

[rubjel]

Here's an internet pic of a GPA 515-8G . Looks like your cone number is correct.

90428

The pic came from HERE! (http://srsystemaudio.blogspot.com/2011/04/great-plains-audio-gpa-515-8c-vs-gpa.html)

The one person that I'm aware of ( who's had more GPA woofers filter through his hands > over in the EU ) is Stephane Rame ( the author of the Blog I just linked you to ) .

(BTW ) He's had a few threads here at LHF.

Here's a short thread about some changes ( he's observed ) to the GPA 515-8G. See GPA 515-8G ( cosmetic differences ) (http://www.audioheritage.org/vbulletin/showthread.php?30463-GREAT-PLAINS-AUDIO-GPA-515-8G-Difference-manufacturing)

Here's a good thread ( that includes Stephane ) over at melaudio ( in french ) (https://forums.melaudia.net/showthread.php?tid=1604) My Chrome browser is set to auto-translate most languages.

If you could get his attention, he might be a good resource to shed some light on your funky TS parameters .

:)

Thank you very much Earl, this is of great value to me!
I will check out the french forum and see if I can get in touch with Stephane :)