Hi ,
I have a pair of vintage 12"drivers , Richard Allan CG12 super which were cheap so I'm thinking of 'design mule'project for the workshop . These have a published Qts of 0.105 , which seems ridiculously low , and Fs of 30Hz . Although I am unsure how accurate the published specs are , these immediately appear to be like a guitar speaker with low Fs . Originally the drivers were mounted in a 55l sealed enclosures which did not deliver much bass , even in the corner . Modelling in Hornresp these seem ok for basshorn use due to the high BL , low Qts , but I just don't have the space for a pair of whacking great basshorns
The drivers seem to be sensitive (high 90's) so I'm thinking perhaps add some mass to the cone via some small neodymium magnets and mount in vented boxes , I can easily lose 6dB if it means getting some bass out of the things . I've consulted the Loudspeaker Cookbook and a few other sources and can see that by adding mass Qts will increase , Fs decrease as will BL , but what about Vas and other parameters ? I'm no expert , help appreciated 
cheers
316a
I have a pair of vintage 12"drivers , Richard Allan CG12 super which were cheap so I'm thinking of 'design mule'project for the workshop . These have a published Qts of 0.105 , which seems ridiculously low , and Fs of 30Hz . Although I am unsure how accurate the published specs are , these immediately appear to be like a guitar speaker with low Fs . Originally the drivers were mounted in a 55l sealed enclosures which did not deliver much bass , even in the corner . Modelling in Hornresp these seem ok for basshorn use due to the high BL , low Qts , but I just don't have the space for a pair of whacking great basshorns
The drivers seem to be sensitive (high 90's) so I'm thinking perhaps add some mass to the cone via some small neodymium magnets and mount in vented boxes , I can easily lose 6dB if it means getting some bass out of the things . I've consulted the Loudspeaker Cookbook and a few other sources and can see that by adding mass Qts will increase , Fs decrease as will BL , but what about Vas and other parameters ? I'm no expert , help appreciated cheers
316a
Hi,
I had a pair of these as a 3way (Pavane) in 1971. When 10W to 20W was sufficient power.
They are more efficient than a Tannoy HPD385 in 100L vented cab.
But they only handle 25W (that maybe includes the other drivers and xover losses) and will not like added mass due to limited thermal capacity.
Try adding small series R instead to raise the Q.
ps I don't think the Qts is quite as low as you quoted, what was your source?
pps BL will not change.
I had a pair of these as a 3way (Pavane) in 1971. When 10W to 20W was sufficient power.
They are more efficient than a Tannoy HPD385 in 100L vented cab.
But they only handle 25W (that maybe includes the other drivers and xover losses) and will not like added mass due to limited thermal capacity.
Try adding small series R instead to raise the Q.
ps I don't think the Qts is quite as low as you quoted, what was your source?
pps BL will not change.
316a:
Do you have any other specs on that driver besides Qts? Dc resistance and Qes would helpful in figuring how much any given added resistor would both raise the Qts and lower the sensitivity.
DC resistance, (Re), acan be measured with any voltmeter, analog or digital. If we absolutely have to, we can probably estimate Qe as being just a touch above Qts.
Two formulas can help us.
A) Resistor = [(Qts required / Qts measured) X Re] - Re. We can, if we want, substitute the specified Qts for Qts measured.
B) Qes' = Qes(1+(resistor/Re))
If we can calculate the change in Qes, I can plug the numbers into BoxModel and give you the drop in sensitivity. That is if I have a value for Re. And depending, of course, if the value of Qts is indeed 0.105
Do you have any other specs on that driver besides Qts? Dc resistance and Qes would helpful in figuring how much any given added resistor would both raise the Qts and lower the sensitivity.
DC resistance, (Re), acan be measured with any voltmeter, analog or digital. If we absolutely have to, we can probably estimate Qe as being just a touch above Qts.
Two formulas can help us.
A) Resistor = [(Qts required / Qts measured) X Re] - Re. We can, if we want, substitute the specified Qts for Qts measured.
B) Qes' = Qes(1+(resistor/Re))
If we can calculate the change in Qes, I can plug the numbers into BoxModel and give you the drop in sensitivity. That is if I have a value for Re. And depending, of course, if the value of Qts is indeed 0.105
When using the two formulas above to select the value of the resistor, then filling in the resulting new Qes value into Bullock and White's Boxmodel freeware, we end up with a Qts reading slightly lower than what we aimed for. The discrepancy is not great, and a good box can be built using either the aimed for value even if the accurate value is Bullock and White's.
So, I'll just list some useful Qts values.
Aimed for Qts = 0.26 Resistor = 13 ohms. Qes = 0.268. B&W Qts value = 0.24. 96.2 dB sens.
Aimed for Qts = 0.32. Resistor = 19 ohms. Qes = 0.34. B&W Qts value = 0.30. 95 dB sens.
Aimed for Qts = 0.4. Resistor = 26 ohms. Qes = 0.427. B&W Qts value = 0.37. 94.2 sens.
I give the above numbers under advisement. Intuitively, the resistor values seem too high for the comparatively small decrease in sensitivity. Adding a 26 ohm resistor to a driver with an Re of 9 ohms and a sensitivity of 100 dB only brings the SPL rating down 6 dB?
Seems shaky, but that is where the numbers and programs seem to lead. So if anyone wants to jump in, please do so.
So, I'll just list some useful Qts values.
Aimed for Qts = 0.26 Resistor = 13 ohms. Qes = 0.268. B&W Qts value = 0.24. 96.2 dB sens.
Aimed for Qts = 0.32. Resistor = 19 ohms. Qes = 0.34. B&W Qts value = 0.30. 95 dB sens.
Aimed for Qts = 0.4. Resistor = 26 ohms. Qes = 0.427. B&W Qts value = 0.37. 94.2 sens.
I give the above numbers under advisement. Intuitively, the resistor values seem too high for the comparatively small decrease in sensitivity. Adding a 26 ohm resistor to a driver with an Re of 9 ohms and a sensitivity of 100 dB only brings the SPL rating down 6 dB?
Seems shaky, but that is where the numbers and programs seem to lead. So if anyone wants to jump in, please do so.
Hi ,
I've just noticed that WinISD has provision for adding different values of series resistance . I've added 15 ohms series resistance , and used a 100l cabinet with 36Hz port tuning . -6dB point is 37Hz , seem to getting somewhere now , otherwise I'm totally barking up the wrong tree
cheers
316a
I've just noticed that WinISD has provision for adding different values of series resistance . I've added 15 ohms series resistance , and used a 100l cabinet with 36Hz port tuning . -6dB point is 37Hz , seem to getting somewhere now , otherwise I'm totally barking up the wrong tree
cheers
316a
I have two pairs of CG12 Supers, but they are physically different.
The shallower type pictured is dated Oct 1973; the deeper one Jan 1975. I am shortly expecting in the post a second pair of the shallower type. The Re of both appears to be about 6.2 ohms (from a recently bought but not yet calibrated or checked VTVM), and about 6.0 interpolating from my irritating DMM which appears to insist on about 0.5 ohms, uncertainly, in the leads ... I'll try to get a more accurate still figure but this is much more realistic for a clearly marked 8ohm speaker than the higher values guessed at earlier.
I believe I've seen a "Dual Super" elsewhere, which perhaps is the "ss" type in the Richard Allan T_S parameters linked to earlier.
I've just downloaded Hornresp and WinISD but haven't played with either yet. I'm interested in what cabinets might suit best, possibly could consider a largish or very large horn, and also wonder what I might do with two identical pairs - whether in a horn or large box - and how about an isobaric configuration - any advantages in either cabinet, anyone? What other (free) box software might I use?
The diameter of the cone exactly to the paper edge is 240mm.
Clearly the deeper cone is going to have slightly more mass.
If one was going to add mass, what about a controlled amount of varnish (artists, dammar?) via say an airbrush, or some other form of doping ... or, as I have thought looking at the light grey of the shallower pair, some black watercolour or thinned acrylic;-) But there would be no going back, and the result would be uncertain!
However I am prepared to leave mine untouched and just find the ultimate cabinet, or perhaps horn, perhaps one for the two identical ones and another for a single pair (the deeper one).
I'm not teally quite sure where to start as yet so am all ears!
The cabinet one pair came in is marked 30W Music Power so I'd suspect more like 15W continuous than the 25W mentioned above, but don't know. Here's a link to a pic of the exact same cabinet type (the internal box is a square port with a 90 deg exit) as the ones I have, and is the second pair I have bought (just the drivers - the freight was bad enough for those!) - my other pair came in rediculously shallow sealed cabinets barely deeper than the speaker. I had been using them as rear speakers high up at the wall-ceiling corner in a Dolby ProLogic setup. The large pair (like this picture) have been in storage after failed mid/tweet experiments!
http://www.trademe.co.nz/Browse/Listing.aspx?id=53852031
Thanks for any ideas! I'll be building some valve amps sometime so the high sensitivity and low power might just suit in any case.
Ross M
The shallower type pictured is dated Oct 1973; the deeper one Jan 1975. I am shortly expecting in the post a second pair of the shallower type. The Re of both appears to be about 6.2 ohms (from a recently bought but not yet calibrated or checked VTVM), and about 6.0 interpolating from my irritating DMM which appears to insist on about 0.5 ohms, uncertainly, in the leads ... I'll try to get a more accurate still figure but this is much more realistic for a clearly marked 8ohm speaker than the higher values guessed at earlier.
I believe I've seen a "Dual Super" elsewhere, which perhaps is the "ss" type in the Richard Allan T_S parameters linked to earlier.
I've just downloaded Hornresp and WinISD but haven't played with either yet. I'm interested in what cabinets might suit best, possibly could consider a largish or very large horn, and also wonder what I might do with two identical pairs - whether in a horn or large box - and how about an isobaric configuration - any advantages in either cabinet, anyone? What other (free) box software might I use?
The diameter of the cone exactly to the paper edge is 240mm.
Clearly the deeper cone is going to have slightly more mass.
If one was going to add mass, what about a controlled amount of varnish (artists, dammar?) via say an airbrush, or some other form of doping ... or, as I have thought looking at the light grey of the shallower pair, some black watercolour or thinned acrylic;-) But there would be no going back, and the result would be uncertain!
However I am prepared to leave mine untouched and just find the ultimate cabinet, or perhaps horn, perhaps one for the two identical ones and another for a single pair (the deeper one).
I'm not teally quite sure where to start as yet so am all ears!
The cabinet one pair came in is marked 30W Music Power so I'd suspect more like 15W continuous than the 25W mentioned above, but don't know. Here's a link to a pic of the exact same cabinet type (the internal box is a square port with a 90 deg exit) as the ones I have, and is the second pair I have bought (just the drivers - the freight was bad enough for those!) - my other pair came in rediculously shallow sealed cabinets barely deeper than the speaker. I had been using them as rear speakers high up at the wall-ceiling corner in a Dolby ProLogic setup. The large pair (like this picture) have been in storage after failed mid/tweet experiments!
http://www.trademe.co.nz/Browse/Listing.aspx?id=53852031
Thanks for any ideas! I'll be building some valve amps sometime so the high sensitivity and low power might just suit in any case.
Ross M
Attachments
Try www.richardallanaudio.com
Those figures you showed for the CG12S came (via me) directly from Richard Allan about 2 years ago. I have a couple of HP8B drivers and the quoted parameters match my measured ones fairly well.
Those figures you showed for the CG12S came (via me) directly from Richard Allan about 2 years ago. I have a couple of HP8B drivers and the quoted parameters match my measured ones fairly well.
Hi,
when you start putting some numbers in for these very low Q speakers the optimum size of box is going to be much less than Vas. This results in a High Fb which cuts off all the bass.
If, you either build a bigger box than optimum or tune to a lower Vent frequency, you can extend the frequency response downwards and end up with a very droopy low end response.
You can alemiorate the droop with equalisation but the limited power of these old speakers will seriously limit the amount of eq you can apply and risk blowing the drivers if you turn up the wick.
I may be wrong here so please come in and correct me I am still learning about speakers and there are very big gaps.
I suggest you go for a horn if you can afford the space and complexity of the box assembly. To minimise the mouth requirement you MUST use some reinforcement from adjacent boundaries. Try for at least two, eg. floor and wall or ceiling and wall.
Using two boundaries cuts the mouth area by a factor of four.
when you start putting some numbers in for these very low Q speakers the optimum size of box is going to be much less than Vas. This results in a High Fb which cuts off all the bass.
If, you either build a bigger box than optimum or tune to a lower Vent frequency, you can extend the frequency response downwards and end up with a very droopy low end response.
You can alemiorate the droop with equalisation but the limited power of these old speakers will seriously limit the amount of eq you can apply and risk blowing the drivers if you turn up the wick.
I may be wrong here so please come in and correct me I am still learning about speakers and there are very big gaps.
I suggest you go for a horn if you can afford the space and complexity of the box assembly. To minimise the mouth requirement you MUST use some reinforcement from adjacent boundaries. Try for at least two, eg. floor and wall or ceiling and wall.
Using two boundaries cuts the mouth area by a factor of four.
316a said:I'm thinking perhaps add some mass to the cone via some small neodymium magnets and mount in vented boxes , I can easily lose 6dB if it means getting some bass out of the things . I've consulted the Loudspeaker Cookbook and a few other sources and can see that by adding mass Qts will increase , Fs decrease as will BL , but what about Vas and other parameters ? I'm no expert , help appreciated
This is an interesting article, if a little complex-seeming at first:
http://www.birotechnology.com/articles/mass.html
It seems to exactly address the approach you're considering.
He notes that "It may or may not be interesting to note that the electrical damping and total system damping will change if we add either mass or resistance, that the free-air resonance and mechanical damping will change only when we add mass, and that VAS will not change with either added mass or added series resistance."
Adding mass or series resistance surely won't change BL which is a function of the length of wire & the magnetic field. don't you think?
As far as the mass itself - I don't think magnets are a good idea!
He comments: "Attaching a mass of a few grams to an un-doped paper cone driver should present few difficulties as long as you use high quality adhesives and are careful to not get any of the adhesive on the surround or other moving parts other than the cone. Epoxies in particular seem to be well suited to this task. The mass could come from just about anything--lead shot, plastic beads, even the epoxy itself." but also "Adding a blob of mass to a driver's cone will have predictable effects at low frequencies where the cone is moving as a piston. However, at higher frequencies where the cone ceases to behave pistonically, the blob you've added will have completely unpredictable and usually undesirable results. So if you're planning to cross-over the driver above a couple hundred Hertz, use series resistance alone to reduce the sensitivity."
As for my own thoughts on using CG12-S, I've been puzzling over the parameter entries in WinISD. I now know that Weber/M(sq) = Tesla, but I seem to see orders of magnitude difference in the listed CG12-S Cms parameter of "7.83 M/N" and what WinISD automatically throws up in units of, apparently, m/N, mm/N, µm/N.
[That's Alt-230 for µ, or as WinISD has it, u
]Actually I've been having trouble getting it to accept a finished entry - did it once, then tried to 'improve' it and wrote over it.
Anybody succesfully entered a reasonable WinISD parameter file for the CG12-S from the RA TS parameter gif linked earlier? I am aware that these low Qts drivers do not produce sensible box results, but just wanted to explore the various relationships and results despite.
Otherwise, I've been looking at horns ... horn sites, basshorns, etc.
Might explore some of the published and DIY Tannoy designs at
http://www.hilberink.nl/speaker.htm
The Duelund Horn looks amazing if extremely complex
http://www.muyiovatki.dk/duelund/duelund.htm
(check out http://www.muyiovatki.dk/duelund/gif/plan_5.gif)
(plan_6.gif gives the dimensions for the 8" version - the 10-12" version with 22mm walls vs 19mm and scaled is 1384mm x 563mm x 522mm. Is that *really* too large to have in a lounge;-? But of course, the CG12's are not full range - although was there not a whizzer cone version? - and so mid and tweeter drivers might be hard to integrate into such a behemoth cabinet construction.)
All of this is a long-term back-burner dreaming project for me; I came to this thread from a search on "Richard Allan", specifically looking for info on the CG12-S, and I'm very pleased I found it!
I personally would like to optimise a cabinet for the driver; if it's a large horn, so be it; I live alone, so WAF is not an issue
Hope you don't mind that I've gone a bit beyond the mere "adding mass" of the subject line, but the link at the top should be of help.
Regards, - R.
Re: Re: Low Qts drivers : Adding mass
I wrote:
There's an example of a present CG10 whizzer cone auction here (images available for ~45 or 60? days or while it lasts) (so save!!)
http://www.trademe.co.nz/Browse/Listing.aspx?id=54906936
and here is an image of 2 x CG8 & 2 x CG10 from an earlier auction.
http://i3.tinypic.com/wrdzk0.jpg
Beautiful whizzer cones, n'est pas? At least on the CG8 ... yeah!!
There was a company called Rola here in NZ & OZ which also made "full-range" crafted paper cone & surround & whizzer speakers too.
I have a couple of examples, incl 15 ohm ... a lovely shape like that.
Enough for now ... keep alive!!!
R~.
PS: <rave on;->
But I have always (well, recently;=}) hearkened after truncated (however smoothed off - golden ratio?) pyramid cabinets too ... so
<bit of a rave>
What about mentally extending duelunds to a truncated pyramid; scaling, reconsidering (con=with, sider=star) (the expansion ratios, and bubbling out the top! - quick here:- we're in international yachting too, and - all sorts!) possible profiles;- maybe ballooning out to the front or up above might be very advantageous in the ?
</bit of a rave> [And rounding off, soccer balls, best projection? ... ]
And baffle step ... but imagine if any CNC or other posssible cabinet routing was available to you ... cost no object <but of course it isn't!> ... then what would you choose, all things considered poss?
Regards again, and best wishes ~
So I guess this brings up a new topic;:= Integrate shapes further?
And so what I think is: bring out the front and new curved shapes in the top to integrate not only tweet & mid but even WMTMW configs?
Or.
Why not some smoothed off hemisphere on top of truncate pyramid?
But at least a mid tweeter array. And I want 2x CG12-S in an array!!
[somehow! :=) ]
The author asserts his rights...=})) Eh? Rights?? What rights???
RdM <rave off;->>
I wrote:
RdM said:
There's an example of a present CG10 whizzer cone auction here (images available for ~45 or 60? days or while it lasts) (so save!!)
http://www.trademe.co.nz/Browse/Listing.aspx?id=54906936
and here is an image of 2 x CG8 & 2 x CG10 from an earlier auction.
http://i3.tinypic.com/wrdzk0.jpg
Beautiful whizzer cones, n'est pas? At least on the CG8 ... yeah!!
There was a company called Rola here in NZ & OZ which also made "full-range" crafted paper cone & surround & whizzer speakers too.
I have a couple of examples, incl 15 ohm ... a lovely shape like that.
Enough for now ... keep alive!!!
R~.
PS: <rave on;->
But I have always (well, recently;=}) hearkened after truncated (however smoothed off - golden ratio?) pyramid cabinets too ... so
<bit of a rave>
What about mentally extending duelunds to a truncated pyramid; scaling, reconsidering (con=with, sider=star) (the expansion ratios, and bubbling out the top! - quick here:- we're in international yachting too, and - all sorts!) possible profiles;- maybe ballooning out to the front or up above might be very advantageous in the ?
</bit of a rave> [And rounding off, soccer balls, best projection? ... ]
And baffle step ... but imagine if any CNC or other posssible cabinet routing was available to you ... cost no object <but of course it isn't!> ... then what would you choose, all things considered poss?
Regards again, and best wishes ~
So I guess this brings up a new topic;:= Integrate shapes further?
And so what I think is: bring out the front and new curved shapes in the top to integrate not only tweet & mid but even WMTMW configs?
Or.
Why not some smoothed off hemisphere on top of truncate pyramid?
But at least a mid tweeter array. And I want 2x CG12-S in an array!!
[somehow! :=) ]
The author asserts his rights...
=})) Eh? Rights?? What rights???RdM <rave off;->>
AndrewT said:
Yes this seems relevant - recent reading for you too? Was for me.
http://www.users.bigpond.com/tunnelgap/Tannoy/lowq.html
There's another version of the same document I saw elsewhere.
Ross M.
IMO Adding mass lower Fs and in the same ratio highten all Q's proportionaly. Sensitivity falls as the ratio four powered.
I've read on other forum about another solution. Try this: To lower Qe use some ferromagnetic material arranged on the outer circumfence of magnet (thick pieces of wire, cutted nails etc.). This will remove some part of induction from the gap and heighten Qe. And sensitivity falls by the same ratio. It is less than with adding mass or with resistor (ratio squared).
From my experience I'd say the only reasonable way to up the Qe/Qt of any such overdamped driver is by adding a series resistance. (right in the way that has been pointed out already) I already have destroyed a couple of drivers in my life by experimenting with other "solutions"...
Adding mass would give comparable benefits only in theory, in practice IMHO there are way too many riscs involved. Glueing anything onto the moving parts of a driver will severly influence its performance, however well you do it. Besides possibly creating an irreversible change you'd first have to care for the giant acceleration forces acting upon your additional mass and the according mounting thereof.
The only "thinkable" solution for adding mass that I found "somewhat" working was to apply lots of heavy coating to the cone. (Thick laquer with brass powder, in multiple levels, with intemediate drying & measuring, hehe, don't do that at home...)
Similar unwanted effects in terms of driver behaviour changes would/will result from fiddling with the magnet system. Not at all recommended either!
Last but not least: changing Qe/Qt purely by a resistor will not only give you the chance to fine-tune your final speaker on the fly, it will allso influence any thermal compression effects to the better. (Besides that your amp is now looking at a quite higher impedance. Some amps really like that!) The voice-coil in addition with the series resistor will provide a neat voltage divider, which - in case the coil heats up and increases it's own resistance - provides a tad of compensation. With series resistors in the range of vc-dc-resistance, this could in fact give you a reduction of thermal compression effects of a few dB...
regards
Adding mass would give comparable benefits only in theory, in practice IMHO there are way too many riscs involved. Glueing anything onto the moving parts of a driver will severly influence its performance, however well you do it. Besides possibly creating an irreversible change you'd first have to care for the giant acceleration forces acting upon your additional mass and the according mounting thereof.
The only "thinkable" solution for adding mass that I found "somewhat" working was to apply lots of heavy coating to the cone. (Thick laquer with brass powder, in multiple levels, with intemediate drying & measuring, hehe, don't do that at home...)
Similar unwanted effects in terms of driver behaviour changes would/will result from fiddling with the magnet system. Not at all recommended either!
Last but not least: changing Qe/Qt purely by a resistor will not only give you the chance to fine-tune your final speaker on the fly, it will allso influence any thermal compression effects to the better. (Besides that your amp is now looking at a quite higher impedance. Some amps really like that!) The voice-coil in addition with the series resistor will provide a neat voltage divider, which - in case the coil heats up and increases it's own resistance - provides a tad of compensation. With series resistors in the range of vc-dc-resistance, this could in fact give you a reduction of thermal compression effects of a few dB...
regards
Hi ,
I've modeled various drivers on WINISD it is interesting to see how adding series resistance can modify the response , especially using EBS alignments . Quick question ; how does amplifier output impedence interact ? All the amps I build are valve with no feedback , output impedence is usually around 2-3 ohms . Can I also assume that larger value air-cored inductors would also affect Q ?
cheers
316a
I've modeled various drivers on WINISD it is interesting to see how adding series resistance can modify the response , especially using EBS alignments . Quick question ; how does amplifier output impedence interact ? All the amps I build are valve with no feedback , output impedence is usually around 2-3 ohms . Can I also assume that larger value air-cored inductors would also affect Q ?
cheers
316a
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