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 Post subject: Re: Questions about Radio Shack full range driversPosted: 04 Dec 2008, 12:31

Joined: 04 Dec 2008, 12:27
Posts: 35
Location: Clifton Park, NY USA
The first set of T/S parameters listed in the thread are correct. I have eight of these drivers that I picked up a few years ago when Radio Shack was discontinuing selling them and they measure very close to the properties listed in the first post. If you want the complete set of T/S parameters I can post the average values for the eight drivers tonight when I get home.

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 Post subject: Re: Questions about Radio Shack full range driversPosted: 04 Dec 2008, 17:35

Joined: 04 Dec 2008, 12:27
Posts: 35
Location: Clifton Park, NY USA
As promised here are the averaged measured parameters from eight RS 40-1286C drivers.

fs (Hz) = 51.77
Qes = 1.669
Qms = 6.122
Qts = 1.305
Re (ohms) = 7.56
BL (T-m) = 4.333
Sd (cm^2) = 214.0
SPL (dB/W/m) = 87.9

I looked at the near field SPL measurements I made at the time and these driver look pretty good. They have been sitting stacked on my workbench for years, not sure why I never tried them.

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 Posted: 04 Dec 2008, 18:03
 Editor

Joined: 28 May 2008, 21:53
Posts: 4592
Hi Martin, good to see you here.
Thanks for sharing your measured T/S parameters for the Radio Shack 40-1286C.

Greg, I think you are looking at an OB baffle system for these. You should take a look at Martin's information on Open Baffles Speakers: http://www.quarter-wave.com/OBs/OB_Theory.html as it is an excellent resource.

Cheers

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 Posted: 04 Dec 2008, 19:44

Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
Greetings gentlemen!

Mr. King, it is neat to see you respond to my inquiry after having read about many of your projects. And having measured specs...how can you beat that?? Thanks!

Gio, Thanks for the link. It is already in my favorites. One of many. Can't wait to get started now.

Regards, Greg

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 Posted: 04 Dec 2008, 20:54

Joined: 04 Dec 2008, 12:27
Posts: 35
Location: Clifton Park, NY USA
Not trying to sound like a broken record but, pair the RS 40-1286C with an Eminence Alpha 15A on a 20" x 40" open baffle and you have a very nice system. Cost would be very low, seems to show a lot of potential in the quick simulation I just ran.

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Martin

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 Posted: 05 Dec 2008, 05:13

Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
Sounds like a great idea. I will be sure to keep this thread updated as I go.

Until later, Greg

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 Posted: 05 Dec 2008, 19:00

Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
Either of you gentlemen care to expound on things such as treating cones, mods to whizzers and baskets, etc.? Are some of these things helpful, or are they just a bunch of hooey? I know there are some pretty far out things so called "audiophiles" try.

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 Posted: 05 Dec 2008, 20:57
 Editor

Joined: 28 May 2008, 21:53
Posts: 4592
Hi Greg, you can try them and seen if you can hear an improvement. Damping the back of those drivers seems like a good idea and I do it all the time. Cone treatments are tough for me to buy into particularly since no one can objectively show that they make a change for the better.

I have used phase plugs. They may help the upper midrange range, but it is not universal across all drivers. They do come with a price of hurting the off axis response and decreasing the maximum SPL on drivers that originally had a sealed dustcap. I also found the need for a super tweeter after I added them to a pair of radio shack 40-1197.

I would like to see how the removal of a sealed dust cap affects the distortion. You would think that if it actually helped that the designers would have used a relieved dust cap as opposed to sealed.

This is a worthwhile read: http://www.geocities.com/rbrines1/Pages ... Plugs.html

Cheers

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 Posted: 06 Dec 2008, 05:10

Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
Thanks Gio and Martin for the advice and help!

I think I will venture forward with this build and share my findings with the others here who may have an interest. I can say what I have learned so far about full range has been from people who have done the same. As I alluded to earlier, this will be a sort of practice run in hopes of using it as a stepping stone to other builds. I think that's a natural progression. If I decide to try mods to the dust caps or whizzers and screw something up, it's not like I can't regroup and move forward.

Best regards, Greg

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 Posted: 06 Dec 2008, 11:11

Joined: 04 Dec 2008, 12:27
Posts: 35
Location: Clifton Park, NY USA
Quote:
Either of you gentlemen care to expound on things such as treating cones, mods to whizzers and baskets, etc.? Are some of these things helpful, or are they just a bunch of hooey? I know there are some pretty far out things so called "audiophiles" try.

I am not sure I can provide a nice comprehensive paragraph that describes my position on some of these mods, I have not tried many of them and am reluctant to try something non-reversible on some of my drivers. So I will throw down some random experiences in no particular order.

1) With respect to phase plugs, I have three different phase plugs for my Lowther drivers. I tried all three, and the no phase plug configuration, a few years back after building my Lowther DX3 ML TL. Differences were very small if at all and to be honest I preferred the no phase plug or the cheap bullet phase plug, they both sounded about the same. No eureka moment with the phase plugs.

2) I have had a pair of treated Fostex FE-126E drivers for a year or two, the cone is coated and dotted to the latest recipe, but they have never made it off my bench and into my system. Too many other things to do. I did measure the T/S parameters of the pair and they were no different then a stock pair. I have a tough time believing that they will be that much different sounding then a stock pair. Maybe that is why I have not prioritized trying them out. Soon .... I hope.

3) I have seen the various basket mods that people apply but to be honest I am a little skeptical that they do anything. This includes the magnet mounting schemes people also use.

Those are my experiences. Here are my opinions on driver mods.

1) I don't believe that any mod will take a poorly designed and performing driver and make it a world beater.

2) I believe that mods can make small differences in a driver's performance, probably some better performance and some worse performance at the same time.

3) There is a lot of snake oil and voodoo associated with mods and people report hearing dramatic changes associated with wild non physics based explanations of why it happened, actually that applies to the whole field of audio. Then others will report no audible difference. I always look at such claims of dramatic improvement, that don't have simple and verifiable results presented, with some degree of disbelief. I am particularly skeptical when the reporter is also the inventor.

4) If the driver is well designed and manufactured then I believe that a better system design, both enclosure and filters and room, can yield a bigger improvement in speaker system performance then some weird tweak to the driver cone.

5) Everything has a simple explanation. If a proponent of some tweak or mod is using convoluted rocket science to explain the physics, beware it is probably tchno-babble. I have more faith when someone talks about some tweak and admits they have no idea why it works.

In concusion, I believe that some tweaks might produce small changes in the performance of a well designed and made driver, some of these changes may actually be beneficial. When I look at a tweak, I try and understand what it does and why. If I cannot come up with a simple physics based explanation then I am very skeptical that it will do what the inventor claims. As of today, I am not about to start applying experimental non-reversible mods to anything in my driver collection.

End of babble,

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Martin

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