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PostPosted: 27 Nov 2008, 10:57 
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Location: Chillicothe, Ohio
I acquired a pair of NOS 40-1286C 8" for close to nothing, which may be what they're worth, LOL. In spite of that, I thought it would be the perfect opportunity to "practice", so to speak, by doing my first full range build, with a goal of doing something of a bit more quality later. I've seen that they are most suited to an open baffle, which is fine by me. Wondering if anyone can give me some idea of what size panels should be used, and maybe some tips about placement experimentation. I would be using a tweeter to help the upper reaches. Also, I understand these can be used successfully in a horn loaded enclosure, but it would have to be huge, yes? My room is 12' x 24', so I have some space. Any specifics would be great.

Driver specs that I have are:
Radio Shack 40-1286C Full Range Drivers wrote:
Fs 53Hz
Vas 1.73
Qts 1.16
Qes 1.43
Qms 6.06

Thanks, Greg


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PostPosted: 27 Nov 2008, 17:13 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi Greg,

Since those drivers have a high Qts (just above 1) they will be well suited for use in an open baffle. They will also work in a sealed enclosure or an aperiodic enclosure, but the box will have to be very large.

Here are a couple of open baffles that may give you some ideas:
Image
Fullsize image: http://diyaudioprojects.com/Gallery/dis ... php?pos=-5

Image
Fullsize image: http://diyaudioprojects.com/Gallery/dis ... hp?pos=-50

Image
Fullsize image: http://diyaudioprojects.com/Gallery/dis ... p?pos=-137

Cheers

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PostPosted: 27 Nov 2008, 20:55 
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Location: Chillicothe, Ohio
Thanks Gio! Just what I'm looking for.

Regards, Greg


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PostPosted: 30 Nov 2008, 10:12 
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Location: Chillicothe, Ohio
If I were to opt for a sealed enclosure, how much volume are we talking about? And how critical is placement for an open baffle?

Thanks, Greg


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PostPosted: 30 Nov 2008, 12:50 
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Hi Greg,

An open baffle speaker setup will need to be away from the wall. That distance will be primarily a function of the room.

To get an idea of size for a sealed enclosure, you can do a very quick check with ISD online:
http://www.linearteam.dk/default.aspx?pageid=newdriver
Likely 2 cu ft. or so and that will be a bit warm in the midbass region.

If you want to go with a box, you could try fashion something after the Omega B200, but that driver has a reported Qts of 0.75 so this radio shack driver may be a stretch in a reasonable sized enclosure even with aperiodic loading.

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PostPosted: 30 Nov 2008, 21:07 
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Location: Chillicothe, Ohio
Hi Gio, Thanks for the link. From all indications I probably will stick with an open baffle. It seems the drivers I bought are very limited, but I will use them as I intended to when I bought them...for practice and experimentation. If I can get a satisfactory midrange from these I will pursue taking it to the next level by adding a tweeter and subwoofer. My goal is to build something of higher quality eventually, as mentioned before, so I wouldn't want to get too carried away spending a huge amount on these. Another reason to stick with the open baffle.


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PostPosted: 30 Nov 2008, 21:27 
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That is the approach I would take. Of course you can always upgrade the 8" unit later and keep the LF driver and tweeter. I have the Radio Shack 40-1271 which seems similar and I think you will find that these need more support down low than they do up top.

Cheers

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PostPosted: 03 Dec 2008, 19:08 
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Location: Chillicothe, Ohio
Well, a new development has come to light. While doing a little searching for info about these 40-1286C drivers, I found an entirely different set of parameters than I found earlier. Copied directly from a thread on http://www.gainclone.com

Quote:
40-1286C specs on 8" full range woofer by Radio Shack
Fs 39 Hz
Vas 2.0 cu. ft.
Qts 0.45
Qes 0.56
Qms 2.4
Re 6.25 Ohms
Le 0.6 mH
BL 6.9 T/m
Eff (SPL) 89.8 dB 1W/1m

Drastically different than the other parameters.


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PostPosted: 03 Dec 2008, 22:08 
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Hi Bluesman,
Can you post a photo that shows the magnet. A small magnet generally means a higher Q. Anytime I have seen a spec for this driver, it is Qts > 1.

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PostPosted: 04 Dec 2008, 04:49 
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Joined: 04 Oct 2008, 11:29
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Location: Chillicothe, Ohio
Thanks Gio! One of the few specs actually listed on the box is the magnet size, which is 9.8 oz., or 277g.

I can post a picture later if needed. Got to get to work for now.

Cheers, Greg


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