Radio Shack RS 40-1271 8" Full Range Driver

[gmilitano]

I have read through all the archives that mention the 40-1271 driver. There have been several trials posted in there that have included various baffles sizes: 16X36", 24X39", 13X25", 31X35" and the tapered design noted by GM in this threed. In addition there was a 1ft^3 closed box and a 1.5ft^3 vented box design!

Most importantly, I found a message by Thorsten with instuctions on how to properly use his spreadsheet. Using his spreadsheet, I have settled on the following:
RED GREEN BLUE
Driver Resonant Frequency (Fs - Hz): 82.93 82.93 82.93
Driver Electrical Q (Qes): 3.30 3.30 3.30
Driver Mechanical Q (Qms): 9.45 9.45 9.45
Driver Equiv Volume (Vas - liter): 32.84 32.84 32.84
Thermal Power Limit (P - VA): ???? ???? ????
DC Resistance (Re - Ohm): 7.92 7.92 7.92
Pk-to-Pk Excursion (Xmax - mm): ???? ???? ????
Effective Cone Dia. (D - mm): ???? ???? ????
Baffle Hight (mm) 1050 1200 914
Baffle Width (mm) 250 300 400
Hight above floor (mm) 900 900 700
Dist. rear Wall (mm) 100 125 100
Dist. side Wall (mm) 300 300 300

RED GREEN BLUE

I am leaning towards the RED baffle dimensions. Does anyone have any suggestions on how to improve this reponse, or this about as good as I can get using a rectangular baffle?

Cheers,
GM.

[GM]

Did you sim my tapered design? Using a 1/3 octave RTA, their in-room response was considerably smoother than any of these.

GM

[gmilitano]

Originally posted by GM
Did you sim my tapered design? Using a 1/3 octave RTA, their in-room response was considerably smoother than any of these.

No. I do not think that the Thorsten spreadsheet can simulate a tapered baffle. Also, I do not have the knowledge or tools to do the simulation manually or otherwise. I don't even know what a 1/3 octave RTA is!

Since I will not be using these is a common room, I am now open to the tapered idea (since it seems like the best sounding). However, I would like to see some simulation of the response.

On the bright side, I have a 33-2050 SPL meter now! I'm going to see if I can get a FR of this driver.

I appreciate all you help to date.

Regards,
GM.

[GM]

You're welcome!

1/3 octave is the resolution. RTA = real time analyser. It feeds a pink noise signal through the speaker and shows its response, plus any room, etc., interaction depending on where the mic is located.

Sorry, I didn't bother to record it.

FYI, the older RS SLM's require a correction chart to get a ~accurate plot, so check around to see if the later ones have one or use the old one.

GM

[gmilitano]

For the 33-2050 SPL, Eric Wallin has a lot of information on his website, plus there have been some posted in here.

So is there no way to model the response of a tappered open baffle? How much better is the tappered design compared to the baffles I posted?

Would building the baffles that I have modelled be a waste or will the sound be ok?

Cheers,
GM.

Originally posted by GM
You're welcome!

1/3 octave is the resolution. RTA = real time analyser. It feeds a pink noise signal through the speaker and shows its response, plus any room, etc., interaction depending on where the mic is located.

Sorry, I didn't bother to record it.

FYI, the older RS SLM's require a correction chart to get a ~accurate plot, so check around to see if the later ones have one or use the old one.

GM

[gmilitano]

I scored some free plywood that was close to my rectanular baffle dimmensions and I finally got around to putting this project together.

My findings were the same as other users of this driver, that being that the 40-1271 is an 8" extended midrange/tweeter.

In 2 channel mode this driver sounded distant and small. Adding a sub helped quite a bit, but it still does not compare with a bookshelf or tower speaker.

However, I found that they were not too bad as the main or rear speakers as part of a HT setup. They were rather good for use with TV shows and most movies and football games!

Experimenting further with HT applications, I compared them to my JBL 2-way micro sattelite speakers. The comparisons were favorable, and I seem to like the 40-1271 a little bit better than the JBL. The 40-1271 have better LF response. On axis was very similar to the JBL, but the off axis response was much better than the JBL.

I will give these some more listening when I finish my tube amp to see if that helps the sound at all.

This driver is still available for $30CDN through Radio Shack Canada. However, I think that the money could be much better spent on several other full range drivers.

Thanks to all those who provided me with info regarding this driver and open baffles.

Cheers,
GM.

[GM]

Yeah, that's a bit steep for these, the 40-1272 is much better (if still available), though it has a high Fs/Qts, so no help in the LF.

There are a few tweaks that will help these though, damping the chassis inside and out with ductseal or similar, filling the motor/chassis joint with Liquid Nails or similar, and filling the gap between the cone and whizzer with polyfil or acoustic foam dense enough to damp the HF standing waves between them (AKA '$0.98 tweak').

Last, but not least, it needs to be mass loaded, i.e. clamped to the baffle in a manner to preload it. Here's a closed box version that you can figure a simple variant for OB if need be: http://melhuish.org/audio/images/press-screw.gif

GM

[DigitalJunkie]

Many moons ago a friend and I found a pair of those at a local RadioShack,for $5 each,same deal...we counted up all our money and got them..

About a week later my friend build up a crude bandpass box for one of them.
It didn't get extermely low,but it was great,for an 8-inch.
He rattled the house with that one 8-inch driver,in a 14-year olds attempt at a thing called a "bandpass box"...
I was seriously impressed! Not bad from an old POS stereo..probably only 20w per channel-max. But I put a big 19,000uf stiffening cap on the power supply for him.
About 6 months later the rectifier diodes fried..