It is possible to determine the T/S parameters by adding mass to the cone. Is it ever done to add mass permanently. What are the pro's and cons?
Added mass is probably the most common technique. Just make sure that you keep the added mass close to the voice coil connection to the cone. I have used clay but I prefer solder pieces (heavy lead) with a little dry adhesive as it makes a tighter fit to the cone - added mass must be firmly attached to work right.
I have added mass to a speaker in subwoofer apps for example. I just glue on pieces of solder. Balance it as well as possible.
I have added mass to a speaker in subwoofer apps for example. I just glue on pieces of solder. Balance it as well as possible.
mitchyz250f said:
I dont' think so. You'll need to run a test with a dedicated woofer tester instrument. They are for sale at PE.
The classic Snell Model A used add mass on the RCF 12 inch woofer. They poured a resin around the porous dust cap to about 1/2 inch depth. It lowers the Fs and efficiency is sacrificed as the trade-off.
mitchyz250f said:
If you look up the basic equations for TS parameters its easy to see what added mass will do. It lowers Fs and raises both Qes and Qms.
speakerdoctor said:
There are other options.
For next to nothing with Speaker Workshop and a handful of parts.
WinISD Pro can simulate a box and allow you to add mass to the driver to see the effect it will have on the driver in that box. Ideal if your doing a ported or sealed box 🙂
For purposes of testing "poster caulk" ( sold at office supply stores ) works ( see audioXpress November 2008 p 35 ).
Usually 200 grams or less is used.
For permanent application - lead ( as in solder recommended above ).
Also lead foil is sold in golf pro shops
Usually 200 grams or less is used.
For permanent application - lead ( as in solder recommended above ).
Also lead foil is sold in golf pro shops
This is just a thought as I've not tried it, but would epoxy with a suitable filler like barium oxide or powdered nickel be any good for adding mass permanently??.
I ask as I still have a litre of West Systems epoxy and powdered aluminium and stainlees stell left over from a heatsink experiment.
Regards
Ted
I ask as I still have a litre of West Systems epoxy and powdered aluminium and stainlees stell left over from a heatsink experiment.
Regards
Ted
in latest Jan. 09 Voice coil article:
"The drivers selected for testing were
two 8¡È woofers and two 6¨ö¡È woofers.
Based on a recommendation by George
Augspurger, we tested each woofer with
three different values of test weight, then
averaged the Vas values. The results of
these tests are listed in Table 5.
In the 6¨ö¡È unit 1 of the woofer testing,
the Vas variations from three different test
weight values were 0.958 (44.4g), 0.901
(59.5g), and 0.808 (74.7g), with the average
= 0.889 the others are not listed."
Here the driver is Dayton DC160S-8.
The Mms in the specification is 25.38 gms.
The mass added is 44.4~ 74.4 gms.
Many suggest that added mass be nearabout Mms.
This is important for getting proper Vas.
Vas is most important for proper dimension design of enclosure.
So value of added mass becomes important.
what must be the ratio of added mass compared to mms of driver?
"The drivers selected for testing were
two 8¡È woofers and two 6¨ö¡È woofers.
Based on a recommendation by George
Augspurger, we tested each woofer with
three different values of test weight, then
averaged the Vas values. The results of
these tests are listed in Table 5.
In the 6¨ö¡È unit 1 of the woofer testing,
the Vas variations from three different test
weight values were 0.958 (44.4g), 0.901
(59.5g), and 0.808 (74.7g), with the average
= 0.889 the others are not listed."
Here the driver is Dayton DC160S-8.
The Mms in the specification is 25.38 gms.
The mass added is 44.4~ 74.4 gms.
Many suggest that added mass be nearabout Mms.
This is important for getting proper Vas.
Vas is most important for proper dimension design of enclosure.
So value of added mass becomes important.
what must be the ratio of added mass compared to mms of driver?
If the goal is to lower fs, why not modify the suspension? Cut the spider or change the surround to a softer one would also lower the fs.
I doubled the moving mass of my Celestion drivers fitted to the Tannoy B950.
I tested T/S from zero added mass in 20gm increments to 130gm.
I found that Fs was as predicted by the model.
Q did not vary with the model.
I used the measured Q to model the vented box.
I did find that VAS is very susceptable to room temperature and to how long it was since the last test/s. The surround seems to stiffen with lower surround temperatures.
The higher temp can be caused by ambient and/or by heat generated in the surround due to inherent damping (power absorption).
I tested T/S from zero added mass in 20gm increments to 130gm.
I found that Fs was as predicted by the model.
Q did not vary with the model.
I used the measured Q to model the vented box.
I did find that VAS is very susceptable to room temperature and to how long it was since the last test/s. The surround seems to stiffen with lower surround temperatures.
The higher temp can be caused by ambient and/or by heat generated in the surround due to inherent damping (power absorption).
mhtplsh said:
There is no "must" ratio, use whatever is convenient, but the idea of using several different masses and averaging is good. Too much mass is not a good idea since it will perturb the system too much. Enclosure tuning is not that sensitive to Vas.
MJL21193 said:
I wouldn't wish that on my worst enemy 🙂
I can't even imagine building speakers without my Parts Express Woofer Tester. It's an amazing product. It measures speaker parameters in a matter of seconds, and it's inexpensive. It's also invaluable for verifying that a box is built properly, because the impedance curve of a loudspeaker can tell you a lot about your construction.
Speaker Workshop is a clever product, but measuring T/S parameters with it is painful arduous and slooooooow. It has a nice crossover program tho.
Moondog55 said:
A few years back I added mass to the cone using fiberglass or epoxy. Can't remember which.
It destroyed the woofers 🙁
The surround disintegrated from the fumes!
My preferred method these days is to use polyurethane glue, like liquid nails or the equivalent. It adds mass without trashing the surround, waterproofs the cone, and increases the rigidity at the same time.
I have found that one must be careful when using the WT on a speaker with a heavy cone during the adding mass exercise. If you test with the speaker on it's back (cone facing up), the weight of the cone with affect the Fs.
Test these types of woofers with the cone pointing sideways - at least for applications where the woofer will be used in that orientation.
I used a two part resin/hardener system sold at Michael's craft store. It dries clear. For my project, I first used rope caulking around the dust cap to determine the desired amount of mass to add. I then placed the woofer on it's back on top of a scale and carefully poured the resin mixture around the cone until the weight came up to my target.
Test these types of woofers with the cone pointing sideways - at least for applications where the woofer will be used in that orientation.
I used a two part resin/hardener system sold at Michael's craft store. It dries clear. For my project, I first used rope caulking around the dust cap to determine the desired amount of mass to add. I then placed the woofer on it's back on top of a scale and carefully poured the resin mixture around the cone until the weight came up to my target.
Interesting thread - I've been looking at the ESS 10" woofer for use in a low power (50w) sealed sub.
90.6db 1w/1m 27hz Fs Qts 0.48 vas 49.55 litres
Its not normally used like this but just looks great in winisd and more than enough efficiency. So then I was thinking to do a sealed isobaric(f3 40hz, 25litres) altho these drivers are not budget.
Then I read this and thought about treating the paper cone to add mass/lower the Fs.
90.6db 1w/1m 27hz Fs Qts 0.48 vas 49.55 litres
Its not normally used like this but just looks great in winisd and more than enough efficiency. So then I was thinking to do a sealed isobaric(f3 40hz, 25litres) altho these drivers are not budget.
Then I read this and thought about treating the paper cone to add mass/lower the Fs.
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