I found further directions to measure VAS (two sections in the manual) I'll play with this some more soon as I can. I'll reinstall DATS software and make sure everything is setup properly and remeasure everything.
Measure V(as) by the Selected Method
Before any measurements are made this command is disabled (grayed out). After making a free air measurement this command becomes enabled and can be used to measure the V(as) of a driver by any of four methods. The V(as) test method is selected at the Parameters Bar at the right side of the main window. You can also Measure V(as) by clicking the same named button at the Impedance Bar at the left side of the main window. The four methods are: Test Box, Added Mass Specified SPL and Specified M(md).Items commonly used for added mass include: coins, modeling clay, carpenters putty, rope caulk and tape rolls. In general you should measure the weight of the added mass accurate to 1/10th of a gram. In a pinch, US coins can provide an easy source of standard weights. One US nickel ($.05) weighs 5.0 grams.
- Test Box: This method is probably the most widely used and trusted. For this method you will need a test speaker enclosure of suitable size for the driver being tested
- Added Mass: Although the added mass method can employ added mass in the simple form of coins added to the cone it is best to make sure the added mass actually adheres to the cone so that it moves with the cone at all times. If the mass "decouples" as the cone moves then accuracy will be compromised. Use an added mass that will shift the F(s) lower by about 25-50%. An added mass equal to the driver's Mms is just about right. DATS will warn you if the shift in the measured F(s) is not within the above recommended range.
Each of the four methods of measuring V(as) requires that you enter the Piston Diameter of the driver. The piston diameter is the effective diameter of the acoustic piston formed by the speaker. The piston diameter is measured as the diameter of the speaker cone and normally includes about half of the surround on each side of the cone. For example, a nominal 8 inch woofer would probably have an actual piston diameter in the range from about 6.25 to 6.5 inches.
- Specified SPL: This is a simple V(as) method as it requires no test box or added masses. It is also probably the least accurate as it depends strongly on the accuracy of the SPL you specify.
- Specified M(md): This is another simple V(as) method. It requires that you know the actual moving mass of the driver. This method is especially suitable for use by driver manufacturers where the driver's components are readily available for weighing. It is also a good method for comparing similar drivers.
Seems like the added mass method would be the easiest to do at home. Using nickels or other coins because of the consistent weight values seems tempting, but how does one attach nickels to the cone so they don?t decouple?
Clay seems like it would stick just enough, and there are inexpensive scales available that go down to .01 grams.
I've used painters tape as opposed to masking tape, it's more easily removed. Tear a short piece and roll it into a loop with the adhesive facing out. Stick the nickel to one side and the other side to the speaker. Comes off easily.Originally Posted by Elitopus1
Your neighbors called. They like your music.
416-8B-1.jpg....416-8B-2.jpg....416.8B-3.jpg....416.8B-4.jpg
I think the DATS on these is accurate because of the fact that I have an original (not reconed) 416-8C that tests almost right on published specs. I'm not sure why so much variance going on here. Actually maybe not so much variance but not on par with published specs. I guess recones essentially half Altec half GPA. I see why many like to keep the original cones. I wish I could afford a new pair of GPA 416-B's just to compare. Price on those is out of reach for most of us on a budget.
Last edited by Mercury3; February 14th, 2020 at 12:11 AM.
I?m kind of surprised the specs on those drivers are different like they are. I would think that being done all in a row, with recone kits from the same batch would make very similar specs when tested. But maybe variations in the motors themselves account for some of that?
Do you know how close the woofers are in production dates to each other?
Well I boxed them back up again until I'm ready to use them so I can't look for serial numbers right now. I should have thought of that I guess.
However I don't think so. They were not obtained together but in two separate pairs. The frames look new condition and look like late model b versions. The cones had blemishes which was one of the reason I wanted them reconed. Once I get them installed I wanted them looking like new. That and for sure I wanted the magnets recharged.
One uses small neodymium magnets in pairs with one of each pair on either side of the cone.but how does one attach nickels to the cone so they don?t decouple?
They won't de-couple, there's no tape to create a compliance between the mass and cone, and there's no sticky stuff to pull up pulp fibers or leave sticky residue on your pristine cones.
Not all vegetables make good leaders.
Yes, that's a good way and used slot car magnets [or bits n' pieces of] for small drivers, but woofers take enough weight to lower Fs by 1.56x that between this and the ideal of having the weight centered on the Vc that I used various size deep bottom plastic mugs to place over the DC and pour sand in till I got the desired lower Fs.
Curious though, recently just got some of the little Nd mags and they're so powerful even compared to the AlNiCo 5 that seems like it would be easy to damage the diaphragm surface just trying to pry them apart?
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
For added mass I used (search ebay) "25 Pcs Super Strong N35 Neodymium 6 x 2 mm Disc Magnets " and a steel ring from a $5 Walmart tribet (3 concentric rings, easily pulled apart into individual rings). Then you have multiple rings, appropriate for various sized drivers.
The tribet ring goes on the front, magnets on the back to hold it 'centered'. Magnets allow you to adjust the centering... but beware that if you break the magnetism the little disc magnets will find a home wherever they can in any little crevice (or get stuck to the back of the surround goop). So count how many you start with and make sure you end with the same number. :-) Keep some tweezers or a hemostat handy to pluck them out of tight spaces if need be.
Well I believe the latest specs I posted above are pretty accurate due to a comparison to a 416-8c I have tested and the specs almost match published specs.
I'm disappointed with the high FS especially one measuring 40hz. That could still work fine if I decided to use it with subwoofers below 50hz or so but I originally had my heart set on MLTL cabinets. However I'm unsure if the QTS of .5 on one woofer isn't to far off for MLTL design too. Seems better suited to sealed or aperiodic loading.
I don't regret having the four woofers reconed because as mentioned the cones all had blemishes and such due to age. I wanted them to look new which they do now.
I'm not in any hurry to complete this design as this is suppose to be a retirement project for me. My plan was to collect everything needed but actually do the build around spring of next year when I retire and have extra free time on my hands. (still a year away)
Hence I'm just going to think on this design a lot between now and then. Another problem I'd mentioned in my MLTL thread is I'm not sure where the put the horns because of the cabinets needing to be so tall in order to use two 416's per channel.
Lots to plan and think about. Thanks to everyone who has replied to all of my threads here. I've learned a lot already and appreciate everyone's suggestions / ideas!
Mark
Bookmarks