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1.7 frame damping

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Posted on December 23, 2016 at 11:13:29
zulugone
Audiophile

Posts: 65
Location: Seattle, Washington
Joined: August 31, 2013
A question for those who have experimented with frame damping schemes....post warranty.

I have read posts about replacing MDF frames with wood and various schemes for stands and damping mostly with skepticism. My skepticism comes from not seeing much in the way of before and after measurements. I can feel the frames vibrate with bass but I can't see the frames move back and forth though it seems reasonable that they might move in the range of thousandths of an inch. I have never seen the Mylar move. My ears are measured golden by a board certified audiologist however the CPU to which they are attached not so much. I can only guess that stands work given their popularity.

I came across a post somewhere by josh358 stating that Jim Winey said metal frames would be ideal but would weigh too much to ship. That got me contemplating more steel.

On either side of the Mylar in front there is a 1/2" x 2" space and in the rear a 1/2" x 3 1/2" space. Both run most of the height of the 1.7. Any thoughts on the damping effect of filling both spaces with steel flat bar with or without a layer of damping material between the steel and the MDF? The flat bar could be drilled, countersunk and through bolted all hidden under the sock. This would add over 70 lbs. to each speaker. I could also have the top bolt stick through the sock to be bolted to a brace angled to the feet though I wonder if the Mylar vibrations would be able to move all that steel.

 

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RE: 1.7 frame damping, posted on December 23, 2016 at 11:57:02
Audiophilander
Audiophile

Posts: 30022
Location: Fort Worth (D/FW Metroplex)
Joined: March 31, 2000
Have you checked out Mye stands? They're available for 1.7 model Maggies. Grant's stands are the bees-knees, in my estimation. Do they work (provide rigid support that substantially reduces frame vibration)? Absolutely!

I can understand the DIY hobbiest POV, but there are only so many ways to reinvent the wheel. In some areas, yielding to existing engineering expertise may be the more prudent choice to trial and error. My 2 cents.

 

RE: 1.7 frame damping, posted on December 23, 2016 at 11:58:49
russ69
Audiophile

Posts: 912
Joined: December 13, 2009
Feel free to try and post the results. Personally I'd pick lighter and stiffer materials for this job but your are the designer so use what you desire.

 

RE: 1.7 frame damping, posted on December 23, 2016 at 12:23:35
zulugone
Audiophile

Posts: 65
Location: Seattle, Washington
Joined: August 31, 2013
Yes I did and the many positive Mye reviews. However posts refer to damping the entire frame (razor) XOR bracing the frame (at one point usually). Those two concepts overlap to some degree though I have no way of comparing effects in advance.

 

RE: 1.7 frame damping, posted on December 23, 2016 at 14:59:17
Satie
Audiophile

Posts: 4289
Joined: July 6, 2002
I would go with Aluminum L braces with an elastic damping material to press the frames into place to damp them and increase rigidity of the MDF, I would mount the speakers on big feet (spiked or not) then use a cross brace from the top 1.3rd to the back of the feet to provide the basic rigid form of a triangle.

 

RE: 1.7 frame damping, posted on December 23, 2016 at 15:10:59
neolith
Audiophile

Posts: 3779
Location: Virginia
Joined: February 21, 2002
Contributor
  Since:
December 2, 2004
Look in the tweaks section - several years ago AndyR posted several modifications and tweaks for his IIIa including bracing and frame stiffening. Most of the tweaks are applicable to the 1.6.



I married the perfect woman. The downside is everything that goes wrong is my fault.



 

RE: 1.7 frame damping, posted on December 23, 2016 at 23:01:43
andyr
Manufacturer

Posts: 11429
Location: Melbourne
Joined: September 2, 2000
I'm wondering why you are wondering ... whether your 1.7s can be made to sound better?

Because:

a) You seem to be lumping together (and confusing) at least 3 separate - and distinct - concepts?:

1. is there an advantage to braced stands which stop the frames from swaying backwards and forwards, from bass transients?

2. does the 'razor' method (ie. damping the holey-metal pole-piece) do any good?

3. does replacing the MDF frame with hardwood deliver any benefit?

and b) You want before & after measurements - not anecdotal evidence - before you take a step. :-))

But re. your comment "though I wonder if the Mylar vibrations would be able to move all that steel" ... I suggest they will! My Maggies are equivalent to Tympani IVas with only 1 bass panel - not 2. So I have 2 heavy, hardwood frames each side and each frame has a braced stand, like so:



These are the stands for the mid panels and ribbons. There is another stand - with a much heavier base - for each bass panel.

The hardwood frames for the bass panels weigh about 30lbs each - in spite of this, if I rest my fingers on top of the bass frames, I can clearly feel the bass vibrations (when the bass is pumping :-)) ). But because the mids & ribbons are in separate stands ... they have no movement.

70lbs of steel mass loading will of course reduce the MDF frame's vibration - but I don't think it will eliminate it.

In terms of replacing the stock MDF frame with a hardwood frame ... there are a couple of things at play here, which improve the sound:

* the hardwood is stiffer.
* the driver is now fixed more firmly to the frame. If you were curios enough to see what Maggie looks like "in the flesh", you would find - after removing the sock - that the driver is stapled into the MDF frame. Staples and MDF are not a 'solid' combination! :-((

If you read my "Tweaks" article, you will see what I did to my IIIas long ago, before Peter Gunn had come up with the idea of hardwood frames. This was to clamp each side of the driver to the MDF using steel 'L-section' - the long arm of the 'L' lays against the back of the MDF frame (and was bolted to the MDF), the short arm went down into the rebate, pressing against the back of the driver.

This did 2 (good!!) things:
* the driver was now locked to the MDF frame - much tighter than with the staples, and
* the steel L-section running the full length of the MDF frame stiffened it.

Andy

 

RE: 1.7 frame damping, posted on December 24, 2016 at 09:49:48
zulugone
Audiophile

Posts: 65
Location: Seattle, Washington
Joined: August 31, 2013
Yep, I am intentionally combining everything to do with vibration. My theory is that a little damping in some place will have the most effect and thereafter adding more will proportionally do less good....though there is concrete :).

I had the sock off of a 1.7 and noticed that the frame thins between the outside edge and the Mylar leaving lots of room for damping material. I can guess that making the frame thicker in front close to the tweeters might case a sonic problem. I don't know if a lot of steel nearer the magnets could cause any problem or if Magnepan made the frame thinner in places for sonic reasons or just to keep shipping costs down.

For damping material I have been looking at butyl tape (cheap) and Sorbothane products (not cheap) rather than the automotive stuff. Steel wins on density and price.

I found lots of interesting acoustics reading on damping outside of the HiFi world. One idea was to only dampen 25% of a vibrating surface (like the magnet frame?) as more damping didn't improve more.

I did find one post here that mentioned using an accelerometer....some of which cost more than the speakers. I found a cheap one used for speaker box design I will look into. The idea is to produce a graph similar to the REW waterfall for box vibrations by frequency. I braced a 1.7 to the wall behind (very rigid) for a quick test and could detect no change with REW but that test didn't deal with more significant bass.

My first tupid thought on speaker sway was a clear fishing line secured at the end of the front and back feet and the top of the speaker....but first I have to get an accelerometer.





 

RE: 1.7 frame damping, posted on December 24, 2016 at 13:21:59
Satie
Audiophile

Posts: 4289
Joined: July 6, 2002
Since you have done some reading on vibration control and dissipation more broadly then you should recognize that Magnepan chose to float the magnet board frame in the
MDF as a low mass approach to keep the MDF from coupling too well with the steel driver frames. Relying on air damping of the magnet board.

There are 4 vibration issues you want to deal with in the magnepans.
1. Swaying and general MDF bending effects. Due asymmetrical anchoring of the panels at one end.
2. magnet board ringing
3. radiation on the listening axis from the MDF frame, including diffraction.
4. transverse waves in the mylar diaphragm being reflected back from the steel edges of the driver frames.

Each of the approaches to vibration damping and rigidity leave less for the others to do - as in belt and suspenders. The damping of the steel frames with damping material between the steel frame and L brackets bolted through the MDF as AndyR has done, should provide a good damping of the magnet board edges on the vertical and leave little for the CLD "razoring" to do.on the magnet board itself. It would control both ringing of the magnet board and damp the transverse waves in the mylar.

The bow and arrow mod will also provides damping at the center of the panels in an easy and reversible way by essentially installing springs. But unlike the CLD damping at the steel frame edges it would not do much for transverse waves in the mylar - the kazoo noise that bothers people who have noticed it as a separate coloration.

Though I find that the fabric itself is good enough to control diffraction, things could be improved further using felt on the MDF front surface near the tweeter and in the TIV and 20.x around both mids and tweeter.

AndyR's frame takes care of any possible rigidity issues and IIRC he used elastomer damping strategically in the mounting of the wood frames that serve also to damp self noise from panel ringing to kazoo noise. Hopefully AndyR will correct this or provide further detail if I got it wrong or missed something.

The PG bolted hardwood frames take off ringing and kazoo noise and transfer them to the hardwood frame and radiates them away from the listening axis. The cross braces add to rigidity and thus deal with all the vibration control issues on the maggies. Perhaps not completely but effectively, as many who have applied the mods or had PG build it for them have noted.

For my TIV/Neo8 I put on big feet oak on the bass panels and braced the center of their tops to the sidewalls. The mounting on the feet includes a leaf spring aspect where the 1/4 inch brackets leave the panels hanging over the feet, that is wedged to vertical orientation using hardwood shims That provides a spring damping for large vibrations. For the mids and tweeter I have not done any significant bracing, Just damping of the Neo8 mounting rails with foam weather stripping between the hardwood slats and the MDF. I also added strips of foam vertically along the sides of the Neo8 drivers to suppress ringing and diffraction. The fabric turned out to be enough on the diffraction side, and it did not control the ringing enough to matter. There will be some CLD damping along the center line and edges when I get to it. Testing temporary CLD I put together from copper strips on carpet tape and foam mounting tape indicated that the results would be very good. But required that I cut u the copper sheet into thin strips - which is both too expensive and not that easy to work with so will get automotive CLD for it as Dawn Razor had done. .

 

RE: 1.7 frame damping, posted on December 24, 2016 at 18:56:29
pictureguy
Audiophile

Posts: 7164
Location: SoCal
Joined: October 19, 2008



2 major approaches.

1. Brute Force using steel and lots of weight. This will 'ring' at some frequency and IMO is not the best approach. Bridgebuilding for the amateur, IMO.

2. Ingenuity using real wood and sinking to floor. Rigidity is more important than weight. Ingenious design and attention to detail rules.


Early concept drawing with roller coupling to floor. Triangulation improves rigidity with minimal weight impact. It should be possible to modify to a ball bearing system.
Panel will be attach to frame with 6.5mil Teflon and a spring compression system to provide even pressure without drilling and no pressure points.
Intended material of frame would be 3/4" PlyBoo while current version of frame front is truncated, not straight.

Too much is never enough

 

RE: 1.7 frame damping, posted on December 26, 2016 at 18:54:05
zulugone
Audiophile

Posts: 65
Location: Seattle, Washington
Joined: August 31, 2013
Thanks for the feedback.

I vaguely recall reading something recently that mentioned "air damping" and "float" though I wasn't sure if those were terms of art or science :). My acoustic reading was mostly on vibration isolation and damping materials from 3M, Sorbothane and other companies.

One local vendor does acoustic damping for the marine trade...like damping room size diesel engines that sound below 20 HZ for the mechanics in the engine room and the passengers outside... thinking about bass trapping.

I have to admit that it does not seem obvious to me that the MDF bends or sways from the Mylar moving. I can barely feel the MDF vibrate and then only at highest db. I didn't do any exhaustive feel testing but one at a time notes on an electric bass didn't seem to cause as much vibration as more "congested" music with bass. I actually saw the Mylar vibrate yesterday (sock off) from rumble listening to some Christmas tunes recorded in the '40s. Apparently the CD engineer wasn't listening with a subwoofer. I have noticed that when I use the Oppo crossover at 40 or 50 HZ REW shows very little change in the curve above about 37 HZ but does drop the 20 to 30 HZ range and REW distortion goes down.

For giggles I taped a 4' piece of toilet paper (Charmin 2-ply) top front. As soon as the music starts the bottom of the TP moves to the Mylar and stays there most of the time. Static electricity beats air movement?

I will likely try razoring the magnet board with some 3M CLD tape. I could remove the driver and reinstall it over Sorbothane strips or on gel standoffs but I think there must be easier ways to reduce MDF vibration. (Assuming the manufacturer's numbers hold in this application vibration would be reduced between 54% and 95%.)

I found a local source for lead I could use to fill in the 4' x 3 " X " indentations on the back. I'm pretty sure the moving Mylar will not induce any resonance in lead :). For purely aesthetic reasons I like having everything under the sock.

One thing I noticed about the comes-with stands is that they do not hold be speakers perfectly plumb side to side or front to back and how they position is not consistent from foot to foot or speaker to speaker. So even if I set them on a leveled piece of MDF I still have to shim the ends of the feet to plumb the speakers.

The error rate is something like 3/8" side to side and " front to back. My goal was to be able to easily adjust tilt in to a precise angle on an out of level concrete floor and eliminate comb filtering which according to the experts is either the root-of-all-acoustic-evil or inaudible.

Just addressing sway I do not see why a dowel from the top center of a 1.7 to the wall behind would not work almost as well as any stand.

 

RE: 1.7 frame damping, posted on December 27, 2016 at 00:14:50
Satie
Audiophile

Posts: 4289
Joined: July 6, 2002
The bending and swaying is mostly a bass issue The results of bracing reported by me and ,many others is tighter bass and better dynamics. It makes a particularly big difference if you listen at real life levels as in the front orchestra. On single panel maggies the midrange clarity improves as well, We can ascribe that to less IMD from the frame motion.

The midbass region usually has substantial dynamics to it and maggies don't distort much in that region, as opposed to the bottom octave. But the response to bracing is significant in improving performance there.

The vibrations in the MDF come mostly from bass as the floating panels don't transfer much energy midrange and up - the MDF is not a good impedance match to the steel nor is the steel a good impedance match to mylar. So the ringing and transverse waves that are the self noise of the planar drivers are trapped in the panels and are eventually damped by air. In the meantime they muddy up the sound.

The stands usually have adjustable spikes or flat feet that you can use to level the speaker. I put some on my feet but it is too inconvenient to reach so I use shims instead.

Your idea of using a gel or foam between the driver frames and the MDF is a good idea. and will help damp the driver and reduce the transverse waves and the kazoo noise they cause. Once you have done it you will notice what it does.

The CLD on the magnet board should control the ringing without you needing to cover the entire back of it. Start with the center 1/4 and go from there if it seems worthwhile to do more of the surface.

The bracing of my TIV bass panels to the sidewalls is done with a dowel like you suggest. It is very effective and makes a big difference at high volumes. It should do as well as doing a triangular brace if the feet are well anchored. Big weights can take care of that side of things.
. .

 

RE: 1.7 frame damping, posted on December 30, 2016 at 10:11:27
pictureguy
Audiophile

Posts: 7164
Location: SoCal
Joined: October 19, 2008
I agree, but try telling people that ingenious design is better than brute force.
Too much is never enough

 

Rigidity is more important than weight. , posted on January 1, 2017 at 07:19:00
watts
Audiophile

Posts: 339
Location: B.C.
Joined: June 30, 2004
Carbon fibre? I am not sure how one could source strips of this stuff, or how to "glue" or fasten the ends like hardwood. I do remember meeting a guy years ago in the motorcycle racing scene who made his own front fender from the stuff; he bought the cloth, soaked it in the appropriate resin, then baked it in his mom's oven. I am no help for you locating a 6 foot oven though.

 

RE: Rigidity is more important than weight. , posted on January 1, 2017 at 10:40:47
pictureguy
Audiophile

Posts: 7164
Location: SoCal
Joined: October 19, 2008
No mention of Carbon Fiber, at least in my post.
TEFLON is just an idea. I have some 3M no.5481 which is 1/2"wide and 6.5mil thick with an adhesive back.
The PLYBOO I mention is Bamboo Plywood and is a 'manufactured' product. If you are curious, send off for some samples. The 'Neapolitan is the heaviest (densest) by far. The 3/4" thick version would seem to be most useful to someone wanting to build a frame for Maggies.
Too much is never enough

 

RE: 1.7 frame damping, posted on January 8, 2017 at 07:53:46
Music Man Bob
Audiophile

Posts: 431
Location: Atlanta, Georgia Area
Joined: March 14, 2009
Regarding this particular subject, the most learned individual I found was a gentleman we called "Peter Gunn" or John Krucezek. He completed my Magnapan 1.6 speakers and they are as solid as rocks. Being well pass 70 years old, I could not imagine trying to lift speakers weighing more than 200LBS as some of these ideas may suggest. I've got to say, my speakers still play with a beauty I can't explain. Each time I upgrade my cables, TT cartridge, fuses for my power/preamp, etc, my Maggie 1.6's sound better. Peter Gunn was a master at figuring out how to keep the Maggies from making strange noises even at a loud playing level. He was also a master at figuring out how wood (various types) could help the Magnapan speakers, no matter which model sound wonderful. The guy did an awesome job on my speakers and I plan to get them back to him for upgrading. He completed them before I left Baltimore back in 2012 and moved here to Georgia. If anyone is interested, I will try to figure out how to post photos of my Maggies. Thanks for listening.
An African American audio, classical & jazz music lover. I love all great jazz, classical and folk music. Am also a lover of 1/2 track (15ips) reel to reel tape decks.

 

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