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Magneplanar MG-II panel vibration problem at low frequency

135.23.154.247
Posted on December 3, 2016 at 11:11:44
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009
 Hi all, I have had these panels in storage for the last several years, as I couldn't figure out what's wrong with them (and still can't).

I replaced tweeter wires and crossover caps, but the problem is not related to this.

The speaker panels buzz/vibrate at a very specific mid-low frequency. Please see the video. I can't figure out where the vibration is coming from. Has anyone experienced something like this before?

I can play any music for hours, but it looks like the problem is only at this note. The video has bass test CD as a source. The speakers work fine at any other frequencies, including much lower notes.

https://youtu.be/5JRZFR3xQqI

Thank you.

 

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RE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 3, 2016 at 11:39:54
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009
 I keep reading the forums... So sounds like the infamous magnepan slap. Is there a way to fix it? There are so many suggestions on the forums, but most of them obviously didn't work.

Should there be a way to tighten the Mylar? Or are the speakers done?

 

RE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 3, 2016 at 13:19:22
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 What are you using for amplification? slap is more likely to occur with a current limited amp.

 

RE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 3, 2016 at 15:07:43
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009
 I'm using Rotel rx-604 receiver. But I'm sure I had this problem with Dynaco st-70. I don't have this problem with another MG-II pair with ST-70. I'll go bring Carver M-1.5t from storage just to double check.

 

RE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 3, 2016 at 16:36:58
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009
 Well, Carver was a no go, so I brought my Dynaco MKIII pair. Same thing.

 

Typo in link? Not working? (Nt), posted on December 3, 2016 at 17:42:53
Jonesy
Audiophile

Posts: 3156
Location: Winnipeg, Manitoba
Joined: September 1, 2005
Contributor
  Since: March 1, 2018
 Nt


"I know just enough to get into trouble. But not enough to get out of it."




 

RE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 3, 2016 at 18:08:21
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 I would be suspicious of either a delamination or possibly a loose panel in the frame or crossbar. Does the buzz/vibraiton occur in both channels? and at the same frequency? Usually a buzz from delamination is heard over a range of frequencies. The easiest way to determine delam is to put your ear close to the panel and listen to where the buzz seems to be coming from and then gently push on that spot with your finger and see if you can surpress it.
It is possible that the driver is loose in the frame - it is held in only by staples similar to a picture in a frame. Your MGIIs are ancient and the staples may have worked loose.
If it were me, I would remove the skirts to better examine the drivers. I would leave the skirts off unless you have a WAF problem. New skirts from Magnepan are $30-50 and are made of better material than the original "burlap" material. You should be able to identify visually delamination or a loose driver. Some times the metal bars that run across horizontally work loose as well and these can be glued back to the perforated metal plate with epoxy.



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 3, 2016 at 18:34:54
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009



The socks are currently off. The tweeter wires have been replaced (along with crossover caps). The banana peels and some spots on the bass panels have been fixed. The Mylar diaphragm panels are solid riveted to the frames.

It's definitely the infamous slap. It happens in both speakers, at exactly the same heavy mid-bass passage. It happens on the bottom parts of panels, where the distance between cross-braces is the largest.

Someone on AK forum posted Magnepan instructions on how to adjust clearance between Mylar diaphragms and magnets, but it's a scary procedure (pushing onto the cross braces "evenly" through the Mylar, essentially bending the magnets away from the diaphragms.

One thing I cannot examine are those cross bars, as the Mylar diaphragms frames are riveted (not stapled) to the speaker frame. Those rivets are very well made, no vibrations or movement.

 

RE: Typo in link? Not working? (Nt), posted on December 3, 2016 at 20:17:51
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009
 Sorry, YouTube took my video down because I used 18 seconds from some copyrighted CD. Just wow for YouTube.

 

RE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 3, 2016 at 21:07:07
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 then you must have low clearance as the magnet boards must have been flattened from the magnet side at some point. Looks like the bending procedure is probably necessary. Alternately use a pair of subwoofers crossed over around the 80hz. Just check that that is just above the freq where your slap occurs. .

The small tube amps don't have the damping capacity but also don't have enough voltage to displace the diaphragm far enough to induce slap in a normal "healthy" speaker. The 1.5t should have had enough current to damp the slap in a normal MG2.

 

RE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 5, 2016 at 09:33:48
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 Reading further into your description of the refurb project I suspect your bolting of the frame to the MDF may have flattened the curvature of the magnet board so the 1st thing to check is if the problem disappears when you detach the panels from the frame and float them instead - with staples or screws (driven sideways into the frame) to hold them in place. For similar results to direct bolting to the frame in damping the frame-panel interface use rails to push the panels into the frame and an elastic material in between the rail and the steel driver frame. Then bolt the rails to the MDF.

Bending them while they are bolted to the MDF frame will not work because the bolted structure will not bend permanently and may harm the MDF with the rivets digging into it and possibly cracking it. .

 

IRE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 5, 2016 at 10:26:07
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 I never had a "slap" with my IIb, IIIa or 3.7i. OTOH I listen almost exclusively to classical music and jazz and very little bass heavy sources and usually well below 90 db (typically peaks below 85db). It would seem to me that increasing the bend in the metal panel might not help as it would just reduce the stretch of the mylar, probably by the same amount as the increased spacing. Is the buzz at a frequency that allows a cut-off and use of a sub, although from your picture it looks like you may already have a sub in place. Perhaps talking to Wendell at Magnepan may be helpful - I have gotten good response from him but others may beg to differ. FWIW I thought my IIb's actually had a deeper bass response than my IIIa's.



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: IRE: Magneplanar MG-II panel vibration problem at low frequency, posted on December 18, 2016 at 15:50:00
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009
 I'll wait a bit before trying to bend those magnets. Something just doesn't add up with that idea. I'll fix my Carver M-1.5t in the meantime, so to be sure that if I give them enough power, maybe this pair won't slap.

 

RE: IRE: Magneplanar MG-II panel vibration problem at low frequency, posted on January 5, 2017 at 15:23:19
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009
 So just a quick update - bending was a no-help at all. I followed Magnepan instructions that someone posted on AK - apply 100-170 lbs through a towel onto the crossbars (from the Mylar side).

Made zero difference. Popped some staples where the outer frame is stapled, had to fix that...

Oh well. And I was running Rotel RMB-1075 amp, which according to S&V magazine goes into clipping around 260 Watts per channel into 4 Ohms. I wasn't clipping obviously, but I was playing close to reference level on the preamp.

I'll put these together and get rid of them. I just don't know what else I can do to this pair.

 

RE: IRE: Magneplanar MG-II panel vibration problem at low frequency, posted on January 6, 2017 at 07:53:42
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 I don't know if it is a realistic option shipping wise, but Magnepan could fix them.

 

RE: IRE: Magneplanar MG-II panel vibration problem at low frequency, posted on January 6, 2017 at 11:40:59
viperz
Audiophile

Posts: 25
Location: Toronto, ON, Canada
Joined: April 21, 2009
 Unfortunately, by the time I crate and ship these from Canada to USA, I'll probably be able to buy 3.6R for the same cost.

 

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