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Magnepan 3.5 low end dropofft and some high end harmonics/dropoff

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Posted on November 24, 2015 at 05:23:07
Scot
Audiophile

Posts: 13
Joined: March 3, 2001
 I have a pair of Maggie 3.5s and they need a bit of work.

I've use REW to generate signals which show off some slight resonances at different frequencies coming from the tweeters. I've tried using two different amps, and of course switching l/r but the sounds come back at slightly louder than normal sounds (80db) and seem to be around 20db below (just a guess) the primary sound. At the very high end the sound starts to roll off at about 18khz.

For those issues my answer appears to be to call up magnepan and get replacement units shipped, I replace and send them my cores. I love DIY so this sounds great.

On the lower end is a bit more of a concerning (to me) problem. My units show a drop-off starting around 70-80hz, 5-7db down by 60 and going through the floor after that. I am not expecting to have huge bass, but this is a bit much.

This is measured at seating position with a calibrated mic and REW to generate signals. No amount of moving the speakers around seems to fix the issue, my NFR645s do not show any drop-off at the low end, nor do a few other speakers, so I am fairly certain my mic is still up to snuff.

Not sure what could cause this on both speakers. There is no buzzing at all in the panel, the coils all seem to be firmly attached to the mylar when looking through the sock. So I'm at a bit of a loss as to what could cause this on both speakers. Could the capacitors be giving up the ghost in the external XO?

Any other ideas?

 

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RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 24, 2015 at 06:39:14
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 It might help to post the fs from REW. The slight rolloff of the treble is normal and, according to Wendell Dillar at Magnepan, is actually desirable. He told me that a 1 db per octave drop above 500 hz is actually what they try to achieve.
I suspect some of the other peaks are actually room related. Also very important - check the polarity of the connections. If the bass panels are in opposite polarity, you could get significant cancellation as well as poor imaging. You may want to pull the fuses on the mid and treble and just do a fs on the bass and also do scans on the individual speakers.



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

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 24, 2015 at 06:59:46
Scot
Audiophile

Posts: 13
Joined: March 3, 2001



My right speaker is similar, but I must have accidentally deleted the run with it. The only real difference is a 50hz hole on the right side, but that is due to the room.


 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 24, 2015 at 07:46:51
ahendler
Audiophile

Posts: 5151
Location: San Antonio, Texas
Joined: January 24, 2003
 Is the bass response a new problem? What amps are you using?
Alan

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 24, 2015 at 07:56:54
Scot
Audiophile

Posts: 13
Joined: March 3, 2001
 Not new. Same basic "issue" in two different rooms (in two different houses).

Amps used are a behringer ep1500 and a mccormack DNA-125. Output looks the same on either one, also tried the amp in the receiver, marantz 5010 without any change.

Using the receiver's Audessey feature, it automatically sets the crossover at 100hz for the Maggies. If I use my NFR 645s in the same location and using the same mic locations for readings, those show up as either 40hz or full range.

Maggie's are about 2.5ft from the back wall, no improvement moving forward or back about a foot (moved an inch or two at a time).



 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 24, 2015 at 08:21:19
Davey
 Your posts are confusing.

If your Audessey setup is implementing a 100Hz high-pass crossover why would you not expect the bass of your speakers to roll off?

It sounds to me like your speakers have no problems at all and you're just misinterpreting your measurement and/or setup scenarios????

I suggest to operate the speakers completely by themselves with a full range signal driving and no subwoofers and re-perform your REW sweep. That might yield a more expected result.

Dave.

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 24, 2015 at 08:29:37
Scot
Audiophile

Posts: 13
Joined: March 3, 2001
 Crossovers and audessey were disabled during the measurements. Just using that as a statement to show multiple measurements seem to point in the same direction (low bass output)

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 24, 2015 at 08:38:35
Davey
 If the transducers are good....wires not separating....no buzzing....etc, etc, there's no method by which the bass response should fall off unexpectedly.
If you think it might be a possible issue with the external crossover then I would suggest eliminating it (temporarily) and driving the woofer panels directly. The external crossover is a low-pass filter only and shouldn't change the bottom end response if eliminated.
Also, it doesn't make sense that an issue/problem would present itself on both speakers at the same time. This still leads me to believe your issue is measurement related and not a problem with the speakers.

Cheers,

Dave.

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 25, 2015 at 10:49:00
Scot
Audiophile

Posts: 13
Joined: March 3, 2001
 Yeah, I would agree it is strange. I was thinking maybe age (either mylar or components), but others don't seem to have similar issues and I would expect each speaker to show up differently.

Measurement setup:: ECM8000 spaced equidistant from both speakers, facing upwards and using an usb preamp. It was placed in a stand at my seating position, no adjustment between tests.

I could try to measure closer to each speaker to try to take the room out of the equation. Just seems funny if this room does the same to the bottom end for these units as my old house.

As for the equipment, I'm sure it works and reports lower signals. I've checked with my other speakers (two pairs of NFR, an 8-1-30 and a 645, plus my sub) and they all show proper output at my seating position. I just still greatly prefer the total sound from the mg3.5s, even with the issues.

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 25, 2015 at 13:02:22
josh358
Industry Professional

Posts: 12332
Joined: February 9, 2010
 Try plugging your room dimensions into an online mode calculator. You may just have an unfortunate combination of room modes and placement/listening position. 10 dB room-dependent swings in bass aren't at all unusual. Dip a bit above 100 Hz could be modal or cancellation from the front wall reflection. Solutions would include new placement, bass trapping, and supplementation with a sub or DWM's.

No sense in measuring the woofers from 1 meter, they'll show a lot more bass in the near field. Dipole bass has to be measured further away.

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 25, 2015 at 18:10:03
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 I noticed the scan is at a somewhat low amplitude (60 db). I assume you calibrated the built-in SPL meter before starting. I usually run my scans at 80db (matching to an old RS analytic SPL meter, C weighted). I don't know if this is the problem but I would try another scan 10 or 20db louder if you don't have a meter for calibration, or 80db, if you can calibrate, and assuming you have the headroom - the sound will be loud but not uncomfortable.



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

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 26, 2015 at 14:38:43
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 That is very low bass output, I would even guess there is at least one loop on each bass panel with a disconnect.

Check out the impedance on the bass panel terminals - if you have something other than 4 ohms or so then you likely have a problem. If it measures 8 ohms then you likely have the disconnect and you should look for it in the wires or the solder joints. You can also play the amp connected directly to the bass panel and see if you get good output to make sure there is nothing wrong with the low pass filter in the XO. .

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 26, 2015 at 17:44:32
Scot
Audiophile

Posts: 13
Joined: March 3, 2001
 Removed the crossovers to check the resistance, 4.1 ohm in both. So that seems to be within the margin of error for working properly.

My system has been "in use" by my daughter for two days now, so I haven't been able to re-test using just the bass hookups, bypassing the crossovers. Soon!

One strange thing, I looked in the crossover boxes, one side had 3 richey caps on the bass side, two 100s and one 75mf. The other speaker had four, 1 75, 2 50s and a 100mf. Guess they ran out of 100s that day :)

 

RE: Magnepan 3.5 low end dropofft and some high end harmonics/dropoff, posted on November 27, 2015 at 10:11:42
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 If they were scraping the bottom on their stock of caps they may have used ones that were suspect. If the bass improves dramatically on a switch to direct connection to the bass panels without the XO then you might want to go to active biamping to bypass the XO..

 

I am having the same issue with my 2.7QR speakers, posted on November 30, 2015 at 13:09:18
gmack
Audiophile

Posts: 20
Joined: November 19, 2015
 My speakers high end seems lacking and the base does not appear to go as low as it once did. I Purchased them new 20ish years ago and never played them hard enough to blow a fuse. I did not use them for four years and since playing for the last two years they have never sounded right. I placed my MMG's next to them and the base from the MMG seems deeper. I brought in a second pair of young ears and he came up with the same opinion on the sound as I did.

I checked the phase wiring, removed the fuses and could hear the mid and treble engage as the fuses were placed back in the circuit.

I was wondering if the crossover capacitors in magnepans have a lifespan and that they could be degraded for his 3.5 and my 2.7 as they are both from the same timeframe? If true this could explain issues in the high and mid frequency.


On the low frequency (I believe the base panel is the same in 3.5 and 2.7) maybe the bond between the wires and the mylar is broken in places. I do not have any buzz or wrap sound just a loss of frequency sound. I have not pulled the socks yet to inspect and was wondering if the socks were removed on the 3.5 speakers to inspect the bond of the wires on the mylar?

 

RE: I am having the same issue with my 2.7QR speakers, posted on December 1, 2015 at 07:04:08
Roger Gustavsson
Audiophile

Posts: 2055
Location: Huskvarna
Joined: February 12, 2010
 3.5 and 2.7 does not share the same bassdriver. The bass is not separate in any of them. The 3.5 have bass and midrange on the same sheet of Mylar. The 2.7 have bass, mid amd tweeter on the same sheet of Mylar. The separation of the various sections are different. The bass sections have the same number of wires/magnets, if that is what you mean.

 

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