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RE: Acquired MGIIIA

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In Reply to: RE: Acquired MGIIIA posted by Beardy on December 07, 2023 at 22:42:52

It's possible that the bass panel wires are delaminating from the mylar. It's a very common problem. The wires are aluminum and tend to corrode over time as well and go open circuit, despite being insulated/coated wire. Try running the palm of your hand up the back side of the panel near the top and bottom, gently. If you feel lifted wires at either end you will know without having to remove the speaker cloth.

If you do remove the cloth, keep in mind that it's got a ton of staples holding it on at the bottom edge and usually removing them is going to cause fabric tears or runs that might make it useless to put back on. Maagnepan doesn't use the burlap fabric anymore so you would be stuck if you decided to try to return them after removing the cloth. Decide if you are willing to keep and rebuild them or have magnepan rebuild them before taking the speaker cloth off of them.

Yes there could also be a tear in the mylar causing a bass note problem. No real way of knowing until the cloth comes off. Whatever is wrong in there can be fixed, it's just a matter of time/expense and whether it needs to be serviced by Magnepan or not.

At what volume do you start to hear bass distortion? Another possibility is the the bass panel mylar has stretched and not taught enough to prevent it from slapping the magnet screen.

Follow Ups:

RE: Acquired MGIIIA - Beardy 08:09:44 12/08/23 (18)
Its not a slap and I dont hear "snare drum" like rattling or buzzing. Its just like the bass goes soft (rounded, blobby?!), maybe smeared is a better term. I've only had them for a couple of hours so need to spend a bit more time working out what I am hearing.
May of course be something in the amplifier chain, but volumes are not massive and XPA-200 should do 240W into 4 ohms, so I don't think I am pushing it.
Could be something in the 35 year old crossover electronics.

Regardless lots learn and play with.
- RE: Acquired MGIIIA - UncleMeat 08:20:22 12/08/23 (17)
  Bad electrolytic caps in the crossover boxes is definitely a possibility with muddy sounding lows. Sometimes they are just stubborn about charging if they have been sitting unused for a long time.
  - RE: Acquired MGIIIA - UncleMeat 17:28:50 12/08/23 (16)
    Also, double check the phase of the inputs/outputs at the XO box. If OK, then try inverting the input to the XO box, it could be that the absolute phase is inverted.
    
    If that doesn't improve the bass note, try reversing the bass connection between the XO box and the speaker, just in case the bass panels are internally wired backwards (not likely but stranger things have happened).
    - RE: Acquired MGIIIA - Beardy 20:54:41 12/08/23 (15)
      I have since spent more time listening with more familiar music and at reasonable volume levels it seems fine. I think it was a combination of factors, not the least of which was a crappy choice of media.
      PS Ribbons are great
      
      Edits: 12/09/23
      - RE: Acquired MGIIIA - UncleMeat 01:19:06 12/19/23 (0)
        
        In Reply to: RE: Acquired MGIIIA posted by Beardy on December 08, 2023 at 20:54:41
        
        I just got a pair of IIIa's from a recycler for cheap. They only had one mid and one bass driver working when first tested. Checked the ribbons, both were not soldered correctly. I attached jumpers just to get them working, and gave a listen for a couple of nights. To get some balance in the bass/mids I connected one T-IV bass panel to the bass output section of the IIIa crossover box (not ideal, but to get -some- balance, it worked).
        
        My initial impression is that the IIIa is much more forward in the midrange than my modified T-IVa's. It's good in the sense that the vocals are more forward in the presentation, but a bit of a loss in the total image because the musical program gets reduced, at least in the mid-highs and the mid-lows. This could be a reason why people tend to consider them 'power hungry'. Increasing volume will bring up the background, and your ears will attenuate the vocals as SPL increases.
        
        Keep in mind that I didn't do any proper placement, or room EQ and they were sitting directly in front of the T-IVs. Still, amazing sounding even as such. The extreme highs seemed to have a bit more sparkle than the T-IV's do so I'll be looking into why that is, but it could be lack of room EQ on that issue.
      - RE: "Ribbons are great" ... - andyr 19:27:06 12/09/23 (13)
        
        In Reply to: RE: Acquired MGIIIA posted by Beardy on December 08, 2023 at 20:54:41
        
        That's great to hear! :-))
        
        Maybe your next step - just because you can , with the IIIAs - is to replace the external XO box with an active XO ... and actively bi-ap them!
        
        RE: "Ribbons are great" ... - Beardy 23:26:56 12/09/23 (12)
        
        In Reply to: RE: "Ribbons are great" ... posted by andyr on December 09, 2023 at 19:27:06
        
        Already chewing on that!
        :o)
        
        RE: Excellent ... - andyr 23:28:50 12/09/23 (11)
        
        In Reply to: RE: "Ribbons are great" ... posted by Beardy on December 09, 2023 at 23:26:56
        
        What amp are you currently driving your new IIIAs with?
        
        RE: Excellent ... - Beardy 09:02:37 12/10/23 (10)
        
        In Reply to: RE: Excellent ... posted by andyr on December 09, 2023 at 23:28:50
        
        An Emotiva XPA-200.
        
        My plan is to build 2 or 3 Pass F5 clones and biamp/triamp, but I am still chewing on the active crossover. I'd prefer to build rather than buy and this
        https://www.diyaudio.com/community/threads/diy-biamp-6-24crossover.357657/
        
        is the current favored approach. I am working through exactly how to set this up. I have your MUG tweaks page up in a seperate tab.
        cheers
        
        RE: I would suggest ... - andyr 13:43:56 12/10/23 (0)
        
        In Reply to: RE: Excellent ... posted by Beardy on December 10, 2023 at 09:02:37
        
        You keep your Emotiva XPA for the bass panels ... and build an F5 for the mids+ribbons - or an F5 for the mids plus an F5 for the ribbons (ie. 3-way active).
        
        Even then ... you may find (although the only way to do this is to borrow other amps, to compare) that the F5s aren't really powerful enough. :-((
        
        Why do I say this? Because for about a year (before I then got rid of my Frankenpans) I used 2x 40w-into-4-ohms AKSA ' Alpha Nirvana ' Class A
        amps on my mids & ribbons. Actively driven. (You can find the AKSA AN thread on DIYaudio.)
        
        Hugh Dean - the designer - came over and had a listen; he knows my system well and admitted he was a little 'underwhelmed'. :-(( Which surprised him - as he knew how good the amps should sound.
        
        Yet when he came over subsequently - to listen to the same amps driving my new 'zero baffle' spkrs - he was amazed at how good the amps sounded.
        
        My conclusion was that ... although my ANs were the "4 ohm" version (to optimise their delivery into 4 ohm spkrs rather than 8 ohm - and they are stable into 2 ohms!), the Maggie mids & ribbons really needed more power.
        
        The Pass XO should be ideal. I myself (nearly 30 years ago) used Rod Elliott's P09 L-R XO circuit (modded to provide 'Maggie' slopes) - which worked well.
        
        RE: Excellent ... - Roger Gustavsson 09:59:37 12/10/23 (8)
        
        In Reply to: RE: Excellent ... posted by Beardy on December 10, 2023 at 09:02:37
        
        Pass F5 is only 40 W into 4 Ohm. That is not enough!
        
        RE: Excellent ... - UncleMeat 10:38:16 12/10/23 (7)
        
        In Reply to: RE: Excellent ... posted by Roger Gustavsson on December 10, 2023 at 09:59:37
        
        I tend to agree here, but I'm running a ~50W (@8 Ohm) tube amp right now driving the T-IV's full range and it's sounding good/detailed. If he's going to bi-amp with the Pass amps it -might- be enough if the room is on the smaller side.
        
        I say appx. 50W because the amp is designed for KT-120's and I'm using 6550's instead, so it's output is less than the design spec of 75WPC. As I've stated before, I only need about 15WPC (on 8-Ohm meters) for the room to start feeling 'too loud', however.
        
        RE: Excellent ... - Beardy 14:04:33 12/10/23 (6)
        
        In Reply to: RE: Excellent ... posted by UncleMeat on December 10, 2023 at 10:38:16
        
        Output volume is unarguably related to I^2R. With my DVM I measure typical AC voltages of 5-6 volts at speaker terminals when playing loud. However this meter does not have the temporal response to read accurate values for the peaks, so let me get back to you on that once I have a decent analog AC Voltmeter to play with.
        
        My unfounded belief is that much of this preoccupation with massive power is a reflection of the amplifier architecture required by low impedance speakers. A power supply that can readily provide the current required is feature of a better quality amp. The degradation in sound quality that one might hear from lower power amplifiers may be the impact of shortfalls in the power supply dept.
        
        My expectation is that at `my volumes' there are peaks to perhaps +/-20V, and potentially the impedance of planar may be as low as 2.5 Ohms. This suggests an F5 with a power supply that can give 40V/2.5 Ohms (16A) might do the trick.
        However, my wife tells me that on occasion I am wrong.
        
        RE: Excellent ... - UncleMeat 14:20:05 12/10/23 (5)
        
        In Reply to: RE: Excellent ... posted by Beardy on December 10, 2023 at 14:04:33
        
        Keep in mind that Magnepans are one of the most capable speakers at producing impulse transients like drum/cymbal percussion. These instantaneous changes in voltage approach infinite wattage/current in the instant they are generated.
        
        The signal path from the source through to the amplifier all have to try to reproduce that signal/current demand, of course at lesser extremes with lower voltages. When it gets to the power amp, that current demand goes way up as it tries to drive the low impedance load (relatively) of the speakers.
        
        So it really depends on the amp, and it's current delivery capabilities to be able to keep those notes sharp/accurate. Magnepans are so revealing that deficiencies of the amp can be heard, where they may not be with a standard speaker that's not 'fast' enough.
        
        RE: Excellent ... - Beardy 14:23:23 12/10/23 (4)
        
        In Reply to: RE: Excellent ... posted by UncleMeat on December 10, 2023 at 14:20:05
        
        Understood - that echoes my thoughts.
        
        There is always the turbo...
        :o)
        
        RE: Excellent ... - andyr 16:14:12 12/11/23 (3)
        
        In Reply to: RE: Excellent ... posted by Beardy on December 10, 2023 at 14:23:23
        
        As Dennis said: " So it really depends on the amp, and its current delivery capabilities to be able to keep those notes sharp/accurate ."
        
        Maggies are not the only spkrs that sound better when the amp driving them has bags of current-delivery capability. A mate of mine had some stand-mount B&Ws for many years. He first drove them with a very good-sounding Oz-made 40w tube amp. They sounded very nice - if a little bland ... so one day he decided to try a 150wpc ss amp. That made a huuuge difference ... and he thought he was done! Then, a wicked friend brought over his Magtech to try (500w into 8 ohms, 900w into 4 ohms ... and stable into 2!). Russ then bought a Magtech! :-))
        
        RE: Excellent ... - UncleMeat 00:50:07 12/12/23 (2)
        
        In Reply to: RE: Excellent ... posted by andyr on December 11, 2023 at 16:14:12
        
        Well, with all forms of conversion to mechanical motion from electricity, it's the magnetic field of the permanent magnets interacting with the magnetic field of the voice coil, or in the case of Magnepans, the linear voice wires. The magnetic field of the wire is generated from the current flowing in the wire. Voltage and current are inter-related but the current (flow of electrons) is what generates the magnetic field.
        
        RE: Excellent ... - Roger Gustavsson 01:16:33 12/12/23 (1)
        
        In Reply to: RE: Excellent ... posted by UncleMeat on December 12, 2023 at 00:50:07
        
        Still I=V/R. As the Magnepans driven active is a pure restive load there is not a lot of currrent running through them. The power amps used by myself will not run out of current but of voltage. They can deliver a maximum peak current of 80 A but that will only be the case with some completely stupid speakers which need to go back to the designing board. With the 4 Ohm basses of a Magnepan peak current may be about 10 A (400 W in 4 Ohm).
        
        RE: Excellent ... - UncleMeat 19:07:25 12/12/23 (0)
        
        In Reply to: RE: Excellent ... posted by Roger Gustavsson on December 12, 2023 at 01:16:33
        
        I think it depends on the amp, some amps spec'd at high voltage/wattage will fall short on current delivery under load with dynamics, which again will create higher than 'average' instantaneous current/voltage demands. A lower wattage amp that can deliver high current can be OK, if it can keep up with the instantaneous demand (at lower volumes, of course).

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