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In Reply to: RE: "the push-pull ribbon of the T1-D" ... posted by Roger Gustavsson on December 07, 2023 at 06:53:39
At minimum some strips to shim the ribbon to the correct depth so it's not protruding in the front, or a new MDF panel to get everything installed in better cutouts would be needed.
Not sure about rolling the bass drivers off earlier, IIRC the second panel is a mid-bass driver, tuned to the area where you want to reduce the response of the bass panels (500-800Hz). If you roll the bass off too early you could end up with a hole in the sound if the mid can't be driven that low. You would also be sacrificing the radiating area of the mid-bass driver since it won't operate in the low-bass frequencies.
There isn't a lot of directional sound at those low frequencies, maybe with drums in live performances or low freq. wind instruments mic'd for location in an orchestra performance? I agree that time/distance alignment will help with image, but there might not be very much stereo program at those low frequencies. Some sacrifice of time alignment is a necessary evil with multi-panel drivers like the Tympani(s), unless you go to active crossover/time alignment with delays to account for distance.
Maybe I was not clear. The low bass up to about 400 Hz and the midbass to 800 Hz. The push-pull tweeter above 800 Hz. Yes, I am aware there will be some fiddling with a suitable crossover. I prefer to use active crossovers. Well, there is a difference between the Tympani IIIA or IIIB to the Tympani ID in imaging. The "wide mouth" effect of my modified IIIA back then was far less present than through the ID.
Yes, that sounds about right for crossover freq's. Does the 1-D have a separate crossover section for the mid-bass driver? I'm curious about my T-IV's, why there is no XO filter for that panel.
The on the photo of the T1-D P-P tweeter panel, are the horizontal cuts and those curved cuts at the bottom in the MDF to reduce resonance of the panel? Seems like it would have been better to leave unused areas thicker of MDF instead of hollowing it all out and then trying to dampen the thinner section. Maybe it was a weight consideration for shipping/handling
"The on the photo of the T1-D P-P tweeter panel, are the horizontal cuts and those curved cuts at the bottom in the MDF to reduce resonance of the panel? Seems like it would have been better to leave unused areas thicker of MDF instead of hollowing it all out and then trying to dampen the thinner section. Maybe it was a weight consideration for shipping/handling."
Tympani ID is not MDF like later models. The thin sheet of Masonite is glued to some particle board frames covered with the usual metal strips. The picture below show one of the bass panels.
I found a pair of MGIIIA and the ribbons look in great shape and they play OK.
Bass bloats a bit when the volume is higher but seems better behaved at lower levels - not sure what that is about.
Otherwise they seem a fair bit more bass heavy than the 1.6QRs (more than I am used to), but I do like the highs.
I have 14 days to return them and freedom to whip the socks off and check them out. Aside from playing them and performing a visual check on the ribbons and panels is there anything else I need to do?
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.
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.
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.
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).
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
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.
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!
Already chewing on that!
What amp are you currently driving your new IIIAs with?
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
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.
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.
Pass F5 is only 40 W into 4 Ohm. That is not enough!
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.
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.
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.
Understood - that echoes my thoughts.
There is always the turbo...
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! :-))
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.
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).
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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