Magnepan Tympani IVA refurb
Spring 2021
Background:
The Tympani IVa was introduced in 1985 as Magnepan's top of the line speaker, and was the last of their Tympani series or of any multi-panel speakers until their $30,000 model 30.7 was introduced in 2017. From The Absolute Sound magazine, here: "The 30.7 represents an attempt by Magnepan to build upon and surpass the legendary Tympani IVa, an elaborate six-panel design that continues to enchant a select group of audiophiles."
The Tympani IVa originally sold for $3,800 (which, after inflation, is $9,500 in 2021 dollars). They made 452 pairs of these speakers between 1985 and 1991.
The Tympani IVa is a planar magnetic/ribbon speaker system which consists of three 16" wide by 72" tall by 1.5" deep panels per channel. There are two bass panels along with a third panel that houses both the midrange and 5 foot tall ribbon tweeter. All three panels are connected together with hinges. The midrange-tweeter panel, however, can be removed (un-hinged) from the two bass panels to be positioned separately (as shown above). The crossover between the midrange and tweeter is contained in the mid-tweeter panel, and an external crossover box is used to cross over between the bass panels and the mid-tweeter panel. In addition, Magnepan sold an optional XO-1 passive crossover for bi-amping the system, which was placed between the preamp and the mid-tweeter amplifier. In that configuration, the external crossover box provided the crossover to the bass panels.
The original Magnepan press release for the Tympani IVa is shown below:
This is an advertising photo from Magnepan showing the typical setup of the three panels per channel.
This photo (not my setup, photo found on the web) shows the speakers without their grille cloth. On the left, you see the mid-tweeter panel with the thin ribbon tweeter on the far left and the midrange driver to its right. The two panels on the right are both woofers.
This project:
I've owned a number of pairs of Magneplanars over the years, and have wanted to try a pair of Tympani's in my current listening room. I found this pair of Tympani IVa's locally which had recently come back from a complete refurb at Magnepan in mid 2020, still sealed in their unopened cartons. At Magnepan, they completely strip and clean the voice coil wiring off the mylar diaphram and rebuild each driver with new wiring and adhesives, so these were as close to the day they were originally built as possible, and in fact a bit better due to improvements in adhesives made over the years. They also had new grille cloth at the factory, so the basic speakers looked very good.
There were, however, several issues I wanted to address with these speakers, some unique to this pair and some applicable to other Magnepans, each discussed in more detail below.
Missing feet
Missing external crossover
Input connector replacement
Fuse holder replacement
Internal crossover parts upgrade
Side rail cosmetic cleanup
Final setup
Addendum: midrange driver level optimization
A special thanks to Gary Edwards, the Production, Sales Service Manager at Magnepan for help with this project!
- Missing Feet
The Tympani IVa's came with 8 feet, missing from my pair, which are needed if you plan to separate the mid/tweeter panel from the two bass panels. Fortunately Magnepan still stocks the feet and new replacements were easily purchased at a reasonable cost.
2. Missing external crossover
The crossover in the Tympani IVa is divided into 2 parts. The mid-tweeter crossover is contained in the mid-tweeter panel (discussed in section 5 below). There is also an external crossover box (that crosses over at about 250Hz) between the dual woofer panels and the mid-tweeter panel. Since this crossover box was missing with these speakers, I built a new one in an oak case. Note that aluminum boxes will affect the values of the crossover inductors and should NOT be used for speaker crossovers. The stock Magnepan crossover is wood and non-magnetic stainless steel.
The factory Tympani IVa external crossover.
An internal view of the factory crossover (with some non-factory bypass caps).
My new crossover box - bottom view. Made of 1/2" oak to match the side rails of the Tympanis.
New crossover boxes - top view
The new parts to build the external crossover. Although Magnepan used electrolytic caps for the large 200mfd caps, I prefer the closer tolerance and better reliability of film caps. In my crossover, all of the caps are polypropylene, and all inductors are steel laminate to match the stock parts both in inductance and DC resistance. The 200mfd caps are made up of four 50mfd caps on the left, and the 75mfd caps for the mid-tweeter panels are composite of multiple high quality caps on the right.
The caps were all selected to be within 1% of the target values, and the chokes were custom wound within a couple percent.
Internal view of the assembled crossover. The input is at the top, outputs at the bottom in this photo. The low pass section is on the left, high pass section on the right.
I made the two crossovers mirror imaged, like the speakers themselves, for cleaner cable runs (to the mid tweeter panel) than the stock crossovers.
The completed external crossover. The oak is stained to match the Magnepan side rails and finished in spray-on polyurethane.
I had a custom aluminum label made for the crossover by Burton at https://www.ebay.com/str/audiotagsiowa.
I used Superior BP-30 dual binding posts for all the external crossover connections (6 dual binding post sets).
3. Input connector replacement
Magnepan's speaker connectors are not very flexible - they only allow use of bare wire or banana plugs. I decided to replace them with more traditional binding posts for better connections, including the ability to use spade lugs. Since the woofer panels fold together for transport, the Superior BP-30 dual binding posts (like I used on the new external crossovers above) protrude too far, and would damage the adjoining panel during transport. I found that Vampire BP-HEX gold binding posts fit nicely, low enough to fold the speaker panels. I replaced all 4 (two on the mid-tweeter panels and two on the woofer panels).
The stock Magnepan terminal plate showing the speaker connectors on the left.
Note the rivets in the fuse holders - we'll discuss those in the next section.
My Vampire BP-Hex posts were intended for mounting in thicker panels, and had to be trimmed shorter to fit inside the 3/4" thick Magnepan panel.
The terminal plates with the new gold binding posts (woofer on the left, mid-tweeter on the right)
Rear view of the plates. Those fuse holders will be modified next...
4. Fuseholder replacement
Magnepan uses in-line fuses to protect the ribbon tweeter and midrange drivers. Unfortunately, these fuse holders are a known failure point, sometimes causing intermittent or failed connections (which I experienced). I originally replaced mine with new fuse holders from Magnepan, but was still unhappy with the riveted connection to the lug and the ferrous parts in the rivet itself. After some thought, I devised a fuse holder mounting that looks stock from the outside but actually mounts the fuse holder beneath (as opposed to on) the terminal plate. It eliminates all unsoldered and ferrous connections.
First I cut off the rear portions of the fuse holder (that actually held the fuse) and tossed them, leaving only the black front trim pieces shown here.
Those trim pieces were glued in place on the terminal plate to keep the stock look.
Next I built a wooden sled (removable with 2 screws to return the speakers to stock if needed) to hold a pair of high quality Littelfuse fuse holders, which will be glued to the sled. The sled and fuse holders are positioned to sit directly below the black trim pieces shown above when the terminal plate is screwed in place.
This shows the sled and fuse holders in place (mirror imaged from opposite channel above) in place ready for wiring.
The black wire to the left goes up to the top of the ribbon tweeter.
This shows the back of the terminal plate and the new fuse holders wired up. Tweeter attenuation resistors to the left.
This new setup has no riveted connections (all soldered), and no ferrous parts in the signal path.
5. Internal crossover parts upgrade
Parts quality (and our knowledge about how parts affect sound) has improved in the decades since this speaker was designed. In particular, capacitors more suitable for audio than the original mylar capacitors are readily available and make improvements in transparency. I also replaced the tweeter attenuators (originally inexpensive 10 watt ceramic resistors) with Mills 12 watt non-inductive wire-wound resistors. both for their closer 1% tolerance (for channel to channel matching) and reliability.
For anyone who hasn't worked on Magnepan speakers, this shows a handful of the several million staples that must be removed to open the grille cloth to gain access to the crossover components.
This shows the stock Magnepan mid-tweeter panel crossover. The caps to be replaced are all mylar: a 10 mfd in the midrange circuit and a 12 mfd (10 in parallel with a 2) for the tweeter. I left the air core chokes stock as they fit nicely in the tight space and I don't believe there is much benefit to more exotic ones. Also, chokes with different DC resistance will cause the frequency response to vary from the original target design.
This shows the two caps removed, awaiting replacements. The originals are simply hot-glued in place, so not difficult to remove.
Test fitting the new caps in place. I used a 10 mfd Evox polypropylene for the midrange cap (the blue one) and a composite of two ASC polypropylene caps bypassed with an MIT Multicap for the 12 mfd tweeter cap.
As with the external crossover, the caps were selected and matched to 1% of their target values.
Everything wired up. The tweeter attenuator resistor (to the top left of the fuseholders) is specified at 1 ohm, but I've been experimenting with a parallel combination resulting in 1.5 ohms for a bit more attenuation, as shown here.
I was curious about how changes in the tweeter attenuator resistor affected the frequency response, so I measured the relative impact of changes in that resistor. Relative to the stock 1 ohm resistor (shown as the black flat line), a 1.5 ohm resistor (in blue) is down about 1dB at 10KHz, and a 2 ohm resistor (in red) is down 2db.
This shows the terminal plate in place with the new fuse holders looking just like original, but now more reliable and with better connections.
6. Side panel cosmetics
Since these speakers are about 35 years old, the oak trim rails showed some wear and stains. I removed all the rails and stripped the finish, re-stained a golden oak color, then finished with several coats of semi-gloss Minwax spray polyurethane.
This photo shows 8 of the 12 rails being refinished.
7. Final setup
This shows the speakers as set up, from the listening position. Note the mid-tweeter panels are separated from the woofer panels which sit behind and outside of the mid-tweeter panels.
The mid-tweeter panels in this case are driven by a pair of 425 watt (into 4 ohms) Purifi 1ET400A amps, details on that project here.
The woofer panels are driven by a pair of Hypex FA501 plate amplifiers with digital signal processing (DSP), below.
Rear view of the mid-tweeter panel and new external crossover.
This speaker system provides a number of setup options, ranging from using a single amp using the external crossover to various bi-amping setups. I've done quite a bit experimentation, and in my room, I've settled on a bi-amped setup with DSP for the woofers to allow both the crossover EQ and some room correction.
This is a photo of the two 500 watt Hypex plate amps (FA 501s) used for the woofer panels, in a simple cherry case built to hold them. Per Magnepan's spec, the panels are crossed over at 18dB/octave at 250 Hz, and there is some DSP room correction for a 60-70Hz peak in the room.
Although I experimented with the Magnepan XO-1 crossover for the mid-tweeter panels, I got poorer mid-bass performance using that approach versus simply using the passive mid-tweeter portion of the external crossover.
This shows the frequency response at the listening position of the two channels, using ERB smoothing, which more closely simulates how we hear than simple 1/3 or 1/6th octave smoothing. HERE's a good video at AudioScienceReview for those new to ERB smoothing.
In the Hypex DSP for the woofers, I have included a 15 Hz high pass filter that attenuates the very low end, which I'll likely remove to boost the first octave.
8. Addendum: Midrange driver level optimization
This is actually the first work done on these speakers. When I first listened to these speakers, they didn't have a precisely balanced stereo image. Testing of the individual drivers showed identical frequency response and output levels from each of the 4 woofer panels and from both tweeters. However, the midrange panel in one speaker had a bit lower output level than the other. I disassembled the speaker and confirmed the problem was with one midrange driver having slightly lower output. Inspection showed both panels to be physically almost identical, with all the new wiring looking identical on both panels. The panel with lower output, however, had a bit larger bow in the perforated backplate of the driver, which meant the magnets were further away from the voice coil wires hence the lower efficiency. This variance between the two channels may well have been within Magnepan's tolerances, but I wanted them to be as closely matched as possible. Magnepan uses a technique of cross braces on the woofer panels to keep them flat, so I added a couple similar braces behind the midrange to lightly push the perforated back panel closer to flat, resulting in an output level matching the other speaker.