Sennheiser Tullamore factory tour: How the world's best headphones are made in Ireland

It’s a relatively common practice for brands to have separate facilities for parts manufacturing and product assembly, whether it’s for cost or other reasons. Even then, we were a little confused when we were invited by Sennheiser to visit Tullamore, Ireland. As it turns out, even though Sennheiser's headquarters are still in the town in which the company was formed (Wedemark near Hanover, to be exact), much of the company's main manufacturing and assembling activities actually take place in its factory in Tullamore, Ireland. Why Tullamore? And what exactly gets made there? Join us as we find out.

Automation and technology is amazing

Located about a 90-minute drive outside of Dublin, the Tullamore factory is where the brand’s audiophile products are manufactured and assembled. We started with a tour of the factory’s automated manufacturing line, hosted by Sennheiser’s Tullamore Plant Manager Pat Fulton, who has been working there for over 30 years. There are multiple drivers that Sennheiser produces here for its range of headphones, and while some can be done fully by hand like the 56mm driver in the flagship HD 800S and HD 820 headphones, there are also some that are either fully automated or use a blend of automation and manual assembly.

Different materials and foils are used in the transducer manufacturing process, with some foils for diaphragms being just mere microns thick – far thinner than a strand of hair. This gives you an idea of just how delicate the process is.

The foils are heat-stamped into different shapes on machines before being combined with magnetic coils and the like as the diaphragm travels down the automated manufacturing line. 

The tolerances required are incredibly tight and the whole line is automated without human variance, but even the smallest error when putting the parts together can cause an issue. Therefore, quality checks are held at each station along the way with a full acoustic test held at the end to check for distortion, sensitivity, polarity and more, making sure that each transducer lives up to Sennheiser’s standards.

When the factory first started, there was only one automated line that ran straight down. But as time passed and more technologies were introduced, the line got longer and longer, until it reached a point where it didn’t make sense to keep extending it. Therefore, Sennheiser created bridges overhead, where the transducers could be lifted up and moved over, thus shortening the assembly lines and making them more compact. This was made possible because the machines used in the lines were designed and made by Sennheiser itself.

There's also a unique feature to these machines; they are able to adapt and manufacture different transducers for the other headphones without needing specialised machines, thus cutting down on overall manufacturing costs.

Aside from headphones, some of Sennheiser’s in-ear monitors are made here in Ireland as well. The 7mm True Response transducers for the IE 900 and IE 600 IEMs are made on the automated line before being hand-assembled, with the workers using microscopes and the like because of how small the transducers are. But if you’re curious like I was, it turns out the shells are machined elsewhere before being shipped over to the Tullamore factory for final assembly, testing, and packaging.

For the more affordable IE 200 and IE 300 models, the drivers are still made in Tullamore, but are then shipped off to be assembled elsewhere.

A German brand in... Ireland?

At this point, you might be wondering, why Ireland? Sennheiser is a German brand, with decades of history in audio products, and some of the highest-end products have always been made in Germany previously. However, it seems that the high-end audiophile products are now all made in the Tullamore factory while design and R&D work are still done in Germany.

While Pat Fulton couldn’t tell us exactly why the decision was made to move production to Tullamore, he did emphasise that there was a wealth of talent available locally with a great culture, alongside engaged workers who take immense pride in what they do every day. 

That pride was very evident throughout the entire tour, with Pat telling us that the engineers from the very first automated machines were still working in the Tullamore factory to this day. Amongst the operators, there were also people on the team who had been manufacturing drivers and assembling them from back when the HD 600 was launched in 1997. 

From making the coils to assembling the diaphragms into the chassis, these operators can do everything the automated lines do, but manually. Some headphones like the HD 800 can use a mix with automation for some parts, but items like diaphragm forming and assembling the coil to the diaphragm are still done by hand.

When asked about the advantages of this mix, Pat Fulton mused: “I think the blend of automation and hand assembly goes well together for us (..) it creates a clear link from one to the other. It benefits us very much from a quality perspective and an innovation perspective.”

Time to try our hand at assembling headphones

We got to try our hand at assembling the headphones that were being made that day, the Drop x Sennheiser HD 6XX. The process differs slightly for each headphone model, but the set-up is the same. There are five individual stations manned by a team of four people, with the first station in charge of checking the driver and chassis to ensure there are no imperfections or dented grilles before putting in a thin foam layer and clipping in the earpads. The attachment of the velour earpads was probably the hardest part of the process, with the clips needing to be lined up perfectly with the locking system before the operator could push it in and get a secure lock.

Then the earcups get sent on to the next station, where they get attached to the headband. This step really required a lot of strength, and the operator there actually showed us a tip where we could get the general alignment down first, before using our body weight to lock in the earcups by pressing them firmly against a padded worktop. I was quite afraid of breaking them at first, but it really just goes to show how durable the headphones are. 

Cables are then attached and the headphones are now sent along into an anechoic test chamber to check for any issues that might have occurred during assembly, whether it’s a crushed foam layer or issues with the driver. 

At another station, boxes are hand-folded and sent over to the final packing station. Honestly, the boxes were another station where I was left in awe of the operators. Obviously, it boils down to muscle memory, but it was so impressive to watch the operator fly through the boxes while I was as slow as a snail trying to make sure I got all the folds correctly.

Finally, the headphones that passed testing are bagged and put into the box along with information booklets and additional accessories like cables and adapters. Despite my ineptness at the boxes, I managed to assemble three units, so I’m rather proud to say there might be some HD 6XX headphones out there in the wild assembled by me. But don’t worry, all the units have to pass the final test before they can be shipped out.

The top-of-the-line HE-1 system

After that, we had the pleasure of meeting the man who manufactures Sennheiser’s most expensive product, the Sennheiser HE-1, which is apparently going for US$76,000 (~S$100,000) now, up from its US$60,000 price tag a few years ago. Damian is possibly the loneliest person at work because he operates alone in a room that’s specifically only for the HE-1. This over-the-top headphone system is hand-assembled right in the Tullamore factory, with around 3,000 different parts to bring together. 

Some parts have to be bought, of course, as Sennheiser can’t manufacture everything, but the assembly, the making of the switch units and such are all done by Damian. It takes about two weeks to make a single unit, and the testing is all done on-site as well, with a climatic chamber inside that ensures the HE-1 can withstand different temperatures and humidities. 

Aside from testing the acoustics of the unit, the physical testing can take up to 600 cycles, with the opening and closing of the lid and the iconic lifting of the tubes as the unit turns on. 

You can read more about the Sennheiser HE-1, about the fantastic materials used like Carrara marble, the Class A amplifier and more in our demo with it, but suffice it to say, it’s still as impressive. I managed to listen to a variety of tracks on vinyl, including stuff from Daft Punk and Pink Floyd, and it's incredibly clean and airy. There’s gorgeous texture and detail, with fantastic dynamics and timbre. If there is ever a chance to demo this system at hi-fi shows or in-store, I would highly recommend trying to get a slot. 

Closing thoughts

It’s really rare to see a brand combine both manufacturing and assembly under the same roof, and Sennheiser said that it offers benefits like better transducer matching and such. That definitely makes a lot of sense, and it was eye-opening to get to see the standards that the Tullamore factory operators hold themselves to – to improve every day and make sure that the products they assemble and ship are satisfactory to the end consumer. 

If you’re a frequent reader of our audio reviews, you’ll know our one common complaint that we have about Sennheiser’s products is their high prices. Thanks to this tour, I have a new-found appreciation for their products and understand the premium that they command.