DIY Speaker Build - Troels Gravesen's Poor Man's Stradivari

[Graeme_Finlayson (The Mad Scientist)]

Hehe, you’ll have to speak to my wife once I’ve passed away! She’ll be having the yard sale of the century!

A tungsten grinder is used to prepare tungsten electrodes for TIG welding (GTAW).

As a novice welder, you spend a lot of time regrinding your tungsten electrode(s) to remove the metal contamination after you’ve either dipped the tungsten in the puddle or stuck the filler rod to the end of it!

Regrinding with a bench grinder or angle grinder is a laborious process, so I bought a proper machine which meant I could spend more time learning to weld than grinding tungstens.

[garym]

I don’t want Graeme’s workshop. I need his talents, not just the tools. I just want to be his good friend that lives nearby. I’ll bring the Whiskey.

[tahsu]

OK @garym, you have changed my mind! Where are we all moving too?

@Graeme_Finlayson

Hehe, you’ll have to speak to my wife once I’ve passed away! She’ll be having the yard sale of the century!

A tungsten grinder is used to prepare tungsten electrodes for TIG welding (GTAW).

As a novice welder, you spend a lot of time regrinding your tungsten electrode(s) to remove the metal contamination after you’ve either dipped the tungsten in the puddle or stuck the filler rod to the end of it!

Regrinding with a bench grinder or angle grinder is a laborious process, so I bought a proper machine which meant I could spend more time learning to weld than grinding tungstens.

Thanks for the explanation, I think being present for the odd car boot might be worth it too, and you won’t need to shuffle off this mortal coil!!!

[Graeme_Finlayson (The Mad Scientist)]

I buy mine in 25 kg bags, which are small and manageable. Wouldn’t want it in bigger quantities

The bare metal table after filling was 41 kg. Then there’s the 8 kg of oak for the shelves.

I used the same shot in the PMS plinths and they’re 17 kg each.

Besides the mass of shot-filled objects, the vibration damping is nothing short of spectacular!

On the previous shelf, the grinder would vibrate so much at the high speed setting for 3.2 mm tungstens, that it could shake the power switch to off!

[Graeme_Finlayson (The Mad Scientist)]

Some of you will be aware from the recent sale of my beloved Benchmark HPA4 that I’m some way down the rabbit hole towards a fully active setup with my Poor Man’s Stradivari.

The limited space inside the cabinet necessitated an external crossover box which conveniently allows separate access to all three drivers on each speaker:

Having 2 Benchmark AHB2s already, I considered adding a third. However, with the other components needed, price vs performance objective thinking kicked in and I decided to go with a pair of Hypex Nilai 500 DIY monobloc kits instead. Measurements are very close to the AHB2, and level-matched listening comparisons render them indistinguishable from each other.

The kit comes with a pair of normal binding posts, so some hacking was needed to fit Neutrik Speakon connectors to fit my existing cabling arrangement. I sincerely wish more speaker/amplifier manufacturers would integrate Neutrik Speakon connectors into their designs, though I guess that would obviate the snake-oil peddlers with their unobtanium speaker cable/connector combinations.

[Graeme_Finlayson (The Mad Scientist)]

For the active crossover, I’ve decided to take a deep dive into Acourate. It’s apparently the best solution out there, but far from the most user friendly.

Acourate generated filters can be run via Muse in Roon, but… The best way to host those filters outside of Roon is with Mitch Barnett’s Hang Loose Convolver.

My HiFi listening room is our lounge. Mrs MS tolerates the acoustic treatments - somewhat balanced by enjoying TV sound via the HiFi.

So the active filters need to be available to both music and TV. Hence, the use of Roon’s Muse was not an option here.

A lot of head-scratching was involved. A way of dealing with the TV’s 48/16 TOSLINK and the output from my RPi4B RoPieee Roon endpoint was needed. Also, a multi-channel DAC wasn’t appropriate here, rather a multi-channel interface was needed.

Additionally, a means of easily switching between the two was required.

The solution was a S/PDIF autoswitcher taking the output from the TV and switching it with the coax output from a JustBoom Digi HAT connected to the RPi feeding the S/PDIF input of a Motu Ultralite Mk 5. The Motu has up to 10 balanced outputs configurable between Hang Loose Convolver and Motu’s CueMix 5 software.

S/PDIF input on the Motu is limited to 96/24, but as I’m 54 and my hearing tops out at 16 kHz, anything more is superfluous.

Great!

The next challenge was controlling the volume. The Motu has a variable output (in the digital domain) controllable from the “MAIN VOL” knob on the front panel, but no means of remote control, so a means of controlling the 6-channel outputs remotely was required.

The only currently available solution is the Lundahl VC2361. Although entirely passive in its construction (relay-switched precision resistors), input and output impedances are such that with sensible equipment, absolute transparency is assured.

Everything is hooked up via interconnect spaghetti:

Now all that remains is a big suite of measurements to generate the linear phase crossover filters.

[Michael_Harris]

And Graeme when exactly do you retire?

If this is what you do when you have a bit more free time, I imagine your wife will send you back to work within a short period

It was already a really good project to follow, but now you are taking it to a whole new level.

[Graeme_Finlayson (The Mad Scientist)]

@Michael_Harris

And Graeme when exactly do you retire?

29/05/2025.

Having heard the difference DSP room correction can achieve, active filtering is the next step. Acourate is capable of generating filters with ridiculously steep slopes and perfect step response. Things that ware well beyond the realms of passive crossover filter components.

@Michael_Harris

If this is what you do when you have a bit more free time, I imagine your wife will send you back to work within a short period

Fortunately she travels quite a lot with work, so she’s largely oblivious to what happens in my free time. Provided projects in the house are progressing at an acceptable pace, she’s happy

[Michael_Harris]

@Graeme_Finlayson

she’s happy

They are the magic words.

Good luck with the rest of this project as it comes to its conclusion, and progress with the Boss’s projects as well.

[Mike_O_Neill]

@Graeme_Finlayson

29/05/2025.

No doubt your birthday , I am also a 29 May baby BUT older 1950 vintage

[Eve_Fox]

FYI, you can control the level of all channels on the recent-ish Motu interfaces like the Ultralite Mk5 remotely.
They just don’t ‘link’, so you need to send separate commands to each channel.

I can check my notes from when I had one to see what I was sending exactly? Basically, each channel had their own ‘trim’ and then I’d adjust all them (in a way that would respect the original trim offset) IIRC

[Graeme_Finlayson (The Mad Scientist)]

I’ll update on progress with the active setup as time allows.

We’ve flown to Glasgow this weekend to visit my Dad in the Queen Elizabeth University Hospital, and next weekend, we begin our annual holiday in Scotland, where we’ll hopefully spend some more time with him either in hospital or at home.

My Dad, age 77, was recently diagnosed with CLL and SLL, two forms of non-Hodgkins lymphoma. Relatively indolent forms of cancer with which many sufferers survive many years sometimes without any treatment. Even more recently, however, he was diagnosed with a cancer around the parotid gland in the left side of his face, which it transpires is a metastasis from a melanoma he had removed from his forehead last year. It’s an aggressive cancer with a poor treatment prognosis, however it was still within the window for surgical intervention. A little over a week ago, he underwent a 10 hour procedure by a 15 member surgical team to remove the tumor, a number of lymph nodes in his neck, his left ear and surrounding tissue and make 2 skin grafts to close the wound.

Post surgery, he’s doing well, and is dealing with it all with his usual healthy dose of humour.

He’s receiving the best care possible, and in times where our free health service is often criticised, we sincerely appreciate and can’t thank enough the truly exceptional people in the NHS who dedicate their lives to caring for others.

[Graeme_Finlayson (The Mad Scientist)]

Yes. You can also link as many of the 10 analogue output channels as you like into the main monitoring group and control them all simultaneously.

From a safety perspective, I prefer a hardware means of controlling the overall volume, hence my inclusion of the Lundahl VC2361.

[Jim_F]

I hope your dad has a good outcome. Many times the NHL is related to the others. Hopefully they got all the melanoma and he should be OK. Indolent NHL may never be a problem.

[Eve_Fox]

Took me some escalating calls with Motu’s people to get a clear answer on how their volume trim was implemented internally, from a technical (not control, that was easy) standpoint.

If I’m not mistaken, you can link the channels to the knob but you can’t control them as a group via the API? At least I think that was the case back when I delved into this for a bit. Had an Mk5 and an AVB, wasn’t hugely impressed and moved on. Fantastic interfaces for the money tho.

I too prefer some physical attenuation / means of control after D/A to be frank.

[Graeme_Finlayson (The Mad Scientist)]

Thanks Jim. Hope all went well and you get the all clear!

The lead surgeon is confident that they got all of the cancer. Once he’s sufficiently recovered he is set to undergo a 5 day a week, 6 week course of radiation therapy. There’s a lot of travel to and from the hospital involved, so I may spend a few weeks in Scotland to help chauffeur him to and from treatment sessions.

[Jim_F]

My paternal grandmother’s family was from Edinburgh, Scotland. Paternal grandfather’s family was from Ireland.

[Graeme_Finlayson (The Mad Scientist)]

@Eve_Fox

If I’m not mistaken, you can link the channels to the knob but you can’t control them as a group via the API?

In the latest version of the API, you can link them to the main monitoring group and control them all together

[Glimmer]

I hope that your Father’s treatment is successful and that you have many more years of humour and kinship.

[Glimmer]

Let’s hope that you are with us for many more years to come!