Troels Gravesen's PMS (Poor Man's Strad) DIY build

[Rob Wright]

Amazing. What an outstanding result.

[ENIGMA]

Well done, Gratifying.

[crtexcnndrm99]

Quite the journey and a half to get to listening impressions. Glad to hear you’re chuffed with results and wife baffle sound. Enjoy 

[The Mad Scientist]

I finally got around to breaking out REW the other evening and set about trying a newer technique using inversion.

 

The results weren't bad at all. There are a couple of room related dips left, but on the whole, it's much better and there's definitely audible improvements.

 

Before (L & R):

 

 

 

After (L & R)

 

[rand129678]

Gorgeous looking speakers. Assuming you don't want to add subwoofers ?

 

I know excessive correction gain is frowned up in room correction and understand all the arguments - BUT have you tried more correction to achieve the below?

 

75dB at 20Hz is still decent SPL. Of course music will be a bit lower in level.

 

Worth a try and listen ?

 

Edited October 5, 2023 by rand129678

[The Mad Scientist]

2 hours ago, rand129678 said:

Gorgeous looking speakers. Assuming you don't want to add subwoofers ?

 

I know excessive correction gain is frowned up in room correction and understand all the arguments - BUT have you tried more correction to achieve the below?

 

75dB at 20Hz is still decent SPL. Of course music will be a bit lower in level.

 

Worth a try and listen ?

 

 

Many thanks for your suggestion. I have a full Benchmark rig, so lots and lots of very clean gain is at my disposal! 

 

Subwoofers are definitely not on the horizon. That would be straying into the minefield of marital discord!

 

I redid the filters with 10dB adjustment limits rather than the original 5 dB suggested in the literature and unchecked the "exclude notches" box. -10 dB of headroom management was needed in Roon to stop the clipping indicator from lighting up periodically, but the results are very satisfying:

 

 

The difference in some of the test tracks I played earlier is enormous.

 

Bubbles by Yosi Horikawa is just mindblowing!

 

Edited October 5, 2023 by The Mad Scientist

[El Tel]

This has been a very satisfying thread to follow.

 

You're a gifted craftsman, Graeme. Thanks for all the effort you put in to keep us enthralled and entertained. It's been a wonderful journey.

 

I hope those beasts keep you happy, with many years of listening pleasure ahead.

 

Well done, my friend.

[PKay]

1 hour ago, El Tel said:

This has been a very satisfying thread to follow.

 

You're a gifted craftsman, Graeme. Thanks for all the effort you put in to keep us enthralled and entertained. It's been a wonderful journey.

 

I hope those beasts keep you happy, with many years of listening pleasure ahead.

 

Well done, my friend.

Agreed entirely. This has been the most enjoyable thread in a very long time. 
 

@The Mad Scientistyour craftsmanship is exceptional.  Well done on such an amazing build. 

Edited October 5, 2023 by PKay
Typo

[The Mad Scientist]

1 hour ago, El Tel said:

This has been a very satisfying thread to follow.

 

You're a gifted craftsman, Graeme. Thanks for all the effort you put in to keep us enthralled and entertained. It's been a wonderful journey.

 

I hope those beasts keep you happy, with many years of listening pleasure ahead.

 

Well done, my friend.

 

Thanks Tel.  I've really pushed the envelope with these, and I'm sure in addition to some good judgement, there's been at least an equal measure of good luck in the execution!

 

Mistakes were made along the way, but I seem to have been able to recover most of them.

 

I'm loving the sound coming from these wide, shallow boxes. After finalising the filters, I plugged my way through the optional Rephase corrections. Icing on the cake. Never knew that 2 channels could deliver "surround sound"

 

I just have to tear my backside away from the sofa now and get on to making a nice set of stainless-steel plinths to properly finish them off.

 

The WAF is on the low side, but my enthusiasm seems to be infectious. They're slowly growing on Katy.....

[rand129678]

7 hours ago, The Mad Scientist said:

 

Many thanks for your suggestion. I have a full Benchmark rig, so lots and lots of very clean gain is at my disposal! 

 

Subwoofers are definitely not on the horizon. That would be straying into the minefield of marital discord!

 

I redid the filters with 10dB adjustment limits rather than the original 5 dB suggested in the literature and unchecked the "exclude notches" box. -10 dB of headroom management was needed in Roon to stop the clipping indicator from lighting up periodically, but the results are very satisfying:

 

 

The difference in some of the test tracks I played earlier is enormous.

 

Bubbles by Yosi Horikawa is just mindblowing!

 

 

It looks like the delta between 20Hz and the rest is still similar to before.

 

REW can be a pain but would be interesting if you can bring it close to something like the target I showed earlier.

 

More just as a fun exercise, not necessity. Great to hear it is sounding great !

[rand129678]

@The Mad Scientist can you google drive link your mdat REW file?

 

And include exact details of your preferred target curve?

 

I wouldn't mind having a crack at something and you can try and listen

 

 

Edited October 6, 2023 by rand129678

[lucmor444]

Interested in what are the overall benefits correcting to 75dB rather than what the speakers are achieving with the latest result. A correction to 75dB seems a significant reduction in headroom to gain a more even response between 20-40Hz?

[rand129678]

10 hours ago, lucmor444 said:

Interested in what are the overall benefits correcting to 75dB rather than what the speakers are achieving with the latest result. A correction to 75dB seems a significant reduction in headroom to gain a more even response between 20-40Hz?

 

At the moment playback of 20-40ish Hz signals in music will be around 10+ dB below what they should be..

 

DSP involves tradeoffs - there is give and take with everything.

I did mention in my first post that excessive correction gain is usually not something to chase.

 

As I mentioned in a previous post :  as a fun exercise only (not a necessity if everything is already sounding great) it would be fun to try to make this more linear (to his own preferred target curve of course) - yes at the sacrifice of excessive correction gain.

 

He has very high gain DAC and amp.

 

It may sound better, or may sound worse. 

 

Something to maybe try.

 

Edited October 6, 2023 by rand129678

[The Mad Scientist]

2 hours ago, rand129678 said:

 

At the moment playback of 20-40ish Hz signals in music will be around 10+ dB below what they should be..

 

DSP involves tradeoffs - there is give and take with everything.

I did mention in my first post that excessive correction gain is usually not something to chase.

 

As I mentioned in a previous post :  as a fun exercise only (not a necessity if everything is already sounding great) it would be fun to try to make this more linear (to his own preferred target curve of course) - yes at the sacrifice of excessive correction gain.

 

He has very high gain DAC and amp.

 

It may sound better, or may sound worse. 

 

Something to maybe try.

 

I've sent you a PM. The forum seems to have been down on and off today.

Edited October 6, 2023 by The Mad Scientist

[lucmor444]

19 hours ago, rand129678 said:

 

At the moment playback of 20-40ish Hz signals in music will be around 10+ dB below what they should be..

 

DSP involves tradeoffs - there is give and take with everything.

I did mention in my first post that excessive correction gain is usually not something to chase.

 

As I mentioned in a previous post :  as a fun exercise only (not a necessity if everything is already sounding great) it would be fun to try to make this more linear (to his own preferred target curve of course) - yes at the sacrifice of excessive correction gain.

 

He has very high gain DAC and amp.

 

It may sound better, or may sound worse. 

 

Something to maybe try.

 

Thx for that.

 

Agree - something to try.

 

For me I would be concerned by the compression of the dynamic range above 40Hz.  It's potential benefit would also be influenced by the type of music preferred (eg does it include a lot of bass below 40Hz).

 

Hopefully The Mad Scientist will share his thoughts if he tries what you have to offer:)

[rand129678]

3 minutes ago, lucmor444 said:

For me I would be concerned by the compression of the dynamic range above 40Hz.  It's potential benefit would also be influenced by the type of music preferred (eg does it include a lot of bass below 40Hz).

 

Yep but you can do measurements to see if this is even a real problem.

 

Or you can just listen to music and if you like what you hear, all is good.

 

Can't really generalise this stuff, which is why I haven't made any claims above - best looked at case by case after giving it a try.

 

 

Edited October 7, 2023 by rand129678

[The Mad Scientist]

I'll get into redoing the filters today.

 

43 minutes ago, lucmor444 said:

For me I would be concerned by the compression of the dynamic range above 40Hz.  It's potential benefit would also be influenced by the type of music preferred (eg does it include a lot of bass below 40Hz).

I'm not really anticipating that this will be a problem - I still have  about 35 dB of gain on the HPA4 to play with and the amps are switched to their lowest sensitivity setting at the moment.

 

As a quick experiment, I dropped in a low shelf parametric EQ in Roon to bring the LF up from about 40 Hz downwards. The change isn't dramatic, but there's an overall increase in "fullness" to the sound.

 

I'll do it properly in REW and try to take some measurements with the filters in place. SWMBO is out for a few hours today, so I might get a chance to get the measurement gear out again!

 

[The Mad Scientist]

Ok, I've had a play around with generating new filters and here's the result:

 

 

Still have to go back and do all of the Rephase stuff again, but the initial listening impressions are much better. Double bass certainly sounds much better balanced with the rest of the instruemnts on the tracks I've listened to so far.

 

Edited October 7, 2023 by The Mad Scientist

[rand129678]

11 hours ago, The Mad Scientist said:

Ok, I've had a play around with generating new filters and here's the result:

 

 

Still have to go back and do all of the Rephase stuff again, but the initial listening impressions are much better. Double bass certainly sounds much better balanced with the rest of the instruemnts on the tracks I've listened to so far.

 

 

Looking much better and great hear sounding better

 

There's still hours/days/months ahead of iterating your favourite target curve/s

 

Some tracks you may want less of that deliberate bass bump, others you may want it. It all up to personal taste / preference in the end.

 

But with Roon i believe you can switch different convolution profiles on the fly ?

 

Lots of fun ahead

Edited October 8, 2023 by rand129678

[KRSDarwin]

Maaaate, nothing short of amazing.

 

To the extent your aim was to have a Hi-Fi store or show set of speakers indistinguishable from the commercial brands you have succeeded in spades. 
 

It is gratifying to see there are still people around with such a range of skills as well as the commitment, patience and ingenuity to pull off such a project. 
 

Thanks for sharing, it was a great read. 

Edited October 8, 2023 by KRSDarwin

[The Mad Scientist]

10 hours ago, rand129678 said:

But with Roon i believe you can switch different convolution profiles on the fly ?

 

Yes, you can indeed. Presets can be saved and then just picked from the list within Muse, Roon's rebranded DSP engine.

[The Mad Scientist]

6 hours ago, KRSDarwin said:

Maaaate, nothing short of amazing.

 

To the extent your aim was to have a Hi-Fi store or show set of speakers indistinguishable from the commercial brands you have succeeded in spades. 
 

It is gratifying to see there are still people around with such a range of skills as well as the commitment, patience and ingenuity to pull off such a project. 
 

Thanks for sharing, it was a great read. 

 

Many thanks for the kind words.

 

I have to admit there were occassions when I really thought I'd bitten off far more than I could chew, but I'm glad I stuck with it.

 

I just have to get on and make the plinths now!

[PKay]

If there was a Stereonet speaker build of the year yours would get my vote. An amazing build and journey. 

[The Mad Scientist]

I've finally got the Rephase adjustments done. I have serious post COVID brain fog at the moment and complex taks are a challenge!

 

The additional gain in the bottom octave makes everything sound just right. It has also had quite a dramatic effect on the midrange. Switching between this profile and the previous one without the bass lift, the midrange sounds "honky" by comparison, so I'm definitely sticking with the new profile.

 

I was initially a little concerned by the fact that I could see the woofer moving now, but it's only a millimetre or so. Apparently the CA22RNX has 12mm of linear excursion, so I don't think I need to worry!

Edited October 8, 2023 by The Mad Scientist

[The Mad Scientist]

I'm long overdue an update on this thread. Work on the proper stainless plinths was hampered by what seems to have been the greyest, wettest winter I have ever experienced. Grinding and polishing stainless is best done outdoors - the man cave houses my server cabinet which contains a very expensive Synology Rackstation and extension bay, my desktop PC and an enterprise network switch. Even with dust extraction and air filtration, this is not the sort of equipment which wants to be exposed to electrically  conductive metal dust!

 

The plinths are made from 3 mm thick 304 stainless, TIG welded with 308 filler wire and filled with steel blasting shot for added mass and vibration damping.

 

The starting point was creating a 5 mm thick aluminium template which would then be used to cut out the stainless top and bottom plates:

 

 

Roughed out template shape:

 

 

Coupons cut out with a mag drill fixed to the template for rounding the corners:

 

Template after corner rounding:

 

 

Roughing out the stainless with a carbide holesaw:

 

 

Machining the stainless to the aluminium template:

 

 

 

 

First stainless piece machined to shape:

 

 

All pieces machined out:

 

 

Drilled out, ready for assembly:

 

 

Inserts in place and clamped up ready to weld. Welder lubricant supplied by my local brewery and taproom:

 

 

Edited May 30 by The Mad Scientist