Rebuilding some old loudspeakers

[sploo]

For reasons too longwinded to detail, I found myself needing to rebuild a pair of old floorstanding loudspeakers in what would be more of a bookshelf format. As this was during the depths of one of the Covid lockdowns, construction materials were in limited supply, so I decided to go "full Yorkshire" and see just how little money I could spend in doing the job.

I had a bunch of surplus IKEA kitchen doors - 16mm chipboard covered in white laminate. Hardly ideal, but it was available, and free.

The original speakers (approx 255x255x900mm) were built from a design by Wilmslow Audio, and featured a ported enclosure with an 8" midbass and a treble. They've been great, but my main concerns were the lack of internal bracing with the enclosure design, and the fact the port tube was a straight piece of of 2.5" diameter pipe. That diameter was arguably a bit small for the design, and could lead to audible "chuffing" under high load.

Because I was going to use the same drivers and crossover, the front baffle width must remain unchanged, as must the driver placement and internal volume. The port tuning would also ideally match the original design.

Based on https://jahonen.kapsi.fi/Audio/Papers/AES_PortPaper.pdf I came up with a "better" port design; incorporating the curves described in the paper. The move to a smaller cabinet height, combined with the larger diameter of the port, meant that the port had to be rear firing; rather than on the front face like the original floorstanders.

A quick prototype in SketchUp resulted in the following layout:

The ports were then 3D printed (in two parts, due to the size):

To be continued...

 

[sploo]

Next I cut some of the panels (a mixture of the table saw and CNC machine), and checked the fit of the port:

 

[sploo]

Good quality damping material for the inside of loudspeakers is quite expensive, but a pile of thick carpet tiles you already have only costs you a can of spray on adhesive:

 

[sploo]

Next I chamfered the front baffles, and later applied some iron-on melamine edging that I had spare:

Parts from original speakers removed and ready to fit:

Installing the crossover board:

Wadding/stuffing:

 

[sploo]

Continuing the cheapskate theme, I didn't want to cut out the frames for the speaker grilles from large sheets of material, so I tried making some "jigsaws":

The multi-part front grilles worked well, but the rear ones didn't, so I recut them, and stained them all:

 

[sploo]

And that's what we end up with:

 

[sploo]

In reality, the above took ages (started last September). Usually I'd design an enclosure fully, and the construction would use rabbets and dados. Because I was mostly making up the insides as I went (based on what material I had left) it was all a bit ad-hoc, with lots of Dominos used to join parts. Unsurprisingly that took way longer than just designing it "right" in the first place.

Whilst the angled internal bracing was harder to make, the idea is that it splits un-braced panels into areas of varying size (meaning they don't resonate at a single frequency). A "knock" test of the old vs new enclosures indicates the new ones are a bit better - though far from completely "dead".

I actually completed one new speaker fully before moving the components from the second old speaker to the new, so I could run some comparisons:

The results of a fairly amateur double-blind test setup were interesting; short answer was that it wasn't possible to reliably distinguish between the old and new design. With very low frequency bass samples there was a slight preference to the old design; which might indicate I didn't get the port tuning quite right, but (at least based on my dodgy understanding of stats) the difference wasn't statistically significant.

 

[Richard_C]

Nice job. The drivers look in good condition, I did up some old ARs a couple of years ago, reused same cabinets but AR have a very different approach, all sealed, no ports. I did have to refoam the drivers though, the rubberised cone edges had degenerated. It's nowhere near as difficult as it seems as long as you take care to keep it all centred. So I now have some 42 year old speakers working nicely with my 42 year old record deck. It's the 70 year old ears that are knackered.

The capacitors in the crossovers are said to be a point of failure, they don't fail completely and are easy to replace with same spec or higher capacity. I did mine while it was apart. Maybe think about it if you dismantle again.

I found a very good forum, US based, think it was called classicspeakerforum or similar. Full of helpful people with a slight tendency to nerdy-Ness.

In terms of listening, I reckon the environment makes more difference than the fine detail of set up. We have a large glass sliding patio door, pull the curtains at night and the acoustics change. There is a phone app called physics toolbox, free, which has a spectrum analyser among many other wonderful things.

Wilmslow Audio has a good reputation so it looks like you have some excellent kit to last you many more years. And it looks good.

 

[sploo]

Well.. there's a story to the drivers... in that only one of the midbass units comes from the original speaker pair... but that's a story for another day

In an ideal world I'd have loved to try making an active crossover, but the time/learning curve/need for multiple amps just made it impractical.

Environment is absolutely a massive factor in audio. In a "previous" life I did a fair bit of acoustic room treatment, but family now makes the installation of such kit impossible.

The midbass unit used in these speakers is no longer made by ScanSpeak, so the original speaker design (by Wilmslow, called the Nemesis) is no longer available. Bit of a shame as it was a highly regarded driver. That said, I assume it's been surpassed in the ~20 years I've had these speakers.

 

[Mike57]

Thank you both @sploo and @Richard_C for a fascinating read with my 5am morning tea.
I have some 40+ year old Mordaunt Short speakers lurking unused under my computer desk and too much spare time. Maybe with a bargain Chinese valve amp to replace the headphones??
That is, if I can put the 'Physics Sensor' app down.

 

[rafezetter]

T'ain't nowt wrong wi' that.

 

[Sandyn]

They certainly look great. How do you like the sound? that's what really counts. I like the use of materials.

 

[sploo]

They certainly look great. How do you like the sound? that's what really counts. I like the use of materials.

They're good. The 8" midbass is ScanSpeak's 8554 kevlar driver; very low distortion. The treble is the 9500, also from ScanSpeak. I'm told the treble in particular is liked for the sound it produces (sometimes even over drivers higher up in their model range).

The late/great speaker designer Siegfried Linkwitz used the 8554 in one of his designs (because it tested well). I've no doubt the sound would be improved by moving the upper mid to a smaller mid driver, and I do cross them over to a subwoofer to handle the really low bass.

 

[sploo]

Thank you both @sploo and @Richard_C for a fascinating read with my 5am morning tea.
I have some 40+ year old Mordaunt Short speakers lurking unused under my computer desk and too much spare time. Maybe with a bargain Chinese valve amp to replace the headphones??
That is, if I can put the 'Physics Sensor' app down.

I don't know much about valve amps, but I hear they can be "fussy" in terms of pairing with the right speaker. To be honest, one of the cheap class D amps would probably get them up and going (unless they're huge).

 

[Mike57]

I don't know much about valve amps, but I hear they can be "fussy" in terms of pairing with the right speaker. To be honest, one of the cheap class D amps would probably get them up and going (unless they're huge).

The sad thing is that my hearing is unlikely to notice much difference these days and (in a very shallow way) I just like the idea of glowing valves. And it gives me another chance to bore the grandchildren that at their age my portable MW radio had a 100v battery and was the size of a briefcase.
But genuinely, forums like this do give me the opportunity to listen to people who do know a lot about the subjects I dip in and out of and I do enjoy that. For instance, I now know far more about all the various species of solitary bees and even the different diameter of holes needed in a nesting box to control the ratio of male to female eggs. All that from thinking I'd simply make some insect hotels for my grandchildren and doing a little googling.
So please don't let my light hearted comments distract from the real nuggets on here.

 

[Richard_C]

Pre lockdown we went to a local auction house just to see how it all worked, not sure what to do with ex father in laws huge stamp collection. Anyway, I was astonished that some of the later house clearance lots included cameras, hifi etc., and some kit went for silly low prices. TEAC amp which someone would have chosen carefully and saved up for going below £40, shiny B&O deck and amp stuff (not a fan) maybe £100. Walked past a second hand shop, charity I think, which had all sort in the window. To get your speakers going you should be able to find something decent for not much money, before you spend on fancy valve jobs. EBay has some, but also some silly-high prices.

 

[sploo]

The sad thing is that my hearing is unlikely to notice much difference these days and (in a very shallow way) I just like the idea of glowing valves.

The great irony is that the overwhelming demographic of audiophiles is adult men; who generally can't hear anything over the mid teens kHz, but will sometimes spend the value of a small car in order to have a system with a frequency response that only their dog can appreciate

But I do agree that valve amps look really cool.

 

[dickm]

This slightly autiophile old man, with with definite upper register hearing loss, is more than happy with the seconhand Mission 70s recently bought to replace the ones he "lent" to younger daughter and somehow never got returned. But admire the craftsmanship and research of the OP.

 

[Megaweasel]

In reality, the above took ages (started last September). Usually I'd design an enclosure fully, and the construction would use rabbets and dados. Because I was mostly making up the insides as I went (based on what material I had left) it was all a bit ad-hoc, with lots of Dominos used to join parts. Unsurprisingly that took way longer than just designing it "right" in the first place.

Whilst the angled internal bracing was harder to make, the idea is that it splits un-braced panels into areas of varying size (meaning they don't resonate at a single frequency). A "knock" test of the old vs new enclosures indicates the new ones are a bit better - though far from completely "dead".

I actually completed one new speaker fully before moving the components from the second old speaker to the new, so I could run some comparisons:

The results of a fairly amateur double-blind test setup were interesting; short answer was that it wasn't possible to reliably distinguish between the old and new design. With very low frequency bass samples there was a slight preference to the old design; which might indicate I didn't get the port tuning quite right, but (at least based on my dodgy understanding of stats) the difference wasn't statistically significant.

In reality, the above took ages (started last September). Usually I'd design an enclosure fully, and the construction would use rabbets and dados. Because I was mostly making up the insides as I went (based on what material I had left) it was all a bit ad-hoc, with lots of Dominos used to join parts. Unsurprisingly that took way longer than just designing it "right" in the first place.

Whilst the angled internal bracing was harder to make, the idea is that it splits un-braced panels into areas of varying size (meaning they don't resonate at a single frequency). A "knock" test of the old vs new enclosures indicates the new ones are a bit better - though far from completely "dead".

I actually completed one new speaker fully before moving the components from the second old speaker to the new, so I could run some comparisons:

The results of a fairly amateur double-blind test setup were interesting; short answer was that it wasn't possible to reliably distinguish between the old and new design. With very low frequency bass samples there was a slight preference to the old design; which might indicate I didn't get the port tuning quite right, but (at least based on my dodgy understanding of stats) the difference wasn't statistically significant.

Nice job - I built a pair of these years back and that tweeter is just absolutely fantastic - still hard to beat today. I reused the components, adding some extra drivers (all Scanspeak) and new crossovers to build the North Creek rhythms. Later I rebuilt them with some laminated and curved enclosures (pic attached). One of the innovative things about that design that worked well was that they used the ports stuffed with drinking straws. That then let’s you push the straws in and out to tune the port length. Worked well and worth a try for a few quid. Stuff them in quite hard otherwise they get fired out the back under high volumes!

 

[flying haggis]

Just reading this thread reminded me that I still have a copy of the Badger Sound Services catalogue /speaker building guide


obtained when I fancied building a pair of ls3/5a's. never did build a pair! I bought some instead (bbc staff discount....)

if anyone wants me to scan any designs just PM me