CNCed folded Voigt pipe… the 3rd edition.

[Type 1]

About 10 years ago, we were speaker hunting, and settled on Martin Logan Ethos after being offered a healthy 25% discount.  Sadly they are now broken with a $4000 repair needed.

 

So, looking at a different option, I started looking at Single driver DIY speakers.

( part of the attraction to ML is only one crossover).

 

So this is the 3rd attempt.   I have a fairly long music area, so, I figured I couldn’t go less than a 8 inch driver and fill the room effectively… 

I looked at Voigt pipes, but I have to please the Lady wife, so the next best option looked like folded pipes, and easier to make too.

 

My first attempt followed a Japanese plan I found on YouTube using 15mm plywood.  I used a 18mm Australian hardwood plywood assembled in China as I had free access to it.

 

I was surprised by how “ live” it sounded… it was a bit “warm” and the bass wasn’t super tight.

Next some 28.5mm off cuts became available ( work at a Plywood place)

 

Wow! So now Everything is punchy, tight, and a Wider choice of music sounded good.

So I knew that I was onto something… confirmed by the Lady Wife, she has better ears and doesn’t get hung up with “ gear issues”.

 

So the latest idea is an attempt to reduce cabinet distortion and reduce the need for stuffing.

I’m most of the way through the cabinet assembly, but as I planned an economical option, I have created some problems for myself..

 

Part of my motivation for this project was create an affordable kit product that would be easily available to those without access to Professional wood machining technology… I’m still ironing out bugs…

 

 

[Type 1]

So, to fill in some blanks.

I’m using SB Acoustics 8” full range driver, SB20FRPC30=8.

It seemed to get the best reviews of the the cheaper drivers, and once it’s run in, ( I’m currently running in a new driver which is a bit “shouty “ so running in, is a reality), it’s pretty mellow and sounds “right” to me.

 

The mark 2 box was made from 28.5mm F17 plywood ( used for floors in Shipping Containers), but for this box I used 25mm non structural plywood from the same company, because it was free.

 

Although it looks very similar on the outside, I suspect that there are more voids, ( open knot holes in the core) than the F17 stuff.

 

This box has conventional sides, but the centre section is made of 9 x 25mm layers. 65 pieces of plywood per box!
Apparently sound travels differently through timber, depending on which way it hits the fibre, so this is a chance to find out if my suspicions are true. ( When building a guitar or a piano, the way the timber grain runs is very important).

So we will see if I’m on right track in a week or two!

 

Sending a photo of mark 2 speaker

 

[Ian McP]

Here's a tractrix horn that works very well with an 8 inch driver

 

https://www.diyaudio.com/community/threads/alfreda-horn-plan-1.346718/

 

some background on it

 

https://www.diyaudio.com/community/threads/plans-for-alfredo-horn-from-alf-lepp.174814/page-2

[Type 1]

Hi Ian I guess that you have made a few of these Tractix horns or at least have listened to a mates Tractix horns and so can explain why they are Amazing! ?

[Ian McP]

Not built them myself, I knew Alf who first built them, good bass extension. Several were built by others on stereonet. Not exactly a beginner's woodworking project! The Frugel horn family is interesting too.

https://www.frugal-horn.com/

 

[Type 1]

Hi Ian… yes it looks like a Huge woodworking problem… like many backloaded horns..

if you have a low power amp or a driver with low bass response this type of box could be good.

I don’t have either problem, so a box that gives me an even frequency response is much more desirable..

[Jehuty]

Following with interest as I am a big fan of full range drivers myself.

 

Using Goodmans Axiom 80 in backloaded horn and I got a pair of vintage alnico Supravox T215 looking for boxes to put them in. And I think your cabinet would be perfect for them.

 

Out of curiosity, what's the estimated sensitivity once you get the SB Acoustic drivers into the boxes?

 

Cheers,

Will

[Type 1]

Hi Will!

you have some fancy drivers!

SB Acoustics claims 92db sensitivity..

They are more sensitive than the ML Ethos that I had, which from memory were claimed to be 92 db as well.

Other than that, I’m not sure.. they plenty loud enough and my room is quite big..

I was tempted to do single driver speakers after listening to the “ Real World Audio “ guy on YouTube. Be warned, he is pretty boring though!!

[crtexcnndrm99]

10 hours ago, Jehuty said:

Following with interest as I am a big fan of full range drivers myself.

 

Using Goodmans Axiom 80 in backloaded horn and I got a pair of vintage alnico Supravox T215 looking for boxes to put them in. And I think your cabinet would be perfect for them.

 

Out of curiosity, what's the estimated sensitivity once you get the SB Acoustic drivers into the boxes?

 

Cheers,

Will

Hi Will,

 

I read your speaker description and wondered if the Supravox LF drivers could go in this living voice airscout style system? I’ve always thought the bass horn between the two rear loaded horns is a neat low power amp system…

 

[Jehuty]

4 hours ago, crtexcnndrm99 said:

Hi Will,

 

I read your speaker description and wondered if the Supravox LF drivers could go in this living voice airscout style system? I’ve always thought the bass horn between the two rear loaded horns is a neat low power amp system…

 

Love it!

 

If you have the space, why not.

 

I only heard the Supravox in open baffle and they were excellent. Can't put them in living room because they are ugly (JE Labs open baffle) and need space behind them to breathe.

[Type 1]

So the new boxes have been finished and plugged in.  I will report on the difference in sound tomorrow!

[crtexcnndrm99]

30 minutes ago, Type 1 said:

So the new boxes have been finished and plugged in.  I will report on the difference in sound tomorrow!

Those look great! Should be some SQ improvements in the latest iteration  

[Type 1]

Thanks Ash!

The end grain plywood looks a bit the “Zebrawood” veneer we used to sell!

 

I suspect using the end grain of the plywood changes the structural strength of the box.. ( box number two is make of F17 structural plywood 28.5mm thick. There are stronger plywoods, but not many!)

[Type 1]

Soooo, I’m currently doing back to back comparisons with boxes 2 and 3..

so with box 2 a spent a far bit of time tuning the stuffing to reduce some harshness.

The driver was only partly run in then.

With box 3, I deliberately put the minimum stuffing in it based on hoping the adjustments that I had made to the interior of the box would smooth things out and the different construction might help with that to. And my suspicions seem to be correct.

 

 

So far, box 3 has more bass, but it’s not as clear and lacks some impact.

It’s not shouty in the midrange or top end which is good.

 

The Lady wife ( who has better ears than me), says that there is some “grainyness “ in the male vocals. She also gets a bit bored listening to the mark 3 speakers….

 

Hmm, so what is happening?

Probably the experts among you already know?

I suspect that the mark 3 boxes lack the rigidity of mark 2 and the box is adding some extra unwanted vibration and is smearing some of the music?

I may experiment with stuffing mark 3 a bit and trying to find ways to make it more rigid…..

 

 

 

 

 

 

 

[Type 1]

I added some stuffing on the back wall behind the driver and it sounds like we are heading in the right direction!!

[Type 1]

Sorry for the delay in posting…the tuning process took a little longer than I expected and then I wanted to verify my results with other listeners to prove to myself, that I wasn’t faking it!,

 

So I finally think that I’ve got the sound about right!

It’s been a frustrating journey as they are quite sensitive to tuning, and I’ve gone backwards once or twice trying to get them right, but now they sound close to Amazing!

 

The previous speaker Mark 2 played all sorts of music well in a nice fireside, enjoying an aged port wearing comfy slippers kind of way..

 

The type 3 is not like that… it’s full of energy, exciting, detailed, fast, full of rhythm, plays musical instruments as they appear in real life.

 

I got involved in Electrostatics because there was no “box sound”…

These have no “box sound”, but the bass, midrange and top end are totally together..

 

People used to say that there is a gap between the bass and the rest on the Martin Logan speakers, but because l like the style of sound, I didn’t hear it..

 Now I hear it… 

I’m starting to look at Type 4 which would be a box that will be easy to manufacture and assemble and will give you close to “ guaranteed results “ of amazing sound at an affordable cost..

 

Let’s see where the journey goes!

 

 

The journey isn’t over yet… but it is getting Exciting!

 

[Jehuty]

Single driver speakers are indeed sensitive to tuning. It's really hardwork doing the balancing act.

 

I love the look of the 3rd version, they look classy and have high WAF 

 

May I suggest if you could design the front panel to be swappable. That would be very desirable as I know many single driver lovers love to play with different drivers. Perhaps something similar to this:

Source: https://rutcho.com/speaker_projects/03_the_universal_horn/the_universal_horn.html

 

Thanks again for sharing!

[Type 1]

Thanks Jehuty for your support!

Hmm… the interchangeable baffle idea certainly is interesting and I understand why it’s convenient!

 

I will have to think about it..

I have deliberately made the box as narrow as possible and the driver up as close as possible up into the top curve of the box….

not leaving any real space for strength for interchangeable baffle plates… also the design behind the driver would make it tricky…

 

Another consideration is that, I believe a lot of the reason that this box is much more expressive than a standard box is because the the sound waves behave quite differently thru the end grain of the timber.

Plywood is generally considered to be be within thickness if it’s plus or minus .05mm of the required thickness.. when you have 9 core layers then this inaccuracy will multiply..

And I’m quite Convinced that using MDF will NOT get anyone the answers that they are looking for.

Of course plywood that is closest to its correct thickness would be chosen.. the width of the box would vary making it hard to guarantee the perfect fit of a replaceable panel…. Still, there may be away!

Thanks again!

 

[Type 1]

So it’s been a while since the last post…

In the meantime I’ve been able to get the Martin Logan Ethos running again and compare a number of different speakers and have had some other people comment on some of them..

 

First of all the comparisons between speaker 2 and 3.

Speaker 2 has Great bass, punchy, defined and warm, which leads into rich, seductive sounding vocals, but the top end is still tight and exciting..

 

Speaker 3 has so much information through the top end and vocals. I’m hearing rhythms that are between the vocals and the treble section that I’ve never heard before and they sound very light on their feet. In comparison, the bass isn’t as noticeable on certain tracks.

 

The Martin Logan’s in comparison seem to lack some liveness and emotion in the vocals and at times the bass section can get confused with tracks that have complicated bass.

 

Sadly it’s a fail for the MLs…..perhaps if they were brand new, the gap might close a bit.

 

We cruised through a Hifi shop on the weekend to do a sneaky comparison… and while it’s true our Hifi memory isn’t always accurate, it gives me a bit of an idea. ( often Amps, sources and cables in shops can be big $$$) so it’s never quite Apples and Apples.

( also they have big $$$ spent on room treatments, I’m too tight to do that!!!)

 

Anyway, we were doing a comparison of speakers in the $6k range.

The first thing that surprised me was how much bass and low bass some of these smaller boxes had, then I realized that some of them were quite boomy.. perhaps because the speakers were placed closeish to the corners of the room?

( I had got used to listening to speaker 3 which can be light on in the bass department)

The vocal quality of any of them wasn’t as engaging as speaker2 or 3.

 

it’s always nice to come home and realize that your money can stay comfortably in my wallet for a while!

 

What I have learned recently is that mark 3, while does some amazing things, needs some work in the bass department..

I will have to try out some ideas..

Thanks for reading !