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Re: My 3π adventure [message #95385 is a reply to message #95380] Tue, 15 March 2022 14:40 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18395
Registered: January 2001
Illuminati (33rd Degree)

ppkstat wrote on Tue, 15 March 2022 12:39
I am still surprised at how much the tweeter signal gets attenuated. I understand that this is to compensate for the difference in loudness between the two drivers. When fed with a 2V sine (P-P) at the crossover point (1KHz) I am getting a 1V sine at the woofer output and a 150mV signal from the tweeter! Naturally the tweeter signal increases in greater frequencies.

Lookin' good. That's exactly what it's supposed to do. The waveguide doesn't just provide directivity but also provides acoustic impedance matching, which makes it more efficient. So we increase on-axis SPL both by narrowing the beamwidth and horn loading. It's about a 10x increase.
Re: My 3π adventure [message #95424 is a reply to message #95260] Wed, 23 March 2022 11:21 Go to previous messageGo to next message
ppkstat is currently offline  ppkstat
Messages: 38
Registered: February 2022
Baron
Having received the two waveguides yesterday I soon realized that these have to be sanded and painted. They're completely fine as they are but if you're going for the max aesthetic result its something that has to be done.

The instruction of Wayne was to sand just the face of these in order to remove the parting lines without touching anything related to the flare and throat. With this in mind I decided to make the following setup: wet sanding with wet/dry sandpaper on a marble block:

/forum/index.php?t=getfile&id=3024&private=0

This produced excellent results! I did the bulk of the sanding at 400 grit. The parting lines were gone and then I did some more sanding to make it completely flat (not necessary at all but my OCD was killing me). I then smoothed it out by sanding at 600, 800 and 1000 grit. I could go much higher than that, essentially polishing it but there is no way paint is not going to cover the scratches made at 1000 grit. Below is an image of the treated vs the untreated waveguide.

/forum/index.php?t=getfile&id=3023&private=0

I even measured the thickness of the face before and after sanding. Turns out I removed around 0.2mm of material. Not bad!
Re: My 3π adventure [message #95434 is a reply to message #95260] Thu, 24 March 2022 08:53 Go to previous messageGo to next message
ppkstat is currently offline  ppkstat
Messages: 38
Registered: February 2022
Baron
I am having great difficulties finding suitable insulation locally.

The closest thing I can find is 5mm unfaced fiberglass sheet. This is around 2in.

/forum/index.php?t=getfile&id=3030&private=0

Wayne is this going to be enough? I can also get 4mm and somehow glue two together to reach R13 thickness? I don't know if that's even a thing (or how to do it).

I have not abandoned all hope yet, I'll try to have a look on industrial supplies as well.

Apart from that there are several other options here, including mineral wool, Muhwolle, Acoustic foam, Visaton's polyester and Paintable Damping Material.
Re: My 3π adventure [message #95438 is a reply to message #95434] Thu, 24 March 2022 09:49 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18395
Registered: January 2001
Illuminati (33rd Degree)

The 5mm sheet will work just fine.
Re: My 3π adventure [message #95537 is a reply to message #95260] Tue, 19 April 2022 09:16 Go to previous messageGo to next message
ppkstat is currently offline  ppkstat
Messages: 38
Registered: February 2022
Baron
Any thoughts on suitable mounting hardware for the 12PLB100s? I am trying to find suitable bolts and tnuts.

I am a bit puzzled about the size I am supposed to choose. The 12PLB100s have a thick gasket on front made from some cork-like material. Is the screw head supposed to sit on top of this material or is it supposed to sit on the metal body beneath the gasket.

Any information including specs for the hardware would be great!

As an update the waveguides are being professionally treated with a very thin glossy black coating. I will post an update when available. These are going to be mounted with M5 bolts and tnuts.
Re: My 3π adventure [message #95538 is a reply to message #95537] Tue, 19 April 2022 09:49 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18395
Registered: January 2001
Illuminati (33rd Degree)

I like using T-nuts, 10-32 size with button head or hex head screws. The screw head should go through the cork and apply clamping force directly to the cast basket frame. Also, when installing the T-Nuts, don't just tap them in because that often just bends the tangs. See the notes in the link below:
Re: My 3π adventure [message #95539 is a reply to message #95260] Tue, 19 April 2022 10:06 Go to previous messageGo to next message
ppkstat is currently offline  ppkstat
Messages: 38
Registered: February 2022
Baron
Thanks for the answer Wayne. 10-32 would be an equivalent of M5 over here, I can get the tnuts and try to locate a screw with a suitable screw head size.

PL is not available here so I had the idea of using gorilla glue for this purpose. It is self expanding and requires wet surfaces. I am reading in DIY forums that it's a good solution for gluing t-nuts.

Others solutions available here include standard epoxy glue and construction adhesives. Let me know your thoughts.
Re: My 3π adventure [message #95543 is a reply to message #95539] Wed, 20 April 2022 08:05 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18395
Registered: January 2001
Illuminati (33rd Degree)

The Gorilla glue will work just fine.
Re: My 3π adventure [message #95544 is a reply to message #95260] Wed, 20 April 2022 15:47 Go to previous messageGo to next message
ppkstat is currently offline  ppkstat
Messages: 38
Registered: February 2022
Baron
I have located a knowledgeable cabinet maker here. When I finish with the plans I'll show it to them and hopefully move on from there.

These are sort of tricky to convert to the standards that are being used here. Imperial units have to be converted to metric and they have to be rounded in a way that the internal volume or proportions are not messed up and in a way that the maker can actually construct it with locally available MDF sizes. I've decided to use 19mm MDF which is slightly thicker than the original size (it's closer to 3/4). I will post the completed plans here in order to spot any possible issues before the construction.

However before that there is one area which is especially troublesome to convert and this is the bass reflex port. This 2 1/2in area is impossible to construct with any available MDF sheets here. It might be possible to construct it with a block of thick wood or by combining MDF sheets of various sizes and then probably taking off a millimeter or something but I'll have to discuss this with them. That aside cutting a hole with a diameter of 63.5mm is impossible. With that in mind I had the idea to use a plastic port, specifically this

https://www.monacor.com/products/components/speaker-technology/diy-/mbr-70/

I had the idea to cut this with a saw to an appropriate size by using the tuning frequency (30Hz) and the internal volume of the cabinet which in my calculations ended up being 108cm3. Given that the hole diameter of this is a bit larger than the original (66mm) the length should be around 57.4mm(2.26in). I don't know if I'm even able to cut it to this exact size and I don't trust my calculations at all!

I really don't know what's the best solution here. Maybe someone has constructed the port in metric before?
Re: My 3π adventure [message #95545 is a reply to message #95544] Wed, 20 April 2022 16:15 Go to previous messageGo to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18395
Registered: January 2001
Illuminati (33rd Degree)

I like to use 18mm and 19mm Baltic Birch for some cabinets, so I know what you mean.

For port sizes - length or diameter - consider acceptable tolerance to be +/- 1mm. For cabinet dimensions, tolerance is +/- 1.5mm. As long as you stay within that range, you're fine.

You can use a plastic port if you want. No problem at all. But you can certainly stack wood panels with one planed down to make overall thickness 63.5mm, which as I said, could actually be 62.5mm - 64.5mm.

Stack blocks on the baffle until you exceed 63.5mm, and then plane off the top block until the overall is 63.5mm. Then glue and clamp 'em and drill through that to make the port. I'd probably buy a 2-1/2" hole cutter to drill with, just to make that easy. You can find one online and have it shipped to you.
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