Second pair of SDA-2As

invalid

Looks like it works really good.

Nightfall

I'm never going to Tony's house I guess. Take care of your mold spores problem dude.

xschop

I call dog piss. Happy Friday folks.

Tony M

I had just brought the speakers home. They were like that.

Craig's list purchase. They came from a VERY nice somewhat-newer home. Original owner. Older couple.

But I did have a white mold bloom in the back room many years ago...I cleaned EVERY surface that showed it. That was a traumatic week or more for me!

Then years later, the same thing. It was worse. So I ordered $$$$ mold bombs and liquid mold killer from a pro company. That stuff was amazing! I still have a lot of it left.

After that, I put A/C out there in the back room and haven't seen any more mold for a couple of years now. Humidity sucks sometimes.

I'm trying to clean and seal my house from any air infiltration from my crawlspace by sealing the ductwork-vents that are located against the walls or flat on the floor.

I did that stage and have been working on making my HVAC room more sterile. I'm ALMOST done doing that.

Tony M

Nightfall wrote: »

I'm never going to Tony's house I guess. Take care of your mold spores problem dude.

I'm still a big germaphobe!

I used to be a huge germaphobe. I changed when I decided to regularly eat at a Golden Corral buffet restaurant years ago. Talk about germs...

I still wear a long sleeve shirt to the movie theater.

VSAT88

GOOD LAWD !!!!!!!!! The Fungus is Amoungus !!!!!!!!!!

spongebobsquarepants

I cleaned the cap with windex and a qtip, looks great!

Still sounds bad. I took a video:
https://youtu.be/ZIh1goVnyo4

I pushed the cone out from the inside, and the spider seems securely attached.

I can push the cone up and down without any noise.

Think it's a shifted magnet?

Gardenstater

I'd guess either the Pole Piece has shifted or the voice coil has partially separated from the cone or the spider is cracked. Or Lordy Be maybe all three at the same time??? I'm trying to keep this brief so as not to upset the powers that be or draw any wrath (or slander). I had an experience with one of mine that was found to be a cracked spider near, but not right at, where it joins the cone. I tried a couple times to repair it with some limited success but I was using Gel Super Glue and I may have been better off with that Ayleens Glue. Anyway, it was VERY hard to spot and I had to use a magnifier and a pencil beam light while pushing very hard from the inside, on the cone. I have now retired that driver because I started hearing occasional malfunctions on bass heavy material.

spongebobsquarepants

Yeah, I might roll the dice and buy a few used ones from ebay. There's a lot of them listed at the moment. Hopefully they're not worse than this one.

Gardenstater

Some of the knowledgeable people here are very helpful with guidance on the right ones to *gamble* on and were helpful to me a while ago. I'm shocked at a couple of those, like the one with the bad voice coil (10 Ohms?!) and the one with the damaged cone! I think it is always a good idea to ask the seller questions before the purchase. If they won't even answer or tell you something stupid like they have no way to check, then go elsewhere.

PS: How does the voice coil resistance go up, I mean what sort of failure causes that? Anyone know?

spongebobsquarepants

This 1986 pair (the new sticky ones) has almost no hot glue inside compared to my 1987 pair.
I wonder if thats why they did so poor on the "push test"

spongebobsquarepants

I hate these new cabinets. I'm thinking about making new replica cabinets from 3/4 baltic birch plywood. My friend with a cnc router offered to help. I can't decide if it'll be a lot of work for a worse sounding /looking speaker, or a solid good looking mod.

Gardenstater

You got me curious to do some researching online. My suspicions have so far been confirmed that Baltic Birch is obviously much lighter than MDF, but it is also stiffer and will have a higher frequency panel resonance for a given thickness. I think bracing is key but the resonant frequency may or may not be a problem without damping materials. When they do subwoofers, especially with opposing drivers that cancel out the forces, it is generally good to use BB with bracing, to get the resonant frequency up above and well away from the operating frequencies. I would speculate that two layers of 3/4" MDF *may* just be superior for a large SDA cabinet, keeping internal volume the same.

invalid

spongebobsquarepants wrote: »

Yeah, I might roll the dice and buy a few used ones from ebay. There's a lot of them listed at the moment. Hopefully they're not worse than this one.

I bought some 6510's from eBay a few years ago, they were mint and even the labels had Mathew polk's signature on them.

littlewoodboats

spongebobsquarepants wrote: »

I hate these new cabinets. I'm thinking about making new replica cabinets from 3/4 baltic birch plywood. My friend with a cnc router offered to help. I can't decide if it'll be a lot of work for a worse sounding /looking speaker, or a solid good looking mod.

I did new cabinets for M7 series II using MDF for the sides and HDF for the front and rear. Did most of the work with a 4x8 cnc.

Gardenstater

Where do you get HDF? I had some more thoughts (uh oh!). One other possibility for a modded cabinet that should have reduced amplitude of resonance and be stiffer than the original, while retaining the original cabinet volume AND not requiring veneer work, might be to use Baltic Birch on the outside and MDF on the inside. For the front baffle you could do cutouts for the windows of the MW drivers and Passive Radiator, so as not to restrict air movement to the passive, in the MDF layer. The advantage of the Baltic Birch on the outside is that you could do a combination rabbet/miter joint at all the corners and you wouldn't have to veneer the cabinet and it would look pretty nice stained and oiled. Of course, the outer dimensions would be 1-1/2" larger in each direction, which may be a drawback, in addition to the added weight of the plywood.

Gardenstater

If I ever try this I think I will use a pair of router bits like this, and build the outer box
except for the top and bottom first, clamped tight and glued, then laminate in the inner MDF pieces. The top would be dropped in with the MDF already laminated to it. Bottom could be glued in against preinstalled corner braces with no special joinery necessary.

https://www.eagleamerica.com/product/p16-4044/h

littlewoodboats

Kevin at the cabinet shop added the two sheets MDF and one sheet HDF to his regular order. Your local lumber yard should have it or be able to get it for you.

Gardenstater

littlewoodboats wrote: »

Kevin at the cabinet shop added the two sheets MDF and one sheet HDF to his regular order. Your local lumber yard should have it or be able to get it for you.

Interesting. Do you know what the density in Lb/ft^3 is of that HDF, or what a 4ft x 8 ft panel weighs? I found that standard MDF is about 45lb/ft^3 but I can't find the value of HD stuff.

https://na.arauco.com/en/resources/download/TRUPAN_spec-HighPlusHD

https://www.plywoodcompany.com/MainSite/Store1/Content/SiteContent/1/Home/Item/trupan_mdf.pdf

spongebobsquarepants

Side note: the factory sda-2a cabinets appear to be made of particle board for all panels except the mdf front panel where the drivers are mounted..Perhaps the baltic birch will sound better than the particle board. A/B testing will be fun... if we ever get around to starting... let alone finishing this project.

Back panel where the crossover is mounted:
Various size fibers with voids


Front panel where tweeter is mounted:
Uniform size fibers without voids

invalid

I didn't think any MDF was used on the 2a's, if there was it has a different density than the stuff they consider MDF today.

Gardenstater

invalid wrote: »

I didn't think any MDF was used on the 2a's, if there was it has a different density than the stuff they consider MDF today.

The 2nd link I posted above shows 4 different densities of MDF made under the name Trupan, and one of them they call HD MDF, or High density Medium density fiberboard. Ya can't make this stuff up .

invalid

Gardenstater wrote: »

invalid wrote: »

I didn't think any MDF was used on the 2a's, if there was it has a different density than the stuff they consider MDF today.

The 2nd link I posted above shows 4 different densities of MDF made under the name Trupan, and one of them they call HD MDF, or High density Medium density fiberboard. Ya can't make this stuff up .

I have a foosball table made out of MDF that is very dense, the table weighs in at 350lbs.

littlewoodboats

Gardenstater wrote: »

littlewoodboats wrote: »

Kevin at the cabinet shop added the two sheets MDF and one sheet HDF to his regular order. Your local lumber yard should have it or be able to get it for you.

Interesting. Do you know what the density in Lb/ft^3 is of that HDF, or what a 4ft x 8 ft panel weighs? I found that standard MDF is about 45lb/ft^3 but I can't find the value of HD stuff.

https://na.arauco.com/en/resources/download/TRUPAN_spec-HighPlusHD

https://www.plywoodcompany.com/MainSite/Store1/Content/SiteContent/1/Home/Item/trupan_mdf.pdf

I will have t ask Kevin for the tech documentation. Monitor Series II cabinets left much to be desired so when I bought a pair with damp bottoms it seemed the perfect time to play. I can say the new cabinets are much more substantial than the particle board. I did not do anything special for covering so never considered plywood from a finish point of view. I think it came from Madisound but bought vinyl for the front baffle and the same wood grain stuff Polk used for the sides.

My pair is still painted Matte Black and see no good reason to change other than make them look finished but no one looks. I would never fault those who do but for me Furniture grade Audio is not my cup of tea.

If I was going to build in plywood I would spend the extra bucks for certified marine grade. (no voids, no repairs) Pick the outer shade you like to get your final finish. Cabinet grade plywood is not what it used to be.

xschop

You can experiment with adding Butyl Mat to the surface of the particle board.
We did this to the 10B SDAs and the cabinets had a nice dead thud to them afterwards.
We used inexpensive U-Seal which is 0.060" thick and same polymer as Dynamat. $20 did both speaks.

I'll be picking up more on my next Homie Depot trip....

https://www.homedepot.com/p/USEAL-USA-Band-6-in-Aluminum-Foil-Self-Adhesive-Repair-Tape-8872AF6/202086180

xschop

So which sets is getting the new RDO's?

spongebobsquarepants

@xschop both are going to have RDO for easier AB testing, so I have another pair of un-needed SL-2000s if you have any use for them. I probably would've ordered more tweeter plates if I knew I was buying another pair of speakers.

I'll have to get rid of whichever ones I like less, too much SDA for my 600sf house (bungalow).

I'm trying to learn how to use fusion 360 to save my friend some computer work. I've never used any cad software before, but it seems like a great thing to learn. Beats the hell out of graph paper!

Here's what I've got so far:

xschop

Send them my way, I'll mod them up with new silks.
Your Billet plates are on their way.
I saw a tung oil rubbed birch panel that looked very nice.

If you're going 1" thick for the front baffle. I would radius the back side MW thru holes.

spongebobsquarepants

@xschop What did you come up with for the fillet radius for the tweeter corners? I stuck a penny in there (19mm) and that fit pretty snug, but 19mm looks funny in the drawing.

Also, do you think 1" is necessary for the front baffle? I was thinking of doing all 18mm baltic birch single layer. It's gotta be stronger than that particle board.

xschop

Same radius as SL2000. 18mm would be fine, strength wise, I'm not sure how they would sound compared to the 3/4" MDF however, since the densities are a little different.