Core 2-Way - Build Tread

[MrkCrwly]

A while back I decided to construct Paul Carmody's Amiga or a variant. Since the RS180s were no longer available I talked to Paul about a new version with the new non shielded RS180-8 and the popular RS28F. That thread can be viewed here:
http://techtalk.parts-express.com/sh...ighlight=amiga

Paul kindly agreed to give it a try, so I had PE ship him the RS180-8 and the RS28F so he could work his magic. With a pinch of lizard leg and some eye of newt, the Core was born. (I may be wrong about the design methodology but hey I'm just a cabinet builder so what do I know.) Actually 2 versions of the Core are being hatched. One with the RS28F and one with its brother the RS28A. I'm sure Paul will post the designs to his web site as they are finalized.
http://sites.google.com/site/undefinition/diy

I will construct the cabinets with heavy flake quarter sawn white oak veneer with solid oak cap and base. Walnut accent wings will be contructed below the top.
I have already cut the mdf and some parts of the cabinets have been biscuited and glued. I hope to post some progress pics this weekend.

[MrkCrwly]

Attached are my construction drawings. Note that these drawings do not fully follow Pauls original cabinet that was used in the design of the crossovers. See Paul's site for the "official" cabinet design.
http://sites.google.com/site/undefinition/diy-trs-80
http://sites.google.com/site/undefinition/diy/amiga

Core - A101.pdf Core - A102.pdf Core - A103.pdf

[Paul Carmody]

Paul kindly agreed to give it a try, so I had PE ship him the RS180-8 and the RS28F so he could work his magic. With a pinch of lizard leg and some eye of newt, the Core was born. (I may be wrong about the design methodology but hey I'm just a cabinet builder so what do I know.)

Yeah, it's something like that. Sometimes I hold a seance to invoke the spirits of Henry Kloss and Harry F. Olson.

Anyway, the crossovers are all done. I'll post them here. I just wanted to take some off-axis measurements first. Should have those done in the next few days.

[Paul Carmody]

All right, here we go with crossover diagrams, and lots of graphs.

First, here is the crossover diagram for the aluminum version


The crossover for the silk version is exactly the same, except that you omit cap C4 on the tweeter circuit.

Here's the simulated Frequency Response


And the Impedance. Nice n' safe.


And here are some actual measurements. These have a fairly short window, because the floor bounce shows up pretty early otherwise. You can see that there is a dip centered around 3 KHz. This is always going to happen with a tweeter centered on an 8" wide baffle. The dip goes away once you move off-axis a bit.
100cm on-axis.


This is my preferred listening position: speakers pointed straight ahead, me at the center.

[MrkCrwly]

Top ready to biscut to side panel.

Top glued.


Back attached.

Stops for removeable crossover access panel on bottom of rear.

[MrkCrwly]

View of cabinet without front baffle attached.

Window Brace - Baltic Birch

Back of Cabinet

Low Head Cap Screw and Inserts.
So far I am really impressed with how easy it is to install the inserts.

[MrkCrwly]

Here is the bill of materials for both the RS28A and RS28F versions of the Core 2-Way. Please let me know if you see any mistakes. (Paul: I added better descriptions in this version vs what I sent you previously. I will send you an updated xls.) Note: The Cross Over diagram shows C2 as a .11 uf cap. The BOM shows C2 as a .10 cap and this is acceptable.

[james_e5]

Nice, clean work Mark!

Say, where did you purchase those hex head screws and inserts? Those look like they would come in handy!

-j

[MrkCrwly]

Nice, clean work Mark!

Say, where did you purchase those hex head screws and inserts? Those look like they would come in handy!

-j

In a thread about inserts someone here mentioned MSC and the EZ-Lok inserts. My son belongs to a Toyota Land Cruiser club that has an account at MSCDirect and he got them for me. The screws look just like the screws in the RS29 tweets.
http://www1.mscdirect.com/CGI/NNSRIT...PMPXNO=2072123
http://www1.mscdirect.com/CGI/NNSRIT...PMPXNO=8217907

Even better my son bought me the parts from MSC to plumb compressed air in my workship and garage. Now that is a great Xmas present.

[Filius]

I don't claim to know what I'm talking about, at all. But I thought I read somewhere that you don't want any overhanging edges on the baffle. It interferes with the soundwaves or something? I love the cabinet design, sort of a neo-classical look, but I thought those kinds of protrusions on the front of a speaker were a no-no. Am I misinformed?

[MrkCrwly]

I don't claim to know what I'm talking about, at all. But I thought I read somewhere that you don't want any overhanging edges on the baffle. It interferes with the soundwaves or something? I love the cabinet design, sort of a neo-classical look, but I thought those kinds of protrusions on the front of a speaker were a no-no. Am I misinformed?

Yes that is true. Every surface will affect the sound.
I do not claim to be a "speaker" designer and hope I make it clear that I leach off of others (so far it is Curt and Paul) for the guts. I included a disclaimer in one of my early posts: "Note that these drawings do not fully follow Pauls original cabinet that was used in the design of the crossovers. See Paul's site for the "official" cabinet design."
That said I do try and minimize the effects my changes have on the original speaker sound. In this case I only used horizontal elements and I have convinced myself that the top acts as a wave guide.
Of course if I find out that my speakers sound like crap I can easily correct that with a new power cord or silver speaker wire.

[fastbike1]

I don't know Mark, maybe you should just glue one of the Hologram bracelets to the top or write happy thoughts with the magic red pen.

I suspect the esthetic treatments are unlikely to cause audible problems.

Of course if I find out that my speakers sound like crap I can easily correct that with a new power cord or silver speaker wire.

[Filius]

Well anyway, the design is ingenious. I hope to make a feeble attempt at copying it. Have you made any further progress since you last posted pics? I especially want to know your listening impressions. I had almost decided to do the Amigas when I heard about the Cores and now I'm in a quandary.

[MrkCrwly]

I don't know Mark, maybe you should just glue one of the Hologram bracelets to the top or write happy thoughts with the magic red pen.

Good point. I could probably get a "factory refurbished" bracelet on the cheap.

[MrkCrwly]

Well anyway, the design is ingenious. I hope to make a feeble attempt at copying it. Have you made any further progress since you last posted pics? I especially want to know your listening impressions. I had almost decided to do the Amigas when I heard about the Cores and now I'm in a quandary.

Thank you. I have the baffle routed for speakers and just will glue it on as soon as I find some open cell foam to line the walls. The oak caps and base are cut and ready to sand.
Paul Carmody would be better to ask about the sound since he has recently heard the Amigas and designed the Core. The Amiga's tweet costs less so that may be your best bang for the buck. I'm a visual guy and I love the look of the RS28A/F. Not sure there is a wrong or right choice just preferences.
Here is Paul's Core 2 Way design link that may help:
http://sites.google.com/site/undefin...aytonrs180rs28

[MrkCrwly]

Baffle routed for speakers. I will knock out the centers after the laminate is trimmed. I cut the speaker recesses 1/8" shy to allow me to route a little mdf when I trim the veneer. Intent is to minimize the possibility of veneer tearout. Not sure if it is a good idea but I dont see how it would hurt. Picked up some heavy polyester batting at JoAnn's to line the cabinet walls.

[Filius]

The pictures will be a big help once I get started building, so thanks.

By the way, how do you like your Tritrix, soundwise? When you decided to build the Amigas/Cores, was it because of anything lacking in the Tritrix, or just the itch to do another project? I ask because I'm still not 100% decided on what to build, though leaning heavily toward the Amigas with your cab design.

[MrkCrwly]

I love my TriTrix. It is pretty much a dedicated 5.1 home theater setup and I wanted a music system upstairs. I decided on the Core's (Amiga Family) because Paul said they had a "boutique" sound. (I figured anybody that can use french words to describe a speaker must know what he is doing.) Actually my reason for building the Core is I like the tall slender cabinet 2 way look. I was also considering Marty's elegant Coppers.
The TriTrix are an absolute bargain at $120 a pair. Just the other night my wife said that the TriTrix make Glee a must watch program. (OK that is a downside, but you get the point.)
So yes, I just had the itch.

[Filius]

I agree on the look of the tall cabs with the 2-way drivers. I wanted a floorstander this time. Plus the fact that I have built Paul's OSMTMs and love their sound, and he says the Amigas sound similar (but presumably even better).

[MrkCrwly]

Cabinet lined with $13 KMart twin size bed topper foam pad. It is probably better as a speaker liner than a bed topper.

Foam lining at top of cabinet.

View from inside of cabinet without baffle.

Baffle installed with biscuits and glue.

Cold press veneering of removable panel. Trying Titebond II. Put a thin coat on both the veneer and the cabinet using a autobody plastic spreader.