I have a question based on interchanging components.
If I start the build with the base model components (Eminence) and later upgrade to the higher end components (JBL and B&C), will the existing cabinet and crossovers still work?
Will the screw holes for the woofer and mounting location for the compression driver be the same?
Are the resistors and capacitors the same on the crossover board?
And most importantly, will I be able to install the needed upgrades through the existing openings for the woofer and waveguide?
If anyone has gone through an upgrade, I'd love to hear about it!
Wayne Parham Messages: 18783 Registered: January 2001
Illuminati (33rd Degree)
The woofer and tweeter are direct replacements, and they can be exchanged through the front of the baffle. The cabinet stays the same.
There are some crossover changes required, but they are inexpensive and pretty easy to do. Some resistor values are different for the DE250 because it has slightly higher voltage sensitivity than the PSD2002. You can see the components used for each option in the "Notes" section of the crossover document.
Here are some of my thoughts about the upgrades available:
Your note at the bottom states that "Measurements were taken at a distance of 10 feet from the baffle and drive voltage was 8.62vrms. This is equivalent to 2.83v/M and 1W/1M values since average impedance is 8Ω."
Interpreting the graph, it looks like the 4 Pi speakers clock in around 98-99 dB/W/1M. This is incredibly efficient!
This should be able to provide ample power to drive these speakers. A quick calculation taking into account 99 dB/W/1M efficient speakers and 60 Watts of Power at 8 feet listening distance in a room with speakers positioned ~2 ft from the walls gives a an estimated SPL of 115 dB. This is more than enough.
Wayne Parham Messages: 18783 Registered: January 2001
Illuminati (33rd Degree)
If you search here for "flanking sub crossover" you'll find lots of threads where we discuss different crossovers and amps. Some are plate amps and some are separate crossovers and amps. But the truth is, you're right, that most plate amps offer only a fourth-order slope.
One of the exceptions is miniDSP. Not only do they provide stand-alone crossovers but they also offer plate amps. So that makes it really easy - just set it for "100Hz BW2" and you're done. Naturally, the subs need 10dB more gain than the mains too, which can be done either by attenuating the mains or boosting the subs.
Don't make 'em loud enough that you can hear them distinctly - They should be very subtle. You should be able to turn on or off the subs and notice very little difference except for more bass extension. The lower midrange will be smoother too, but that's subtle. So basically, the SPL should be set so the subs aren't noticeable. Each side becomes like a three-way speaker that sounds like a single seamless sound source.
Wayne Parham Messages: 18783 Registered: January 2001
Illuminati (33rd Degree)
Awesome news you got your JBLs! But Rusty's right - Do check the quality of the wood. Lowe's is an excellent retailer, but the ones in Tulsa and Northwest Arkansas definitely do not carry Baltic Birch or even a good grade of MDF. They provide sheets of stuff that's probably good for some kinds of home projects and other similar structures like sheds, shops and garages. But it isn't suitable for loudspeaker enclosures.
Your local Lowe's might be different, but I doubt it. You can easily identify true Baltic Birch - It is sold in metric values of thickness, like 18mm. That's 0.7" which is pretty close to 3/4" and it will have 13 plys. What you'll probably find at Lowe's will be plywoods with much fewer plys than that, like 5. That's the sure indicator it's not Baltic Birch. Another way to tell is it's usually sold in 1.525M square sheets, which is 5' x 5'. It will also usually have a Cyrillic letter on it. Seems like all the sheets I've bought had an "F" (which looks like "ф") on the face somewhere.
Thank you Wayne and Rusty for the sound advice (pun intended). Unfortunately, I did purchase 3 sheets of 8x4' birch. It's good stuff but definitely not Baltic Birch or Russian Birch.
I did locate a high end lumber yard in Pittsburgh and I'll be picking up a few sheets of the good stuff. In other news, I'll be building a work bench, a couple new boxes to house my vinyl records, and a step stool for my son.
I most certainly have a use for this wood. I'll be practicing my dado and rabbet cuts and gluing. That way when I start formal construction, it won't be my first time on a table saw.
Rusty Messages: 1184 Registered: May 2018 Location: Kansas City Missouri
Illuminati (3rd Degree)
Good idea. Hone your skills on some other projects before you crack your knuckles and go for the big pay off project. That birch ply will make some attractive record storage and work bench. Did you buy a table saw? Only ask because you mentioned circular saw initially.
I got a small job site table saw which I'll use for small cuts, rabbets, and dados.
The table saw is too small to make long rips, so I got a corded circular saw. I bought finishing blades for each. I also picked up a router and I'm looking into circle jigs for recessed cut outs.
The project was a success and I have a laundry list of lessons learned:
Use the correct glue
Make your enclosure absolutely air tight
How to solder
How to read wiring diagrams
How to bondo
How to spray paint
How to sand 220grit through 1200 grit
How to polish
Dialing in the amplifier settings
General trouble shooting
The blast box was a great learning experience but it has me craving more. So here I am.
.... Actually I was thinking about building a pair of 1Pi speakers with a subwoofer and having a lithium battery back and 2.1 bluetooth amplifier (50W x 50W x 100 W) for an even better bluetooth (semi-mobile) speaker.
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