Speaker Upgrade Project Begins

This will be the first post about my new speaker project. I saved up enough money to purchase pretty much any high performance speaker system I wanted, however after much research and debate I decided to build my own. I could not turn down the opportunity to learn new things and use my skills to fabricate something with my own two hands. I'm going to divide the project into 4 distinct phases.

Phase I - The Left, Center, Right top cabinets. Top I define as the tweeter and midrange cabinet. These cabinets will be of high sensitivity and cover roughly 80hz to 20Khz without use of a Helmholtz resonator.

Phase II - The midbass system. This system will relieve the tops from somehwhere around 120-200Hz on down to about 40Hz. Final crossovers will be determined during implementation.

Phase III - Surrounds. Timber matched as close as possible to the tops, using the same tweeter. I place lowest priority on the surrounds and may actually complete the subsystem before surrounds?

Phase IV - Subwoofer system. As potent as the dual Acoupower 18" system is, at this point it will be the weak link and will be upgraded with a system capable of more air displacement for the lowest octaves.

My primary focus on this upgrade will be on the left and right channels. The midbass system will ONLY apply to the left and right. The center "top" will be identical to the left and right and extend to 80Hz only, which will satisfy movie playback to the THX standard. Center channel information below 80Hz will be routed to the left and right channels. The system will be modular in nature and a a versatile as I can make it. As Steve Guttenburg recently stated, something like 99% of all the recordings out there are 2 channel. I want to do that REALLY well and the rest is a bonus. I hope you follow my journey!

Acoupower Subwoofer Drivers

I compiled some videos about the subwoofer drivers in my audio system. It is an introduction and comprehensive look at the metal and soft parts which make up an Acoupower driver. You may have seen the introduction posted here before, but this includes videos of the inside of the drivers. A full 20 minutes worth. I'll soon publish a post showing the buildup of my cabinets and other data.

A quick summary of specs on these amazing 18" drivers :

- 6" copper 2 layer voice coil in an underhung configuration.
- Largest neodymium magnet used in any loudspeaker
- 97% of magnetic field lines in the gap
- Entrainment techniques used to eject hot air from the motor
- 5 sqft. of heatsink surrounding the motor
- 18mm of one way throw and still at 100% linearity on the BL curve.
- 39mm of one way peak throw
- 1% odd order distortion with 1KW input power

Subwoofer Location Tests

When I initially installed my Acoupower subwoofers, I placed them in the center, behind the screen and sat the center channel on the top. I knew this probably wasn't optimal for coverage of multiple seating locations, but it was a start. Having two subwoofer cabinets, at least they were mutually coupled and I would not have any phasing issues with the collocation. I decided it was time to move them around and see how the response changes. At the moment I don't have any way to separately adjust the phase or delay of the two independently so I have to strictly rely on physical placement and luck. Before making any changes, I setup my measurement system, a Windows 7 notebook computer with Room EQ Wizard software, my EMU0404 sound interface, and Nady CM100 condenser mic at the main listening position. I also turned off Audyssey MultEQ processing from the Onkyo Pro 885 and disabled the Linkwitz Transform circuit (Marchand Bassis) so I have a native raw room response. I also turned off all the active monitors, so only the subwoofer was being measured.

With the screen removed, here you can see the physical configuration of the LEFT, CENTER, RIGHT channels along with the Acoupower subwoofers in the center. As you can see, there isn't much room to jockey things around. The front wall is 12ft wide, however 2 ft of each corner starts a taper towards the wall due to triangular basstraps in each corner. The only solution was to place the LEFT and RIGHT monitors on top of the subwoofers as they were placed in the corners. This raised the tweeter level a little higher, which really isn't much of a problem, especially for my higher "second row seating".

And here is the new corner loaded configuration. The CENTER channel stand isn't the ideal stand, but it was all I had for the moment. I was also able to rotate the center vertically, keeping the tweeter height the same as the LEFT and RIGHT. I also introduced a bit of toe in on the LEFT and RIGHT channels, another listening experiment I wanted to try.

Now for the measurements...(click to enlarge)  This was taken at the MLP (main listening position) amd shows how both configurations measure without moving the microphone.

Interestingly, the response is all but identical from 15Hz to about 45Hz, with some deviation above that particularly around 90-100hz. Keep in mind, this is with absolutely no equalization at all and no smoothing of the graph. I still get the room gain down low, which works well with the sealed subwoofers and the upper end rolls off because the crossover in the Onkyo 885 is still enabled. I really should have taken multiple position measurements before I began, and again afterwards. I'm going to have to save that for next time and just use my ears for now. I am happy that there weren't any major cancellations or deep notches in the new response. This is probably due to the fact that each subwoofer is still equidistant to the mic and adjacent walls. The fact that the response changed insignificantly under 45 Hz is great news for a future modification I've been thinking of. So what did I learn here? The original center position on the subwoofers seem to be smoother around the crossover frequencies, at least in the main listening position. More tests to come, as well as more changes!