Building C830 Center Channel to match Boston Acoustics T830, T930, T1030

[tvdantv]

History:
I own a T830 pair that I purchased in the mid 90's. I've had them in 4 different homes and at least 6 different rooms. I originally drove them w/ a Yamaha RX-300 receiver, then later w/ an Adcom GFA-535, and now currently w/ an Adcom GFA-2535 as LR of a HT.

I have always loved their reproduction of mid-bass up thru highs, but they lack low extension. I resolved this by adding an M&K MX-200 to the HT a few years ago and crossing them over at 80 Hz. In an effort to build out the HT, I tried a Velodyne CHT Front Row center channel for a while. And although the tweeter was close to the CFT 3, it was not the same. I eventually replaced the Velodyne w/ a CenterSat7 and have been using it for about 3 years.

Current State of my HT:
L/R are Boston T830, Center is Boston CenterSat7, Surrounds are Velodyne CHT Front Row satellites, Subwoofer is M&K MX-200. Receiver is Marantz SR4300 (used as pre/pro, and amp for surrounds). Amplifier is Adcom GFA-2535 in three channel config to drive L/R/C.

Issue:
I’m not happy w/ the CenterSat7 for a few reasons. First and foremost, the mids do not match the mids of the T830. There is no smooth transition across the sound stage. It does not present any portion of midrange (majority of vocal information) as well as the T830. Secondly (and I know that I’m being picky) design philosophies of early Boston products were completely abandoned. The enclosure is constructed of plastic, the grill not acoustically transparent, and it is bass reflex via passive radiator.

Project:
Build a C830 using drivers, cross-over and binding posts from a T830. The new enclosure needs to fit on my TV stand below the TV and not block any IR remote sensors. It will be made of MDF w/ finish to be determined. Original grill will be used, if possible, to cover the woofer. I will attempt to keep the vertical alignment of the drivers. The enclosure will most likely take the shape of a short inverted T with the mid and tweeter mounted to a ‘sail’ sticking up from a woofer cabinet. The woofer cabinet will be taller in front than in the rear to accommodate the 8” woofer, but still fit between the bottom and middle shelves. It will be braced internally in the same manner as the T830.

To date I have acquired a ‘donor’ pair of T830’s, ordered replacement surrounds for the woofers, and reviewed a pencil sketch w/ a carpenter friend who will help w/ the cabinet construction.
Photos, trials and tribulations to follow. I’d love any advice that veteran cabinet builders have to offer, especially when it comes to center channels. Has anyone else cared enough to undertake such a task?

[sreten]

Hi,

There are some subtleties to centre and L+R matching often ignored.

Look at : Zaph|Audio - ZA5 Speaker Designs with ZA14W08 woofer and Vifa DQ25SC16-04 tweeter
and Zaph|Audio - ZDT3.5

Zaph is a mine of useful information.

rgds, sreten.

[tvdantv]

Donor speakers picked up off of Craigslist. The seller delivered w/in 15 min of my house and was as happy to get rid of them as I was to get them.
All drivers, w/ the exception of the woofer needing new surrounds, are perfect. One cabinet has been gutted. Removing the crossover w/o damaging the fiberboard proved extremely difficult.

New surrounds are in the shop. I decided to go w/ the kit from Midwest Speaker Repair that includes shims for the voice coil. This will be my second time re-foaming, but first time cutting off the dust cap and shimming. Midwest Speaker Repair - Refoam Kits


Terminal cup for outboard mounting of the mid and tweet arrived.
Amazon.com: Bi-wire Terminal Cup: Electronics


Enclosure design is complete and in CAD. Should have it cut on the CNC router this week.

[David Gatti]

You should get a vacuum cleaner onto that dustcap.

[tvdantv]

"Napkin sketch"

2D CAD to come shortly.

[tvdantv]

Ran into 'fit' troubles. CNC router was off by 1/32" on all cuts. This made each hole for the drivers and terminal cups 1/16" too small. My carpenter friend is guessing that the CNC bit is either worn, or was just sharpened. Also, the I did not account for the width of the woofer's mounting lip. The woofer's hole needs to move up 1/4" so that the lip does not overhang the bottom of the enclosure.

I can work it out for the terminal cups as they are plastic and have a ramped edges. A rubber mallet pops them in and out. But the drivers will not go in. The plan is to cut off the face of the box w/ a table saw and build a new face.

[tvdantv]

Pics of components (have not installed new surround or dust cap yet) and the first attempt at the enclosure. Face will be re-cut this week w/ larger holes and 1/4" additional space below the woofer.

Fit in the TV stand is perfect.

[tvdantv]

Fit test on the new face. Much better.

[tvdantv]

Donor and patient, front w/ finished woofer (midwest speaker repair kit worked great), rear of unit.

Finish will be applied later in the summer.

[tvdantv]

In place and RX re-calibrated. The Center sees the bridged side of an Adcom GFA-2535.

Adcom GFA-2535

I'm extremely happy w/ the results. It will be very difficult to go back to the the CenterSat7 later in the summer so that I can dismantle the C830 to apply a finish. I'm going to apply a black lacquer that will require multiple coats and may take up to a month to complete.