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Serious center-channel speaker

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Project by ferstler posted 1614 days ago 3227 views 8 times favorited 10 comments Add to Favorites Watch

In an earlier article I discussed how I had built the left and right speakers for my smaller home A/V system. The center speaker in that installation, built to match some Dunlavy Cantata left and right speakers used there for a while, was different and not really stylistically compatible with the new left and right mains.

The new center is built to match the new left and right units I built to replace the Cantatas. The top, bottom and sides are select pine and the front and back are mdf. Different woods in a speaker enclosure are a good idea, because it helps to break up resonances inherent in one type of wood. The cabinet is 38 inches high, with a 4-degree backward slope to the front. The width is 7 inches and the depth at the top is also 7, with 9 inches of depth at the bottom.The front is angled back because the midrange and tweeter drivers are arranged in a vertical MTTM array, and that kind of configuration tends to focus the output vertically, helping clarity and detail. You want the “beam” to be aimed at seated ear height; hence the angled front. (The left and right speakers I built earlier are each four feet high, and the MTTM arrays are themselves centered at seated ear height, which means no front-panel sloping was needed.) The horizontal dispersion of the driver array is very wide, however, which is what you want for good sound propagation.

The first picture shows partial assembly, and also shows the woofer and one each of the tweeters and mids, along with the double connector cups that would be mounted on the back.

The second shot shows the front/back clamp up. Interior moldings were first glued into position and then the front and back were glued to them. For both gluing jobs I used PL construction adhesive, because it is thick enough to both glue and also seal any potential air leaks. Large cutouts in the back allow for the two crossover networks: low-pass for the woofer down below, and high and low pass for the tweeters and midranges in the top section. A baffle board separates the upper and lower sections, thereby isolating the open-back midrange drivers from pressures generated by the low-mounted woofer.

The third shot shows the stained, urethaned, and painted cabinet before the drivers and networks were mounted. The cabinet interiors (upper and lower) were filled with echo-damping polyester fill before the components were installed.

The fourth shot shows the two crossover networks after completion: woofer network to the left, tweeter/mid network to the right. They are each mounted on 3/4-inch pine boards that were themselves screwed and glued to masonite pieces. The masonite is slightly oversized in width and length, and drilled out on the edges to allow screws to secure the removable boards to the back panel. Gasket tape insures a good seal. These sections are electrically coupled together in the finished system by long jumpers in the back. Removing the jumpers would allow the system to be biamped. I opted for just a single amp, however. All wiring here is done point to point, because I have an aversion to those printed circuit boards one finds advertised for building circuits like this.

The fifth shot shows the finished speaker, with the grill not installed. The grill itself is made out of thin wood framing, with cloth stretched over it and glued in place, and with velcro tabs for attachment to the cabinet front. I cut the framing sides for the grill assembly out of an old broom handle (using a band saw to quarter the dowel lengthwise), because the hickory wood they are made of is stiffer than the pine used to make typical quarter-round moldings.

The sixth shot shows the new center in place, flanked by the previously built left and right speakers.

All three of these speakers are decently flat responding in terms of room/power output (I use a 1/3-octave RTA to validate this), and they are also electrically equalized for ruler-flat final response. All three have been compared to the Allison IC-20 systems in my main installation and the similarities in performance are remarkable.

The subwoofer shown in the final photo (the sub has a big stuffed bear on it) is a Hsu VTF-3 (MK) that extends the low end of the multi-speaker package down to 20 Hz, flat and smooth.

Howard Ferstler





10 comments so far

View RexMcKinnon's profile

RexMcKinnon

2593 posts in 1792 days


#1 posted 1614 days ago

Cool

-- If all you have is a hammer, everything looks like a nail!

View SignWave's profile

SignWave

135 posts in 1631 days


#2 posted 1614 days ago

Nice to see a vertically aligned array for a center channel speaker, for the reasons you mentioned.

That looks like a nice setup. I’m guessing the MTTM components match the L/R towers? Do you have the surrounds to go with it?

Enjoy!

View Beginningwoodworker's profile

Beginningwoodworker

13337 posts in 2269 days


#3 posted 1614 days ago

Nice speakers.

-- CJIII Future cabinetmaker

View Maveric777's profile

Maveric777

2687 posts in 1673 days


#4 posted 1614 days ago

Sweet!

-- Dan ~ Texarkana, Tx.

View oldskoolmodder's profile

oldskoolmodder

760 posts in 2276 days


#5 posted 1614 days ago

I used to be into the a/v thing back in the 80’s even built a replica set of speakers modeled after a set of $1000 speakers. The crossovers were the hardest part and I gave up making them after that set was done. This is a nice compliment to the existing set.

-- Respect your shop tools and they will respect you - Ric

View ferstler's profile

ferstler

333 posts in 2116 days


#6 posted 1614 days ago

Hello, SignWave,

The left and right speaker-driver arrays are close in terms of design to that of the new center. The tweeters and woofers are the same, but instead of three-inch Tang Band midrange drivers the left and right units use four inchers. I woiuld have used four inchers in the center, too, but the company discontinued them. The only disadvantage to using the three inchers is that they will not play as loud down to as low a frequency cutoff point as the four inchers.

The solution was to cross the smaller mids in the center system to the woofer at 400 Hz, instead of the 300 Hz I used with the left and right speaker mids. The mid to tweeter crossover point is 3500 Hz with all three systems.

The surrounds are quite different. There are four of them (my Yamaha integrated amp can drive four surrounds, as well as three up-front systems), with the ones in the left and right front corners (Yamaha calls those “effects” channels) basic tweeter over, midrange under jobs like those commonly found all over the audio world. (The tweeters are Allison units, with Radio Shack mid/woofers.) The side/rear surrounds are unusual, in that they have two four-inch mid/woofer drivers aimed upward, with two tweeters mounted on side-angled panels. The idea there is to have the surround output spread out as much as possible. An earlier article on this site by me outlines the construction of the surrounds, with photos included.

Note that this is my “small” AV system. I have one in a larger room that is, well, pretty big, and I built the center speaker for that one in the same style as the smaller one, but with larger midrange and woofer drivers. I did an article here a while back showing how I refurbished the Allison Model four speakers used for the surround channels in that system.

Thanks to the rest of you for the complements.

Howard

View Mathew Nedeljko's profile

Mathew Nedeljko

583 posts in 2426 days


#7 posted 1613 days ago

Hello Howard… I seriously contemplated building new front and center channel speakers for my recently completed basement home theater, but then I found out about HSU speakers and decided to get the HB-1’s for the fronts and the HC-1’s for the center.

Wow, are they loud and crystal clear even at high volumes and there is absolutely no hum or hiss.

Thanks for sharing your build with us. I am still contemplating building the surrounds for my system :)

-- Aim high. Ride easy. Trust God. Neale Donald Walsch

View ferstler's profile

ferstler

333 posts in 2116 days


#8 posted 1612 days ago

Hi, Matthew,

I reviewed the Hsu HB-1 satellites in issue 113 (Aug/Sept, 2007) issue of The Sensible Sound. Decent performers, although they would, like virtually all other speakers, benefit from 1/3-octave EQ to get them closer to ruler flat. (I have never auditioned the HC-1 versions.) Note that even the speakers I built here, as well as the superb Allison IC-20 models in my main system, are all given equalization by me for regular program use. My designs, as well as the IC-20s, are all within +/- 3 dB from 80 Hz on up to 12.5 kHz, unequalized. However, by using equalization I get the tolerances down to +/- 1 dB over the same range.

Hsu is one of the sharpest designers out there, although lately he has been having his smaller subwoofer products and satellites built in China. His VTF and TN series subwoofers would run with the best made by anybody else.

As I mentioned in a previous comment, there is a review on this site describing the surround speakers I built a while back. You might want to give it a lookover.

While I follow well-known design rules with my speaker projects, the bottom performance line for any of them is to haul them into my main room and do a level-matched A/B comparison against the above-mentioned IC-20 units. All do-it-yourselfers need to have some certifiably superb reference speakers on hand to use as final determiners of design and construction success.

Howard

View Millo's profile

Millo

543 posts in 1646 days


#9 posted 1232 days ago

Are the stuffed bears for acoustical treatment (broadband absorption)?

Awesome stuff! I will have to carefully look at your articles later. Thanks

View ferstler's profile

ferstler

333 posts in 2116 days


#10 posted 1231 days ago

The bears belong to my wife, but they probably do have some acoustic benefits. Having all boundaries padded is not a good idea, but having a few absorbing surfaces helps reduce slap echo and other reflective annoyances.

A couple of web sites now have reprints of my The Sensible Sound articles. Amazon actually SELLS copies (with me not getting a sent), but some sources offer them up for free. (Do a Howard Ferstler name search for outlets.) The only problem is that the various diagrams I included in many articles are not reproduced.

I also published two books on audio and home theater, although by now they are so out of date that only a small part of the information they contain (mostly involving speakers, fortunately) is relevant. For example, my final AV book spent pages discussing the 12-inch laserdisc. I also published two books of recording reviews, and one of those may still be in print. I also helped to edit The Encyclopedia of Recorded Sound (second edition) and the Routledge Guide to Music Technology (basically a shrunk-down, technical-article version of The Encyclopedia edition). The Encyclopedia had a list price of something like three-hundred bucks, but the Guide is affordable.

Howard Ferstler

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