# Serious center-channel speaker



## Howard Ferstler (Sep 27, 2007)

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 those new left and right mains.

The new center is built to match those 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 and crossover boards (not yet with the electrical parts installed) 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 of the enclosure, 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 finished speaker, with the grill not installed. The grill itself (not shown here) 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 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.

The speaker, like the other two, has crossover networks mounted on removable boards that are installed into cutouts in the back panels. All slopes are second order, with crossover points at 400 and 3500 Hz. The dual tweeters are Allison/RDL models, the 6.5-inch woofer is also an Allison unit, and the midrange drivers are 3-inch Tang Band cones, with phase plugs. The left and right speakers used 4-inch Tang Band models similarly designed, and with the same Allison tweeters and woofers.

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 low range, from 90 Hz on down to 20 Hz, is handled by the Hsu VTF-3 (MK3) subwoofer shown in the last photo. It is the thing with the big stuffed bear sitting on top of it.

The bear collection belongs to my wife.

Howard Ferstler


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## Geoguy (Feb 22, 2008)

Holy Cow!, Howard. That is awesome. You kinda put me to sleep with the discussion on electronics but the photos are spectacular! I don't read too good so I like books with pictures.

Actually, I'm envious of your knowledge of electronics. And, I had no idea that the wood type could effect sound so much. I don't do electronics but the wood is beautiful. Good job.:thumbsup:


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## TimPa (Jan 27, 2010)

nice howard! what are you driving them with?


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## DerekG (Dec 28, 2009)

It is time for DIY sub. Get a nice 18 or 21" driver in there


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## Howard Ferstler (Sep 27, 2007)

TimPa said:


> nice howard! what are you driving them with?


In this room the satellites are powered by a nice Yamaha DSP-A1 integrated amp. Of course, the Hsu subwoofer has its own amp on board. 

The Yamaha puts out 110 wpc with the three fronts and two side/rear surrounds, with another 35 watts each for the two front "effects" surround channels. The Hsu sub has 350 watts.

The system can play more than loud enough, needless to say, and the amps are as clean sounding as any.

I have another system in my main room that is powered by a Yamaha RX-Z11 receiver. The mains there are Allison IC-20s, with a custom-built center speaker that is basically an oversized version of the one discussed in this thread. The subwoofer in there is a Velodyne F1800. The surrounds are four Allison Model Fours and I think I posted an article on how I refurbished them some time back.

Howard


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## Howard Ferstler (Sep 27, 2007)

DerekG said:


> It is time for DIY sub. Get a nice 18 or 21" driver in there


I have toyed with doing this. I have both a spare Hsu sub driver (same as in the VTF-3 shown in the photo), as well as a spare SVS driver, with both stored in my parts cabinet.

However, that Hsu sub shown in the photo is really pretty good. I have another AV system in another part of the house and it has a Velodyne F1800. It is pretty good, too, with both able to go flat and loud right down to below 20 Hz.

What's more, I have a modified (by me) SVS 16-46 sub, outboard amp, and Hsu optimizer equalizer stashed in a closet as a backup should one of the other subs crash. So, I really do not need any new subs right now.

Still, it would be fun to make one, and I could get the tube parts (for a ported design) and amp from Parts Express. Maybe one of these days.

Howard


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## woodnthings (Jan 24, 2009)

*Howard question*

Years ago I built 2 ported bass reflex cabinets per Electro Voice plans to house a pair of EV 18" woofers. They've been stored in a heated space for about 10 years, Are they good for anything these days of foam voice coils and all. I've been out of the audio world for years.
Resonant frequency was 38 CPS if I recall.
Awesome work on your speaker systems, all this has come a long way from my days! PM me if you prefer. Thanks, bill


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## Howard Ferstler (Sep 27, 2007)

woodnthings said:


> Years ago I built 2 ported bass reflex cabinets per Electro Voice plans to house a pair of EV 18" woofers. They've been stored in a heated space for about 10 years, Are they good for anything these days of foam voice coils and all. I've been out of the audio world for years.
> Resonant frequency was 38 CPS if I recall.
> Awesome work on your speaker systems, all this has come a long way from my days! PM me if you prefer. Thanks, bill


Hi, Bill,

I will answer here, so other interested parties might benefit.

The only way to tell is to haul them out and give them a try. Many, if not most, woofer (and subwoofer) drivers made over the past 30 years used urethane foam surrounds that have a 12 to 15 year usable life span (even in a good environment). Gradually, they will soften and crumble and need replacing. Fortunately, outfits like Simply Speakers (a Google search will locate them) offer kits that a do-it-yourselfer can use to replace the surrounds. The results should be good as new.

If the surrounds are not urethane (say, pleated paper, polypropylene, treated cloth, butyl rubber, etc.) they might last for decades. You can check yours by just touching them with moderate finger pressure. If they are overly soft (or fall apart) then they need replacing.

As for the performance of the better like-new subwoofers, well, again, give your units a try. They might work quite well. However, I will point out that many older woofer (and subwoofer) designs do not go all that deep. Many only go down solidly to 30-40 Hz, with a fast rolloff below that. Ported designs roll off with particular steepness. Today's super subs can get to 20 Hz and below with ease, and pipe-organ and synthesizer freaks will prefer those. Also, many modern DVD movies have solid (and loud) bass down to 25 Hz and even sometimes lower.

Fortunately, 30-40 Hz kind of reach is deep enough for most music, and even most movies, and the big deal then will be if they can do that with adequate volume ouput to satisfy the user. Again, the only way to tell is to run them up and see what happens. 

Howard


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## woodnthings (Jan 24, 2009)

*Thank you Howard*

I'm always amazed by the specific knowledge other than "woodworking" by members here. Audio systems, computers, airplanes, guitars, etc. by all you guys and gals. Thanks for the reply. When they were in use on a concrete slab in my living room they would rattle all the floors in the entire house at moderate volumes. A synthesizer played through them was awesome. That was then, and no comparison today. :no: bill


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