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Small speakers for surround channels

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Project by ferstler posted 1730 days ago 2101 views 3 times favorited 11 comments Add to Favorites Watch

For years I had a pair of Allison Model Four bookshelf speaker systems hooked up in my smaller AV installation.These had been used as surround speakers and to tell the truth they were simply overkill for that job. Worse, because of their size both the wife and I have occasionally bumped our heads on the things. Great speakers, but out of place in that particular room.

The replacement units that I just completed are far smaller; each about 1/3 the size of a Four. They weigh 13 pounds apiece, and each uses two 4.5-inch midrange drivers on top, facing upward, with genuine Radio Shack tweeters on the angled panels. Actually, they are shaped like miniature Model Fours, although their finish is quite different.

All of the panels are mdf, with the oak-finished ones actually vinyl veneer. Hey, don’t panic, yet, because it cost me about six bucks apiece to build the things! I had the wood on hand (the oak finish stuff was cut from vinyl shelving I had left over when I downsized some equipment racks a while back) and the mdf was left over from the earlier speaker projects. The chokes and capacitors in the crossover network were just sitting in my parts bin, as were polyswitch bistable resistor fuses that protect the drivers from electrical overload. The speaker drivers were left over from projects in the past, too. All I had to purchase was the 5-way binding post cups for the hookups in the rear and the black paint. Even the grill screens were cut from old Allison speaker screens I had on hand. The edges of the units still need a couple of coats of satin black paint to smooth them, but otherwise the finish is done. I’ll do that recoating down the line, but there is no rush. The speakers are essentially finished.

I use an AudioControl RTA to evaluate speakers (both those I used to review for magazine reports and any that I build myself), and I temporarily set the new units up as main speakers in my larger system to check their absolute performance before setting them up as surround speakers in my smaller system. They measure nowhere near as smooth as the Model Fours they are replacing (the Fours have been a kind of reference standard for two-way speakers for years), but for surround-channel duty they are fine, and when I listened to them as a stereo pair as part of my “voicing” work they actually sounded quite good. The angled-panel design, delivering the resulting spaciousness, somewhat offsets the less than perfect curve flatness. Actually, their measured curves were better than some I have run on assorted systems sent to me in the past to review for magazine reports.

While this project was anything but a woodworking challenge, the result was surprisingly workable (and notably low in cost!) and now all I have to do is sell those spare Model Fours. I already have two offers, because they are cult classics. Hey, don’t worry about me shortchanging myself. I have four additional Model Fours in my larger main system in another part of the house doing surround-channel work there. I even did a refurbishing article about them here a while back.

One of the fun challenges with woodworking is using leftover stuff to build useful items on the cheap.

Howard Ferstler





11 comments so far

View a1Jim's profile

a1Jim

112000 posts in 2179 days


#1 posted 1730 days ago

Looks great nice build

-- http://artisticwoodstudio.com Custom furniture

View dmann's profile

dmann

80 posts in 2409 days


#2 posted 1730 days ago

Very nice!

-- David / Durham, NC

View RexMcKinnon's profile

RexMcKinnon

2593 posts in 1797 days


#3 posted 1730 days ago

This upgrade would be perfect for myself. Already favourited.

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

View bunkie's profile

bunkie

411 posts in 1749 days


#4 posted 1730 days ago

Hey, another speaker-builder here on Lumberjocks!

Interesting design, and a victory for recycling and thrift! How do they sound?

-- Altruism is, ultimately, self-serving

View scarpenter002's profile

scarpenter002

466 posts in 2507 days


#5 posted 1730 days ago

Great job.

-- Scott in Texas

View ferstler's profile

ferstler

333 posts in 2122 days


#6 posted 1729 days ago

To Jim: thanks for the complement. My wife is happy to have a smaller speaker that no longer bumps her head. I am now putting the Model Four units these new models replaced (larger, and still terrific performers) up for sale. Anybody interested can get back to me, but the price will be $200 each, plus shipping. The Allison Model Four is the best bookshelf two-way speaker I have ever encountered, but as noted in my review it is simply overkill for this kind of work and I would rather sell them to somebody who would appreciate them than stick them into storage.

To Blaine: the 901 bounces 89% of its sound off of the front wall and has to be pulled out a foot or two for it to work properly. These new speakers I just built (as well as the Allison Model Fours they are replacing) do bounce a lot of sound, since the tweeter side-panels and upward-facing midrange drivers allow this to happen, but not as emphatically as the Bose systems.

To Bunkie: they sound quite good. Nowhere near as smooth measuring as the Allison Model Fours they are replacing, but more than adequate for surround-channel use. The midrange drivers are rather mundane and simply are not flat enough between 800 Hz and 2.5 kHz (the selected crossover point) to be considered world class. The Radio Shack tweeters (canibalized from some R-S minispeakers several years ago) are good up to about 8 kHz, and then roll off smoothly above that point. The rolloff is really no big deal. I have analyzed commercially built speakers for magazine reviews (I was a product reviewer and writer for years) that performed no better (at least above the low-bass range, since these are designed to be used with a subwoofer), but by no means can these units compete with the better designs out there. The drivers are simply not good enough to do that. But, hey, I had them in storage and that saved me money.

To Scott: thanks for the complement.

To Rex: any passable woodworker can build cabinets like this, or better. There are two limitations. First, they need to be able to do the crossover work, and that involves a fair amount of diddling to get things right. Second, they need some kind of decent test gear. I use an AudioControl SA3051 real-time analyzer. However, a decent job can be done with a good test disc (one with discrete tones at 1/3-octave intervals) and a good SPL meter. Radio Shack has those.

To David: thanks for the complement.

View daiku1's profile

daiku1

24 posts in 2401 days


#7 posted 1609 days ago

Hey! It would be great if you could post the plans somewhere for us beginner speaker builders. Looks great!

-- jim

View ferstler's profile

ferstler

333 posts in 2122 days


#8 posted 1606 days ago

Hi, Jim,

The photos and the comments I made should be decent plans as they stand, at least for the woodworking part of the task. Most good woodworkers can make the boxes and cutouts, and I suggest they contact an outfit like Parts Express to find out about, and ultimately order, the required capacitors, chokes, resistors, and binding posts. Some of the stuff I used, namely the barrier strips to do the interior network/driver hookups and the wire, I got at my local Radio Shack. I suppose a schematic would be good, but actually the best way I can think of is to purchase one of the how-to books that are available. Vance Dickason’s “Loudspeaker Design Cookbook” may be the best, and even the Parts Express catalog has a couple of diagrams and specification charts to help people select what they need.

One thing that is required is a good measuring tool. You can go to Radio Shack and get an SPL meter, and in combination with a good test disc (with discrete tones) you can get into the ball park when it comes to determining how flat and smooth the result is. However, a better way is to get a good 1/3-octave real-time-analyzer (RTA) and use pink noise (most units have a PN generator built in, but some test discs also have such signals) to literally paint a picture of the response of the speaker. Some critics think that the RTA is a rather simplistic measurement tool and prefer something like a “gated” device that uses a computer program to eliminate room reflections and just let the device record the direct output of the speaker. (You can do this with an RTA, too, if you haul the speaker outdoors and measure in that non-reflective environment.) Some independent testing programs can be downloaded to one’s computer, but a microphone input would still be required, and microphones can be pricy, too.

I think that gated devices can be used to evalute individual drivers before installing them in the cabinet, but I am kind of old-fashioned and still prefer using an RTA to measure the full-room output of the completed system. The only problem with an RTA is that even cheap 1/3-octave versions are kind of expensive. Mine is an AudioControl SA-3051 (which comes with its own “dedictated” microphone) and it has a list price of over a grand. (As a product reviewer and writer years ago I was lucky enough to only have to pay a discounted “accommodation” price for my unit.) The 3051’s strong point is that it allows the user to do cumulative measurments while moving the microphone slowly over a given space in the room, with the device coming up with an average. The result is a readout that smooths out hot-spot artifacts and gets the result closer to a true power-response measurement. On the other hand, more reasonably priced models can at least give spot readouts and the careful user can do his own cumulative analysis if he does several of those.

One other item that is nice to have on hand is a good “reference” speaker. I have a pair of Allison IC-20 models in my main AV system, and I continue to believe that model is among the best speaker ever made. (My units are now each 19 years old, and I recently rebuilt the crossover networks and replaced all of the capacitors.) You can then set up a level-matched A/B comparison between your home-built speakers and those reference units and see just how well you did. I did this and was happily satisfied with the results.

One-octave RTAs are also available, but while those can show the relative spectral balance of a speaker for a quick checkout (say, after moving the speakers back into position after cleaning your listening room) the device cannot determine tighter peaks and dips that will still be audible.

Also, even the very best speakers are not perfectly smooth and flat responding, and so I use 1/3-octave equalizers to further flatten the outputs of all three of the front speakers in both of my AV systems. To use an equalizer that way, needless to say, you definitely need an RTA. Doing the work by ear is going to be an exercise in frustration. Also, most lower-priced A/V receivers do not have the back-panel hookups that allow one to insert an equalizer between the preamp and power-amp sections of the receiver. A more upscale model would possibly allow this, however. Both of my processor/receivers are upscale Yamaha models., with my equalizers being now discontinued AudioControl and Rane units.

Doing the job right requires not only woodworking skills, but also requires that the builder have some electronics knowledge and a decent amount of test gear. However, once that threshold has been reached, I believe that an individual can build speakers that match and even surpass typical factory-built systems. I have auditioned and reviewed quite a few of those, and I know of what I speak.

Howard

View bunkie's profile

bunkie

411 posts in 1749 days


#9 posted 1606 days ago

Daiku1,

I know that what Jim described sounds like a lot and while I certainly agree that it’s good to have that equipment when designing speakers, I’d like to suggest that you don’t absolutely need all that to get started. Here’s how:

First, if you go with established designs, you can avoid the design work altogether. Jim mentioned PartsExpress (www.partsexpress.com) which has a library of speaker projects. Another great resource is www.diyaudio.com which is a meeting place for builders of all kinds of projects, not just speakers.

Then there’s the magazine AudioXpress which has been around for quite a few years. There are some truly great speaker designs out there that are available to everyone. Do a google search on the designs of James D’Appolito for a start.

Finally, I would suggest that you check out my transmission-line speakers on my web site (www.audio.thesonicboomers.com). I have plans and a fully-documented construction guide. Unfortunately, the woofers I used are discontinued (one of the great crimes in the world of speakers, they were fabulous) but I can certainly suggest an alternative model.

I got started many decades ago when the test gear was out of reach of everyone and lI earned to depend on my ears. I think I got very good at it. My TLs are outstanding speakers, with detailed, accurate bass that is surprisingly deep, a very smooth and clean midrange and a pretty decent high-end. The other day I was listening to the Telarc recording of Stravinsky’s Firebird and the sound was thrilling; clean, detailed and with an incredible kick on the transients that made me start even though I knew it was coming.

Speaker building is exceptionally satisfying. Once you hear what your music really sounds like, something funny happens: it hits you on an emotional level. And to amplify what Jim said, I believe that even beginners can build speakers that sound far better than what you can get outside of a high-end hifi store.

-- Altruism is, ultimately, self-serving

View ferstler's profile

ferstler

333 posts in 2122 days


#10 posted 1606 days ago

Hi, Bunkie,

Good points. Remember, however, that the posting you are referring to was written by me. I was responding to Jim.

I published a few articles recently in AudioXpress. Actually, two of them were slated to go to The Sensible Sound, but the magazine folded before that could happen. (I had already published dozens of articles in TSS over the years.) I did do one article specifically for AudioXpress, however.

The magazine does have some good how-too pieces, but it also has had some rather tweakish essays published in it in the past, and that is one reason (other than just being tired of the journalism grind) that I opted out of writing for the magazine any more.

The ears are fine, and that is what needs to be satisfied. However, I have yet to find anybody who can, from scratch, voice and tune a crossover network and speaker package by ear. The ear may eventually validate the results, but using the ear to hunt for dips and peaks in the response of a speaker, and then flatten them out by adjusting resistance and reactance values in the network would be a maddening enterprise.

Howard

View bunkie's profile

bunkie

411 posts in 1749 days


#11 posted 1605 days ago

Howard and Jim,

Sorry about getting your names mixed up…

Howard, I’ll look for your byline. I’ve been a subscriber since day one. I agree that, at times, the magazine has a weird viewpoint. A few years back they ran a series by Charles Hansen on updating a Scott 299 amp. It created something of a firestorm in the Scott community (I used to work for H.H. Scott).

Having said that, there’s no other publication that covers the same subject material.

-- Altruism is, ultimately, self-serving

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