New Speakers
I really enjoyed my first foray into building speakers (the first ones were here, and were an L-C-R for the home theater). So I tried building a new pair.
The home theater speakers are behind the projection screen (the big gray thing in the picture). The speakers definitely lose something behind the screen. Though it is no big deal on movies, for music I wanted speakers outside the screen. I needed something with high WAF (a term very common on audio discussion boards, it stands for wife acceptance factor) but that sounded good. In effect, I needed something relatively small that filled a big room.
These are bipolar speakers, which does not mean they are good at playing Rage Against the Machine albums. It means they have two drivers, usually at 180 degrees from each other. The advantage if well designed can be more full, room-filling sound. These have the second driver mounted on top, rather than in back. The reason for this is that I knew they would be close to the wall, and bipoles with rear-mounted drivers need space I did not have. I built them roughly to this design, though I used MarkAudio Alpair 7.3 drivers instead of those in the design, and I moved the port to the front from the bottom.
These are full range driver speakers. The driver actually runs from about 60-ish Hz to over 20,000 Hz and is pretty dang flat over that range. The advantage of this is we get rid of the electronic crossovers between the woofer, mid, and tweeter. Often the crossover frequencies sit right in the most sensitive range of the ear, as well as in vocal range, such that even small irregularities degrade the sound. Also, the sound is coming from a single point source, which sounds great, and the speaker is more efficient. The downside, of course, is that it is asking a lot of a driver to cover this wide range.
These speakers sound amazing (I will spare you the audio review-speak that sound so eerily similar to wine-snob-speak). You would simply not believe the sound that comes out of these little drivers. The bass is pretty solid too, though I think I will add a subwoofer on the bottom. The bass reinforcement comes from the quarter-wavelength transmission line design, the theory of which is discussed in great depth here. You can find a lot of this sort of design in stores, as the tall thin tower look is aesthetically appealing, and has the fortunate side effect of working well for bass reinforcement (probably the number one role of any cabinet). I spent a lot of time in Mathcad on these. I am starting to reach my goal of eventually building speakers of my own design -- for these I modeled and then modified an existing design.
The boxes are built out of 3/4-inch baltic birch plywood, again with all large saw cutting done by the lumber yard, while I did the rest at home. This is my first experience with veneer, which i in this case is black-dyed ash and it came out great, though I put the satin polyurethane coating on a bit too think and got them a bit glossier than I wanted. They are well braced on the inside and the back is removable to tune them with more or less fiber stuffing -- at first I only had a bit and the bass was too boomy, but adding more along the length of the speaker tightened the bass as well as the mids a bit.
This was a very easy project, much easier than the first speakers I built. As I learned the first time, with router jibs, round holes are actually easier than square ones. If someone is looking for a great starter project, these speakers, with just one driver, would be my choice. Markaudio is a great driver manufacturer, not only because they are making what may be the best full-range drivers out there, but their proprietor spends a ton of time on the boards interacting with the DIY community to find out what they would like to see changed.
Jake:
Coyote, thanks for posting on your home built speakers. I know it's not your usual topic, but being an amateur wood-worker myself, it's fun to see what you've built and how you went about it. My reading list generally runs to political bloggery, and this made a refreshing change for today.
My projects have all been furniture or other wood items, but for my next one, maybe I'll consider making a wooden housing for something with electronics inside. I hadn't thought of that before. Anyway, thanks for sharing, and I very much appreciate your blog!
September 16, 2011, 9:29 amRuss R.:
How on earth do you have time to do this, on top of managing a company, raising a kid, and updating multiple (excellent) blogs?
September 16, 2011, 9:34 amDrTorch:
Agree w/ Russ. You do all this and enjoy your home theater?
My wife has a cousin who works for a speaker manufacturer, I'll send him this entry.
September 16, 2011, 9:55 amRichard:
Very nice work. As a home speaker builder myself, I have a lot of admiration for others like me! Every single one of my audio systems has consisted of home-built amplification and speakers, starting back in the early 70's (at age 12) with a mono 4W 6V6-based amp and puny 5" speaker mounted into a used Westinghouse TV cabinet. Since then, I've progressed through multiple iterations of amplification, tube, transistor and MOSFET, as well as different kinds of speaker tunings (ported, acoustic suspension, horn). My latest is an 8x12-inch subwoofer array (18 Hz @-3dB) with 2500 watts biamped with two smaller satellites at 400 watts. It's in the basement in my theater, and rattles the shingles on the roof when I crank it up!!! I wish I could post pics here, but maybe I'll upload them to flickr or picasa later for your enjoyment!
Keep up the good work.
September 16, 2011, 9:57 amChris:
To knock down the gloss on the finish you can buff it with 0000 steel wool. I do this all the time on furniture projects, it will give a nice satin finish.
September 16, 2011, 10:51 amDoug:
I work on consumer mp3 audio (which some sound snots will claim is an oxymoron) electronics. I have always found it amusing how in the electronics end of things, you bust your butt to get a truly flat response, where a 0.5dB deviation would be considered to be entirely unacceptable. As good as your driver is, from the spec sheet you see that "pretty danged flat" means a peak-to-peak deviation of perhaps 20dB in the audio passband. If the electrical device's frequency response deviation was as large as the transducer's frequency response, the electrical device would be laughed off the market. But show me a speaker system with peak-to-peak deviation of 10dB? Why, it's as pure as pure can get!
The concept behind a loudspeaker hasn't changed in a hundred years. I keep wondering if eventually we'll see a completely different transducer that will convert electrical energy into mechanical energy with far more efficiency and far less distortion. Coyote, perhaps you should consider a flame loudspeaker for your next project: http://tinyurl.com/5wc9b3j Or a plasma speaker: http://tinyurl.com/69hbyb4
September 16, 2011, 2:19 pmScottE:
Coyote learns fast, already abandoned that nasty MDF.
I've been wanting some 7.3s (for open baffle) but hadn't heard any reports on them yet since they first came out. They're trying to keep it a secret I guess.
September 16, 2011, 2:45 pmJeff:
Nice work. I wouldn't expect anything less from you.
Can we hear an audio sample? ;^)
Regards
September 17, 2011, 6:11 ambobby b:
How much power are you running through them?
In a perfect world, would you go higher powered, lower powered, or do you think you're at an optimum point?
September 17, 2011, 1:56 pmcoyote:
1. yes, MDF is a lot easier to machine but the baltic birch really does make for a stiffer cabinet.
September 17, 2011, 4:28 pm2. The drivers are rated for 20W max. The volume is really limited by the excursion on the speaker, which has to be small in this speaker. That is why I think a subwoofer will do wonders and let me go louder with them. Right now I have a 200 wpc amp on them so I am being very careful, though the drivers are wired in series. I want to try my hand at building a small amp (the J-5 classic design, if anyone knows what that is) and I am thinking about biamping the two drivers - I built it with two inputs so it can be biamped.
3. Love the Alpair 7.3 drivers. I really think that right now, these are the best full range drivers out there. Look cool too
coyote:
PS, I will try the 0000 steel wool. I have seen that idea before and will try it (probably on the bottom first, not that I don't trust you)
September 17, 2011, 4:29 pmMark:
You call the one on the right Stepford Boehner, and the one on the left Stepford Pelosi?
September 20, 2011, 8:23 am