This time, I'd do it right. I decided to build a "Picolino 2" from the german "Hobby Hifi" magazine, to replace the E 90 Northridge from JBL, which I never liked to be very honest. I'd have to give it a try.
Sadly, I don't have a picture of these little speakers anymore, however, a search on Google images gives you a pretty good idea what they were and how they looked like (here).
Shortly afterwards I decided I'd try to build a pair of my own (with some more elements that two caps). I continued reading the "Hobby Hifi" a lot, and there were some interesting models, but none that would really impress me. I was looking for a sort of transmission line, maybe a bit bigger, but not too large, and mixed with a tweeter perhaps. I wasn't sure if to take a full range chassis (from Fostex, for instance) or a woofer. What I was sure about, they'd have to be towers, and the sound source should be concentrated on top, around 1 meter high.
After serious searching and some monetary considerations, I chose:
- A tweeter: Audaphon TWS 30/4 (Datasheet here)
| Audaphon Frequency Response |
- A midwoofer: Peerless HDS Exclusive 6.5" Midwoofer (Datasheet here, english). As it turned out in the end, I didn't use this midwoofer after all.
I chose those models because they have a decent frequency response. The tweeter has an overall higher efficiency than the woofer, but that can be overcome adding a resistor in series.
The speaker would have two spaces inside, one for the tweeter, where I didn't regard volume as an issue, and the second a transmission line for the midwoofer.
I remember reading somewhere, I just can't recall where exactly, that if the resonance frequency of the speaker is Fs, the length of the transmission line should be λs/4, where λs = c/Fs and c: Speed of sound in the air (approx. 343 m/s). It's a rule of thumb. The Peerless has an Fs of 41.9 Hz, that results in a transmission line of 2.04 meters. Mind you, transmission lines are a very tricky business, according to what I read. I went on with the project on a gut feeling more than anything else, knowing that I could get a pair of real crap expensive speakers! But hey, no risk no fun!
Then I had to fit the 2 metres inside the speaker. I settled on something like you see below (the thickness of the wood is 18 mm):
While researching speakers on the website / shop where I would eventually buy them, i noticed that Peerless offered a similar (if not almost equal) midrange woofer for the same price, with the same measures, and the same name:
- Peerless E 6-33/08 (HDS Exclusive 180, Datasheet here). This is the one I chose in the end.
Now the
crossover. The cutoff frequency would go at about 1 KHz, and the tweeter
output had to be reduced to about 5 or 6 dB. Eventually I settled down
after some Excel-sheet like calculations for the following design. At
least on paper they made a very good impression, the sum of both
filtered sound pressure levels looked quite linear. (Red: Midwoofer, Green: Tweeter, Blue: Expected result after crossover)
A note of
some importance, I guess. I made the calculations using a 2.2 Ohm series
resistor, that looked good on paper. When I made a test on and
unfinished speaker (box ready, lack of paint) I found the highs a bit
too high. After I changed to a 3.3 Ohm series resistor I was happy with
the overall sound. What you see here is the actual built crossover.
| Expected Frequency Response (Theory) |
Now the fun
part! I went to the local hardware store in Bremen (well, there are a
few) and bought following pieces of wood according to the design above:
| Qty. | Length(cm) | Width(cm) |
| 4 | 36 | 22 |
| 2 | 32,4 | 22 |
| 4 | 22,5 | 22 |
| 4 | 55,4 | 22 |
| 4 | 109 | 36 |
| 2 | 105,4 | 22 |
| 2 | 95,3 | 22 |
In my garage all this wood looked like this:
As you can
appreciate, I took this picture when some of the parts were glued
together and a hole was made. Just in case, the only power tool I used
was the drill you see on the table, the rest was pure muscle! If you
look at the left end of the table you'll see two planes I got for
rounding the edges.
I used dowels for all connections, corners and walls.
Now, pay attention Double Oh Seven, notice the two chambers. In the larger chamber I glued some polyurethane foam on the walls on the back. Why? I really only want the low frequencies to go through, the rest can stay inside, anything over 100 Hz would only interfere with the frequency response. After I closed the box, I put my ear on the hole where the midwoofer would go, and I didn't hear anything. At all. At least on the opposite direction, nothing was coming through. I'd have to see (hear). Another thing, once the box was closed, I would only be able to remove the damping material on the top, on the front and from behind, in case I needed to.
When I
finished the raw speakers I decided to run a test on the garage. That
was a bad idea. The amp I had in the garage was a test amp, and I had
then still the 2.2 Ohm resistor in series with the tweeter. I wasn't
very happy with the first result. I decided to replace the resistor
(with the 3.3 Ohm) and remove the foam from the top and from behind
(top) of the box, the pieces just behind the midwoofer. And then I'd
see.
After a couple of more days of rounding the edges and varnishing the boxes with a slightly darker tone, the result was this:
What about
the sound? Well, what can I say, after the initial disappointment and a
few hours of running, I noticed they do sound excellent! At the moment
of this writing my family is on vacation, that is, my wife and my girls,
so, I had the chance to crank up some of my all time favourites. The
speakers have been working for about three weeks already, and I'm the
type of guy that has always some music playing. Due to the restricted
size of the living room, I simply cannot put the amp to an all time
high, it's just too much. But at a high level, where normal conversation
would be difficult, the speakers deliver a fantastic sound. I really
like the fact that they reproduce more bass than the previous ones. I
had never noticed, until now, that there is a very very low bass sound
on Pink Floyd's "Marooned" from "The Division Bell". I was also just
watching / listening to the "Pulse" DVD, and it sounds great. Or the new
Beatles editions, "Sgt. Peppers" and "Abbey Road", it was definitively
worth the time and money.
Oh yes sir, I'm very happy with my speakers now!
If you got
this far, I hope you enjoyed reading. If you're tempted to start with
your own speakers, just do it! Some friendly advice: be patient! It took
me all in all about 3 weeks to complete the speakers from the moment I
got the wood. I guess I spent in total around 2 or so months from
planning till completion.
Cheers!
Cheers!
