Evaluation
Description of Process
Midway through Term 1 I decided to change my options and move from ‘Film and Tv’ into ‘Workshop’, lured by the chance to make some functional speakers. At the end of the first lesson Terry suggested making a pair of Electrostatic speakers each to Kenji and I.
I had never heard about electrostatics before, so me and Kenji researched them and found some information about how they worked and the theory behind them. Basically the when a long skinny sheet of aliminium with tonnes of holes in it is stuck in place in front of a speaker, the sound waves travel up the metal sheet and are then evenly dispersed. This results in a clearer, more refined, higher sound quality then what you get with normal speakers. We also found that electrostatic speakers normally retail for a considerable lot for then their normal speaker counterparts.
After finding out all this information it was decided that it was a good idea, and so we started making our speakers – it was also Terry’s (teacher) first attempt at electrostatics.
The first thing I did was decide on the shape for my speaker cabinet. Apparently a box with a rectangular front, and a skinnier rectangular back, with a trapezium shaped top (when looked at from directly above) would give the best sound quality so I did that.
Once I had the basic idea of the shape of my cabinet I needed to work on its dimensions. This was actually relatively easy as I had the actual tweeters and woofers I was going to use present, so I was able to make a trial front template experiment to see what size would best fit the parts. I then cut holes out of the template fore where the woofer, tweeter and port would be going using their actual sizes for this. I ended up with having an oblong shaped front plate 300mm W by 400mm L. Getting the dimensions for the front plate was the important part, the other dimensions were largely personal preferences so it was pretty easy to sort out those – the only condition was that it would need to fit in with the trapezium top view shape.
I drew out my fronts, backs, sides and tops onto a big sheet of 18mm thick MDF. I used a set square and ruler to ensure that the lines I was drawing were straight and able to be parallel and perpendicular to each other when needed. I then cut these shapes out using the band saw to get a vague outline, and then used the belt sander to perfect this. Since my shape was trapezium like, it meant the edges of the side plates needed to be on an angle so they would slot together well with the fronts and backs. I did this angleing by eye, slowing sanding the sides down until they got to an angle which worked. This took me a while as I was using a belt sander which is quite crude, and the angle needed to be pretty precise and correct otherwise I would have to start again.
I then marked out the where the holes should go on the front plate for the tweeter, woofer and port on the front plate and a small hole on the back plate for the input, and used the circular saw to cut these holes out. Then I stuck all my individual plates together to make the framing for the speaker, I glued tops to front, and then sides to that. This left the bit where the back should go a bit irregular so I gave that a quick sand. I used PVA glue and screws to put the plates together bit by bit. Before I could put the back plate on I needed to line the insides of the speaker with carpet underlay to cancel out any unwanted frequencies that could possibly arise, so the sound quality of the speakers would end up being better. I then glued and screwed on the back plates. I then put in a brace from the front to back to stop any flexing of the wood. When drilling the screws I made the screws go in a few mm deeper then the outside of the wood, so there were indents that needed to be filled in with bogger to give my speakers a flat surface to paint on. I then sanded away the excess bogger, and gave my speakers a final sand with 400 grain sandpaper to get them ready to prime.
I then used the spray gun to give my speakers a coat of grey primer. Once it dried it turned out to be a pretty rough grainy sorta job, so I sanded it with some super fine wet 800 grain sandpaper so that it would smoothen it out without taking away too much paint. The surface of my speakers was now super smooth, but there were a lot of indentations which had become a lot more visible due to the paint. They made my speakers look pretty shoddy so I bogged them up and sanded away the excess –with a few difficulties – and then gave my speakers another coat of primer and then sanded it smooth. This meant the next coat of paint would stick and look better. I used black spray paint because it was already loaded in the gun. I gave my speakers two coats of black so they had a nicer finish.
This meant my cabinets were finished so it was time to make the crossovers. These where actually pretty easy, I just designed my circuit on circuit wizard, copied the black and white version of it into freehand, traced along the edges of the circuit, transferred the tracing onto 2D design and then printed it out on PCB board using the CAM machines. My circuit came out pretty good so I went straight onto drilling holes for the wires and components to go into. I stripped and tinned some wires and soldered them onto the appropriate area, and I soldered the components to the right areas. This process took a while, and then I tested out my crossovers and they seemed to be going pretty good, so I put them into my speakers, attaching them to the inside brace. I soldered the woofer, tweeter and input to the crossover wires and fixed them with screws to my cabinet.
I tested out my speakers and one did not work, and the other one sounded pretty bad and would crap out at any heavy bassy bits at a loud volume. I redid the input of the one which did not work and the speaker started working after that but the sound quality still wasn’t good. Terry tuned the ports for me and it improved the sound but there were still some faults.
I took out the woofers and tweeters of the speakers and redid the soldering as the soldering was done not to well before. I so far have tested one of the speakers and there is an improvement. I am hoping there is an improvement in the other speaker too.
Once I get my speakers sorted out I am hoping to cut out the metal needed for the electrostatic and put it on and get my speakers working fully to plan.
I’ve still got quite a bit of work yet to do, but I think I will be able to finish with a bit of extra work.
I put different crossover in and the speakers worked great after that.
I have not yet met the requirement of my brief to produce "a pair of high quality functioning speakers" , as I am still yet to put on the sheet of metal to turn my speakers into electrostatic speakers. However at present the speakers are sounding good, and I will come in to class sometime early on next year to finish them off. I expect cutting the metal and putting it on my speaker will only take a few periods, and then I will have met the requirements of the brief. I have met the other requirements of the brief, to create a functioning crossover and have speakers of an original shape.
Problems Encountered
I had a few problems in building the cabinets for the speakers, but I didn’t have any major ones. My first problem was having my front, side and back plates even and align well. When I cut them out they weren’t all entirely the same length. I overcame this problem by clamping all the plates together and then sanding them together at the same time on the belt sander. This got all the plates to precisely the right length. Another difficulty I encountered was getting the side plates to slot in well as they had to be on an angle. As I mentioned above I had to work out the correct angle by a trial and error process and eventually it worked.
When I put my first coat of primer on, it really highlighted a lot of blemishes and imperfections that were on the speakers. They looked pretty bad and I knew they would only look worse with a fresh coat of paint on them. So I bogged up the gaps and sanded away the excess, then redid the coat of primer. They looked a lot better after that so I was able to continue on.
My next problem was with the painting, Kenji and I had not cleaned the spray gun out properly so the paint ended up drying inside it and blocking it. We had to wait for about a lesson before this was cleaned out.
The tweeters had an extra rectangular shape extruding from them so I had to rasp out the hole for my tweeters to allow for this. It worked well but it created a lot of dust in the speaker which I had to get out later.
The pipe for the ports didn’t fit so we had to get some PVC pipe from a plumbing shop, and that ended up working fine.
When soldering the input plug I soldered the wires onto the 2+ and 2- bits without realizing it was wrong. I had to knock the inputs out4 of my speakers to redo them. I had to use a mallet and a chisel to knock them out.
When I tested my speakers out they sounded real shit, so I had to take them out and see what was wrong with them. The soldering onto the woofers and tweeters looked dodgy, and there were a few loose strands of wire, so I redid the soldering, hoping that a better connections would help with the flow of current through the circuit. This helped a bit and the speakers stopped cutting out at high volume, but the sound quality was still pretty bad and sounded very distorted.
I took the crossover out from the speaker and the tracks were quite faint especially in one of the crossovers. I tested out the multimeter and there was definitely some electricity breaching the tracks. I used the scriber to define the tracks more and now the crossovers seem to be working well. I will test out my speakers next workshop lesson.
