Saturday, October 20, 2012

Speaker wire comparison

Our group is to hold a meeting where we will do blind comparisons between different materials and typologies of speaker wire. See the following link.

I have had trouble finding 64 feet of barbed wire without buying a huge roll of the stuff so I have decided to go the DIY route and create my own out of galvanized steel wire. A 100' roll of 17 gauge cost under $3.

The popsicle sticks come from Dollar Tree and a $1 pack is way more than enough. I simply drilled two small holes about three inches apart and then used hot glue to get the popsicle sticks to stay roughly in place. I am just going to leave the wire un-terminated. I don't want the sonic purity of the steel contaminated by gold, silver banana plugs etc. The wire is not insulated except for the popsicle sticks and glue.

I am putting barbs on one set of the cables. This should raise the cables above the floor and we can do a comparison on barbed versus the un-barbed which will lie on the floor.

You don't see too many speaker wires like this.

I haven't tried them yet but I will hook them up prior to the meet and bask in their sonic splendor.

Monday, September 17, 2012

Visiting Swordfishy (aka GregH2)

For those of you who have built a Fetzilla, you might be interested in my visit to Greg (aka Swordfishy and now GregH2) who lives on the outskirts of Brisbane. Greg was one of the main developers of the Fetzilla amplifier.

Greg along with his dogs. All three were very friendly.

Greg's paddock.

The BMW.

The Buick engine that eventually will go into the BMW.

Greg's version of  the Fetzilla.

Listening to Greg's system. The speakers are Yamaha.

Greg's Fetzilla is a little different from the version that we all built with the boards from Hugh. One obvious difference is that he uses a larger value inductor which he reckons produces a more relaxed sound. In addition Greg's power supply is not on the board.

We started off listening to a Dayton class T amp from Parts Express that cost about $100. To be honest, I was not that impressed by it though the bass was good. There was just no 'air' about the instruments and singers. Greg then hooked up his Fetzilla and the improvement was very dramatic. The 'air' was there and the bass was much tighter. I had bought a friend along who is not interested in hifi at all and even he immediately could tell the difference. We could have listened for hours but it was time to go. I can't comment on whether it sounded different to my Fetzilla but if there is one factor in common, it would be that these amps are very easy and very satisfying to listen to.

Before we got into the listening session, Greg took us down to the basement where he had stored his Tesla coil experiment that he built when he was 15. He wound the coil by hand.

Giant transformers.

That is one humongous variac.

We really enjoyed our time at Greg's place. He has a couple of ideas for future amps and hopefully these will come to fruition.

Sunday, May 13, 2012

Full range speaker competition

Our full range loudspeaker competition (May 2012) proved to be very interesting. After all of our discussions about 'helper' speakers to assist at the bass or treble ends, none of the five entries used them. Unfortunately we were not able to use the small meeting room at the library and we had to be in the large (38' x 38') room. I thought there might be problems with small full range speakers generating enough volume, but all were able to play loudly enough.

We did find an interesting room node however. If you stood at one spot, the image of an instrument was between the speakers. Move six inches to the right and the instrument moved into a corner of the room, twenty feet away.

First up were David's Fountek FR88 EX speakers in a half litre cabinet. These were not really designed to be run full range and had a capacitor designed to roll off below 200 hz to protect the small speakers.

Next were Don's Tangband W5-1880 speakers in a 4 litre aperiodic box. Don has wood working skills that I can only begin to dream about.

Steve used Mark Audio Alpair 7s in his MLTL speakers. These were approximately 5 feet tall and were made from 1x8 pine cut to the appropriate lengths. Steve used Martin King's spreadsheets to calculate the dimensions. It was nice looking pine.

Ray used the less expensive Mark Audio CHR-70 Version 3 speakers in what he calls an H frame horn. There is a write up on the construction of these concoctions here.

Our final entry was John's simple open baffles using the GRS 8FR-8 speakers. The cost for both speakers was under $30.

We used David's 813 amp which we also used in the Russian line stage competition last year. It easily drove all the speakers to loud enough volumes. In fact we were asked to turn down the volume by the library staff at one stage.

The emphatic winner and liked by all was Steve's MLTLs. They did everything well. The smaller cabinet speakers did really well on the female voice tracks but suffered from the expected lack of bass on the more complicated tracks. Both sets of speakers were designed to be used with subwoofers and I reckon they would sound very good with the extra bass. By comparison, the MLTLs really provided the foundation that some of the music required though some comments noted that some bass notes were a little boomy. One of our test tracks (some incidental music to William Walton's Henry V - Meridian CDE 84349) sounded pretty awful on the small speakers but much better on the larger speakers. It just shows that not all of the test tracks should be of audiophile quality. 

The horns produced mixed reactions. The treble seemed rolled off compared to the other speakers which suited some tracks, but not others. Some liked the mid range but others were not so keen. The bass is definitely there and is probably the best part of the speaker. It's not boomy. I've been looking at the scoring sheets and somebody described the imaging as 'big'. I would agree with that description and this really helped the orchestral music. I'm biased of course, but I think that the difficult Walton track sounded best on these horns. After listening to them for a few weeks now at home where my seat is just 8 feet from the front of the horns, I would say there is a sense of being in a cave with them when you sit directly in front of them. In my house they sound better when I am not in my usual listening position, but off to one side. To me they sounded much better in the larger room where I could sit well away from them. If I were to experiment more with the design in the future, I would add an upward facing tweeter to provide a more airy top end.

We auditioned the open baffle speakers after we had been asked to turn the volume down so they suffered a little compared to the other speakers. It's a very inexpensive driver and does well in this application with more bass than I expected. However, John was the first to admit that his Visiton B200 speakers sound much better in the same baffle, but their price was above our $200 limit. The GRS mid range did not sound as clear as the other speakers.

Both David and I have built some sand amps as a change of pace. David built a Nelson Pass F5 and I built a Fetzilla which we tried out later in the day after the competition was over. You can see it on the right hand chair. Perhaps we will listen more to these amps at our October meet. My wife and I inherited a cat and I don't feel comfortable having it walk around my tube amps. 

The horns had to be disassembled and we tried an interesting experiment just before we left. Here is Steve holding the horn in front of his MLTL. Some else did the same on the other speaker. We would listen to some music and at the same moment, the horns would be removed so that we could hear the difference, which was dramatic. We all immediately noticed the expected drop in volume. What I did not expect was the sudden collapse in the sound stage and the loss in richness of the midrange. Somebody had commented after the test of the H frame horns that compared to the other speakers, it seemed like the 'Loudness' button was on. I may have to experiment more with these monsters in the future, but since my wife has been more than patient allowing these monsters into our house, the cones were thrown into the dumpster. Nobody wanted to take them home with them. I did keep the drivers however and I plan to use them in a pair of frugel horns.

Our next meet will probably be in the second half of October. We've started to think about our competition for next year and it will probably be an amplifier again. We are thinking that it should be a spud amp (one tube per channel) and the tube needs to have a compactron base.

Saturday, March 31, 2012

H Frame Horn

For our Bottleneck 2012 competition, we decided that we should all build a speaker built around a full range driver. After some discussion we decided that the full range driver could be augmented at the high or low frequencies by a tweeter or woofer. The total cost, including crossover parts if used, would need to be less than $200. Cost of the enclosures was not to be included. The speaker should not just be a copy of an existing design.

I considered doing something along the lines of the Martin King H frame high qts woofer for the low end and some sort of full range speaker for the mid range and highs. However, it gets difficult to stay under $200 because of the cost of the cross over parts, particularly the inductors. I would thoroughly recommend going to the above link and reading about his various projects, particularly the open baffle H frame projects. If you find the open baffle  speakers interesting, you could also read about the Manzanita which is similar but different to the Martin King concepts.

After some thought, I remembered an idea I had wondered about years ago to build back to back horns. There would be no compression chamber as usually found in a horn, but in effect it would be an open baffle H frame but in a horn shape. I downloaded the Mathcad software that Martin uses to model his H frames but the package does not want to load on my small netbook for some reason or other. Still, I decided to proceed to see what happened.

Here is the finished product in all its glory. Essentially a front cone, a back cone and the full range driver mounted on a sheet of 1/2 inch plywood that I had lying around from a failed project.

Each horn is roughly 32 inches in diameter and 16 inches deep.

 The driver recessed into the plywood. It's a Mark Audio CHR-70 Generation 3 which I purchased from Madisound for $36 each. They are nominally 8 ohms, fs 65 hz, qts .55, xmax 4 mm and 85db.

The 1/2 inch plywood is way too thin and should be at least 3/4 inch. The holes surrounding the speaker are used to mount the polycarbonate to which the cones are attached.

Before we go much further, I had certain problems designing the speaker that are non sound related. First, I don't have a van to cart the finished product around. To get it to the competition in my car, I need to be able to disassemble the monster and fit four huge cones into the car. I have two in the back seat, one in the front passenger seat and one in the boot (trunk).

Next the speakers are way too large to sit comfortably in my listening space. Some people might think that they are God awful ugly as well. These were not going to be keepers by any means. In fact, they are disassembled already and hidden away so that guests will not be horrified when they come to our house. I was fortunate that my wife put up with them for a week or more.

Finally, I am not very good at woodwork.

Our house had a leak in the roof and I repaired it by replacing a few shingles. In the process I bought a roll of felt roof stuff for a bit under $20 from Home Depot. It's 36 inches wide and as far as I can make out, you get about 72 feet of the stuff. I had oodles left over from the roof repair so I decided to try this stuff.

Tractix and exponential horns would be out of the question for me to build so I went with simple conical.  After some messing around with some small trial models, I finished up with this pattern. The pie piece taken out is approximately 135 degrees. I cut a small hole in the center so that I can turn it into a cone. I kept this piece as a template and cut out extra cones as I needed them. It helps to have a white pencil to stand out against the black of the felt.

Two more of the ingredients. In the middle is the double sided tape that costs about $5.00. If I were to do this again, it would be cheaper to buy the 37 foot roll for $16 to allow for mistakes. The smaller roll shown here only has 5 foot of tape.

The other component is a piece of polycarbonate (8" x 10" for $4) to which I attach the cone. First I cut a 3 7/8" hole in roughly the middle and drill some smaller holes to mount the polycarbonate (and cone) to the plywood. More about this later.

The double sided tape ready for the cone to be created. It wasn't all that difficult to form the cone and form the overlap. At this stage, the cone is definitely floppy.
The cone is now ready for the treatment. First, I placed it on some scrap pieces of felt to protect the deck. The polycarbonate is weighted down by one of those handy pencil holders that you can buy at Ikea. A bit of weight is needed to make sure the cone retains its shape.

A small level makes sure that the polycarbonate is horizontal.

The final ingredient. Great Stuff expanding foam. In this case I tried Gaps and Cracks for a bit under $4. I had used theWindows and Doors ($6) and noticed that it excellent glueing properties as well as creating a somewhat rigid foam. Having tried both, I think you can probably get as good results with the cheaper version.

Be warned. Read the label before using and wear gloves and eye protection when you use this stuff. If it gets on you then it is very very difficult to get off.

So here is my first attempt. I sprayed first under the polycarbonate to make sure I had plenty of the stuff attaching the polycarbonate to the cone. Then I just kept going around and around until the can ran out. I tried to make sure I got a good amount at the large mouth of the cone. It only takes a few minutes. Unfortunately you need to do all very quickly. If you stop for a few minutes half way the foam stuff clogs in the application tube. I'm sure if you used this foam stuff every day you would get good at getting a steady stream of foam coming out of the application tube. Obviously I don't do this every day and it's all somewhat haphazard. You can tell when you getting close to the end of the can since the volume of foam drops off.

When done, make sure the polycarbonate is still level and then walk away from it for several hours to let it cure. The foam starts to form a surface very quickly but takes about 8 hours to cure completely.

I made sure the cones would fit in the car.

This was my test run with the cheaper foam. The cone was reasonably sturdy and did not flex too much so I created two more cones with the Window and Door foam but after applying the foam I placed about 100 small craft sticks from Dollar Tree into the foam in various patterns to provide more rigidity. For some reason or other, I don't seem to have a close up photo of the process but if you look closely in the first picture at the top of the page, you can see the sticks.

I decided to try a sandwich effect with an inner and outer cone with foam in between. I cut out some small blocks of faom about 1/2 inch thick and attached them to the outside of the inner cone with the double sided tape.

Then I drilled some 1/4 inch holes about half way up the outer cone. The foam applicater tube is not all that long so the holes would allow me to insert foam into the middle area of the cone.
I then squirted in the foam first at the throat end and then at the mouth. Then into the holes half way up. As you can see, it was a sloppy process and foam leaked all over the place. I then let if overnight to dry.

Inside the sandwich at the mouth. I would have to say this was not entirely successful and I could feel where there were voids in various areas of the sandwich. However, the sandwich cone was stiffer than the single cone version.

The following day, I attached the polycarbonate to the cone with an extra can of foam. When it dried, I just cut out the foam in the 3 7/8" hole in the polycarbonate. With sufficient force you can separate the polycarbonate from the foam but it does take some force. There is no danger of the cone falling off the polycarbonate.

Next I attached the polycarbonate to the plywood with bolts and nuts and connected the speakers. After the recommended 30 hour breakin for the drivers I've been pleasantly surprised by amount of bass coming out of these 4" speakers. I don't have any sophisticated measuring equipment so just used a signal tone generator to see how low it would go. It got down to 30 hz or so but of course the level was way down. Still I was impressed.

The speakers are way too big for my listening area and they sound much better the further I get away from them compared with my usual relatively closeup listening position. I suspect they might sound half way decent in Steve's room at the actual competition.

For a few hours I tried the H frame horns in one channel and just the speaker in the plywood in the other channel. There is definite an increase in sound level in the horn version.

One of the speakers uses two of the single cones and the other speaker uses two of the double (sandwich) cones. To be honest I can't tell the difference between them.

My wife is a quilter and she uses all of the wall surfaces in our house to display her quilts. She had taken down the usual resident of this blank space so that she could mount a Christmas quilt. Seeing that I had an opportunity, I hung up my original full scale test version. She didn't notice it for about 30 minutes but let's just say that the Christmas quilt is now installed in the place of honour.

In the foreground is the left over roll of felt. I could get a dozen or more horns out of what's left of that roll. It was a lot of fun working out how to do this and I probably will get additional ideas later on how to stiffen the horns.
You might have gathered that the cones will be going to the dump after the competition and you would be correct. If I were to keep them, I would keep the single cones and apply more sticks and foam to cover the entire cone. The sandwich idea was ok but too uneven.

 I asked my daughter to review this page to see if it made sense to her. She suggested adding chicken wire to the outside of the cone / foam to see if that improved stiffness. That led me to think about other inexpensive lightweight stiffening methods. Last night I thought of the grate stuff that lies below fluorescent lights. Cut it up into small sections and distribute around the outside into the foam.

I've also started to think about painting the inside of the cone with something like polyurethane to provide a less sound absorbent surface than the felt. I might also try some Minwax wood hardener.

I've since tried the Minwax wood hardener and it is marginally effective, but not too much improvement.

We held the competition which you can read about here. As I suspected, the speakers sounded better sitting further away in a larger room. Opinions were mixed about these speakers. The roll off in the treble was noticeable compared to the other speakers, but in some ways I liked it. I felt these speakers did better than the other entries in the more complex orchestral music. Somebody mentioned that these speakers sounded as if the old 'loudness' button was on. If I were keeping the speakers, I would try adding a tweeter facing upwards between the horns.

Perhaps the most interesting part of the day occurred after I had disassembled the horns. A couple of the guys each held one horn in front of another set of speakers mimicking what I had done but without the backward facing horn. At a signal, the horns were removed quickly and the difference in sound was dramatic. Naturally the volume of sound decreased, but in addition, to my ears, the sound stage became flat and lifeless without the horns. I'm now wondering why.

So the speakers were disassembled and the cones put in a dumpster. My wife is very patient with my hobby, but even I know when enough is enough.

Wednesday, February 8, 2012

December 2004 meet

We met at the Elkton Library.

I think these were Thor speakers.

 Ray's 829B amp working in only one channel.

Doug's line stage.

I seem to remember Randall built this lovely looking amp.

829B amp working. Late in the day it sounded very sweet and airy.

I think this is Mark's chip amp made out of a kettle.

Doug Piccard. He and I got the group started and since he moved out to Detroit we have really missed both his presence and his amps.