Progress update

The (new) second cabinet is now built and waiting the final coat of paint. The first crossover is built and mounted in the first cabinet, which is now in use. The second should be up and running in two weeks.  One mildly interesting anecdote: while I had the speaker on it's back (the crossover is mounted inside the base), one of our cats decided to sit on the tweeter. Light for a cat she may be, but 8lbs crushes a soft dome tweeter. Somewhat mortified, I removed the driver, and then the dome and voice coil from the magnet. From the back I gently pushed the dome back into shape and smoothed out the wrinkles (!) with my thumbnail. (High tech stuff, speaker building). Without much in the way of expectation I remounted the driver and ran some tests. I then ran the same test with an undamaged tweeter of the same make and model. Result? There is really no noticeable difference in the frequency response. So it turns out that you can crush a tweeter's dome and as long as it's dome shaped it seems not to matter.

Setback

Today I realized the second cabinet has to be rebuilt. Painting it before it was finished structurally cause the wood to swell and bow, and go out of true. The baffle, which was not yet in place, was now too wide at the top and bottom and too narrow in the middle. Neither the baffle not the cabinet could be planed into shape any more, and no amount of coercion was going to get the baffle to bed into the cab properly. While I could have simply made a new baffle, the bow on the cabinet walls was such that I decided that it would be easier to start anew. Having dismantled the cabinet with a mallet (most satisfying), and looking forward to another three weeks worth of work, while I know that was the right thing to have done, have to say I'm a little despondent about the setback. The mistake was the result of a false economy in time and money.Live and learn I suppose.

Conception to realization

Conception

Realization

One done

One of the cabinets is finished. Looks better (I think) than the Mk1. Sounds OK through the first order Mk 1 crossover, but measurement and testing begins this afternoon.

Several lessons learned this time. First, don't use a light colored primer under the black spray on the front. The smallest scratch and it shows through. Second, make absolutely sure that joints are sealed. I discovered that the bass cab isn't air tight. The hole must be fairly small but it's enough. Whether this matters much I don't know yet.Another is don't use Duck masking tape to prevent the wood getting painted. It makes a real mess coming off leaving glue and bits of paper all over the wood. I've still got to figure out the painting. The red spray pain has left a fine stippled effect which is not what I wanted.  And I spent some much time sanding and priming and re-sanding and re-priming... 

This design uses two silver flute 8" drivers in parallel for the bass but one is a 4 ohm with a 3mH inductor in series with the driver. The ideas was to give a little boost to the very low (<100Hz) frequencies which these drivers don't handle overly well. We'll see this afternoon whether the idea worked.

Uneven progress

At the weekend, things seemed to be going slowly until I made several breakthroughs; the first was the decision add a base and then to increase the height of the base to allow the crossover to be mounted under the cabinet but not inside. That meant I could finish the wiring and not have to wire the binding post thought the inside of the cab. Aside from the last set of connectors the wiring is now finished. I also decided to glue the baffle in place which mean the mid cab had to be braced and filled from the top; which it was, and the top is now on and glued and the whole things trimmed and planed into shape. Filler was applied to the exposed pieces of particle board and the first unit is ready for sanding and painting. When I get the additional wood needed for the base I'll be able to complete that at which point the unit will be reading for measurement and testing. I'm waiting for the binding posts and terminals but, Fedx permitting, next weekend, I will be mounting the drivers. 

Slow progress

The Phase IV Mk2 is proving much more complicated to build than the Mk1. Partly it's the shape, but what seems to be holding me up is sequencing. I roughed out the top and bottom and these need to be trimmed. I probably need to paint the cabinet (which will be white) before gluing in the baffle (black). I need to make sure that the crossover will fit though the woofer's hole in the baffle which means getting the mounting board for the crossover built, located and then removed again... I am still figuring out details as I go such as how to mount the crossover, how to connect it to the external links in the base that connect to the drivers. I also learned something about quality: the more linked steps there are in a manufacturing process, the more quality matters. Screwing up (for me) is almost inevitable; but it matters more when a large number of antecedent steps are wasted as a result.

Phase IV Mk2 construction underway

After very little thought, I decided to see if I could improve on the Phase IVs. A new cab design was created in Sketchup (which I'm now getting better at using) in fairly short order. Judith was asked for her thoughts on the three variants I generated (each with slightly different baffle widths) and she chose the right one.

A weekend of fairly hard work, and not all of it plain sailing. I built part of a new pair of cabinets (this time I decided to build a pair). I'm not cabinet maker so I'm learning as I go, and almost all is trial and error. On Sunday there was a lot of error. The plate joiner joints between the side panels and the corners weren't at all clean and didn't have any structural strength, something which became very clear when I kicked one of them (to test the gluing, not out of frustration that the join wasn't mating cleanly - honest guv).

I'm going back and forth between the real artifact and Sketchup, updating the drawing as I make small adjustments in the process of building. For example, I added the cabinet bracing to the drawing and found that there may be a problem with the brace hitting the back of the mid range driver. We'll see soon enough. I'm quite pleased with structure in the back half of the cabinet. Now, I need to think about how best to build the fronts.

I ordered the drivers today (two 8" Silver Flutes for the bass @ $36, a 5 1/2" Silver Flute mid $20, and I've got some Vifa D27TG-45 tweeters to use up). I also ordered some ferrofluid in case the poor HF response (6db drop >15kHz) of the D27TG-45s has something to do with the old ferrofluid. I've no idea but it's worth a try. If that doesn't work I'll try replacing the voice coil.

One nice thing though; I was looking at either the Vifa XT25BG60-04 or the XT25TG30-04 as tweeter if I can't the the D27TG-45s to brighten up at the top and the mountings are identical. So if I can't get a pleasing sound from the D27TG-45s, I can swap them for either of the XTs without rebuilding the baffle (which is good because this time they're going to be glued not screwed in place).

The other change I'm anticipating is putting the crossovers inside the cab (a bit radical, I know). The drivers will be here by the weekend (I hope), an incentive to get the cabinets finished.