Sparsness revealed

Listening to Pat Metheny "Bright Size Life" I realize for the first time how sparsely 'populated' it is. Having never looked closely at the sleeve (I listened to it mostly - but not exclusively - in the car for some reason) I see now that it's a trio! Of course having Jaco Pastorius on bass helps give the illusion of many more people, but even so...   

So why does this matter? Well, that I noticed I think suggests that the MkIIs are reveling much more detail than the DM6s. When you're listening for differences it's not hard to imagine ones that sometimes aren't really there. But this time I wasn't; I just put on the disk for something to listen to and the instrument separation leapt off the page. They may not be perfect but they're good enough to keep.

One month on..

A month of living with the Mk IIs and I'm not disappointed. They're not as clear as perhaps they could be, and spatial separation doesn't leap of the page, but they do reveal more detail than the DM6s. This may be a function of reflection in a small room. Of course, you might rightly suggest that a pair of 40 year old loudspeakers is hardly the best benchmark. Not only is physical deterioration potentially a problem, but technology and design have moved on since the 1970s.

That being said, it's all I've got (other than a pair of Kef bookshelf speakers I bought in 1990 - which I don't know I can find anyway). So I'm going to use the staircase approach. The Mk IIs are better than the B&W. The Phase V should, if I get things right, be better than the Mk IIs.

Of course, I'm not entirely sure what happens when the next design is worse than it's predecessor. However, using better drivers (I have already bought the AC 250F1s for the woofers) in the Phase V should reduce the likelihood of that happening.    

Phase IV complete

Sunday evening. The painting is finished, the cabinets polished. All that remains is mounting the drivers: Which was going fine until the last unit, which was taken from the original Mk 1 prototype (left rear, white cab). These drivers were 6 months or so older than the ones in the Mk 2s (red) and turns out weren't exactly the same size. They were significantly (about 1 mm) larger in diameter, which meant the openings in the baffle had to be re-routed. Without anything in the middle to locate the router this is a bit of a problem. Silver Flute has a long way to go in terms of manufacturing consistency.

However, 6am Monday morning, before it got too hot, I cut a plug to go into the baffle opening and re-routed the hole. By 8:30 they were finally finished.

Both were tested. The graph below shows the two Phase IV units (one black, one red) and one of my old DM6s (blue). I was (am) concerned about one of the Phase IVs having a 9dB drop around 162 Hz but then THe DM6 has a drop of 14dB @ 248 so the problem isn't quite as horrible as I first thought. Still it's not great; and worse yet I don't know what's causing it. I thought for a moment it was a polarity problem between the woofers and the mid-range but reversing the woofers polarity made things worse so that wasn't it. Most likely it's a feature of the cabinet which is a bit of a shame since at this stage I don't really know what I can do.

However they sound very different in the mid and upper mids from the B&Ws. I think they resolve a lot more detail but I'm so accustomed to the B&W sound - rather warm and soft like an old pillow - that the Phase IVs will take a little getting used to.

Finally, I'd like to thank Mark Zachmann for creating Speaker Workshop which has been an invaluable tool.

This will be the last post for a while. I have a three more projects lined up (replacing the B&W crossovers, building a smaller version of the Phase IV with only one 4ohm woofer, the then the Phase Vs for which the design work is done). But for the moment I'm going to spend some time getting used to the Phase IV Mk2s. 

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.