Mounting the Drivers and Final Assembly

After 48 hours of dry time (twice that called for on the paint can instructions) for the repainted fascia, we began work on final assembly of the speakers. The steps left to do are as follows:

  • Sand the back of the fascia so they can be glued in place
  • Bundle and cut the straws to length for each port tube
  • Apply the stick-on gasket tape to the Casita woofer openings
  • Cut and stuff the cabinets with the Dacron stuffing
  • Mount the drivers on the fascia
  • Connect up the drivers
  • Secure the fascia to the cabinet

Of course after that we plan to spend some serious time running a break-in period on the speakers before we do any serious listening or perhaps any listening to real audio at all. When we build our first pair of Casitas a few years ago, we definitely heard the speakers change over the first 30 days or so of use in our home theatre application. There was a certain harshness that became much smoother over time. We had always wondered about speaker break-in but no more. It was and is real!

Our plan is to put at least 48 hours of break-in time using the Isotek disc before we listen at all to the speakers. Although I have doubts about some of the claims of this system enhancement disc, from the reviews I have read it provides the fastest speaker break-in signal. We will see if we have the patience to actually follow through with this plan.

Sanding and preparing the Fascia for gluing

Because our ultimate goal is to glue the fascia to the Parts Express cabinets we needed to sand the mating surfaces of the fascia so that the glue will adhere properly. There is a lot of overspray that has found its way onto the surface and we decided to sand them clean with some large-grit sandpaper before continuing with final assembly.

This photo shows one corner of a fascia with the left edge sanded and the right edge showing the overspray.

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After close inspection of the painted fasica, we decided to apply a second layer of glue to the inside of the woofer openings to better seal up things and make a nice smooth surface. We originally put the first coat on during the lamination of the plywood to the MDF layer which can be seen in the first fascia photos. There is also a bit of black overspray which makes the surface a little rougher than before, so this will seal them up again.

This photo shows the Kitty Kat fascia from the back after the second layer of glue is dry.

Click for Hi Res Version

This photo shows the Casita fascia from the back after the second layer of glue is dry.

Click for Hi Res Version

Port Tube Straws

One of the unique features of the North Creek designs is the use of a bundle of drinking straws placed inside the port tube for tuning and turbulence reduction. We did some searching through comments on the internet and other places to obtain a better picture of what is actually happening with the use of straws. The obvious lengthening of the tube when using the straws was easy to comprehend but we wondered about the source of this idea. At the end of the assembly instructions George Short of North Creek Music says the following:

"For those that are curious about the origin of this procedure, to the best of my knowledge it was first discussed in writing by Neville Theile himself. The earliest reference I know of was in an article by Dr. Theile in an ASA journal from the mis '60's, on non-linear port behavior. Which article and year it was precisely [discussed] is now unknown to me. -GS"

We also found this set of comments George Short made on a review of the North Creek Borealis speaker (North Creek Borealis home Page):

"A second area that requires more discussion is our method of port tuning, or "the straws." It would be nice to say that it was invented here, but it was actually discussed first in writing by Dr. Neville Thiele himself, in an ASA journal in the late 1950s. The purpose of the straws in the port tube is to force laminar air flow through the port at high volume levels. Dr. Thiele found this to be more effective that flaring the port's egress, a method used by many manufacturers at the time and recently reinvented. The method we developed of tuning the port - by keeping the port tube length constant while changing the length of the straws in the port - allows the builder to control both the tuning frequency and port Q. This in turn allows the Borealis' low-frequency response to be precisely tuned to the builder's listening room and electronics." (See "Kit Review, Testing the North Creek Borealis Loudspeaker Kit, Joseph D'Apploito, Speaker Builder, July 2000)

The assembly instructions have us use the port tube to hold the straws in place while they are taped and bundled together. The following photo shows the beginning of the process.

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Here is the Kitty Kat straw bundle

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In reviewing the assembly instructions, we found a discrepancy between the original Casita and Kitty Kat instructions and the currently posted Kitty Kat assembly instructions on the length of the straws in the port tube. We decided to cut them to a 3" length and wrap tape two places to hold them in place. If they turn out to not be long enough, we can always make more later.

We found the easiest way to cut the bundle to length was to use a very sharp kitchen knife, usually used to chop vegetables. It sliced neatly through the bundle of straws in just a few strokes, leaving a nice sharp edge on the straws. We applied tape to both ends of the 3" bundle before cutting to keep things aligned.

The following photo shows the straw bundle inside the port tube of the left channel Casaita set to be about 1/2 inch inside the cabinet past the edge of the port tube.

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After installing the straw bundles it was clear that they have a very tight fit and would be difficult to adjust once things were buttoned up. As a result, we wrote to George Short a quick email to ask how he adjusts the straw length and tunes the port. His answer and what we did appears in the next article about port tuning.

Casket Material for Casita Woofers

The SEAS Excel W18NX-001 woofer does not come supplied with a gasket, so it is necessary to apply a adhesive backed foam to the fascia. This material was supplied by North Creek in the Casita kit and is easily applied.

The following shows a Casita fascia with the gasket applied. We started the application at the top pre-drilled hole so that we would have at least one reference point for the screws.

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Kitty Kat Driver Mounting

Our goal for this evening was to get at least the Kitty Kats finished enough to put them on the power amplifier and start the burn-in. As a result we decided to do the stuffing,driver mounting, and fascia attach for the Kitty Kats before we returned to the Casitas. Up until now the Castia and Kitty Kat construction has been done completely in parallel.

Here is a photo of the right channel Kitty Kat with the fascia in place, no drivers, and no Dacron stuffing.

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The Parts express cabinets come with screws in each corner and a blank baffle. The idea is that while experimenting with the box, one can try different ideas and wiring removing the baffle as needed. Then when a final configuration has been decided upon they can be glued in place, and the screws used as a clamp during drying. In addition, the Parts Express cabinets come with a magnetically attached grill that uses the screws as attach points. It turns out that this idea is a good one but has some problems as we will see later on.

Because we knew that port tuning is a very important part of the Kitty Kats matching to a room, especially as they are designed for near-wall use, we were concerned about how to adjust the port straws after final assembly. It seemed best to keep the fascia unglued for this time and as a result we decided to mount the drivers to the fascia first, then connect them up to the cabinets. (This later proved to be the wrong order of assembly)

We mounted the tweeters first, marking where the positive or red terminal was as it is pretty much hidden by the thick fasica. The tweeters come with a gasket in place and therefore can be mounted without special treatment.

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Next we mounted the woofers. Here is a photo of the woofers as delivered as a match pair.

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Click for Hi Res Version

Dacron Stuffing for Kitty Kats

The assembly instructions say to cut the supplied Dacron into six pieces and stuff them into the box with a slit cut for the port tube. We cut a slit into the first two pieces and placed them into the cabinets behind the center brace being careful to route the tweeter wires through the same slit, and secure the other wires between the folds and layers of the Dacron to prevent them vibrating against each other and the cabinet. The final layer goes the front of the cabinet between the fascia and the brace that we added to the Parts Express boxes. We also cut a small slit for the woofer wires to come through so they wouldn't be next to a cabinet side.

The following photo shows a Kitty Kat box with two layers of dacron stuffing applies, with the port tube end exposed.

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The following photo shows the right channel Kitty Kat box with all three layers of Dacron in place.

Click for Hi Res Version

Securing Fascia to Cabinet

We found in earlier driver and crossover testing that the Fast-On terminals on the North modified Scan Speak 8530 woofers were very soft and flexible and bent easily especially with the relatively stiff 12 gauge wire coming from the crossovers. We became worried that this flexing would cause them to break as the connectors were put into place back when we temporarily connected up each driver to test the crossovers and wiring. This proved to be true, as the negative terminal on the left speaker woofer did break off during assembly. With a combination of soldering and a bit of super glue we were able to re-attach the Fast-On terminal but it wasn't easy. As a result of the very difficult repair needed, we decided to do all operations in the future by leaving the fascia in place on the box, and removing or mounting the drivers one at a time. This was probably the best way to do things in the first place, but live and learn.

The North Creek Fascia were designed with the original Part Express boxes in mind. These boxes used a mushroom/socket combination for securing the grill to the box. The North Creek fascia are much thicker than the original fascia and required the holes to be much deeper for the Parts Express supplied screws. Unfortunately, the Parts Express boxes were changed to a magnetic mount style grill attachment after we obtained the North Creek Kits. As a result, the screws are now way too deep for the magnets to connect with so we will have to come up with another way to secure the grill. In addition, the diameter of the screws was slightly larger and we had to drill out the holes in the fascia, both the MDF and Plywood layers so that the screws would still work. Finally after experimentation we were able to secure the fascia with screws. We plan to glue them in permanently later on after break-in and port tuning.

We were originally concerned with a possible interference between the backside magnets of the woofers and the top of the large woofer crossovers in the bottom of the cabinets. Even with our best planning and dry fitting, the woofer magnet just barely clears the top of the crossover capacitor stack. The thickness of the Dacron stuffing is enough that a small amount of interference can be felt. We are concerned enough that we are going to explore working on the crossovers just a bit to reduce their height giving a bit more margin.

Please see the next article in the series Kitty Kats break-in and First Listening Test

Copyright © 2010 David L. Bytheway