Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

B&W 803-inspired Zaph ZRT Build
B&W 803-inspired Zaph ZRT Build
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 22nd June 2015, 04:08 AM   #1
rulzahl is offline rulzahl  United States
diyAudio Member
 
Join Date: Jan 2015
Talking B&W 803-inspired Zaph ZRT Build

I really like the look of the B&W 803 so I tried imitating their curve with a Zaph ZRT build. This was my first build and I wanted to get something that I (and one day a spouse) will enjoy living with forever. The technique I used to get the curve is different than anything I've seen before and although it ended up being a lot of trial and error, it turned out perfectly.

Side note on the technique-- I think itís a great alternative to the typical approach of bending 1/8th sheets of hardboard/masonite. I dabbled with that approach and failed to get the hardboard sheet to match the tight curve without bowing out in places. Some people get this to work just fine, but if you've had problems there in the past or are working with tight curves, consider trying this method out instead! It probably takes more time but the results are excellent!

The curve is elliptical but results in the same front baffle size and internal volume as the original design. Lots of time with an Excel spreadsheet to come up with the proper curve after finding the base formula for area of a partial ellipse. That was fun and brought me back to the good old days of high school geometry!

B&W 803-inspired Zaph ZRT Build


Once I had the formula for the ellipse, I traced it out on some 3/4" MDF to make a pattern.

B&W 803-inspired Zaph ZRT Build


Cut it out with a bandsaw but left room to do the final shaping with a vertical sander. I didn't get the curve quite perfect but later on I found ways to compensate for that.

B&W 803-inspired Zaph ZRT Build


After I had that one pattern, I rough cut a bunch more. These would be used as the top and bottom caps and also the internal braces. The internal braces were cut with holes in the center for venting. The bottom caps had 4x6" holes cut in them to allow easy placement for the crossover later one. Once I had all these pieces rough cut, I used a router with a flush bit to get these pieces to match the pattern perfectly. Well, matching the outside of the pattern, at least. The insides were left umÖ artistically freehanded. It didn't really matter because they'd never be seen.

B&W 803-inspired Zaph ZRT Build

B&W 803-inspired Zaph ZRT Build


Now that I had these pieces, I cut out the front baffles. The left and right edges of the baffle were cut at an angle inwards. You'll see why soon. I also cut out the holes for the drivers and port. Mainly because this was the last chance I'd have to round off the inner edge of the woofer hole, as recommended in the ZRT design. While I was rounding off edges, I decided to round off the inner edges of the braces as well. My hope was to ensure smooth airflow inside the tower and reduce internal edge diffraction but I'm not actually sure if it does much.

I assembled the baffle and braces with some wood glue and used a combination square to make sure the braces were perpendicular to the baffle. Some scrap wood was enlisted to hold things in place until the glue set.

B&W 803-inspired Zaph ZRT Build


While that was drying, I cut out a bunch of 1/2" by 42" pieces of MDF. The MDF happened to be 1/2" thick instead of 3/4" because that's what I had available. The concept was to glue these sticks to the curved brace like slats on a fence.

B&W 803-inspired Zaph ZRT Build


Once the baffle and brace set-up was ready to handle, I started gluing these pieces down. I also used a micropinner to secure things. One tip here is to make sure the strips are butted up securely against each other. Due to the curve, there were v-shaped gaps between the strips-- you can see that if you look picture above. I planned to fill these gaps with Bondo but worried about that being too thick to get into the deepest parts of the V. So I poured wood glue in and worked out the bubbles with a thin piece of wood. A bit unorthodox but oh well. I think about 3/4 of a gallon of wood glue went into this step. It took several hours per tower and was probably the single most time-consuming step.

B&W 803-inspired Zaph ZRT Build


Once all the strips were in place and the glue had dried, I sanded excess glue off with a random orbital sander and then filled the cracks with Bondo. Itís essentially the same as Minwax wood filler but cheaper. Warning that it does get pretty smelly. I ended up using about a quart for each tower, for those making a supply list.

B&W 803-inspired Zaph ZRT Build


Once it was about halfway cured but still malleable, I scraped off the excess with a putty knife. That saves a lot of sanding time once the stuff has fully hardened. I did some sanding once it was fully hardened.

B&W 803-inspired Zaph ZRT Build


The next step is where I had to do lots of experimenting. The problem was that while the sticks outlined the curve, it was still a little and that would have shown through the veneer. I tried covering it all in 1/8" hardboard/masonite but wasn't able to get it to bend properly. I tried Formica (laminate countertop material) and while it worked for smaller imperfections, it was unable to smooth out the curve in the rear of the speakers. This is where the curve was its tightest and the V's between the sticks were the biggest.


What ended up working great was 1/8" wiggle wood (aka bendable plywood or wacky wood). I cut it about an inch longer than needed in both directions. Then, I got it damp and scraped Gorilla Glue on it with a wide putty knife. After laying the sheet down on the top of the cabinet with the help of a friend, we fastened it with mover's wrap. Mover's wrap ended up working much better than tie-down straps because it allowed me to get even pressure across the whole cabinet. The tie-down straps applied uneven pressure where the ratcheting mechanism was and they caused dips and bulges in the wiggle wood.
B&W 803-inspired Zaph ZRT Build


After this, I cut off the material hanging over the edges of the cabinet with a jigsaw. That was just the rough cut and so to get it perfectly flush with the edges, I used a router with a top-bearing flush trim bit. To trim off the material overhanging the top and bottom of the cabinet, I cut out a pattern from MDF in the same curved shape but smaller diameter so it fit "inside" the area that had the overhanging material. Then I set the router bit depth to be exactly the same as the depth of this pattern. This means that when I set the router on the edge of this pattern, the bit just barely touched the surface of the MDF endcap but cut off anything that was sticking up beyond it. Wish I had a picture of that because it's hard to explain. Itís the same basic concept as the jig pictured below. See how the bit would cut anything that sticks up higher than the surface of that oak board -- thus the pegs get shaved off to be perfectly flush with the surrounding wood.
B&W 803-inspired Zaph ZRT Build


In my case, I also needed the top-bearing flush trim bit in order to guide the router along the pattern's curved edge. I cut off the material overhanging the edges of the front baffle in the same way.

So at this point, the shape of the cabinets was perfect. The curve was nice and smooth and any excess material had been trimmed off. I did the countersinking for the driver mounting holes in a similar way to how I cut off the excess material. Just this time, router ran along the inside of the curve and I set the bit to be lower than the wood it rested on, instead of flush. This picture is from a different speaker but illustrates the concept. I also countersunk the 4x6" hole in bottom, since I'd be covering this hole with a plastic plate and wanted it all to be flush with the bottom.

B&W 803-inspired Zaph ZRT Build


The one problem with wiggle wood is that is pretty soft and so in handling the cabinets, I had put some dents in the wood. To prevent further dents, I covered them with countertop laminate which is much tougher of a material.
B&W 803-inspired Zaph ZRT Build

The laminate cuts easily with a router and so I was able to easily get back my driver holes and countersinks using a bottom-bearing flush trim bit.

So finally I was ready for applying the veneer. I chose to use East Indian Rosewood-- it had caught my eye as I was watching a street musician in Pike's Place Market. Her guitar has rosewood sides and it was beautiful. Wish I had seen that before I had bought a big sheet of walnut veneer! The veneer had to be applied using contact cement because the traditional veneer glues don't stick to plastic laminate. The veneer also had to be paper-backed because nothing else works well with contact cement. Unfortunately, I only learned that after my raw rosewood veneer came in. So I had to buy my 3rd round of veneer. Sigh.

I cut the veneer using a razor blade but would recommend buying a veneer knife. The razor blade didn't cut cleanly enough and instead tore out some small splinters from the veneer, resulting in edge blemishes.

For the final finishing step, I sanded to 320 and wiped-on Minwax Fast Drying Polyurethane. Fine Woodworking gave this stuff "Best Value" and it ranked very closely behind the "Best Overall" General Finshes Arm-R-Seal in their review of wiping varnishes. I wet sanded with 400 after the second coat and put on four coats total.

Here's the result:
B&W 803-inspired Zaph ZRT Build

B&W 803-inspired Zaph ZRT Build

B&W 803-inspired Zaph ZRT Build


I'm really happy with the way they turned out visually. They sound amazing too, thanks to John Krutke's brilliant design. I wanted to make sure that this construction technique didn't mess up the sound though. So I built a traditional cabinet and compared it to the curved cabinet with some measurements. I made these using an EMM-6 microphone at 1 meter using Room Equalization Wizard. For some reason my system was not measuring correctly (the response shouldn't be sloped). I tried different software (ARTA) and configurations but kept getting something like this. Even though I can't believe the accuracy of the measurement, the precision and repeatability of the measurements make me comfortable using it for general comparison purposes. Thankfully, it showed no concerning differences between on-axis frequency response of the curved (light blue) vs traditional (light pink) or 45-degree off-axis response of the curved (dark blue) vs traditional (dark red).

B&W 803-inspired Zaph ZRT Build


Later on, I was able to get a correct-looking measurement for on-axis response of the curved speaker. I don't know what changed, except that I had reformatted my machine and put a slightly older version of Room Eq Wizard on there. Too bad I'd already dismantled that traditional cabinet or I would have re-measured it.
B&W 803-inspired Zaph ZRT Build


Anyway, thanks for reading! Hopefully this new construction technique will be useful to somebody!
  Reply With Quote
Old 22nd June 2015, 06:37 AM   #2
diyaudnut is offline diyaudnut  United States
diyAudio Member
 
Join Date: Feb 2015
thanks for the detailed description and photos. Great work. Congrats.
  Reply With Quote
Old 22nd June 2015, 08:33 AM   #3
orangeart is offline orangeart  United Kingdom
diyAudio Member
 
Join Date: Jul 2010
They turned out real nice. Good vennering job. For future reference these curved designs are much easier using bendy ply and a vacuum bag. Granted you've got to build a vacuum system in the first place but then you are ready to go quickly when you make the next speaker.

Stefan
  Reply With Quote
Old 22nd June 2015, 08:50 AM   #4
richie00boy is offline richie00boy  United Kingdom
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
B&W 803-inspired Zaph ZRT Build
Thanks for the explanation. End result looks great and I like that east indian rosewood.

How do you find that handheld Makita router? I have been thinking about one to replace my 1/2 inch router which I find unwieldy.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
  Reply With Quote
Old 22nd June 2015, 02:18 PM   #5
Inductor is offline Inductor  Portugal
diyAudio Member
 
Inductor's Avatar
 
Join Date: Feb 2006
Location: Cascais
they look very nice, congratulations. (saved to favorites)
  Reply With Quote
Old 22nd June 2015, 09:36 PM   #6
pop4richard is offline pop4richard  New Zealand
diyAudio Member
 
Join Date: Oct 2009
Location: Wellington, New Zealand
Great job and thanks for all the photos and details. Love the vertical sander for the curved sections.
  Reply With Quote
Old 23rd June 2015, 05:07 AM   #7
rulzahl is offline rulzahl  United States
diyAudio Member
 
Join Date: Jan 2015
Thanks guys! Glad you like them. Certainly a labor of love.

The handheld router is a Bosch Colt Palm-Grip. They are great for light-duty work because you have a hand free to hold the piece. Probably not quite as powerful as your existing two-handed router though.
An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.


RE: vacuum molding. That does sound pretty slick. I started poking around and found something on Joe Woodworker where a guy uses that technique for building harps. Any links where people are using this for speaker cabinets?

Looks like the hard part is building the mold. I found people online using CNC machines to cut curves in foam they use for building airplane wings. Some places offer this as a service-- custom foam cutting.
  Reply With Quote

Reply


B&W 803-inspired Zaph ZRT BuildHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Custom Zaph Audio ZRT 2 way build shizzon Multi-Way 47 9th November 2014 03:50 PM
Zaph ZRT 2-way build td1836 Multi-Way 15 1st November 2014 04:39 PM
Some Ambiguities, Zaph ZRT Creddy Multi-Way 15 15th November 2012 05:14 PM
Zaph ZRT - Help for variation cyberlancer Multi-Way 15 8th October 2012 07:49 AM
Help with first Build (Seas CNO MkII or Zaph ZRT) whimsical Multi-Way 2 6th July 2009 05:40 PM


New To Site? Need Help?

All times are GMT. The time now is 05:52 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki