It was a cold winter night just before Christmas, a hot fire in the wood stove... lots of power tools, wood and beer with too much snow for anyone to bother you.  Good tunes in the background and no phone or computer.  DECWARE's self-prescription for a badly needed vacation - results pending.

Paul and I have been building a new pair of speakers for ourselves.  You may remember from taking the visual tour of Decware, the Bendi speaker(as it has come to be known)?  

Just thought it would be fun to share some pics of our recreational activities as they happen.  

I'll be adding more pics as things progress over the next few days..

Cheers  ;D

Hey flip those babies over with the speakers on top and they would be perfect!  I wish I lived closer to someone that would help me build speakers, I have to make jigs to hold the other end most of the time.  Takes me as much time making things to take the place of another person than to make the speakers.  I can now cut a piece of MDF by myself with great precission.

Keep us posted Steve, I like this kind of project.  If only I had the room for the Jensen Imperial Horns, that project sure looks a like the Imperial horn, but a little smaller.

TG

Chris,

The only obvious advantage is strength.  MDF has more mass.  I've made these imperials from MDF before.  The weight is lucid.  These are being built from Luan (sp) a form of Redwood.  It can lay outside in the rain for the entire summer and will not warp.  I have gotten so many splinters from this stuff I just quit taking them out.

Terry,

These are the 1956 Imperials, however we have redesigned them to be twice as strong and twice as easy to build.  If you've ever seen the original 1956 plans, they are a joke.

We will be running these with the woofers on top.  I had planned to run coax drivers but I ran into a few things, 1) not very many to choose from, 2) pricey, 3) most have limited low freq. response.   I have decided to go with conventional pro woofers and load a horn with a good 2 inch compression driver.   We already know that this requires a serious horn lense for the compression driver to keep up.  With two 15's in each cabinet it will be even more difficult.

I needed a challenging project while Paul was gone so I decided to build the horn lenses myself.  I've done this before, but they were only 20 inches wide.  This time I'm going to make them bigger




The trick to building these is self-inflicted temporary ignorance of the compound radius angles involved.  Once you reach that state you may begin. (beer helps) Then once you've spent the entire day cutting parts the realization that there are severely complex angles to cut is balanced by the time you've invested and you really have no choice but to press on.



We've got both speakers together now, just working on the cleating and trim.  I'll post some more pics tonight or Friday.

Steve

[quote author=Terry  link=1040842968&amp/0#5 date=1040945554]


Steve,

To me the lighter more porous the wood the lower its resonance, and if it resonates below the usuable frequency of the driver all the better in my opinion.  TG



[/quote]

Terry,  actually the lighter the wood (less mass) the higher its resonance will tend to be.  You could not get a speaker cabinet to resonate below the usable frequency of a woofer unless it was concrete.  Most objectionable panel resonance in speaker cabinets can be found between 140 and 600 cycles.  As we add bracing or increase the panel stiffness (by adding another panel for example) we push the resonance up past this area so that it no longer effects the mid bass and lower mid range of the woofer.

The plans are a joke because they are dimensioned like a puzzle with conflicting measurements and angles that don't jive.  Also it is obvious by looking at the original design that is was intended to be as light as possible.  The joinery is weak, as is the cleating technique.

Terry-  Yes, that's exactly what it is.  Plywood resonance can add objectionable OR pleasing colorations to the sound.  In the case of these Imperials, the bottom and top are double thick, as are the sides of the enclosure area (source of energy).  The horn is intentionally left as a single thickness and supported by large stiffening cleats.  This allows the large rear panel to resonate in a complimentary way.  Not unlike a musical instrument, careful design and control of panel resonance can make or break the signature of a loudspeaker.  It's an esoteric and ambitious way to build speakers making it obvious why so many just go for inertness.  Here is a photo of the rear panel and stiffening members from looking down the horn.

I can hear the "Tim the Toolman" grunts from here...

Just kidding !  Okay back to working on the story!

Cheers,

Steve

The story about a first test listen to one cabinet in mono.

As I mentioned, we couldn't stand the anticipation and even though drivers have been ordered we just wanted to hear something come out this new horn.  We dug around and each of us found a woofer.  One was an old bass musical instrument speaker and the other was more along the lines of a PA driver.

The idea was that we would play the radio through one cabinet while we continued to work on them.  We thought we'd kind of get an idea how these cabinet alterations and improvements effect the bass.  To drive them I simply unhooked a floor monitor that was in the room and replaced it with an Imperial.  The amplifier behind it is a 400 watt Ross - the equivalent of a decent audiophile solid state amp.  

The source was a $70.00 Pioneer tuner with no antenna fed into the mixer behind my drum kit.  I listen to this stupid tuner through the monitors all the time when I work out here and have never once stopped and said, "gee that sounds really good!".  

As soon as we turned it on, Paul and I both stopped for about a minute and stared at it.  The sound I heard was so tight that I made the comment I thought maybe the two woofers were wired out of phase.  We listened to it for a few minutes frankly not sure what to think.  

Continued...