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Lucent Model T 'Prototype', Build Details

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  • Lucent Model T 'Prototype', Build Details

    I should clean up my website and post this there, but I just never seem to get to that. Well ok then, onward ho.

    Lucent Model T

    The Lucent is a concept speaker that began in a very modest fashion. I was looking at drivers as I often do and one popped out at me as being something with real potential. I googled and searched and couldn't find anyone using that driver in an established design, so I set forth in a modest capacity to make a build with it. Going in I never expected the design to come out with any serious merit. Life can throw us an occasional surprise though and I feel strongly that over the speakers I've built that this one is a true gem. Sometimes things just all come together and the sum of the parts is more than anyone would expect.

    The driver in question is the SB Acoustics SB26ADC-C000-04. This is a 1" metal dome tweeter with phase shield and excellent performance. It has an optimized motor for low distortion and shaped rear chamber for excellent low end capabilities. I could post up my measurements but it is easier to link to AudioGurman's tests of it: SB26ADC tests. It is a foreign language site, but the tests speak for themselves.

    Since I was interested primarily in exploring the tweeter, I simply picked a woofer I hadn't used before but had excellent reviews from other builders. I also didn't want to waste dollars on a project that might not come to much, so cost was a factor. I chose the W5-704D as used in Johnny Richard's Tasha and Wolf's Canvas. It is capable of nice bass for a small 5.25" woofer, F3 vented in the low 40s, though it is SPL limited from its small size. It is nothing special, but nothing wrong with it either and its is easy to work with. If it has a down-side, it is that QC seems to have varied over the production years and your T/S params aren't going to match spec well based on my experiences. More on that a lot later.

    To say I started in a modest capacity is no joke. I took the cheap BR-1CAB cabinets offered by Parts Express to make my job easier and remove most of the cabinet assembly. Since neither driver fits the cut-outs of that box, I took a jig saw and simply hacked off the baffle leaving a window in place (there is a support front to back in the middle of the box). After I did that I scraped off the vinyl laminate from the rest of the baffle, cut a sized 1/2" plywood piece, and glued and clamped that onto the box. I used the Jasper Jig to router the holes for the drivers without any countersinking. I already knew there were two others things I wanted to explore in this build, one of which meant I didn't need to worry about flush mounting.

    I left the tuning of the box the same, not adjusting the port at all, and it worked out nice for bass response much to my surprise. Here is the model that came out using trusty old Unibox:

    As you can see, the power handling is the only issue. The Xmech limit of the TB seems to be considerably higher than its Xmax however and it can take a thumping given you don't expect it to push out 100db at 10 feet. I've never heard substantial motor noise from it with bass tones, it is a well vented little woofer.

    The first of the two other concepts I wanted to explore with the design was the maximum effect of foam on a baffle. In order to do that I decided to buy some 1" thick PSA acoustic foam and place that onto the baffle around the drivers. I simply needed to cut the foam for the drivers and to the size of the front baffle. Easy-peasy. WRONG. I learned then that cutting foam is not as easy as one would think. I found myself reminded of the nerdly LotR reference "One does not simply walk into Mordor" except in this case it clearly is "One does not simply cut acoustic foam". I tried the xacto, the hot knife, sharp scissors, and so forth and just ended up with a hacked up nasty looking piece not suitable for human viewing. Ugh. Lesson learned.

    When the Lucent appeared at InDIYana 2015, I shamefully hid the front hacked up piece of foam with a grill. I don't have any static shots, but Ani posted up a video segment with them playing here. If you watch long enough, you can see me almost kill myself by forgetting to turn off the amp when I go to disconnect the speakers :eek:

    When I got back home I started working on a better foam baffle, but still had issues. I ultimately decided on using the scroll saw and with my Dad's help (he is far better with the tool than I) I got something that looked "ok". I decided to attach some white grill cloth... not my best moment to the new foam baffle and I ended up with what I am calling the Gym Sock edition of the speaker... :( I recall Bryan K. asking me if it was "Beer Thirty" when I designed the baffle, lol. I used 1/2" PSA acoustic foam for this version, as the 1" thick was a waste and made no impact on the sonic performance at all.

    I have a final idea for the baffle and how to compensate for the lack of attractiveness for the form, but that is still in progress. I am going to build a semi-translucent grill using screen door material and attach the foam to the inside of the grill and not on the baffle at all. This should give me the benefit of the foam without the nasty look of it on the front baffle. More to come on this in the thread later!

    The benefit of the foam is that almost all reflections and interaction between the tweeter and the baffle are canceled. Sadly I do not have comparison measurements between the baffle with and without the treatment, but rest assured it is a real measurable effect. In my opinion, worth it. Down below you can see the smooth line of the treble response, and while smoothing has been applied it really lacks most of the little ripple you'd see from even a flush mounted tweeter.

    The second concept I wanted to explore with the design was a particular spectral balance. This particular one was presented by Siegfried Linkwitz (SL). It was developed by him as he worked on his Orion speakers. Ultimately he found a specific contour in the response from bass to treble, a downward slope, was more pleasing to the ear than a neutral response. My experience with voicing speakers made me interested in this concept as I was always rolling back the treble and mid more and more in my own builds. Here is the contour as SL envisioned it, and my final in-room measurement of the Lucent.

    As you can see, I took it further and pushed harder than SL. This was an experiment and I figured I'd listen to it and reduce it later, tweaks and all. Ultimately I ended up leaving it as it stood, which surprised me. Part of the reason for that I believe is the apparent warmth and bass boost the speaker seemed to gain from having the midrange and treble dramatically lower. If the speaker was larger and went deeper, I would think I'd have had to adjust the balance up some.

    Finally the build details. Here is the crossover design and build specs for the speaker. You could do just as well to use the .56 cubic foot knockdown box, flush mount the drivers, and then design a foam backed grill (forthcoming work I will show in this thread) as use the BR-1 box as I did in the 'prototype'.

    Foam template Left.pdf - Foam template Right.pdf

    The Model T designation for this version of the Lucent marked the Tang Band woofer. Another version: Model A will feature a larger, more expensive woofer. That speaker will be coming to Iowa with the new foam backed grill design for a sleek look. I'll post up those build details after the event.
    Last edited by JasonP; 07-12-2015, 08:52 AM. Reason: Text corrections
    Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
    Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

  • #2
    Re: Lucent Model T 'Prototype', Build Details

    Look forward to hearing these Jason.
    " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

    Quote Originally Posted by hongrn. Oct 2014
    Do you realize that being an American is like winning the biggest jackpot ever??


    • #3
      Re: Lucent Model T 'Prototype', Build Details

      Very nice. I like that woofer a lot, it really doesn't do anything wrong. Foam is hard to cut nicely, no suggestions there.


      • #4
        Re: Lucent Model T 'Prototype', Build Details

        I had the pleasure of hearing these at DDIY, and due to some logistical planning I got to have them here at home for awhile so I got to do some extended listening on them (sorry Jason - meant to warn you!).

        At Dakota, they were definitely among my favorites of the day - that tweeter is really, really nice. Maybe it is just me, but designs that "jump" rarely get my attention (in fact, quite the opposite). One reason we publish and distribute the house track in advance to our events is to give everyone a chance to familiarize themselves as much as possible with the different pieces of music. It is nearly impossible to accurately listen to a speaker without being familiar with the music (preferably by listening through some nice headphones) at hand. Being familiar with the music gives us a chance to more honestly analyze a designs performance - starting the day blind means the first several designs serve only to establish a baseline. I digress.

        Due to the spectral tilt, right off the bat this design "stood out" to me. I mean this in a good way - too many designs (diy and commercial) have a jump out character that I find hard to listen to for extended periods of time. It is rarely "in my face", and in fact is usually quite subtle. However, there are certain passages on this years house track that were deliberately included to showcase mid-to-treble transition (it isn't female vocals, either). These passed with flying colors. The Tang Band is not a subwoofer, and I am not convinced they should be playing down as low as the models demonstrate they can go but - they are not necessarily a real slouch down there, either. They are outclassed by the tweeter, however - a not uncommon problem this day and age. I ran into a serious mismatch when I used the Tang Band 28-537 with the Peerless HDS 6.5". The poor Peerless never stood a chance against that Tang Band.

        I would like to see measurements of a traditional baffle (flush mounted, roundovers) overlaid on Jason's creative foam work, but his careful consideration of spectral tilt and diffraction control has yielded a speaker that is very listenable for extended periods - I think anyone looking for a design using this woofer has another very valid contender to consider.
        Don't listen to me - I have not sold any $150,000 speakers.