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The Neutrino - A High-Output Mini-Monitor

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  • The Neutrino - A High-Output Mini-Monitor

    In my newly-minted position at Parts Express, I’ll continue to have opportunities to design my own loudspeaker projects on the side, but I’ll want to make sure they can be published as Project Showcase projects, so they’ll need to be designed exclusively using products from Parts Express. However, this project doesn’t fit that mold, so I’m publishing it here instead, because frankly the results have been too good not to share with the community.

    Introduction

    Let me tantalize you, first of all, by saying that what these speakers do should not be possible. You don’t get this performance from a speaker this small, and you don’t even necessarily get this performance from a speaker with a midwoofer two sizes larger.



    I had the idea for the Neutrinos in the spring of 2010, when I lived in a hotel room in Connecticut for two months while working on-site for a major aircraft manufacturer. I had my previous Whetstones design in the room with me, and they did an excellent job, but I began to wonder what the ultimate speaker for this application might be, in case I ever found myself in the same situation again. I surveyed the market, and was impressed by the small speakers offered by Amphion, which used a midwoofer and waveguide-loaded tweeter from SEAS, in a stylish white cabinet with rounded corners, but I thought it might be possible to improve on the overall performance for the application. Since the Amphion Ion had been my inspiration, I decided to pick a name from particle physics, the Neutrino. The name accurately reflects the design goal of creating a neutral-sounding mini-monitor with big performance from a very small enclosure.

    Driver Selection

    The key to the performance I sought from a small speaker was the Tang Band W4-1720, which if you haven’t yet heard, is the ultimate small midbass driver. Everything that has been said about this driver is true; its ability to play loud and low without distortion is legendary, and while it isn’t the very final word in resolution, it’s darn near it. The key to this performance is a motor structure that uses a long-excursion ‘underhung’ topology, and a huge mass of steel and ferrite that barely fits through the mounting hole for the driver itself.

    I decided to look around for a tweeter with an underhung motor structure to pair with the W4-1720, in order to stick with the overall theme, and I arrived at the SEAS 22TAF/G tweeter for that purpose. It has a 20mm-diameter aluminum/magnesium alloy dome diaphragm, suspended with an oversized surround made from a treated fabric material that SEAS calles “Sonomex”, which makes up almost twice as much of the driver’s radiating surface as the dome itself does, making this tweeter effectively a hybrid of a fabric dome tweeter and a small-diameter metal dome, with the metal dome being coupled to the 20mm voice coil. Even though the voice coil is small, the tweeter boasts long-term power handling of 80 watts, thanks to the use of ferrofluid, and a low free-air resonance of 1100 Hz.

    Enclosure Design

    By the time I finally got around to designing the enclosure for the Neutrinos, I had already completed a prior project, the Firestorms, in a CNC-machined cabinet. I liked the quality and consistency of the CNC-milled parts, so I decided to use the same technique here. I used 3D-modeling software to design the cabinet, then transferred the 3D model to 2D drawings for manufacture. (If you know what you’re doing in a 2D CAD program, you don’t necessarily need to model your design in 3D to effectively use CNC machining. The technique was available to me, so I used it. Many CNC programmers can even use fully-dimensioned hand drawings to program their machines.)



    For the Neutrinos, I used a room-aware overdamped vented box alignment tuned to 58 Hz (very close to the W4-1720’s Fs) to minimize excursion and assure linear performance even when placed in a typical room. I performed this room-aware enclosure tuning by first simulating the in-room response of the loudspeaker using Jeff Bagby’s Baffle Diffraction and Boundary Simulator tool, where I entered a worst-case room size of 16 feet by 20 feet, with the speakers located four feet from the back wall and seven feet from the side walls. Then I saved the resulting room and baffle curve as a FRD file and loaded it into Bagby’s Box Designer tool, and optimized the vented box alignment for maximally-flat performance in the given room. This allowed me to keep the enclosure size to a minimum for the given tuning, but you can also use this technique to optimize bass extension instead.



    The Neutrino enclosure has a couple of features that make it a somewhat advanced construction. First of all, the pair of 1” ports are flared at both ends, which requires flanging the exterior end in the rear wall of the enclosure and also in the window brace, and routing 3/8”-radius flares in both panels. Second, both ports are made from 1” nominal-diameter PVC, and captive within counterbores in the enclosure walls at either end to make sure everything remains aligned properly during assembly. Finally, dado joinery is used throughout, so the assembly is self-aligning and incredibly strong. A painted finish is used for my pair of Neutrinos, since I like the look of a well-chosen paint finish, but it is extremely time-consuming to do well. Internal damping material is ” SAE-F15N wool/poly felt throughout, with some open-cell foam added in front of the crossover (behind the midbass).

    Crossover Design

    In designing the crossover for the Neutrinos, I relied upon lessons learned from my previous Firestorms project, where I used an asymmetrical 2nd-order low-pass filter and 3rd-order high-pass filter topology with baffle step correction and single-resistor level correction for the tweeter. In the Firestorms, I relied upon distortion data measured by John Krutke for the Tang Band tweeter employed there, and enjoyed a wonderfully non-fatiguing treble as a result. For the SEAS 22TAF/G tweeter, John’s web site also had distortion data available. In examining the distortion plots for dome tweeters, most tweeters exhibit an inverse-knee in the curve at a particular frequency, below which the harmonic distortion begins to climb, so I chose that frequency (3400 Hz) as the electrical filter corner for the tweeter’s high-pass network. I then settled on a complementary second-order low-pass filter at 1200 Hz for the woofer, for an electrical crossover point of 2740 Hz, and an effective acoustic crossover point of 2180 Hz, with both drivers operating in normal polarity. To achieve a faster roll-off on the mid-woofer, I used a 2-ohm resistor in series with the shunt capacitor.



    I decided to mount the crossover to the bi-amp terminal cup itself, using long #6-32 machine screws as standoffs. Intertechnik Audyn Cap capacitors were used in the high-pass network, and a single Solen Fast-Cap capacitor was used in the low-pass network. Inductors were Jantzen air-core throughout, using 18AWG windings for the low-pass and 20AWG for the tweeter. Resistors were Dayton ceramic resistors in the low-pass network, and Mills non-inductive resistors in the high-pass network. After building the crossovers, I found that they were more difficult to fit through the terminal cup cutout than I had expected, but I was able to widen the cutout by ” at the top and bottom and install the crossover-and-terminal-cup assembly. (Just barely!)

    After buttoning everything up and having a listen (which occurred at 5 AM the morning before MWAF 2012, after pulling an all-nighter to finish the project), I found the tweeter to be very bright. It appears I didn’t trace the impedance curve from the manufacturer’s data sheet correctly, so my crossover values weren’t correct. I added series resistance prior to the high-pass filter (one benefit of using bi-amp terminals is that this can be done externally), but my own impression (as validated by comments at the show) was that the speakers were still overly bright. It turns out I wasn’t going large enough with the resistor; I found that a full 4 ohms of series resistance were needed to achieve the required level padding. However, after adding that series resistance, everything locked in perfectly, so I’ve simply written that 4-ohm resistor into the crossover schematic rather than adjusting the post-filtering series resistance, which would alter the component values and require me to rip my existing crossover apart. (They were hard to build!)

    Stay tuned for part 2. I will also be adding relevant images to this post.
    Attached Files
    Last edited by [email protected]; 09-19-2012, 09:37 PM.
    Best Regards,

    Rory Buszka
    Product Manager, Dayton Audio

    The best way to predict the future is to create it.

  • #2
    Re: The Neutrino - A High-Output Mini-Monitor

    Listening Impressions & Conclusion

    After sorting out the voicing issue described above, the Neutrinos have achieved their goal of being a neutral source that achieves high output levels from a small enclosure. While they aren’t very efficient at about 80 dB 1W/1m (and some would say they are very in-efficient), they play extremely loud when fed with plenty of solid-state juice. I use my APA150 to drive them, and can achieve lease-breaking levels in my room. I think a major contributor to the Neutrinos’ high output is that their enclosure is over-damped and tuned almost exactly to the driver’s Fs, rather than below it as other designs that use this woofer have been. As a result, the mid-woofers remain well within their linear excursion range at high power. I have not been able to detect any port noise, even when playing sine signals at the tuning frequency, though I did have to resolve a couple of air leaks around the drivers. Also, the fairly high crossover frequency used for the tweeters allow them to loaf along within their own linear region, so their output is smooth and non-fatiguing. Imaging is very good, as is to be expected from small monitors, but the soundstage width and depth are startling. This design nicely straddles the line between aggressive and laid-back tonality, and is very listenable for long periods.



    Parts Express discontinued the W4-1720 driver along with the rest of the Tang Band underhung drivers in early 2012, but thanks to popular request, they have reinstated the W4-1720 model. That means you can still build your very own pair of Neutrinos if you desire. I think this is one of the very best small speakers I have heard, and I think you’ll find them very worth your while.

    Crossover Schematic
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    Crossover Simulation
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    Measurements

    OmniMic response plot:

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    This measurement was taken in my bedroom, on a 24" speaker stand, with the OmniMic V2 microphone 1 meter away, and other reflective objects/surfaces at least 1 m away also. Blended windowing was used to get a picture of the low-frequency behavior, but there were some floor- and wall-related artifacts that led to a couple dips in the low end. Actual performance is -3 dB at about 65 Hz, and -10 dB at 40 Hz, but when placed closer to a wall they develop a completely different low-end character that is smooth and extended to at least 40 Hz before rolling off. This means they can be used on a typical desktop (against a wall) without a subwoofer and still provide captivating low-end response. They really are sensational when used in this way.

    Downloads

    Cabinet Plans - Zip file with cabinet Plans in PDF and DXF format
    Simulation Data - Zip file with Neutrino simulation data (generated by Bagby tools) and Bagby PCD session file
    OmniMic Screen Grab - A view of the OmniMic measurement screen during measurement, for FR and impulse data
    Last edited by [email protected]; 10-07-2012, 10:57 PM. Reason: Added measurements and explanation
    Best Regards,

    Rory Buszka
    Product Manager, Dayton Audio

    The best way to predict the future is to create it.

    Comment


    • #3
      Re: The Neutrino - A High-Output Mini-Monitor

      Rory,

      Very nice project, impressive cabinets and very good writeup!
      I am very interested in the tuning approach you used, which relies on the drivers strengths and not using the cabinet to get sumtin' fo' nuttin' which as you expained equates to keeping the woofer happy at elevated volumes. I like designs that are limited by your volume knob, not by excursion.... Well Done!!!

      Comment


      • #4
        Re: The Neutrino - A High-Output Mini-Monitor

        Very nice.

        Comment


        • #5
          Re: The Neutrino - A High-Output Mini-Monitor

          [[email protected];1858236] For the Neutrinos, I used a room-aware overdamped vented box alignment tuned to 58 Hz (very close to the W4-1720’s Fs) to minimize excursion and assure linear performance even when placed in a typical room. I performed this room-aware enclosure tuning by first simulating the in-room response of the loudspeaker using Jeff Bagby’s Baffle Diffraction and Boundary Simulator tool, where I entered a worst-case room size of 16 feet by 20 feet, with the speakers located four feet from the back wall and seven feet from the side walls. Then I saved the resulting room and baffle curve as a FRD file and loaded it into Bagby’s Box Designer tool, and optimized the vented box alignment for maximally-flat performance in the given room. This allowed me to keep the enclosure size to a minimum for the given tuning, but you can also use this technique to optimize bass extension instead.

          /QUOTE]

          Rory - thanks for the great writeup. I'm always the guy with the dumb questions.
          Can you expand on this section and process a bit more? Some graph shots and options along the way
          might be helpful.

          I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
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          • #6
            Re: The Neutrino - A High-Output Mini-Monitor

            Glad to see this project finally come together, Rory. I look forward to hearing them sometime soon.
            Isn't it about time we started answering rhetorical questions?

            Paul Carmody's DIY Audio Projects
            Twitter: @undefinition1

            Comment


            • #7
              Re: The Neutrino - A High-Output Mini-Monitor

              I'm definitely using that shape for my Deadhorse project, which reminds me, is at the 2-year mark this week ;(

              Great write-up. Did you get the crossover worked out properly?

              रेतुर्न तो थे स्रोत
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              • #8
                Re: The Neutrino - A High-Output Mini-Monitor

                Update:

                Crossover schematic, enclosure drawings, and PCD simulation data uploaded.

                (Yes, Grey, I sure did.)
                Last edited by [email protected]; 09-21-2012, 07:30 AM.
                Best Regards,

                Rory Buszka
                Product Manager, Dayton Audio

                The best way to predict the future is to create it.

                Comment


                • #9
                  Re: The Neutrino - A High-Output Mini-Monitor

                  thats nice rory. perhaps pe will let you come to grinnel with them when you bring the door prizes.
                  " 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??

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                  • #10
                    Re: The Neutrino - A High-Output Mini-Monitor

                    Updated with measurements.
                    Best Regards,

                    Rory Buszka
                    Product Manager, Dayton Audio

                    The best way to predict the future is to create it.

                    Comment


                    • #11
                      Re: The Neutrino - A High-Output Mini-Monitor

                      Rory, is the crossover schematic posted here the one just heard at InDIYana 2013, or has it been tweaked further?

                      Pleasure to meet you over lunch in Ft. Wayne. Sorry to hear you weren't feeling completely well.

                      David S

                      Comment


                      • #12
                        Re: The Neutrino - A High-Output Mini-Monitor

                        The above schematic is fully up to date. There should be a 4-ohm resistor before the high pass network, and a 4.5-ohm resistor after.
                        Best Regards,

                        Rory Buszka
                        Product Manager, Dayton Audio

                        The best way to predict the future is to create it.

                        Comment


                        • #13
                          Re: The Neutrino - A High-Output Mini-Monitor

                          I'm curious about sound levels. You said, "... about 80 dB 1W/1m..." and "...they play extremely loud...". Do you mean for near-field applications they play good solid sound? They are really pretty and look like they belong right at head level with a couple of monitors and maybe a keyboard + DAW in between. OTOH, I don't see how a ~30 watt driver starting at 80 dB is going fill a big space. The APA150 looks to be a good match - it will run out of steam right about the same time as the TB.

                          Any consistency issues between the two TB's? I've not had great luck getting matched pairs.

                          Comment


                          • #14
                            Re: The Neutrino - A High-Output Mini-Monitor

                            They filled the conference room rather loudly at InDIYana, so I can vouch for that.
                            Later,
                            Wolf
                            "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                            "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
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                            • #15
                              Re: The Neutrino - A High-Output Mini-Monitor

                              The W4-1720 has an xmax of 5mm. In Rory's box, simulation says they reach xmax w/ 30 watts. At the point they are making 101dB. FWIW, modeled sensitivity is 89.1 / 2.83 volts, 85.9 / 1w


                              Originally posted by xenzmann View Post
                              I'm curious about sound levels. You said, "... about 80 dB 1W/1m..." and "...they play extremely loud...". Do you mean for near-field applications they play good solid sound? They are really pretty and look like they belong right at head level with a couple of monitors and maybe a keyboard + DAW in between. OTOH, I don't see how a ~30 watt driver starting at 80 dB is going fill a big space. The APA150 looks to be a good match - it will run out of steam right about the same time as the TB.

                              Any consistency issues between the two TB's? I've not had great luck getting matched pairs.
                              I was so much older then, I'm younger than that now.
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