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  • Let's post something interesting: the ultimate small speaker build thread.

    I was going to reveal this when it is finished, but seems like this forum needs a boost, so I'm going to post this prematurely. Here it is,

    The ultimate small speaker: The Reference Mini

    Design goal: Build the most accurate, highest fidelity, and highest bass output small speaker possible with DIY components without any budget limitations.

    I started DIY in order to build a great sounding small speaker with good bass, because I couldn't buy something like that on the market. I got sucked in by DIY and it is just exhilarating to design and build speakers that sound better than what I can buy at a store. I really enjoy pushing the boundaries of performance, and I was really curious on how far I can push small speaker performance, and how good I can possibly make a small speaker sound. This is the first time I allowed myself to be careless with budget with anything. This curiosity and one time budget freedom led to this incredibly fun, and absolutely insane project. I should check myself into DIY rehab after this.

    Shout out to JavadS and Kevin K for being incredibly gracious in helping me out with this speaker. I couldn't thank them enough for bringing this project to life.

    Forget about any preconceived notions of small speaker. This entire project is about figuring out how to get all of the normal sized bookshelf/floorstanding speaker performance from a small speaker. Originally it was thought it will still be inferior and a compromise to normal sized speakers, but turns out it is possible to do significantly *better* than normal sized speakers.

    Design summary: this speaker is 6" x 11.5" x 7.25" HWD. It is a 3 way, 4 driver, 2x passive radiator internally amplified active DSP design. It is specially designed so it can be used horizontally or vertically with no performance degradation.

    A few pictures to give an idea of this speaker. It misses a few details like the side firing passive radiators, truncated frames, and the round over.





    I'll start by listing out the features of this speaker that makes it superior to most normal sized speakers. This is very long. Read the paragraphs below each feature if you're interested for the details.

    A 3 way that acts and measures like a single driver point source speaker
    Unlike pretty much any multi-way speaker, there is no horizontal or vertical lobing error by using crossover frequencies equivalent to 1/4'' of the wavelength of the CTC distance between the drivers.

    Because two sound sources couple as one when spaced between 1/4'' of their wavelength, the 3 drivers acts as a point source, and we get the massive advantages of multi-way and point source without the disadvantages of both (or coaxials).

    In order to do this, the spacing between the tweeter and midrange must be minimized to the extreme. The frame of both the tweeter and midrange are truncated in order to place them as close as physically possible to achieve a CTC distance of about 2.2". Even with this extreme effort the tweeter has to be crossed to the midrange at 1300Hz (that's too low? Keep reading)

    Cardioid radiation pattern

    As the frequency gets below the wavelength of the size of the baffle, the sound wraps around the baffle and goes to the back. This is why we need a baffle step compensation. This, however, causes the sound to be reflected from the front wall and interfere with the direct sound. A cardioid radiation pattern suppresses output at the rear of the speaker, and it does this by having a second sound source that is appropriately delayed so that it cancels out the sound at the rear. In this case, the second woofer is the rear woofer, and it is delayed with a frequency dependent phase shifted signal that will cancel the output when the sound from the front woofer travels to the back of the speaker. This gives a better sounding midrange from the lack of front wall reflections, as well as eliminate the Allison effect that plagues almost all speakers that are near the wall of a dip in the 100-200Hz range.

    Equal Loudness Contour

    Have you noticed that speakers get brighter the louder they are turned up? Or a speaker sounds dull and thin at low volumes? This is our ears having different sensitivities to bass and treble at different volumes. At low/normal volumes, our ear is not very sensitive to bass and and to some extent treble, and therefore an anechoically flat speaker will sound thin from lack of low midrange and bass. At high volumes, our ear's sensitivity to treble significantly increases, and many speakers often sound too bright or harsh at high volumes. This is the voicing of a speaker. Many speakers are "voiced" with a downward sloping treble response or a rising low midrange response for this very reason. While a speaker like this will not sound as harsh, low-level listening suffers. This speaker will also have the characteristic of "sounding even better when turned louder". This is just because the greater ear sensitivity to treble is causing the tonal balance to become more balanced as the volume is turned up. A flat speaker will cause listening fatigue at high volumes because of ear's the greater sensitivity to treble at higher volumes.

    I want a speaker that sounds its best at ANY volume. I want to have full sounding bass and flat treble at low/normal listening volumes and a reduced bass and treble at high volumes to prevent listening fatigue. The solution? A dynamic EQ that automatically adjusts the bass, low midrange and treble levels depending on how loud the speaker is playing. This means the bass and treble is gradually reduced as the volume increases. I can't stress how much better the speaker sounds this way. High volume listening is stunning and fatigue free. One dangerous aspect though is that the speaker is so smooth this way that you can play much much louder without even realizing it, causing hearing damage, potential speaker damage, and pissed off neighbors. Screw that, I like my music loud and clean!

    Constant directivity, smooth power response, and extremely wide dispersion

    This is a constant directivity speaker, except it has an unusually wide 180 degree pattern to about 4000Hz. This is special, because most speakers suffer from directivity mismatch near the crossover frequencies due to the woofer dispersion starting to narrow and then beam an octave below the crossover frequency, then matched with a tweeter that has an omnidirectional dispersion pattern around the crossover frequencies. This creates a hole in the power response of the speaker, and several studies show that a smooth power response is crucial to the perceived sound quality. With the small diameter drivers and low crossover frequency, each driver stays in an omnidirectional radiation pattern throughout their entire bandwidth, creating a constant wide directivity speaker with a flat power response throughout the midrange and a smoothly declining power response in the treble.

    Virtually no cabinet vibration or resonance

    Cabinet resonance is an interesting issue. Unlike what intuition would tell you, a thicker wall causes bigger resonance issues! More accurately, a thicker wall causes the resonance frequency to shift higher up in frequency, and for normal thicknesses (3/4", 1"), this falls in the crucial midrange frequencies. Bracing simply pushes the resonance frequency higher.

    So, the solution, is actually to use a thinner wall. In fact, for a 1/4'' wall, the resonant frequency is around 100Hz, according to BBC's research. This is completely out of the midrange band, so the midrange enclosure suffers almost no audible resonance issues within its band. For the woofer enclosure, the midrange enclosure acts as bracing, pushing the resonant frequency up above the woofer's band. Therefore, we have a box that has no resonance issues.

    So with 1/4'' thick walls, this enclosure is going to be $hit right? Well, we can virtually eliminate cabinet vibration by using 2 woofers in a dual opposed configuration. Same for the 2 passive radiators. This way all their mechanical forces cancel out, leaving a vibration free cabinet. Well, not true, because the midrange and tweeter are not dual opposed, but guys, it's a tweeter! (And a 3.5'' mid). It's not gonna do much. The walls are also built with very high quality 1/4'' grade BB 5 ply baltic birch plywood, and it is much stronger and stiffer than you'd expect.

    The woofer enclosure is also too small to have standing wave problems, so no absorption material is used, and they wouldn't be effective for <400Hz anyways. The midrange enclosure uses a trapezoidal shape to reduce standing wave build up through non parallel side walls. It is stuffed with F13 grade wool felt to absorb as much of the rear wave as possible.

    Minimal baffle diffraction

    With the combination of asymmetrical driver spacing to nearby edges for all drivers, as well as wool felt treatment on the front baffle, this speaker should have very minimal amounts of diffraction induced frequency response ripples. The speaker grill is also treated with wool felt on all edges and hard surfaces, so this speaker can have a grill on without affecting sound quality.

    Linear phase and time alignment

    The use of such low crossover frequencies necessitates a steep crossover, but there is a price paid for the nasty phase shift that comes with steep filters. This is where DSP shines. By using FIR filters in the DSP, I can have a linear phase 4th order (or 8th order if I want) crossover. Additional processing can be done to reduce the pre-ringing caused by the steep linear phase filters. Time alignment is trivial to do on a DSP. The result is a time (mostly) and phase coherent multi-way speaker.

    Unreal bass extension and SPL for its size (OK this one is not better than floorstanding speakers, but it'll beat all bookshelves)

    As a bass head, a huge priority for this speaker is to get as much bass out of a small speaker as possible. I want the speaker to play so deep that Adele can roll in it! This is perhaps the most fun part of designing (and listening) to this speaker, and perhaps the biggest shocker when people hear this speaker. The result? This 4L speaker should produce 96-108dB from 40-100Hz, 1M outdoors! Add 3-6dB for a pair (gain depends on distance between the 2 speakers and the frequency), and another 3-6dB when placed in a room! I expect a pair to produce 105-114dB of bass from 1M away in a typical room. Small speakers can't have bass? This speaker is capable of producing deeper and louder bass than any bookshelf speaker that I know of, and can likely beat many floorstanding speakers.

    One other note: something particularly special about the bass performance from this speaker is not just how much deep bass output it has, but how much deep bass output it has while still having exceptional woofer efficiency, which translates to incredibly high midbass and low midrange output. Often times a woofer will sacrifice efficiency (and hence midbass output) to get better deep bass performance. Just look at the dreadful 82dB sensitivity rating on the Tang Band W5-1138SMF. This speaker achieves amazing deep bass performance without sacrificing sensitivity.

    See the woofer and passive radiator section for details on how this is achieved.

    Multi-band compressor

    In order to get 38Hz extension from this tiny speaker, up to 17dB of bass boost is required. This is usually problematic because the speaker quickly runs into excursion limits, and very much limits the maximum volume for the speakers to be safely played at (by as much as 17dB). Therefore, to prevent the speaker from distorting when the SPL exceeds the woofer's capabilities, a multi-band compressor is used to limit the woofer's deep bass output to below its limit without affecting the rest of the woofer band, allowing the speaker to play at almost any volume without overt distortion or the "pumping effect" with single band compressors (ahem miniDSP).

    A vented enclosure with sealed enclosure group delay behaviour

    The problem with vented enclosures is that there is significant group delay, which can be a reason for sloppy sounding bass in vented enclosures. This problem is made much worse by the shelf filter bass boost that worsens the group delay even further. This is not an issue with sealed enclosures.

    The solution is a neat way (that I won't go into detail) to compensate the group delay with FIR filters without using too many taps. The result is a vented speaker that has the clean low group delay of a sealed speaker, making the speaker even more accurate.

    Superb dynamic performance

    Small speakers have restricted dynamics and can't play loud right? Not this one. The high efficiency of the system (93dB on the woofer, 90dB on the midrange and tweeter) and active crossover with powerful amps allow this speaker to play incredibly loud and dynamic. A pair should be able to produce peak SPL of just under 110dB 1 meter away. Unbelievable? Well, this speaker is really a 3 way, 4 driver floorstanding speaker packed into a small speaker. All that extra air space in a floorstanding speaker just increases the <150Hz efficiency of the speaker. I can achieve nearly the same bass performance in a small speaker, I just need way more power.


    Continued on the next post.
    Last edited by bcodemz; 03-12-2017, 11:44 PM.

  • #2
    Finally, let's get to the details of the speaker components.
    Driver selection:

    Tweeter: Scanspeak Illuminator D3004/6040-10 1'' Beryllium Dome Tweeter

    This is the finest small format tweeter available with exceptional distortion performance. While very expensive, at $250 (from Solen) it is actually very cheap for a Beryllium tweeter and it performs just as well as the large (and much more expensive) Scanspeak Beryllium tweeters. It has good sensitivity, dispersion, and exceptionally low distortion down to 1000Hz. Best of all, all that performance is in a tiny 2.44'' face plate tweeter that can be further cut down to ~2'' to reduce size even further.


    Midrange: Scanspeak 10F/4424G 4'' Neodymium midrange

    This is the best sounding ~3.5'' cone midrange available, and the largest midrange I can accommodate to achieve a 1/4'' wavelength crossover frequency with the tweeter. While there are 3'' domes, they are all bigger than the 10F, and it must be crossed much higher at around 600-1000Hz when I want the midrange to be crossed low closer to 300Hz to take advantage of the clarity of the midrange as much as possible. A woofer capable of the same clarity as the Scanspeak 10F would be extremely costly and may not be suitable for bass duties. Even if I did use a driver of that quality, the woofer compartment won't be fully stuffed like the midrange chamber to absorb the rear wave, which will result in an inferior sound.


    Woofer: 2x Wavecor WF152BD05 6'' Glass-fibre woofer

    A *TON* of work was put into this task. The woofer search gave me a lot of trouble due to the sheer number of choices and trying to find one suitable for bass. This is a classic compromise problem of bass and midrange clarity. Not only many of the high quality and high fidelity 5-6'' midwoofers do not reproduce bass very well at high excursion levels, most are not designed for small enclosures and have "high" Vas and low Fs, both are not "ideal" for small PR enclosures, which leads to very poor PR efficiency and less overall bass output of up to 3dB for the same input power. A driver that is ideal for high output bass reproduction, such as the Tang Band W5-1138SMF, does not have high fidelity midrange, which would be unacceptable given the best in class sound quality of the other components.

    I almost gave up and just used a high fidelity woofer and sacrifice bass output, but after some serious digging, I found a little known driver from Wavecor that has almost the best of both worlds. It had pretty much the ideal T/S parameters suitable for my design, while having extremely good sound quality comparable to Scanspeak Revelators. The result is a woofer that is 2-3dB more power efficient in the 40-55Hz range than nearly all high fidelity midwoofers, and just 1dB less than the W5-1138SMF, the ideal miniature subwoofer driver for this application, and avoiding the 7dB less midbass because of the dreadful sensitivity. A high efficiency pro driver has great midbass output, but not nearly enough excursion for low bass. The Wavecor does it all, high sensitivity, high compliance that results in about as much low bass and mid bass output as possible from a 5L speaker.


    Passive radiator: 2x Tang Band PR14 oval passive radiators

    The passive radiators are special. This is a special oval passive radiator from Tang Band with ribbed surrounds to reduce rocking modes. It is the only passive radiator that has enough excursion and linearity to only use two PR to keep up with the 2 woofers, tune them to a very low 42Hz, and still fit in the enclosure. It should have much more linear excursion than the 5.25'' Peerless PR, as Tang Band recommends just 1 of these PR's to go with the W5-1138SMF, a woofer with higher excursion than the Wavecor. It is a shame Tang Band absolutely refuses to sell these PR's separately. So the only way to get them is to buy a bundle with either the W5-1138SMF or the W6-1139SIF, from Europe! This was not an easy (or cheap) PR to get to say the least.

    DSP: external miniDSP 2x4 HD

    This is the heart of the system that does the crossover, driver response manipulations, phase correction, time alignment, bass boost, high pass, limiting, and more.

    Amplifier: 1x ICEpower 50ASX2 SE, 2x ICEpower 50ASX2 BTL


    I will be internally amplifying using the ICEpower 50ASX2 SE (for stereo) for the midrange and tweeter, which will provide 50W @ 4 ohms for each driver. The two woofers will be powered by the bridged version of the 50ASX2, one woofer each, which will deliver up to 170W @ 4 ohms to each woofer. The woofers need a LOT of power to overcome the tiny airspace. Even though they only need about half the power, but its important to have spare headroom so the amp isn't straining. The ICEpower amps are very high performance class D amplifiers that should sound much better than most of the class D amplifiers on eBay and Alibaba that may have questionable designs and parts quality. There will be no doubts on the excellent sound quality, power output, and build quality of ICEpower amps. They have integrated power supplies, the dimensions are incredibly small and they're not horribly expensive like the Hypex NCores.

    It's going to be another few months before this gets built and gets tuned properly. Love to hear your comments in the meantime. I hope this has been interesting as it has been for me.
    Last edited by bcodemz; 12-28-2016, 10:29 AM.

    Comment


    • #3
      Wow, I have little to say at this point other than it looks like an impressive project.

      Will you have a way to making changes to the DSP, etc., externally? I think it would be fun to be able to tinker with those aspects of the design w/o having to break the box open to attach cables, etc.

      Comment


      • #4
        The only critique I would have for this is that even though the amps are very efficient, having a closed box may not be the best option for cooling.

        If you can modify the design somewhat to allow for an external heatsink to allow for a path for the heat to get out of the enclosure, that might be a nice option.

        Love the choice of woofers. Those are some fantastic performers.
        R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio

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        • #5
          Wow, very ambitious and impressive project! I will be excited to see this come together. Of those drivers I only have experience with the 10F, and will say it is a fine choice.
          Projects:

          transcenD: http://techtalk.parts-express.com/fo...5035-transcend
          Summits: http://techtalk.parts-express.com/sh...75-The-Summits
          References: http://techtalk.parts-express.com/sh...-My-References
          Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

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          • #6
            Impressive project. You must bring them to DIY Iowa.

            Ron
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            The good thing about science is that it's true whether or not you believe in it. - Neil deGrasse Tyson
            http://www.youtube.com/watch?v=cjuGCJJUGsg

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            • #7
              This does look amazing! Can you give a estimate of what the total build cost will be for a pair?

              Edit: I just looked up the cost of the tweeters alone, there goes my hope for building these beasts...

              Comment


              • #8
                Wow, nice... would be fun to see this at Indi, hope you complete in time. Mine got derailed pretty recently, due to driver issues.... but there still time. looking forward to this build thread

                Comment


                • #9
                  Originally posted by Tijmen View Post
                  This does look amazing! Can you give a estimate of what the total build cost will be for a pair?

                  Edit: I just looked up the cost of the tweeters alone, there goes my hope for building these beasts...
                  Since this is an active solution, you have options. You can build a similar speaker with different drivers if you understand the principals and DSP programming.
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                  • #10
                    yes, many a good $50 tweeter can be substituted for it, and tweaked in the DSP, though you would need measurement equipment. Those tweeters are really nice, but this is an ultimate build. Wavecor drivers are also difficult to source in the US (which is why even they are more reasonable in cost and offer fantastic performance, there are not many builds with them). if any the PRs would be the biggest hurdle. There simply isn't a great choice in PR. and PR is a must for small box low tune, as the ports gets ridiculously long in these applications... though clever solutions like Bills resonance traps exists. Also icepower amps are not readily available... though they come up for sale now and then

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                    • #11
                      Where did you get the idea for that tweeter?

                      Any preference on the FIR software?

                      Comment


                      • #12
                        Thank you everyone for the compliments!

                        Originally posted by philthien View Post
                        Wow, I have little to say at this point other than it looks like an impressive project.

                        Will you have a way to making changes to the DSP, etc., externally? I think it would be fun to be able to tinker with those aspects of the design w/o having to break the box open to attach cables, etc.
                        Yes, the DSP is external for this very reason. Eventually I want to put the DSP inside for a really clean all-in-one package, but it'll likely be 1-2 years before I can get to that point.

                        Originally posted by Pete Schumacher View Post
                        The only critique I would have for this is that even though the amps are very efficient, having a closed box may not be the best option for cooling.

                        If you can modify the design somewhat to allow for an external heatsink to allow for a path for the heat to get out of the enclosure, that might be a nice option.

                        Love the choice of woofers. Those are some fantastic performers.
                        You're right, and unfortunately heat is an issue that I don't have a good solution for. The speaker is too darn small and it really limits what I can do.

                        Originally posted by Tijmen View Post
                        This does look amazing! Can you give a estimate of what the total build cost will be for a pair?

                        Edit: I just looked up the cost of the tweeters alone, there goes my hope for building these beasts...
                        It costs about $3000 for a pair. ​I don't really recommend anyone trying to build this. It is exceedingly difficult and expensive to build and some parts are really hard to get. Part of the joy is the struggle to really push the limits and not settle for anything other than the best. For the money I also had an absolute blast during the whole year long process of designing this speaker, way way WAY more than say, a vacation would bring, and that's an incredible amount of enjoyment that others won't get when duplicating the speaker.

                        Even if you modify it, significant changes would need to be made that would greatly change the size and performance of the speaker.

                        Originally posted by ani_101 View Post
                        Wow, nice... would be fun to see this at Indi, hope you complete in time. Mine got derailed pretty recently, due to driver issues.... but there still time. looking forward to this build thread
                        ​I hope they'll be done by then. I should be able to attend InDIYana since it is just a 7 hour drive away.

                        Originally posted by Ron_E View Post
                        Impressive project. You must bring them to DIY Iowa.

                        Ron
                        ​I'll try to attend DIY Iowa, however the flight is quite expensive as I'll likely be in Europe during that time. However I will find a way to get you to hear this like I promised before.
                        Last edited by bcodemz; 01-01-2017, 11:51 AM.

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                        • #13
                          Originally posted by rickcraig View Post
                          Where did you get the idea for that tweeter?

                          Any preference on the FIR software?
                          Haha no one in particular (looks away from you)

                          I only got to try 2 since nearly all of them are paid software. I liked FIR designer, quite powerful and not hard to use. rePhase is nice too for some simpler stuff. Want to try Acourate, but it is very expensive.

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                          • #14
                            How much room will they need around them? Will a U-shaped bracket to hold them horizontally(these are gonna be heavy like a chunky traditional amp) be possible w/sheet metal, or will it have to be small solid stock? Love the idea, tho I'm wary of Be in humid places.(we'll know in 5 or ten years if they last 5 or ten years, I'll just let others be the test mammals). Plenty of small form tweets around good enough for old ears.

                            Thanks for showing us this, looking forward to seeing it built.

                            Comment


                            • #15
                              Brian,
                              What an impressive speaker you're designing. I'm hoping to hear these at the 2017 MWAF? I'm so glad I'm staying for the open unlimited, lots of tasty treats in that category so far!

                              TomZ
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