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  • The ultimate small speaker - final design critique/improvement

    Hi everyone. I'd like to get some feedback for a design that has been in the making for a year or so now. The goal is to design the very finest small speaker with the challenge to pack as much performance into a speaker that physically looks small, which I determined to be a wide but short speaker like a sound dock. This project stems from when I needed a small speaker for a small room and my utter disappointment with the sound quality of small commercial speakers and sound docks. The combination of extreme size restrictions and high fidelity requirements presented an extremely interesting and enjoyable challenge. After way too many hours of researching, modelling, testing and thinking, etc, I think I got to a point where the design is mostly complete, and I want to share it here and get some comments on possible improvements from members here that knows much more than I do. This silly challenge has been much more expensive than anticipated (but way more fun than anticipated too), so I'd like to get the design really right before I build. The value factor is a solid -1/10, but the fun factor is definitely a 12/10.

    For those interested, I talked about my previous attempt at such a speaker here. What I'm proposing here is a successor that improves upon every performance aspect after learning everything from the previous build.

    Design goal: Build the highest fidelity small speaker possible with as much bass output as possible down to 40Hz.

    In more specific speaker design goals, I wanted to achieve the following, in no particular order:

    1. Excellent clarity, deep bass response, and extremely high dB per liter ratio for bass.
    2. Minimize/eliminate horizontal and vertical lobing errors
    3. Matched directivity and smooth polar response
    4. Minimal cabinet vibration
    5. Excellent off axis response
    6. Linear and minimum phase response
    7. Good dynamics
    8. Transient perfect response
    9. Time aligned drivers
    10. Minimize baffle diffraction
    11. Ruler flat frequency response
    12. Flat power response

    Driver selection:
    Tweeter: Wavecor TW030WA13 Neodymium 30mm tweeter

    Originally I planned on using the Scanspeak D3004-602000 tweeter. However, it was brought up to me that the Scanspeak's very low sensitivity of 86dB (measured from Medley's Musings) might strain during higher volumes. I also wanted to use a very low sub 1500Hz crossover with the tweeter to achieve a crossover frequency at the 1/4'' wavelength of the CTC of the midrange and tweeter, and this tweeter does not seem suited to be crossed under 2000Hz.

    Therefore, I will be using the Wavecor TW030WA13. This is a 1.2'' tweeter flangeless 4 Ohm tweeter. This tweeter has a sensitivity of 93.5dB @ 2.83V, which is 7.5dB higher than the Scanspeak. Wavecor's specs are known to be very accurate, so I believe the 93.5dB sensitivity is real. The 57% larger Sd and 3x higher Xmax means the tweeter will likely to play a lot lower with less distortion at high volumes. I don't know if it'll sound as good as the Scanspeak as they are the benchmark small format tweeter. I do expect it to sound very close, and the benefit of the vastly higher sensitivity for dynamics and higher peak SPL should outweigh the slight sound quality advantage of the Scanspeak.

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

    This is the best sounding ~3'' 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 physically bigger than the 10F, and it must be crossed much higher at around 600-1000Hz when I want the midrange to be crossed lower at around 400Hz because the woofer compartment won't have damping material (the reason is explained in the cabinet design section). The dual opposed woofers also requires a crossover frequency around 400Hz as they will be 90 degrees out of phase at 566Hz. The woofer's response also stops being omnidirectional above ~500Hz.

    I actually tried very hard to use the Audax HM100Z0 because it is a more detailed mid and 6dB higher sensitivity for better dynamics and higher maximum midrange SPL. However, it required the box to be 0.75'' wider and taller to accommodate the bigger size, and the speaker is already too big as it is, so it was ultimately abandoned.

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

    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 as a high Vas leads to very poor PR efficiency in a severely undersized enclosure and less overall bass output of up to 3dB for the same input power. A driver that is ideal for high output bass reproduction and has a small Vas, 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 the Scanspeak 5'' Revelator midrange. 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 bass driver for this application and 2dB less than an ideal hypothetical driver that has ideal specs like the Tang Band but also have an unrealistically high motor strength. The two woofers should be able to put out a stunning 95-108dB from 40-100Hz from *each* speaker.

    Passive radiator: 2x DIY PR from modifying the Tang Band W5-1138SMF.

    Using the Peerless 5.25'' PR would be the easiest solution, but there is only space for 1 PR per driver, and the PR's 6mm xmax is not enough excursion. I can use 3 of them, or 1.5 PR per active driver, which would be close, but the mass needed to reach a 42Hz tuning at almost 2x the Mms, might be too much for the PR's suspension to handle. It also unbalances the dual opposed design of this speaker and will cause unnecessary vibrations.

    So a solution could be to make a DIY PR. The Tang Band W5-1138SMF is a very good candidate as it has a 9mm xmax, so the xmech must be a lot higher than 9mm. The driver has at least 2x more excursion than the Peerless PR, which should be enough for the woofer. The Mms of the driver, at 29g, is 2-3x higher than a typical 5'' woofer, which means the suspension has the greatest chance of handling the ~60g of Mms needed to hit the tuning. At $30 each, it is not expensive either considering it has more displacement than 2 of the $13 Peerless 5'' PR's.

    Enclosure design

    The enclosure will be 14.5'' x 6'' x 6'' built with 1/4'' baltic birch plywood. In the horizontal configuration, the driver configuration looks like
    Code:
    W  P
    WMTP
    The enclosure is a pair of dual opposed configuration. The woofer and woofer will be back to back, and so will the PR's. This configuration will cancel out any mechanical vibrations acting on the enclosure, allowing me to use a 1/4'' BB plywood and still get a vibration free cabinet. The tweeter and midrange will be arranged vertically in the horizontal placement. This allows me to use a 1/4'' BB for the enclosure and still have a vibration free cabinet. Every driver will have their frame/face plate cut off to reduce the physical size for mounting on the baffle. The midrange chamber is 3.75'' x 3.75'' x 4'' HWD and will be heavily stuffed with wool felt and polyfill. There will be no damping material of any sort in the main enclosure because:

    1. The cabinet is too small to have standing wave issues <400Hz where the mid to woofer crossover is.
    2. According to BBC's research, 1/4'' thickness walls will have a resonance frequency <100Hz, which is out of the midrange band and too low to damp anyways, and at ~500Hz, which is above the woofer's band.
    3. Damping material are not very effective for frequencies that low, especially the most I can put is 1/4'' thickness of felt.
    4. Damping materials will reduce passive radiator efficiency and reduce bass output

    One downside is that I cannot have a configuration where I turn the speaker into an MTM and bypass the 10F.

    The midrange tweeter will be in a vertical configuration to save width. All drivers will have their frames cut off to reduce size and so they can fit closer together, especially the midrange and tweeter. When drivers have a crossover frequency that is the same frequency as the 1/4 wavelength of the center to center distance each other, the sound of the two sources couple as if it is coming from one source like a point source speaker. This eliminates any vertical or horizontal lobing errors, so the speaker can be placed horizontally like a sound dock or vertically when used as a pair with no performance degradation. Imaging and coherence is improved, and the directivity is matched between the woofer and tweeter, improving imaging further.

    DSP processing:

    A miniDSP 2x4 HD will be used as the crossover and compressor. FIR filters will be used to achieve linear phase. The speakers will be time aligned. The crossovers will be LR4, and things like baffle step correction, bass boost, high pass, and driver response correction will also be done after the speaker is built as I prefer to measure instead of relying on simulation graphs.

    The crossover will be set at 400Hz LR4 between the mid and the woofer. The crossover for the tweeter and midrange will be at the 1/4'' wavelength frequency of their center to center spacing, LR4. Another configuration will be set for 1/2'' wavelength when very high volume is needed.

    The speaker will be DSP'd flat to 38Hz and a 48dB/oct high pass will be applied at 35Hz. The speakers are tuned for 42Hz, and a vented system will provide a boost up to 1/6 below the tuning frequency, which in this case is 38Hz. A 35Hz high pass is used to protect the system from unloading below tuning while avoid messing up the flat response to 38Hz.

    A 2 band compressor will be used to protect the speaker. I'm thinking of leaving the >50Hz band uncompressed, and the 40-50Hz band will be compressed with a ratio of 50 and an attack of 1ms. This is extreme, but so far it has been working pretty well with the previous speaker. I need to learn more about compressors before I experiment to find better settings. Any tips here would be helpful.

    Amplifier:

    I will be internally amplifying using the ICEpower 50ASX2 for the midrange and tweeter, which will provide 50W @ 4 ohms for each driver. The two woofers will be powered by the ICEpower 125ASX2, which will deliver 125W @ 4 ohms per channel to the woofers. 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.

    Thanks for reading through this very long post. What do you think of the design? Any comments or suggestions for improvement would be greatly appreciated.
    Last edited by bcodemz; 26 August 2016, 13:13 Friday.

  • #2
    This is undoubtedly an interesting project, for a very specific end result, and your research has likely selected components well suited to your requirements.

    My own experience is that Hypex products sound better than ICEpower amplifiers, as well as measuring better. There are some newer integrated products coming out from them, but may only be available to OEM- for your application, your current choices may be quite reasonable. A DSP approach to filters and crossovers gives great flexibility, but relies on the DAC quality built in to the DSP, which can be a limiting factor, especially when relying on a digital volume control, which I find unsatisfactory. With the DSP you can implement driver delay and other processing (assuming sufficient memory and power are available- you had better check this) and use conventional drivers and mounting and yet realize some of your goals.

    But that would be a consideration more for a high end approach- though I can't help but wondering what might be achieved with a Hypex amp and passive crossover. Some of us are old school... DSP is more useful in commercial products which include power and level and frequency limiters to prevent over drive and driver failures.

    I should disabuse you of one notion though- a difference in driver efficiency does not necessarily mean that the more efficient driver will play louder with less distortion- it only indicates that it will take less electrical power to do so. In fact, less efficient drivers often have an advantage in ultimate output level for a given level of distortion, due to having more excursion reserve in the motor.

    I would STRONGLY recommend you get a full measurement system and confirm your driver characteristics and assumptions before proceeding further in your design. So far you have presented a lot of goals and data sheet evaluations, but no hard data regarding driver performance or your intended physical configuration.
    DFAL
    Dark Force Acoustic Labs

    A wholly owned subsidiary of Palpatine Heavy Industries

    Comment


    • #3
      Originally posted by Evil Twin View Post
      This is undoubtedly an interesting project, for a very specific end result, and your research has likely selected components well suited to your requirements.

      My own experience is that Hypex products sound better than ICEpower amplifiers, as well as measuring better. There are some newer integrated products coming out from them, but may only be available to OEM- for your application, your current choices may be quite reasonable.
      I 100% agree that the Hypex NCores sound better than the ICEpower amps, and is probably the best sounding class D amp available, and I'd love to use them. Unfortunately they are way out of my price range. I need 4 channels of amplification for each speaker, and 4 NCores + power supply would cost well over $1500 for each speaker. I thought the $300 for the ICEpower amp setup is pretty darn expensive already! Unfortunately this isn't a price no object build, just a build with a relatively large budget.

      Originally posted by Evil Twin View Post
      A DSP approach to filters and crossovers gives great flexibility, but relies on the DAC quality built in to the DSP, which can be a limiting factor, especially when relying on a digital volume control, which I find unsatisfactory. With the DSP you can implement driver delay and other processing (assuming sufficient memory and power are available- you had better check this) and use conventional drivers and mounting and yet realize some of your goals.

      But that would be a consideration more for a high end approach- though I can't help but wondering what might be achieved with a Hypex amp and passive crossover. Some of us are old school... DSP is more useful in commercial products which include power and level and frequency limiters to prevent over drive and driver failures.
      I have to disagree with you there. A digital volume control is far superior to an analog pot volume control that has real performance differences depending on the quality of the parts and the input buffer of the amp. I see no performance disadvantage purely from the digital volume control as it does an essentially mathematically perfect amplitude change of the signal with none of the possible frequency response and phase variations and channel crosstalk that an analog volume control can have. I would agree with you if you said relying on an analog volume control, in that case I could see how the quality of the analog section of the DAC could have an impact when used with an analog volume control.

      I think the performance would be significantly lower with a passive crossover. This speaker requires up to 17dB of bass boost to get it flat to 38Hz. A compressor and a HPF is needed when applying such extreme boosts to protect the speaker. The speaker could not be played loud safely with a passive crossover as there's no protection on the woofer. The size of the amplifier would be massive as well. Even without power losses due to the crossover, I need around 250W of amplifier power for each speaker to get the most out of them. With a passive crossover you'll need at least twice the power from component losses. A good 500W/channel amps are expensive to say the least. The frequency response would not be nearly as flat from the fine adjustments I can make on a DSP to correct driver frequency response errors. Linear phase and time alignment would have to be sacrificed as well.

      Originally posted by Evil Twin View Post
      I should disabuse you of one notion though- a difference in driver efficiency does not necessarily mean that the more efficient driver will play louder with less distortion- it only indicates that it will take less electrical power to do so. In fact, less efficient drivers often have an advantage in ultimate output level for a given level of distortion, due to having more excursion reserve in the motor.
      I agree. I've seen it over and over during my research on woofers. However, the Wavecor tweeter is both 7dB more sensitive AND has over 3x higher Xmax than the Scanspeak, and that's what led me to predict that the Wavecor can play louder and with less distortion.

      Originally posted by Evil Twin View Post
      I would STRONGLY recommend you get a full measurement system and confirm your driver characteristics and assumptions before proceeding further in your design. So far you have presented a lot of goals and data sheet evaluations, but no hard data regarding driver performance or your intended physical configuration.
      You're right. I do have a measurement system, and I do plan on doing just that. I wanted to get some opinions first, because maybe someone knows a better driver that I didn't know about. Construction is the hardest part here with so many physical modifications and extreme physical size limitations, so I have to really do my research carefully before I spend weeks building. To give an idea: with the current design, this little sucker will cost around $2500 to build! :E
      Last edited by bcodemz; 26 August 2016, 13:15 Friday.

      Comment


      • #4
        With 1/4" ply, I really hope that you have plenty of bracing.
        SEOS 12/AE TD10M Front Stage in Progress

        Comment


        • #5
          Originally posted by Face View Post
          With 1/4" ply, I really hope that you have plenty of bracing.
          The dual opposed configuration of both the woofer and the passive radiators will cancel out the mechanical forces from the moving mass of the drivers, and result in an essentially vibration free cabinet. Do you think bracing is still necessary?

          Comment


          • #6
            The overall system vibration will be reduced by your configuration, but each panel will be excited by the internal pressure. Brace it frequently enough that the resonant frequency is above your XO to the midrange.

            Comment


            • #7
              You will need some bracing or dowels at least.
              SEOS 12/AE TD10M Front Stage in Progress

              Comment


              • #8
                re digital volume controls...

                I have to disagree with you there. A digital volume control is far superior to an analog pot volume control that has real performance differences depending on the quality of the parts and the input buffer of the amp. I see no performance disadvantage purely from the digital volume control as it does an essentially mathematically perfect amplitude change of the signal with none of the possible frequency response and phase variations and channel crosstalk that an analog volume control can have.
                If you are using 17 dB of boost, you are working in a more severe compromise of Hoffman's Iron law. If you are using 17 dB of boost with a relatively high high pass frequency (35 Hz) I would strongly suggest modeling the transient response and group delay before proceeding. With 17 dB of boost, I would consider a sealed system with EQ, which would likely have much cleaner transient response with less overhang. (and need less boost and power).

                You have asked for suggestion and comment; realize that many would come to this from different perspectives and expectations about sound quality. At least you didn't want to make it a Bluetooth speaker, too... did you?


                When I speak of the limitations of digital volume controls, I am referring to high precision volume controls implemented in DACs like the AURALiC Vega, the Berkeley Alpha DAC, and the TotalDAC-D1/D2... and high quality analog solutions can be shown to exceed their performance as regards noise floor, distortion, and equivalent Bit resolution. Just look at some of the better relay stepped attenuators or multiplying DAC controlled attenuators. In the end, it's your ears that count. Been there, done that, using analog these days.

                When you have an AP and are prepared to make comparative measurements, come back to this discussion about volume controls and resolution.


                I have the DACs and the AP.
                DFAL
                Dark Force Acoustic Labs

                A wholly owned subsidiary of Palpatine Heavy Industries

                Comment


                • #9
                  Originally posted by Evil Twin View Post
                  If you are using 17 dB of boost, you are working in a more severe compromise of Hoffman's Iron law. If you are using 17 dB of boost with a relatively high high pass frequency (35 Hz) I would strongly suggest modeling the transient response and group delay before proceeding. With 17 dB of boost, I would consider a sealed system with EQ, which would likely have much cleaner transient response with less overhang. (and need less boost and power).
                  Hence why I recommended this woofer in other threads:
                  http://www.diysoundgroup.com/anarchy-woofer.html
                  SEOS 12/AE TD10M Front Stage in Progress

                  Comment


                  • #10
                    Originally posted by Evil Twin View Post
                    If you are using 17 dB of boost, you are working in a more severe compromise of Hoffman's Iron law. If you are using 17 dB of boost with a relatively high high pass frequency (35 Hz) I would strongly suggest modeling the transient response and group delay before proceeding. With 17 dB of boost, I would consider a sealed system with EQ, which would likely have much cleaner transient response with less overhang. (and need less boost and power).
                    That's a good point. Which program can model the transient response with bass boost filters?

                    Why do you say it requires less boost and power? I'm fairly certain a sealed system would require more boost and power because there is no PR boosting the low end efficiency. It will take less power to exceed driver limits with no PR reducing the excursion on the active driver, but it should take more power to hit a certain SPL compared to even an extremely undersized vented alignment.

                    Originally posted by Evil Twin View Post
                    You have asked for suggestion and comment; realize that many would come to this from different perspectives and expectations about sound quality. At least you didn't want to make it a Bluetooth speaker, too... did you?


                    When I speak of the limitations of digital volume controls, I am referring to high precision volume controls implemented in DACs like the AURALiC Vega, the Berkeley Alpha DAC, and the TotalDAC-D1/D2... and high quality analog solutions can be shown to exceed their performance as regards noise floor, distortion, and equivalent Bit resolution. Just look at some of the better relay stepped attenuators or multiplying DAC controlled attenuators. In the end, it's your ears that count. Been there, done that, using analog these days.

                    When you have an AP and are prepared to make comparative measurements, come back to this discussion about volume controls and resolution.


                    I have the DACs and the AP.
                    That's interesting, I'll readily admit that I do not have in depth knowledge of the preamplifier side of things. So far I've only heard about bad things about the various issues of analog volume controls. I was not aware that there are high end analog controls that can outperform digital volume controls. I think I'll leave it at that because that's not really the topic of discussion here and you know way more than I do in this.

                    Although I gotta say: I will make it a Bluetooth capable speaker 8O. One reason for building this speaker is so I have something nice to listen to during trips. Sometimes it is just unwieldy to listen to music while lying in a hotel bed with a long cable dragged across the room.

                    Originally posted by Face View Post
                    Hence why I recommended this woofer in other threads:
                    http://www.diysoundgroup.com/anarchy-woofer.html
                    I considered it, but using the Anarchy woofers would make the speaker far too big for me to be considered small. It would require at least 2-3'' increase in width, 1'' in height, and 1-2'' in depth to a speaker that I already find a bit big to be called small. I'd also sacrifice lower midrange fidelity, the cabinet would rock much more, and even at 125W/woofer it would only drive the woofers to around 7mm of excursion because of the extremely small airspace and thermal compression.

                    Comment


                    • #11
                      Dimensions would be affected, yes. But you will no longer need passive radiators. Low midrange fidelity being affected, no. I recently used the Anarchy woofer with Scanspeak's small face plate Be Illuminator. They were well received at a local DIY competition.
                      SEOS 12/AE TD10M Front Stage in Progress

                      Comment


                      • #12
                        Originally posted by Face View Post
                        Dimensions would be affected, yes. But you will no longer need passive radiators. Low midrange fidelity being affected, no. I recently used the Anarchy woofer with Scanspeak's small face plate Be Illuminator. They were well received at a local DIY competition.
                        Could I hear more about that build? I'm surprised an Anarchy woofer can hang with a Revelator or an Illuminator midwoofer for midrange clarity.

                        I'm very interested in your opinion of the small face plate Be Illuminator. I've used the normal version D3004/6020 before, and I always wonder how much better the Be version is.

                        On another note: After some analysis, I have reason to believe Medley's Musings sensitivity measurements for tweeters are incorrect. It seems every tweeter he tests comes out 4-6dB less sensitive than the manufacturer's ratings. Scanspeak has a reputation of accurate/conservative specs, and another measurement suggests that the sensitivity is 90dB instead of 86dB. Therefore, I will most likely switch the tweeter back to the Scanspeak D3004/6020 as the Wavecors no longer have the huge sensitivity advantage, especially when they rate the sensitivity as an average of 5-20KHz when their tweeters have a rising top end. Now the question is if it is worth splurging $320 more and get the Be version.

                        Comment


                        • #13
                          I don't have an official build thread on them, but here is a little info: http://techtalk.parts-express.com/fo...76#post1281876

                          It was used in a waveguide and crossed at 1.5k. As for it's SQ, smooth but detailed is the best description I can come up with. I did compare the Be to a SS R3004 in the same guide and they did sound very similar, but the Be version sounding slightly better. If you already down a pair of D3004s, I would at least try them before jumping ship.

                          As for the woofer, a single Anarchy woofer in a sealed .67cf cabinet had enough low end to make everyone happy. With DSP, you could make the enclosure much smaller or even add a second woofer and still shrink the enclosure.

                          The waveguide and SS Be have been swapped over to an enclosure with an Accuton C220. The design isn't quite done yet as the Accuton is more difficult to work with. Add in a recent hernia surgery and even more recent knee surgery, a crossover the size of a piece of carry on luggage, and it's no surprise the design isn't done yet.
                          SEOS 12/AE TD10M Front Stage in Progress

                          Comment


                          • #14
                            Originally posted by Face View Post
                            I don't have an official build thread on them, but here is a little info: http://techtalk.parts-express.com/fo...76#post1281876

                            It was used in a waveguide and crossed at 1.5k. As for it's SQ, smooth but detailed is the best description I can come up with. I did compare the Be to a SS R3004 in the same guide and they did sound very similar, but the Be version sounding slightly better. If you already down a pair of D3004s, I would at least try them before jumping ship.

                            As for the woofer, a single Anarchy woofer in a sealed .67cf cabinet had enough low end to make everyone happy. With DSP, you could make the enclosure much smaller or even add a second woofer and still shrink the enclosure.

                            The waveguide and SS Be have been swapped over to an enclosure with an Accuton C220. The design isn't quite done yet as the Accuton is more difficult to work with. Add in a recent hernia surgery and even more recent knee surgery, a crossover the size of a piece of carry on luggage, and it's no surprise the design isn't done yet.
                            Take care of yourself! On the bright side, I find recovery to be the best time to actually enjoy my speakers. Generally I don't have the luxury to sit down and just listen to music.

                            I have used the D3004/602010 in my previous speaker. It does sound very good indeed. I have some health issues called upgraditis , so when I see the Be I wonder how much better is it. At least Troel eased the condition a bit by reporting that the small Be measures and sounds just as good as the $454 large Scan Be tweeter, just with less sensitivity =), and it is only $280! What a deal!

                            Do you think you can immediately tell the sound quality improvement from the Be when compared to the R3004 or is it something you gotta really listen for to hear the improvement? I don't think I will upgrade if it is something I have to really listen to hear the improvement.

                            The problem with the Anarchy is that I can't make it smaller. If I simply remove the PR, the cabinet dimensions will still have to be the same because I can't make the cabinet too deep due to phase issues from the dual opposed woofers. If I make an MTM, in addition to several inches added in each dimension, the cabinet will rock a good bit more. Either way the Anarchy will make the speaker too big. To give you an idea, the current design gives each woofer just 0.08 cu ft of airspace! 8O

                            Come join the dark side of DSP active speakers! A miniDSP is well under a pound and definitely not the size of a piece of carry on luggage

                            Comment


                            • #15
                              Hi, interesting goals. Some of them seem rather similar to a build I did (and am finishing up a variation on) -- http://www.diyaudio.com/forums/multi...mall-syns.html. I went with passive crossover, but external minidsp 2x4HD EQ (good choice on that, btw), because I wanted to simplify the system. I've had active multiway setups, and the complicated array of cabling, difficulty in setting up and moving, (and the general fear from anyone in my family who were intimidated by having to power up all that stuff together!) convinced me that, although active crossover is definitely a better performance way, practically it just wasn't so great. Multiply your intermittent bothers and wiring complexity by the number of active crossover pairs!

                              I instead did the crossovers passively and adjust the response and linearize the phase with the 2x4HD (feed it digital stream from a media center, get analog out, so the minidsp acts basically as my DAC and the volume control complete with IR remote). The currently running pair are quite small, and are using a Linkwitz transform to achieve low (-ish) bass, which works better than I would have ever believed. The speakers also operate against the back wall, which helps bass depth and efficiency and allows the room to be bigger in terms of usefulness. I didn't go to great lengths to avoid cabinet diffraction because of cosmetic requirements, and because the waveguide will steer higher frequencies away from edges (and at mid or lower frequencies, edge rounding has to be quite large to really help much).

                              I think if you are really serious about polar pattern control, you should maye consider waveguides. A Synergy type waveguide arragement allows you to have it all (no lobes in vertical or horizontal, and very continuous directivity patterns), though at some non-trivial amount of extra build effort.

                              Not telling you to do anything the way I did, BTW, just thought you might like to read about other approaches to some similar goals.

                              A few comments on statements made in the thread --
                              The dual opposed configuration of both the woofer and the passive radiators will cancel out the mechanical forces from the moving mass of the drivers
                              I don't think that's really true, except maybe for a subwoofer to keep it from moving around. Vibrations will also be conducted to the cabinet from the driver frames, vibrating longitudinally as well as by inward/outward pressure from the air in the box, and the dual opposed arrangement won't do anything for that other than excite both ends of the box better. How much of a problem that might be I can't say, but I'd bet with only 1/4" unbraced ply, the panels would be singing a lot. Short wavelengths of midrange frequencies will also limit the ability of anything to really cancel there, things don't meet instantaneously.

                              Which program can model the transient response with bass boost filters?
                              Seeing as you'll have dsp with FIR capability, I can't see how that would matter. You have essentially independent control of phase response, awhich is the same as transient response. Just measure what you have (essential), load the frd file into RePhase, adjust the phase eq there to generate the FIR file and load it back to the minidsp. It will take you less time to do than about any other part of the project.

                              Good luck

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