M8 DIY Speaker System in development

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  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15214

    M8 DIY Speaker System in development

    Hi all,

    After Bing and I practically hijacked Huskerduck's thread over in the AV Chalet, it occurred to me that we should start two new threads here in DIY, (at least two!) to discuss tweaks and mods to the 281 Adire design (generally, cabinet related), and the concept and designs behind the small speaker project I'm working on now, for now just called the M8. Flashy name, huh? You can tell I'm not in marketing, in spite of the things they've made me do over the years at Infineon.

    The M8 is being developed to fill a need for a relatively compact bookshelf sized (not placed!) speaker, for several friends, and also my own use. Somehow, I just couldn't see building another pair of SLAM Klones for the bedroom....

    Why an 8" two way, of all things? This is not normally a promising configuration; heck, even a lot of 6-1/2" or 7" two ways leave something to be desired.

    Let's consider the goals I had. Yours may be similar, they may be different, but discussing illuminates the points.

    1. Fairly wideband response at SPLs up to 100 dB at 1 meter. These speakers are designed for rooms like bedrooms, study's, and living room apartments. They don't have to pump dB's at vanishingly low distortion like a SLAMM or Whisper. Wideband means 30 Hz to 30 kHz.

    2. Compact- relatively. No more than 50 liters or so external volume. Stand mounted for flexibility; that way floor distance, side wall, and rear wall can all be optimized independently for smoothest bass in room.

    3. Highly uniform axial response and power response- (averaged total room response) which requires either a dipole design (not practical at this size) or wide polar response throughout the frequency range. That becomes a tough nut, particularly with a typical two way.

    4. Reasonable bill of materials, with upgrade potential. Baseline, and upgrades, depending on means of "customer/constructor".

    5. Minimal driver and cabinet resonance. Drivers must be operated largely in pistonic range, and cabinet should be stiff and inert to the highest degree feasible within size and weight constraints.

    First, it's a two way, because building a quality three way crossover is literally twice as expensive. Also, there are some very real issues about interaction between upper and lower crossover points that makes developing a three way bandpass a real bear; they must be at least 3 octaves displaced.

    For a two way, the crossover frequency could first be dictated by the diaphragm sizes and their radiation patterns. For an 8" two way, the ideal crossover is in the range of 1-1.5 kHz. For the tweeter, the issue becomes LF power handling. Not many tweeters have much of it! High sensitivity is an asset, because this eases power handling if the tweeter is padded down 5-6 dB relative to the woofer. My favorite tweeters, it seems are all 92-93 dB efficient.

    Selecting drivers is both simple and frustrating. Simple, in that to achieve reasonable LF output in a smallish box, a ported system should be used, which dictates driver Q and some other characteristics. Frustrating, in that once you start looking for drivers this wideband without breakup modes, you'll find its a very narrow field.

    Two alternative mid-bass drivers were selected for the M8; the "baseline" choice being the Focal 8V4211, the upgrade being the Eton 800/37.

    For the tweeter, the MBTT1 is the "baseline" choice; a 1" titanium dome, I have experience modifying it, and have used it for years. It has also been used by Avalon Acoustics and others.

    The enclosure design is roughed out, using a Woodstyle 123REV cabinet as the basis and cosmetic shell.



    I'll flesh this out and update as time permits during the weekend.

    When finished, complete plans will be available in PDF form for those interested, along with documentation of the measured performance, including MLSA (quais-anechoic) and in room RTA averaged response.

    Best regards,

    Jon




    Earth First!
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    We'll screw up the other planets later....
    Last edited by ThomasW; 11 September 2006, 17:41 Monday.
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  • AndrewM
    Senior Member
    • Oct 2000
    • 446

    #2
    Hmmmm, I have a question about this design. Why the choice of the MBQuart tweeter? I can't seem to find them anywhere (I find some other Quart models at Madisoun). Why not go with something like the TC90 series Focal, they have a pretty low FS (850Hz I believe) and should get pretty close to where you want to be. Just curious

    Andrew

    Comment

    • JonMarsh
      Mad Max Moderator
      • Aug 2000
      • 15214

      #3
      Hi Andrew,

      Good question re the tweeter- let's see how well I answer this.

      There are various factors which go into how well a tweeter works down low, including mechanical suspencion compliance, acoustic loading, distortion, Q, etc.

      I've used Tioxid Focal tweeters a fair amount, and love them in specific applications. Particularly the T120dx2, which is killer in the range above 2 kHz, great efficiency, low distortion, reasonably good off axis dispersion, and genearlly well damped. It's used in my X1 SLAMM klones, in ThomasW's Whisper Klones, and in a new project I've just started using an Eton Woofer and Accuton midranges. The TC90 could seem a reasonable choice, but in my experience it doesn't quite cut it in the low end. Fs is not the only indicator, unfortunately. Another example in the low cost area would be the SEAS H400; Fs is quite low, under 500Hz, but it doesn't work very well down low either, and it has some upper range colorations; not bad in a "budget system" - I've done several with it- but not usable in this system.

      The choice of the MB Quart came about in researching which manufacturers offered a wide range fairly high power handling, high efficiency tweeter back in the late eighties. Focal's products at that time (like the kevlar version of the TC90) weren't as well damped, didn't go as low, and had more problems with diaphragm breakup in the upper end. This is why the MB tweeter was chosen for early Avalon models (their founder and original chief deisgner, Charlie Hansen, used to work with me, and I gave him some prototypes which inspired development of the first Avalon models).

      Since then, their have been a lot of other tweeters come out, and some others may be good candidates for this demanding design- such as the Vifa XT series. My only significant reservation about the Vifa is the use of a concentric radiator design which decouples part of the tweeter above certain frequencies- you can see some interesting glitches in the impedance curve, and I have to wonder if there are any audible side effects.

      My initial testing on tweeters or any other speaker is always with MLS signals which stimulate them full range. You can get a real good idea of the tonality and capabilities of any driver this way. The MB is one of the most robust tweeter I've come across still, which nonetheless has a fairly extended top end. It's LF resonance is defined more by the airmass compliance than the suspension compliance, which may be why it works better than most in the range we use it.

      The standard dispersion diffusors create some problems, and they must be removed and replaced with protective grilles. Avlon has used a version specific to their requirements, with certain modification that were manually incorporated into the standard tweeters for early Avalon production.

      Naturally, I wouldn't want to discourage anyone from experimentation and measuring on their own. As I mentioned, the Vifa tweeter may have good promise in a design like this.

      To some extent, titanium tweeters have gotten the reputation of having a "hot" highend, or being hashy, or too bright. This has been said of the Quart, as well as Focal and other brands. My own experience is that these tweeters are ruthlessly extended and clear in repsonse; any problems with electronics, CD player, cables, etc., will be reproduced quite accurately. On the Madisound forum, several recently commented in a thread that they thought that about the Focal tweeters until they heard them in systems with good tube electronics.

      Now, I'm not a tube advocate particularly, though I got my start with them. If you gave me the choice between a Conrad Johnson tube amp, and a Crown solid state, it wouldn't require a moments reflection- give me the CJ! However, their are many good solid state designs, and the availability is improving steadily, including the availability of true zero feedback designs, such as from Theta and Ayre Acoustics.

      Just a few weeks ago while on vacation, I heard a "vintage" pair of Avalon Eclipse's at their original designer's, hooked up with the new Ayre V5 power amp, and the D1 CD/DVD player (which may be the finest CD player available in the world- bar none, at any price).

      The V5 is something of a heresy by Charlie's past philosophy, as it has bipolar as well as FET devices. It is probably the finest sounding amp they make now, matching or exceeding their reference monoblock V1's in some areas. I heard it in ThomasW's system with the Whisper Klones, and later at Charles's. It is built to a price, but designed without reservation of skill or effort; that's probably why I ordered one last month after hearing it- it should be in late next week when I get back from my trip to Chicago. I'll probably post a review here after breaking it in and doing some listening and measurements. Maybe I'll finally get around to "reviewing" my Palladiums, too!

      Best regards,

      Jon




      Earth First!
      _______________________________
      We'll screw up the other planets later....
      the AudioWorx
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      In Development...
      Isiris Mk II updates- in final test stage!
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      Resistance is not futile, it is Volts divided by Amperes...
      Just ask Mr. Ohm....

      Comment

      • Bing Fung
        Ultra Senior Member
        • Aug 2000
        • 6521

        #4
        Now that is a very nice design!

        Love the drawing, did you draw that with Mechanical destop, Inventor?

        Looking forward to the test results Jon




        Bing
        Bing

        Comment

        • JonMarsh
          Mad Max Moderator
          • Aug 2000
          • 15214

          #5
          Thanks Bing,

          Actually, my mechanical stuff is all still done in AutoCAD; current AutoCAD 2000. I'm an AutoCAD guy from way, way back; from the days when it would fit on a single high density floppy, and when IBM systems didn't have high density floppis! (Think TI Professional, 1983, 720X350 16 color graphics (basicall EGA before IBM did EGA) with Sony 720K diskette drives (not a standard item for the TI, but the existing bios support and minor DOS tweaks would make it work).
          I've looked at a few other packages over the years, and I have CADKEY because of interoperability issues with some customers (I do a little consulting from time to time), but I just keep upgrading my AutoCAD; version 2000 really is quite nice; a ton of user interface improvements from earlier versions, especially for 3D work, and a totally revamped plotting/printing interface; I've been quite happy with it.

          My friend's move date to Detroit has been moved up, so I'm going to be very busy in the next couple of weeks- particularly since I have to go to Chicago next week for PCIM (Power Conversion Intelligent Motion control) to present a couple of papers and do booth duty. The pictures and photo's with paragraphs and arrows on the back will probably not be complete until the second set is built, since my Sony Camera is in route from Denver.

          Stay tuned for further developments, and thanks for the interest.

          Best regards,

          Jon




          Earth First!
          _______________________________
          We'll screw up the other planets later....
          the AudioWorx
          Natalie P
          M8ta
          Modula Neo DCC
          Modula MT XE
          Modula Xtreme
          Isiris
          Wavecor Ardent

          SMJ
          Minerva Monitor
          Calliope
          Ardent D

          In Development...
          Isiris Mk II updates- in final test stage!
          Obi-Wan
          Saint-Saëns Symphonique/AKA SMJ-40
          Modula PWB
          Calliope CC Supreme
          Natalie P Ultra
          Natalie P Supreme
          Janus BP1 Sub


          Resistance is not futile, it is Volts divided by Amperes...
          Just ask Mr. Ohm....

          Comment

          • Bing Fung
            Ultra Senior Member
            • Aug 2000
            • 6521

            #6
            Excellent Jon, I have Autocad 2000 but have not loaded it yet, Im a R14 guy that has just started using Autodesk's Inventor.

            So how much redesign would be required to make that speaker a tower with say 1 or 2 more 8" drivers? Sorry if thats like grafting arms on the Venius, but I'm just curious..




            Bing
            Bing

            Comment

            • JonMarsh
              Mad Max Moderator
              • Aug 2000
              • 15214

              #7
              See Bing, I haven't even been to the AutoDesk site since getting my copy of 2000; I'm afraid to see what they have new!

              Changes like you suggest might not be too hard; for example, two eights could be setup with different crossover points to achieve baffle step compensation, and the overall tuning kept the same; desirable enclosure volume would be about 65 - 70 L.

              There's even a Woodstyle tower cabinet amenable to that. In years past I built a WMTMW system using ScanSpeak Kevlar 8's with MB mids and tweeter, using that box, but the mids and tweeters were lower physically than I liked.

              The other system I'm debating between a full custom enclosure and an adaptation of the Woodstyle tower in the reverse configuration (deeper than wide) is the three way using the 11" Eton, the Accuton C44-8 driver (I've got a pair of those I've been measuring and listening to), and probably the old reliable Focal Td120dx2 tweeter on top. It might wind up being an MTM for the upper range, with a single woofer.

              BTW, the "high end" version of the M8 will use the Eton 800/37, and the possibly Accuton C23, probably the finest 1" tweeter in existence. That would make an interesting upgrade in a tower with doubled eights. I'd have to analyze the overall parameters, and see which might give the best combination of LF output, mid polar response, etc. This system would use a downard firing 4" or larger port. For the 11" Eton, it would be tuned to about 25hZ. That probably wouldn't work so well with the 8's. The 11' may actually be capable of more extended and higher output levels; the problem is a good midrange unit- the only drawbacks to the Accuton's being price. And what drawbacks!

              Some thoughts to ponder while I'm in Chicago....

              Best regards,

              Jon




              Earth First!
              _______________________________
              We'll screw up the other planets later....
              the AudioWorx
              Natalie P
              M8ta
              Modula Neo DCC
              Modula MT XE
              Modula Xtreme
              Isiris
              Wavecor Ardent

              SMJ
              Minerva Monitor
              Calliope
              Ardent D

              In Development...
              Isiris Mk II updates- in final test stage!
              Obi-Wan
              Saint-Saëns Symphonique/AKA SMJ-40
              Modula PWB
              Calliope CC Supreme
              Natalie P Ultra
              Natalie P Supreme
              Janus BP1 Sub


              Resistance is not futile, it is Volts divided by Amperes...
              Just ask Mr. Ohm....

              Comment

              • Bing Fung
                Ultra Senior Member
                • Aug 2000
                • 6521

                #8
                Those are some interesting proposed designs Jon, I like sounds the 2 x 8"x MTM design. How much work would be involved for a novice like me to tune these in? I know nothing of crossover design or measurement technique, much less how to tune based on what is measured.

                These wood style cabinets you speak of, are they a prebuilt cabinet?




                Bing
                Bing

                Comment

                • ThomasW
                  Moderator Emeritus
                  • Aug 2000
                  • 10934

                  #9
                  Bing

                  The Woodstyle cabinets Jon is referring to are available from Madisound. http://www.madisound.com/woodstyle.html
                  Your cost for shipping, tax, etc would be quite high. Best bet would be just to copy the design. It's not that complicated, and they could be a match for you sub.




                  theAudioWorx
                  Klone-Audio

                  IB subwoofer FAQ page


                  "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                  Comment

                  • JonMarsh
                    Mad Max Moderator
                    • Aug 2000
                    • 15214

                    #10
                    Hey Bing, Hi Thomas (glad your lung crud is subsiding)


                    The tower style cabinet is kind of heavy, I think it just barely makes it for UPS shipping. The shipping on the W123 REV cabinets wasn't so bad- about $40 to me in CA from Wisconsin. The towers might be double that.

                    Eight's are big for an MTM- and actually, the Eton drivers are "nine's"- the 800/37. The Focal driver I'm using in the first version of this, which should be finished in the next week, is being discontinued, and it's replacement has a much higher Fs, smaller Xmax, and in general is weird, unless your goal is to make a small box with punchy mid bass but no real low end. Disappointing.

                    With two eights their are two possible ways to go; one is an MTM with a crossover similar to that proposed, but adjusted for load impedance; the other is to run one driver up the tweeter, without baffle step response, and do a gradual then steep roll off on the second driver, so that it fills in the baffle step and ups the low frequency efficiency. That would have twice the number of low frequency crossover components, but it still wouldn't be as complicated as a full three way using the Eton 11", and say, the Accuton mid and Focal tweeter.

                    Truthfully, I'm not sure which would sound best; the 11 would go lower, and move plenty of air, and with the Accuton dome mide above 700, would have excellent midrange dispersion. Also, with dedicated mids and tweeter crossed over higher, power handling would be better. The system using doubled Eton nines would cost less.

                    Probably the only way to know for sure is to build both!

                    It wouldn't be hard for me to model and develop a crossover for the double nine inch system, if you wanted to persue that- I even have a pair of tower boxes I'm considering "deconstructing" which could be used to meaure the drivers in, to confirm LF parameters. Tweaking or developing it further (other than adjusting tweeter level by ear) wouldn't be easy without some test gear.

                    That's one of the problems of this hobby- other than building cookbook subs, which is quite popular, as you can see, full range speaker projects are "in for a dime, in for a dollar"- it does take some commitment. The current combination of gear and software that ThomasW and I use has been accumulated over a period of about 25 years. The baseline investment I'd say is necessary, for full range speaker development, is something like CLIO Lite, and the standard version of LSPCAD. This combination is about a $750 investment, but well worth it- if you're not familiar with acoustics principles and crossover filter theory, then a copy of Vance Dickason's Speaker cookbook is highly recommended.

                    If you have a good wood shop, and are experienced/familiar in finishing techniques, then building from scratch makes sense. Here, in CA, I have very limited wood working space (condo with small garage, part of girl friend's garage on weekends, occasionally), and since it's easy for anyone to build on and modify a Woodstyle box, and have nice looking results, it's something I thought would make an easy project if others are intersested.

                    NOTE- it is a fair amount of work just making up the braces, sub panels, etc., for this M8, and gluing everthing together. I've almost finished both speakers; the paint is drying on the modified front sub panels, and the ports are ready to install; all braces are complete. The boxes are very stiff now, and close to twice the weight they started at. There are a few changes from the initial AutoCAD drawings, with some new braces, such as 1X3 Oak above and below the main woofer cutout. Also, the tweeter is in a completely isolated sub enclosure, which probably wasn't shown clearly in the drawing.




                    Here's a recent image after completing routing the port holes (note bevel relief, done with 45 degree Bosch roller bit), and the partly assembled port pieces, after being cut to the correct lengths.

                    Regards,

                    Jon




                    Earth First!
                    _______________________________
                    We'll screw up the other planets later....
                    Last edited by ThomasW; 11 September 2006, 17:43 Monday.
                    the AudioWorx
                    Natalie P
                    M8ta
                    Modula Neo DCC
                    Modula MT XE
                    Modula Xtreme
                    Isiris
                    Wavecor Ardent

                    SMJ
                    Minerva Monitor
                    Calliope
                    Ardent D

                    In Development...
                    Isiris Mk II updates- in final test stage!
                    Obi-Wan
                    Saint-Saëns Symphonique/AKA SMJ-40
                    Modula PWB
                    Calliope CC Supreme
                    Natalie P Ultra
                    Natalie P Supreme
                    Janus BP1 Sub


                    Resistance is not futile, it is Volts divided by Amperes...
                    Just ask Mr. Ohm....

                    Comment

                    • Huskerduck
                      Moderator Emeritus
                      • Oct 2000
                      • 129

                      #11
                      Do you stuff these with poly fiber? If so how many ounces?




                      Mark


                      Ducks Meager Theater
                      Mark


                      Ducks Meager Theater

                      Comment

                      • JonMarsh
                        Mad Max Moderator
                        • Aug 2000
                        • 15214

                        #12
                        Because these will be a bass reflex, they will be primarily lined (first, heavy felt, then either poly batting sheet, such as is used for quilts, or high density fiber glas). Occasionally one might stuff portions of a reflex box, if necessary to subdue midrange reflections, or if it turns out the driver damping in the port tuning range is not what you predicted by simulation- but too much stuffing will kill the box "Q", and prevent reflex operation. Since the reflex operation is what lowers the driver travel and distortion, as well as extending the bass, this would not be a "good thing". It's particularly important to keep damping material away from the port and the port entrance and exit.

                        Ported reflex systems are different from TL's, in that the TL will normally be stuffed, sometimes with variable density, over the length of the line, as well as loosely stuffed behind the driver.

                        Regards,

                        Jon




                        Earth First!
                        _______________________________
                        We'll screw up the other planets later....
                        the AudioWorx
                        Natalie P
                        M8ta
                        Modula Neo DCC
                        Modula MT XE
                        Modula Xtreme
                        Isiris
                        Wavecor Ardent

                        SMJ
                        Minerva Monitor
                        Calliope
                        Ardent D

                        In Development...
                        Isiris Mk II updates- in final test stage!
                        Obi-Wan
                        Saint-Saëns Symphonique/AKA SMJ-40
                        Modula PWB
                        Calliope CC Supreme
                        Natalie P Ultra
                        Natalie P Supreme
                        Janus BP1 Sub


                        Resistance is not futile, it is Volts divided by Amperes...
                        Just ask Mr. Ohm....

                        Comment

                        • Eric S
                          Senior Member
                          • Sep 2000
                          • 175

                          #13
                          Hi Jon: Looks like a nice speaker that you have there!

                          I have a question for you concerning the Focal TC120tdx2 tweeter. I've seen a few other impressive DIY systems that use these tweeters (like the Andromeda) and they have spiked my interest. My question is do you know of a place that will sell me a match pair? I know that Zalytron and a few others sell them, but there is no indication that they will match them to any specific tolerance...

                          Thanks for you input!
                          Eric
                          My DIY Theater Projects

                          Comment

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