New 2.5-Way DIY speaker design

Collapse
This topic is closed.
X
X
 
  • Time
  • Show
Clear All
new posts
  • Patrick Sun
    Super Senior Member
    • Aug 2000
    • 1380

    New 2.5-Way DIY speaker design

    Just taking a lead from Mark H., and starting a new thread on my 2.5-way DIY speaker design project. Yes, please share your HDS measurements!

    Specs:

    Tweeter - Vifa D25AG05
    1.0 Midbass - Peerless HDS 439
    0.5 Midbass - Peerless HDS 439

    Ported with two 2" wide ports around 6" long for a tune of 50Hz in a 1 ft^3 braced enclosure (10"x21.5x12.5").

    The idea behind a 2.5-way is to use the tweeter and one of the midbass driver as the nominal "2-way" speaker, and then you throw in the 0.5 midbass to fill in the bass that you lose from the baffle step loss. My cursory understanding of the baffle step loss: bass radiates in 4pi space all around the baffle, while tweeter radiates in 2pi space in front of the baffle, so there is anywhere from 3dB to 6dB loss in the bass region if you don't account for the baffle step loss. The compensate for it, most people can elect to put a parallel R-L circuit in series with the tweeter and this effectively lowers the tweeter output to match and compensate for the loss in bass from the baffle step. The only drawback is that you lose a little bit of overall speaker sensitivity but you gain a fuller sounding speaker. Here's a link on baffle step loss which better explains it. There are more than one way to skin a cat in this case.

    So by using a 2.5-way, I can roll off the 0.5 midbass driver with a 1st order (inductor) around 400-500Hz which compensates for the baffle step loss, without muddying the midrange from 500-2500Hz before the midrange/tweeter crossover kicks in. This also preserves the overall speaker efficiency to match the midrange (around 87.5dB).

    Originally I was going for a TMM configuration on my speaker's front baffle. But a kind gentleman, (Paul V) over at the Madisound audio discussion board shared this nifty baffle diffraction frequency simulator (excel spreadsheet) which allows you to simulate various driver placements to get the "best" configuration for the drivers on the front baffle. So after I spec'd out the front baffle dimension (8.5"x20"), he came up with a "optimum" driver layout, and it happens to look like a MTM design, but the drivers are offset from the center vertical line by 0.75" and the drivers are very close to the tweeter (5.4" = center-to-center distance (CtC)) and the tweeter is located around 9.85" from the top of the front baffle.

    The other interesting thing is that you get some really nice reduction in baffle diffraction if you also incorporate a roundover on the baffle edges with a radius of 1". I will try to do a roundover with a radius 0.75" if I can find the right roundover bit without costing me an arm and a leg.

    Using the Peerless HDS 439 allows me to get the CtC for the tweeter and midbass drivers as close as 5" because the HDS439 has its top and bottom flanges sliced off just for this purpose. Here's a front shot of the driver.

    Since I'm using the Vifa D25AG06 which has a Fs of 1500Hz, I needed to crossover near twice the Fs, around 3000Hz. Using the rule of keeping the CtC equal or less than the wavelength of the crossover frequency, I decided on crossing the midrange and tweeter at 2750Hz, and most likely the midwoofer crossover will be a 4th order Linkwitz-Riley filter, while I may play around with the tweeter crossover, using either a 2nd order L-R or 3rd-order L-R and let the tweeter's natural slope help out.

    The quick and dirty calculation for the CtC is to use CtC=13585/Fc, where Fc is the desired crossover frequency and the 13585 is the velocity of sound in inches.

    I will most likely have to pad the tweeter down around 3dB to match the sensitivity of the midrange (88dB vs. 90/91dB).

    Here's a link to the Vifa D25AG05 specs and the site for Vifa main site.

    Why this particular model, and not the chambered version D25AG35? Well, I just happen to have one of these tweeters, and I've read mostly favorably reviews of it (though it has the high Fs, resonant frequency), and the D25AG35 isn't available locally for me, while the D25AG05 is.

    I have considered the Vifa D27TG45, but it seems to have more critics and unreliable Fs from the current production run (but the variance of the Fs seems to bump it up from the specs of 650Hz to around 1250Hz, so while still a workable tweeter with a ruler flat response - which doesn't seem to be in vogue currently for those who want a super low crossover point near 2000Hz-2200Hz. There are many other choices like the Morel MDT-30, the Seas 27TFFC, the Hiquphon OWI, all of which I considered but I didn't like the price on the Morel ($50 per tweeter), the Seas ($26) would be comparable, maybe a little better than the Vifa D25AG05 ($22) that I'll be using, and the Hiquphon OWI ($75) cost a bit too much but has a remarkably flat response out to 20KHz, and very nice off-axis response. Of course, the highly regard ScanSpeak 9500 ($85), 9700 ($$$) aren't really options for me at this point because of their high costs.

    As to why I choose the Peerless HDS439 midbass driver, well, I've used both Vifa and Peerless before, and Peerless spec are really pretty spot on for their production units. The HDS 439 ($47) has a nice flat response from 100Hz to around 3500Hz, and then a bump from 3500-4000Hz (the 4th order L-R lowpass filter at 2750hz is supposed to tame that peak). Here's a link to the Peerless HDS drivers page - click on the "850439" link on that page for the specs.

    The contenders for the midbass driver were the Vifa M18WO09 ($50, paper cone, which I like, but had this weird dip around 1400Hz, otherwise not a bad midwoofer), Vifa P17WJ00 ($38, never a big fan of polycone woofers, but still pretty highly recommended), Vifa PL18WO09 (a bit pricey at $63, but didn't do so well in the distortion tests that Linkwitz ran on a bunch of midrange driver, ScanSpeak 18W/8545 (just way too pricey ~$140?), Seas P17REX ($45)(while highly recommended, their frequency response graph might have been too revealing). A quote from the Linkwitz article: "The Peerless HDS 850439 is the definite leader in the performance versus price category for this group. It is well designed and built." So that just about sold me on the drivers enough to order 4 of them today.

    Also over at Dillon Acoustics there's a $60 plans for "The Metaphor" speakers that you can buy that specs out the HDS439 for use with the Hiquphon OWI tweeter. You'll note with just the TM configuration, his efficiency is around 86dB, I should gain that 1.5dB with the added 0.5 midbass driver. Now is it worth it? I'll find out! I figure I'm exchanging $92 in 2 extra midbass drivers for that extra bit of efficiency over paying $100 more for the Hiquphon OWI tweeters. Hope I made the right choice.

    Just bought the MDF tonight, and hope to start cutting it into panels by the weekend.

    For determining the crossover component values, I'll be using the SpeakerMania website, where you can click on their "Filter Design" link for the crossover components, and their "Correction Circuits" link for the L-pad for the tweeter, and maybe a Zobel to normalize the impedance of the HDS midrange if needed.

    Well, hope I didn't bore all 3 of you who'll read this. I hope to make some progress with this project, and of course document it for a future webpage. It won't be the cheapest 2.5-way DIY project, far from it. I just don't see the point in using pot-luck parts on sale and have to finesse the crossover enormously to get good sound from the inexpensive parts to tame peaks with notch filters or traps. If I'm going to put them in my house, I might as well make them look and sound good and know that I have quality parts and that others have a shot of duplicating the project without having to worry about getting the same spec'd out drivers.




    PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
    PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    #2
    Well good luck

    This really isn't the way to go about creating a proper design.

    The "cookbook" method you describe will work. The results will be less than optimal and you'll end up solving any design problems "after the fact" with trial and error compromises.

    Also taking one persons recommendation for a mid, another person's for a tweeter ,etc, etc, ignores the fact that a loudspeaker is a "system", hopefully with a synergetic interaction between the componnents. Linkwitz's choice for a mid is based on his wants/needs for the specific project he's working on. It's not a generic endorsement of that driver for all applications.

    Using mfgr's supplied data and baffle step modeling programs isn't a reliable way to obtain accurate info as to how the driver will function in a box/baffle you design.

    I suggest creating series of test boxes dimensioned per the desired finished size for the drivers. Measure the speakers performance in these test box. This is the only way to have accurate info about how the driver/drivers will perform in the baffle you want to use. Then take this info and input it into a good XO design program and start tweaking.

    In addition please consider investing in LspCAD. This is a "tool" just like your router. It is pretty accurate and will more than pay for itself through the years. The program includes a good XO design/performance modeling and test sim with a computer soundcard. Recently added is a speaker testing module for making actual real world measurements of any design you want to test.




    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
      • 15271

      #3
      Hi Patrick,

      I fully endorse the basic concept you're using for a 2.5 way speaker- built my first speaker using that concept in 1982, using SEAS 5" midwoofers and SEAS tweeters. It can be a very successful approach to dealing with baffle step compensation, but you'll need to measure the drivers on the baffle/enclosure you build; relying on mfr's data for a different setup can lead you far astray.

      I have to strongly second ThomasW's recommendation to get a copy of LSPCAD, or at least something similar. I've blown a lot of money on test programs and design software, it's all been worth every penny; LSPCAD is one of my favorites; I'm also still using SoundEasy for some analysis issues.

      Drivers. They're as important as anything else you use in your system. No matter how much work you put into an enclosure, or crossover design, the drivers can impose some very fundamental upper limits to performance.

      Now, let me ask you a question. What is your time worth? Can you put a dollars and cents to that? Or more importantly, let's put a Dollars and Sense to it. How many hours do you plan on putting into a project like that- let's multiply that by the minimum amount you'd charge someone else to do that work for them. Then let's go back and look at your driver budget, in light of the work equivalent expenditure you're making.

      You've obviously taken some time, and put some thought and effort into your driver selection- but I'd like to ask you to reconsider, given how much work a system like this will be once you've finished it, if you want to do it *right*.

      First off, doing a two way with a tweeter that has an Fs of 1500 Hz is asking for trouble. The high pass function of the tweeter is 2nd order, and with a self resonance at 1500, you'll need a full resonance impedance control zobel, and have to take into account the transfer function of the tweeter when realizing your crossover's acoustic target. I wouldn't run a tweeter with an Fs of 1500 at a crossover below 4 kHz. That's too high to make a good two way- even if the lower driver has output up to 3-4 kHz on axis, it will be incredibly beamy at that point, and the room power response will be very irregular near the crossover frequency. A typical mistake when designing 6.5" two ways.

      Another hint. Discussed and used for many years, and at the core of Avalon Acoustics' success:
      (the founder of Avalon Acoustics, Charles Hansen, used to work for me in the early 70's, and I gave him one of my early prototype systems when I got married in 1982 and my wife didn't like these 200 lb cabinets for a 10" four way- where do you think Avalon got the layered MDF contruction and rigidity ideas?)

      * Keep all drivers in the pistonic region, if you want the clarity and focus of a good planar speaker.*

      That means examine the impedance curve carefully, look for ripples indicating cone decoupling and breakup modes, and crossover from cones as low as possible. Since you probably don't have laser inferometry, a good substitute is to use two condensor mic's, one at the cone center, one at the edge, and use the outputs to drive X and Y inputs on a scope. If there is no cone break up or phase shift, a straightline plot results.


      Who makes some of the best cone speakers? Eton. Why? Their honeycomb construction using nomex and kevlar is lighter and stronger than almost all other cone materials out their- compare the cone mass of an Eton 360 or 370 with a ScanSpeak 7" driver- it's one half!

      There are many tweeters to potentially select from with total resonance in a range to permit a 2 kHz crossover for two way system. Important parameters are reasonably low resonance, and a compliant suspension that will allow some driver excursion at the lower frequencies. On a budget, the MB Quart tweeters, used by Avalon with some modifications, are a good choice. I would recommend the Tioxid Focal tweeters, the TC90Tdx is a fine sounding driver, with a very well self damped diaphram because of the tioxid dome construction.

      Think about these ideas, and think about how much work you'll put into this system. With a little extra money, thought, and work, this could go from being a decent system to something really special. Good luck with your project, and above all, have fun.

      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-Saƫns 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

      • Patrick Sun
        Super Senior Member
        • Aug 2000
        • 1380

        #4
        Thanks, guys! I appreciate the comments and suggestions. Amphiprion was nice enough to share his results/graphs/impressions from his Morel MDT37/Peerless HDS439 2-way, and he got some really nice results from this combo. So, I'm sure I'll be tossing out the Vifa D25 and entertaining the Morel MDT37 or maybe another similarly price tweeter which will allow me to cross it over around 2KHz or under. I have some more time to consider more options (can't cut the MDF until next week). I want to do it right, but also under a certain budget (which is spiraling upwards as I type!).

        You both have given me more food for thought.




        PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
        PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

        Comment

        • ThomasW
          Moderator Emeritus
          • Aug 2000
          • 10934

          #5
          A little follow-up

          I know Patrick is sensitive regarding buying components at a price point; so in keeping with that theme and Jon's recommendations look at the following tweeter, SEAS-25TAC/G aka H-400. We've used this tweeter in many 2-way designs. It sounds pretty good and has a low Fs. If you want a textile version of that dome look at the Vifa-D27TG-15

          MCM electronics has a very nice carbon fiber 6.5" mid-woofer that is $25 frequently on sale for $16ea. go to http://www.i-mcm.com and do a search for part number 55-1545. This is the big brother to the driver Adire uses in the "Pop"




          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

          • Patrick Sun
            Super Senior Member
            • Aug 2000
            • 1380

            #6
            "Price sensitive"? Moi?

            I wish I could throw all kinds of money into these projects (especially after seeing what you and Jon cook up). That's just not in the cards at the moment for me.

            That MCM site is tough to navigate (and I simply don't have the experience to know what's really good from that website). Thanks for the pointers for the midrange drivers. Unfortunately, I've already ordered the midrange drivers I'll be using for this project. Doh!




            PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
            PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

            Comment

            • ThomasW
              Moderator Emeritus
              • Aug 2000
              • 10934

              #7
              PI@

              To get info on the MCM driver just go to the site, enter as a guest, and then enter the part number in the search function.




              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

              • Patrick Sun
                Super Senior Member
                • Aug 2000
                • 1380

                #8
                That was the hard part, I don't see the "search" funtion even though I see a tab for search which gets me to a page that doesn't have a place to enter a search string. I tried both IE and Netscape. Maybe MCM just doesn't like me.




                PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
                PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

                Comment

                • ThomasW
                  Moderator Emeritus
                  • Aug 2000
                  • 10934

                  #9


                  In the upper right hand corner it says "Product Search"




                  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

                  • Patrick Sun
                    Super Senior Member
                    • Aug 2000
                    • 1380

                    #10
                    Ah! You have to fully expand the browser window to see their search box. I also run 2 browser windows side by side, and the MCM site doesn't make my browser side-to-side scroll bar show up, so I had no idea! Thanks.




                    PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
                    PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

                    Comment

                    • Patrick Sun
                      Super Senior Member
                      • Aug 2000
                      • 1380

                      #11
                      Update: I've decided to go with the Morel MDT30's for the tweeters. Those are on order, and it might another 2-4 weeks before I to make some good progress on this project.




                      PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
                      PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

                      Comment

                      • Patrick Sun
                        Super Senior Member
                        • Aug 2000
                        • 1380

                        #12
                        Just an update: I've finally gotten all the MDF wood cut into the panels I will need for this new speaker project. I've already glued the plywood (for the t-nuts) to the inside of the front baffle, and will cut in the driver holes tomorrow on the front baffle. Then I will be able to start glueing the side panels together and the bracing (need to cut the driver holes so I'll know where to line up the bracing for the rest of the box.




                        PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
                        PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

                        Comment

                        Working...
                        Searching...Please wait.
                        An unexpected error was returned: 'Your submission could not be processed because you have logged in since the previous page was loaded.

                        Please push the back button and reload the previous window.'
                        An unexpected error was returned: 'Your submission could not be processed because the token has expired.

                        Please push the back button and reload the previous window.'
                        An internal error has occurred and the module cannot be displayed.
                        There are no results that meet this criteria.
                        Search Result for "|||"