The AlTi's, a 2-way bookshelf speaker design.

Discussion in 'DIY Speakers and Subwoofers' started by Matt Grant, Aug 15, 2017.

  1. #1 Matt Grant, Aug 15, 2017
    Last edited: Feb 13, 2020
    The AlTi is an inexpensive 2-way bookshelf design using the aluminum cone HiVi M5N midbass and Dayton DC25T-8 titanium dome tweeter. You can probably guess how I arrived at the AlTi name.

    [​IMG]

    This is a new design I've been working on for the past few months, it evolved out of another very similar design I built as a wedding gift that had used some buyout paper cone woofers and in which I used the DC25T-8 tweeter for the first time. I liked how that design sounded and was especially pleased with the tweeter so I decided that I should find another woofer which would work in the design so others could build it if they wanted to. The M5N had the T/S specs and response I was looking for, best of all it had an identical frame diameter and dropped right into the cutouts I had made for the buyout woofers so I was able to do some preliminary testing in the original enclosures before handing them over.

    As I said I really like how the DC25T-8 sounds, it's detailed without being harsh and blends exceptionally with the M5N. The speaker is more dynamic then I expected and they can handle being cranked up, most inexpensive soft domes that I am used to using tend to get a little stuffy at higher output levels but these remain remarkably clear. Bass response is decent with the predicted f3 of just about 50hz in this enclosure, that makes them enjoyable enough for most music without using a sub. Even though the xmax is only listed as 2.7mm the M5N has very clean mechanical travel and remains well composed even when pushing them a good bit further that.

    The enclosures I built for these are 11.75" high x 8" wide x 10" deep, I used 3/4" edge glued baltic birch panels that were on clearance at my local hardware store but MDF or quality plywood is just as suitable. Tuning in the 0.3cuft net enclosure ends up in the low 50's, I measured 50hz exact with a 3/4" MDF flare added to the inside port termination of the 1-7/8" flared port that PE sells.

    Cost for the drivers, crossover and port tube is roughly $55 per speaker, though additional savings could be made using a 10uF NPE cap on the woofer circuit instead of the poly cap bringing it closer to $100 for a pair (excluding enclosure materials and assorted hardware).

    Updated V3 crossovers 8-16-18 (improved midrange and treble):
    [​IMG]
    [​IMG]
    The crossover is approximately 2.5khz, with acoustic slopes being roughly LR3 on the woofer and LR4 on the tweeter. Impedance is 8 ohm nominal load, dipping to 5 Ohms at 200hz.
    [​IMG]

    The woofer breakup at ~9khz which isn't terribly prominent on this driver gets well suppressed by a tank filter in the low pass being notched down more then 40dB.

    On axis the tweeter's response is pleasantly smooth out past 20k though when moving off axis and the phase shield does cause some extra rolloff at the top end and a notch between 13-14k but it really isn't an issue until you get more then 30 degrees off axis.

    There is a slight dip in the response of 1-2dB between 2.5-4k directly on axis however this flattens out slightly when you move off axis and I found leaving it sounded better as it gives a smoother power response.

    On axis response 2m outdoors gated 1/48th octave smoothing, (note below 200hz is not representative of actual bass response):

    Note the V3 crossover (added 8-16-18) flattens the midrange hump between 800-1500hz, fills in a little below 800hz and brings the tweeter level down slightly. Older measurements shown below as I don't have a full set of new measurements yet. [​IMG]
    0-90 degrees off axis horizontal:
    [​IMG]
    Response average 0-90 degrees:
    [​IMG]
     
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  2. #2 Matt Grant, Aug 15, 2017
    Last edited: Mar 14, 2020
    More detailed build description:
    For the enclosure using 3/4" thick material,
    Front and rear baffle: 11.75" x 8"
    Sides: 11.75" x 8.5"
    Top/bottom: 6.5" x 8.5"

    The tweeter and woofer are positioned so the top/bottom edge of their frames are 1" from the top and bottom of the enclosure. This equates to the tweeter center being 2-15/16" down from the top of the enclosure and the woofer center being 3-3/16" up from the bottom of the enclosure. The rear port is positioned so that it's centered behind the tweeter, the same 2-15/16" down from the top to the center applies there.

    The woofer OD is 5-11/16", ID or inner cutout is 4-9/16" and mounting flange is 5/32" thick (for flush mounting).
    The tweeter OD is 3-15/16", ID is 2-7/8" and mounting flange is also 5/32" thick. You do need to make small cutouts for the terminals on this tweeter.
    The port cutout is 2-11/16", I can't remember how it fits at that size it may need to be opened up slightly since the port is press fit.

    The bracing is simple I just used two 1.25" wide pieces of 3/4" MDF and positioned so that the front to back brace lands on the back of the baffle between the woofer and tweeter cutouts. The side to side brace is attached directly under that one and centered front to back.

    More photo's of the speakers:
    [​IMG]
    [​IMG]
    [​IMG]

    MDF port flare added to inside port termination:
    [​IMG]

    Drivers used in this design:
    [​IMG]

    Enclosure damping, used R6.7 ultratouch recycled denim for mine (one 48" long roll is perfect for two speakers) though polyfill or foam should also suffice. I Lined the walls of the bottom portion of the cabinet leaving an open space for the crossover near the bottom back:
    [​IMG]

    Crossover mounted in the box:
    [​IMG]

    Edit: New picture of the updated crossover board:
    AlTi-1.jpg

    -Link to Crossover PCBs for the AlTI Design I have up on Ebay available for purchase-
     
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  3. #3 mmmbacon, Oct 18, 2017
    Last edited: Oct 18, 2017
  4. Looks like everything is correct as far as the wiring goes on that PCB.
     
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  5. Hey Matt! I am finally getting around to building these. Do you still have those PCB's? I would love to grab a set from you. If not, where could I find them online?

    Cheers
     
  6. I might have couple left but I am also going to be changing the crossover a little bit as well and that crossover PCB won't really work as well without gluing a couple extra parts on top of others.

    After more listening to these I've noticed a few things I want to adjust. At high volume levels I did come to notice the tweeter can get a little harsh with complex content, so I want to bump the crossover up just a little. The upper midrange and high frequencies are also a little too forward and I found that adding a zobel type network with some other adjustments to the crossover will help fill in the broad dip in the 200-600hz region and bring down the level above that range just a little resulting in a more balanced sound.
     
  7. Thank you for sharing your experiences regarding this build. I am an engineer but I have never build a speaker system before. I would like to build a set of stereo speakers and decided to start with an existing build. I always likes the way the HiVi drivers looked so the OS was my Top pick. But I had some second thoughts about the 'small' tweeter and the 4" driver. That is why I really likes this build when I saw it! I am going to build a pair of my own.

    Could you please share your suggested improvements in more detail? I am also very curious regarding the result.

    I am going to make a YouTube series on the build if you are ok with it. If you are interested I am able to make some 3D drawings of the cabinet to make advanced build plans.

    Greetings!
     
  8. No issues making a youtube build video. I've added the new updated crossover schematic and parts list.

    Feel free to make 3D drawings of the cabinet if you want. I'd have made a quick mockup in Sketchup like I did for the Nexus designs if there was enough people asking about it.
     
  9. Thank you Matt for the additional information! Just what I was hoping for. I cannot find your listening impressions so van you tell us of they sounded better to you after improving the crossover? I was also planning on using sketchup, so if you've already made a drawing I'm not sure mine will be of more use to you. (But perhaps for others?)
     
  10. I just completed my version using an existing pair of .25 33C26EF3-B216-4405-A437-6AE56240E9CD.jpeg cuft oak cabinets that built years ago. I adjusted the ports to 1-3/8” dia x 2-1/2” long.
    The result blows away the other configurations I have used in these enclosures.
    Wonderful in a small room.
    Thanks for a great design.
     
  11. Glad to hear someone else has come to enjoy this speaker design.
     
  12. Updated crossover board photo to reflect latest design and added link to crossover boards I have for sale.
     
  13. First post here guys,

    Just wanted to submit my AlTi build. Very impressed! Running them with a Dayton 2.0 built-in plate amp using AirPlay. Very clean sound and precise imaging.

    Crossover is built in the latest iteration.

    Thanks Matt!
     

    Attached Files:

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