The AlTi, a DIY 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: Jul 20, 2022
    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 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. Most inexpensive soft domes that I have used around this price point 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 (I measured a little higher then that but my tuning also came in a little low), it allows them to be enjoyable enough for most music without using a sub at modest volumes. The rated 2.7mm xmax is real however, the woofer certainly has clean mechanical travel past this point but any exceptionally heavy bass notes will start to modulate the midrange output as the coil moves out of the gap. Use with a subwoofer is best for higher playback levels. Though the single mid-woofer does still struggle as you near 100dB/1m in the low midrange upper bass which can be seen in the compression sweeps.

    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 ~47hz with a 3/4" MDF flare added to the inside port termination of the 1-7/8" flared port that PE sells. Without that flare the tuning will be a tad higher should actually give a flatter bass response.

    Cost for the drivers, crossover and port tube is just under $80 per speaker, though additional savings could be made using a 12uF NPE cap on the woofer circuit instead of the poly cap bringing it closer to $150 for a pair (excluding enclosure materials and assorted hardware).

    December-2021 Crossover update - New more detailed measurements taken on my outdoor turntable revealed some response issues that had been masked previously. The new updated crossover design is posted below:
    Crossover Schematic 20 Ohm.png

    If you are upgrading from the previous crossover, you will need to replace R1, R2, R3, C2 and C4*.

    *For C4 you could add a 2.0uF in parallel with the existing 10uF to make 12uF or use the 2.2uF removed from C2 as 12.2uF won't really measure different.

    The new parts required are C6, L3, R4 that make up the added filter which can be wired to the LF output terminal if you have an existing crossover PCB.

    Update Jan-2022: I tested a new pair of woofers and they had slightly reduced midrange output (~1dB less) compared to my older ones. I changed R3 from 15 to 20 Ohms to correct this.


    Crossover Parts:
    C1(4uF) - C2(1.5uF) - C3(0.22uF) - C4(12uF) - C5(80uF) - C6(22uF)
    L1(0.4mH) - L2(1.5mH) - L3(2.0mH)
    R1(8 Ohm) - R2(7 Ohm) - R3(20 Ohm) - R4(10 Ohm)

    -Optional Crossover PCB Kit-

    Drivers:

    Hi-Vi M5N - Dayton DC25T-8

    Port Tube:
    1-7/8" x 5-5/8"

    -Full detailed measurements for the AlTi Design with the updated crossover can be found here-

    The crossover is approximately 2.6khz, 2nd order on both tweeter and woofer. C2 on the tweeter providing some minor contouring in addition to the two resistors providing padding as well. The woofer side has C3 acting as a notch filter to suppress the cone breakup while the two parallel filters are there to even out response lumps from the baffle step and diffraction.

    If you are using a class D amplifier you may want to add an ~8-20 ohm resistor in series with the C3 capacitor. This will not change the frequency response of the speaker but prevents issues from the capacitive load in the ultrasonic range which some switching amps do not like. This resistor can be small anything over a 1 watt rating should work.

    Note this sim is using gated indoor measurements so low frequencies are not accurate:
    Crossover FR SIM.png

    Crossover imp SIM.png

    Nominal impedance of the drivers is 8 ohms but with the crossover does dip to just above 4 Ohms between 200-300hz so you will want a decent amp if you want to drive these hard. If performing light playback an amplifier rated for 8 ohms should be fine.

    On axis the tweeter's response is decently 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 20 degrees off axis.

    There is a slight dip in the response of ~1dB between 3-4k 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.
     
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  2. #2 Matt Grant, Aug 15, 2017
    Last edited: Jan 21, 2022
    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, I used R6.7 ultratouch recycled denim for mine (one 48" long roll is perfect for two speakers) though poly batting or acoustic foam of similar thickness should also suffice. I lined the side walls and the bottom and rear of the cabinet leaving an open space for the crossover near the bottom back:
    [​IMG]

    New crossover mounted in the box:
    IMG_3086-sm.jpg

    Edit: New picture of the updated crossover boards (2021).
    Now includes a daughter board which cab be mounted separately to hold the additional components for the new LCR network on the woofer. I split those components onto a separate board as I didn't believe a single larger board would be able to be able to fit through the woofer cutout and/or mounted easily in the enclosure. The secondary board should be wired to the LF output of the main board along with the woofer, I've added an additional terminal block on the main board to handle the extra wires.
    AlTi-new-1.jpg

    *Note* I was late to notice a mistake on the first batch of these new boards where I forgot to add a trace to one side of the 12uF Cap. I'll send a pair to whomever wants them for $7, you need only solder a jumper wire between the unconnected lead of the 12uF cap and ground.



    -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:

    Matt Grant likes this.
  14. #14 Matt Grant, Dec 4, 2021
    Last edited: Dec 5, 2021
    I've tested these on my new turntable and made some adjustments to the crossover design which I have posted above.

    The new full detailed measurements with the new crossover can be found here.
     
  15. Hi @Matt Grant, happy new year!

    I've been looking to build something compact and have considered the S2000s, Speedsters and a few others before stumbling on the AlTi - the spinorama measurements and preference score look absolutely unreal.

    Two quick questions for you:

    • Have you considered designing an MTM version; and
    • I was considering having the cabinets made locally from 0.75" thick bamboo.

    Cheers!
     
  16. I hadn't really considered building an MTM design, though it's not totally out of the question since I have all the parts here.

    Bamboo cabinets would be perfectly acceptable
     

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