USM-2 DIY Speakers (ND91-4 + ND16FA-6)

Discussion in 'DIY' started by ultrabike, Nov 26, 2017.

  1. iFi audio

    iFi audio MOT iFi Audio

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    It's good that you experiment and not end the project early, even if it meant redoing some parts. That's a big mistake DIY people do.
     
  2. ultrabike

    ultrabike Measurbator - Admin

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    Alright, redid the freaking baffles again (should have left it alone), and completed both speakers. The crossovers are now both finalized and installed. All things are finished (including cosmetics).

    Measurements:

    Frequency Response (left and right vs HD600):

    frequency_response_HD600.png

    Frequency Response vs JBL305:

    frequency_response_JBL305.png

    Frequency Response vs MR5MK3 (Mackie):

    frequency_response_MR5MK3.png

    Note this speaker uses a 3" woofer (nominally 3.5" but that's due to the bracket, the cone area is really 3"). Yeah. Nice bass for such a tiny speaker. It maybe partly because I designed this speaker, but in as much as unbiased as I can be, I like this much smaller design better than even the larger JBL305 and Mackie MR5! It may not reach down to 50 Hz, but it reaches 70 Hz with ease. The imaging, perhaps due to the size of the drivers, is phenomenal (achievable clean SPL may be the trade-off due to smaller driver area). In real life, it sound AWESOME! And plenty loud (I don't have an auditorium).

    Unlike most monitors I've seen, this design employs a front firing port, because that's what I wanted. The port is tuned to 70 Hz.

    I did some tiny modifications to the mounting of the tweeter but it's not 100% flush, nor I give a shit about it. I don't care what the "experts" claim, this small tweeter was designed to be mounted with a small blip since it's a press on design. And the results IMO are great.

    I spend a good amount of time listening to all kinds of stuff and I'm impressed by the wide sweet spot while still retaining great imaging. This things are really accurate and engaging. I can hear all the details and the sound is expansive while still retaining pin point localization.

    I'm very pleased with the results. I'll put up some pics today or later.
     
    Last edited: Sep 11, 2018
  3. ultrabike

    ultrabike Measurbator - Admin

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    Care should be taken when reading distortion measurements. These where in room and a bit loud. Some furniture stuff will vibrate and may result in "fake" distortion. Still, I suspect that the 3" woofer will have a trade off between distortion performance and extension. The woofer is sort of build like a mini-sub with nearly full range response.

    Note crossover is at around 3 kHz (which correlates with distortion profile), and this was done to support as wide a sweet spot as possible using the much smaller tweeter for the higher frequencies. Target low frequency extension was 70 Hz which was achieved.

    Distortion Right:
    Distortion Right.png

    Distortion Left:
    Distortion Left.png
     
    Last edited: Sep 11, 2018
  4. ultrabike

    ultrabike Measurbator - Admin

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    BTW, it is possible to milk more bass out of these drivers. However, while the bass will extend, it may start to tilt down. I preferred as ruler flat as possible response which required a tuning of 70 Hz with the right box dimensions. Stuffing can also tilt down the low frequencies. On active speakers with integrated DSPs, this can be equalized. But this is a passive speaker designed to work with dumb amplifiers and sources.

    A lot of air will come out of the port relative to the dimensions of the speaker. So I choose a relatively large port diameter to avoid noise. This meant the port had to be about 7" in a small box. I used an L shaped port to fit that kind of length. I have heard some "experts" call an L or C shaped port "retarded". Well, I don't see the issue at all, so I don't get what the f**k is so "retarded" about it. How else am I going to fit it? Reducing the diameter of the port will allow for a smaller port length, but now one may have to deal with port noise. I also don't like impotently small little ports.

    I could not find a ready made box with the right dimensions for this driver (based on the information I had), only somewhat close stuff that would result in some bass humps. Which is why I cut my own boxes at the dimensions I wanted for these drivers.

    I also did not like what I got from crossovers that other folks used for the same drivers. So I came with my own values and approach. It was hard to keep things manageable since there is not a lot of room to put oversized electronics. And volume is primo real state here.

    What I gathered from this exercise is that to get best results, one cannot just put filling or extend/reduce ports to fine tune. The size of the box is important, and that's hard to tune unless one makes it bigger and fill in with sand or whatever to reduce volume as needed. This is not an option if one wants the smallest possible enclosure. Maybe as an R&D thing till the right volume is achieved, and then go full on with the final enclosure design. But I wanted to minimize that. I think in the end the free design tool did a great job in getting that done. It saved time, frustration and money.
     
    Last edited: Sep 11, 2018
  5. maverickronin

    maverickronin Friend

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    Now I'm browsing through Parts Express tweeters trying to pick out something to go with the ND91-4 for some kind of sideways mini MTM. This thread is giving me too many ideas...
     
  6. ultrabike

    ultrabike Measurbator - Admin

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    :headbang:

    There are a few. I liked the ND16FA-6 because the ND91-4 is "full-range" and can cross a bit higher. I know some "experts" are hell bent against small tweeters, because distortion. Well, not what I measured. In fact, I believe the ND16FA-6 has to be attenuated a bit by the crossover because it's more sensitive.

    I prefer a smaller tweeter if I can cross high because I likely will get better response at different angles (better sweet spot).

    That said, I expected the ND16FA-6 to be more flat from 7 to 8 kHz...

    Check what they have in the 5/8" and 3/4" departments. The ND20FA might be easier to mount flush.

    There is also another woofer that maybe comparable to the ND91-4. I'll see if I can find it...

    EDIT: I think I found it https://www.parts-express.com/dayto...luminum-cone-full-range-driver-8-ohm--295-522
    I think I played around with it a little with the simulation tool. I'll check what I got. But it is a nice looking driver. I think they claim it can only go down to 80 Hz on a vented box, but I can't remember what the simulation actually yielded. The ND91 is hard to beat at that given same diameter.
     
    Last edited: Sep 11, 2018
  7. maverickronin

    maverickronin Friend

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    I'm trying to see if I can build something respectable at some pretty tiny dimensions, maybe 4.5 inches tall or wide max, and hopefully make up the volume with depth. That's all I might be able to fit on my desk, either under my monitors or on either side of the primary one. Or possibly go with something more normally proportitioned and mount them on monitor arms above my monitors.

    What do you think of Dayton's AMT and planar tweeters? They sound good in theory, but the spec sheets show the FR as less even that their conventional domes. I wonder if the distortion and CSDs would make up for it. I'll use a miniDSP and biamp then anyway (since I've never done it before and it seems fun) which would make that easier.
     
  8. ultrabike

    ultrabike Measurbator - Admin

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    This one is 7" (height) x 5" (wide) x 5.5" (depth) of external volume, and 6" x 4" x 4.5" of internal volume (0.5" thick walls with some routing to fit the boards). Total internal volume is 108 in^3 = 1.76 litters. The optimal volume is around 1.57 litters, but some of that volume will be taken off by the port and crossover. So those dimension work out.

    It maybe possible to take about 1" in height, but that would place the drivers very close and you would still not hit 4.5". Even if you take the tweeter away and go for something like the full range Sprite, 4.5" of height is aggressive. But maybe doable:

    https://sites.google.com/site/undefinition/sprite

    Could do something like a 4.5" (height) x 4.5" (wide) x 9.5" (depth)... Maybe. No tweeter though. Or could just put the tweeter on some tiny box somewhere... Port might be either top or back firing...

    Be aware that a small driver with large xmax in full range duty may develop issues at high frequencies due to mechanical inter-modulation distortion (low frequency woofer vibration causing the high frequencies center to vibrate too much).

    EDIT: Made some corrections to the internal volume calculation. Too many things in my mind.
     
    Last edited: Sep 11, 2018
  9. maverickronin

    maverickronin Friend

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    It only has to be that narrow in one direction. Either long and skinny like soundbar/center channel or tall and skinny like a miniature floor standing tower. That will leave room for the tweeter somewhere.

    Going to do have to do some reading and check out that simulation program you mentioned at the beginning of the thread....
     
  10. maverickronin

    maverickronin Friend

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  11. ultrabike

    ultrabike Measurbator - Admin

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  12. ultrabike

    ultrabike Measurbator - Admin

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    Making 3 more of these to fully replace my Mirage nanosat 5.1 speaker system. These really kick ass.

    Note that at 5" wide x 5.5" deep x 7" height these are close to the same size as the Energy Take 5 which are 4-1/8" wide x 4-1/8" deep x 6-7/8" height (except the center which is 10-1/4" wide).

    The Energy has a 3/4" tweeter, while these have a 5/8" (smaller) tweeter. Woofers are the same size.

    The Energy cover 110 Hz to 20 kHz, which is better than the nanosats, but not the 80 Hz minimum requirement I have for crossing over to a subwoofer.

    These ones (which I shall call from now on USM-2 for Ultrabike's Small Monitor 2-way because I like Zaph's nomenclature approach), hit down to an F-3 of 65 Hz and an F-10 of 52 Hz both by design and measured. And it shows in performance. I can't stand the nanosats anymore.

    After the next 3, I might do something equivalent to these w another set of drivers and replace my MR5 system also and put those on sale along with the stands.
     
    Last edited: Sep 22, 2018
  13. ultrabike

    ultrabike Measurbator - Admin

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    Pictures:

    Assembled cross-over, sweet and simple:
    IMG_6634_SCALED.JPG

    Left and Right in HT duty:

    IMG_6636_SCALED.JPG

    IMG_6637_SCALED.JPG

    I actually measured these speakers by moving them to the edge of the table.
     
    Last edited: Sep 23, 2018
  14. ultrabike

    ultrabike Measurbator - Admin

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    Took another picture just right now to give a better sense of their size and utility. My daughter is watching Mulan.

    IMG_6639_SCALED.JPG

    The brick with the orange light is the power supply for the Xbox 360 (found out having it inside the cabinet was causing the supply to overheat and cause random console shut-downs).

    A speaker can easily be turned on it's side and act as a center w/o too many issues given the size of the drivers.

    The TV is 46". A larger screen would further dwarf the speakers and get them completely out of your way. Note the large sweet spot and short distance driver integration (given driver size) means you all can seat relatively close to the TV and all enjoy nice engaging sound. Front port should reduce interaction with walls and further placement flexibility.

    Given the F-3 of 65 and further F-10 of 52 Hz, things sound really good even w/o a sub-woofer. The extra extension allows for many options for crossing over with a sub-woofer as well, depending on room acoustics.

    They are not super efficient. But my old cheap Yamaha receiver drives them like a champ. I used this receiver to measure them in fact. My kids and wife many times tell me to keep things down, and still have plenty of headroom.
     
    Last edited: Sep 23, 2018
  15. ultrabike

    ultrabike Measurbator - Admin

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    As I read more about this things, I always kept in mind what you guys mentioned:
    1. I'm more convinced that the dip at 6-8 kHz has nothing to do with the mounting of the tweeter and everything to do with the location of the tweeter edges to the speaker baffle edges, which are in the 1.2" to 1.5" range. Not much I want to change about the dimensions of the baffle to "fix" that. Baffle diffraction IMO seems to be more of a on-axis problem. Listening a little off axis solves the problem. Things look and sound very flat even at +/- 15 degrees and up. I could do +/-5 degree measurements as well. In fact I think I did and measurements came super flat, but did not save those. I more than like what I got here.
    2. I have frequented a number of sites and modeled their speakers. I used only PSD-Lite. But I will eventually use Bagby's spread sheet as well. This was more of a PSD-Lite tool sanity check than a design check. The designs Amiga and Core-2 by Carmody come out really well and learned a bit from them. Bagby's Tangos came out really well in the simulation, and in fact I consider his RS180-8 crossover really sweet and simple. The Helium by Scott, which predates and is similar to the design I choose for HT duty, came out a bit bright. It is not a bad design. But I get similar results to what he publishes if I forget baffle step compensation, which at some point I did and end up making a last minute change which seemed to work. This is not a Helium. It is tuned a bit more flat IMO and based on actual measurements at several angles and against other well known entry level pro monitors. I did learn a lot from Scott and do praise his efforts. I do not known many speakers this size that can be considered competitive HT speakers given very few will even go lower than 100 Hz.
    3. Many seem to want to explore a different driver such as an ND90. This is a very different driver. A closer driver would actually be a DSA90-8, though the crossover may have to be retouched.
    4. This is a small woofer and distortion will be problematic if pushed very far. The design is such as to minimize distortion at large xmax relative to driver area though, and I consider it very far from crap. I can confirm that the issue at 400 Hz shown in the past was speaker vibration due to resonance. Put it on some nice damping feet and it seems it's gone.
    5. Distortion at bass is indeed very low, and it is heard as very low. I'm lately running movies through these w/o a subwoofer and I still can't believe there is no sub support given how small these are. Not because of impact but because of how well bass and drums are conveyed, again given size. Once I start on the center channel (not MTM just sideways TM), I will hook everything up again. Not sure about replacing the nanosats as back L and F channels given they are high. But I do have full set of components to make 3 more speakers. Will have to check vertical dispersion.
    6. The price paid here is sensitivity. The model yields a 76 dB or so of sensitivity. Still, not bad given the frequency range and size. I can drive these fine with my POS Yammy receiver.
    As a side note, I will continue checking out other designs and tools to see what works. I like the RS180-4 driver (more so than the RS180-8) and I like the latest 1-1/8" Dayton reference tweeter. May do something about that later. Time will say.

    LOL! I think every one that has done something with the more expensive Scanspeak drivers have done something with the RS180 driver and may even commit the blasphemy of comparing the two.
     
    Last edited: Oct 9, 2018
  16. direstraitsfan98

    direstraitsfan98 D2Girls v2.0

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    L shape port definitely isn't retarded. Yamaha uses them in their flagship ns-5000 monitors. And btw awesome thread. I just spent the last 30 minutes reading thru it. I'm always in awe of artists, and artisans. People who can make something from nothing, using the power of their mind. Writers, artists, woodworkers, leather makers, etc etc. You actually need to know a lot of science as well when making speakers as there is a lot of math involved. Anyway, nice job! I'm super jealous of your skillz.
     
  17. ultrabike

    ultrabike Measurbator - Admin

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    Thanks!

    It's fun stuff :)
     

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