"modular" - DSP based 3-printed DIY speaker system

This page is about DIY-speaker system I build and keep experimenting. I try to build the system so that I can exchange different parts of system easily, hence the name "modular".

I live in apartment building, and prefer to do critical music listening "close-field". So I don't need to play music loud and this naturally affects some of my design choices. For example I know I can make 3 way system working with 4.5 inch midwoofer in my use - that would be impossible in large well damped wood frame house with habits of playing loud.

Basic princibles of "modular"

DSP used as crossover, time alignment and equalization

I prefer active crossovers and directly connecting amplifiers to drivers. Naturally this requires 8 amplifier channels for 4-way stereo system, which will cause some extra cost. For me flexibility of being able to try different settings realtime without first buying crossover components and soldering is the most important reason for active crossover. In my opinion subwoofer and midbass sound much better when there is no 1ohm resistor in series with the bass driver, specially with good amplifiers with large damping factor.

System must work for nearfield and in general use

I prefer to listen music nearfield, but watch television/movies from sofa which is about 2x distance compared to critical music listening spot. Sofa is also in back wall, and near field listening position more ideally 1/3 room length away. Mostly this can be easily achieved by setting delays and levels in DSP. Some combinations of tweeters and midranges in their enclosures will not produce room power response suitable for such different snenarios.

3-way or 4-way configuration

I want to experiment with different combinations, e.g. large midbass with very large waveguide on tweeter vs. small midrange and small waveguide on narrow enclosure or maybe go really wild and use bare tweeter without waveguide :) and naturally 4-way with more optimally sized drivers.

3D-printed midrange and tweeter enclosures with standard front panel

I expect most innovation and prototyping to happen with midrange and tweeter enclosures. I'm specially interested on designing different waveguides for tweeters to optimize directivity and power response in room.

In order to try different midranges with different tweeters, or different enclosures for either one I have chosen few common dimensions to be used, let's call this "v1" specification:
- front panel width 160mm with 18mm rounding in corners...
- ...at bottom of tweeter enclosure and top of midrange enclosure (otherwise free shape)
- Two M5 bolts sticking out from midrange enclosure: 55mm from centerline, 40mm from front panel

Most likely at some point I will also try B&W 802 kind of round midrange enclosure without actual front panel. That will not be "modular", but naturally I'll use the same subwoofer and midbass system.

Midbass cabinet/speaker stand

I'll use 800mm heigth and 200mm width midbass enclosures made from wood. They will either server as midbass or just as an speaker stand. When used as midbass they will either be midbass in 4-way system or midrange in 3-way system combined to large (max 200mm) waveguide for tweeter.

Separate 3D-printed panel is used for the driver, allowing multiple different drivers to be used. Enclosure volume can be adjusted to suit the driver. Midbass always in sealed enclosure, which if full of damping material.

Subwoofers integrated part of system

The "modular" system is never intended to work without subwoofer. I see no point designing 2-way speaker, which would need to work without subwoofers and any of my main speakers never would be good or even usable by themselves.

Subwoofers are in small sealed wood cabinets, there is many of them and they are distributed in room to minimize standing waves. Small sealed enclosures are easy to place to good locations, but don't go very low: in order to compensate Linkwithz-transformer is used and each driver has ~400w power available. Subwoofers are driven with 2 amplifier channels and delays can be set to compensate different distances.

Journey or destination?

Over the years I have had many speakers, but in the end I have always returned back to my DIY speakers I built on 1990s. I know I would be happy with pair of Genelec 1237A or Amphion Krypton 3, but I would never "invest" that much money for home audio.

Commercially sold 4-way system including Scanspeak Illuminator 7"+4"+tweeter (or similar Seas Excel parts) would cost >10000€. Drivers itself cost less than 2000€. Commercial speaker needs to be designed as a compromise to suit all usage scenarios and rooms. So there is also good change to reach very good "destination" with basic understanding of speaker design, physics relevant to speakers and willingness to learn and improve by building prototypes.

Goal of this "project" (hobby could be better word) is naturally to get good speakers for music listening, but for me it's as important to study, learn, innovate, design and build different solutions. This project has failed if it becomes ready :)




Driver notes - Tweeters

Dayton AudioND16FA-4pdf.
Dayton AudioND20FB-4pdf.
Dayton AudioNHP25Ti-4pdf.
Dayton AudioRST28A-4pdf.
Dayton AudioDC28FT-8pdf.
Dayton AudioPTMini-6pdf.
Dayton AudioAMTPRO-4pdf.
GRSPT2522-4pdf The PT2522-4 is open back planar tweeter. It has dropping response (on manufacturer's measurements) between 4Khz and 1.5kHz, so it will take large waveguide very well, as it will smooth the frequency response nicely.
GRSPT2522C-4pdf PT2522C-4 is a closed back version of the PT2522-4, otherwise seems to be the same. Due to the closed back it drops about 12-15db/octave below 2kHz. The closed back has raised the 2-3kHz level, and on-axis the frequency response is practically flat from 2kHz all the way to 20kHz within few decibels.
GRSPT6825-8pdf The PT 6825-8 is mid/tweeter. It's radiating area is about 170mm x 50mm, so even it goes all the way to 20kHz, it might be best used as midrange; the vertical directivity is "too" high at highest frequencies. Manufacturer says that is usable from 250Hz, but more realistical is to cross it little higher around front baffle step range.
MorelSupreme ST 1108pdf.
PeerlessDA32TX00-08pdf Great metallic dome tweeter, which can be crossed quite low even without waveguide. I really like how this tweeter sounds. Unfortunately Peerless is only selling this in large batches, and therefore it's not available for purchase - unless some store buys large batch.
SB AcousticsSB19ST-C000-4pdf.
SB AcousticsSB21RDC-C000-4pdf.
SB AcousticsSB21SDCN-C000-4pdf
SB AcousticsSB26ADC-C000-4pdf ADC variant has aluminium dome, which is anodized to black. On manufacturer's measurements this version seems to have more "beaming" at high frequencies compared to the "ceramic" version. Interesting to see if there is any difference in my own measurements using different waveguides. By eye the dome shape looks exactly same in ADC and CDC. ADC and CDC are mechnanically same, and therefore same 3D-printed waveguides can be used. I personally would have preferred lower Fs than the ~750Hz on these. For horn/waveguide usage the "throat" of the horn can be quite narrow, about 33mm - this is much smaller than those tweeters, which have wide surround.
SB AcousticsSB26CDC-C000-4pdf CDC variant has "ceramic" dome, which is white.
SB AcousticsSB26STWGC-4pdf
SB AcousticsSB29RDNCpdf
SB AcousticsSB29TXN-Bpdf
SB AcousticsSatori TW29BNWGpdf As I'm mostly wanting to experiment with my own waveguides I wanted one good manufacturer made reference. I would have hoped little lower Fs for my use cases, but I guess manufacturer's need the high sensivitity to sell these.
Scan-SpeakR2604/833000pdf R2604/833000 raised my attention because of being ring radiator, which according to some sources work well in waveguides. Also it has very low Fs of 440Hz, which helps keeping the resonance far away from the operating range even with very large waveguides making possible crossover frequency 1000-1200Hz. Due to ring radiator design the "throat of the horn" needs to be very large, about 39mm.
Scan-SpeakD3004/602010pdf D3004/602010 is one of my favorite soft dome tweeters. It has nice very nice sound and very small front diameter (diameter 62mm), which makes very narrow enclosures possible.
Scan-SpeakD3004/606200pdf D3004/606200 is Textreme version of Illuminator small front plate tweeter.

Driver notes - Midranges

Dayton AudioPS95-8pdf.
Dayton AudioRS52AN-8pdf.
MorelMDM 55pdf.
PeerlessGBS-115N25AL01-04pdfThe PDF resolution sucks, here is picture of the frame dimensions.
SB AcousticsSB65WBAC25-4pdf.
SB AcousticsSB12CACS25-8pdf.
SeasExcel W12CY001pdf This 4.5 inch midrange has very nice sound. While figuring out 3D printer improvements to be able to print large ABS enclosures, I used this from 110Hz to tweeter for over a year. In this use case 24db/octave filter is definitely needed to survive with the 3mm Xmax.
Tang BangW4-1320SJpdf.
Tang BangW4-1337SDFpdf.

Driver notes - Woofers

ManufacturerModelDocumentationQtc @ 9.2lF3(Hz) @ 9.2lQtc 0.707 / Vb(l)Qtc 0.707 / F3(Hz)Description
Dayton AudioSIG180-4pdf 0.64781.1 7.0 82.0.
Dayton AudioRS150T-8pdf0.54698.54.196.3 Dayton Audio quality control is awful - the skrew holes are about 5° compared to truncated frame.
MorelEW 638pdf0.52995.44.093.1 Comment before never actually using the woofer: woofer suspension is really stiff and the resistance pressing cone up is considerably larger vs. pressing cone down. Very hard to believe this woofer would have 5mm Xmax, maximum few mm of somewhat linear operation.
PurifiPTT6.5X08-NAA-08pdf0.64764.9 7.0 65.5.
SB AcousticsMW16TX-4pdf 0.61480.1 6.4 81.5.
SB AcousticsSB17CAC35-8pdf 0.75761.0 11.259.7.
SB AcousticsSB34NRX75-16pdf N/A N/A N/A N/A12" open baffle woofer
Scan-Speak15WU/8741T00pdf 0.434113.02.5 101.9.
Scan-Speak18W/8545K00pdf 0.62774.7 6.8 75.9.
Scan-Speak18W/8531G00pdf 0.85565.0 15.459.7.
SeasL16RN-SLpdf 0.70863.8 9.3 63.8.
SeasU18RNC/Ppdf 0.62188.4 6.3 89.3.
SeasExcel W18E001pdf 0.77164.3 11.962.6.
SeasP17REXpdf .... Over the years used many speakers but always returned to DIY speakers built on 1990s, using this midrange. Interesting to compare these to modern woofers. EDIT: Time has not been kind to these woofers; the Fs is over 70Hz, so these can't be anymore used.