This is an idea which has been noodling about in my head for some time. A small portable active speaker, of modest cost. Something I can easily build multiple copies of, something I can give as a gift if I choose. I have friends who are decent woodworkers who have inquired about making a copy of one of my existing speakers, but they have balked at the expensive drivers and electronics I use… so this is something I can point to and say “you can copy this…”
I also like the idea of an expandable speaker where a second woofer cabinet can be added to extend the bass response and give higher SPL capability. I got this idea from the Barefoot Sound, where several of their very fine monitor speakers are expandable in this way.
========== =============
Primary Goals
The finished system shall be a compact, active, 3-way with 8” woofer, with a total internal volume of 16-24 liters, with sealed box bass alignment. Update: 10" woofer in a 25 liter volume.
Performance Goals
A single 2x4HD shared between two speakers will not provide the necessary 6 channels of signal required by a pair of 3-way speakers. But a single 2x4HD could be used in an active/passive speaker. This is something that has interested me for some time. A passive crossover from tweeter to mid, then active crossover from mid to woofer. There would be 2 amplifier channels required. I find the challenge of this architecture intriguing.
The interesting thing about this approach is that the passive crossover does not need to perform any EQ of the drivers within their individual pass band, nor does it need to manage the overall EQ or voicing of the speaker. This can all be done by DSP. The DSP can also provide BSC for the woofer channel and the mid/tweeter channel. The DSP can tailor the bass response of the woofer. The passive network will need to provide a high-pass and low-pass function for each driver, and relative level matching between tweeter and mid. The passive network will manage the relative magnitude and phase of the drivers through the crossover, and as a result of this, it will manage the directivity index.
The passive network will also manage any out-of-passband EQ. The most likely need for this would be a notch filter on the woofer or midrange at a frequency above the low-pass filter. For example, if the midrange passively crosses to the tweeter at 3k, but the mid has a + 9 dB breakup peak at 8k, the DSP will not be useful in managing that peak. Any EQ at 8k would affect the tweeter response, which would be quite unfortunate. Thus the passive network will need to handle that.
So at this point, I believe this is how I will proceed. There are a lot of amplifier options which offer low cost and acceptable performance, so this remains an open decision.
j.
================== Update 2/01/2024 =================
Index to important posts or milestones
post numbers are included with links
Decision to use a 10” woofer 119
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7447588
Process of defining cabinet dimensions 132
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7449092
Simulating flat face tweeter vs tweeter with waveguide 124 135 164
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7448383
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7449284
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7450834
Concept sketch 197 236
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7452598
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7455272
Decision to use SB15NBAC 236
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7455272
Electronics block diagram 280
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7457445
Prototype testing of tweeters 289 314
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7457716
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7472903
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7471898
Simulations with prototype data to define mid/tweeter spacing 344 351
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7482295
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7482756
Cabinet construction photos 413 452
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7514053
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7522584
Structural bracing and damping strategy 429 439 442
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7517669
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7518089
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7518208
Cutting tapered bevels 466 467
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7526218
Cabinet assessment – looking for resonances 503
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7539527
Driver polar responses measured in finished cabinet 506
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7539853
Final passive crossover design, and system level polar response and Power&DI 583 605
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7558072
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7567335
Frequency response of Class D amplifiers 613 627 634
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7570120
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7570523
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7575669
Documentation
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7586028
I also like the idea of an expandable speaker where a second woofer cabinet can be added to extend the bass response and give higher SPL capability. I got this idea from the Barefoot Sound, where several of their very fine monitor speakers are expandable in this way.
========== =============
Primary Goals
The finished system shall be a compact, active, 3-way with 8” woofer, with a total internal volume of 16-24 liters, with sealed box bass alignment. Update: 10" woofer in a 25 liter volume.
Performance Goals
- Bass response F3 = 40 Hz.
- On axis within target response +/- 1.5 dB from 100 hz – 16 kHz.
- Directivity Index within target response +/- 1.5 dB from 500 Hz – 10 kHz
- No specific max SPL goal or harmonic distortion goal, other than these performance attributes shall be optimized to the extent possible given the drivers selected and the other requirements.
- Low driver cost and low electronics cost. At this point, “low cost” is not really defined, but low driver costs would be in comparison to Scanspeak Revelator, Satori, Bliesma, Purifi, etc. I was thinking on the order of $250 of drivers per side, but this is flexible. In terms of electronics, “low cost” means significantly less than a Hypex FA-123 ($550 per side).
- Easily replicable. This means easily built with readily available parts. I may want to make multiple copies to give as gifts.
- Simple cabinet finishing that does not require weeks of shaping, sanding, veneering, sanding, varnishing, polishing, etc.
- Easily portable.
- A modular design which would allow me to design/fabricate a second bass driver/cabinet later. This would extend the bass response and expand the SPL capability. Update: Modular design is no longer needed with the change from 8" to 10" woofer.
- An opportunity to try new techniques and learn new skills which can be applied to my future high end projects.
- An opportunity to discover new information which would be of use to other DIY speaker builders and developers.
A single 2x4HD shared between two speakers will not provide the necessary 6 channels of signal required by a pair of 3-way speakers. But a single 2x4HD could be used in an active/passive speaker. This is something that has interested me for some time. A passive crossover from tweeter to mid, then active crossover from mid to woofer. There would be 2 amplifier channels required. I find the challenge of this architecture intriguing.
The interesting thing about this approach is that the passive crossover does not need to perform any EQ of the drivers within their individual pass band, nor does it need to manage the overall EQ or voicing of the speaker. This can all be done by DSP. The DSP can also provide BSC for the woofer channel and the mid/tweeter channel. The DSP can tailor the bass response of the woofer. The passive network will need to provide a high-pass and low-pass function for each driver, and relative level matching between tweeter and mid. The passive network will manage the relative magnitude and phase of the drivers through the crossover, and as a result of this, it will manage the directivity index.
The passive network will also manage any out-of-passband EQ. The most likely need for this would be a notch filter on the woofer or midrange at a frequency above the low-pass filter. For example, if the midrange passively crosses to the tweeter at 3k, but the mid has a + 9 dB breakup peak at 8k, the DSP will not be useful in managing that peak. Any EQ at 8k would affect the tweeter response, which would be quite unfortunate. Thus the passive network will need to handle that.
So at this point, I believe this is how I will proceed. There are a lot of amplifier options which offer low cost and acceptable performance, so this remains an open decision.
j.
================== Update 2/01/2024 =================
Index to important posts or milestones
post numbers are included with links
Decision to use a 10” woofer 119
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7447588
Process of defining cabinet dimensions 132
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7449092
Simulating flat face tweeter vs tweeter with waveguide 124 135 164
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7448383
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7449284
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7450834
Concept sketch 197 236
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7452598
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7455272
Decision to use SB15NBAC 236
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7455272
Electronics block diagram 280
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7457445
Prototype testing of tweeters 289 314
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7457716
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7472903
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7471898
Simulations with prototype data to define mid/tweeter spacing 344 351
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7482295
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7482756
Cabinet construction photos 413 452
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7514053
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7522584
Structural bracing and damping strategy 429 439 442
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7517669
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7518089
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7518208
Cutting tapered bevels 466 467
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7526218
Cabinet assessment – looking for resonances 503
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7539527
Driver polar responses measured in finished cabinet 506
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7539853
Final passive crossover design, and system level polar response and Power&DI 583 605
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7558072
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7567335
Frequency response of Class D amplifiers 613 627 634
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7570120
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7570523
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7575669
Documentation
https://www.diyaudio.com/community/threads/compact-low-cost-active-3-way-speaker.402812/post-7586028
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