Hi everyone. I'd like to get some feedback for a design that has been in the making for a year or so now. The goal is to design the very finest small speaker with the challenge to pack as much performance into a speaker that physically looks small, which I determined to be a wide but short speaker like a sound dock. This project stems from when I needed a small speaker for a small room and my utter disappointment with the sound quality of small commercial speakers and sound docks. The combination of extreme size restrictions and high fidelity requirements presented an extremely interesting and enjoyable challenge. After way too many hours of researching, modelling, testing and thinking, etc, I think I got to a point where the design is mostly complete, and I want to share it here and get some comments on possible improvements from members here that knows much more than I do. This silly challenge has been much more expensive than anticipated (but way more fun than anticipated too), so I'd like to get the design really right before I build. The value factor is a solid -1/10, but the fun factor is definitely a 12/10.
For those interested, I talked about my previous attempt at such a speaker here. What I'm proposing here is a successor that improves upon every performance aspect after learning everything from the previous build.
Design goal: Build the highest fidelity small speaker possible with as much bass output as possible down to 40Hz.
In more specific speaker design goals, I wanted to achieve the following, in no particular order:
1. Excellent clarity, deep bass response, and extremely high dB per liter ratio for bass.
2. Minimize/eliminate horizontal and vertical lobing errors
3. Matched directivity and smooth polar response
4. Minimal cabinet vibration
5. Excellent off axis response
6. Linear and minimum phase response
7. Good dynamics
8. Transient perfect response
9. Time aligned drivers
10. Minimize baffle diffraction
11. Ruler flat frequency response
12. Flat power response
Driver selection:
Tweeter: Wavecor TW030WA13 Neodymium 30mm tweeter
Originally I planned on using the Scanspeak D3004-602000 tweeter. However, it was brought up to me that the Scanspeak's very low sensitivity of 86dB (measured from Medley's Musings) might strain during higher volumes. I also wanted to use a very low sub 1500Hz crossover with the tweeter to achieve a crossover frequency at the 1/4'' wavelength of the CTC of the midrange and tweeter, and this tweeter does not seem suited to be crossed under 2000Hz.
Therefore, I will be using the Wavecor TW030WA13. This is a 1.2'' tweeter flangeless 4 Ohm tweeter. This tweeter has a sensitivity of 93.5dB @ 2.83V, which is 7.5dB higher than the Scanspeak. Wavecor's specs are known to be very accurate, so I believe the 93.5dB sensitivity is real. The 57% larger Sd and 3x higher Xmax means the tweeter will likely to play a lot lower with less distortion at high volumes. I don't know if it'll sound as good as the Scanspeak as they are the benchmark small format tweeter. I do expect it to sound very close, and the benefit of the vastly higher sensitivity for dynamics and higher peak SPL should outweigh the slight sound quality advantage of the Scanspeak.
Midrange: Scanspeak 10F/4424G 4'' Neodymium midrange
This is the best sounding ~3'' cone midrange available, and the largest midrange I can accommodate to achieve a 1/4'' wavelength crossover frequency with the tweeter. While there are 3'' domes, they are all physically bigger than the 10F, and it must be crossed much higher at around 600-1000Hz when I want the midrange to be crossed lower at around 400Hz because the woofer compartment won't have damping material (the reason is explained in the cabinet design section). The dual opposed woofers also requires a crossover frequency around 400Hz as they will be 90 degrees out of phase at 566Hz. The woofer's response also stops being omnidirectional above ~500Hz.
I actually tried very hard to use the Audax HM100Z0 because it is a more detailed mid and 6dB higher sensitivity for better dynamics and higher maximum midrange SPL. However, it required the box to be 0.75'' wider and taller to accommodate the bigger size, and the speaker is already too big as it is, so it was ultimately abandoned.
Woofer: 2x Wavecor WF152BD05 6'' Glass-fibre woofer
The woofer search gave me a lot of trouble due to the sheer number of choices and trying to find one suitable for bass. This is a classic compromise problem of bass and midrange clarity. Not only many of the high quality and high fidelity 5-6'' midwoofers do not reproduce bass very well at high excursion levels, most are not designed for small enclosures and have "high" Vas and low Fs, both are not "ideal" for small PR enclosures as a high Vas leads to very poor PR efficiency in a severely undersized enclosure and less overall bass output of up to 3dB for the same input power. A driver that is ideal for high output bass reproduction and has a small Vas, such as the Tang Band W5-1138SMF, does not have high fidelity midrange, which would be unacceptable given the best in class sound quality of the other components.
I almost gave up and just used a high fidelity woofer and sacrifice bass output, but after some serious digging, I found a little known driver from Wavecor that has almost the best of both worlds. It had pretty much the ideal T/S parameters suitable for my design, while having extremely good sound quality comparable to the Scanspeak 5'' Revelator midrange. The result is a woofer that is 2-3dB more power efficient in the 40-55Hz range than nearly all high fidelity midwoofers, and just 1dB less than the W5-1138SMF, the ideal miniature bass driver for this application and 2dB less than an ideal hypothetical driver that has ideal specs like the Tang Band but also have an unrealistically high motor strength. The two woofers should be able to put out a stunning 95-108dB from 40-100Hz from *each* speaker.
Passive radiator: 2x DIY PR from modifying the Tang Band W5-1138SMF.
Using the Peerless 5.25'' PR would be the easiest solution, but there is only space for 1 PR per driver, and the PR's 6mm xmax is not enough excursion. I can use 3 of them, or 1.5 PR per active driver, which would be close, but the mass needed to reach a 42Hz tuning at almost 2x the Mms, might be too much for the PR's suspension to handle. It also unbalances the dual opposed design of this speaker and will cause unnecessary vibrations.
So a solution could be to make a DIY PR. The Tang Band W5-1138SMF is a very good candidate as it has a 9mm xmax, so the xmech must be a lot higher than 9mm. The driver has at least 2x more excursion than the Peerless PR, which should be enough for the woofer. The Mms of the driver, at 29g, is 2-3x higher than a typical 5'' woofer, which means the suspension has the greatest chance of handling the ~60g of Mms needed to hit the tuning. At $30 each, it is not expensive either considering it has more displacement than 2 of the $13 Peerless 5'' PR's.
Enclosure design
The enclosure will be 14.5'' x 6'' x 6'' built with 1/4'' baltic birch plywood. In the horizontal configuration, the driver configuration looks like
The enclosure is a pair of dual opposed configuration. The woofer and woofer will be back to back, and so will the PR's. This configuration will cancel out any mechanical vibrations acting on the enclosure, allowing me to use a 1/4'' BB plywood and still get a vibration free cabinet. The tweeter and midrange will be arranged vertically in the horizontal placement. This allows me to use a 1/4'' BB for the enclosure and still have a vibration free cabinet. Every driver will have their frame/face plate cut off to reduce the physical size for mounting on the baffle. The midrange chamber is 3.75'' x 3.75'' x 4'' HWD and will be heavily stuffed with wool felt and polyfill. There will be no damping material of any sort in the main enclosure because:
1. The cabinet is too small to have standing wave issues <400Hz where the mid to woofer crossover is.
2. According to BBC's research, 1/4'' thickness walls will have a resonance frequency <100Hz, which is out of the midrange band and too low to damp anyways, and at ~500Hz, which is above the woofer's band.
3. Damping material are not very effective for frequencies that low, especially the most I can put is 1/4'' thickness of felt.
4. Damping materials will reduce passive radiator efficiency and reduce bass output
One downside is that I cannot have a configuration where I turn the speaker into an MTM and bypass the 10F.
The midrange tweeter will be in a vertical configuration to save width. All drivers will have their frames cut off to reduce size and so they can fit closer together, especially the midrange and tweeter. When drivers have a crossover frequency that is the same frequency as the 1/4 wavelength of the center to center distance each other, the sound of the two sources couple as if it is coming from one source like a point source speaker. This eliminates any vertical or horizontal lobing errors, so the speaker can be placed horizontally like a sound dock or vertically when used as a pair with no performance degradation. Imaging and coherence is improved, and the directivity is matched between the woofer and tweeter, improving imaging further.
DSP processing:
A miniDSP 2x4 HD will be used as the crossover and compressor. FIR filters will be used to achieve linear phase. The speakers will be time aligned. The crossovers will be LR4, and things like baffle step correction, bass boost, high pass, and driver response correction will also be done after the speaker is built as I prefer to measure instead of relying on simulation graphs.
The crossover will be set at 400Hz LR4 between the mid and the woofer. The crossover for the tweeter and midrange will be at the 1/4'' wavelength frequency of their center to center spacing, LR4. Another configuration will be set for 1/2'' wavelength when very high volume is needed.
The speaker will be DSP'd flat to 38Hz and a 48dB/oct high pass will be applied at 35Hz. The speakers are tuned for 42Hz, and a vented system will provide a boost up to 1/6 below the tuning frequency, which in this case is 38Hz. A 35Hz high pass is used to protect the system from unloading below tuning while avoid messing up the flat response to 38Hz.
A 2 band compressor will be used to protect the speaker. I'm thinking of leaving the >50Hz band uncompressed, and the 40-50Hz band will be compressed with a ratio of 50 and an attack of 1ms. This is extreme, but so far it has been working pretty well with the previous speaker. I need to learn more about compressors before I experiment to find better settings. Any tips here would be helpful.
Amplifier:
I will be internally amplifying using the ICEpower 50ASX2 for the midrange and tweeter, which will provide 50W @ 4 ohms for each driver. The two woofers will be powered by the ICEpower 125ASX2, which will deliver 125W @ 4 ohms per channel to the woofers. The ICEpower amps are very high performance class D amplifiers that should sound much better than most of the class D amplifiers on eBay and Alibaba that may have questionable designs and parts quality. There will be no doubts on the excellent sound quality, power output, and build quality of ICEpower amps. They have integrated power supplies, the dimensions are incredibly small and they're not horribly expensive.
Thanks for reading through this very long post. What do you think of the design? Any comments or suggestions for improvement would be greatly appreciated.
For those interested, I talked about my previous attempt at such a speaker here. What I'm proposing here is a successor that improves upon every performance aspect after learning everything from the previous build.
Design goal: Build the highest fidelity small speaker possible with as much bass output as possible down to 40Hz.
In more specific speaker design goals, I wanted to achieve the following, in no particular order:
1. Excellent clarity, deep bass response, and extremely high dB per liter ratio for bass.
2. Minimize/eliminate horizontal and vertical lobing errors
3. Matched directivity and smooth polar response
4. Minimal cabinet vibration
5. Excellent off axis response
6. Linear and minimum phase response
7. Good dynamics
8. Transient perfect response
9. Time aligned drivers
10. Minimize baffle diffraction
11. Ruler flat frequency response
12. Flat power response
Driver selection:
Tweeter: Wavecor TW030WA13 Neodymium 30mm tweeter
Originally I planned on using the Scanspeak D3004-602000 tweeter. However, it was brought up to me that the Scanspeak's very low sensitivity of 86dB (measured from Medley's Musings) might strain during higher volumes. I also wanted to use a very low sub 1500Hz crossover with the tweeter to achieve a crossover frequency at the 1/4'' wavelength of the CTC of the midrange and tweeter, and this tweeter does not seem suited to be crossed under 2000Hz.
Therefore, I will be using the Wavecor TW030WA13. This is a 1.2'' tweeter flangeless 4 Ohm tweeter. This tweeter has a sensitivity of 93.5dB @ 2.83V, which is 7.5dB higher than the Scanspeak. Wavecor's specs are known to be very accurate, so I believe the 93.5dB sensitivity is real. The 57% larger Sd and 3x higher Xmax means the tweeter will likely to play a lot lower with less distortion at high volumes. I don't know if it'll sound as good as the Scanspeak as they are the benchmark small format tweeter. I do expect it to sound very close, and the benefit of the vastly higher sensitivity for dynamics and higher peak SPL should outweigh the slight sound quality advantage of the Scanspeak.
Midrange: Scanspeak 10F/4424G 4'' Neodymium midrange
This is the best sounding ~3'' cone midrange available, and the largest midrange I can accommodate to achieve a 1/4'' wavelength crossover frequency with the tweeter. While there are 3'' domes, they are all physically bigger than the 10F, and it must be crossed much higher at around 600-1000Hz when I want the midrange to be crossed lower at around 400Hz because the woofer compartment won't have damping material (the reason is explained in the cabinet design section). The dual opposed woofers also requires a crossover frequency around 400Hz as they will be 90 degrees out of phase at 566Hz. The woofer's response also stops being omnidirectional above ~500Hz.
I actually tried very hard to use the Audax HM100Z0 because it is a more detailed mid and 6dB higher sensitivity for better dynamics and higher maximum midrange SPL. However, it required the box to be 0.75'' wider and taller to accommodate the bigger size, and the speaker is already too big as it is, so it was ultimately abandoned.
Woofer: 2x Wavecor WF152BD05 6'' Glass-fibre woofer
The woofer search gave me a lot of trouble due to the sheer number of choices and trying to find one suitable for bass. This is a classic compromise problem of bass and midrange clarity. Not only many of the high quality and high fidelity 5-6'' midwoofers do not reproduce bass very well at high excursion levels, most are not designed for small enclosures and have "high" Vas and low Fs, both are not "ideal" for small PR enclosures as a high Vas leads to very poor PR efficiency in a severely undersized enclosure and less overall bass output of up to 3dB for the same input power. A driver that is ideal for high output bass reproduction and has a small Vas, such as the Tang Band W5-1138SMF, does not have high fidelity midrange, which would be unacceptable given the best in class sound quality of the other components.
I almost gave up and just used a high fidelity woofer and sacrifice bass output, but after some serious digging, I found a little known driver from Wavecor that has almost the best of both worlds. It had pretty much the ideal T/S parameters suitable for my design, while having extremely good sound quality comparable to the Scanspeak 5'' Revelator midrange. The result is a woofer that is 2-3dB more power efficient in the 40-55Hz range than nearly all high fidelity midwoofers, and just 1dB less than the W5-1138SMF, the ideal miniature bass driver for this application and 2dB less than an ideal hypothetical driver that has ideal specs like the Tang Band but also have an unrealistically high motor strength. The two woofers should be able to put out a stunning 95-108dB from 40-100Hz from *each* speaker.
Passive radiator: 2x DIY PR from modifying the Tang Band W5-1138SMF.
Using the Peerless 5.25'' PR would be the easiest solution, but there is only space for 1 PR per driver, and the PR's 6mm xmax is not enough excursion. I can use 3 of them, or 1.5 PR per active driver, which would be close, but the mass needed to reach a 42Hz tuning at almost 2x the Mms, might be too much for the PR's suspension to handle. It also unbalances the dual opposed design of this speaker and will cause unnecessary vibrations.
So a solution could be to make a DIY PR. The Tang Band W5-1138SMF is a very good candidate as it has a 9mm xmax, so the xmech must be a lot higher than 9mm. The driver has at least 2x more excursion than the Peerless PR, which should be enough for the woofer. The Mms of the driver, at 29g, is 2-3x higher than a typical 5'' woofer, which means the suspension has the greatest chance of handling the ~60g of Mms needed to hit the tuning. At $30 each, it is not expensive either considering it has more displacement than 2 of the $13 Peerless 5'' PR's.
Enclosure design
The enclosure will be 14.5'' x 6'' x 6'' built with 1/4'' baltic birch plywood. In the horizontal configuration, the driver configuration looks like
Code:
W P WMTP
1. The cabinet is too small to have standing wave issues <400Hz where the mid to woofer crossover is.
2. According to BBC's research, 1/4'' thickness walls will have a resonance frequency <100Hz, which is out of the midrange band and too low to damp anyways, and at ~500Hz, which is above the woofer's band.
3. Damping material are not very effective for frequencies that low, especially the most I can put is 1/4'' thickness of felt.
4. Damping materials will reduce passive radiator efficiency and reduce bass output
One downside is that I cannot have a configuration where I turn the speaker into an MTM and bypass the 10F.
The midrange tweeter will be in a vertical configuration to save width. All drivers will have their frames cut off to reduce size and so they can fit closer together, especially the midrange and tweeter. When drivers have a crossover frequency that is the same frequency as the 1/4 wavelength of the center to center distance each other, the sound of the two sources couple as if it is coming from one source like a point source speaker. This eliminates any vertical or horizontal lobing errors, so the speaker can be placed horizontally like a sound dock or vertically when used as a pair with no performance degradation. Imaging and coherence is improved, and the directivity is matched between the woofer and tweeter, improving imaging further.
DSP processing:
A miniDSP 2x4 HD will be used as the crossover and compressor. FIR filters will be used to achieve linear phase. The speakers will be time aligned. The crossovers will be LR4, and things like baffle step correction, bass boost, high pass, and driver response correction will also be done after the speaker is built as I prefer to measure instead of relying on simulation graphs.
The crossover will be set at 400Hz LR4 between the mid and the woofer. The crossover for the tweeter and midrange will be at the 1/4'' wavelength frequency of their center to center spacing, LR4. Another configuration will be set for 1/2'' wavelength when very high volume is needed.
The speaker will be DSP'd flat to 38Hz and a 48dB/oct high pass will be applied at 35Hz. The speakers are tuned for 42Hz, and a vented system will provide a boost up to 1/6 below the tuning frequency, which in this case is 38Hz. A 35Hz high pass is used to protect the system from unloading below tuning while avoid messing up the flat response to 38Hz.
A 2 band compressor will be used to protect the speaker. I'm thinking of leaving the >50Hz band uncompressed, and the 40-50Hz band will be compressed with a ratio of 50 and an attack of 1ms. This is extreme, but so far it has been working pretty well with the previous speaker. I need to learn more about compressors before I experiment to find better settings. Any tips here would be helpful.
Amplifier:
I will be internally amplifying using the ICEpower 50ASX2 for the midrange and tweeter, which will provide 50W @ 4 ohms for each driver. The two woofers will be powered by the ICEpower 125ASX2, which will deliver 125W @ 4 ohms per channel to the woofers. The ICEpower amps are very high performance class D amplifiers that should sound much better than most of the class D amplifiers on eBay and Alibaba that may have questionable designs and parts quality. There will be no doubts on the excellent sound quality, power output, and build quality of ICEpower amps. They have integrated power supplies, the dimensions are incredibly small and they're not horribly expensive.
Thanks for reading through this very long post. What do you think of the design? Any comments or suggestions for improvement would be greatly appreciated.
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