I've built a kit or two before but I'm planning to build my first speaker design as a boombox with two TCP115-4s and SB 26STCNs. I've built a box that is roughly 8.5l tuned to around 58 hz. In the front and middle will be a closed box for an infotainment radio and the rest of the box will be opened to both woofers. Dimensions are 46x22x17cm and space is getting tight especially when using some LiFePo4 batteries at the bottom.
First question is port location. Due to there not being so much room I'm left with having to mount a single round flared port facing one of the sides. Is there some reasons this will be a bad idea? I see many youtubers and even JBL using side mounted PRs but I don't know if the extra cost is worth it nor do I like Winsid showing I'll have a lazy slope downwards when I want this to "boom".
Second is the port width. I have the options of using 35, 42.7 an 50mm ports. Winsid shows that the 50mm first port resonance is 1017hz. I read about subwoofer port resonance but it doesn't really satisfy my situation. The crossover point will be around 2400hz if this helps. What size port is usually used for 4" speakers?
3rd is the tuning. Essentially each TCP will be getting 4.25L and winsid projects a 1.5db bump occurring around 60hz and the f3 being around the speaker's FS. From vituixCAD the FR starts rolling down around 100hz. With the woofers getting their rated power, will I run into any mechanical issues?
Any other advice would be welcomed. The wood is 15mm and there is some battens and extra bracing for the radio enclosure inside the box. This is my first iteration and I mainly want to use it to test what will work and what won't especially since some of my friends already want me to build them one already, heh. Perhaps one last outgoing question is what to do concern putting foam inside the box. In my country I can easily get 1-2cm foam for the walls and polyfil but will a more polyfil solution be better?
First question is port location. Due to there not being so much room I'm left with having to mount a single round flared port facing one of the sides. Is there some reasons this will be a bad idea? I see many youtubers and even JBL using side mounted PRs but I don't know if the extra cost is worth it nor do I like Winsid showing I'll have a lazy slope downwards when I want this to "boom".
Second is the port width. I have the options of using 35, 42.7 an 50mm ports. Winsid shows that the 50mm first port resonance is 1017hz. I read about subwoofer port resonance but it doesn't really satisfy my situation. The crossover point will be around 2400hz if this helps. What size port is usually used for 4" speakers?
3rd is the tuning. Essentially each TCP will be getting 4.25L and winsid projects a 1.5db bump occurring around 60hz and the f3 being around the speaker's FS. From vituixCAD the FR starts rolling down around 100hz. With the woofers getting their rated power, will I run into any mechanical issues?
Any other advice would be welcomed. The wood is 15mm and there is some battens and extra bracing for the radio enclosure inside the box. This is my first iteration and I mainly want to use it to test what will work and what won't especially since some of my friends already want me to build them one already, heh. Perhaps one last outgoing question is what to do concern putting foam inside the box. In my country I can easily get 1-2cm foam for the walls and polyfil but will a more polyfil solution be better?
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I'd be tempted to use a second pair of bass drivers on the rear of the box instead of using ports or PR's. I'd use a Linkwitz transform to get them EQ'd the same as your modelled ported box.
I've also read about small portable speakers using psychoacoustic processing to use harmonics to trick our brain into reconstructing fundamentals. I'm sure I've seen mention of a dsp processing chip that does this. Link here discusses it a bit.
Waves Maxbass 3000 was the chip.
Rob.
I've also read about small portable speakers using psychoacoustic processing to use harmonics to trick our brain into reconstructing fundamentals. I'm sure I've seen mention of a dsp processing chip that does this. Link here discusses it a bit.
Waves Maxbass 3000 was the chip.
Rob.
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A side, bottom, or rear firing port is fine. The wavelengths involved are so long that the distance is irrelevant on something this small.
Passive radiators are often used on very small boxes where the port won't fit easily (or fit at all).
The lazy downward slope in your model is likely due to an improperly tuned or incompatible passive radiator. The radiator has its own set of parameters that need to work with those of the woofer and the box. Sometimes it's just not a happy marriage, and changing passive radiators can help. But also be aware that most passive radiators allow for added mass (typically up to 2x the base moving mass) - most often you are trying to get the response to match that of a ported box. That can take a bit of fiddling with the mass.
Port diameter is typically set based on velocity of air in it. 17 m/s is one of the standard limits used. There should be a plot showing this.
There should be a graph that shows cone excursion vs. frequency for the rated power and a line at Xmax. Typically below fb a ported box will have rapidly increasing excursion. How dangerous this is is mostly related to your tendencies with the volume knob. For many, it's no big deal. For users that get carried away, some designs include a high-pass/infrasonic filter to limit excursion at low frequencies.
Depends on what you are trying to do with it. True acoustical foam is often better if you want to absorb sound, but the lower in frequency you go, the thicker it has to be. There's typically a graph for the material that shows this.
If you want to move sealed box resonance lower, a combination of foam-lined walls plus poly fill is a decent choice.
I wonder if I can use the maxbass app on the infotainment radio. Would be a fun experience. I'll definitely try to see what it's going to up sounding like before adding extra to the design. Just saw that linkwitz transformation and it looks like a doozy. A network between the network the amp? I'm still worried about the shielding of the rca to aux cable making noise.
I did tinkering with different types of radiators wand in single or double configs and I just wasn't happy with any of the results.
Thank you for reminding me that there are other functions on winsid! Even with the 35mm port the velocity maxes out at 9m/s
The foam Im looking into is: https://allegro.pl/oferta/welna-owcza-do-wytlumiania-obudowy-zgrzeblona-250g-12464007582 It seems like 'legit' speaker acoustic foam. Others I see is the acoustic egg foam from 2-5cm to line the walls with. Thank you for the help.
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One more question. I have a chinese 12 volt 2 din radio that will just be used for bluetooth and as the 'infotainment' center. An external amplifier will be the one actually powering the speakers. How many watts and amperage would you guys estimate the radio draws just to be on while using bluetooth? Perhaps also if the wifi is also being used.
You may want to to ask that one in the Car Audio forum. Though ultimately you may just want to measure it yourself if you're looking for a precise number.
At this point taking some self measurements make sense. After the battery pack and wiring is done I'll try to post up some numbers for anyone else that want's to do something similar.