As Chris said, there is free software that can help with that job. You enter some of the driver's Thiele-Small parameters, and a few mouse-clicks later, you have what you need.
The link you posted is to a nominally 5" speaker. I'm a little confused, because I've never seen a ukulele big enough to accommodate a 5" speaker.
But if I've understood you correctly, and you plan to actually fit that rather large speaker into a 'uke, you will need all the internal volume you can get - my suggestion is to use the entire volume of the inside of the instrument. Don't try to build a smaller enclosure inside. As I mentioned earlier, deep bass and small enclosures are a very inefficient combination.
Even without WinISD, we can hand-wave our way to some interesting conclusions. Your chosen speaker has a 44 Hz resonant frequency, and a Vas of 13.4 litres.
If you mounted your speaker in a hypothetical infinitely large sealed box, it would have a 44 Hz resonance. If you mount it in anything smaller than that, that resonance frequency gets pushed higher. The springiness of the air trapped in the box adds to the springiness of the speaker's own suspension (surround and spider), and has much the same effect as putting stiffer springs in your race car - it raises the resonant frequency.
The concept is easy enough, but we need something a bit more quantitative. How much smaller than "infinity" does the box have to get, to have a significant effect on bass response?
Well, by definition, Vas is the volume of air which (if contained in a sealed enclosure behind the speaker) has the same spring stiffness as the speaker's own suspension does. In other words, if you were to mount your speaker into a box with a volume of 13.4 litres, that would double the spring stiffness of your speaker's suspension - which would raise the bass resonance frequency by the square root of two, or roughly 40%, to around 60 Hz.
Adding a sealed box also changes the flatness of the frequency response. A smaller box will cause the bass to start falling away more abruptly below resonance, and may cause a bass peak on resonance. Which is why we use software to work out an optimal volume, usually to produce a maximally flat response.
So it's not clear that 13.4 litres is the optimum size to use - but it IS clear that anything smaller than this will push your bass resonance frequency even higher than 60 Hz.
That's why I think you're going to need all the volume you can get inside that U-bass.
-Gnobuddy
I see what you mean - I managed to completely miss the link the OP posted to the U-bass in question until now.
-Gnobuddy
"Bass" ukulele bottom note is 82Hz, not 42 like a "real bass". It is in fact more a guitar than a bass. (Contrabass Uke goes to 42Hz.)
Don't need software to compute sealed-box response. Fs and Qt tell the tale. For 44Hz and 0.29, infinite box response is down 11dB at 44hz. If we stiffen the suspension (usually by enclosed air to be less-infinite) F and Q go up together nearly as square-root of box volume going down. Generally response above F is flat and response below F is -12dB/oct, though with low-Q tune the slope is less.
We would usually set F a hair higher than the lowest note to be reproduced. For Rock in small boxes it is OK to set F around 75Hz so the e-bass and kick main range is covered (few stage/portable bass amps really go near 42Hz). A ukulele band may have different balance (half the band can't go below 200-250Hz).
Q=1 gives maximum "punch for the money/size" but this driver will be falling through most of the bass uke's bottom octave. Q between 0.5 and 0.7 seem likely compromises: falling bit not as fast at the bottom. I have noted the per-driver box volumes for the several Qs.
What space is available? I eyeball the gourd as 8.5"x13"x4" (correction welcome) = 413 cuin or 6.8 L. Curiously, this suits two of those speakers (if soundhole is blocked).
Don't need software to compute sealed-box response. Fs and Qt tell the tale. For 44Hz and 0.29, infinite box response is down 11dB at 44hz. If we stiffen the suspension (usually by enclosed air to be less-infinite) F and Q go up together nearly as square-root of box volume going down. Generally response above F is flat and response below F is -12dB/oct, though with low-Q tune the slope is less.
We would usually set F a hair higher than the lowest note to be reproduced. For Rock in small boxes it is OK to set F around 75Hz so the e-bass and kick main range is covered (few stage/portable bass amps really go near 42Hz). A ukulele band may have different balance (half the band can't go below 200-250Hz).
Q=1 gives maximum "punch for the money/size" but this driver will be falling through most of the bass uke's bottom octave. Q between 0.5 and 0.7 seem likely compromises: falling bit not as fast at the bottom. I have noted the per-driver box volumes for the several Qs.
What space is available? I eyeball the gourd as 8.5"x13"x4" (correction welcome) = 413 cuin or 6.8 L. Curiously, this suits two of those speakers (if soundhole is blocked).
Attachments
Check this out, bass with built in amp, speaker, and drum machine.
Rare Vox Apache - 2B Bass Guitar - musical instruments - by owner
Rare Vox Apache - 2B Bass Guitar - musical instruments - by owner
It was funny that all the Youtube vids showing the bass never showed the internal speaker sound. This one does, he plays acoustically on it at first then turns on the speaker.
YouTube
Don´t worry, I never considering experimenting a silly thing
And agree that random sequential posting often leads to confusion.
Take care
That Apache bass you posted a link to, has a six-pack of AA cells. These days an alkaline AA cell will typically have 2500 mAh capacity at 1.5 volts, or 3.75 watt-hours of stored energy. So six of them have about 22.5 watt-hours.
The Apache ad. claims "up to 26 hours of playing time". Dividing 22.5 watt-hours by 26 hours yields 0.865 watts.
So there you go, it's a whopping one-watt amp, more or less.
(Either that, or idle power consumption is a watt; it's hard to be sure from that rather vague advertising claim!)
-Gnobuddy
So, I have taken delivery of my new bass ukulele, the TPA3116 amp, and the SB Acoustics speaker, and so I've hooked it all up and tried it out. I'm not happy. I get a pretty bad buzz from the driver, and I think it's Xmax is just not sufficient. I can get the frequency response I want no problem just with the EQ on the uke's pick-up with the driver in a temporary 3L sealed box, but if I drive it too hard, it buzzes.
So I am thinking or replacing the SB Acoustics driver with a Dayton Audio ND140-4:
Dayton Audio ND140-4 5-1/4" Aluminum Cone Midbass Neo Driver 4 Ohm
Rated Xmax is similar to the SB driver, but peak to peak excursion is 20mm, more like what I need. Thoughts, anyone?
So I am thinking or replacing the SB Acoustics driver with a Dayton Audio ND140-4:
Dayton Audio ND140-4 5-1/4" Aluminum Cone Midbass Neo Driver 4 Ohm
Rated Xmax is similar to the SB driver, but peak to peak excursion is 20mm, more like what I need. Thoughts, anyone?
Sorry to hear of your troubles.
Are you applying bass boost? This causes a dramatic increase in the amount of power the speaker has to handle, at the same frequencies where the driver is already struggling with large cone excursions. Bad idea.
I would go in the other direction, and cut bass, perhaps with a dedicated high-pass filter.
Yes, this will thin out the tone of the instrument, which isn't ideal. But trying to get deep, loud, bass from a tiny 5" speaker is fighting against the laws of acoustics.
You know all those stories about guitar amps being destroyed because someone plugged in a bass instead of a guitar? Some of them are true. It takes a robust speaker in the right housing to survive the abuse from a bass guitar (or bass 'uke, in your case.)
I think you will have to give up on at least one of the three corners of your original specification (deep, loud, tiny.)
You can manage any two of them in one speaker system, but trying to achieve all three is a losing proposition.-Gnobuddy
Thanks, Gnobuddy
I think you are right, I also came to the conclusion that I will need a high pass filter, I think there is a lot of unnecessary LF down below 40-50HZ feeding to the driver.
Can someone point me to the best way to figure out component values for a high pass crossover with a cutoff of 45Hz or so? Or what about having this in line before the amp?
Behringer BEQ700 Bass Graphic EQ Pedal at Gear4music
I think you are right, I also came to the conclusion that I will need a high pass filter, I think there is a lot of unnecessary LF down below 40-50HZ feeding to the driver.
Can someone point me to the best way to figure out component values for a high pass crossover with a cutoff of 45Hz or so? Or what about having this in line before the amp?
Behringer BEQ700 Bass Graphic EQ Pedal at Gear4music
I designed one for you. Schematic and LTSpice simulation attached.
No guarantees on whether this will save your 5" driver's bacon, though. I am doubtful that a 45 Hz high-pass will help the tiny speaker adequately.
If you halve the values of C1,C2,C3 (use 47 nF, i.e. 0.047 uF), this will be a probably more useful 90 Hz high-pass filter. By "more useful", I mean "More likely to save the little speaker's bacon."
I like graphic EQ pedals in general. IMO they are the Swiss Army Knife of guitar pedals, incredibly useful in many situations. (I don't know anything about that specific pedal, though, and my bass-playing abilities are novice-level, so I'm not qualified to have an opinion.)
A custom-designed high pass filter may provide steeper bass roll-off and a more well-defined EQ curve than you can get just from the EQ pedal. But building your own is certainly a little bit of a pain in the rump.
Also, if you find out that 45 Hz is not sufficient filtering, the graphic EQ pedal is quicker to adapt to the new reality - all you have to do is turn down the 120 Hz slider as well as the 50 Hz one. If you use my circuit, or something similar, you have to desolder and remove the three 100 nF (=0.1 uF) caps, and replace them with 47 nF (=0.047uF) caps. And then you have a 90 Hz high-pass, which may or may not turn out to do what you want it to do.
IMO it's not a bad idea to use a bass graphic EQ pedal to experimentally determine exactly what frequency response is necessary to avoid killing the little 5" speaker. Having determined that, then go ahead and design the custom filter, knowing that it will do what you actually need it to do. However, that Behringer pedal doesn't give you a lot of options down at the low frequency end - you can only choose between 50 Hz, 120 Hz, and 400 Hz centre frequencies.
I've used a (guitar) graphic EQ pedal for a similar purpose, to voice guitar amps I'm designing and building. It's very handy to be able to make quick and easy changes to the frequency response.
-Gnobuddy
Attachments
Wow, thanks Gnobuddy!
I have received my new Dayton Audio ND140-4 driver, and I hooked it up. Same problem - a very distorted sound when I drive it even a little hard.
So I tried something else: I hooked up my old NAD 3020 and played the uke through that - no problem! So the driver is not the problem (actually it sounds great, and handles the sounds the uke makes fine even in a 3L enclosure, much smaller that the specified optimum for the ND140)
The problem is the TPA3116 class D mono amp I got.
TPA3116D2 Subwoofer Digital Power Amplifier 100W AMP Board Audio Module UK | eBay
It seems to distort very easily. It has a stereo 3.5mm input, and the uke is obviously mono, should I be feeding the signal from the uke to both channels, or just one? The board has a NE5532P op amp on the input, what does this do? Do I need some sort of impedance matching between the uke and the amp input?
Basically, I am trying to figure out if the amp is defective, or if I am doing something wrong.
I have received my new Dayton Audio ND140-4 driver, and I hooked it up. Same problem - a very distorted sound when I drive it even a little hard.
So I tried something else: I hooked up my old NAD 3020 and played the uke through that - no problem! So the driver is not the problem (actually it sounds great, and handles the sounds the uke makes fine even in a 3L enclosure, much smaller that the specified optimum for the ND140)
The problem is the TPA3116 class D mono amp I got.
TPA3116D2 Subwoofer Digital Power Amplifier 100W AMP Board Audio Module UK | eBay
It seems to distort very easily. It has a stereo 3.5mm input, and the uke is obviously mono, should I be feeding the signal from the uke to both channels, or just one? The board has a NE5532P op amp on the input, what does this do? Do I need some sort of impedance matching between the uke and the amp input?
Basically, I am trying to figure out if the amp is defective, or if I am doing something wrong.
Until someone cleverer comes along, I'll hazard a guess for you.
I don't know what the output of the pickup is, but I'm guessing it's quite low. You could possible need a preamp to bring the signal up to line level, which the power amplifier will be expecting.
The specs on the power amp are confusing though - it does state two channels in the description, yet only has one speaker output, so not sure there? I would assume it's mono though, and thus your mono input isnt the problem.
Lastly, is your power supply up to spec? If you;re trying to run the amp with insufficient power, that could be causing the distortion.
I don't know what the output of the pickup is, but I'm guessing it's quite low. You could possible need a preamp to bring the signal up to line level, which the power amplifier will be expecting.
The specs on the power amp are confusing though - it does state two channels in the description, yet only has one speaker output, so not sure there? I would assume it's mono though, and thus your mono input isnt the problem.
Lastly, is your power supply up to spec? If you;re trying to run the amp with insufficient power, that could be causing the distortion.
Thanks, Jim
The pickup on the uke is powered by a 9V battery, so I would assume it puts out line level, which is about 1.7V if I remember correctly. Actually, I just googled and discovered that it probably puts out an "instrument level" signal, a bit less than line. But would that just mean it would be a bit quiet? Feeding an instrument level signal to a line input shouldn't cause distortion...right?
Yes, the description on Ebay for the amp is a bit confusing. It has a 3.5mm stereo input, but only one speaker output, so I guess it's designed to be a sub-woofer amp that mixes the right and left signals to one mono output.
My power supply is a 20000mAh battery:
20000mAh Mini slim 12V Car Jump Starter Pack Booster Charger Battery Power Bank | eBay
It's 12V, and seems to be able to do up to 200A(!) so should be fine to give enough power to the TPA3116 to drive an ample sound from a 40W RMS, 88dB sensitive 4ohm driver, or what?
The pickup on the uke is powered by a 9V battery, so I would assume it puts out line level, which is about 1.7V if I remember correctly. Actually, I just googled and discovered that it probably puts out an "instrument level" signal, a bit less than line. But would that just mean it would be a bit quiet? Feeding an instrument level signal to a line input shouldn't cause distortion...right?
Yes, the description on Ebay for the amp is a bit confusing. It has a 3.5mm stereo input, but only one speaker output, so I guess it's designed to be a sub-woofer amp that mixes the right and left signals to one mono output.
My power supply is a 20000mAh battery:
20000mAh Mini slim 12V Car Jump Starter Pack Booster Charger Battery Power Bank | eBay
It's 12V, and seems to be able to do up to 200A(!) so should be fine to give enough power to the TPA3116 to drive an ample sound from a 40W RMS, 88dB sensitive 4ohm driver, or what?
To be honest, that power bank looks like junk. Anything claiming to hold 20,000maH thats as small as that is usually lying. It also says "can only start the car ,can not use like a power bank for long-term." That rings some alarm bells too.
The amp is also obviously confusing matters, with us not being entirely sure what it is/does!
If it was me (and I do make small battery powered speaker systems with 3 and 4" speakers so have some experience here) is to start again with the batteries and amp.
First up I would consider the power source. The battery bank that you originally linked to (the 24v model) looked good, but perhaps staying away from esoteric batteries may be a good idea? I'd try running two standard 5v/2A power banks in series to give us 10v.
I use these: https://www.amazon.co.uk/Anker-Powe...ocphy=1007220&hvtargid=pla-563106500803&psc=1
Then, I'd get a new power amp that will work with 10v, such as this: TPA3118 PBTL Mono Digital Amplifier Board Module 1X60W 12V 24V POWER AMP TE740 4894663155131 | eBay
In my experience, a single 4" driver can't handle that anyway, and that's recorded, compressed music - not something as peaky as bass.
Anyway, that should give a better benchmark. At worse, you;ll end up with two nice power banks for personal use and a wasted £5 on the amp board. At best, you;ll get what you're after.
The amp is also obviously confusing matters, with us not being entirely sure what it is/does!
If it was me (and I do make small battery powered speaker systems with 3 and 4" speakers so have some experience here) is to start again with the batteries and amp.
First up I would consider the power source. The battery bank that you originally linked to (the 24v model) looked good, but perhaps staying away from esoteric batteries may be a good idea? I'd try running two standard 5v/2A power banks in series to give us 10v.
I use these: https://www.amazon.co.uk/Anker-Powe...ocphy=1007220&hvtargid=pla-563106500803&psc=1
Then, I'd get a new power amp that will work with 10v, such as this: TPA3118 PBTL Mono Digital Amplifier Board Module 1X60W 12V 24V POWER AMP TE740 4894663155131 | eBay
In my experience, a single 4" driver can't handle that anyway, and that's recorded, compressed music - not something as peaky as bass.
Anyway, that should give a better benchmark. At worse, you;ll end up with two nice power banks for personal use and a wasted £5 on the amp board. At best, you;ll get what you're after.
With a 12V battery, your supposedly "100 W" amp is limited to a maximum of only about 12 watts RMS into a 4 ohm speaker. That's not much when it comes to deep bass from a tiny speaker.
I think you're running out of available amplifier output power, because your battery voltage is far too low. As Jim Croisdale said, it's also possible that your battery bank is unable to supply enough power, and internal protection circuits are kicking in.
Does the thing sound good at lower power settings? Then there's no mysterious impedance matching issue, etc. (And an impedance mismatch doesn't manifest itself the way you describe, with clipped and distorted bass.)
In your first post, the link you posted mentioned a 24 volt battery. If your chip can handle it, that supply voltage would raise output power to somewhere around 60 watts. I looked up the TPA3116D2 datasheet, and it's rated for 50 W RMS per channel into 4 ohms at a 21 volt supply.
Is there some sort of switch on your 12V battery that will raise the output voltage? The initial link mentioned multiple output voltage up to 24V.
Or is this a different battery pack than the one you linked in your initial post?
-Gnobuddy