Mottlefeeder

2 hours ago, Stub Mandrel said:

Looks good, unfortunately my TLRTs have run out for today 😞

That's a new one for me - what's a  TLRT?

David

Some progress, but mainly cosmetic

3 coats of Tuffcab matt black, and an aluminium back panel - to be sprayed black when completed.

David

I bought a Samsung TV that had no audio output sockets, and average rear-facing speakers. I ended up buying a USB D to A convertor so I could feed analogue audio into the Hifi. 

One thing I did find is that even with a sound bar and TV from the same manufacturer, the volume control for the TV cannot be used to control the volume of the sound bar.

David

3 hours ago, Matt P said:

@Mottlefeeder it sounds like you have it all under control! Looking forward to the finished amp.

 

Matt 

Sadly, being able to fix the problems I have found so far does not equate to having it all under control - but thanks for that vote of confidence.

David

5 hours ago, Matt P said:

very interesting build, what kind of heat will the amp be putting out? have you got a plan to keep it from getting too toasty? 

 

Matt

The manufacturer's data sheet for the chip states

"The high efficiency of the TPA3130D2 allows it to do 2 × 15 W without external heat sink on a single layer PCB. The TPA3118D2 can even run 2 × 30 W / 8 Ω without heat sink on a dual layer PCB."

Also, although the amp is rated as 40 W into 2 ohms with a supply of 13 volts, playing bass through it, I'm measuring a supply current peaking at 0.9 Amps - so probably averaging about 0.5 Amps. Assuming the amp is taking 13V * 0.5 A = 6.5W and it is 80-90% efficient, taking the worse case, 20% of 6.5W is slightly under 1.5 W.

The amp will be vertical on the back of the cab,  a 15 mm thick module mounted in the 35mm deep void between the cab back and the aluminium electronics cover, so I'm assuming that ventilation holes above and below the amp will provide enough airflow to keep it cool, Testing it flat on the bench, it might have been a few degrees above ambient, but not warm to the touch.

David

A little more progress -

Edges rounded off, front baffle painted with blackboard-paint, fitted with grill stand-offs, and off-cut of grill cut to size. I considered whether to stain and varnish the cab, but based on the tide marks I got staining a bass body, I decided to go with boring Tuff Cab black - now on order.

Electronics space painted, component placement worked out and sheet aluminium on order -

• Near edge: battery fuse, amplifier fuse and external power/charger pigtail - likely to last longer than a fixed fragile plastic socket.
• Centre: 40 W Class D amplifier. Allegedly a TPA3116D2 containing two paralleled pairs of bridged amplifiers, capable of driving 100 W into 2 ohms. I doubt that this design would, and I'm not going anywhere near that.
• Blank area: EQ - most of my basses have active EQ, and for those that don't, I have an EQ /DI pedal. The function I use most is a variable HPF, so the space will have a home-built FDeck HPF pre, and possibly a gain stage to drive the amp.
• Top edge: instrument in, volume, HPF frequency, on/off switch and charge/external power switch.

David

First bass, school project - blockwood body, teak neck, Formica fretboard, no intonation adjustment, no truss rod, string height adjustment by grinding metal off the bridge. It worked, just.

Bought and sold:
Yamaha BBN4: upgraded to a 5-string, then sold this one.
Cort Curbow: 5-string (owned for about a week, didn't like the tone through my rig, exchanged for RBX 765)
Yamaha RBX765: 5-string - still got this
Warwick Corvette 4-string fretless - Bubinga body, Wenge neck, Ebony fingerboard. Tuned BEAD. First attempt at fretless, eventually upgraded to a 5-string
Warwick Corvette 5-string fretless - Swamp-ash body, Ovankol neck. Neck heavy compared to 4-string: tried various fixes then sold it
Steinberger CR5M: 5-string EUB - hands couldn't cope so sold it.
Yamaha TRB1005: 5-string fretless - nice to play, but my playing did not make the progress I had hoped for - sold it.
Ibanez EWB205: 5-string ABG -still got this
4-string headless bass kit: started as a Hohner Jack copy and then I clipped its wings so it's an asymmetric paddle - still got it, but not playing it. 
Countryman Bass ukulele: tried EADG, then BEAD then decided to stick with 5-string basses only. Sold it 
Hohner B2 V: 5-string headless - nice and small for playing under a gazebo in the rain (I'm a busker) Still got it.

David

My usual rig is a pair of 10s  powered by an Ashdown MiBass 500W amp, but I can also use one of the 10s with a small battery amp for acoustic nights and small gigs. Unfortunately, at 300 * 300 * 450 mm, even that is a little bit too big to be unobtrusive, so I started thinking about something as loud as my 10 inch battery rig, but somewhere between a Phil Jones briefcase and a Roland Bass Micro Cube in size.

Obvious first question, why not just buy one of those? Answer, the PJB costs more than I wanted to spend for something that would be used occasionally, and I haven't been impressed with the Bass Micro Cubes I have tried, possibly because I play low-B 5 string basses.

My small battery rig is a class D stereo amp producing 12 W @ 8 ohms / 20 W @ 4 ohms per channel, and according to WinISD, will produce 106 dB from 100 Hz upwards at max volume using one 8 ohm Eminence Basslite S2010. The -3dB point is 66 Hz. That is what I want to achieve in a smaller box.

After a bit of searching, I found a 5 inch Faital Pro driver, available in a 4 ohm version, and two of those in a cab 350 * 350 * 170 mm will produce the same frequency response and the same volume. However, Hoffman's Iron law kicks in here, in that a speaker can go low, go loud, or be efficient, but only two of those at a time. These smaller speakers take 4 times the power of the single 10 inch speaker to reach the same volume. However, for a battery-powered pub session of 3-4 hours,  I can do that on one battery charge.

A few pictures of the build - 

1 The basic shape - speakers at the front, vent in between them, electronics compartment recessed into the back face

2  The cab is sized to include the battery, which sits on a sledge which comes in through an airtight hatch in the back wall.

3  I'm not sure if this is 'you can never have too many clamps' or 'you can never have too much bracing' Bill Fitzmaurice seems to have standardised on 15 mm ply and a shelf brace every 200 mm, and I'm using 9 mm ply, so I'm bracing every 150 mm.

4  Have I missed anything before I glue the second side on?

More to follow

David

I made a U-shaped sleeve for my Ashdown MiBass Mk1, and added kitchen-cupboard kick-panel brackets to a speaker cab top and to a sleeve bottom so that I could clip it together to make a combo or a stand alone. This one is finished in TuffCab.

David

As of today, I will no longer be monitoring this thread. If you want me to help, send me a pm

David

5 hours ago, Chienmortbb said:

I have been in electronics since I left School and have done a smaall amount of coding/programming professionally, The thing I should always remember is that a good knight's sleep often gives you the answer.

I forgot that the outputs of the opamps in the circuit above have 100 ohm resistors in line. With my headphones being connected in parallel and having a combined impedance of 16* ohms, the output will be attenuated by 15-16dB (* the exact amount depends on the impedance of the heaphones at a particulat frequency). So by taking the output directly from the opamp output, the headphones will recieve more power. Unfortunately this means soldering a wire directly onto the PCB but as much of the preamp is hardwired, it is  not a massive problem.

Rod Elliott recommends using the 100 ohm resistors on the outputs to ensure stability, especially when connecting cables to those outputs, so if you dispense with the resistors it might be advisable to put a small capacitor in parallel with the feedback resistor to roll off the gain at high frequencies.

David

I'm not a nerd, honestly, I just happened to be searching for components when I checked into Basschat for a break.

Digikey stock a switch which looks similar, but we need to check whether the pin spacing, etc, is the same. If your unit is USA designed thirty years ago, it may be imperial, and most components these days are metric.

ENG_CD_1825290_A3.pdf

The switch drawing in squares C6-C7 is the type you need (I think) so can you check the dimensions of your switch against this drawing. The pin-spacing-grid width and length is important, as are the locating lugs on the corners. The length of the operating lever might also be important if you want it to work.

David

OK that's a side-operated two-pole 3-way slide switch with a long actuating lever. The first problem will be finding a replacement of the right size. Failing that, have you got all the bits from the existing switch?

I'm happy to do a bit of digging, but I make no promises - I'm based about 5 miles out from Altrincham.

David

45 minutes ago, Bassfinger said:

Im sure this has been asked before, but can anyone recommend flats that work well on an acoustic?

I'm using D'Addario Chromes and I can recommend them. Also, although it may be a minority interest, I'm using a 5-string acoustic, an Ibanez from their 'Exotic woods' series.

My string adaptor just sits on the end of the existing nut. The nut end face is angled slightly, so the string tension pulls the adaptor towards the back of the neck.

Also worth checking is the 'Overlord of Music' nut and bridge set, sometimes sold individually. That nut will take standard strings, but it clamps them by bending them through 90 degrees, which some strings will not take. I don't know if it is a drop-in replacement for the existing nut assembly.

David

I'm having mixed results, probably due to low internet connection speeds - there is no fibre I can get to, and since the exchange is at the end of our street, we are not likely to be upgraded until everyone else has.been.

I started with a Behringer UCA222 with an analogue mixer, and then moved on to a Behringer 302USB. Both are fine if all you want is to record onto Audacity, and play back backing tracks, but both had latency that was too great for JamKazam, even with the generic ASIO driver ASIO4ALL.

I'm currently running a Steinberg UR22C which gives you the option of an HPF on each track going in, and EQ or other built-in FX on either the inward track or the outward track. It works well with Jamulus, but I'm still not flying on JamKazam. One-to-one seems to work, but when I join someone else's session I get no audio.

David

17 hours ago, Woodinblack said:

Oh that looks nice, what are they like?

Nice woody tone. The bass is big compared with a 5-string Yamaha RBX, but it's light, and comfortable whether I am standing or sitting. It's a 34 inch scale, and the neck feels good to me, and B string works well - there aren't many 5-string acoustics around, and I preferred this to the Boulder Creek at nearly double the price.

David

EWB205WNE - 'exotic woods' 5-string with flatwounds.

David

5 hours ago, Phil Starr said:

I'm not an expert on the maths around fluid dynamics. the only time I studied it was back in the 60's so this is really broad brush. The thing that causes compression and the wind noise is turbulence in the port at high velocities. Turbulence will add in an additional resistive element to the port reducing the radiation of the cab around the tuning frequency. The port only really radiates sound at the tuning frequency so isn't going to affect the frequency response apart from around the tuning range.

I don't think anyone can reliably answer the question about 'allowing' for 100W. Without knowing exactly how you play and what eq you will use in the future it's almost impossible to say what level of discount you could reasonably apply and how frequently and by how much you'd exceed 15m/sec in the port. Remember too that these guideline port velocities are just that, guidelines. The people that developed the theories behind all this differ in what sort of port speed is acceptable and I've seen figures between 14 and 20 given as ideal.

To give you a wattage figure we'd need some basis in theory to make a calculation and we don't have that. If you look at the port velocity at 50W you are looking at 3dB down, if it is 6dB down it is 25W.

Port dimensions around the sizes you are thinking of seem fine to me and so does a 64 hz tuning. 

4 hours ago, Balcro said:

If you calculate upon a 100W input, nothing changes except the pressure within the port as I said previously. Remember Phil's comment about squeezing a balloon.

The up-side:-  if you change the smaller vent dimension to 3.8cm you are given a port length of 19.26cm i.e 19.3cm. You will need an air gap beyond the end of the port. If it's possible, make it equal to at least 3.8cm.

The down-side:-  the air velocity calculation shows a rise to 18m/s at 63Hz. Balloon squeezed, but still within recommended bounds.

Thank you both, and contributors to the previous thread.

In summary, I have a viable design based on the maths and the experience of others and no defined route, other than trial and error, to making the cab smaller by using a smaller volume port. I only want to build this once, so that sounds like a good place to stop.

David

24 minutes ago, Balcro said:

... Do you still only need to run the speakers at half your amplifiers rated output (150w)?  I've run a variety of models with different amplifier inputs & enclosure volumes using your earlier rough guide to the speaker, and I 've found that with an 11.4L enclosure and a 75w signal from the amplifier, the 30Hz speaker output is at least -30dB below the output at 60Hz. With filters switched in, the difference is even larger; so large, it goes off the bottom of the scale.

With a rectangular vent of 3.8 x 10cm (internal) and tuning set to 64Hz, the calculated port length is 19.26cm. Is this port length impracticable?

 The peak air velocity through the port is only 15.7 @ 63Hz. At the same frequency and with the 60Hz filter switched in, output from the speaker is down -4.6dB. Chuffing is not going to be an issue.

With a 75w input the speaker is calculated to deliver 108dB from 80Hz & upwards, and with the 60Hz filter in the chain, xmax is not exceeded, even down to Zero Hz.

 

My earlier thoughts were to use the two 4 ohm speakers, each fed from a 20 W amplifier, with the option to connect them in series to connect to a 75 W @ 8 ohm / 150 W @ 4 ohm amplifier when I needed more volume. I've since found a 50+50 W @ 4 ohms module so I'm going up from 75 W total input to 100 W total input.

We all seem to agree that the 30-60 Hz octave is unlikely to be a problem, so  I am interested in your thoughts on porting at 64 Hz - do I need to allow for 100W at that frequency, and if not, how do you decide how many watts to design for?

With my current layout of components, I can accommodate a 200mm long port.

David

1 hour ago, Phil Starr said:

Not quite, the point is actually really simple physics. The fundamental is the note produced when the string is vibrating as a whole. It's fixed at the bridge and nut (nodes) and the middle of the string is the bit that is moving furthest (antinode). The antinode for the fundamental on an open string is at the 12th fret and that is the only spot where you'll get full output of fundamental. The closer to the bridge you place the pickups the less fundamental you'll get.  The note is irrelevant if your bass is 34" scale the fundamental dominates only 17" into the string at fret 12. if your PUP is at 4" from the bridge it isn't going to get much fundamental.

https://www.physicsclassroom.com/class/waves/Lesson-4/Nodes-and-Anti-nodes

You've found that on your bass it is 12dB down and this is typical, in fact what I predicted. That means at the point where your amp is turned up loud not much of the power is going to be in the lowest frequencies which will cause over excursion. If you are running at 100W into the speakers it's unlikely that 10 of those watts are going to be fundamental unless you are using a lot of bass boost. If you are my feeling is that the speakers are going to be overwhelmed before you get a noticeable level of chuffing from the ports.

You've run WinISD, the plots you need to consider are the excursion plots and the maximum power plots which tell you whether the speakers are coping or not. That is a concern, but with little drivers like yours I wouldn't worry about chuffing. Experienced builders are telling you a single 68mm bit of pipe (outside diameter of course) is going to be enough and that is good advice IMO. I've got 12" drivers here with a pair of ports this size running at 300W at gigs and I've never noticed problems with port noises at gigs. i'm probably getting some problems with compression due to port resistance but again in practice I haven't noticed.

Speaker design is like squeezing a balloon, you squeeze one problem and another pops up. You can't really achieve perfection don't let that be the enemy of building something good.

I get the impression that we are running on similar but slightly different lines of thought, so I'm not getting the answers I was hoping for. Having said that, I'm grateful for the explanations you have provided. They have filled in a lot of gaps for me.

With my bass, the fundamental is 12 dB down, and since there will also be a 60 Hz 18 dB/octave HPF in the pre-amp, I agree that the fundamental is not an issue in my design.

The speakers are rated at 80 watts each, and in a cab of the appropriate volume (11.4 l), are capable of taking 100 W at any frequency above 57 Hz.

The excursion plots show that with the HPF in circuit, the speakers are below Xmax at all frequencies at 100 W.

The proposed cab is tuned to 64 Hz, which seems to give the best compromise of size, smooth roll-of and bass extension, but a port capable of handling 100 W at 64 Hz makes the cab bigger than I want, so reducing the port power-handling capacity is a compromise I'm investigating.

As I posted earlier, the spectral analysis of my lowest bass notes shows equal volumes at 60 Hz and 120 Hz, so I was hoping someone could comment on whether it was reasonable to assume that a low 100 W note could be regarded as for example 45 W at 60 Hz, 45 W at 120 Hz, and 10 W for everything else. That would give me the 'science' I need to reduce the size of the port and still be confident that it would do what I wanted. Am I oversimplifying a complex problem?

Also, I was under the impression that if I reduced the port power handling capacity too much I would get chuffing, but you suggest that compression would be the more likely outcome. What does port compression do to the response of the cab?

David

2 hours ago, Phil Starr said:

You are probably over-thinking this. What your amp will do is actually trace a complex waveform which tracks all the different harmonics added together. It will do this until it runs out of volts or sometimes the power supply in the amp will run out of current. If you are putting music in rather than a test signal then the notes decay over time and there will be gaps between the notes. Your amp will pump out its full power at all frequencies over its pass band if you put the right signal in.

You are back to where you were in the other thread. Your bass pickups aren't in the middle of the strings so won't give you as much fundamental as harmonics, you'll find all your fundamentals are down about 12dB or 1/16th of the power compared to the 2nd harmonic unless you are fretting higher up the neck just as I said last time, your own measurements confirm this. The advice to keep wind speeds below 18m/s are from people designing for hi-fi use It's nice if you can achieve that but sometimes you can't in a practical cab especially if you are trying to build something really compact. In practice this is not going to be a problem.

Unfortunately it's my nature to analyse things to death, and I still cut wood to the wrong size ...

Taking your second paragraph first, I've taken on board that the harmonic mix will change as I move around the fretboard, but I chose the low C because it is the note most likely to overwhelm a port tuned to its harmonic. 

With regard to what the amp will deliver, I'm assuming that at some point I will turn up the amp and it will start to clip - 5 inch speakers are not as efficient as 10 inch speakers, so this is inevitable. Turning down slightly from that volume, the amp will be delivering its maximum voltage to the speaker, and the signal will initially have the lowest two harmonics predominating as each note decays.

Using that scenario, I'm questioning whether I can derate the power handling of the port, but you appear to be saying that a port overload for the initial fraction of the note can be ignored.  So, if the aim is to avoid chuffing, is chuffing a continuous overload of the port, or just overloading during the initial transient?

David

Following on from my thread about whether WinISD was giving me bad advice, 

I'm now trying to work out whether I need a port sized for full power, or something less that full power.

I downloaded a spectrum analyser and played a low C through it (lowest available fretted note). The analyser shows that the signal at ~30 Hz is about 12 dB below the signal at ~60 Hz, which is the same level as the signal at ~100-120Hz. 

For a port tuned to 60 Hz, my question is, if the voltage applied to the speaker is mainly two frequencies, and one transducer is reproducing those frequencies, the power must be split between those frequencies, so is it reasonable to design the port to take a maximum of half the amplifier power at 60 Hz, on the basis that the rest of the power will be at other frequencies?

David

Sold

15 hours ago, basstone said:

That would be handy, I could potentially  pick up from Portishead no problem, it's less than an hour from me. I'm in no particular rush with no gigs at the moment :-(.

Do you have a trip planned at all?

No trips planned at the moment, so it would be a few months away, but it is an option.

David