Thinking about ways to automatically turn off the PSU of an active speaker. I have two options on my mind:
Locally switching PSU, with a floating input detection circuit
Remotely switching PSU, with a power signal line from audio source
Option 1 has the advantage that if it’s not connected to anything, the speaker will turn itself off. Also, no remote power signal is needed, so it can be connected with just a mono jack. However, to switch it off remotely, the source has to disconnect its output. An audio signal detection circuit would prevent the need for that, but I don’t like to turn off the amplifier when there is no signal e.g. between songs. This option needs a little battery to keep the detection circuit powered.
Option 2 has the advantage of being a little simpler, especially on the amplifier side. There is also no need for a battery. It does however need a stereo jack. Disconnecting input turns on the PSU, but I guess a simple “on/remote/off” power switch next to the jack could solve that.
1. Locally switching PSU, with a floating input detection circuit
Idea is to inject a miniscule DC sense signal (e.g. 4V through a 1MΩ inject resistor) onto the amplifier input, and use a comparator to measure impedance. If impedance is very high (input is floating so voltage is high, especially if amplifier has a coupling capacitor), keep PSU off, if impedance is lower (input connected so voltage is low), turn on PSU.
To prevent audio signals turning off the PSU, filter out the AC at the comparator (e.g. low pass using 1MΩ sense resistor plus 1µF capacitor). I doubt 4V DC at ~4µA would do anything to the source output so I don’t think I need coupling capacitors there.
Comparator would power an SSR that turns on/off the PSU. To power the sense signal and comparator as well as SSR, use a small Li-Ion battery. Float the battery from PSU using an isolated buck converter when powered on. Preferably use a protected battery. If I stay under 100µA, a 2000mAh 18650 could last over 2 years without power. Unfortunately, the most widely available comparator (LM393) draws closer to 400µA which brings battery life down a bit. Could run it with a timer and latch circuit to bring down average current to maybe 100µA, but that seems like a lot of work. Either get a lower power comparator, or just use a protected cell and accept that once every couple of months the amplifier needs to be turned on.
Would have to figure out how to drive the SSR module directly from the comparator without much current draw in off state.
To remotely switch off from the source, the source would need to lift its outputs. Putting anything in the signal path introduces noise, but something like a TS5A23157 analogue switch module with relatively low R_on and very low distortion should be inaudible.
Parts list:
18650 protected cell
isolated buck converter set to battery float voltage + output diode
LM393 comparator module (plus SSR drive circuit)
SSR module
1MΩ Resistors and 1µF capacitor
TS5A23157 module for source
2. Remotely switching PSU, with a power signal line from audio source
Use a stereo jack cable; TRS with control signal on the ring. 5V turns the active speaker off, 0V turns it on. In active speaker, use 5V NC SSR board in two modes:
Off / Control = 5 V: Power the SSR board directly from the 5 V signal line. Current draw is negligible (few µA or less, just leakage).
On / Control = 0 V: Signal line can’t supply 5 V any more. Instead, power the board from a small 42 V→5 V DC converter.
Buck converter must be isolated to prevent ground loop, and use Schottky diodes to prevent backfeeding into the control signal line. Use a capacitor by the SSR large enough to bridge the gap between powering on PSU and buck converter giving 5V.
There should never be 5V and signal at the same time through the wire, so no added noise expected as long as 0V is really 0V. I guess I can use an optocoupler, another isolated 5V buck converter and a pulldown resistor to audio gnd, to prevent injecting noise onto 0V. To prevent damage from DC with wrong connection, limit 5V output to just enough current to keep the SSR board powered.
Alternatively, directly inject 5V DC control signal onto audio signal. This allows using a mono jack cable instead, and again, audio and 5V should never be on the line at the same time. However, this would require filtering out AC at the SSR, and DC at both the amplifier and the source, and might be more difficult to prevent ground loops and noise. Also, higher chance of damage if connecting a different amplifier. Separate wire seems like a much better idea.
Reflection, issues
Option 1 seems elegant but very sensitive, e.g. to floating ground and false triggering. Switching module at source will likely add pops/noise when turning off amp.
Option 2 seems more robust, but need to think about wiring. For instance, can the source handle connecting a mono cable, shorting the 5V to gnd? I guess with good current limiting, that shouldn’t be a problem.
Ultimately, both options seem like a lot of work and can potentially introduce noise, without solving any real problems. Is it really so bad to have to get up and control a physical on/off switch, instead of a software one?
I’ve decided that “loud bass practice amp” and “low bass extension with force cancellation” are not really ideal from the same cabinet. So the 2.1 sub will be a different project.
That leaves the pipe woofer as only a bass guitar case & practice amplifier.
Easiest would be to have a single driver permanently attached on one end, with amplifier and knobs and connectors on that side too, and some sort of screw cap on the other side for accessing the bass guitar. That cap could house a reflex port.
Currently looking at the 8″ SB20PFCR30-4. In a 120cm pipe, with two 60mm ports 20cm long, the response is nicely flat down to F3@46Hz, F6@40Hz, F12@31Hz. Up to 50W input power (4 ohm) and with a 2nd order high pass, displacement stays nicely under xmax. Without the high pass and at 46W input, xmax is reached below 35Hz but there should not be much signal there from a 4 string bass. At 46W, output is about 108dB (half space) so might be loud enough to play with a drummer.
Amplifier: TPA3221 can do about 46W into 4 ohm at 20V, or for some more headroom can do about 100W at 30V (but don’t go over 32V). That seems like a good fit.
Could be powered from an 8S “24V” LiFePo4 pack (25.6-26.6V from 20-80% SoC, 27.2V for 100% SoC) or even 9S (28.8-29.9V from 20-80% SoC, 30.6V for 100%). Or a 7S “24V” Li-ion pack (25.9-27.3V from 20-80% SoC, 29.4V for 100%). Would only pull 4A max, so any 21700 will do – a 7x5000mAh pack (€14 in cells) would run the thing at rated power for 100 minutes. Or I could do a 9x4000mAh 26700 LiFePo4 pack (€14 in cells). A built-in battery also means that I could get away with a smaller power supply and still be able to play loud, perhaps a 30V CV+CC power supply like Meanwell HLG-40H-30A (€36.31) or HLG-60H-30A (€40.63). Or perhaps a little CC+CV DC-DC coverter module – but be careful that they are good quality and the output does not drift. Or just a small CC+CV lab supply. Anyway, a small CC+CV power supply would keep the battery topped up to 80%, powers amplifier during use at low levels, at high levels the battery takes over some of the load. LiFePo4 can be float charged at 3.3-3.4V so 30V for 9S would be perfect. Power supply would need to be good quality with max 2% voltage tolerance, preferably less. Maybe 8S would be safer with the 32V amplifier limit. Then also RSP-75-27 (€33.53) is possible (2.8A current limiting, adjustable voltage).
Maybe a current limiting power supply is not such a bad idea anyway, to protect the amp from burning itself. Battery could be external/optional to save weight. Anyway, datasheet says 80-85% efficiency at 50W into 4 ohm, so up to 10W dissipation – that looks to be about the maximum that the passive heatsink could dissipate. 75-100W current limiting would give some headroom but prevent prolonged high power use. On the other hand, maybe I want more headroom to be able to push the driver into distortion – at the driver’s rated program power of 100W, excursion is gently over xmax between 50-95Hz. RSP-150-27 (€35.02) set to its maximum voltage would (according to the TPA3221 datasheet) allow for 100W into 4 ohm at 1% THD, with power to spare. But then the amplifier definitely would need a fan.
Maybe go with the TPA3255 module instead and 48V 200W PSU for about 170W into 4 ohm – to really drive the woofer into distortion. And probably break it. Ok maybe 100W is plenty and having the amp clip before damaging the driver is not so bad.
Parts list:
Cabinet: 20cm PVC pipe (have), ~120cm long
Baffle & end cap: 3D printed (€?)
Port: 2x 6cm PVC pipe ~20cm long (~€6.00/scavenge)
Driver: SB20PFCR30-4 (€37.05)
Amplifier: TPA3221 module (have, €7.52)
PSU: RSP-150-27 (€35.02)
Preamp: ?
Connectors & knobs
Foam to prevent pipe resonance but mostly to protect bass guitar
Thinking of designing a plug for my 2×6″ horn reflex bass cabinet, so I can use it as a closed cabinet subwoofer in a 2.1 system with software EQ.
Checking Hornresp, if I plug the end of the horns, I get a closed cabinet with a Qtc of 0.70. Max SPL (quarter space):
Original
Closed 16L
30 Hz
74 dB
90 dB
40 Hz
85 dB
95 dB
50 Hz
94 dB
99 dB
60 Hz
102 dB
102 dB
100 Hz
126 dB
111 dB
That’s actually a useful level, I think? Max SPL is mostly independent of volume so I don’t have to think too much about the shape of the plug(s), driver volume etc. It would however need a lot of EQ to get some bass out the 12db/oct declining response. Actually a 2nd order low pass at 30 Hz might already give a decent response as well as could function as a 2nd order crossover around 150 Hz? Phase is then -90 degrees around 150 Hz, might have to reverse polarity.
Let’s look at power. Assuming the above active EQ, and aiming for max excursion at 30Hz, power requirement would be 60W total into 4W. A TPA3116D2 or TPA3221 module according to their datasheets should be able to reach that at 24V, but without headroom – a TPA3255 module >32V might be a better fit. Or TPA3223/TPA3250/TPA3251 at 32-36V.
Idea: dedicated woofer for 2.1 system. Opposing drivers to cancel vibrations.
Kallax compartment is about 335x335x390mm. A 335x335mm baffle could just about fit an 8″ passive radiator and a 6.5″ driver, but it’s very close – 8″+5″ would be a better fit. Assuming 12mm plywood, internal volume using maximum dimensions is 3.11×3.11×3.66=35.4L. Subtracting driver volume, that’s about 34L cabinet.
Let’s run some options in Hornresp (including max SPL, quarter space radiation)
Driver (2x)
Drone (2x)
F3
F6
F12
SPL@35Hz
SPL@60Hz
SB16PFCR25-4
SB20PFCR-00
54 Hz
42 Hz
33 Hz
100 dB
110 dB
Visaton W130X
SB20PFCR-00
48 Hz
33 Hz
29 Hz
97 dB
103 dB
Dayton DA135-8
SB20PFCR-00
47 Hz
37 Hz
29 Hz
95 dB
101 dB
W5-1138SMF
SB20PFCR-00
46 Hz
35 Hz
29 Hz
107 dB
113 dB
W5-1138SMF
none
66 Hz
46 Hz
29 Hz
101 dB
110 dB
SB20PFC30-4
none
69 Hz
54 Hz
36 Hz
104 dB
113 dB
Ok so assuming I can do some EQ in the low end to bring up the response, for the same money I can better just put in a pair of more powerful drivers and no passive radiators.
Looking at smaller drivers, I’m intrigued by a 2×5″ SB13PFC25-4 sub that could potentially do 91+ dB (quarter space) down to 30 Hz at xmax and would need less than 30W for it – at only 6.1L internal volume. That could fit in a 22cm cube, including space for a TPA3221 amplifier and a laptop charger to power it. But if I have the space in a Kallax compartment, 2×8″ SB20PFC30-4 looks great, much louder so probably cleaner at lower levels, and at Qtc of 0.75 should be relatively easy to EQ and crossover.
Idea: a pipe subwoofer that is triple-use: room sub for a 2.1 system, practice bass amp, and bass guitar travel case that I can put my weird small scale bass guitar in. Made out of 20cm PVC pipe (5mm wall thickness) that I already have and including an amplifier – I already bought a TPA3255 module and an 48V 200W Meanwell PSU for it.
My first idea was a transmission line to extend bass, with one or multiple drivers on one end. For instance, with a single 8″ SB20PFC30-4 driver, a 210cm pipe has its -3dB point around 40Hz and 180cm pipe at around 45Hz. However, at 120cm response gets rather peaky with -3dB around 65Hz. The pipe I have is long enough for the longer options, but the shorter one is much more practical.
Second idea is just a “closed box” – a PVC pipe closed on either end. Perhaps 2×6.5″ would be better than 1×8″, with a driver on either end. My bass guitar is 92cm long, the 6.5″ driver is 8cm deep. Minimum total pipe length would be 108cm so let’s go with 120cm. If I use 2x SB16PFC25, Qtc is about 0.74 which is close to ideal and should be pretty musical. Response is typical for a closed box, with -3dB at around 75Hz and shallow roll-off below that. Max SPL (xmax limited) in half space:
F3
max SPL 40Hz
max SPL 60Hz
max SPL 80Hz
Driver weight
Qtc (120cm)
1x 8″ SB20PFC30
75 Hz
95 dB
102 dB
107 dB
1.43 kg
0.60 (tight)
2x 8″ SB20PFC30
70 Hz
101 dB
107 dB
112 dB
2.86 kg
0.94 (boomy)
1x 8″ HW202
50 Hz
95 dB
103 dB
108 dB
1.5 kg
0.90 (boomy)
1x 8″ HDS-P830869
65 Hz
97 dB
104 dB
108 dB
1.74 kg
0.65 (ideal)
2x 6.5″ SB16PFC25
65 Hz
94 dB
100 dB
105 dB
1.92 kg
0.74 (ideal)
1x 10″ SSF102.40
50 Hz
100 dB
107 dB
112 dB
3.5 kg
0.81 (punchy)
1x 5×8″ SB15SFCR39-4
70 Hz
93 dB
100 dB
105 dB
1.65 kg
0.53 (tight)
2x 5×8″ SB15SFCR39-4
65 Hz
98 dB
105 dB
110 dB
3.3 kg
0.76 (ideal)
1x 12″ W250S-4
100 Hz
97 dB
105 dB
110 dB
3.0 kg
0.68 (ideal)
With the 1x 8″ option, the driver could be permanently attached and the other side could be an easy-access cap for putting the bass guitar in, or it could house the knobs and connectors and perhaps the amp. For the 2x 8″ option, all the amp things would need to be connected to the side of the pipe. For the 2x 6.5″ option, I could perhaps mount the drivers off-centre and use the extra space for knobs and connectors. In any case, 3d printed end cabs would probably the easiest.
Not sure yet how to make one side accessible to put the bass guitar in but also remain rigid enough as a speaker enclosure, especially if that side also houses a driver. Let’s go with the 1×8″ driver for now. I doubt I need the extra volume, and it just seems a better option than 2×6.5″.
For protection from overexcursion at high volume best pair with a high pass filter to bring xmax down to Pmax. Could probably make a switchable first order high pass filter using capacitors – e.g. 220+470µF in parallel (€9.45 at Reichelt) would be 690µF or 58Hz at 4 ohm.
If I want to pair this pipe speaker with my existing 2×6″ cabinet, I need to take into account sensitivity (in case I want to run parallel) and phase response. Looks like phase doesn’t match very well – matches ok up to 100Hz but switches to 180 degrees out of phase from 300Hz on. Guess I could use a high crossover to match up better. 150µF (€3.97 at Reichelt) at 4 ohm would be 265Hz 1st order: 0 degrees phase at 150Hz and -180degrees phase at 350Hz for 2×6″, 0 degrees and -60degrees for 1×8″ pipe subwoofer. Maybe something else and/or reversing polarity?
Amplifier: TPA3255 according to its datasheet could do 250W into 4ohm at 48V or 445W into 2ohm at 1% THD+N single channel PBTL, or 2x4ohm 235W or 2x8ohm 130W dual channel. I doubt this Chinese board can even reach half of the datasheet rating, but then most of the above options have a program power less than that, so should be enough power even if I connect the 2×6″ cabinet in parallel or on a second channel.
Perhaps for bass guitar, 2×8″ would make more sense SPL wise, but then (besides the boomy Qtc) there would be significant comb filtering because of the 120cm driver distance: cancellation at 143Hz, peak at 286Hz, cancellation at 429Hz etc. Maybe a 1×10″ or 1×12″ option would be better, but that’s hard to mate to the 20cm pipe and even heavier than 2×8″. A 10″ LaVoce SSF102.40 for instance would get about the same max SPL at all frequencies as well as better low end extension, although at 8ohm and lower sensitivity it would need a better amplifier to drive it to its maximum. 2x 5×8″ (SB15SFCR39-4) could work, but side by side are even bigger than 1×10″.
So far 1×8″ HDS-P830869 is looking best, with good F3 and Qtc, low weight, single driver, high xmax. Would need a 46Hz 1st order high pass to bring xmax down to Pmax – a single 470µF capacitor, €5.48 at Reichelt, would be 42Hz, close enough.
Next up: think very hard if I want this project.
Would be nice for a 2.1 system because it can go very low, would still need some DSP to get response flat but that’s okay. Alternatively, with DSP I can get the same SPL down to 70Hz with my current bass practice amp, but because of the horn reflex the maximum SPL drops quickly below that. Maybe try first if it can already do what I need in a 2.1 system before I continue with this pipe woofer project. Might want to install the TPA3255+PSU in my current practice amp instead.
For bass practice, again my current practice amp is better suited >75Hz, and this project would only extend bass down at lower volumes. ~100dB max SPL at half space might still be enough for my needs though.
For bass travel case, I guess this would be great, except without the speaker it would be lighter and easier. Only makes sense if I always want a practice amp together with my bass, which I guess I do most of the time? I don’t currently have a band to play with and if I did play with a drummer, this project would likely not be loud enough (not sure if the current 2×6″ would be either). Carrying both the pipe and the current 2×6″ cab is maybe doable but not ideal with other luggage as well.
Edit:
SB20PFCS30-7: Qtc 1.20, very peaky
SB20PFCR30-4: Qtc 0.60, exactly as SB20PFC30-4
SB23NRXS45-4: Qtc 0.59, nice response, F3 65Hz, +1dB max SPL compared to SB20PFC30-4, expensive
SB23N(B)ACS45-4: Qtc 0.67, nice response, F3 50Hz, +1dB max SPL compared to SB20PFC30-4, expensive
SB23CACS45-4: Qtc 0.68, almost exactly as SB23NBACS45-4, expensive
SB23MFCL45-4: Qtc 0.50, tight response, F3 60Hz, +5dB max SPL compared to SB20PFC30-4. Very heavy & expensive
SLS-P830667: Qtc 0.98, boomy
Some more options:
F3
F6
max SPL 60Hz
Qtc
Weight
Price
SB20PFC30-4
75 Hz
53 Hz
102 dB
0.60
1.43 kg
€ 36.84
DC200-8
55 Hz
40 Hz
99 dB
0.67
1.57 kg
€ 42.90
HDS-P830869
65 Hz
45 Hz
104 dB
0.65
1.74 kg
€ 56.90 (out of stock)
DA215-8
70 Hz
50 Hz
101 dB
0.58
2.45 kg
€ 63.90
CW202
65 Hz
50 Hz
103 dB
0.76
2.40 kg
€ 69.66
GBS-200F35CP02-04
70 Hz
50 Hz
105 dB
0.52 (but very peaky resp.)
2.28 kg
€ 69.95
HWB200-4
65 Hz
45 Hz
104 dB
0.65
2.75 kg
€ 79.38
2x SB15SFCR39-4
70 Hz
50 Hz
105 dB
0.76
3.40 kg
€ 85.42
SIG225-4
70 Hz
50 Hz
102 dB
0.61
2.63 kg
€ 89.00
RS225-4
55 Hz
40 Hz
102 dB
0.67
2.98 kg
€ 89.00
RS225-8
55 Hz
40 Hz
103 dB
0.64
2.98 kg
€ 89.00
DCS205-4
60 Hz
45 Hz
106 dB
0.51 (but very peaky resp.)
3.33 kg
€ 89.95
FW222
55 Hz
40 Hz
104 dB
0.78
2.30 kg
€104.95
SB23NBACS45-4
50 Hz
35 Hz
103 dB
0.67
2.70 kg
€116.95
8H2CP
55 Hz
42 Hz
103 dB
0.72
2.70 kg
€121.18
SB23MFCL45-4
60 Hz
40 Hz
108 dB
0.50
4.70 kg
€137.26
HDS-P830869 seems to be the best balance of max SPL, F3 and weight at a decent Qtc, but is currently out of stock likely until December/January. Fountek FW222 would be great, lower F3 and comes with a built in grill, but is a little more expensive and heavier. SB23MFCL45-4 is basically the price, weight and SPL of two drivers in one. It is also the only option which gets possibly high enough max SPL to play with a drummer, without being peaky.
Rough weight estimate:
PVC pipe: 5 kg
Baffle & end caps: 1 kg
Driver: 2-5 kg
Bass guitar: 4 kg
Amplifier & PSU: 1 kg
Total: 13-16 kg
In other words driver weight doesn’t affect total weight a whole lot.
Maybe I should just experiment with the cheap option first, either DC200-8 or SB20PFC30-4 + EQ the low bass response up, and if it’s not loud enough I can always get the heavier more expensive option later. Or wait for the HDS-P830869 to come back in stock.
Idea: make the driver side baffle slanted. Then the pipe can stand up on its back vertically and still point its driver roughly towards listener(s), plus it gives space for knobs and connectors and possibly amplifier + PSU. Could even rotate the drivers 90 degrees and possibly mount 2×8″ vertically on the same baffle. Would be a big 3D printed piece though, and not many options to get a decent Qtc with two drivers. And probably much easier to keep the baffle straight and just point the whole pipe using legs.
Idea: make it a horn reflex cabinet instead. 1×8″ with SB20PFC30-4 and a slightly increasing reflex port from 54cm² to 108cm² brings F3 down to 41Hz, F6 to 37Hz, max SPL 108dB@60Hz/105dB@40Hz – the latter is louder even than the SB23MFCL45-4 ind a closed cabinet. The horn/port could be external, in a 3D printed end cap that inverts for travel. Some max SPL is lost below 30Hz but I don’t need that anyway.
Or a regular reflex cabinet with SB23MFCL45-4, straight 54cm² port brings F3 down to like 25Hz, max SPL 111dB@60Hz/108dB@40Hz. But the port would have to be unrealistically long.
Idea: for home 2.1 sub use, two opposing drivers (push-push) would be ideal to completely cancel cabinet vibrations. Some design ideas: putting the drivers on either end of the tube, or perpendicular to the tube facing outwards, or slot loaded facing inwards. None of these are ideal for frequencies above subwoofer level, because of comb filtering, but maybe not critical for bass guitar practice. Horn reflex 2×6.5″ or even 4×5″ with back-to-back drivers?
Idea: dual speaker baffle fits inside pipe, inverts after travel to give bigger volume. Nice idea but even with 5″ speakers doesn’t fit inside 20cm pipe, can only work with non-opposing driver up to 6.5″, or 5″ if sideways and I also want to include the amp+PSU in the same module. Not ideal with drivers at opposite ends, and/or non-integrated amp because of the cabling. So would only work with a vertical array of 5″ speakers on one baffle, or a single 6.5″ at the top.
Idea: passive radiator on one side. Available PRs are tuned too low to be useful, would need smaller box and 2x PR Sd*Xmax compared to driver Sd*Xmax.
So far dual 6.5″ or 8″ (one on each side of the pipe) with a port seems to make the most sense if I want to keep with the multipurpose idea. Could possibly make one side extendable, uncovering knobs and connectors and housing amp+PSU. In any case, not sure how I would get a non-leaky fit between the baffle and pipe end that can be opened to get the bass guitar out.
Either that, or drop the 2.1 requirement and make it a 1×8″ or even 1×10″ design with less low end focus, more efficiency focus. Use a separate woofer for the 2.1 system which is more focused on low end extension but at low volume and without having to play beyond 150Hz, focused on small box and no vibration (e.g. two opposing 5″ perhaps with opposing passive radiators).
Early 2015. 10″ tapped horn “subs” to go with my 2×6″ “top” cabinet, for bass guitar. Also used as bass speakers for house parties at the time. Currently gathering dust, not sure what I will do with these.
These are copies of THAM10 as designed by Anders Martinsson, except with Mivoc AWM104 drivers instead of B&C 10NW64. I don’t remember modifying anything besides the drivers. I went with these drivers because I think they were about a third the price, they have 9mm xmax and they were available in 4 ohm. They model okay down to 60Hz in a THAM10 enclosure – a little more peaky in the bass, but also less efficient outside of the horn response so less noise there and therefore a little easier to cross over. Hornresp modelled response and max SPL at Pmax&xmax with AWM104 (black) vs original 10NW64 design (grey):
They actually sound pretty good for bass guitar with just a THAM10 and the 2×6″ top cabinet, without any crossover. Weight is about 16kg each (10kg wood, 6kg driver). I powered them using a Behringer iNuke NU1000. Iirc, one of the cabs rattles a bit at full volume.
January 2015, text/instructions from back then too. I’m a little sad that I mounted the tweeter up top, and not in the middle as a “nose” with little teeth as drawn as an option in the cutsheet picture. Still, I love how it sounds for bass guitar. Still a great practice amp, only thing I changed since 2015 is put little wheels under it. Might one day make it active by putting a plate amp in the back.
For this 2×6″ top cab, I was mainly inspired by Arjank’s Piccolo8 horn reflex cab, since I really liked the clarity of bass lines on my small horn reflex bookshelf speakers. I was also inspired by greenboy’s cabs that have 6″ mids and a tweeter as a vital part of the sound. I was also inspired by Bill Fitzmaurice’s XF guitar cabs that mount two speakers in a cross-firing position and with a rear tilted baffle. I designed the cab using Hornresp. When I’d finished it, it was a bit peaky in the 100-300Hz region but after stuffing the driver volume it sounded a lot better.
At practice volume, the 2×6″ goes low enough on its own. Over ~40W, I needs a high pass filter >150Hz to keep from farting out (xmax) and I add one or two of the TH cabs.
— Wood — This design uses 12mm plywood. If you are REALLY careful, you can cut all but the tweeter baffle from a quarter sheet (1220x610x12mm). See the cut sheet in the Sketchup file. The entire driver enclosure is tilted backward 9 degrees compared to the horn port. The two 6″ drivers are crossed inward at 20 degrees each. NOTE: the two baffle pieces, the piece at the top of the baffle and the top part of the cab therefore have a few 9 or 20 degree cut angles that you should not overlook!
— Drivers — This design uses two Fane Sovereign 6-100 6″ drivers. The volume behind the drivers and the length of the horn are based on Hornresp simulations of the frequency response of the cab with these particular drivers in it. Using different drivers will have a very big impact on the frequency response of the cab; you will probably get a big thump around 150Hz and not much response in the frequencies below that. At the bottom of this file, you will find the Hornresp values that I used if you wish to try modelling different drivers. That said, the tweeter (Mivoc XGH 258 ALU) could be replaced by a different model or even omitted. If you go for a different model tweeter, you may need to change the crossover. My cab benefitted a lot from stuffing the volume behind the drivers with the insides of a pillow. You could also use actual BAF wadding or wool, and/or line the inside with felt. This will help dampen unwanted sound reflections.
— Crossover — The crossover that I used is a simple passive second order crossover around 2550Hz. The woofers have a combined impedance of 16 ohms around this frequency and the tweeter as well. I used a 3.9uF capacitor and a 1.0mH inductor for both the low pass and the high pass sieds. Make sure the capacitor is bipolar and the inductor is of reasonably low resistance. I am new to crossover design though so I’m sure there are better ways to go about it.
— Crossover switch — If you want to be able to switch between running the 6″ drivers full range, or adding the tweeter via the crossover, use a rotary switch. I’ve used a 4P3T rotary switch that in the third switch position adds an 8 ohm resistor in series with the tweeter. This pads the tweeter a bit, but it also changes the crossover point slightly so this is not the best way to pad the tweeter. I mounted the rotary switch in the horn mouth, where you can easily access it.
— Using the cab — If you use the cab on its own, note that it will fart out if you push more than approx. 40W into it. If you wish to get more output, you can add a high pass filter and cross over the lower frequencies to a different cab. That way, the cab can handle about 200W. I use a tapped horn cab crossed over to the 2×6″ cab around 175Hz. The TH design that I used (THAM10) is freely available on the website of Anders Martinsson, the designer, at http://www.martinsson.cc/
— A suitable amplifier — If you wish to make the cab into a combo, or just want to have a small amp for it, I recommend looking into the TPA3116D2 amplifier. You can order a board cheaply from China (<$20) and its output is perfect for this cab. If you use a 19V laptop power supply, it can push about 35W into the cab at below 0.1% distortion. With a 24V power supply you could get about 60W out of it. If you run in PBTL mode, it is 2 ohm stable and you could get up to 100W if you add another cab. You can set the gain at either 20, 26, 32 or 36 dB. With both pickups at 100% on my jazz bass, I found that the gain was enough to practice without a preamp, but I recommend setting the gain to 32 if you have a passive bass and will not be using a separate preamp. More on this amp at diyAudio here: http://www.diyaudio.com/wiki/TPA3116D2_Boards
— Hornresp input data — Ang 2.0 x Pi Eg 2.00 S1 70.00 S2 280.00 Con 47.00
Sd 139.20 Cms 8.00E-05 Mmd 23.94 Re 6.90 Bl 13.25 Rms 1.35 Le 1.15 Nd 2P
I think I built these in 2014. They’re a copy of the “Leuk & simpel hoorn reflex monitortje met FRS8” project by meiborg on zelfbouwaudio.nl forum. I first wanted to modify it into a triangular shape because of my room at the time, but decided against it because I didn’t have the woodworking tools or skills required.
They use a Visaton FRS8 full range driver, and a horn reflex port to bring the response down to about 100Hz. I like how they sound, I even built someone a second set as a gift.
