Red Spade Audio

80L CSS SDX15 sub - part 4

2012-01-26T03:28:00.000-08:00

Edges trimmed:

Edges were trimmed with the hand plane. You might notice the gouges where I've used the plane. Unfortunately I was in a bit of a hurry at the time and didn't check the blade. On closer inspection later I found that it had been damaged and needed grinding back. The gouges aren't a serious concern because they will soon be covered with bog anyway.

Filling holes:

Bog filler applied over butt joins, then sanded:

Next up, I applied a roundover to the edges, 3mm on the bottom edge, 6mm to all others.

I also cut a groove at the join. The idea here is to conceal the join so that if any cracks appear over time, they will be hidden in the groove.

Clamping the feet. Fixed with polyurethane glue, chosen for its very high strength. It is four times as strong as ordinary PVA and expands when curing to ensure a good bond. The oozing glue was wiped over the edges to seal them up.

Preparing for painting over MDF butt joins

Have you ever seen an MDF box where paint has been applied over butt joins? In virtually every case where great care isn't taken, a hairline crack appears. It is caused by the ends of the MDF soaking up paint and then expanding more than the rest of the material. How am I handling this?

Firstly, I've cut a groove at the join so that any cracks will be concealed if they appear. Secondly I have buttered up all the edges with two part bog. This will tend to avoid the edges soaking up paint. I've also applied polyurethane glue over the edges as a second layer. The plan is to spray the box with automotive paint with a satin black finish.

80L CSS SDX15 sub - part 3

2012-01-23T03:52:00.000-08:00

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Rythmik dual opposed tapped horn sub

2012-01-21T18:15:00.000-08:00

I have always been happy with the sound of my Rythmik subs. I have a pair of sealed 12" servo kits that have been in 70L sealed boxes. They are equal to the best I have heard. I achieve 15 Hz extension in room without any more EQ than is included in the servo system. I have found that I can find their limits thermally with music and have managed to drive them to thermal shutdown twice (since 2006). This is a limitation inherent in nearly all subs. Low efficiency combined with amps intended for home theatre with a lighter duty cycle results in subs that can overheat with music turned up.

I'm very reluctant to let these go so my solution is to start with active woofers running down to 40 Hz. I have 18" pro woofers driven by a pro amp - no chance of running out of steam. The Rythmik subs will then simply add extension and carry a lighter thermal load. Tapped horns will make the box carry more of the load and increase the sensitivity so that instead of around 88 dB from a pair I get around 94 dB.

Here is the concept:

These are around 400L and yes that is big! Boxes will sit under the floor and be attached to it, hence the need for dual opposed mounting. The box is around 400 x 600 x 2250mm.

1w1m simulated:

94 dB with some sacrifice of anechoic extension to achieve higher efficiency. I need only to get down to 25 Hz and room gain gets me down to 15 Hz with a sealed box. I'm aiming for sensitivity and headroom over extreme extension.

Max SPL as limited by the amp:

Excursion:

The excursion peaks at 31 Hz (16.7mm) - xmax is 18mm.

How to avoid over-excursion

The driver will bottom as with a vented enclosure if not carefully protected. The trick is to add a high pass. The amp includes a first order HP which won't be enough when pushed. I will add a 2nd order HP, probably around 20 Hz. I can then test with tones, using a 30 Hz sine wave and noting excursion. Then applying a 10 Hz sine wave with a check on excursion. The excursion below the cut-off should never be able to exceed that above. When that is achieved, the output will be limited only by amplifier clipping and I will be sure that xmax will not be exceeded. This means when unexpected heavy bass hits in a movie, I won't have to worry about damage to subs. I will have set up the system so that the drivers are protected from all conditions.

Achieving headroom

I don't want to create the impression that Rythmik subs are lacking output. However, asking 12" subs to match the headroom of a high sensitivity horn system isn't realistic. To get down to 20 Hz it is necessary to move a lot of air. This could mean one giant super hero woofer with a very powerful amp, but I prefer a number of more modest subs. So for those who want SQ loud, a number of Rythmik subs is a good way to go. I may in fact build two of these, one in each corner.

80L CSS SDX15 sub - continued

2012-01-21T04:43:00.000-08:00

Cut sheets:

Circle jig for the router:

A piece of plywood forms the jig. Since this isn't a plunge router, it's useful to have a flexible material.

Cut outs for bracing:

Double layer thick baffle:

Bracing:

Next >

80L CSS SDX15 sub

2012-01-20T03:09:00.000-08:00

Driver: Creative Sound Solutions SDX15 15" sub driver
Box: Sealed 80L

This is a basic matrix-braced sealed box with a down-firing orientation.

It's good to have a cut plan so that you can cut efficiently. I like to set the table saw up to cut to a width, then do all the cuts of a given width. Otherwise you end up setting it to 450mm, then 414, then 450 then 564 then 414 and so on. It takes time to set it up accurately and you will never get it quite the same twice.

Pieces cut:

S2 Synergy vertical directivity measurements

2012-01-16T20:09:00.000-08:00

Previously I measured horizontal directivity but ran out of time to measure vertically.

Horizontal measurements >

Vertical measurements are much more challenging in this case. On my measurement rig, it means rotating the horn 90 degrees so that it is now tall instead of wide. This allows me to use the angle markings, but I found that without assistance the horn was unstable and my quickly rigged up struts were not up to the task. I would need a person to hold it in place carefully, or spend a lot more time making sure it stays up there. You will get some idea what I'm talking about if you see the setup for horizontal.

In the end I settled on a different setup where the horn was placed on the ground with thick foam on the first reflection point. So the horn was placed on the ground firing horizontally, and then the horn itself was rotated to the angles required, with the mic in place. I printed out a guide for the angles. I also placed foam around reflection points. This is certainly not ideal and the results show obvious problems, but still give some idea of what is going on.

Measurement steps are 10 degrees. So the first line (black) is on axis, the next is 10 degrees, then 20, all the way up to 90 degrees. 45 degrees is shown in black also. So the first 3 lines are within the defined 40 degree coverage angle. All other angles are what will be seen by the floor and ceiling.

The peaks and dips are related to reflections - the horn itself is much smoother than shown. Yet you can see observe a trend in dispersion. Notice how the lines are bunched together at the bottom? This means it is an omnidirectional source down there. However, above about 260 Hz the dispersion does start to narrow slightly, shown by the lines becoming further apart. Overlooking the peaks and dips, the overall trend is a gradual broadening of dispersion up to about 1k.

What does this mean?

Shown here is the vertical dispersion of this 90 x 40 degree horn. What this shows is that you want to arrange the horn it so that you are sitting with your ears within that 40 degree vertical window where the response is consistent. The floor and ceiling see the other angles.

Horizontally, S2 controls directivity down low, but vertically the smaller mouth dimension means that this can't be maintained. So the ceiling will see more lower midrange than the side walls. I'd be inclined to leave side wall reflection points along (no treatment) but consider ceiling treatment that might absorb more lower midrange, like say an RGP BAD panel.

Fury's JBL waveguide speakers

2012-01-16T04:23:00.000-08:00

Last Saturday we had a measuring session for fury's (Danny) new DIY active speakers, shown above.

Rack includes a Tascam CD player, Behringer Ultramatch and two Behringer DCX crossover units, as well as an Altronics multi channel volume control below, a power conditioner/sequencer and three beefy Yamaha pro amps.

We measured the speakers outdoors on my rotating measurement rig.

You can see that it looks very much like a Geddes speaker. It features a BMS 4550 compression driver in an Autosound Oblate Spheroidal waveguide and reticulated foam that was cut by me. I have posted about this previously (a search will show previous posts). The midwoofer is a 12" JBL 2206H.

BMS 4550 compression driver + Oblate Spheroidal waveguide

The waveguide provides good control of dispersion even down as low as 600 Hz, below which point pattern control is quickly lost. There is some freedom here to cross low if desired. Above 15k the pattern narrows slightly.

JBL 2206H

This measurement was perhaps a little surprising in that the woofer measurements tended to indicate there was some flexibility with crossover point as well.

Measurement laptop + DCX + power amp + audio interface.

Crossover measurements:

Black - response 22 degrees off axis
Red - axial response (note the diffraction dip around 5k)
Blue - the result of letting auto align mess things up

After some experimenting and measuring, a crossover at 900 Hz was chosen. We took some extra measurements to confirm that the filters were set correctly and ran auto align only to find that in this case it might be called "auto mis-align!" We used the EQ prediction capability of REW to work out the settings to EQ the top end, resulting in the flat response shown above. The axial response must not be used because there is a diffraction dip.

We ran out of time and didn't get a chance to listen with the new crossover settings, so we heard them without CD EQ applied. The midrange was clean and controlled and I could not help but feel that it was partly due to the 50mm thick cabinets as well as very good drivers.

S2 update

2012-01-12T18:35:00.000-08:00

More filling and sanding with bog. The goal is to get a smooth transition, very much like a JBL progressive transition waveguide or an oblate spheroidal waveguide applied to a different cross section.

Baffles now glued on, more filling and sanding ...

S2 in a corner on top of a 60L sealed bass box for my 18" driver.

Celestion 4" mid test

2012-01-10T02:52:00.000-08:00

Celestion 4" closed back mid tested on S1 Synergy horn

Black: Hornresp sim
Red: Measured nearfield

The dip is not as pronounced when measured, and this remained true when the CD throat was blocked while taking the measurement, or left open. Either way there was little effect. Only one driver was used, so all of the ports were open. The top end extension is well predicted. The driver measures with more extension than modelled as well as a peak and dip that weren't predicted.

Synergy mid driver mounting and phase plugs

2012-01-09T17:11:00.000-08:00

An issue that has been raised with the midrange mounting in the Synergy horn is the aspect of phase. Where the distance from the port to various parts of the cone are far enough apart is large enough relative to the wavelengths concerned, phase issues can occur. This can be reduced by having the port concentric as shown below:

This of course imposes a limit on the number of drivers that can be used. Another way to mount is shown:

This would potentially mean being able to use larger drivers. Can we add a phase plug? On the right, a phase plug is shown, but notice how the front chamber has almost no volume now. This changes the port tuning and reduces the desirable bandpass effect. On the left is an attempt to bring this volume back with a spacer, but it does appear to be less than ideal because we've lost the smooth transition. We've now created a direct path to the port as well as a detour, meaning the phase issue has now been re-introduced. This is probably not a good solution.

Coming soon: S3 - my next Synergy horn

2012-01-06T00:58:00.000-08:00

Currently planning my third Synergy, the one that I intend to keep.

It will be based largely on S2 and based on preliminary sims it will remain a 2 way horn with active bass modules below. DE250 compression driver with a 4" Celestion mid.

The smaller mids means they can run higher, aiming for 1.2 - 1.5k. Due to the large size of the horn, the mids still have very good bottom end extension so I'm expecting they will get down to 250 Hz. With woofers in the horn, the high efficiency only extends down to about 200 Hz and below that point all drivers operate as direct radiators, hence there is little benefit. The cost of extra drivers and amps isn't justified.

S3 has a smoother response than S2 with better top end extension and no bottom end bump. There is a slight loss of extension on the bottom.

Differences with S3:

smaller mid (Celestion 4")
higher crossover to compression driver
CNC cut ply horn
more solid construction with composite applied to the exterior
slightly less extension
reticulated foam added
bass more closely coupled

S2 + Synergy bass

2011-12-31T23:20:00.000-08:00

Synergy bass - part 4

2011-12-29T19:31:00.000-08:00

Currently working on getting the boxes ready for painting. You can see an expressed join around the front baffle, but all other butt joins have had a groove cut, then filled with two part filler.

Right side. The vertical on the right is the expressed join. All edges have a 3mm roundover.

Joins have all been filled at least twice, then a smooth filler is applied.

Front view:

Rear view

Part 3 >

Sanding tools - Bosch belt sander, Ryobi random orbital sander, Ozito palm sander

2011-12-29T19:23:00.000-08:00

When you are planning to spray a high gloss paint finish over MDF, it pays to have some good sanding tools to make the job quicker and easier. I'm using a two part builders filler. I believe it is similar to automotive body filler, but intended to adhere to timber. I'm also trying out a filler over the top to get things smooth. It is premixed.

Belt sanders are extremely handy. I like to use the belt sander over butt jointed edges and it can help get things flat and it does a quick job. You can start with coarse grit paper but you can't expect it to get smooth and there is always a join. They also make a lot of mess so it's a good idea to get a good one. Bosch have a good filtration system. When you pay a bit more for a Bosch when compared to say a Ryobi or some of the cheapies, that's what you get. It's worth the extra.

After the belt sander, these two units come next. On the left is a Ryobi random orbital sander. You have to buy the special sanding discs that will stick on and they also have the holes - see the first photo. The beauty of this one is that it has suction built in so that most of the sawdust goes in to the bag. It costs little more than the cheapies and has variable speed and a better filtering system. If you use the belt sander in your workshop, it will cover everything in sawdust, but this unit doesn't have that problem. The paper only goes up to 240 grit so that does limit its use.

The palm sander on the right is a cheapie. I bought this one primarily to use with fine grit paper prior to polishing a painted surface. It needs not special paper, so you can buy big sheets and cut to size, meaning it's more economical. It has a 3 year warranty. The filtration system only works with a vacuum cleaner attached. This is why this unit is so cheap!

Celestion 4" closed back midrange TF0410MR

2011-12-17T23:25:00.000-08:00

I'm considering this Celestion 4" closed back midrange for a new Synergy horn.

It appears to be a well made driver with suitable parameters. The smaller size is appealing as the mounting is much simpler than that used with S2 with drivers overlapping the horn and needing extra baffles.

Parameters

From Celestion:

Power handling: 30w
Sensitivity: 90 dB
8 ohm
400 - 4k
1" VC
fs 400 Hz
Re 5.65

Measured:

* f(s)= 438.70 Hz
* R(e)= 5.69 Ohms
* Z(max)= 48.49 Ohms
* Q(ms)= 12.230
* Q(es)= 1.627
* Q(ts)= 1.436

See simulation vs measurements >

Synergy bass - part 3

2011-12-16T20:34:00.000-08:00

Part 1 >
Part 2 >
Part 4 >

Box is now assembled and the driver cut outs are done.

I've used a router bit to cut a grove along butt joins. Normally when painting over MDF butt joins a hairline crack appears over time. One strategy to combat this is with a groove, another is to then fill the groove with two part bog filler. I plan to trial both on this box.

You can see the cut out for the speakon terminal at the back.

Part 1 >
Part 2 >
Part 4 >

Dastrix bass traps before and after - part 2

2011-12-11T22:19:00.000-08:00

As seen on StereoNET thread

Synergy bass - continued

2011-12-11T03:51:00.000-08:00

Part 1 >
Part 3 >

Bracing and top and bottom panels

Inside layer of the front panel added:

You may notice that I don't use a lot of clamps compared to many other builds posted online. I prefer to glue and screw because it allows me to keep working, as the screws hold things in place without the need to wait until the glue achieves adequate strength.

The vertical members below serve as bracing for the angled back walls. They also enabled the bracing to be connected together without adding any but the top and bottom panels.

Side walls were attached after the frame, followed by the back, with the angled sections added last.

Box now assembled:

The box is double layer on the front, single layer elsewhere. It will have a composite material applied on the internal walls later.

10mm strips were added so that I could do angle cuts on the table saw.

No, my fingers didn't get that close! Held in place for the photo to show how they were cut.

Part 1 >

Part 3 >

Synergy bass

2011-12-04T02:31:00.000-08:00

Part 2 >

This is the beginning of bass for my Synergy horns. The driver is an Eminence Magnum 18LF, an 18" pro woofer. It could work well in a 110L vented box but in my particular room a 60L sealed box is a good choice because the bottom end will be handled by subs. In this situation a vented alignment gains little except a bigger box.

The design is a simple sealed box with bracing and a shape which fits closer to the corners.

MDF has been cut and I've started to put together the bracing.

Part 2 >

Melbourne round trip GTG

2011-11-27T03:26:00.000-08:00

The Illuminators

2011-11-19T04:57:00.000-08:00

I had a chance to listen to some SGR Illuminators this afternoon.

These were featured at the Australian Hifi show in Melbourne a few weeks ago. It's an active speaker and what surprised me was how hard this thing can hit! The accuracy was no surprise - I expected as much.

Dastrix bass traps before and after

2011-11-14T23:23:00.000-08:00

Room measurement case study 1

2011-11-12T01:45:00.000-08:00

Here is a case study of one room that I measured as a preliminary investigation. The purpose of this measurement session was to determine how well the proposed plan will work in the region dominated by the room, below 200 Hz. This is Graham's home theatre room that will soon have some Ewaves and some 18" bass bins for some Peavey 18" pro woofers. We measured 10 potential bass box locations and four listening positions to represent two rows of seating. Since this is a preliminary investigation and the final speakers have been built, an Osborn floorstander was substituted. Once all speakers and bass boxes are complete, measurements taken for bass integration are different.

Positions 2 and 4 were desired so bass bins could be built under the screen, after some work on the front wall.

Here you can see the measurement setup - I brought my PC equipped with software to measure the drivers and the room, as well as simulate a suitable bass bin design. Positions 7, 8 and 9 are across the rear wall and 10 on the side wall. Ignore the location of the mic stand!

The mic and bass speaker positions were reversed, so the speaker went in the listening position, then the mic was moved. This works fine for a preliminary assessment, and speeds up the process.

First we establish that the baseline, testing the speaker used for bass with a nearfield. The speaker in question is a conventional ported floorstander, chosen because it's bass driver is near ear level and also due to the ease of measuring into the lower midrange.

Nearfield measurement of port and driver:

The smoothness of the response is due to the absence of room influence. The mic is placed very close so the measurement is dominated by the direct field. In looking at all following charts, keep in mind that this speaker is not flat all the way down and has roll-off below 30 Hz.

Front corners and centre front:

All three show a strong 50 Hz mode, but the centre position is smoother overall than the corners. You can see how the corners together could smooth each other out. Out of these three, the best single sub solution is the centre. As it turns out, Graham had already chosen this position for a Shiva sub.

Centre (grey), and positions 2 and 4 under the screen.

Both these positions combined work out similar to the central position.

Waterfall plots show decay behaviour.

Here we are looking for modal ringing.

Corners vs centre position:

If this waterfall doesn't display as animated, you may need to right click on the image and open in a new tab or window.

From the main listening position, right corner:

Left corner:

Centre:

Among other things we learn that this room does not support low bass well. It isn't surprising since it is a large lossy room, with a lot of openings, windows and light construction - timber floor, plasterboard (drywall) light framed walls and ceiling. Notice how the centre position excites the dominant 50 Hz peak less strongly and up to about 120 Hz the decay is more even with less ringing. Above about 150 Hz, all three positions have a lot of ringing in a region where it is sonically a bigger problem for psychoacoustic reasons. This suggests that a suitable treatment scheme might include distributed small bass traps that are effective above 120 Hz.

All measurements from the main listening position:

Confusing? Absolutely, but also useful. Two things stand out - the dominant 50 Hz mode and the roll-off below that point. This suggests that EQ will likely be effective to tame that peak and that brute force is needed to get extension in this room.

How good is the bass where the mains are positioned?

Front centre (grey) is compared to the left and right main speakers in their current position. Note: we didn't measure the actual current main speakers (Bose 901), but instead the response using the same Osborn speakers. With both positions together, the result is fairly similar, although on an individual basis, the centre position is smoother. The lower midrange is likely to lack body and fullness in the lower midrange, based on this measurement.

Four listening positions were measured, but for the sake of brevity, I won't show them all.

All measurements from the rear row (middle position):

Compared to the previous position some trends can be seen. The 50 Hz mode is still present but we also see more extension and a 30 Hz mode related to the room depth along the listening axis. When we move back closer to the rear wall, the room is now able to support the axial depth mode. We also notice some dips around 50 - 80 Hz which will unfortunately cause a loss of bass impact, and here we start to grasp a problem with optimising multiple rows in a big room. If we achieve extension and bass impact in the main position, the back row will become bass heavy, with a bloated bottom end and missing midbass. A simple solution such as one sub with some EQ will not optimise the entire room well. One choice might be to focus on the prime position and let the chips fall where they may elsewhere. Or a more sophisticated bass integration may be chosen to get more consistent results.

Front corners vs centre:

Now you can see the extra extension and midbass suckout.

Corners vs the centre (back row):

If this does not appear animated, then right click and view in a new tab or window.

Left corner:

Centre:

Right corner

So what happens if we add another sub in a different position?

Front centre shown in grey, compared to the rear corners (green right magenta left).

Now we can see that the midbass suckout is removed. A small sealed helper sub could work well here with some care given to avoiding localisation. A bandpass sub with a sealed rear chamber and a 75 Hz low pass with a steep slope would be a good place to start.

How would this affect the main position?

This helper sub if made sufficient in extension could add some bottom end by as much as 10 dB at 30 Hz and the right corner could smooth out the midbass as well. A little more EQ is needed around 50 Hz. Overall, it appears that it would actually improve the main position as well.

This is a preliminary investigation. The final speakers will need to be measured in place with the chosen bass management settings, treatment and EQ all in place in order to fully optimise the bass. So at this point, we are looking at the big picture and aiming to find the solutions most likely to work.

Bass bins

Graham bought my Peavey 18" woofers to go in some bass bins under his screen (positions 2 and 4). We ran some sims using these drivers in both a vented and tapped horn design. As much as I was hoping he might go for a tapped horn for the fun of it, I had to admit I could not see any major advantage in the sims. We came up with a large vented box with a slot port.

How do these positions measure in the four measured positions?

Superimposing all positions, and both bass bins, again noting that they aren't built yet, but we are looking at the measurement with substitute speakers, we can see the greater extension in the rear row.

Main listening position:

Clearly they are smoother together.

Left seat in the front row:

Rear row placed 1.4m from the rear wall:

Both share a deep notch at 60 Hz.

Rear row moved closer to the rear wall (750mm).

All up around 50 sweeps were taken and much of this data isn't shown here.

3 sub options

Now many are familiar with a certain Harman paper on multiple subs. It recommends subs at the centre of the front and rear wall for many rooms. This turns out quite well with peaks and dips often coinciding:

Unfortunately due to a window this is purly academic. If the rear right sub is added, the suckout is also removed:

Conclusion

From these results we can see:

the proposed locations will work quite well
two bass bins are better than one in terms of smoothness
the current sub position (front centre) appears to work best as a single sub solution
the front row is reasonably smooth but lacks extension
the rear row has midbass suckout but greater extension
a rear corner helper sub has the potential to solve both problems
bass trap treatment should ideally focus on absorption down to 50 Hz along with distributed smaller traps to target the region above 120 Hz
a good result is possible in the front row with one sub, moderate EQ and compact bass traps

Synergy horn measurements

2011-11-08T16:53:00.000-08:00

Synergy horn measurements taken on my polar measurement rig with Arta. Shown below are directivity plots.

See measurement setup >

1. Yorkville Unity

2. S1 - my first prototype (60 x 60)

3. S2 - my second prototype (90 x 45)

What do they show? The Yorkville has a pattern that narrows around 2 - 3k, revealing that the compression driver when mounted on the horn is starting to beam at the low end but when it transitions to the mids, probably somewhere around 1 - 1.5k, the pattern becomes wider. The horn is too small to control directivity any more, a compromise to achieve reasonable size.

S2 is a larger horn which manages to control dispersion more, however it does have some dips on axis, hence it requies some toe-in so that it isn't heard directly on axis. As a result, the plot could not be normalised like the others. A normalised plot is based on a perfectly flat on axis response.

S3 is much larger again and controls dispersion all the way down to 300 Hz, a very good result. The dispersion is more uniform than the others, most likely due to a combination of size as well as a second flare angle to avoid beaming. With S1 there is some slight beaming at the bottom end of the compression driver's passband, below about 1.6k. With S2 the transision is perfectly smooth, and there is nothing in the polar response to suggest the crossover point, while in the other two you can see changes across the crossover.

More about understanding directivity plots >

These plots show the same data, but now it is shown in 3D rather than a birdseye view with SPL represented in colour. Again the order is the same:

1. Yorkville Unity

2. S1 - my first prototype (60 x 60)

3. S2 - my second prototype (90 x 45)

At a glance you can see that the third (S2) is overall much smoother than the others. Both the Yorkville and S1 have some dips on axis suggesting that toe-in should be used to get the smoothest response. This isn't necessary with S2.

Overall this represents very good results.

Now some comparisons:

The dark line shows the - 6 dB point which is the reference for a given nominal dispersion. The straight line shows the nominal intended dispersion.

The Kruger-Dunning effect

2011-11-07T21:25:00.000-08:00

The Kruger-Dunning effect provides some very interesting insights into human behaviour, with implications for the audio community. What is it? In a nutshell, it refers to the tendency of the unskilled to be overconfident because they simply don't know what they don't know.

Kruger-Dunning effect in more detail >

There are two sides to it. There are those who over-estimate their abilities due to ignorance - this is referred to as illusory superiority, a form of cognitive bias. Others tend to under-estimate their abilities, partially due to being more informed and aware of their own limits, and perhaps overlooking that most others are not equally competent.

Do you suffer from illusory inferiority? If so, people probably praise your abilities and you feel that you don't quite deserve the acclaim. You might feel the need to balance it out by pointing out how much you still have to learn. If that's you, give yourself a pat on the back! You probably don't give yourself the credit you deserve.

Do you suffer from illusory superiority? If so, you probably aren't the one that is suffering. It's others, who see things that you can't, or don't want to see. Jesus had wise words to say that relate to this issue. "As a guest, don't take the highest seat so that the host has to ask you to step down and give it to someone else. Instead, take the lowest seat so that the host can then offer you a better one."

What to do about it?

Two suggestions:

1. Encourage those who under-estimate themselves, give them the kudos they deserve, despite what they say they will appreciate it.
2. Ignore those who blow their own horn. Smile knowingly. Life will dish out what is deserved.