IKEA HiFi

It is obvious, not only did I not post a lot lately, I am also very late in the game what IKEA electronics is concerned. After having talked about HiFi gear made from PVC-tubing, there was not much left to degrade my standards in high fidelity audio, I figure. And here I am, talking about IKEA as the next audiophile (maybe not) source of gear.

A while ago, I contemplated using JBL Flip4 speakers as improvised stereo setup. This worked all fine, one the app recognized the speakers and finally configured those into a stereo pair. Maybe that was the tech of that time, I don't know, but, it (finally) turned out that an easier way is possible.

Coming onto the scene, the IKEA Eneby gen 2 BT speakers. Not only those speakers are 60% of the price I paid for the JBLs, they also remember the (stereo) configuration they were set up in.
While the original Eneby speakers might sound equally good as the 2nd generation, stereo pairing of those was not an option. Solely for that reason, I could not be bothered with the Enebys. 
However, this has all changed now. One can configure two identical Eneby gen 2 speakers to act as a stereo pair and the speakers will keep this setup, unless reset to factory settings.

What the sound is concerned, I think they sound very nice. Initially my impression was that they are a bit bass heavy, however, this might have been due to the music I tested them with in the first attempt. Listening to "Sweet Smoke" now, the speakers seem well balanced and the stereo image is very pleasing, just like I remember the record when played on vinyl on a big rig years ago.

The speakers can get surprisingly loud. 

Even as a stereo pair, one can control the balance by individually adjusting the volume of the respective speaker. While this makes sense with balance, this also can be done to the bass and treble response of the individual speaker... I am not sure if that makes any sense.

The Eneby gen 2 speakers do have an analog jack input. I have not yet tested if one can run a stereo paired setup with analog input. That's a test for a future post.

Boom boom pafffff

Something totally off topic today, OK, it's audio, no electronics involved however.

IKEA is known for some interesting projects here and there, beyond the famous bookshelf. Lately, they introduced a product range which appears to be a collection of random stuff, the collection being "FREKVENS". There are even products that could be interesting for a blog concerned with electronics. No worries, I wont be writing about a silver rain coat or a silver cushion cover either.
Let's have a closer look at the only real IKEA flat pack product in the collections, the FREKVENS Cajón (drum).
No, this is not a drum, this is a cajón, and instrument well known in Spanish and Afro-Cuban music. A cajón can create sounds similar to various parts of a drum kit, which is a matter of great skill, which I don't have.
There are a few more things wrong in the product listing, at least what the images are concerned. The side with the big whole is the back-side (or reverse, depending on your style of English). Hence, the guy in the photo sits on it the wrong way. Also, he appears to be slapping the sides of the instrument, which are made of much thicker material and not supposed to be the main playing surface.

Anyways, I bought one of those flat-pack instrument kits and build it according to the provided instructions. BIG mistake! The more I learn about the instrument, the more obvious this should have been.
The assembly instructions take a similar order to something like a nightstand. Which, seen from IKEA's perspective, does make sense. However, when following the leaflet, it is almost inevitable to create a misaligned box  that does not sound right.

Step 1
The instructions start with mounting the snares to the (front of the) bottom-plate, so far so good.

Step 2
The side-walls are screwed to the bottom-plate. This is the first instance where things can go wrong. The alignment of the outer edges of bottom-plate and side-walls needs to be precise. This might not be that important on the bottom-plate, desirable however.

Steps 3 and 4
According to the instructions, the top-plate is now mounted to the side walls, very similar to bookshelves, nightstands,  etc. I cannot emphasize enough, don't do this yet. I did it and I ended up with a slightly misaligned top-plate. This misalignment kills the instrument!

Step 5
In this step, the playing surface, i.e. the front, is mounted. Remember, the front is where the snares are. This is very important for the functioning of the instrument and not clear from the instructions.
This step should be done after step 2, if not before...
If you followed up to now, you will understand that it is important to not tie down any of those screws yet.

Step 6
Here, the back-plate of the cajón is screwed to what we assembled so far. Please note, we skipped steps 3 and 4, so there wont be any (I should have written about that in step 5, sorry!).

Final assembly according to me
If you followed my advice, you skipped steps 3 and 4. What you should have by now should be a square wobbly bucket with no lid.
At this stage, carefully work the top-plate into its position. This might be a bit tricky, therefore, we did not tighten those screws. Once the top-plate is in place, we want to first tighten the screws of the front-plate including the ones we skipped. This will auto-align the top-plate to the side-walls. This alignment is most important to the good functioning of the instrument.
Once this alignment is established, screw down and tighten the 2 front screws on the top and the side-walls.
Now apply all the remaining screws. And tighten all screws on the back and the lower half of the screws on the front.

Tune up
In case of all screws being tight, you will have to hit the cajón very hard to get the snare effect. This will result in an imbalance between the snare and the bass drum sounds.
Therefore, what you are looking for is a small gap between the top-plate and the front-plate. To realize a somewhat even gap to your liking, you have 5 screws in the top half of the front-plate to play with, i.e. loosen and tighten. Every little bit of tension here and there will change the tone and snare sound created by the cajón. It took me a while to balance the right and left corners of the upper playing surface.

Conclusion
IKEA is good in creating wooden flap-pack products. The FREKVENS Cajón is no exception, when built and aligned correctly.
There are competing products available from musical instruments suppliers, here is an example. This example supposedly requires additional materials for assembly, although at a lower price.
What I am concerned, after having aligned my cajón, I am pretty happy with the sounds it can create and look forward to learning this instrument.

Portable Stereo Stage

This channel has been silent for some time by now, sorry for that! Will be getting more active in the near future.
While this blog started as a RF only outlet, slowly I drifted to all sort of electronics, including speaker enclosure designs using PVC piping material. Yes, those pipes are still in my living room, connected to a class A tube amplifier and fed by some CD players. While sounding pretty good, this is not really portable per se, although, seen against cement speaker enclosure, this is probably relatively portable.
Travelling back and forth nowadays, I was searching for an alternative.

Lately, I found said alternative. Got a couple of JBL Flip 4 BT speakers. Those are connected to my phone using BT.

Those JBL Flip 4 BT speakers can be used as a pair of stereo speakers. Not having read any instructions, I took me some to to figure out how to actually create that stereo stage. Having tested the setup with different kind of listening, from Vivaldi over Herbie Hancock to Dream Theater, I am deeply impressed!
Seen that the setup is that small and inexpensive that fact that I could not find any flaw in the sound experience tells me that I found my next stereo system.
Although in comparison to my tube class A amplifier, some additional noise is evident.

For aesthetic reasons, I chose both Flip 4s to be black. Of course this makes them a little bit more difficult to setup in the right way. A small sticker indicating which is left and which is right should not be a bit deal however.

If you can live with a little bit of pink noise, a setup of dual JBL Flip 4 speakers is highly recommended.

PVC Tubes Driven by Tubes

Dear reader,

please accept my apologies for keeping you in suspense over my latest projects for so long. 2017 was a very intense year for me. During said year, I changed my day-jobs twice, so, the radio hobby and the audio hobby had to take a break. Concerning jobs, I believe to have finally found the position of my dreams with a lot a really nice people in the company... I believe I have never been happier before!
Anyway, this is not about life, this is about driving tubes, PVC that is, with tubes, such as in vacuum.

My pipe dreams, as you know, are employing 3W (8Ohms) broadband drivers, which came with a super-cheap set. By now, I am convinced that those drivers were the most valuable part in the entire kit.

In search for a 2 x 3W class A amplifier, I came across a Chinese kit supplier (Douk Audio, cf. ebay), who sells single-ended class A amp kits based on 6N1 and 6P1 tubes. Said kits are comparably inexpensive and, while provide good quality parts, come without a mains-transformer.

My choice of mains transformer fell on a 100W transformer offered by a supplier in the UK, search for "big.daddy!" on ebay.

The combo works as a charm! The amplifier kit seems to be made for my pipe dreams.

As an audio source, I am presently using a professional grade table top DJ CD player by Numark.
In the future I consider to add a passive equalizer / tone control circuit to the setup in order to allow for compensating deficits from compressed digital audio formats. For now, I am pretty pleased with the raw performance from CDs.

More Pipe Speaker Improvements

The last issue I had with all of my PVC-Voigt-Pipes: resonance of the horn. I read about it, I knew about it... and now, I was bugged by it too.

The solution is very simple: a tripe of cleaning cloth, just below the joint of the driver unit to the horn. The effectiveness of which can be tested by slapping a flat hand on either end of the horn. Without the damping cleaning cloth sound would resonate creating some BOONNNNNG BOONNNNG. With the cloth inserted, this changes to BooB BooB.

BTW, this was effective with the designs I published on this blog.

PVC Pipe Dreams updated design (audio)

My PVC Voigt pipe speakers were in heavy use during the last 2 years. My study allows for housing those slim monsters.

Anyway, I found 2 problems with them:

1. too tall
2. very directional

So, very easily, since those things are all pipes, I slightly changed the design. Have a look!

modified PVC Voigt pipe design

To reduce the length, I changed the position of the speaker in the T-piece and added an elbow to bend the resonator parallel to the the horn. The above image shows the 2 different designs I posted earlier.

Also, I inverted the orientation of the full range drivers. There are some advantages:

• the drivers breathe directly into the resonator (similar to the folded TQWT)
• the direct audio of the driver is less directional
• the drivers are better protected

As a first observation I would like to mention that treble and bass seem prominently present in the horn, while the mids are emitted by the driver directly.

As a consequence, that could mean that the horn should be above the driver, since the stereo field is determined by high frequencies.

The next step would be to put a wooden box around the T-piece driver part of the design. This way, the contraption can be held upright and all the ugly part would be hidden away nicely.

If it all seems rubbish what I write about PVC plumbing, give it a try yourself. All parts are readily available in your local hardware store. 

Concerning the inverted speakers, I am not yet sure myself. However, for the time being they appear to create a pleasant listening experience.

3 Inch HiFi PVC Pipe - The Alphorn (MLTQWP)

Finally I found some time to tell/show a little bit more about the speaker enclosures I was bragging about so much lately.

Most importantly, why was this so interesting to be posted on a blog concerned with RF. Well, to my very own understanding, the principles behind emitting sound waves it somewhat similar to the principles of emitting radio waves.
Here is why:

Analogy between a quarter-wave vertical and a quarter-wave speaker enclosure

On the left hand side, the above sketch shows the good old vertical quarter-wave antenna driven by a gamma-match. Indicated in blue, the current distribution along the radiator. Of course, this current will emit a magnetic fields (green), which was the purpose of the antenna in the first place.

On the right hand side, you see a loudspeaker cabinet called quarter wave pipe (QWP). In such a pipe design, similar to the gamma-match of the vertical, a driver (in acoustics loudspeaker chassis are called drivers) creates pressure waves (green) somewhere in the middle of the "conductor". Similar to a quarter-wave antenna, the conductor is excited at a resonance frequency. The blue line indicates the air speed, i.e. current, through the pipe. The red arrows indicate sound emissions.

• The driver emits sound to the front side of the cabinet.
• The standing wave emits sound at the open end of the pipe.

While the driver emits what ever is present in the AF signal, the pipe predominantly emits sound at its resonant frequency and harmonics thereof. The latter, of course, is a problem! In musical terms, this could lead to a "One Bass Note Samba", something nobody would enjoy, contrary to the "One Note Samba" having quite some more notes than one only.
Consequently, the bandwidth of the pipe needs some severe broadening!

Back to aerials, there are 2 ways to make an antenna broadband:

1. add more resonators (e.g. log-per, dipole fan)
2. add Ohmic resistance (e.g. T2FD, Beverage antenna)

In acoustics, both can be done too. As I indicated before, antennas and speaker cabinets have a lot in common!
In acoustics, one can add more resonators by tapering a restrictive volume and add resistance by stuffing said volume with dampening material.

For a HiFi speaker cabinets one needs a very homogenous emission over several octaves, i.e. close to 0Hz up to 22kHz (those are, of course, extremes). A mixture of multiple resonances and some severe resistance is used. Actually, there is an added bonus on the resistive part of things... not only does stuffing material add resistance, it also lowers the velocity of sound within the medium. A stuffed enclosure looks larger to sound-waves than the same enclosure not being stuffed.

PVC piping, at last we leave the theory part of things, is a very convenient stuff to work with. Now we talk about pipe in the sense of water pipe. Have I forgotten to mention that the word pipe could have several interpretations, sewage pipe, water pipe, organ pipe, pipes of bagpipes, etc. OK, pipes, i.e. PVC pipes, fittings and stuff thereof. Here is the B.o.M:

PVC parts

The parts serve the following functions:

• tubing form the pipe's body, obviously
• the elbow is the resonator's "mouth", bending pressure waves towards the listener
• the T-piece is to the driver
• the reduction pieces will taper the resonator
• and the end cap will be the end cap, i.e. terminating the resonator.

The elbow, T-connector and fat tube form the lower part of the pipe. This is all 3" piping. The length of the tube it 1m.
The upper part of the pipe is tapered down to 2" and 1.5" PVC tubing. The respective tubes have a length of 50cm each. Obviously, fittings add length to the final product.
Adding 1 additional diameter to the taper, will just add 1 more resonance (and its harmonics). Hmmm, "Two Not Bass Samba", really?!  No, that does not help!
The tubes therefore receive insets. The process of making those is pretty easy. My preferred method is using heating pipe insulation foam tubing. Cut in half, the stuff can be easily be cut diagonally. A result of this is tapering for pressure waves.

Tapering inserts

That's the tapering part dealt with... Those speakers are called TQWP.

However, before putting everything together, we need to address the resistive part of broadening the bandwidth of the pipe and lowering its resonance. There is no photo of this step. The material involved is polyester from an IKEA pillow, the cheapest acoustic stuffing on the market!
I complemented the inserts with the pillow stuffing and shoved it down the respective 50cm PVC tube.

We are nearly finished... there is just one other addition, before the "cabinet" can be assembled. In order to prevent the creations of unwanted harmonics, dampening material (cleaning cloth!) has to be added behind the driver (within the T-piece).

Here is a photo of the finished speaker:

The Alphorn speaker

Yeah, this is a very tall speaker. For obvious reasons, I call this speaker "Alphorn". The image above shows the thing from floor to ceiling, as installed in my attic.
The sound of those speakers is amazing! From classical to hiphop, via kizomba, funk and rock... the sound of those speakers blows me away!
Mind you, those are very cheap 3" drivers...

The drivers came in a stereo set priced less than €40.
Why am I mentioning this? The price for the PVC plumbing parts, used for this project, is actually > €42.The passive parts of the project exceed the price of the active ones... not sure what that means in the context of modern electronics.
Speaking money, the Alphorn speakers sound like speakers in excess of at least 1k€.

Back to theory... the total length of the pipe is about 225cm. 2,25m in quarter-wave reflects 9m of wavelength, which in itself equates to a sound frequency of about 33Hz. This would be the resonance of the empty (non-tapered) pipe.
As said before, the upper part of the pipe is stuffed with IKEA pillow material, hence the real resonance frequency will be even lower. Stuffing enclosures is called "Mass Loading".

There are 2 sharp steps in the taper, one at 120cm and one at 175cm. Those steps add resonances at 62.5Hz and 43Hz, which of course will also have harmonics too.

The resulting speaker enclosures qualify for the MLTQWP... and... they sound amazing!

UPDATE on alternative design thoughts. Thoughts only. On the internet a couple of designs float showing curved structures, involving a plurality of bends and elbows. Similarly to stepped tapers, those bents create reflections and disturb the air-column of the standing wave pretty good. Bending the design to limit height of the speakers seems however a very attractive thing to do.
My gut feeling tells me that 45º bents at carefully selected lengths could work. Maybe two of those just above the feeding T, followed by a reducer and two more 45º bents. Such a design would keep the tallness of the speaker at about 140cm. However, I still believe that such a measure will reduce the amplitudes of the lowest frequencies.

More Pipiness in the Audio Department

More improvement to report on the PVC pipe speaker enclosures (Voigt pipes).

Today I decided to stuff the upper pipe resonator. Stuffing reduces the velocity of sound due to increased density of the resonance volume. Such an increase of density lets the resonant volume appear larger to the sound-waves.
Quick excursion to a previous post: those pipe-enclosures are just broadband quart-wave resonators, having a pressure node at the closed end of the pipe and a velocity node at the open end.
Reducing the velocity of sound inside the pipe will therefore lower the quarter-wave resonance, resulting in more bass.

Poor man's stuffing could be cotton wool (cotton batting). This stuff introduces a severe problem! The pipes will be home of moths!

There is help, however, a real poor man's stuffing: polyester fiber from real cheap cushions. At a modern Swedish furniture store, such cushions are as cheap as €2/pc containing 400g of fibers, which is a lot more than needed.

I loosened up the cushion fiber, in order to create a very light and fluffy stuffing. Mind you, with 2" drivers, you don't want to dampen too much. It took just a few grams to lightly stuff the tapered resonators.
The result was quite pleasing. However, running the converters w/o the upper resonator revealed some adverse effects of the horn (lower part of the pipe/resonator).
To remedy this effect, I dropped a quarter cleaning cloth, cut the long side, into the tube, covering the back of the driver and following down as deep as possible.

Finally, my PVC-plumbing Voigt pipes are pretty close to Voigt pipes made from wood, as found on the world-wide-waiting-network, i.e. stuffing above the driver, damping behind the drivers and a horn like bass mouth.

As announced before, the next step has to be the homebrew low noise amp.

PVC Pipe Nightmares

Uhh?! What is going, first he told us how cool those pipe are, and now nightmares?! What is going on?!
Very simple, when pushing one inferior variable to the best possible, another one will take the place of being the disturbing one... the one that spoils all the fun and excitement.
Well, this time, it was the stereo that was driving the fun, as I thought.

Although I still believe this is a very nice device, I have to report that this device creates a hizzzzzz under "normal"circumstances. As soon as any of the buttons is tampered with, the hizzz is absent, just to return after a few seconds... VERY ANNOYING!

This "feature" was audible only with my PVC Voigt pipe-type speakers. What do we learn from this?!

• When using a cheap stereo, use the speakers supplied, so you don't hear the deficiencies!
• When hooking up a cheap stereo to some decent sound converters, you may be able to hear the defects the respective sound converter has.
• Dimensions given by your sound-Guru are relative... does a 1.5m Voigt pipe sound better than a 2+m Voigt pipe?! Probably not... shorter pipe, less bass..

Am I happy with my more than 2m long Voigt pipes driven by 2" drivers? Yes I am! I think those are the most amazing cheap speakers I ever listened to!

Remedy for the hizzzzzz problem: build a dedicated AMP (opamps/LM368) in a classical way...

Pipe Dreams X(X)L

Guess what, I am still experimenting with sound reproduction, HiFi audio that this. And of course, I am still on the cheap, sort of.
In my previous pipe dreams post, I discussed improvements of a stuffed transmission line made from PVC pipe. I still like the results, however, there is some bass missing... Depending on the genre to listen to, this is fine, however, lets assume the bass is really needed in a certain presence.

There was a certain Mr Paul G.A.H.Voigt, who is a simple speaker design named after. The Voigt pipe. And indeed, this design in a pipe, the like pipe of an organ. Actually a bass pipe, a broadband bass pipe.

The interested thing about such pipes is that they work similarly to what we know as "gamma match" in radio. At a certain fraction of the length of the pipe, a standing wave is created. While in a aerial, the current at 0 Ohms determines the radiation. In an audio speaker, the open end (zero resistance) aka mouth, does the same thing. As in aerial design, speakers have near and a far field responses.

Here I am, running a "gamma match" speaker, i.e. a speaker that functions as a pipe of an organ.
An organ pipe, of course, resonates at exactly one frequency. This is not ideal, unless playin' the "One Note Samba" by A.C. Jobim at the resonance frequency.
When using RF dipoles having (slightly) different resonance frequencies, the bandwidth of the antenna system can be widened easily (cf. log-pers and dipole stacks). 
Also, added Ohmic, i.e. lossy, resistance does a trick of broadening the resonance (cf. T2FD).
Pressure waves in sound follow the exact same principles. Instead of a dipole array, a resonating body is tapered. Instead of adding Ohmic resistance, damping material is added.

Here is a difference:

• In radio, we want to transmit on one particular frequency. Any other frequency, we want to suppress as much as possible (unless running wide spread spectrum, that is).
• In HiFi audio, we want to emit the entire spectrum as evenly as possible, the flatter the better!

However, there is a problem in HiFi audio with deep frequencies (long wavelengths). Pressure of such wave seems to collect in upper corners of rooms having a finite size, creating unpleasant rumble/mumble. So, the question is, how low do we need/want to go?! In a workshop about studio acoustics a once learned that studio monitors smaller than 5 inches are better suited, since those don't create said deep bass frequencies being so disturbing.


So, let's see what we have... 2 inch scrap speakers (salvaged from a dead small flat screen TV) as full range drivers.
In the precious posts, you see how those did in a damped 1m TL PVC pipe setup.

Same divers, similar back horn setup (removed all damping material from the back horn). Well, actually, there is no real back horn any longer. What used to be the back horn is now part of a pipe.

PVC Voigt pipe

The elbow containing the driver is replace to a T-piece. The upper part of the T-piece is connected to a reducer piece, which reduces the pipe diameter of 32mm.
The length of the closed 32mm pipe is 1m.
A Voigt pipe is not only closed, in order to create a standing wave (to the mouth), but also tapered, in order to widen the bandwidth. In my setup, I decided to taper the pipe by adding a angled cut of a cult in half insulation foam pipe, which I was writing about before.
Here a photo of the such a cut in half foam pipe.

imagine this diagonally cut in half, creating 2 similarly tapered pieces

Such foam is inserted in the upper (closed) end of the tubing, creating a tapered resonant body (stacked dipoles).
The lower half of the upper pipe's tubing is stuffed with 1/8-ths of a cleaning cloth, in order to reduce further reduce resonances (Ohmic part of the game).

To further improve sound response, some damping material was added behind driver. Care should be taken not to reduce the volume the driver breathe from.

Up to now, I played with 2 inch drivers only, there are drivers of greater diameter in my scrap box.

=> Stay tuned for more speaker madness!

PVC Pipe Dreams (audio)

You have seen speaker enclosures I made from PVC plumbing pipes. For stuffing the pipes, I initially used heat pipe insulation (the grey stuff in the image below). It worked OK, at least to an extend I was surprised, concerning those tiny drivers.

speaker stuffing material

I experimented a bit with household cleaning cloth, as shown in the image... the stuff you would clean for bathroom with. The stuff was on sale, €1,- for 2 sheets.
What the hack, I rolled one up and stuffed it in the speaker pipe. Clearly, the mouth of the pipe now only did "mmmm mm mmmmm" (referring to very deep bass notes). The all over volume of the speaker went way down. I guess, I restricted cone motion quite a bit with that much mass.

This stuffing:

• 0.5m of the insulation stuff
• 1/4 sheet of rolled up cleaning cloth

was the next experiment.
Now the driver has got nearly half a meter of pure air column to breathe, followed by the insulation foam and some loose stuffing of soft cloth.
In a way, this is like tapered increase of acoustic density.

Again, the result is really interesting, seen the small / cheap drivers. Of course, you would not expect a hammering deep bass.

Still more to experiment, I pushed the cloth stuffing about half way into the PVC tube. This way, I think, the driver has to some volume to breathe from and the longer wavelengths, that made it through the stuffing, can form more homogeneous pressure fronts, before exiting the enclosure.
Again, some improvement could be noticed.

Speaker enclosures, made from PVC piping, seem to offer endless opportunities to experiment.

PVC Pipe Speakers

Yep, I know, this is not RF, this is AF. However, this post my be of interest anyways.

Recently, my first ever LC-Television died on me. Of course, the device had to be source of parts. And it was! The sound of this TV was not bad, hence, I also took the 2 tiny 2" full range speakers out before I crapped the rest.

After collecting some dust, the chassis are finally put into operation again, wit the help of 2" (55mm) PVC pipes.

The speakers are house in elbows, taped in by electricians tape:

the driver

Followed by 1m of 55mm PVC pipe, providing the air column. The pipe is actually filled with a "pipe insulation jacket" as to reduce resonance effects and also increase the acoustic resistance.

the speaker box

Of course you would not expect the sound of a Klipschorn from this device, however, you will be surprised how much bass a 2 inch speaker can deliver, being placed in a decent enclosure.
I am sure that sound quality can be improved by stuffing the tube properly, however, the foam tube insulation was just so tempting to do, cheap and easy, and it works surprisingly well.