Küchenradio

Ohne Küchenradio kann man nicht gut kochen. Das Tivoli One war zwar schön, aber der Radioempfang war dürftig. Um entspannt zu kochen, wurde das Tivoli zu einem Internet-Radio umgebaut. Ein Raspberry Pi kümmert sich jetzt per WLAN um den perfekten und unkomplizierten Empfang von Radiosendern aus aller Welt. So kocht es sich gleich viel besser!

radio

Peerless Aktiv-Subwoofer

Dieser Subwoofer wurde für den flexiblen Einsatz in high-end HiFi-Systemen entwickelt, z.B. zur Kombination mit der S24. Die Tieftöner werden von einem eigenen Verstärker mit Digital-Filter und -Entzerrung angetrieben, was eine sehr ausgewogene und tiefreichende Basswiedergabe ermöglicht. Die gegenüberliegende Anordnung der beiden 12-Zoll Tieftöner führt zu einer gegenseitigen Auslöschung der Vibrationskräfte, die von den Tieftönern ausgehen. Dies minimiert unerwünschte Vibrationen des Gehäuses, was dem Subwoofer zu einem äusserst klaren und natürlichen Klang verhilft.

Eine detaillierte technische Beschreibung ist noch ausstehend.

peerless_subwoofer

Photo 1: Einer der beiden Peerless-Tieftöner

Peerless_Subwoofer_drawing

Mangerbox

mangerbox_3

Dieser einzigartige Lautsprecher beruht auf dem berühmten Manger Schallwandler (MSW). Im Gegensatz zu konventionellen Lautsprechern mit steifen Membranen funktioniert der MSW nach dem Prinzip der Biegewellen, die sich auf der hochflexiblen Membran vom Zentrum radial nach aussen bewegen – ähnlich wie die Wellen auf der Wasseroberfläche, wenn man einen Stein ins Wasser wirft.

Eine detaillierte technische Beschreibung ist in einem separaten PDF-Dokument verfügbar (englisch).mangerbox_1 mangerbox_2 mangerbox_plan

Tube Speaker

tubespeakerThis is a small speaker which I designed as an improved clone of a Bang&Olufsen designer speaker. Unlike the B&O model, however, the Tube Speaker is made of real metal and sounds really good. It uses two 11-cm Seas-Excel mid-woofers (yes, the ones with the magnesium membranes) and a Scan-Speak D2905/930000 soft-dome tweeter mounted in a d’Appolito arrangement. The metallic outside is backed with a 2-cm thick layer of sand-filled epoxy, which results in an extremely «dead» enclosure.

Drivers

Since these speakers are only 15cm wide I had to use very small woofers. The only good woofers in this size (about 12cm max. outer diameter) I could find at the time were the Seas Excel drivers. Their outer diamter is about 11cm and there’s even a model with the famous magnesium-membrane by Seas. Because these woofers are so small I had to use at least two of them in each speaker to get reasonable bass-response – so why not mounting them in d’Appolito style? I never built a d’Appolito speakers before so I decided to try it. Well, it was worth it: the sound qualtiy and the 3D imaging of the Tube-Speakers turned out the be very good!

The magnesium membranes have a very strong resonance peak at at about 11 kHz. This is way higher thant the cross-over frequency, so this resonance is not a problem in this design. The tweeter should be of the same good quality as the mid-woofers. I ended up using the ScanSpeak 9300 tweeter, befcaus it is a very good tweeter and it’s not too difficult to design a suitable cross-over filter network for it.

Enclosure

The design of the metal enclosure is where the Tube Speakers are different from every other speaker I have come across so far. But when you get off the beaten track, things can get rough…

The first major problem was to get a suitable metal tube. I called a metal-working companies, who told me that a suitable tube with cut-outs and a flat face plate to mount the drivers would cost a fortune. That means two fortunes for a stereo pair. Finally, a friend who works as a metal-working teacher took up the project and built the tubes for me. Thank you Erwin!

The second major problem with a metallic enclosure is that it would resonate like a church bell, very bad for a speaker cabinet. My first idea to solve this problem was to fill the metallic tube with concrete from the inside, but I was afraid the concrete wouldn’t stick to the metal. So, what else? Epoxy is really sticky… so I mixed epoxy with as much sand as possible. This gives a very heavy and solid material after the epoxy is hard. I put about 2 cm of my epoxy-sand mixture on the inside of the metal-tube. To do this I put a carton-tube inside the metal-tube. The carton-tube’s outer radius was about 2 cm less than the radius of the outer metal-tube which left the required gap to pour my mixture in. Epoxy has some disadvantages, though. Firstly, it is expensive. And secondly, it gets very hot when hardening and after becoming hard it cools down again which also means it contracts a little. This contraction caused the epoxy-sand-mix to loose contact to the metal-tube so I had to pour some more epoxy into these gaps. The result of my epoxy treatment is a very rigid and perfectly air-tight speaker-cabinet with virtually no vibrational resonances.

Crossover filter network

I used a 3rd order low-pass filter for the woofers (both woofers in parallel) and a 2nd order high-pass filter for the tweeter. Together with the natural low-frequency roll of the tweeter, this results in a 3rd order slopes in the frequency responses of both the woofers and tweeter, as required for a school-book d’Appolito design. The cross over frequency is about 2 kHz. The figure below shows the frequency response (measured with MacSpeaker using an MLS-signal), which is very flat (±1.5 dB between 500–8000 Hz, and ±3 dB throughout the entire frequency range of the measurement).

tuberesponse

Anechoic frequency response of the Tube Speaker

Leider ist diese Seite zur Zeit nur auf Englisch verfügbar.

ScanSpeaker

scanspeakerI designed the ScanSpaker as a mid-sized but high-end two-way speaker using Scan-Speak drivers. This floorstanding speaker uses the Scan-Speak D2905/990000, a 1″ soft-dome tweeter, and the Scan-Speak 18W/8545-00 mid-woofer, which has a 17-cm diaphragm made out of carbon fibre and paper.

1. Drivers

As the ScanSpeaker name suggests, all the drivers are made by ScanSpeak. I used the 8545 woofer (17cm diameter) and the 9900 tweeter (aka «The Revelator», 28mm dome). These are very good, but expensive drivers. The 8545 midwoofer has the reputation of very smooth reproduction of voices. This wasn’t true in my speakers at all until I added impedance-compensation for the impedance-rise caused by the voice-coil. The 8545 has a strange „bump“ at about 600–700 Hz. It doesen’t look like a membrane-resonance at the waterfall-diagrams so it can be corrected with an LCR-network. The 9900 tweeter has a special frontplate which is supposed to improve lobing behaviour. I heard and read rumors suggesting that this special frontplate design causes a slight resonance somewhere between 10–20 kHz, but I couldn’t see it on my measurements. The dome diameter is 28mm and the resonance-frequency is at 530 Hz, so the Revelator goes lower than most other tweeters. The 9900 has a reputation to acts a bit like a «diva» when designing the crossover, which I attribute to the very pronounced impedance peak at resonance.

2. Enclosure

case

Drawing of the ScanSpeaker enclosure

I used a bass-reflex construction for the ScanSpeaker. I put two bass-reflex channels in the bottom of the case, «aiming» at the floor. This works because the speaker stands on spikes at about 2 cm above the floor. The internal volume of the case is about 18 liters. The front is 18.8 cm wide which is about the minimum possible with the 8545 woofer. An ideal case does not vibrate at all – the driver’s membranes are the only thing that should move. To get a «dead» case I built the case from 18 mm particle-board (inside) and 10 mm MDF (outside). Enclosure vibrations are further dampened by a layer of ceramic «bathroom» tiles and a layer of «Hawaphon» on the insides of the enclosure walls. A layer 10 mm felt and some wool  dampen internal sound resonances and eflections in the case. In addition, I installed a piece of cardboard at the top of the case with some foam glued to it. The cardboard is angled at about 30° relative to the face plate, which helps to avoid standing waves along the long axis of the enclosure.

3. Crossover network

The final crossover filter networks for the midwoofer and the tweeter are shown in the figures below. The initial design started out by calculating theoretical parts values, which were then optimized by acoustic measurements and by ear. As mentioned above, the 8545 woofer frequency response shows a slight «bump» at about 600–700 Hz. This is compensated using an LCR network. Also, for proper operation of the tweeter filter, the impedance peak of the 9900 needs to be compensated. This is achived by an L-pad in between the tweeter and the filter network. The L-pad is also matches the tweeter SPL to that of the woofer.

ss_xover_woofer

Midwoofer crossover filter network

ss_xover_tweeter

Tweeter crossover filter network

The parts values for the midwoofer filter are:

  • L1 = 1.8 mH
  • L2 = 15 mH
  • C1 = 10 µF
  • C2 = 15 µF
  • C3 = 3.9 µF
  • R1 = 5.6 Ohm
  • R2 = 4.4 Ohm (tot. resistance of LCR including L2)
  • R3 = 1 Ohm

The parts values for the tweeter filter are:

  • C4 = 3.9 µF
  • L3 = 0.82 mH
  • R5 = 10 Ohm
  • R6 = 8.9 Oh

Leider ist diese Seite zur Zeit nur auf Englisch verfügbar.