Birthday Build

Birthday Build

Rasmus Munk Larsen

Project Category:
Tower Speakers

Project Level:

Project Time:
20+ Hours

Project Cost:
$500 – $1,000

Project Description:
Here is my “Birthday Build” for my friend Mike, commissioned by his wife as a surprise present for his birthday. Mike, our wives and I love to get together to listen to music. Mike is a constant source of learning about cool artists, old and new, for us, so I really wanted to build something excellent that we could enjoy together over the years to come.

Design Goals:
My goal was to create a great sounding and beautiful floor-standing speaker, putting to use all the skill and knowledge I have accumulated over the last few years of building, experimenting, and listening to more experienced speakers designers, here on Parts Express and other online forums.

Driver Selection:
The speaker uses a Vifa XT25BG60-04 1″ Shielded Dual Ring Radiator Tweeter, and a Peerless 830875 6-1/2″ Nomex Cone HDS Woofer. I have used the Vifa XT25 in previous projects and love the very detailed and neutral sound it has. I also think it creates an incredible 3-D soundstage. I had not used the Peerless Nomex cones before, but saw many people recommending them. I am very happy with this choice as it was easy to work with, plays surprisingly deep, and looks great.

Enclosure Design:
The enclosure is a 25 liter bass reflex box tuned to 42 Hz. I simulated it in WinISD.

Enclosure Assembly:
The cabinet has 3 internal window braces, foam dampening (mattress topper) and a 3″ port made from ABS pipe, using a 60 degree knee to make it fit, and flared on the outside using a chamfer bit. The sides of the baffle have a 1/2″ roundover. The cabinet is covered in zebrawood veneer and finished with Polycril.

Crossover Design:
The crossover is adapted almost exactly from a design by Jay a.k.a. Brewski in an old thread here on Parts Express:

I used a mix of Audyn and Jantzen (the lower end ones) for the series caps and NPE for the large caps in Zobel and the RLC. Inductors were Jantzen. I added an L-pad (not shown in diagram) consisting of a 3 Ohm resistor in series and an 8 Ohm resistor in parallel to match sensitivity and reduce an upwards tilt of the tweeter response.

I am very happy with the way these speakers came out, both in terms of looks and finish and sound.

About the Designer:
Rasmus is a computer scientist and amateur choral singer living in the San Francisco Bay Area. He grew up in Denmark (where all those sweet speaker drivers come from).

Project Parts List:

Peerless 830875 6-1/2″ Nomex Cone HDS Woofer
Peerless XT25BG60-04 1″ Shielded Dual Ring Radiator Tweeter
Bi-Amp Speaker Terminal Gold Binding Post
Jantzen 5203 1.5mH 15 AWG P-Core Inductor
Dayton Audio AC20-15 0.15mH 20 AWG Air Core Inductor Coil
Jantzen 0422 2.7uF 400V Z-Standard Capacitor
125uF 100V Non-Polarized Capacitor
Dayton Audio DFFC-0.47 0.47uF 400V By-Pass Capacitor
Jantzen 0264 10uF 400V Crosscap Capacitor
Jantzen 0272 22uF 400V Crosscap Capacitor
Mills 2.5 Ohm 12W Non-Inductive Resistor
Dayton Audio DNR-3.0 3 Ohm 10W Precision Audio Grade Resistor
004-8 Dayton Audio DNR-8.0 8 Ohm 10W Precision Audio Grade Resistor
Dayton Audio DNR-1.5 1.5 Ohm 10W Precision Audio Grade Resistor


Add yours
  1. 3

    Beautiful towers!!! Love the Zebra veneer here! Not sure about the crossover on the tweeter however – to many components of rather very large values – they will compromise the sound for sure. We use a Scan Speak version of this tweeter with only 5 crossover components and it is stunning!!! Cheers!

  2. 4

    High Rasmus! Greetings from Berlin,Germany. I like your Speakers very much. Not too big and good Proportions.
    I think thay sound as well as they look like. Now my Question: Are there construction -details available? Or it`s not possible to copy your project?

  3. 5

    I have a question it looks like the crossover you are using is designed for 2 woofers (4ohm) load, your using just 1, where’s does that put your crossover point ? Around 4k?

  4. 6

    Would you mind sharing what you did to the mtm crossover to make your tm work, I have (6) 875’s laying around with a couple pairs of r2604/8330 that need some attention, thanks, hope you get this

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