Navigation: DIY Audio Projects / DIY Speaker Projects / Ion DIY 2-Way TMM Tower Loudspeaker Project

Ion - DIY 2-Way TMM Tower Speaker Project

Adam McCall   USA Flag     To email Adam, type out the email address.

Ion - DIY 2-Way TMM Tower Loudspeaker Project

The Ion is a wonderful 2-Way tower loudspeaker that has been designed to produce a very warm and natural sound. It achieves this by using a pair of Audax HM170CO woofer-midranges drivers with a TangBand 25-1372SC tweeter in an TMM configuration and using a 3rd order crossover point at 4000Hz. The Audax HM170CO woofers produce very warm natural tones up through the upper midrange. With the TangBand 25-1372SC tweeter the highs are crystal clear, detailed but far from harsh. Bass response is excellent too! The Ion speaker is a very challenging build but it comes with a huge payoff! These have quickly become my favorite loudspeakers.

General Tower Loudspeaker Information:

  • Tang Band 25-1372SC 1" Tweeter - Inverted Titanium Dome
  • Audax HM170CO 6" Woven Carbon Fiber Mid-Woofers
  • 3rd Order X-over at 4000Hz w/ Impedance Correction
  • 4ohm Nominal Impedance
  • 128 Watts RMS
  • Freq Response 60Hz-20kHz
  • Sensitivity ~93 dB / 1W / 1m
  • 37.5" x 8.5" x 11.5"
  • 60lbs each est
  • Solid MDF and Oak Construction
  • 1.5" Wall Thickness w/ Oak Side Panels
  • Textured Graphite Finish/Stained Hardwood

Enclosure and Crossover Design - Ion 2-Way TMM Tower Loudspeaker

A bass reflex (ported cabinet) enclosure is used for the tower loudspeakers. The overall size of the speaker box enclosure is 37.5" x 8.5" x 11.5" (953 x 216 x 292 mm) and each finished loudspeaker weighs about 60 lbs (27 kg). The enclosure drawing for the Ion speakers is shown below (click drawing to enlarge).

Ion 2-Way TMM Tower Loudspeaker Enclosure Drawing

Figure 1: Enclosure Drawing - Ion 2-Way TMM Tower Loudspeaker

To come up with the enclosure design for the speaker I used Bass Box Pro Version 6 to simulate the frequency response. The X-Over Pro 3 passive network design program was used to design the crossover, impedance equalization network and L-pad circuits. The frequency response and impedance plots generated for the enclosure and crossover are shown in Figure 2.

Frequency Response and Impedance Graphs - Ion 2-Way TMM Tower Loudspeaker

Figure 2: Simulated Frequency Response and Impedance Graphs - Ion 2-Way TMM Tower Loudspeaker

A 2-Way passive crossover network using a 3rd order Butterworth filter at 4kHz is used along with an impedance correction network. The crossover schematic is shown in Figure 3.

Crossover Schematic - Ion 2-Way TMM Tower Loudspeaker

Figure 3: Crossover Schematic - Ion 2-Way TMM Tower Loudspeaker

Crossover Components - Ion 2-Way TMM Tower Loudspeaker

C1 = 3.9 uF, Polypropylene, internal resistance 0.00736 ohms
C2 = 10 uF, Polypropylene, internal resistance 0.0051 ohms
C3 = 15 uF, Polypropylene, internal resistance 0.00435 ohms
L1 = 0.15 mH, Air Core (18AWG), internal resistance 0.16 ohms
L2 = 0.3 mH, Air Core (18AWG), internal resistance 0.26 ohms
L3 = 0.1 mH, Air Core (18AWG), internal resistance 0.13 ohms
Rp1 = 1 ohms, 10W, non-inductive
Rp2 = 33 ohms, 10W, non-inductive
Rp3 = 1 ohms, 10W, non-inductive
Rp4 = 27 ohms, 10W, non-inductive
Req = 3.3 ohms, 10W, non-inductive
Ce = 12 uF, Polypropylene

A photograph of the assembled 2-Way passive crossover network for the Ion Loudspeaker is shown below.

Assembled 2-Way Speaker Crossover Network

Photograph 1: Assembled 2-Way Speaker Crossover Network

Construction Notes - Ion 2-Way TMM Tower Loudspeakers

The Ion 2-Way TMM Tower Loudspeaker will be a challenging build. The best approach is to take your time and be patient. DON'T get wrapped up in all the super precise dimensions; they are impossible I know, but have been provided for reference. I suggest to start off by cutting all of the raw material for the baffles/outside panels and braces but a bit longer than needed. Sandwich your panels together to achieve the noted 1.5" thickness; while keeping in mind to leave a 1" clearance on both the far outside edges. [Note: 1" = 1-inch = 25.4 mm] I suggest setting yourself up a small jig on a work table and cut out a few 1" wide pieces to ensure you're good and square. And then cut the 22.5 degree angle and achieve your needed length that way. The angled corner pieces do the same for, but do not fully assemble by adding the piece that is furthest to the inside of the cabinet till after the 22.5 degree angle has been cut.

Cut Panels for Ion Loudspeaker Enclosure

Photograph 2: Cut Panels and Bracing for Ion Loudspeaker Enclosures

Regarding the port; it is two 1.5" holes in the rear through 3" of MDF. Assemble yourself a 1.5" thick piece which can accommodate the port holes and attached to the rear baffle and then drill out the port holes.

Ion Speaker Box Port

Photograph 3: Ion Speaker Box Port

Make a total of 4 braces, but make them a bit long. You now want to assemble all the outside panels using PL400 adhesive and strap clamps (using tie downs is ok too, I did). Insert the braces at this point too; trim shorter if needed (but keep them equal length to ensure squareness). Allow the adhesive to set. Now take measurement for your side panels and build them. Depending on your choice of lumber you may want to choose a 1/2" thick hardwood and back it with 1/4" MDF. There is then a 3/4" MDF rib that runs the full length for support. Pre-drill your holes for the side panels into the cabinet! Following these steps will help eliminate some headache and ensure a desirable end result. Below are some photos of the construction process.

Speaker Box Assembly

Photograph 4: Speaker Box Assembly

The speaker box has been assembled and is primed using Kilz Oil Based Primer before being painted.

Apply Primer to Speaker Box

Photograph 5: Apply Primer to Speaker Boxes

After the primer has dried, the MDF panels are painted using cans of Rust-Oleum Textured Spray Paint

Painted Ion Speaker Box

Photograph 6: Painted Ion Speaker Boxes

Materials List and Costs - Ion 2-Way TMM Tower Loudspeakers

A list of the parts and materials used for this project and corresponding cost (US dollars) is provided in the tables below. Table 1 shows the speaker parts ordered from Parts Express (USA).

 Parts Express #  Description  Qty   Price (each)  Cost
 TB 25-1372SC 1" Titanium Tweeter 
3/8" Toe Spike Set
16awg Black Primary Wire 100ft
16awg Red Primary Wire 100ft
BPA-38SN Binding Post Satin
Jantzen .15mH Air Core Inductor
Jantzen .30mH Air Core Inductor
Jantzen .10mH Air Core Inductor
Gasketing Tape 1/8"x3/8"x50'
Acousta-Stuff Polyfill 1lb bag

Table 1: Speaker Parts from Parts Express

The remaining speaker parts including the Audax HM170C0 6.5" driver were ordered from Madisound and are shown below in Table 2.

 Madisound #  Description  Qty   Price (each)  Cost
Circuit Board Matrix
Mundorf 33ohm MOX Resistor
Mundorf 27ohm MOX Resistor
 Mundorf 3.3ohm MOX Resistor 
Mundorf 1.0ohm MOX Resistor
ClarityCap 3.9uF PX Poly Cap
ClarityCap 15uF PX Poly Cap
ClarityCap 10uF PX Poly Cap
ClarityCap 12uF PX Poly Cap
Audax HM170C0 6.5" Woofer
#10 1" Phillips Pan Head
#6 3/4" Phillips Oval Head
#8 1" Phillips Pan Head

Table 2: Speaker Parts from Madisound

Materials for the speaker cabinets were purchased from Home Depot and are listed in Table 3. You will be able to find the materials for the speaker cabinets at most home improvement stores.

Description  Qty   Price (each)  Cost
3/4" x48" x 96" MDF Sheet
1/4" x 48" x 24" MDF Sheet
1/2" x 48" x 24" SandePly
Kilz Oil Based Primer 1 qt
 Rust-Oleum Textured Spray Paint 
16 oz Wood Glue
1" Drywall Screws - 1lb
Wood Filler
PL400 Adhesive

Table 3: Cabinet Materials from Home Depot

Speaker Parts: $800.59 (Parts Express and Madisound)
Cabinets Materials: $132.77 (Home Depot)
Total Cost: $933.36 US

Finished Ion Tower Speaker

Photograph 7: Finished Ion Tower Speaker

Summary - Ion 2-Way TMM Tower Loudspeakers

I really love these Ion Speakers! They have met and exceeded my expectations.  The speakers play very warm and clear.  They have a very full and open midrange all the way down.  The highs are very clear, articulate and direct.  They have a great presence down in my office; curious to see how they do in the living room. I didn't find the midrange spike shown on the simulations (Figure 2) to be of any real concern; it certainly isn't annoying or painful to listen to and doesn't show up in the measured response. In the crossover shown the tweeter has been padded by 1.6dB and the woofer has a 2.64dB L-Pad. This setup sounded best for my room. The measured in-room response of the Ion speakers is shown below (click response plot to enlarge). The large peaks and dips that appear below about 500Hz are the "resonant room modes" which are caused by standing waves.

Measured RTA Response of Ion TMM Tower Loudspeaker

Figure 4: Measured RTA Response of Ion TMM Tower Loudspeaker

For more information about myself and photos of other speakers I have built, check out my website at AM Audio. Also, be sure to check out my other speaker projects, the 1.618 HiVi 3-way Tower Loudspeakers and matching 1.618 HiVi Center Channel Speaker and HiVi SP10 DIY Subwoofer build.