Cooltune

Menhir - Single Driver Speaker

Working on the fullrange transmission line (TML) speaker with Manger's Bending Wave Transducer MSW, I made numerous simulations using different programs such as AjHorn, TLBoxMod and UniBox. While the first TML speakers perform very well and the feedback of several music lovers has been encouraging, the construction is rather complicated and time-consuming.

So, I was looking for alternative designs with a similar performance but with less complexity concerning the overall construction. I started to scrutinize the different topologies of enclosures by using AjHorn and my experience.

Although I know it is extremely difficult, if not impossible, to adequately cover the audio band with only one driver, today I am convinced that this transducer, well applied, is one of the best drivers in the frequency range of 90 Hz to 24 kHz and in my opinion well qualified for a fullrange system.

Manger's MSW driver has a flat diaphragm which is bent to produce sound waves, rather than pushed and pulled like a regular "rigid" speaker cone.

Below you will find the Thiele/Small Parameters for the neodynium magnet. Please note that the validity of Thiele/Small Parameters (TSP) is limited. Above approx. 150 Hz the TSP no longer are valid.

Frequency range		80 Hz - 35 kHz
Rise time		13 us
Voice coil inductance		27 uH
Free air resonance frequency	Fs	88 Hz
Radiating surface	Sd	220 cm2
Effective cone diameter	Dd	16.7 cm
Equivalent air volume	Vas	15 l
DC resistance of voice coil	Rdc	7.15 Ohm
Free air mechanical Q	Qms	2.94
Free air electrical Q	Qes	1.25
Efficency 1W/1m/half space 2 Pi	Eta	91 dB
Linear excursion	Xlin	+/-3.5 mm

As mentioned at the beginning of this article, after numerous simulations done, I selected two alternatives: a transmission line solution and a multiple vented solution!

The simulations are guided on the Mirrored sound pressure response as a basis for loudspeaker design discussed in the chapter Loudspeakers - Listener friendly sound pressure response for a 25 to 30 cm front baffle width.

Brown dashed line = Combined response of normalised room sound pressure
response and baffle diffraction loss for a baffle between 25 to 30 cm

Blue dashed line = Adapted 2 Pi loudspeaker frequency response

Red line = Resulting in room sound pressure response

TML Menhir : The Transmission Line Solution Although this solution may not be a classical transmission line design, the main characteristics of a transmission line still remain.

2 Pi Frequency response at 32W power input in "db"

Voice coil excursion in "mm" at 32W power input

Impedance curve in "ohm"

     - Rear chamber volume : 24 liters
     - Throat area : 1500 cm2
     - Mouth area : 70 cm2
     - Line lenght : 75 cm
     - Line flare : Parabolic
     - Box volume : 80 liters
     - Acoustic termination : Fibrous stuffing material
     - Box leakage Ql : No leakage, Ql > 30
     - Effective Qt : approx. 0.9

     - Acceptable box volume
     - Very simple design and straightforward construction
     - Comes close to the room and listener friendly sound pressure response
     - To some extend adaptable to room acoustics (at the expense of varying
        the frequency ripples and max. power input)

Disadvantages:

     - Ugly frequency response ripples
     - Small TML port may cause air flow noise at high SPL levels
     - Mandatory use of ordinary fibrous stuffing material
     - Stuffing of the line may cause losses in bass detail
     - TML and box tuning may be delicate

Drawing Overview:

     - Loudspeaker : Manger WO5/1-2.2.16 , Neodynium, 8 ohm
     - Box walls : 24mm Finnish Birch or Beech Multi-ply Plywood
     - Line damping material : Sheep Long-fiber Wool or Acousta-Stuf Polyfill
    - Line damping density : Approx. 75% to 150%
     - Chamber damping : None
     - Box wall damping : 5mm Idikell 4001 and 10mm Wool Felt
     - Box base : 12mm to 20mm Marble or Slate
     - Base damping (between enclosure and base): High density Cork

AMV Menhir : The Aperiodic Multiple Vented Solution This solution has a regular and an aperiodic port.

2 Pi Frequency response at 32W power input in "db"

Voice coil excursion in "mm" at 32W power input

Impedance curve in "ohm"

     - Rear chamber volume : 78 liters
     - Throat area : 120 cm2
     - Mouth area : 120 cm2
     - Port lenght : 14 cm
     - Port flare : None
     - Box volume : 80 liters
     - Acoustic termination : Sound diffusing and aperiodic port
     - Box leakage Ql : Aperiodic, Ql = 3.5 to 4.0
     - Aperiodic port area : approx. 45 to 50 cm2
     - Effective Qt : approx. 0.82

     - Acceptable box volume
     - Comes very close to the room and listener friendly sound pressure response
     - Simple design and straightforward construction
     - No ugly frequency response ripples
     - To some extent adaptable to room acoustics (at the expense of varying the
        max. power input)
     - Aperiodic driver damping with a reduction of Qm and therefore Qt
     - No need of fibrous stuffing materials

Disadvantages:

     - Loudspeaker : Manger WO5/1-2.2.16 , Neodynium, 8 ohm
     - Box walls : 12mm Corian or Creanit
     - Chamber damping : None
     - Main port damping : None
     - Aperiodic port damping material : Very thin Wool Felt
     - Box wall damping : 1mm Lead , 5mm Hawaphon and/or 5mm Idikell 4001
     - Acoustic diffusion : 10mm Aramid Honeycomb , 40mm Air/Water Filter 20 PPI
     - Box base : 12mm to 20mm Marble, Slate
     - Base damping (between enclosure and base): 5mm Carbon Prepreg

Along with the effort of designing the AMV Menhir 1a, I considered another solution which may have an improved performance. This alternative design is more difficult to construct and therefore more time-consuming.