WTC7ex

Wtc7ex_full_3205.JPG

Introduction
Prototypes
Bass proto
Lower midrange proto
Upper midrange proto
Tweeter proto
Tweeter non-linearity comparison
WTC7ex without woofers
Enclosure
Crossover
Simulations
Measurements
Sound
Summary

Note! This document is truncated. Full version with some useless small talk, simulations and prototypes is available only in Finnish.


Introduction

Target was to make very directive speaker (without horns) to transfer information from record to ears without disruptive room reflections. This enables listening over longer distances in bad acoustics without resonators and special treatment of room surfaces. Sound should be good with good recordings and bad with bad recordings.
Vertical directivity should be much stronger than average - especially to directions creating early reflections (-40°/+50°). Horizontal directivity at midrange should be cardioid or hypercardioid, and as constant as possible. Attenuation to 180° should be about 15 dB. Polar response of bass range should be adjustable. Bass should be weakly pressurizing.

Construction

Sufficient vertical directivity at midrange can be created with MMTMM. Tweeter will be ribbon/planar with moderate vertical directivity. Uppe rmidrange will be 2x4" and lower midrange 2x8", both in resistance enclosure.

Bass unit will be combination of dipole and monopole. Monopole driver is located very close to back side of dipole driver to keep polar pattern constant until crossover frequency. Dipole and monopole will have individual power amplifier which enables adjustability of polar pattern to suit for different rooms, placements and listeners. Polar pattern will be adjustable within dipole...hypercardioid...cardioid...(monopole). Dipole frame will be H-frame located on the monopole enclosure. Monopole driver is partly inside of back transmission line. Back side will be damped if frame is not symmetrical H-frame.

Drivers

Dipole bass 20-160 Hz Peerless XXLS 830845 1 pcs
Monopole bass 20-160 Hz Peerless XLS 830452 1 pcs
Lower midrange
160-700 Hz Seas W22EX001 2 pcs
Upper midrange 700-2500 Hz Seas W12CY001 2 pcs
Treble 2500-20000 Hz Bohlender Græbener Neo3-PDR 1 pcs

Prototypes

Bass proto

Bass_proto_front.jpg Bass_proto_back.jpg

Dipole driver is SLS-12". H-fame is non-symmetric with damped back side. Monopole driver is XLS-10" and box is filled with polyester.

Measurements are done outdoors. Measuring distance is 200 cm and mic elevation 90 cm. Smoothing is 1/12 oct. and time window 100 ms. Angles in diagrams are horozontal only.

Frequency responses (without EQ)

SLS = dipole, XLS = monopole
Bass_drivers_freq.gif
Attenuation to 90° is oly 20 dB because of non-symmetrical H.

Phase responses

Without equalization. Phase difrerence between monopole and dipole is almost constant 150°. Why it's not 180°?
Bass_drivers_phase.gif

At this point frequency response of drivers are equalized to 180° to create cardioid polar response. Dipole has band-stop filter (210 Hz, -8 dB, Q=1) and level of monopole is decreased 2 dB. Phase difference (150°) has left as it was, and not much attention paid frequencies over 200 Hz.

Horizontal directivity 1

This is cardioid. Average attenuation within 20...160 Hz:

45° 90° 135° 180°
-1.3 dB -5.8 dB -14.0 dB -28.9 dB
Bass_proto_cardi-0dBa.gif

Horizontal directivity 2

Level of monopole is decreased 2.2 dB (compared to cardioid setting) to increase attenuation to 90°. Attenuation increases 1.0 dB, and direction of maximum attenuation rotates from 180° to 135°. Average attenuation within 20...160 Hz:

45° 90° 135° 180°
-1.7 dB -6.8 dB -28.1 dB -13.4 dB
Bass_proto_cardi-2dB.gif

Horizontal directivity 3

Level of monopole is decreased 4.4 dB (compared to cardioid setting) to get even more attenuation to 90°. Attenuation to 90° and 180° are now equal. This is good setting if vertical resonances are as bad as horizontal. This is close to hypercardioid where maximum attenuation is at 120°. Average attenuation within 20...160 Hz:

45° 90° 135° 180°
-1.8 dB -8.4 dB -17.0 dB -9.1 dB
Bass_proto_cardi-4dB.gif

Summary

Back TL of dipole frame looks too deep because peak frequency (210 Hz) is too low. Dipole part of final speaker will be symmetrical H-frame to enable full dipole and peak at higher frequency.

Polar response of this kind of hybrid cardiod depends on measuring distance. The reasor for this is distance dependent frequency response and level of dipole unit. Dipole is close to pure driver in near field; there's no clear 6 dB/oct. HP slope or dipole peak. Distance dependency of dipole can be reduced by minimizing the frame. However, it's not possible to make ideal cardioid this way. Fortunately it is not necessary because ideal is not necessarily the best.

According my insvestications, the most flexible polar response is hypercardioid where level of monopole is decreased 3...6 dB compared to cardioid setting. It's more immune to placement than ideal cardioid. Also attenuation of vertical resonaces is better.

Lower midrange proto

Wtc7ex_mid1_front.jpg Wtc7ex_mid1_inside.jpg

Dimensions are 240 x 240 x 280 mm. Internal net volume is about 6.5 liters (9 without internal limiters). Side ports are 2.0 mm steel, 308 pcs of ø6 mm holes each. Cotton fabric ('Finlayson Classic' linen) is clued with PVAc inside the plates. Small top port has 88 pcs ø6 mm holes. Leaking area is 90 % of Sd. Box is filled with polyester. There's also extra 6 layers of polyester (Univisio) on the back side of ports.

Horizontal directivity

The result is good - no need to change anything. Attenuation to 180° would increase by adding some polyester.
W22EX001_hor_freq.gif

Impedance response

Effect of port resistance into impedance response:
- 'Ei koteloa' = free air
- 'Kotelo, ei portteja' = driver is in the box without resistance ports
- 'Ei vanua, Finlayson' = resistance ports are on but no polyester
- '6 vanua' = resistance ports on, filling and 6 extra layers of polyester behind the ports
W22EX001_impedance.gif

Upper midrange proto

Wtc7ex_mid2_front.jpg Wtc7ex_mid2_inside.jpg

Dimensions are 150 x 360 x 260 mm. Internal net volume is about 3.8 liters (7.2 without internal limiters). Side ports are 2.0 mm steel, 88 pcs of ø6 mm holes each. Cotton fabric ('Meidän koti' linen) is clued with PVAc inside the plates. Leaking area is 99 % of Sd. Box is filled with polyester. There's also extra 16 layers of polyester(Univisio) on the back side of ports. Volume is too small because 16 layers of polyester was needed to reach target polar response.

Horizontal directivity

W12CY001_res4_hor_freq.gif

Average of horizontal attenuation
W12CY001_res4_hor_dir_ind.gif

Impedance response

Effect of port resistance into impedance response:
- 'Ei koteloa' = free air
...
- '16 vanua' = resistance ports on, filling and 16 extra layers of polyester behind the ports
W12CY001_impedance.gif

Tweeter proto

Treb_proto8_front.JPG

Bohlender & Græbener Neo3-PDR planar with wave guide is installed on 150 x 20 mm baffle. Wave guide is 0.5 mm aluminum. Shape is calculated with the following formula:

Wx = Wt * cosh(x/x0), where
- Wx = width of mouth at distance x from the throat (mm)
- Wt = width of throat = 37 mm
- x = distance from the throat (mm)
- x0 = 10.84 (sleeve constant to get total width of 120 mm.

Horizontal directivity

Measuring distance 65 cm, time window 4 ms, no smoothing
Treb_proto8_hor_freq.gif

Vertical directivity

Treb_proto8_ver_freq.gif

Average of horizontal and vertical off-axis attenuation
Treb_proto8_dir_ind.gif

Tweeter non-linearity comparison

THD is measured with SpectraLAB 4.32. Frequency step is 1/6 oct, voltage 1 Vrms, which dosn't reveal reaction with high sound pressures.

Treble_THD_compare.gif

Worst results as spectrum:

Harwood Acoustics UR2.0, 7071 Hz
HarwoodUR2_THD_7071Hz.gif

Harwood Acoustics UR2.0, 10 kHz
HarwoodUR2_THD_10kHz.gif

Visaton MHT12, 2500 Hz
VisatonMHT12_THD_2500Hz.gif

Summary

I'm very disappointed with these ribbons and planars. However, B&G Neo3-PDR is really good.

WTC7ex without woofers

Vertical directivity

Measuring distance (100 cm) is from mic to nearest midrange cone
- time window 20 ms, smoothing 1/3 oct.
Wtc7ex_top_ver_freq.gif


Enclosure

Enclosure drawing: Wtc7_dwg.pdf (version 6, 29.06.2005)
Some old versios: Wtc7a_dwg.pdf, Wtc7b_dwg.pdf, Wtc7c_dwg.pdf
Resistance ports (1:1): Resistanssilevyt.pdf

Material is local birch. Thickness of dipole baffle is 30 mm, upper midrange and tweeter box 20 mm and the rest 25 mm. Boxes are oiled/waxed with OsmoColor; first layer with pine pigment and second with clear (3101).

Week 13/2006

Wtc7ex_full_3205.JPG Wtc7ex_top_3202.JPG Wtc7ex_mid2_0015.JPG
Wtc7ex_top_3199.JPG Wtc7ex_twr_3204.JPG Wtc7ex_top_3198.JPG Wtc7ex_mid1_0017.JPG

Week 12/2006

Wtc7ex_top_3176.JPG Wtc7ex_full_3175.JPG
Wtc7ex_sub_3172.JPG

Week 11/2006

Wtc7ex_sub_3166.JPG Wtc7ex_mid1_3167.JPG Wtc7ex_mid2_3157.JPG Wtc7ex_mid1_3161.JPG Wtc7ex_mid2_3162.JPG Wtc7ex_mid2_3163.JPG Wtc7ex_sub_3168.JPG Wtc7ex_sub_3169.JPG Wtc7ex_sub_3171.JPG

Week 10/2006

Wtc7ex_sub_3145.JPG Wtc7ex_sub_3144.JPG Wtc7ex_sub_3146.JPG Wtc7ex_sub_3147.JPG Wtc7ex_sub_3152.JPG Wtc7ex_sub_3153.JPG
Wtc7ex_full_3154.JPG

Total height is only 143 cm.

Week 09/2006

Wtc7ex_top_3143.JPG

Week 08/2006

Wtc7ex_mid2_3102.JPG Wtc7ex_mid2_3121.JPG Wtc7ex_mid1_3119.JPG
Wtc7ex_top_3122.JPG

Week 07/2006

Wtc7ex_mid2_3099.JPG Wtc7ex_mid2_3100.JPG Wtc7ex_mid2_3101.JPG

Week 02/2006

Wtc7ex_mid1_3085.JPG Wtc7ex_mid1_3086.JPG Wtc7ex_mid1_3088.JPG Wtc7ex_mid2_3083.JPG Wtc7ex_mid2_3084.JPG

Crossover

Speaker is active filtered with two Behringer DCX2496; one for the woofers and second for the MMTMM. It needs 10 power amplifier channels. Power amps are Rotel RMB-1066 and Yamaha XM6150. Cable hell...
Wtc7ex_cable_0031.JPG

Parameter files are not available anymore.


Simulations

Crossover topology has strong effect to vertical directivity with MMTMM construction. Drivers are ideal in this simulation. Diameter of tweeter is only 20 mm.

2nd Order Linkwitz-Riley

XO_2ndOrderLR.gi

LR2 has the strongest vertical directivity.


Measurements

Frequency response

- living room, concrete walls and roof
- measuring distance 200 cmWTC7_FR_Room_200cm_ver01_L.gif

Horizontal directivity

Measuring distance 120 cm, time window 20 ms:
WTC7_hor_freq_ver05.gif

Average of horizontal attenuation within 30°...180°
WTC7_dir_ind_ver05.gif

Individual frequency responses

Measuring distance 150 cm, woofers 1 cm:
WTC7_FR_Driver-Split_ver05_R.gif

Individual phase responses

Measuring distance 150 cm, woofers 1 cm:
WTC7_PR_Driver-Split_ver05_R.gif

Harmonic distortion

SPL 96 dB/1m, measuring distance 50 cm:
WTC7ex_HD_102dB@50cm_L.gif

CSD

Measuring distance 50 cm, time window 5 ms:
WTC7ex_CSD_50cm.gif


Sound

Tonal balance? Very good, but bass range was somehow hidden below midrange.
Rhythmic? Not so
Dynamic? Bass no, midrange and tweeter ok
Timing? Not so good; too much phase distortion weakening the transients. Weak attack of piano and kick drum.
Soundstage? Sharp, logical and forward (not behind speaker line). Speakers can't create/reproduce soundstage.
Presence? Depends on record; sometimes excellent but usually not. Floorless/floating images when vocals were near field recorded.
Tune? Good
Bass tracing? Some disintegration at upper bass...lower midrange, but usually good.
Resolution? Very good but not full. DCXs were original and using analog inputs which dropped resolution.


Summary

This project was very complex and challenging. Weakest points were too mild attack and too small size of bass radiator. Importance of time alignment was not so clear to me. Many gurus are still telling fairy tales that it's not audible. Maybe it is't by the ear drum but at leat I can feel it with my body. Size of bass radiator should be bigger than midrange. Otherwise midrange rules received sound information over the bass. I would call it unbalanced resolution and projection.

Page updated 08.11.2010

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