KS-1807

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Introduction
Enclosure
Crossover
Simulations
Measurements


Introduction

KS-1807 is originally designed in 2012. Idea was to make loudspeaker having quite equal resolution spectrum without heavy acoustic treatment, by combining conventional upper midrange and tweeter with directive and large woofer section. It's not common that speaker is able produce balanced resolution from bass to top octave without intentional weakening of high frequency resolution. Average box speaker may have 15 dB increase in directivity index from bass to top octave. Horn speakers may have 20 dB increase woofer part is small omni, and transition could be like a step in the middle of midrange. This may cause quite unnatural resolution balance, where nuances and bling-bling at high frequencies are very emphasized compared to inaccurate and shredded bass...lower midrange. Attention of listener is paid to sharp high frequencies while low end is mostly ignored as inaccurate and impossible to follow.

Another target was to make come-back from horn speaker to more conventional construction. Horn (tractrix) could be painful approach with electronic music, close miced acoustic guitars etc. along with high SPL. String section may sound a bit ugly and live applauses too clatter. Less directive small radiator may have some compression if music spectrum is not "natural" (like pink noise), but the sound stays more tolerable and relaxed no matter which record is played.

WW+WW design was selected to avoid thick and oversized vocals. Large bass radiator close to floor sounds integrated and full-bodied, but sometimes that feature goes too far and unnatural. Lifting half of the woofers above the MTM cabinet drops sound power at lower midrange and lifts sound images at the same level with high frequencies. This combines good features of large & directive bass and small speakers on stands.

I'm still using resistance enclosures for bass. They have well known limits with SPL capacity, authority and bass extension, but some immunity to front wall and corners is still tempting advantage at least in our house. The latest pair (KS-1807ML, picture above) is not made for me/us, but hopefully leaking super-cardioid will work somewhere out there - also in the future.

The first pair (KS-1807SC, picture below) has 45 deg side bevels in the MTM box, and resistance ports are (far) on the side walls. This design spreads sound horizontally and drops directivity index to 5 dB at 500...1000 Hz.
Latest pair has 70 deg side bevels, and resistance ports closer to front baffle. This maintains higher and equal DI of 7 dB at 500...1000 Hz, but has clear diffraction issue with woofer cabinets, creating dip at 1.4-1.5 kHz. Just another compromise without final breakthrough. 15 cm midrange driver is quite small to reach flat DI=7 dB, but crossing with small ribbon at 4 kHz has restrictions.
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Technical specifications

General 3-way, resistance enclosure
Dimensions 350 x 1760 x 455 mm (W x H x D)
Volume WW+WW: 70+70 liters
X/O frequencies 280 Hz and 4000 Hz
acoustically 12 dB/oct and 24 dB/oct
Drivers Peerless SLS-12" (830669)
Seas MCA15RCY
Fountek NeoCD3.0
Impedance 8 / 4 ohm (WW+WW / MTM)
Sensitivity MTM: 93.5 dB/2.83V/1m

Enclosure

Enclosure drawing (without dimensions): KS-1807ML.pdf

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ML/WP_20140829_004.jpg ML/WP_20140913_001.jpg

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Crossover

Crossover is semi-active.
WW+WW section is low-passed and equalized with Hypex PSC2.700.
ML/KS-1807ML_Hypex_Low.png

MTM section is high-passed and slightly equalized with Hypex PSC2.700.
ML/KS-1807ML_Hypex_High.png

Higher crossover at 4 kHz is passive; electrically 2nd order low-pass and 3rd order high pass, acoustically close to LR4.
Coils are air cored Intertechnik (wire 1.0 mm). Capacitors for tweeter are Mundorf M-Cap MKP, and Intertechnik Audyn-Cap MKP for midrange.
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Simulations

Woofers are simulated as four mixed radiators having 42 % monopole and 58 % dipole, in their actual locations.
MTM box is measured on stand for simulation. Proximity of woofer enclosures causes diffraction dip at 1.4 kHz in real life.
ML/KS-1807ML_Simulation.png


Measurements

Frequency response

N/A. See simulations and harmonic distortion measurement.

Step response

Measuring distance 100 cm, on-axis
ML/KS-1807ML_SR_100cm_10ms.png

Excess group delay

- room measurement at 250 cm, time window 45 ms, on-axis
ML/KS-1807ML_GDx_220cm_45ms_20-20k.png

Harmonic distortion

- SPL 100 dB / 1 m
ML/KS-1807ML_THD_100dB_1m.png

- SPL 95 dB / 1 m
ML/KS-1807ML_THD_95dB_1m.png

STI

Room measurement at 250 cm, on-axis
ML/KS-1807ML_STI_250cm_0deg_oh-th_R.png

MTI (OctTI) spectrum
ML/KS-1807ML_MTI-spectrum.png

Acoustical parameters during previous measurement:
ML/KS-1807ML_T30_oh-th_R.png ML/KS-1807ML_EDT_oh-th_R.png

ML/KS-1807ML_C50_oh-th_R.png ML/KS-1807ML_C80_oh-th_R.png


Created 03.10.2014
Updated -