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In the Forum: Audio Discussions
In the Thread: Constructing LF modules to the limits
Post Subject: Constructing LF modules to the limitsPosted by haralanov on: 4/28/2009
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It is well known fact that all loudspeaker enclosures contribute to the sound of a given acoustic system to some degree. Unfortunately the resonances of the baffles have constant monochrome character and if they are too prominent there is always some kind of sound signature coming from the vibrating walls. It’s the same as someone puts sugar on everything he eats. In the case of loudspeakers it’s even worse because the resonances need some time to settle down below audible level, so the reproduced notes become time distorted
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There are some ways which tries to overcome the resonances but the result is not always positive. If the walls are made stronger using very hard material combined with extensive bracing, the resonance frequency gets higher but the Q of that resonance also gets higher and it’s character is very prominent if someone sticks his ear to the enclosure. Ping-ping-ping says the box 
The key is damping the vibrations with huge amount of sand, preferably quartz sand. The wider the contact area with the walls is, the better damping. The other side of the problem are the air-born resonances inside the enclosure. There are only two ways to eliminate them completely – with proper geometry of the box and using “soft walls”, because the standard damping materials are not efficient at low frequencies.
I used thin velveteen layer to hold the sand at proper position without leakage inside the enclosure. The result is amazing – first effectively damping the vibrations of the baffles and second – absorbing all the energy from the back wave inside the box. As we Bulgarians say: “One shot – two rabbits”
This way the only sound I get comes from the cone of my modified ScanSpeak 25W/8565-00s taking the box 99% out of sonic equation. I definitely know why Romy likes so much this driver even I do not have proper amplification at the moment. It is capable to throw absolutely wonderful tone, it makes the Sound full of body and weight, very harmonically rich and the same time very transparent. I listened to the box before the sand filling and the sound was different – the bass was stronger, but not so defined and with less finesse (I do not mean blurred), definitely there was some kind of sonic fog. Now the bass notes are much more meaningful, allowing me to consume musical content more easily. Almost forgot – one of the secrets for proper low bass is having the front baffle as wide as one could afford 
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