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My ht room is approx. 20 x 20 feet, open at one end to a dinging room and kitchen. The floor in this room is timber floorboards that are off the ground by about 2.5 to 3 feet (ie. the floorbaords are not on a concrete slab).


Would I improve the performance of my HSU VTF-2 sub by placing a concrete slab or large ceramic tile underneath it? I have the sub positioned in the front right-hand corner of the room and it would be very difficult (for a few reasons) to move it to another position.


It seems to me that I lose some of the subs performance through the floorboards. The bass is there if I run my 3802 at around 00db but at lower spl's it seems to disappear. Should I run my mains as small and redirect all base to the sub? I currently run my front towers as large plus sub in the set-up menu of the 3802 (Oh no! I swore I would never run a small/large debate in this forum....).
 

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Those room dimensions suggest that you could have some serious room modes which will create LARGE peaks and dips at certain bass frequencies. Try placing your sub at 1/4 or 1/2 across the front wall. This may help things quite a bit. Placing your subwoofer on a large concrete slab should the transmission of the bass through the floor. This will likely decrease the floor vibration while tightening up the sound. If your processor allows for different subwoofer crossover frequencies you may wish to try crossing over your subwoofer at 40Hz or 60Hz.
 

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It seems to me that there are two other possibilities you didn't mention. One is that lower frequencies sound quieter than higher frequencies as you decrease the overall volume. This is why many systems include "loudness compensation".


Also, you don't mention actually measuring the low frequency sound pressure levels at different volume settings. Have you calibrated your system? One thing to beware of when calibrating low frequency SPL is that pink noise readings can be thrown off by room resonances (standing waves). Square rooms are particularly bad, since the corresponding low frequency (and its harmonics) is particularly enhanced. As a result you may have calibrated for the SPL of that particular peak, so that the other low frequencies are much quieter than they should be.


I hope these considerations help a little.
 

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having a "flexible" floor might not be a bad thing; the bass can couple to it with the floor serving as a giant speaker panel. on the other hand, this could provide too much bass or suck up too much energy; whichever, the floor becomes part of the subwoofer. I would guess the effect is similar to positioning the sub in a corner where three walls can couple, sometimes a useful effect, sometimes not.


as far as room dimensions, the standing wave resonances from both H and W will superimpose if the room dimensions are equal, giving you double the problem; which is why the general rule is to not duplicate dimensions; not that you always have the choice. Also the standing waves have peaks and nulls; if you put the sub at a peak (your corner loction), the bass will be augmented, at a null de-intensified; the same is true for the listening position. sound waves are pressure waves with the highest pressures (and therefore volumes) at the room boundaries as well as intermediate peaks. (the example of standing waves is usually illustrated with vibrating strings, where just the opposite is true: the boundaries are the lowest amplitude..the strings are tied down)
 
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