the problem is Martin, theres not enough information avaliable really.
There are many ways to add up to 98dB, it could be a combination of the full spectrum, or a specific tonal component which would give the impression it was even louder.
I'd hazard a guess that its related to size. This will effect the frequency produced, larger bore = lower frequency, and as I say, lower frequencies are the problem ones!! They will enter the cabin and not easily escape. Higher frequencys will be absorbed by the seats and lining materials, the lower ones are much harder to get rid off. This would explain why when you put the windows down its not as bad as the low frequency waves can esape without having to go through the glass.
around 2.5-3k that is probably where the system produces its critical frequency.
a bulkhead would in theory definitely help this as the sound would be more likely to be contained in the rear of the car, with equal amounts of energy leaving the windows and probably a slighter larger percentage through the bulkhead. however, with no bulkhead, the whole car would be subject to these conditions.
The standard covers, although are acoustically lined, would probably only attenuate the mid/high frequencys, with probably 1-3dB max at the lower frequency.
of course the only way to quantify if the bulkhead would help is to test with an OMG. However the principle & theory says it will provide a positive reduction.
There are many ways to add up to 98dB, it could be a combination of the full spectrum, or a specific tonal component which would give the impression it was even louder.
I'd hazard a guess that its related to size. This will effect the frequency produced, larger bore = lower frequency, and as I say, lower frequencies are the problem ones!! They will enter the cabin and not easily escape. Higher frequencys will be absorbed by the seats and lining materials, the lower ones are much harder to get rid off. This would explain why when you put the windows down its not as bad as the low frequency waves can esape without having to go through the glass.
around 2.5-3k that is probably where the system produces its critical frequency.
a bulkhead would in theory definitely help this as the sound would be more likely to be contained in the rear of the car, with equal amounts of energy leaving the windows and probably a slighter larger percentage through the bulkhead. however, with no bulkhead, the whole car would be subject to these conditions.
The standard covers, although are acoustically lined, would probably only attenuate the mid/high frequencys, with probably 1-3dB max at the lower frequency.
of course the only way to quantify if the bulkhead would help is to test with an OMG. However the principle & theory says it will provide a positive reduction.
