Acoustics: a science that deals with the production, control, transmission, reception, and effects of sound
Aerodynamics: a branch of dynamics that deals with the motion of air and other gaseous fluids and with the forces acting on bodies in motion relative to such fluids
That’s Merriam-Webster for you. One could even consider acoustics as a branch of aerodynamics. But it certainly is acoustics inside, in and outside a loudspeaker enclosure.
As to the Beeb-papers, true, but this thread is about the acoustics inside a box. There’s been some progress since then. Be it that stuffing an enclosure completely with the right absorbing material still is very effective.
Okey so after stuffing (lining bitumen, lining felt 5 mm + sheep wool) I got as an indoor measurement at 1 m distance (gated at 50 ms) and 1/48 octave smoothing:
So far this sounds good enough for DIRAC to work with.
In case img does not work:
So far this sounds good enough for DIRAC to work with.
In case img does not work:
I would suggest that if the cabinet wall were ideally solid and fixed, neither the felt nor the bitumen will have any significant effect.
Where it could have an effect is where the cabinet wall moves and damping would occur. It is now acting as a panel absorber, responding to pressure rather than velocity.
Allowing the panel to be flexible so this can happen has the downside of radiating outside the cabinet, better to absorb with conventional damping material inside the box.. but expecting that the wall will vibrate a little regardless and trying to damp it is probably the best course of action.
This is the in-room response of the system. You are definitely measuring your room and not your speaker.
Now make close-range measurements of your woofer and of your reflex port if open again. Close range = about 1cm. Extract the burst decay plot of the measurement of the woofer and make the simple response plot of the port. Use an amplitude window of about 40dB. If any troublesome resonances in the air cavity occur, they will show up in the woofer measurement.
This is not necessarily the case. Any cabinet wall no matter how it is constructed/damped will radiate sound, usually with an extremely erratic frequency response having many high-Q peaks (especially when using thicker material) often audible over the cone's output in the the critical midrange. During development of the LS3/5A monitor, tests showed that there was higher cabinet wall radiation when using 18mm plywood compared with the 9mm thick material finally chosen. Panel output was as much as 10dB higher using the thicker material, and even the incorrect wood used used for the corner fillets was responsible for a 10dB increase in enclosure output elsewhere in the spectrum. Some realities of acoustics are extremely subtle but dramatic in their effect, however they often remain counter-intuitive.
Tomorrow I got time to measure again.
Acoustically or subjectively the bass and drums got a lot tighter, but the room is still not optimal for audio, but I may employ DIRAC only up to 200 Hz or so now.
Pictures will follow tomorrow
Acoustically or subjectively the bass and drums got a lot tighter, but the room is still not optimal for audio, but I may employ DIRAC only up to 200 Hz or so now.
Pictures will follow tomorrow
Allright, did the measurements.
1rst driver
2nd driver
Any thoughts?
1rst driver
An externally hosted image should be here but it was not working when we last tested it.
2nd driver
An externally hosted image should be here but it was not working when we last tested it.
Any thoughts?
If these are nearfield measurements, it looks like both woofers are pretty flat until about 300 hz. Does that meet your needs? If you are using REW, you can also get a Harmonic Distortion plot, which I believe compares the signal fed to the speaker to the signal heard by the microphone, and would show you more of the impact of stuffing in reducing the amount of distortion produced by the entire assembly.
Well this is with crossover in place (digital 8th order LR) at 350 Hz, so it does meet my needs 🙂.
Did you acquire the impulse response? If so, you can extract the CSD or BD (preferred) plot. Be sure the time window is adequate (as in 'big'). The response plot seems rather ok to me, but there are irregularities from 50 to 100Hz. Don't know what caused them.
I was referring to the distortion plot as a way to compare two scenarios: stuffed vs unstuffed, or damped vs undamped. If the cabinet resonates audibly, The resonance would not be correlated to the audio signal fed to the speaker, and the measuring software should register any such difference as distortion. The difference in distortion between two otherwise equal signals, could help us select a cabinet design with less unwanted resonance.
The reason for comparing two distortion plots is that we can't be sure the cabinet is the only cause of the distortion until we compare the distortion readings from two cabinet scenarios with all things being equal except for one variable, such as stuffing or damping strategy.
Six - Mpls.