I have no proof of this, but I suspect that we can perceive group delay issues at very low frequencies (less than 100 Hz). I think this is the difference in what I hear between a sealed box and a BR box. It is not just the room, but that can certainly be a part of it if the room has problems.
So I did some experiments with aperiodic today. As I have some Basotect-open cell foam available around, I just cut round inserts ~1cm thick and inserted them in the ports. I also disconnected RLC in woofer crossover, which was needed for BR. This started to sound very promising, boomy bass (as percieved with certain songs) was gone and even better, midrange got more clarity. I listened to several different songs and they all sounded better, clearer and right. Later I will make some measurements and more listening and experimenting with the foam thickness.
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There are a number of significant differences between the sealed box and vented box that need to be considered in any sort of listening evaluation.
- The sealed box is a 2nd-order system and has a shallower roll-off rate than a vented box.
- Most vented boxes, by design choice, will have a more extended low-frequency response than a closed box.
- The transient response of a vented box rings somewhat more than a sealed enclosure.
- The transient response of a vented box takes longer to die down than that of a sealed box.
🙂👍
Below is the simulated response of a 2nd-order Butterworth filter to a 1/2-cycle 50 Hz toneburst. The 1/2-cycle might be representative of the impulse provided by a kick drum, although the ringing of the drum skin is not being included here for the sake of simplicity. This time domain response is the typical behaviour of a maximally-flat B2 sealed enclosure alignment with a –3dB point at 50Hz.
And below is the simulated response of a 4th-order Butterworth filter to a 1/2-cycle 50 Hz toneburst. This is the typical behaviour of a maximally-flat B4 vented enclosure alignment with a –3dB point at 50Hz.
Clearly, the 4th-order (vented) and 2nd-order (sealed) systems produce quite different time domain responses. Note that both output signals are attenuated relative to the input signal, owing to the high-pass filter response functions both being –3dB at 50Hz. In both cases, the largest output response swing is negative going, so both systems appear to "invert" the input signal to some degree. The initial positive-going peak is almost twice as large for the 2nd-order system, which may have a bearing on how these two types of systems compare in a listening situation. Overall, the transient response of the 2nd-order (sealed) system is much more damped.
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I'm unsure of why you would refer to maximum SPL in the above comment? After all, we are generally assuming that the system is behaving relatively linearly over a range of SPLs, from low to high.
It's also not entirely clear as to why there is a reference to the BR port signal being "one cycle late". We don't hear the port signal as a separate entity. We hear the summed response of the woofer and the port at the listening position, which together produce the output waveform that presents itself at the listener's ears. At the typical very-long low-frequency wavelengths that are involved, the port and woofer can be regarded as being coincident sources of sound.
Witwald, thank you for theoretical aspect. Please remember that loudspeakers never behave linearly like simulations. In this thread and in my general view, we discuss 3-way speakes with quite large bass drivers and large boxes, not typical 10-15 liter bookshelve speakers.
BR port signal is one cycle late at max spl peak of the port signal (regardless of real spl), and then the driver membrane is almost still - practially all of the sound comes from port. BR tuning of many bookselves is 45-55Hz, floorstanders have it around 30-40Hz (B&W even lower around 25Hz)
With dsp it is easy to eq low bass response of a sealed woofer to be flat down to 30Hz (if it has enough Xmax and power) But nearfield response should be sloping, because room gives boost to it, and we listen to room response.
Bass drum signal is typically 50Hz, I've checked it with Audacity and asked friends who make and edit music. So, with many BR speakers, the kick comes only from the port. Kick has also lots of distortion, D2/D3 at 100Hz/150Hz often dominant. So, with BR fundamental is one cycle late to harmonics... how does that sound, soft/dull?
Some nearfield measurements from Stereophile, two floorstanders and two standmounts all with BR tuned woofers.
BR port signal is one cycle late at max spl peak of the port signal (regardless of real spl), and then the driver membrane is almost still - practially all of the sound comes from port. BR tuning of many bookselves is 45-55Hz, floorstanders have it around 30-40Hz (B&W even lower around 25Hz)
With dsp it is easy to eq low bass response of a sealed woofer to be flat down to 30Hz (if it has enough Xmax and power) But nearfield response should be sloping, because room gives boost to it, and we listen to room response.
Bass drum signal is typically 50Hz, I've checked it with Audacity and asked friends who make and edit music. So, with many BR speakers, the kick comes only from the port. Kick has also lots of distortion, D2/D3 at 100Hz/150Hz often dominant. So, with BR fundamental is one cycle late to harmonics... how does that sound, soft/dull?
Some nearfield measurements from Stereophile, two floorstanders and two standmounts all with BR tuned woofers.
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Well, even more nonlinearity in recordings we replay with our speakers, comes in the studio with digital mixing/effect post-processing...
https://www.soundonsound.com/techniques/mix-tips-kick-bass
Overlaid kick drum and bass guitar frequencies, from above
https://www.soundonsound.com/techniques/mix-tips-kick-bass
Overlaid kick drum and bass guitar frequencies, from above
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Many loudspeaker drivers are actually carefully designed and quite linear devices, and can be modelled as such in the simulations. Nevertheless, nonlinearities do exist, and do affect the response. In broad terms, those nonlinear behaviours start to become noticeable at higher output levels.
I'm not sure why there would need to be a distinction between large loudspeaker systems and more compact loudspeaker systems. Would it not be expected that the same operating principles and design approach would apply to both? After all, both the large and small drivers would be designed to be linear devices, in order to reduce distortion production.
👍 I now understand what you were trying to convey. The behaviour that occurs as you describe is simply the result of having a coupled dynamic system consisting of two sets of moving masses and stiffnesses.
That sort of EQ is entirely possible and, as has been noted above, DSP is an excellent way of achieving it in a controlled manner. In his 1961 journal paper, "Loudspeakers in Vented Boxes: Part 1", Thiele discussed the equalisation of vented box loudspeaker systems to obtain improved responses. Of course, to work well, the EQ relies on the loudspeaker system being quite linear in its behaviour.
Those upper frequencies that are labelled D2/D3 aren't really distortion, are they? They are more to do with the harmonics of the resonant behaviour of the drumhead, and maybe a label H2 and H3 would be more appropriate? Of course, filling the inside of the kick drum with damping material (e.g. quilt, towels, etc), will of course dampen down those harmonics, leaving the fundamental of the single pulse more or less intact. That's the basic response that the earlier simplified simulations were representing.
The question concerning soft/dull sound is a difficult one to answer, for me at least. I'm not entirely sure that the transient response of a vented system is going to be affected in the manner that is described above: "with BR fundamental is one cycle late to harmonics". Keep in mind that the group delay that is being indirectly referenced is a feature of the steady state response, which is what is left after the transient response has died down.
The softness that is being referred to may simply be due to the longer transient response of the vented box system relative to the closed box system. The vented box system has four significant peaks in the transient response, while the closed box system only has three. That spreading out of the response in the time domain may in and off itself make the vented box system sound duller, but it is also important to note that the vented box system has output swings that are somewhat lower in peak amplitude than those of the closed box system.
Although there are clear differences, there are also many similarities in the responses of the 2nd-order and 4th-order high-pass Butterworth filter responses to the 1/2-cycle 50Hz pulse. Note that the group delay at 50Hz of a vented system is 11.3 ms, which is about 2.5 times greater than that of the closed box system. It is unclear how that has affected the transient response, especially when it seems evident that the peaks in the transient response of the 4th-order filter occur earlier than do the peaks in the 2nd-order Butterworth filter's transient response. In this instance, the 4th-order Butterworth filter has less delay, is the opposite of the group delay response.
Of course, a mixing engineer might have another approach to tightening up a kick drum sound. For example, "Filter for Clarity – A high-pass filter isn’t used much for bass instruments, but it can clean up the low-end of the kick drum quite well. Don’t overdo the filtering, just below 50 Hz can make the kick drum tight while cleaning up unnecessary low-end." The article, here, suggests that additional filtering can serve to tighten up the sound of the kick drum. There doesn't appear to be any concern for the added group delay introduced by such filtering.
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By certain sound qualities I meant mostly the impression of like there is no room or at least "less" room effects in percieved sound compared to bassreflex speakers. And this impression is similar to what I hear from headphones. Overall sound from closed box was (and I know these words are not favourite here but I am trying to describe my subjective impressions....) fast, had good timing and impact, rich and full, with very clear yet not fatiquing nor shouting midrange. And the most important benefit for me, the most part of recordings sounded well, which sometimes was not the case with bassreflex speakers. For Shamal project I was able to achieve similar good sound with going aperiodic.
I listened to a lots bassreflex speaker previously and did not have problem with the sound, but it either took a lot of time to tune it properly or I was not fully ok with overall sound. I was not also much interested in closed box because it does not go that deep as bassreflex. But 32W T00 Revelator was large enough and went deep enough that it convinced me closed box is worth it and that there were benefits. The more time I spent listening 32W in closed box, and now with 22W aperiodic, the more I like it and see it is correct. It took some mental adjustment, at the first moment it can appear there is something missing in the sound, but it does not, and one realizes it is just clear, balanced and detailed.
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Front baffles were repainted and I started final assembly.
I think I have mentioned this before, but I am very impressed by the construction quality and craftsmanship of your cabinet. The baffle in particular is very impressive with the very large elliptical edge radius and the CNC-machined waveguide directly into the baffle. The overall look of your cabinet is exceptional.
I assume the small lip which protrudes into the waveguide (the frame of the MW16TX) causes no significant issue. Did you verify this by simulation before you built it, or was this determined by building the prototype? I ask because I seem to have reached the limit of my simulation capability, and I may have to build some prototypes... so I am curious about your work flow and your decision process.
j.
I assume the small lip which protrudes into the waveguide (the frame of the MW16TX) causes no significant issue. Did you verify this by simulation before you built it, or was this determined by building the prototype? I ask because I seem to have reached the limit of my simulation capability, and I may have to build some prototypes... so I am curious about your work flow and your decision process.
j.
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Hifijim, thank you....I outsource carpentry and painting, I was lucky to find reliable and enthusiastic carpenter and he is responsible for majority of cabinets for my projects. I am very glad I can realize my ideas, thank to him.
That lip protruding to WG show to be harmless. I like this esthetics better, I did not make any modelling, I just did it earlier for several projects. I think I tried it for N164 project with Monacor WG300 and XT25, and then several times with Visaton WG148R. There might be mild irregularitites caused by this but they were not severe enough I would have to rework it and make larger CtC.
That lip protruding to WG show to be harmless. I like this esthetics better, I did not make any modelling, I just did it earlier for several projects. I think I tried it for N164 project with Monacor WG300 and XT25, and then several times with Visaton WG148R. There might be mild irregularitites caused by this but they were not severe enough I would have to rework it and make larger CtC.
BEM simulation says cutting waveguides does not do anything good to them.
https://www.diyaudio.com/community/...aker-build-abec-modelling.357792/post-6492454
In Pida's case it is less drastic but it will be an extra source of diffraction.