Hi!
Maybe this is a simple question but I didn't find exact answers for it.
So what if the net volume of a vented box is greater than the Vas value of the driver? I know that such a box is generally recommended if Qts is over 0.4, but what if we have, say, 0.3 Qts? In the case of such low Qts, in most cases a smaller box than Vas is recommended. But why? Of course we can see the result on a simulation, which will show an early drop towards the bass and an emphasis at the vent tuning frequency.
So that's all (pretty much)? If we correct the frequency response (say with DSP), do we get a sound as if we had a box that gives such a frequency response in the first place? Of course, taking into account the tuning frequency. If so, where is the limits?
I ask because a larger box has certain advantages (over smaller ones) that could be used this way.
Add.:
I have read several times on this forum that the loudspeaker 'pioneers' established an (in their opinion) optimal Vb/Vas ratio for bass-reflex boxes, and this is Vb = Vas/1.44 if the damping of the driver is adequate (Qts at or below 0.4 if I remember correctly). What is it about this ratio that made the pioneers choose it?
What if we use Vas × 1.44 (and correct the frequency response with DSP) instead?
Maybe this is a simple question but I didn't find exact answers for it.
So what if the net volume of a vented box is greater than the Vas value of the driver? I know that such a box is generally recommended if Qts is over 0.4, but what if we have, say, 0.3 Qts? In the case of such low Qts, in most cases a smaller box than Vas is recommended. But why? Of course we can see the result on a simulation, which will show an early drop towards the bass and an emphasis at the vent tuning frequency.
So that's all (pretty much)? If we correct the frequency response (say with DSP), do we get a sound as if we had a box that gives such a frequency response in the first place? Of course, taking into account the tuning frequency. If so, where is the limits?
I ask because a larger box has certain advantages (over smaller ones) that could be used this way.
Add.:
I have read several times on this forum that the loudspeaker 'pioneers' established an (in their opinion) optimal Vb/Vas ratio for bass-reflex boxes, and this is Vb = Vas/1.44 if the damping of the driver is adequate (Qts at or below 0.4 if I remember correctly). What is it about this ratio that made the pioneers choose it?
What if we use Vas × 1.44 (and correct the frequency response with DSP) instead?
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Hi, I do not remember any of the Qts and Vas stuff and just look at simulator results. I recently learned that tuning low you'll get the upper impedance peak where there is most demand, say around 40-50 Hz or so for PA, or what ever is your application. Smaller box one could tune it so the impedance minima is there instead. You could and should use EQ to shape response of the big low tuned box for same response around 40-50Hz.
Difference between the two is that on impedance peak power delivery is very small and excursion high, which is good for thermal management. Trade-off is you need xmax from the driver and high voltage swing amplifier both available today. If impedance minima was there instead, as with smaller box, it would draw more current and have much less excursion, which is bad for thermal management, but still extended response compared to a closed box.
I guess only difference between now and back then is that they didn't have high voltage amps or high xmax drivers available, nor too much recordings that had very lows so it likely made sense to tune systems higher.
At least VituixCAD enclosure tool shows this stuff so it's easy to experiment with.
Difference between the two is that on impedance peak power delivery is very small and excursion high, which is good for thermal management. Trade-off is you need xmax from the driver and high voltage swing amplifier both available today. If impedance minima was there instead, as with smaller box, it would draw more current and have much less excursion, which is bad for thermal management, but still extended response compared to a closed box.
I guess only difference between now and back then is that they didn't have high voltage amps or high xmax drivers available, nor too much recordings that had very lows so it likely made sense to tune systems higher.
At least VituixCAD enclosure tool shows this stuff so it's easy to experiment with.
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The best advice I can give you is to stay away from these magic number formulas "the Elder" used and use a good simulator. Win ISD is free and will give you near perfect results for closed and vented cabinets. Do some identical simulations and then change parameter, so you can directly compare the results.
You will get a rather high group delay at the tuning frequency, but i guess that's not really audible for very low frequency.
The group delay thing is usualy less important if you go lower than 30 Hz. It is not much music there and low frequency HT effects like an explosion don't care for a few milliseconds.
Anyway, WinISD will show you all the data you may need to decide on a woofer build.
Anyway, WinISD will show you all the data you may need to decide on a woofer build.
Not just low freq GD but GD in general, as was experimented more times with headphones, simulating e.g. a 24dB/octave (or steeper) crossover. So the added GD by the simulated xo didn't caused audible change in the perceived sound. But that's a slight off-topic here.
Yes, it shows, but the two mentioned versions will sound the same if they are EQ-ed to the same frequency response? Assuming there is no driver and amplifier overload or other high non-linarity of course.
If the two versions are EQ'd to have the same frequency response, then theory predicts they will have the same phase and group delay characteristics. I have found that measured reality agrees with this theory, close enough for any kind of design purposes.
If we believe that the sound of a woofer system is dominated by FR, with GD playing a smaller (but still important) role, then yes, the two versions will sound the same.
But I think there may be other factors which can affect sound quality. For the same SPL and frequency, the two versions will have different woofer excursions, and that will create different levels of harmonic and modulation distortion. Also, the excursion-limited max SPL will be different between the two versions. The version with the larger cabinet will have a greater cabinet surface area, so it will have a different (perhaps greater) contribution to the acoustic radiation. These are the potential differences which came to mind, but there are probably additional potential differences.
j.
Hi, since I haven't tried I'll speculate it depends on how much power you feed and depending on the music content. Lets assume bass of your music is around 40Hz and above. If you tune the system to ~40Hz the impedance minima that reduces cone excursion reduces related distortion but now there is possible sounds from the port and tons of current and heat and related issues, which limits the performance. Most energy of your music is here, so it would make sense to get same output but with reduced current for bit more headroom assuming there is enough xmax. Tune the system lower where there is less content and the cone now does the work for the most part around 40Hz with less current due to the impedance peak and also cooling works better, overhung long excursion voice coil needs the excursion to stay cool. I bet this is more stable system of the two, if you must run the system full tilt. I guess the modern pa sub drivers are made specifically this in mind so that tons of power can be fed in to get more output reliably from less boxes.
For home stereo I suppose anything works since there is usually hardly any power fed into the system, especially if the system is big enough, for example a multisub system in addition to some big mains.
If it is multiway speaker woofer and for home stereo use case, perhaps it would be better to limit the excursion for cleaner midrange so perhaps tune higher. The modern super power pa woofers are unnecessary expense in such application, however, there is some argument for home as well if you want response all the way down to 20Hz it doesn't make sense to tune for 40Hz since there must be highpass filter regardless of tuning basically limiting the bandwidth to the tuning. With such modern driver you can drop tuning and highpass filter to teens and also port noise likely drops some as there aren't that much content down there on most music, and just boost the passband you want with EQ. Buy big amp, such drivers seem to handle thousands of watts since its mostly voltage now, due to high impedance. Closed box might do fine greatly reducing issues except there is no vent for heat.
Above is just speculating to list some use cases where you could tune very low and see benefits and trade-offs. I have no real experience comparing these yet but it's kind of obvious that the main difference would be how loud you can play before sound gets bad.
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TTBOMK EBS (aka X-BASS IIRC) actually originated to use the Fb peak to protect the speaker from the pronounced 'rumble' of early turntables, then much later apparently reincarnated as a viable option to vent higher QT digital systems.
So yeah, and EQ boost + high Qt doesn't make for my criteria of 'is it live or is it Memorex?' WRT to the < ~500 Hz BW.
Hi GM! I usually welcome your comments but often don't understand those. Can you elaborate please?
Most of what you're talking about here is for a B4 alignment, going from memory. It is not just a guideline,
but Vas/1.44 assumes very high box Q, with the more typical Ql=7, again from memory Vb=Vas. You need
a bigger box to make up for the lower box Q. Butterworth alignments are maximally flat which means that
they provide the highest bass amplitude without any peaking in the response. Driver Qts after taking any
passive crossover RDC into consideration should be around .4, don't remember the exact number.
The B4 and B6 (+6dB of boost at Fb) alignments are easy to remember because in both cases F3=Fb=Fs,
and for B4, Ql=7, Vb=Vas and for B6,Ql=7,Vb=.5Vas. What may we learn from this? Cut the box size in
half and we loose 6 dB at Fb, making the speaker -9dB there, provide +6dB of EQ boost and we're back to
-3dB or F3=Fb=Fs. A larger box provides more output at and around Fb.
A very important thing to consider is that the system will take a lot of power and produce high SPL at the
Fb tuning frequency because driver cone displacement is minimized there. It peaks at about 1.4 x Fb and
this must be taken into consideration for MaxSPL.
I often choose Fb for where I want max output, 20 Hz for very large systems, 28 for large, and 30 to 40 for
smaller systems that don't have enough volume displacement to support a lower tuning. 20 is to support
any music or sound effects, 28 for a grand piano, and 40 for pop music with electric bass.
You can then size the box and choose the driver to get the desired response.
Yes, use a simulator to figure out what a driver can do, but the above will help you optimize the design and
get you there faster.
There was a technique called alignment jamming and an AES paper on the subject. Not sure why it is not
showing up in a search at the AES library. I think that it came after this paper, not sure of the author:
https://www.xlrtechs.com/dbkeele.com/PDF/Keele (1973-05 AES Published)Sensitivity of Alignments.pdf
I have the paper in my files but I'm not home at this time.
Bigger box = more output at Fb.
Thanks PB2!
Yeah, I figured it out that the Vas/1.44 thing is the B4 alignment, it requires Qts 0.383 but GM said that earlier somewhere it works good with a range of Qts from 0.2 to 0.4. But a different Qts than 0.383 results in other alignment than B4 because the response will be different.
I try to figure it out that there is 'magic souce' (that box simulators don't show) or not about ported boxes.
Moreover I try to figure it out that the frequency response that is matters in the first place or there are other things which are important.
So different box alignments do sound the same or not if they are EQ-ed to the same frequency response?
I'm talking about low-levels here, where driver non-linearities are not yet significant, amplifier power and driver power handling are far from their limits, the boxes are inert enough, the ports are optimized etc.
Yeah, I figured it out that the Vas/1.44 thing is the B4 alignment, it requires Qts 0.383 but GM said that earlier somewhere it works good with a range of Qts from 0.2 to 0.4. But a different Qts than 0.383 results in other alignment than B4 because the response will be different.
I try to figure it out that there is 'magic souce' (that box simulators don't show) or not about ported boxes.
Moreover I try to figure it out that the frequency response that is matters in the first place or there are other things which are important.
So different box alignments do sound the same or not if they are EQ-ed to the same frequency response?
I'm talking about low-levels here, where driver non-linearities are not yet significant, amplifier power and driver power handling are far from their limits, the boxes are inert enough, the ports are optimized etc.
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Greets! It was a 'bare bones' history lesson of very low tuned speaker alignments that someone maybe decided to convert to T/S or unknowingly (re) invented it in concept. The rest was an IME opinion that it's not my idea of a high SQ speaker alignment and since the vast majority of my designs/builds use(d) cheap high QT drivers (up to nearly 3.0! once coupled to a PP tube amp), yet my horn rig was near enough SOTA at the time (~ '65 - '86), so even the most 'tin eared' (a lot of them worked in excessively noisy manufacturing, assembly plants) had any problem deciding that they left a lot to be desired, though suited their needs for the most part (didn't play loud enough except in multiples).