I don't think,it's very useful to design a loudspeaker based on a rule of thumb like Vas/1.44. Specially not for home audio use where you have boundaries.
Optimization considering both driver and room is essential.
That quote above just tell me that who ever said it do not know how to design loudspeakers for residential buildings.
Here are the results for a sixth-order filter-assisted vented-box low-frequency alignment. The enclosure size is 110 litres, and it is tuned to 30Hz. The 2nd-order high-pass filter applies about 6dB of boost at 27Hz. This low-frequency alignment produces f3 = 27.9 Hz, f6 = 25.2 Hz, and f10 = 23.1 Hz. At a nominal 100W power input, the vent velocity is 28m/s, using two vents of 10.0cm diameter and 33.9cm in length. We have used up 3/4 of the woofer's linear excursion capability. Because a peaking low-pass filter is used, the driver is protected from excessive excursion at frequencies below about 20Hz.
View attachment 1337769
View attachment 1337769
The pioneers were all about acoustic efficiency, originally because there was very little power available at reasonable size/cost and later to keep thermal power distortion low at higher power and eventually some shifted it to Vas/1.56x when mega power became affordable.
Ok, probably the SPL/impedance ratio around Fb is optimal when Vb=Vas/1.44, because if we increase the size of the box, the SPL (around Fb) increases, but the impedance around Fb also increases, so the result is an underdamped response (around Fb), which is underdamped not only because there is a frequency response peak at Fb, but also because the electrical impedance is higher at that point. I think the latter fact is important here.
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Here are the results for a fourth-order filter-assisted 70-litre closed-box low-frequency alignment. The enclosure size is quite compact for an 18-inch woofer, and it is tuned to 60.9Hz. The 2nd-order high-pass peaking filter applies about 9.1dB of boost at 38Hz. This low-frequency alignment produces f3 = 36.2 Hz, f6 = 33.6 Hz, and f10 = 31.3 Hz. At a nominal 100W power input, we have used up all of the woofer's linear excursion capability. Because a peaking low-pass filter is used, the driver is protected from excessive cone excursion at frequencies below about 35Hz.
For a more direct comparison, here is the previously computed filter-assisted 6th-order vented-box low-frequency alignment:
For a more direct comparison, here is the previously computed filter-assisted 6th-order vented-box low-frequency alignment:
jawen...
Seems to me like all are focusing of getting as much bass as possible without honoring room gain.
What is your objective?
Thank you so much witwald, but your attached file oeds to a "ops something went rong site" so its nothing there.
regards John
Not sure what went wrong there. I've placed the same results for the filter-assisted 6th-order vented-box low-frequency alignment in Post #26.
The driver have +- 13 mm excursion = 26 mm, that graf shows only 50% of possible excursion.
And I have learned not to appreciate these watt monsters as woofers, they are so stiff in the suspension that nothing happens before several hundred watts.
And i have tried it with Crown xti 6002 at 2 x 2100 watt/4 ohm, and a Krell F.B.I at 2 x 700 watt/4 ohm class A
regards John
Everyone tries to help and I am very grateful for that, then there are almost always "two camps" of opinions & I respect that, because it exists in all industries.
I never build a speaker for "a specifically" room, because you will be so limited if you want to move the speakers to another room or residence.
And my motto is "you can´t have to much bass" ( but most often to weak bass), and to "much" bass you can do something with, but to little bass can't be done magic with. ( and of course the bass must be of sufficiently high quality)
So my objective is to build something that will do good in most rooms.
regards John
Most (living)rooms have significant low frequency room-gain, especially if the speakers are close to wall(s).
The graph is related to the cone excursion in the linear operating range, where Xmax = ±13mm, not 26mm, which is the peak-to-peak measurement. According to the specifications, these drivers have a free-air resonance frequency of fs = 32Hz, which is reasonably low for that size of woofer. They have a large moving mass of around 240 grams, and their Vas = 184.7 litres. Hence, I can see why you would have noticed that their suspension is quite stiff. They are still very sensitive, and having a large radiating area, I expect that there wouldn't be a lot of cone motion when they are generating 96dB for 2.83V. Placed in a standard QB3 vented-box low-frequency alignment, they have a −3dB point at a relatively high frequency of 40.6Hz. Enough to do well when reproducing the lowest note on a bass guitar, but not low enough to do justice to the opening track on Dark Side Of The Moon.
Ciao,
That's because in a standard B4 box (100L tuned at 32Hz) you need "only" 1849W to reach Xmax
This is 100L @32Hz
And this is with 6db EQ and LR4 at 120Hz
And you need 20W to reach Xmax, but consider that the excursion down to 30Hz is 2 mm.
And that's the spl max with the EQ
Ciao
S.
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I think member Witwald has done an excellent job of explaining the massive potential of large efficient drivers where surface area offsets excursion for our purposes in average size home spaces.
It should be understood though that of the goal here is maximum sound quality AND reasonable bass extension, DSP will be essential for a smooth in room response. In other words, the simulations will have little resemblance of reality once the boxes are playing in your space natively.……..with this kind of investment in drivers and floor space, you will need to get out your microphone and laptop and begin an in room tuning. Essentially below 100hz, the room itself is a macro enclosure and part of the performance.
4 of those beasts each in 100 liters will sound simply incredible once a 2x4 DSP unit is employed properly……..I suspect flat response with room gain somewhere in the 20hz range.
Yes i know that, but that "rule" is more for "normal" livingrooms up to 25-30 m2 ( if you have two 10 inch woofer or tree 8 in each)
When your room is bigger (maby with high ceeling), that's a completely different story. ( belive me I have tried and blow both woofers and midramges)
Okey I see, think VAS is 211,4 liters.
Feels like i´ve newer get that cone to move more then a few mm...Yes high SPL then, but want punsh and experiencing 30 -ish hz tones also.
Ciao S
Thanks!
How should I interpret your graphs?
and what is your feeling would be good "enough"?
Regards John
Today they are in about 125 liters, and i have reinforced the PA-box with more "baffle" and also side-support and rockwool/wool.
Also made 4 new grills.
And perhaps reduced the port too much in my attempts.
Regards John
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What mayhem13 said, you should hit 20Hz with room gain and a minimal eq. and - at spl max - I have the suspect your walls be shaking. I would seriously consider a room treatment. With your current box you have this (Fb is about 48Hz / F3 is 47Hz)
Just leave them alone then and get yourself a 2x4 mini dsp with DIRAC or get a measurement microphone and download REW if you don't already have it......not sure there's any value in building new boxes to say 25 liters of space.
At the decibel levels you're likely at, i strongly doubt there's any audible issues with port noise........i'm sure it's all swamped out by the 18 inches of glory.
God i wish i could do that in my family room......i have OB 18's in my studio control room and that's all i'm permitted. LOL
I feel you! I do not have place for one of them in my living room: actually it's so tiny that I could have problem with a floorstander with a 10" woofer.