32 concrete sealed Bass modules.
For the rear wall, behind the 6 x 5 meter (approximately 19.7 x 16.4 feet) stage, 400 kg (about 880 pounds) special concrete blocks were cast and set into a 6 x 3 meter (19.7 x 9.8 feet) wall, using 13 tons of heavy concrete and a further 35 tons for the foundation.
Each concrete block serves as loudspeaker enclosure with pressure-resistant rear chamber which implements the optimized impulse response of a “closed-box” design and maximizes the radiation resistance of the woofers through the acoustically hard surface.
For the rear wall, behind the 6 x 5 meter (approximately 19.7 x 16.4 feet) stage, 400 kg (about 880 pounds) special concrete blocks were cast and set into a 6 x 3 meter (19.7 x 9.8 feet) wall, using 13 tons of heavy concrete and a further 35 tons for the foundation.
Each concrete block serves as loudspeaker enclosure with pressure-resistant rear chamber which implements the optimized impulse response of a “closed-box” design and maximizes the radiation resistance of the woofers through the acoustically hard surface.
A picture of the front of the room as it used to be with Altec 604-8K as LCR main speakers and AE's 4xPB18+ as subs (Same as TD18 H+ but with dust cap instead of phase plug.) The Altecs are now replaced with AE's TD12M + Beyma TPL 150 H. The superchunks have been rebuilt into "doghouses for the new smaller boxes giving a kind of flush mount with 86 cm baffle width.
Boxes are fixed to the concrete front wall, cannot be moved. The 4 8 ohm sub drivers are connected in parallell and then in series giving 8 ohm for 1 channel to the amp. Crossover in AV pre amp was set at 80 Hz.
Measurement 1: REW sweep from 5-200 Hz, the voltage out from the power amp during the sweep varies a bit but goes up to a max of 1,70 V, so less than 1 W total in output. Mic position 1 m from concrete wall centred at room width and height. 1,3 m diagonally to each sub driver.
Measurement 2: At LP 372 cm from front wall at height 90 cm, about 358 cm diagonal to sub drivers. An expected 40 Hz peak from 2nd length mode.
Measurement 3: At physical room centre 393 cm from front wall at 90 cm height, 377 to 381 cm diagonal to sub drivers. Theoretically this spot should show the lowest SPL for the lowest room mode at around 21,9 Hz versus the room length of 7,86 m. More or less only the direct sound from the subs, no gain or dip for about 21,8 Hz. 2 nd length mode a prominent peak as expected.
Measurement 4: Slightly in front of physical mid length = 383 cm, +10 / 4". Measurement for 20 Hz improves a bit. Why = ? . Could be because of resisitive and limp mass absorbers functiuons a bit even that low or room leakages.
Picture 5: 3 measurements with front subs in phase with subs at backwall. (Subs at backwall = 4 x of AE's SPB 15), and out of phase and only front subs. When I later connect an active filter, the backwall subs will be connected out of phase and with a delay versus the front subs. Room modes up to 120 Hz should the be evened out. Theoretically ...
All in all, AE's PB 18+ or TD 18 H+ has no problems to play very low frequncies at high SPL in "the right room". It seems I made the right choice with a concrete room to go for a low Qtc of 0,36 and high F3 at around 112 Hz for the subs as room gain gives a huge peak 1 m away from a wall. Close to room centre SPL around 20 Hz is substantial even if if is supposed to be in a frequency dip. The SPL picks up again under about 20 Hz down to 10 Hz. I suspect the pre amp and power amp starts to fall off below 10 Hz otherwise the SPL should be maintained even lower in frequency. As mains the 18" can be played above 200 Hz, it plays quite well up to about 1200 Hz, then it falls off sharply.
Boxes are fixed to the concrete front wall, cannot be moved. The 4 8 ohm sub drivers are connected in parallell and then in series giving 8 ohm for 1 channel to the amp. Crossover in AV pre amp was set at 80 Hz.
Measurement 1: REW sweep from 5-200 Hz, the voltage out from the power amp during the sweep varies a bit but goes up to a max of 1,70 V, so less than 1 W total in output. Mic position 1 m from concrete wall centred at room width and height. 1,3 m diagonally to each sub driver.
Measurement 2: At LP 372 cm from front wall at height 90 cm, about 358 cm diagonal to sub drivers. An expected 40 Hz peak from 2nd length mode.
Measurement 3: At physical room centre 393 cm from front wall at 90 cm height, 377 to 381 cm diagonal to sub drivers. Theoretically this spot should show the lowest SPL for the lowest room mode at around 21,9 Hz versus the room length of 7,86 m. More or less only the direct sound from the subs, no gain or dip for about 21,8 Hz. 2 nd length mode a prominent peak as expected.
Measurement 4: Slightly in front of physical mid length = 383 cm, +10 / 4". Measurement for 20 Hz improves a bit. Why = ? . Could be because of resisitive and limp mass absorbers functiuons a bit even that low or room leakages.
Picture 5: 3 measurements with front subs in phase with subs at backwall. (Subs at backwall = 4 x of AE's SPB 15), and out of phase and only front subs. When I later connect an active filter, the backwall subs will be connected out of phase and with a delay versus the front subs. Room modes up to 120 Hz should the be evened out. Theoretically ...
All in all, AE's PB 18+ or TD 18 H+ has no problems to play very low frequncies at high SPL in "the right room". It seems I made the right choice with a concrete room to go for a low Qtc of 0,36 and high F3 at around 112 Hz for the subs as room gain gives a huge peak 1 m away from a wall. Close to room centre SPL around 20 Hz is substantial even if if is supposed to be in a frequency dip. The SPL picks up again under about 20 Hz down to 10 Hz. I suspect the pre amp and power amp starts to fall off below 10 Hz otherwise the SPL should be maintained even lower in frequency. As mains the 18" can be played above 200 Hz, it plays quite well up to about 1200 Hz, then it falls off sharply.
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87 Front of room with old Altecs 604-8K now replaced AE TD12M and Beyma TPL150H.jpg -
Meas 5 front and back subs in and or out of phase.jpg -
Meas 4 - 383 cm from front wall = 359 from TV.jpg -
Meas 3 - Physical room center, 393 cm from front wall centered versus width, H= 90 cm, 377 to 3.jpg -
Meas 2 - LP at 372 cm from front wall, 358 cm diagonal to sub.jpg -
Meas 1 - 1 m to frontwall 1,3 m to subs diagonally.jpg
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And a spectrogram from measurement 4. I see a decay with fairly even and low figures in ms for typical room modes as more important than a straight line frequency response curve. The first 5 length modes are clearly visible, it looks looong though for 20 Hz.
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The 32 Lambda Labs OEM CX 15″ ultra-long excursion drivers, with ± 25mm linear excursion capability set in housings made from special concrete. Each is driven by 800 Watt amplifying modules, with the maximum desired SPL reached at an excursion of only ±3mm.
The sound pressure level is beyond 140dB and absolutely equal at any point in the room (not that anyone would need such sound pressure levels). And you don’t have the possibility to feel 7Hz throughout your whole body every day.
The sound pressure level is beyond 140dB and absolutely equal at any point in the room (not that anyone would need such sound pressure levels). And you don’t have the possibility to feel 7Hz throughout your whole body every day.
Yes, variouos traps have been installed. Limp membranes and helmholtzes to save on room volume and superchunks at the front with limp membranes behind, There are also some larger BAD diffsorbers in the room + resistive absorbers at 1st reflection points. The measurements show one should not go only on simulation software and the pretty response curves from them and hope for the best. The curves don't have much in common ... In a lossy room it can be impossible or at least very expensive to get really low bass. In a small well sealed concrete room it can be the opposite of it, too much and boomy bass, very hard to fix.
Nope, you take a low qts driver (needs a small box), tune to the fs (f9 in that case).
Now is the tricky part.
You use a high pass filter with a q of 2, that way it adds 6db @ pole (27hz, at speaker fs) and rolls under it like a subsonic filter.
So, now you have bass from a driver whose qts in too low, in a small box, but now you need at extra 6db of power.
Could anyone, please, remind me what was so wrong with the JBL 4367(even the M2) as the 4367 sounds so goooood still? Yes, a bit shall I say thick in the lower mids but so warm and clean at the same time in the midrange and up? Is it all because of the D2340K?
Guys, please reach a conclusion, find the right horn/waveguide or whatever you call it and let's make that d@mn 2 way that camplo and EVERYBODY needs
Forane12, we've concluded on drivers
Mains
350hz JMLC
JBL 2451, Aquaplas diaphragm >~500hz
Acoustic Elegance 15m 100hz-500hz
Subs
Acoustic Elegacen 18h+ 20hz-100hz
I have to remind myself that the drivers in this project have been groomed well...sometimes I consider abandoning the current tops and springing for the Celestion Axi2050 as I have these comments to ponder
"While the driver can be crossed low, I found the driver lacking in resolution and clarity in the higher frequencies. The Radian 951BePB sounder clearly better. Distortion above a certain frequency is much lower with the Radian driver."
&
"I really like the sound and it is very good having no crossover above 420Hz where I cross them to the 18" below.
Not sure what having a flatter response above 15k would bring to be honest, everything sounds so natural and real as it is. Piano, acoustic guitar and cymbals among the best I've heard. The magic is in the mid range��!"
"While the driver can be crossed low, I found the driver lacking in resolution and clarity in the higher frequencies. The Radian 951BePB sounder clearly better. Distortion above a certain frequency is much lower with the Radian driver."
&
"I really like the sound and it is very good having no crossover above 420Hz where I cross them to the 18" below.
Not sure what having a flatter response above 15k would bring to be honest, everything sounds so natural and real as it is. Piano, acoustic guitar and cymbals among the best I've heard. The magic is in the mid range��!"
The first comment on the Axi2050 vs 951BePB is by Björn Omholt, I suppose?
If you want to cross <500Hz and play at high SPL, the Axi2050 would definitely beat the 951BePB.
I am sure at 300Hz and >115dB, the Beryllium diaphragm won't last long.
Björn Kolbrek stated, he wouldn't hesitate to use the Axi2050 at, or even below 200Hz behind a proper horn at home.
The Axi2050 is (only) about $500 each, if you could order these through an OEM.
Some Romanian guys use the Axi2050 with these EV HP9040 horns:
If you want to cross <500Hz and play at high SPL, the Axi2050 would definitely beat the 951BePB.
I am sure at 300Hz and >115dB, the Beryllium diaphragm won't last long.
Björn Kolbrek stated, he wouldn't hesitate to use the Axi2050 at, or even below 200Hz behind a proper horn at home.
The Axi2050 is (only) about $500 each, if you could order these through an OEM.
Some Romanian guys use the Axi2050 with these EV HP9040 horns:
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The cone resembles the cones of some B&C drivers, but it's probably a clone.
