Yes, nice to build that kind of woofer in concrete... even as it is not very realistic, as only extreme high load industrial floors may be able to carry such a weight. Like in an air port hangar. The cost are far less extreme than one would think. Probably less expensive than Baltic Birch at current wood prices.
The main point I tried to mention is to absorb the used bass at the rear of the room to keep it clean for new bass 🙂 like a good ventilation does with the air.
The main point I tried to mention is to absorb the used bass at the rear of the room to keep it clean for new bass 🙂 like a good ventilation does with the air.
If you start building subs with multiple 18" drivers for HT, you can model hardly any response with the help of the room, a lot of amp power and a DSP.
At some point the woofer (and it's price) get secondary, if you exclude definitely ill constructed chassis.
There are quite some low cost Chinese 18" around, that deliver a cast basket, large enough magnet and usable over all parameter. These are build into all kinds of commercial woofer constructions. If you are in Europe, these start around €170 inc. VAT like this one:
https://www.thomann.de/gb/the_box_speaker_185008a.htm
Made for PA they should never reach their limits in a HT...
You can take maybe 2 , low reaching expensive specialists or 4 cheap universal PA chassis, finally the room dictates what you get. If you go that low in frequency, the free air response gets meaningless.
At some point the woofer (and it's price) get secondary, if you exclude definitely ill constructed chassis.
There are quite some low cost Chinese 18" around, that deliver a cast basket, large enough magnet and usable over all parameter. These are build into all kinds of commercial woofer constructions. If you are in Europe, these start around €170 inc. VAT like this one:
https://www.thomann.de/gb/the_box_speaker_185008a.htm
Made for PA they should never reach their limits in a HT...
You can take maybe 2 , low reaching expensive specialists or 4 cheap universal PA chassis, finally the room dictates what you get. If you go that low in frequency, the free air response gets meaningless.
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At only 5.4mm Xmax, pretty easy to reach "The Box Speaker18-500/8A" excursion limit at very low frequencies, plenty of relatively low cost 12" car audio subwoofers that are available world wide with more clean displacement capability that could be put in smaller boxes.
I agree 5.5 is small but a 12 is just too small an area to couple and move enough air. It’s less than 1/2 the area of an 18
You can push any small driver so far in it's construction, that it matches the air moved by an entry class 18" driver. The resulting sound must be judged by the listener. My experience is, the larger the chassis, the more relaxed the bass sounds, even if the smaller speaker may match the response. You may know that the larger cones give higher efficiency?
If I remember right, the starting point was using 4x 18" drivers. So 4x 12" in small boxes are out.
If you put 4 of these low Xmax 18" into, even a larger, HT, the in room frequency response should be free to choose, using a DSP.
There is also a point in closed volumes ( =room's) where air pressure get's more important than sound waves.
It makes no sense to take 4000 Watt high excursion PA woofer for this task, as you can use only a fraction of the possible cone excursion anyway. 4x 18" chassis moving 5mm in and out will do what ever you may want. You will need quite some serious amp power, even for this "pretty easy to reach" Xmax.
If there is a new discipline "Home Theater dB Drag Race" I don't know about yet, that may change in the future.
I talk about a HT that is used by real humans that want to leave it as healthy as they entered it. Usually 125dB are the limit you can endure for a very short time at low frequency with minor injuries to your hearing. In reality at these level you may already be unable to tell what is shaking, you or the room.
If I remember right, the starting point was using 4x 18" drivers. So 4x 12" in small boxes are out.
If you put 4 of these low Xmax 18" into, even a larger, HT, the in room frequency response should be free to choose, using a DSP.
There is also a point in closed volumes ( =room's) where air pressure get's more important than sound waves.
It makes no sense to take 4000 Watt high excursion PA woofer for this task, as you can use only a fraction of the possible cone excursion anyway. 4x 18" chassis moving 5mm in and out will do what ever you may want. You will need quite some serious amp power, even for this "pretty easy to reach" Xmax.
If there is a new discipline "Home Theater dB Drag Race" I don't know about yet, that may change in the future.
I talk about a HT that is used by real humans that want to leave it as healthy as they entered it. Usually 125dB are the limit you can endure for a very short time at low frequency with minor injuries to your hearing. In reality at these level you may already be unable to tell what is shaking, you or the room.
Any thoughts on BL squared over Re and responsiveness, I’m torn between chasing MMS and hearing more about BL as a more important factor
I did wonder about dividing BL^2/Re by MMS 🤔
I did wonder about dividing BL^2/Re by MMS 🤔
Agreed 100%. For more than forty years now, my bass mantra has been: Move a Lot of Air - GENTLY!
Nothing in that period has swayed me otherwise. For a given displacement volume, a little 10" flapping around at Xmax is never going to sound as good a 21" barely moving. The higher efficiency is in part due to the better matching of larger cone area to the acoustic impedance of the surrounding air, which may or may not contribute to the more relaxed sound. For this reason I have stuck with plenty of cone area in my PA - 6 x 18" and 4 x 21" - in sealed (for low energy storage) enclosures. As you suggest, this requires a lot of power. In my case an honest 20kW of good old iron and copper analogue dinosaurs weighing in at just over 1/4 ton...
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Responsivness? Fast bass is a myth. The speed the cone of a woofer moves at is really slow. The "fast" bass comes from the mid and tweeter.
What you may search for is not found in the chassis, but in the finished box. You can not tell from the chassis data how a speaker "sounds". You can only judge if it is installed in some construction. Then you should not underestimate the influence of the amp you use. If you run a speaker in the region of it's resonance frequency, the amp is quite effective in damping the cones movement. Take it even further and you will discover MFB...
Imo it does not tell you much if you just take some parameter and start calculating something from a raw driver. TSP are explained very well, used by anyone serious about speaker building and there are no magic formulas to be found any more.
What you may search for is not found in the chassis, but in the finished box. You can not tell from the chassis data how a speaker "sounds". You can only judge if it is installed in some construction. Then you should not underestimate the influence of the amp you use. If you run a speaker in the region of it's resonance frequency, the amp is quite effective in damping the cones movement. Take it even further and you will discover MFB...
Imo it does not tell you much if you just take some parameter and start calculating something from a raw driver. TSP are explained very well, used by anyone serious about speaker building and there are no magic formulas to be found any more.
@MrKlinky
This is an important point. Used in the right cabinet, 4x18" can do a party for 500 people in a gym. Sure, you do not play 10-25 Hz test tones over a PA.
If you reduce the room size and keep the cone area, you can use these speakers to produce lower frequency much louder. You can even, at some point, close the vented cabinets or ditch the horn's and use them closed. Which costs a lot of power...
So at some point the room size and even it's construction materials get more and more important. Maybe, in some cases, more important than the actual speaker chassis. A lot of todays modern chassis have only extended the abilities of older ones to play loud.
That is what I want to point out. Discussing sub woofers gets frustrating when you do not know where they are used
This is an important point. Used in the right cabinet, 4x18" can do a party for 500 people in a gym. Sure, you do not play 10-25 Hz test tones over a PA.
If you reduce the room size and keep the cone area, you can use these speakers to produce lower frequency much louder. You can even, at some point, close the vented cabinets or ditch the horn's and use them closed. Which costs a lot of power...
So at some point the room size and even it's construction materials get more and more important. Maybe, in some cases, more important than the actual speaker chassis. A lot of todays modern chassis have only extended the abilities of older ones to play loud.
That is what I want to point out. Discussing sub woofers gets frustrating when you do not know where they are used
Exactly this. The myth that won't die... I firmly believe that the 'speed' of bass which many still discuss and misunderstand (despite Fourier proving it comes from mid and HF as you say) is actually stored energy in the system smearing and extending LF signals as it decays. A quick look at the step response of larger ported and horn-loaded systems show decay times easily exceeding 100ms; some are still ringing 1/4 second after the signal has ceased since they possess very poor damping. My acid test for subs is something like Metallica with their double-pedal bass drumming. A system with low energy storage will reproduce this as a machine-gun like staccato sound as it should be whereas one with a resonant loading (ported) and/or high energy storage blurs the individual drum hits into almost a single ill-defined event.
From a step-response point of view, definitely. Of course they are woefully inefficient and require tons of EQ but otherwise have very few vices and are compact and usually simple to build. As they are quite small, panel resonances are naturally and usefully further away from the pass band.
This 50l 25mm ply enclosure has the driver externally mounted to improve cooling.
Attachments
Interesting is the design shown intended to reduce reflections looks like a small volume
55l; side panel width=135mm; Q~0.5 with the damping and the 18PZB100 driver. Damping also helps to reduce higher order harmonic distortion a little, and all panels are tied together or braced resulting in very high panel resonances due to the inherent stiffness. Big cuboid boxes really are a nightmare to stiffen and damp. The route I have chosen requires many amps and enclosures but at least the latter are small and easily manageable, and the transient response is sensational!
The Acoustic Elegance IB18HT may also be good for what the OP wants i think (just to give more options).
I know people who use it in their hometheater as sub and they claim an F3 of 15Hz from it which could be right if you look at the specs. I've heared the setup quiet a few times about a decade ago and those are the subs that go the lowest that i ever heared.
They use 4 on each side of the screen (they are rich people) amped with Bryston amplifiers and a custom dsp module and use active Klein & Hummel O410 speakers (now sold as Neumann KH420G) as tops for their 7.2 setup.
I know people who use it in their hometheater as sub and they claim an F3 of 15Hz from it which could be right if you look at the specs. I've heared the setup quiet a few times about a decade ago and those are the subs that go the lowest that i ever heared.
They use 4 on each side of the screen (they are rich people) amped with Bryston amplifiers and a custom dsp module and use active Klein & Hummel O410 speakers (now sold as Neumann KH420G) as tops for their 7.2 setup.
I got to experience this bass last Saturday at the Rock N Roll Hall Of Fame in Cleveland, Ohio.
I didn't choose it - they chose me! £125 each!! (They are actually rebadged as Yamaha and were sold as brand new old stock spare drivers).
With EQ in a pub, crossed over at 120Hz and driven by a modest bridged amp a pair will go low enough and loud enough to cause turntable LF feedback requiring a steep 30 Hz high pass filter.