Using same volume displacement chart and simplification as in previous post then to reach 120db @ 30Hz requires about 2000+ cm3 volume displacement. Using ~2400cm3 as thats roughly three 15" woofer worth of cone area with 1cm clean sounding p-p excursion so requires 3pc very good 15" drivers, or about six average ones.
So, getting nice bass is serious business and room claiming THX levels likely has multiple 15" drivers somewhere, or perhaps multiple 18". If there is only few smaller woofers then, it's very likely not capable of such output.
- Two 18" would have similar cone area as three 15".
- Three Seas L26Roys, datasheet says it can do 28mm p-p and has 342cm2 cone area so is capable roughly 1000cm3 volume displacement, so there needs to be three of those for 120db at 30Hz, perhaps sounding clean enough.
- 8pc top shelf 6" woofers capable of clean sounding 2cm p-p as in previous post
- perhaps 16pc 6" woofers which are capable of 1cm clean sounding p-p.
- about 12pc 8" woofers capable of 1cm p-p
So, getting nice bass is serious business and room claiming THX levels likely has multiple 15" drivers somewhere, or perhaps multiple 18". If there is only few smaller woofers then, it's very likely not capable of such output.
Yes but they only have 5-6 mm clean excursion before non linearities come along with the rapid changes in BL/X.
Might do the job.
The low sensitivity does not exactly help either.
I am aware of this for home situations but I really would like to see all the subs used at the theater. We talked about this before and it was made known that the big room helps out in the LF section but I find a disconnect when I need 4-8 18"s theoretically, in a much smaller space, while I could only find 2 18"s at the Imax lol... they surely have more subs than just 2 ported 18"s....... right? 😅
Well, hopefully 🙂 They could also use some other alignment than closed boxes, employ high pass filters, don't mind about distortion and so on 🙂 Yeah it's just a ballpark figure. Point was to kind of go with Randy Bassinga observation that hifi store demo speakers weren't too impressive with reggae and calculate that even though big woofers seem silly for home stereo use they really aren't, couple of 15" is barely enough 🙂
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I see the need for multiple subwoofers and have 4 15's in my set-up. I don't see anyone talking about mutual coupling that adds 6dB per pair. A Quad can add 12dB depending on placement. My 91db sub becomes a 97db mono pair. In a theater with them in a line under the stage there is quite a bit of sensitivity gained this way.
Rob 🙂
Rob 🙂
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Sure they do at least JBL does. They add 6db Q2 at 25hz and high pass at 20hz. That flattens the response. Same alignment:
https://www.lansingheritage.org/html/jbl/specs/home-speakers/1983-b380-b460.htm
Rob 🙂
Hi Rob, I've measured this pretty extensively. Only time I ever see +6dB from doubling boxes, is when they are fully co-located, like side-by-side or stacked.
With about any separation at all, it's usually +3dB, maybe +4dB depending.
I can see that as it would slide with frequency depending on separation. The lower you go the better the coupling vs distance. I did a measurement @ 30 Hz and got a good 5-6db measured between them in my room. Approximately 1/4 wavelength spacing.
Rob 🙂
Gotcha.🙂
I should also say, I always measure SPL using pink across the full-bandwidth of the sub. (or whatever driver section etc)
I trust an integrated measurement of SPL across all contributing frequencies a whole lot more than sines waves....
It's fairly straightforward to highlight the levels needed for simulating real movies or concerts. It is altogether another thing to prove that one has achieved this. The concept of MaxSPL (maximum "clean" SPL level) has been debated for decades and there is no consensus. Something like 10% THD is pointless because it could be (and should only be) 2nd and/or 3rd order nonlinearities which are almost inaudible at high SPLs because of masking effects. This is why IMO it is critical that the BL(x) falloff be very gradual and not sharp as an underhung VC would have. IF you look, for example, at a B&C Bl(x) you will see that it has a very gradual falloff. Thus as the VC nears clipping range its output harmonics are very low order.
This goes along with a study that we did on amplifiers where a hard clipped amp and a soft clipped amp were compared. The results were that the soft clipped amp played louder even though the rails were identical in the two designs.
So my test was subjective. At 120 dB SPL(C) peaks of a live concert recording, I could not detect any audible problems. Try this at a Hi-Fi store!!
The mutual coupling issue is only defined for a free field situation. In a closed room with spaced subs it doesn't work anything like that. Turning one sub on and off will both add and subtract SPL at various frequencies and locations - so much for the mutual coupling concept.
Yep, that's my understanding and experience too. Even for outdoors, +6dB coupling requires tight co-location.
I have found on average though, measuring SPL at in room listening position, using full-bandwidth pink, that one sub vs 2, generally adds about +3dB.
This is for subs always low-passed at 100Hz or less, and in a fairly large room.
I have found on average though, measuring SPL at in room listening position, using full-bandwidth pink, that one sub vs 2, generally adds about +3dB.
This is for subs always low-passed at 100Hz or less, and in a fairly large room.
Must be the reason our lot grows up with PA systems in the bedroom. I had a 15ich pair when in high school! And yes, that was barely enough in yr12 in 1992. In 1997 I think it was that a close friend introduced my to his new range of JL in his brand-new showroom. First, we tried a 15w3 rated very low in efficiency. He kept on showing me JL pamphlet in which JL was begging customers to not judge system output with the driver sensitivity number because the driver is not going to be used raw. Anyway, the single 15w3 outperformed the 2 15" PA drivers and made a nice low kofitable with dancing roaches in the ashtray. The W3 got replaced by a W7 when that was introduced
Currently, it's the SBA doing well in our much tinier place in a retirement estate. So far, I have worked this out after trying all sorts of amps and drivers. To be able to monitor bass at a reasonable nighttime level that can't be heard outside the door:
With volume control very low, to be able to hear a fully defined note matching the vibration of the string in my hand and hear the depth of a short dry kick (how it attacks and decays and be able to dance a bass note with it staying just ahead or behind and mixing it up. Well over 100w available for the bass driver to draw on. A very tight and high excursion bass small bass driver and a filtered signal going to a second larger aux driver to help the E string along for much louder than that level to keep the definition
Guys, don't take offence, but I don't consider those units in the Hi-fi stores as high fidelity. They might be for some low bandwidth music, but not for solid coloured music types. Maybe the qualification should be featured on every system as to what music styles they are not suited to or designed for
Had to share this one, 18th birthday and a friend DJing on the balcony party just outside the bedroom window. Jaycar kit amps and mixer, a couple of decks, a little ghetto blaster with the CD player being taken off the headphone output. The 15" 2-way pair. This was my bedroom system in high school. Minimum for clean basslines that I could afford then
