#1
Seems like a silly question to ask, but how does a bigger closed back cabinet sound 'bigger' than a smaller one?

It seems a bit counter intuitive to me because by the definition of it being closed back, the size of the cabinet's baffle is effectively infinitely large because they do not permit any air that's moved from the front of the speaker cone to behind it or vice versa. This is always the case with any closed back cab regardless of its size.

So with that premise in mind, that implies that the volume of air that's behind the speaker cone makes absolutely no difference because regardless of its volume, it still has nowhere to go. So why does it matter?

I've been pondering this problem further and I've come to the conclusion that the amount of bass response a cab produces is subject to the proportion of the magnitude of compression/vacuum that is exerted on the air as the speaker moves, to the volume of air that is being compressed/vacuumed. So theoretically a larger cab with a larger volume of air behind the speaker does not have to compress/vacuum as far as a smaller volume for the speaker to achieve the same loudness. So therefore the speaker doesn't have to work as hard to make the cone achieve more dramatic excursions. More dramatic speaker excursions means more air is moved in front of the speaker cone, which means more bass is reproduced.

Is this hypothesis correct?

That seems fairly intuitive to me. But if that is true, then wouldn't the effect this has on the volume of air behind the speaker cone in a 4x12 cabinet (for example) be mitigated by the fact that there are more drivers to move? Because if more drivers are present, then the amount of compression/vacuum to make those drivers achieve same degree of excursion becomes 4x larger than a 1x12 cab. Assuming a 4x12 cab is 4 times the size of a 1x12, then the 4x greater volume of air that's behind the cone gets mitigated by the fact that 4x the drivers are compressing/vacuuming it.

And if that hypothesis is also correct, then how is it possible that larger cabinets achieve more bass?

If I'm wrong at any point of this post, please correct me. I intend to encourage technical discussion on this topic.

Edit: I've found the answer: bigger cab = more wood. More wood = MOAR TOAN. /mic drop
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Last edited by T00DEEPBLUE at Aug 12, 2016,
#2
Quote by kabadi.man
not sure if I understood you correctly as i've not much experience with cabs, but my bass cab is closed at the back & it has a vent at the front, so the air at the back of the cone does not compress.

From my understanding, this isn't strictly true. The port/baffle on the front of the cabinet does allow air behind the speaker to vent to the front of the cone to some extent. But the air is still somewhat compressible due to a backpressure that's created by the restriction in size of the port(s), the location of the port(s) relative to the speakers and the length/shape of the baffle(s) inside the cabinet. This all implies that port(s) can drastically affect the frequency response of the cabinet depending on these dimensions, which is why ported cabinet design is a science.

But of course, you already knew that.
Roses are red
Violets are blue
Omae wa mou
Shindeiru



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Last edited by T00DEEPBLUE at Aug 12, 2016,
#3
This all gets WAY more complicated than you want to go into.

Suffice it to say that there's almost no science at all involved in guitar cabinets designed in the 60's (which are mostly what you buy at your local GC today). It's all "speakers on a board" with little regard for which speakers would be used. Manufacturers have simply found it easier to build and promote clones of those old cabinets because guitar players simply don't know the difference and because it's cheaper for them. Any attempt to sort out why *guitar* cabinets do what they do is an exercise in overthinking, because they really don't do what you think they do.
#4
Quote by dspellman
This all gets WAY more complicated than you want to go into.

*snip*

Any attempt to sort out why *guitar* cabinets do what they do is an exercise in overthinking, because they really don't do what you think they do.

So the fact that it's a complex system means its a topic not worth exploring?

If you think I'm wasting my time in asking the question, then you're in no position to argue.
Roses are red
Violets are blue
Omae wa mou
Shindeiru



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Last edited by T00DEEPBLUE at Aug 12, 2016,
#5
Start here. Absorb everything in the two books listed and you'll know more about speaker enclosure design than 99% of the cabinet builders on the planet, and 99.99% of all guitarists.

https://www.amazon.com/Loudspeaker-Design-Cookbook-Vance-Dickason/dp/1882580478

https://www.amazon.com/Theory-Design-Loudspeaker-Enclosures-Benson/dp/0790610930
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#6
Quote by kabadi.man

Also, while the OP and forum is guitar gear (and not bass) i suspect Bass cabs may be less clones and more sciencey based stuff.


Pretty much on the money.
The 4x12 for guitar was "designed" when Jim Marshall decided he needed four 25W speakers to handle his new 100W amp. So they laid out four speakers on the factory floor and drew a line around them. Later, when they realized that the big back panel was vibrating in a noisy way, they put a piece of 2x2 (2x4?) in the middle of the box to move that vibration frequency into a less-audible range and called it a day. Fifty years on, they're the same, no matter what speakers are actually in them.

Bass players, however, have moved into systems that have frequently been used for sound reinforcement, because they use the entire spectrum; low lows and very high harmonics (slap bass). One famous bass player (Phil Lesh?) often used Meyer Sound cabinets (a couple of Meyer Sound Labs 2-18" and a 12"+ high frequency horn), and he's not alone.

I'm using four cabinets originally designed as full range flat response cabinets for bass. The designer utilized relatively new speaker drivers *and* newer cabinet construction techniques. In the past, a lot of bass players used arrays of smaller speakers, because they could move masses of air with cone area using speakers that really didn't have a lot of cone excursion. Thus we have 150-200 lb 8x10 "refrigerators" wearing 125 lb 300-400W tube amps. The cabinets I have utilize a single 15" neodymium-magnet Eminence Kappalite 3015LF low frequency drivers, a 6.5" neo-based mids driver (18Sound 6ND 410 or similar) and a 1" tweeter with wave guide that will easily handle 18Khz or so. The cabinets themselves are slot ported and can easily reproduce the fundamental of the low B on a 5-string bass without farting out. The 18Sound mids driver lives in its own closed-back enclosure within the larger cabinet, and the cabinets are made of thinner plywood than you'd expect, but with a lot of bracing. They're glued together (Loctite's Premium PL), not screwed, and they're airtight (aside from the port), because escaping air wastes power and increases flubby reproduction of lows. The result is a 30" x 20" x 16" single cabinet that weighs at or under 50 lbs all up but is capable of handling 900W with great efficiency. The exterior is not Tolexed, but utilizes a Duratex coating (same as most pro audio cabinets) which is seriously tough but can be quickly and easily touched up. For cabinets that will receive a lot of abuse, LineX spray-on truckbed liner is the coating of choice.

Two of the cabinets have different form factors. They're 26" x 20" x 17" deep with a lateral corner nicked at a 45 degree angle to allow them to be used as floor monitors in addition to standing on end. These are also available (they come from authorized custom builders) with an internal "tophat" that will allow them to be put up on speaker stands if desired.

Each pair of cabinets has one cabinet with a reversed baffle so that they can be stacked without encountering major phase issues.

As mentioned, both versions were originally designed by David Green as bass cabinets, but I use them with modeled guitar, bass and keyboards, and the versions that can go up on stands work pretty well as wide-angle PA speaker systems in a pinch. A single cabinet will hold its own with any Marshall stack and aggro drummer and will provide wider dispersion than any 4x12 throughout the spectrum. A pair of them (with a 1500W power amp) in most venues will convince the sound guy that the bass doesn't need to go to the board, and I've honestly never tried all four pointed at a medium-size audience. I think it would just piss people off.

Ports on cabinets need to be properly sized and placed based on the power and frequencies involved. At one point, air moves in and out of the port, as you'd expect. But there are conditions where boundary layers and turbulence form, and eventually there are conditions where the port simply can't move air and the cabinet begins to operate as though there were no port at all. Badly designed ports can destroy your speakers.

Modern speakers like the Kappalite are found in the pro audio section of the Eminence database, not "guitars." Where the 8x10 cabinets rely on speaker cone area, the 3015LF exhibits relatively huge cone excursion, and can move the same *volume* of air as much wider arrays of smaller speakers.

Even in the guitar world, arrays of 12" speakers were recognized as old school and problematic as far back as the late '60's. Quite a few manufacturers were incorporating 15" speakers and mid/high horns with crossovers by '69 and '70 because solid state amplifiers were allowing them to produce heads with 200W, 300W and up at miniscule weights. Unfortunately, in 1972 (or thereabouts) Nixon opened up trade relations with China, new sources of tubes were revealed, and guitar players clamored for more tube amps and 4x12s. I have one old 2x15 (Altec Lansing 418's) plus horn ported cabinet (it's huge; about 48"H x 30"W x 14"D) with a 275W head from 1971 that's spectacular, and near-perfect for 7-string and drop-tuned guitar.

When I said that trying to make sense of guitar cabinets was way more complicated than you want to get into, I meant that there was really no science in the design at all, but there are a lot of unintended consequences. A 4x12 beams treble above about 450Hz, which means that someone directly in front of it on axis gets ear-splitting icepick treble, but the guitar player, usually well off-center, is thinking that he sounds smooth. Moreover, the usual close-mike on a single speaker setup that goes to the sound board sounds completely different. A 100W amp doesn't have enough power to reproduce bottom end at high volumes with a 4x12, so whatever you're hearing are simply whatever harmonics the speakers can reproduce with the power available. Ports in a 2x12 cabinet loaded with guitar speakers may or may not do anything, but it's unpredictable because the cabinets (and ports) weren't designed with any specific set of speaker parameters involved. Guitarists listen with their eyes and they hear with their pocketbooks. Two 4x12s may have the same speakers and be absolutely identical internally (and usually are), but guitarists will swear they hear something special out of the one that costs three times as much. In short, "intuitive" (from the original post) usually doesn't match either the actuality or the science.

Arby911 suggests starting with a couple of books on the subject, and that's on-the-money advice if you're really curious. Check out what's happening with the people who are making the cutting edge sound reinforcement speakers (Meyer Sound Labs is a good place to start, but that's some seriously expensive stuff) and with cutting edge bass cabinet designers. Guitar players are moving that direction when they get into modelers. Just don't try to make sense of '60's designs that are simply cloned by current manufacturers.
#7
Quote by kabadi.man
I am due to start a 5-string bass build end of this year/start of next. I doubt my current speaker will cope well with the low B, so i'll most likely take that advice, grab a book and make a speaker enclosure my next project after the 5-string.


Check this out: http://www.speakerhardware.com/fearful-156-precut-flat-pack.php

Speakerhardware dot com has crossovers, drivers, the works.

#8
There really should be a cabinet design section on this forum. All the science is truely mind-boggling but its interesting too. From my experience building a cab for a deltalite2 the speaker manufacturer will suggest a volume for a closed-back cab. Any volume(of air inside the sealed box) will not due. The specific volume of air will aid the speaker in pushing in and out efficiently. It seems logical that a bigger infinite baffle cabinet will sound bigger because the sound is escaping through the sides of the cabinet. The energy resonating in the sealed air is causing the box to vibrate at a specific frequency. Other wise it might sound bigger because the speaker is working more efficiently. Maybe
Last edited by geo-rage at Aug 12, 2016,