Speaker cabinets.

Am curious as to why some speakers are noted as needing open or closed back cabinets. Reason for asking is that I would like to put an Eminence Legend 15 inch guitar speaker in a closed cabinet. The web site says N/A on closed cabinets, haven't heard back from them, was wondering why.

Without gettin' into a complicated discussion:

Some speakers are designed for use in open back cabinets.

Some speakers are designed for use in closed back cabinets.

Don't mix 'em up.

Without gettin' into a complicated discussion:

Some speakers are designed for use in open back cabinets.

Some speakers are designed for use in closed back cabinets.

Don't mix 'em up.

Could you get into a complicated discussion? I was looking at the Weber site, for example, and a 10A125 is a recommended speaker for both a BF super reverb (open) and a BF Tremolux (closed). What are the features of a speaker that make it work better in one kind of cabinet than another?

Although it is very subjective as far as sound goes, the rule of thumb is closed backs favour live situations where the cab is miked up as they help project the sound from the speakers straight out of the baffle (more directional) with a tighter bass response. Whereas open back cabs help fill the room with a more even, airy sound (presence if you will).

However, the actual situation will allow these conditions to vary greatly, so its only a general guide.

I personally prefer open backed cabs...although mine has a 3 piece back plate, so I can run the cab either way.

An open back speaker has to have a stiff enough suspension so that when the speaker is driven it does not just flop around. But with an open back cabinet the bass from the back of the speaker comes around and combines with the sound from the front of the speaker canceling some of the bass. So there are two conflicting things happening here. What they have done with these speakers is made it so that the cone is dampened but on the bottom end the speaker has a bit of a resonant peak to make up for the bass cancellation.

When you put this kind of speaker in a cabinet the peak gets more pronounced and moves up in frequency. Theoretically you can equalize the hump in the response down but you also have to boost the frequencies bellow the hump as they are reduced. Basically not worth the problem.

A closed back speaker has less of a resonant peak and it occurs at a lower frequency. When you put it in a cabinet the hump increases the bass and moves it up in frequency. The speaker has to be designed to operate in a specific range of box size, two small and you have the same excessive hump and loss of low end as you do when you put an open back speaker in a cabinet, too big and you loose out on the hump adding bass.

A speaker that is for a closed back cabinet will have a looser suspension and if it is played at loud volumes in an open back cabinet the cone gets beat up as the small amount of air in the cabinet acts to stiffen up the speaker. Not a complete explanation of what is going on but I do not want to complicate it too much.

because of what is noted above, you almost always see bass cabinets as closed cabinets to give more of a cushion to the speaker for the longer excursion. I think the same is true of high power cabinets like the Marshalls, though a twin reverb would be an obvious counter example. A closed back cab will typically have more power handling capability with the same speaker.

Whoa...this is gonna get real complicated, real fast.

There is a ton of math that goes along with this discussion, such as the responsiveness of the speaker at different frequencies, whether the speaker is mounted from the front or the rear (makes a difference!), voice coil thickness/density, Thiele-Small porting if closed, volume of air in closed backs, etc forever.

Designers have been trying to find the magic bullet for over a half century - still no joy, but we've adapted. Witness how one design can produce a cab/speaker combination that will offer a full range guitar-wise (55-16K) from 2-10s, but musically, the combo sounds awful, where as another cab will be frequency restricted with all sorts of peaks, valleys, and comb filtering, but sound absolutely GREAT in context...

I have to disagree with not mixing the two topologies...an open back and closed back together can and do sound pretty amazing when the drivers are properly time aligned and phase coherent.... that is another thread to itself.

is there a rough formal for the size of a box needed for say a 8" jenson mod speaker. thanks. also, have they try to put a bass speaker, and a guitar speaker in teh same cab. would that cover all frequency, or would some overlap and just make for a mud mess.
chris.

I appreciate the discussion, but should have asked up front, would putting a speaker designed for an open back be harmed by putting it into a closed back cabinet?

Depends on the speaker, and what kind of cabinet. A lightweight inefficient speaker may not like the level of air pressure that builds up inside a closed and sealed box - on the other hand, it might.

Lotsa help, huh? :)

I appreciate the discussion, but should have asked up front, would putting a speaker designed for an open back be harmed by putting it into a closed back cabinet?

No, putting a speaker that is designed for an open back cabinet will be happy in a sealed cab. It will reduce the cone excursion putting less stress on the suspension. The other way around may not be so good.

Just heard back from Eminence----won't hurt the speaker, but will change the sound, so it's more a matter of taste than anything else. Doing the vice-versa on the other hand.....

Anybody see the episode of Myth Busters where they were testing the myth of what they called the "brown tone"? Supposedly, someones military theorized that a constant 7hz, at thousands of watts, focused on ones enemy will cause them to take a dump in their pants:shock:. They put like 10,000 watts at 7 hz through cabs of drivers and wore diapers during the test. The cone excursion was so much that it looked like someone was pushing the cones in an out.

Off Topic (sort of) but funny.:lol: