garry
118 posts
Sep 12, 2011
6:25 PM
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i notice that the fender mustang 1 and 2 amps are closed back, where the 3 is open. got me wondering why they did that, and why, in general, once would have an open vs. closed back.
my vt-30 is closed back. i love the sound it makes, and it seems pretty feedback resistant compared to my other amps. but there're no doubt dozens of other differences, so i can't necessarily attribute either of these things to that.
so how do open vs. closed back amps differ, in terms of feedback, sound, etc?
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kudzurunner
2685 posts
Sep 12, 2011
7:32 PM
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I love my Mouse, which is a small solid-state closed-back amp, but years ago my friend Trip Henderson swore to me that the only worthwhile harp amps were open-backed. There's a huge difference. The open back lets the speaker cone breathe and lets sound waves from the back side of the cone flow outward along the wall in a very different way than is enabled by closed back cabinets.
I don't have any training in audio science, just a lot of gigging experience, but I've always preferred open cabinets. Can somebody here put some science behind my preference?
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gene
913 posts
Sep 13, 2011
3:34 AM
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I Googled "open back vs closed back cabinet." I didn't find any science, but I found some stuff that expands upon what you've already said. Here's a couple of copy/pastes...One from a forum and one from e-How:
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Assuming two identical speakers in two identical cabinets, one open back and one closed back, the open back cabinet will have a chimier, more open and complex sound, will spread the sound around the room a lot more, will have looser bass response (but lots of speakers are designed for this, so that doesn't mean you won't have any bass if you have the right speakers). The closed back cabinet will be tighter, punchier, "simpler" and less complex sounding, less "airy" sounding, and much more directional (less sound at the back and sides). If you want to sound like Angus Young, or the Ramones, for instance, that's a closed back cabinet sound. If you want to sound like Tom Petty, that's an open back cabinet sound for the most part.
To complicate this more, some speakers don't sound right in open back cabs, like the Celestion G12M Greenback, which has too small a magnet structure, the bass gets flubby and the breakup gets trashy (not in a good way) in open back cabs, but in a closed back 2x12 or 4x12 these speakers sound great. Conversely, some speakers don't sound great in closed back cabs. The Celestion Alnico Blue sounds much better in an open back cab - it has plenty of bass response either way, but it has more complexity and opennes and chime in the open back cab, it sounds "simpler" and "constricted" in a closed back cab.
If you want some help with this from the forum, let us know what guitars and amp(s) you have, what kind of music you play and what kind of sound you want. References to specific recordings would be helpful - like "I want to sound like Angus Young on Back in Black" or " I want to sound like Tom Petty on Running Down a Dream" - that sort of thing lets people give you specific recommendations.
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Guitar speaker cabinets and combo amplifiers (those with built-in amp and speaker) are designed in one of two ways: open- and closed-back. The type of cabinet chosen is a matter of personal preference, but each type of offers a different sound. The type of wood used and the internal design of the cabinet also contribute to the speaker's tone.
Open-Back Speaker Cabinets
Open-back speaker cabinets are used primarily in small combo amplifiers to produce more sound, but some extension speaker cabinets (those not attached and added to an amplifier) feature open-back design. Although open-backed cabinets are simpler in design, as they don't require "tuning" the cabinet to produce the desired sound, simple design does not necessarily equate to a cheaper amp or cabinet. The open-back design allows sound from the rear of the speaker to emanate and mix with the sound coming from the front. This produces a full-bodied tone, but the low-end bass sound is sacrificed. Open-back cabinets are not fully open, as they contain a rear sound-baffle which partially encloses the cabinet and contributes to tone. A baffle is a piece of wood which helps direct and shape speaker sound.
Closed-Back Speaker Cabinets
Closed-back speaker cabinets are used primarily for extension cabinets, but are also used in some combo amp designs. Closed-back cabinets emit sound solely from the front of the speaker, and project sound in a more directional pattern than open-back cabinets. Closed cabinets often include cut-outs in the front of the cabinet called ports, which allow internal sound from the rear of the speaker to escape and emit from the front of the cabinet. Since the rear speaker sound is misdirected to the front ports, the resulting over-all sound produces more low-end bass than an open-backed cabinet. Some closed-back designs include internal baffles to help shape and redirect sound to the ports.
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kudzurunner
2686 posts
Sep 13, 2011
4:19 AM
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Those advisories are for guitarists, obviously, not harp players, and our needs are somewhat different. But still, I like that word "chimier" These statements certainly corroborate the general drift of my comments
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jbone
642 posts
Sep 13, 2011
4:35 AM
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when i think about it, most or all of my amps have been open back. i have a 4x8 extension cabinet that's closed which i used to use with a peavey delta blues 210 amp. it did project more sound i think, than the 2x10's open back amp itself. the silvertone and bassman which i currently use are both open back.
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http://www.reverbnation.com/jawboneandjolene
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HawkeyeKane
175 posts
Sep 13, 2011
8:45 AM
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I usually play through a Peavey Vypyr 1x8 open back solid state. But on occaision, I get ballsy and plug into our guitarist's Fender Bandmaster with a 1x12 Marshall closed back cabinet. While the Marshall cabinet is louder, my Vypyr's tone is much richer. Even when I have the modeling settings adjusted to have roughly the same sound as the Bandmaster, the Vypyr's tone is just a little more full. Only explanation I can come up with is the open back.
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Hawkeye Kane
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walterharp
1121 posts
Jun 23, 2013
6:07 PM
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Was thinking about this lately, there is some opinion that closed back has more bass, which is something that seems to sound good in harp amps to many, are there more opinions on this? What about partially open?
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Goldbrick
208 posts
Jun 23, 2013
7:18 PM
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Most bass amps have closed backs to focus the sound.
Nice thing about an open back is you can always play with distance from back of the cabinet to a wall and see what you like.
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Rick Davis
2009 posts
Jun 23, 2013
9:02 PM
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Combo amps that are driven by tubes (not solid state) are open back because the amps generate a lot of heat. It needs to be vented.
A closed back cab generally will have more thump and a more pronounced bottom end.
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-Little Rick Davis
The Blues Harp Amps Blog
The Mile High Blues Society
Tip Jar
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arnenym
155 posts
Jun 24, 2013
12:28 AM
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Gary O. - Sonny Jr raised the lower back panel on the last versions of Super Sonny as a performance-enhancing measure.
I tried it on my Bassman RI-LTD. It does the sound more focused and aggressive. Like a sound-beam right out from the front of my amp..
Last Edited by arnenym on Jun 24, 2013 3:32 AM
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puri
110 posts
Jun 24, 2013
2:38 AM
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That's interesting, "Sonny Jr raised the lower back panel on the last versions of Super Sonny as a as a performance-enhancing measure" I was about to post something similar before I notice arne's post. It just something I've found out from making amps & cabinets, I started out with fender's measurements before I started to noticed that maybe the lower back panel that is too low let the sound get away too easily so I tried to raise the back panel so I got about 70 - 80% covered from both panels and yes, from my experience it puts the sound together better tighter, a bit crunchier and more focus. I think this is the way to go for me, don't think a totally closed cab would be good though.
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Rick Davis
2011 posts
Jun 24, 2013
6:45 AM
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A slightly off-topic question: The lower back panel on some bigger amps like Bassman or Bandmaster have openings in them that are covered with grill cloth. Is that a feature that is important to you? Would a lower back panel without openings be just as good?
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-Little Rick Davis
The Blues Harp Amps Blog
The Mile High Blues Society
Tip Jar
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HawkeyeKane
1810 posts
Jun 24, 2013
7:54 AM
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"Combo amps that are driven by tubes (not solid state) are open back because the amps generate a lot of heat. It needs to be vented. A closed back cab generally will have more thump and a more pronounced bottom end."
True enough. My Alamo is a testament to that, and at the same time, an exception to the tube driver rule you mentioned Rick. As you can see here, the Fury is a closed-back tube amp. Probably because it was designed as a bass amp. The single 15" is housed in the bottom compartment and sealed off by the back panel. The tubes hang below the chassis in the top third of the amp cabinet, and you can see below the PT and choke that they left an opening behind the grill cloth to serve as an additional source of ventilation.
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Hawkeye Kane
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chromaticblues
1419 posts
Jun 24, 2013
9:39 AM
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I visted an amp builder in Vermont back 20+ years ago named Bill Caruth. I asked him the same question.
He said that was about 100th time he heard the question! So he invented a foot operated gixmo that he could change the hieght of the back board on an amp while he was playing!
OK I saw this and it's still hard to explain!
It was a drum foot pedal that was extended alittle for more range of motion. He had a rope at the end that went striaght up over a pulley that went back down to this series of boards that were telescopic.
This is the tough part to explain! The rope was thru a hole in what looked like the back board of an amp. when it got to certain hieght there was a board attached on the inside of that on a sliding track. There were a few of these sliding boards.
So he he would play and move hos foot around untill he liked the sound and made a permanent back at that hieght! It was pretty wild! He told me as arule of thumb if it's a fender. Have the back board just high enough to cover the magnet and an inch or two above that. Ther actully is sweet spot where it does make a difference. I amazed when he showed me!
So everyone out with a silver faced champ or a Kalamazoo. Try taking that board that protects the tubes and put in the bottom of the opening!
Not quit a Bill Caruth trick, but it works very well on those two amps.
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