Closed back speakers " VERSES" open

Gary Steele · Post by **Gary Steele** » 19 Jun 2006 3:24 pm

Your opinion, Do you guys think they perform as well? My drummer says my open backs are a little hard on his ears,
GS.

David Higginbotham · Post by **David Higginbotham** » 19 Jun 2006 4:04 pm

I prefer closed back. Better bottom end, more directional, louder, and you get a more consistent sound.

With open back, you have less bottom end, more open sound, not quite as loud in front, and anything behind them affects the tone.

The sound that your drummer is complaining about is possible since a lot of the sound will come from the back of an open back cabinets. Just my opinion!
Dave

Bob Knight · Post by **Bob Knight** » 19 Jun 2006 4:13 pm

Gary,
You and I discussed this the last time you called me, Get a new drummer!!

David Higginbotham · Post by **David Higginbotham** » 19 Jun 2006 4:24 pm

Wow Bob! Why didn't I think of that? Always explore all avenues.

Gary Steele · Post by **Gary Steele** » 19 Jun 2006 4:44 pm

This all is confusing me, Just Kidding. Bob i think he is searching. He looking for a friend to hopefully get him a gig out of the Music City. GOOD Luck HUH. I do think the closed back like Dave said will keep your sound a little more consistent. Mainly because you have the same wall behind you all the time, WALL being the back of speaker.
g.s.

Curt Langston · Post by **Curt Langston** » 19 Jun 2006 4:44 pm

Since when can a drummer hear anything anyway?

Gary Steele · Post by **Gary Steele** » 19 Jun 2006 5:01 pm

ACTUALLY SOMETIMES HE HURTS MY EARS TOO.

Bob Martin · Post by **Bob Martin** » 19 Jun 2006 7:34 pm

Hi Gary, if you have been using open back speakers for a while you'll have fun getting use to closed back. Not that you won't get use to it because you can but for about a month depending on how often you play you might not like it. Just a guess because when I changed I hated it but now I wouldn't ever trade back.

Bob

David Mason · Post by **David Mason** » 20 Jun 2006 2:05 am

It depends on the room somewhat. I have a piece of covered particle board that I can slip into the back of my Peavey to close it up when I want, but the sound coming out of the back can give you a nice "room reverb" in some places, especially if you can set up in a corner with hard walls. I vaguely remember reading something about phase cancellation, "dead" frequencies and blowing speakers faster, but I can't place the details - something about poorly designed closed cabinets causing problems, or problems from changing speakers to a different type than the cabinet was designed for?

Paul Norman (RIP) · Post by **Paul Norman (RIP)** » 20 Jun 2006 2:15 am

When speakers are closed without a base response hole in the front they cannot breathe and it builds up pressure inside the cabinet and damages the speaker. There is a formula somewhere about what size the hole should be to accomadate the area. Cabinets from the factories always have these holes. They dont have to be real big.

T. C. Furlong · Post by **T. C. Furlong** » 20 Jun 2006 4:21 am

I've been doing a ton of research with open versus closed back cabinets. I like both if they are done correctly. Paul is correct that you really should vent the closed cabinet with ports. The result you'll hear if you don't is a loss of lows but it's unlikely that the speaker will be damaged. I have been working on a convertible open to closed to open back design and the ports on the baffle board that are necessary for the closed back mode really need to be blocked off in the open back mode.

The answer to the question of which sounds better is totally subjective. It is the entire system (hands, pick-up, cables, strings, preamp, power amp, room, etc.) that must be taken into account. Although, I think that the speaker itself has the most to do with tone, (all other things being the same). The cabinet really needs to be designed around the speaker. I think that using the accepted Thiele-Small parameters for porting is not what you want to do for a musical instrument cabinet. Maybe for bass guitar it's OK but for steel it's all about shaping the low frequency tone, not reproducing it in a linear fashion.

The closed back cabinet will only reduce high frequencies behind the cabinet. Mids and lows will radiate around to the back. The best steel tone I think I have ever heard was directly behind Paul Franklin's closed back Marrs cabinets. Really solid lows and mids with just enough highs. Awesome.

I like how the low frequencies sound in closed back cabinets (tight and punchy) and how the highs sound in some open back designs (smooth and silky). The jury is still out on mids. I think what I like about the highs in the open back design is the cancellation of some mid and high frequencies when they bounce off of a rear wall and interact with the direct sound.

Believe it or not, electro-acoustics is really complicated stuff and I am really enjoying the quest to understand it a little better.
TC

Kevin Ruddell · Post by **Kevin Ruddell** » 20 Jun 2006 6:29 am

Maybe a compromise is the type of back on several cabinets manufactured utilizing a solid back with a rounded rectangular cutout . You get best of both worlds , a little more low end than the more open back but not the narrrower dispersion forward of the totally closed back . I have an Avatar 15 cabinet that is like this but have seen several other builders use this type of design for the cabinet back . I use a Eminence Delta 15 in the Avatar through a Tech 21 preamp / solid state Carver amp and direct out to a Peavy Classic 30 tube amp in a ReVamp head cab and a nice pine tweed cabinet built by Rick Johnson with an eminence Delta 12. It seems to be a good combination of tube/solid state along with with the two different cabinet designs .

James Marlowe · Post by **James Marlowe** » 20 Jun 2006 8:01 am

Having been a bass player much longer than a steeler, I noticed that the bass cabinets that I'd used were front ported. Much better bass response than rear ported, imo.
So when I started on steel I designed a "lean back" amp stand with a closed back and front ported underneath the amp. Gave a lot of bass, almost too much. Perhaps maybe the cabinet effect of the stand caused this. I never tried just a "back" on the amp. Think I will though and see what it's like. Thanks for the idea.
james

James Marlowe · Post by **James Marlowe** » 20 Jun 2006 8:04 am

And I forgot to mention, I just bought a sub woofer for my van ( was completely lacking bass in the sound). Got to looking at the cabinet and found it's completely enclosed--no opening whatsoever! Never would of figured that!

Ray Minich · Post by **Ray Minich** » 20 Jun 2006 10:09 am

The purpose of the cabinet is to "expand" upon the speaker basket and prevent air (on, for example, a forward cone excursion) from spilling from the front of the cone to the back. It increases the size of the "radiator". Totally enclosed "woofers" (speakers where the back of the cone is open to the air) should be "vented" by a port from the cabinet.

Exponential horns and piezo's (for example) don't need it because their "backsides" are enclosed.

BTW: Can someone expand upon what is the difference between "near field" and "far field" speakers when it comes to using speakers in the studio? TIA

Brad Sarno · Post by **Brad Sarno** » 20 Jun 2006 12:00 pm

Bass porting is often a debated issue. The benefits of porting are that you can tune a cabinet to have extended bass response in proportion to a smaller cabinet size. There are many audiophile speakers and studio monitors that are quite intentionally made with no porting. The problem with no ports is that you need a very large cabinet or a very powerful subwoofer to create hefty bass. The upside to non-porting is that you get a more even and accurate bass response. Ported bass "tunes" the cabinet to ring or resonate at a certain bass frequency range. Some people call this fake bass, because it's actually a tuned resonance of the cabinet that may not accurately reflect the music at that range. In our mastering suite we use a pair of 6' tall Dunlavy SC-4 speakers. No ports whatsoever, but enough air inside to have pretty good bass down to around 50Hz or so. Then we augment those speakers with a powered subwoofer, 1000 watts, 10" driver, and again, no ports. The subwoofer has enough excursion and power to created the desired amount of deep bass, all without the tuned resonances caused by porting. It's a great and balanced sound.

The most popular "nearfield" monitor in the world is the Yamaha NS-10, you know, those black speakers with a white paper woofer that are in just about every studio. Those also are not ported. They have awful bass response. To use them correctly, you either have to touch the cone with your hand to feel the subs, or you need to add a subwoofer. Many people will use the NS-10 to get the mix right, and then use a more full range system to hear the deep lows and the more detailed highs. Most other "nearfield" monitors will likely be smallish speakers but with ports to extend the bass response.

Nearfields are good at creating a nice, accurate sound image at a close distance, like 2 to 5 feet away. Midfields or Farfield monitors are generally larger and need to be placed at a greater distance from the listening position to create a good and useful image.

As far as bass guitar cabinets go, it only makes sense to port them to extend the response, or else it would take HUGE cabinets to get the deep bass.

As far as open vs. closed back for steel, I've become a convert to a degree. I used to swear by open back cabinets, but in recent months I've had the pleasure of checking out some of TC Furlong's SPLIT cabinets. The models I've been messing with are closed back, front ported, 12" cabinets. The sound is really good and even, and from the sides and behind it's pretty balanced too. Big fat, punchy bass response. I've noticed that my sound from stage to stage is more consistent with the sealed back cab. It seems that an open back cabinet puts out so much sound out the back, that the acoustical character of the stage becomes a far more significant variable in my tone, where the sealed cab is pretty consistent no matter where I use it. I still like both, but I'm definitely hot on the sealed thing.

Brad[This message was edited by Brad Sarno on 20 June 2006 at 01:03 PM.]

Gary Steele · Post by **Gary Steele** » 20 Jun 2006 12:45 pm

Wow, Everyone has been very sensible so far on this subject. Keep em coming. Brad i'v used closed backs and liked them too. But the trick is i guess is try to make sure it is ported right. BUTT how do we know for sure. Would be nice to talk to some people that has A-B'd different cabs.
Thanks, Gary

David Doggett · Post by **David Doggett** » 20 Jun 2006 1:23 pm

Well here are some things I have gleaned from a little reading (some in past posts on the Forum) and a little experience. The ideal situation is to put a speaker in an infinite wall. There can be no wrap-around cancellation, and there is no pressure on the back of the speaker to hinder its free movement. However, sound energy falls off with the square of the distance, so beyond a few feet, the effect of the wall becomes negligible. So it really doesn’t have to be infinite. Now if you take the less-than-infinite wall and fold it back around into a closed box, you create what is known as an acoustic suspension speaker cabinet. This is the common home stereo bookshelf speaker. It is completely sealed, so there can be no wrap-around cancellation. The air pressure in the box helps dampen and protect the speaker (not damage it) from overly long bass excursions. However, that same pressure also hinders free speaker movement, and so cuts down on the efficiency (the input signal to loudness ratio). The smaller the box, the less efficient. But an amp with sufficient power can produce adequate volume with small convenient bookshelf speakers for a home stereo.

The typical open backed instrument speaker is a compromise between size and efficiency. It’s folded-back wall is big enough to eliminate most, but not all, of the wrap-around cancellation, which mainly effects the lows (so not a big problem for guitar or steel). Also, almost half of the sound is going out the back of the amp. That sound going out the back is strongly affected by walls, curtains, space, etc. behind the amp. Also, there is no air pressure to dampen and protect the speaker from long bass excursions. This is okay for a guitar amp, as long as the speaker handling capacity is matched to the amps power. It gives a room filling sound in small rooms, and the sound can be heard behind as well as in front of the amp. Open back guitar amps were originally designed to be placed in front of the musician. This arrangement minimized feedback from a mic or the early archtop electric guitars. And the open back acted as a monitor, so the musician could hear himself even though the amp was facing away. Also, an open-back combo is cheaper to make, because you don't have to seal off the tubes and chassis from the sound pressure buffeting they would get if they were inside a closed-back cabinet.

The bass range of a bass requires so much power that efficiency becomes a major concern, so all wrap-around cancellation (which strongly effects bass notes) must be eliminated. Also, those low notes are the ones that will destroy an open back speaker. Therefore, a closed back cabinet is better for bass. It needs to be big, so the pressure inside that protects the speaker will not greatly lower the efficiency. One or more ports on the front preserve enough air pressure to protect the speaker, but kick the sound inside the cabinet out the front, thus increasing efficiency. After bouncing around inside the cabinet, the highs and mids are not coherent enough for any cancellation to occur. Putting in some baffling material on one of each set of opposing sides helps eliminate “boxy” sound that might result from midrange reverberation. The low resonance that results from the free resonance frequency of the speaker, combined with the resonant frequency of the inside of the cabinet, and path size of the structure leading to the port, can be tuned to match the shoulder where the speaker’s bass response begins to fall off (the opposite of cancellation). The bigger the speaker, the lower the shoulder will be, and the bigger the box must be to get a low enough resonance to enhance the shoulder. Placing a “reflex” tube or passageway behind the port or slot both minimizes any bass frequency wrap around and further drops the cabinet resonance frequency without adding cabinet size. Therefore, a closed-back reflex ported design (Thiele design) is a good compromise that is highly efficient, and is big but not huge. The trick to tuning these is to reinforce the shoulder smoothly, without creating excess resonance at any particular frequency. We’ve all heard that one note that booms out with cheap bass rigs.

A closed-back bass reflex or Thiele design for guitar or steel does not have to be as big as a bass guitar cabinet, simply because the strings are shorter, and not as low frequency. Therefore, the fundamental of the lowest string is not as near the shoulder of the speaker response. Reinforcement of the shoulder is less of a concern, so you don’t need a huge cabinet with a low resonance frequency and long reflex path. That’s why something like the Marrs cabinets work for steel, even though they are smaller than bass cabinets. The closed-back models protect the speakers, eliminate wrap-around, and kick all the sound out the front with good efficiency. Some closed-back steel and guitar speaker cabs just have port holes in the front baffle, with no reflex tube. I have found that putting tubes on those eliminates some bass wrap around and improves the bass response a little. Another trick I have used is to take the amp chassis out of a combo (to put in a head cab), put a closed back on the old combo cab, and use the open chassis slot as a port. That’s a pretty big port, with substantial bass wrap-around, so I use a 6-8” wide board to make a shelf below the port and leave an inch or two clearance between the back of the board and the cab back. This creates a reflex path that eliminates some wrap-around and noticeably improves the bass response. My reflex ported Marrs cabs and converted reflex combo cab are not precisely tuned. So they may have non-optimum shoulder response or uneven resonances for a bass, but if so, these problems must be below the lowest string fundamental on my uni pedal steel, because I don’t notice anything wrong down there. These cabinets are very efficient and have great lows for C6 or uni. With two Marrs type cabs, you don’t have to worry about directionality – you just angle the two speakers any way you want.

I don't know the meaning of "near field" and "far field," but it sounds like it has to do with how far you intend the listener to be from the speaker.

------------------
Student of the Steel: Zum uni, Fender tube amps, squareneck and roundneck resos, tenor sax, keyboards

[This message was edited by David Doggett on 20 June 2006 at 05:43 PM.]

Bill Creller · Post by **Bill Creller** » 20 Jun 2006 2:56 pm

This is all great info on cabs. I read something about this in a book on guitar amp theory a while back.
Actually , I quit a band once when they decided to get a drummer. I like a nice tight bass without all the tone-less clatter from drums. (just an opinion)

David Higginbotham · Post by **David Higginbotham** » 20 Jun 2006 6:51 pm

Here are the closed back cabinets I made with two inch ports in the front. They are 18x18x11 and made of 3/4 inch pine. The baffles are particle board. They sound fantastic and have all the lows I could ask for.
Dave

[This message was edited by David Higginbotham on 20 June 2006 at 07:53 PM.]