Speaker Cabinet Frequency Response

[Ron Worley]

This might the dumbest question ever, but what are the differences in frequency response for closed back cabs versus the many types of open back cabs?

My gut sense is that the open back will be better for long waves in the low frequency range because of the back pressure of a closed cabinet... but I may be totally smoking crack....

Also, I seem to recall that speakers lower to the ground project bass frequencies better, i.e. the lower speakers in a Marshall 4x12....

Any thoughts and insights are appreciated!

Ron

[skyboltone]

Ron this is about the deepest subject there is I think. The golden ear crowd in the hi-fi world fight about this stuff all the time.

Reflex cabinets (ported) get the most (if not the best) bass response, (provided the driver is designed for it). See what I mean? Everything is a maybe ahhhh depends.

Good luck. I like open back guitar cabs just about exclusively except sometimes I like closed back, like Marshall 1960A/B maybe. Depends.

Dan

[Andy Le Blanc]

with an acoustic instrument the body of the instrument is what "couples" with
room projecting sound......with an electric instrument its the speaker
the type of box that the speaker is in determines how it is "coupled" to the room....
an open back will allow more "coupling" with the room and how it responds
a closed back projects more efficiently with better definition or focus and the
room is less determinant to its over all tone....

[billyz]

Actually open back speaker cabinets have worse Bass response due to the comb filter wave cancellation of frequencys. The longer bass wave are more affected than the shorted higher waves. Placing the speaker on the floor or nearer a wall increases the boundary effect, which affect the lower frequencies more. A corner placement has the most Boundary effect.

Sound radiates from a driver in different ways. Higher frequencies act like a ray and move in straight lines from a point. As you get lower in the spectrum, they begin to radiate more like a sphere. By the time you get below 500Hz or so, you're getting pretty spherical radiation. By the time you get to 125, it's purely spherical.
imagine sound coming from a driver at say 100 Hz that is coming directly at you. There are other waves that are wrapping around the cabinet and bouncing off the front wall and then back at you. When 2 waves of the same frequency meet in this way (one direct, one having bounced off the front wall) there is an interface of the 2 waves . This is the Boundary effect.

Boundary effect occurs when the 2 waves happen to be in phase with each other. This yields a reinforcement of that frequency or a peak in response. Destructive interference occurs when the 2 waves are 180 degrees out of phase. This yields a partial cancellation of that frequency (the bounced wave has less amplitude) resulting in a dip or null at that frequency.

This can cause WILD variations in frequency response. However, one can sometimes use this to your advantage. If you play with speaker positioning in relation to the front wall (behind the speakers) and the side wall, you can 'tune' the response changes. This can be beneficial when attempting to smooth overall response.

[Jammin'John]

I prefer open back guitar cabs because the sound goes everywhere !
An open back combo on top of a ported cab is a HUGE sound with tight bottom.

JJ

[Ron Worley]

Thanks for the insights guys....

Next question, how does one go about tuning a closed back cabinet port- I imagine that port size (length, diameter) and placement all are important...

Ron

[skyboltone]

Ron:
Use this program

http://www.diamondcut.com/boxplot.htm

[Stanz]

I admittedly have little experience around guitar speakers & cabinets. One question about closed back cabinets, isn't there a resonance frequency depending upon the size of the cabinet. Obviously, it would be in the shorter waves as they bounce of the back and are either in or out of phase with the speaker itself?

[muchxs]

This might the dumbest question ever, but what are the differences in frequency response for closed back cabs versus the many types of open back cabs?

My gut sense is that the open back will be better for long waves in the low frequency range because of the back pressure of a closed cabinet... but I may be totally smoking crack....

To hear the extremes of an open back cabinet simply hook up a speaker without a cabinet. Just a bare naked speaker. It will sound miserable because you're getting maximum phase cancellation between the wave from the back of the speaker and the wave from the front of the speaker.

A poorly designed open back will lose bass due to phase cancellation. So will abitrarily cutting ports in the front of the baffle. One vendor touts his "full frequency port" on the front of the baffle as the best thing to come along in years. IMHO it ain't so.

The other extreme is a closed back cabinet. No chance of phase cancellation there unless you wire the speakers out of phase. The closed back tends to damp speaker motion so the cabinet may be more articulate for extreme distortion tones.

Bass ports... leave those for the kids who want boomy poorly defined bass for their autosound systems. We don't need that kind of low frequency extension for guitar. To my ears the lack of definition and articulation isn't beneficial, either.

"De-tuned" cabinets: They're just fine if you like carrying oversized overweight cabinets. I've spent years making compact cabinets perform. Think about it: If Bose can make compact hi-fi and sound reinforcement systems perform at a high level why can't we?

Speaker choice makes an enormous difference as well. The wrong speaker in the wrong cabinet will make the best amp on earth sound like junk. Matching speakers with cabinets is an endless discussion, everyone has an opinion there.

[Richie]

and to complicate things even more, i've had cabs that would sound great no matter what speakers you had in it..and i have had, cabs that no matter what speakers you used they sounded like crap.
As for other things, most fender open back cabs i have seen,the phase of the speaker pushes in. In the closed back cabs the speakers push out..
I'm sure you could try this for yourself and see if it sounds different..

[muchxs]

and to complicate things even more, i've had cabs that would sound great no matter what speakers you had in it..and i have had, cabs that no matter what speakers you used they sounded like crap.

I use Eminence Legend 10516s in my "signature" cabinets. There is a long list of reasons I use that particular speaker that I won't go into here. Suffice to say it's a killer sounding cabinet, I can plug anything into it and it sounds better. Comparing apples to oranges there's one large speaker array what will give it a run for its money although the cabinet will hold its own against most competition.

One of my customers spent big bucks for a pristine pair of JBL D110s. I had high hopes for the D110s, they're a smaller version of the D120s and I like D120s. Well... it's going to take some work to make these sound good for guitar in my application. They have a shrill top end, great for pinch harmonics but... no bottom end. They work well as midrange drivers for sound reinforcement.

Referring your theory... a wide range of speakers sound great in that particular cabinet but not the D110s.

Next counterpoint: We all have our favorite Celestions but not all Celestions are my favorites. What's their latest, they have a speaker "with no big bottom end to clutter up the tone". I like a speaker that goes down to at least 100hz before it rolls off severely. No bottom end equals shrill sounding. Maybe that works with some of the modeling amps where you can tweak your EQ well beyond our usual passive tube circuits but... none for me, thanks.

It's a fine balance. Many guitar speakers are good down to around 80hz which is o.k., they're guitar speakers. That's all they need to do.

It's pretty easy to build a guitar cabinet that sounds horrible no matter what. I'd use a tuned port to create a resonant peak as low as I could get it. I could easily create a big spike in the frequency response down around 35hz. Then I'd comb out frequencies between 80hz-150hz. For icing on the cake I'd use a passive crossover and a couple piezo tweeters for the top end.

[doveman]

I use Eminence Legend 10516s in my "signature" cabinets. There is a long list of reasons I use that particular speaker that I won't go into here. Suffice to say it's a killer sounding cabinet, I can plug anything into it and it sounds better. Comparing apples to oranges there's one large speaker array what will give it a run for its money although the cabinet will hold its own against most competition.

I use a 2x10 sealed cabinet with Emi Legend 10516s. They came with the cabinet and I fully expected to replace them ... but I like the way they sound. I know if I like the way they sound, nothing else really matters. But I wonder why such a reasonably priced speaker sounds so good. Any experience with these in a sealed cabinet? Is your cab open back or ported? I'd be interested to hear some of that long list.

Sorry for the momentary ... slightly off topic question.

[muchxs]

I use Eminence Legend 10516s in my "signature" cabinets. There is a long list of reasons I use that particular speaker that I won't go into here. Suffice to say it's a killer sounding cabinet, I can plug anything into it and it sounds better. Comparing apples to oranges there's one large speaker array what will give it a run for its money although the cabinet will hold its own against most competition.

I use a 2x10 sealed cabinet with Emi Legend 10516s. They came with the cabinet and I fully expected to replace them ... but I like the way they sound. I know if I like the way they sound, nothing else really matters. But I wonder why such a reasonably priced speaker sounds so good. Any experience with these in a sealed cabinet? Is your cab open back or ported? I'd be interested to hear some of that long list.

The short list of why I use the 10516s:

They're the only 10" speaker Eminence makes for guitar in 16 ohms. I wish I had a choice in 10" Redcoats.

16 ohms in paralell results in an 8 ohm load. I'll go as low as 4 ohms. 2 ohms looks like a short to me. More load rather than less works better with tubes IMHO.

My cabs are semi-open.

If they didn't sound good I wouldn't use them. The spec sheet can be misleading, they look weak on the bottom on paper. The reality of it is they have a good tight bottom end without the flab of 12" speakers. In multi speaker setups they couple with each other.

[skyboltone]

Well, I'll jump in here. My favorite cab is my open back 4/10" with Eminence 1058s. Series parallel wired for 8 ohms. Very complex harmonically, great tight bass and pretty loud too. I've got a 1258 waiting for something to pair it with in a 2 something cab. I might stick it with a Celestion 12-65. I dunno. Maybe another 1258.

[doveman]

I mix my 2x10 Emi 105 8ohm sealed cab with a 1x12 G-1265 8ohm open back cab (4ohm load together) and mix them through a Bluetube stereo mic pre-amp. Each has a Sennheiser e609 mic on it. A little heavier on the 10s is a whole different sound than a little heavier on the 12 - but they are both better when played together.

The head is a D'Lite 22/33 ... so it has it's own sound but I'd say the Emis have a bit of a Fender-ish tone while the Celestion has a bit of the Brit-ish tone. But again just a hint.

I really like the feel they have when blended like this. It's all good.

OK ... back on topic ... sorry for the temporary sidetrack.