Open back cab: harder on speakers?

[michael c]

I just read on this forum that an open back cabinet is harder on a speaker (in my case 2 Greenbacks) than a closed back cab. Is this true? If yes, why is that? I have a Divided by 13 closed back cab w/ 2 Greenbacks and was thinking of using the cab with it's open back option. I have a 50 watt Marshall that I sometimes run with this cab with no issues, but know I need to be careful and don't want to push my luck even more....

Thanks.

[Soundstorm]

My guess is that it would be the opposite, since the trapped air in a closed back would make the speaker move more.

[Darth Tater]

I would think that air in a sealed cabinet would act as a 'cushion' and actually be better for the speaker. I don't know though. I don't think it really matters much for guitar speakers, but subwoofers would make a big difference. That's why 'free air' subs are built with very heavy/stiff suspension.

[bosstone]

An open back cab is going to be more efficient (louder) so, if you compensate by turning the amp down, to get equal loudness, I doubt that there would be a significant difference. I wouldn't worry about it.

[aeolian]

A guitar, directly amplified into a speaker (as opposed to miced and reproduced somewhere) has some pretty tremendous low frequency transients going on. Just look at a cone sometime when you are playing. Any ported or open cab unloads the speaker below the resonance of the port. A sealed cab has increasing resistance as the excursion increases (with lowering frequencies) due to the air acting as a spring.

So yes, for this reason, an open back (or any ported) cabinet will allow the cone to move further and thus be "harder" on the speaker.

[Figher53]

Boy, learn something new every day...

[riverastoasters]

Originally Posted by aeolian

Any ported or open cab unloads the speaker below the resonance of the port. A sealed cab has increasing resistance as the excursion increases (with lowering frequencies) due to the air acting as a spring.

So yes, for this reason, an open back (or any ported) cabinet will allow the cone to move further and thus be "harder" on the speaker.

Of course, by the same token, the closed back cab loads the speaker and the low frequency energy is not radiated acoustically. So more of it ends up in heat.

So the closed back cab is "harder" on the speaker motor.

[mmorse]

Small magnet speakers when pushed passed their operating limits would benefit a little from a closed back cab because the back wave would help reinforce the speakers suspension and curtail cone excursion. Bass is created by moving air and that requires max cone excursion. Small magnet speakes like greenbacks can't control cone excursion as well as larger magnet speakes. That's why Greenbacks flub out in the bass when pushed hard in an open back cab.

So yes, open cabs are harder on small magnet speakes but only when the speaker is being pushed beyond it's practical operating limits.

[Mr. Mandolin]

so its really all just theory and not of much importance in the real world?

[Craftmatic]

Originally Posted by mmorse

Small magnet speakers like greenbacks can't control cone excursion as well as larger magnet speakers. That's why Greenbacks flub out in the bass when pushed hard in an open back cab.

mmorse -

What do you mean by "flub out in the bass?" I have an Emi Legend GB12 (based on the Greenback) that gets quite buzzy on the low E string when I crank it in an open back combo - the Peavey Classic 30. When I have the volume somewhere between 10 O'Clock and noon it gets buzzy. The rest of the strings have a nice speaker breakup going on but the bass buzziness bothers me. I'm used to a G12H30 in that amp (with a 50 oz. magnet) and the bass remains more controlled at high volumes although the low E string still gets a bit buzzy, but nowhere as loose and indistinct sounding as the GB12.

I am worried that I might have caused this by breaking in the GB12 too hard with bass-ey CDs played through it and damaging the speaker. However, the speaker sounds lush, beautiful, clean and controlled at a fairly-loud-but-not-ear-splitting-volume at about 9 O'Clock - and and the low E string/bass register is full and rich. BTW, the speaker has been described on one dealers website as having fast break-up. I just can't tell if the "flub-out" is normal for this speaker. (The Classic 30 experiences tube saturation clipping at the volume mentioned above as well - I can't tell how much is the speaker and how much is the preamp).

[aeolian]

The classic 30 has a pretty small output transformer and doesn't have the best control of the speaker cone. 30 watts is pretty much a distorted output on that amp. So it definitely benefits from a tighter speaker with more self control. i.e. a heavier magnet.

I doubt you broke the speaker in too hard. As long as you don't exceed the cone excursion limits, which you are way more prone to do playing a guitar through it than playing pre-recorded bass tones, you will have just approximated some point in the cone and surround's lifetime.

[Craftmatic]

Originally Posted by aeolian

The classic 30 has a pretty small output transformer and doesn't have the best control of the speaker cone. 30 watts is pretty much a distorted output on that amp. So it definitely benefits from a tighter speaker with more self control. i.e. a heavier magnet.

I doubt you broke the speaker in too hard. As long as you don't exceed the cone excursion limits, which you are way more prone to do playing a guitar through it than playing pre-recorded bass tones, you will have just approximated some point in the cone and surround's lifetime.

That is the most technical and astute feedback I've gotten on this issue. What you say rings so true for me - in fact I can actually feel the tightness of the G12H30 when I bend strings - it almost feels like the strings have more tension, while the GB12 makes the strings feel/sound looser. I thought it was because of a stiff cone on the G12H30, so I'm trying to break that in too.

The music I play through the speakers to break them in are jazz recordings, Grateful Dead, AC/DC and the Stones, so there's more than just pre-recorded bass. I turn the treble down, the bass up and push the volume up to a loudness that seems just shy of pushing the speaker too hard. I'm letting you know this because it seems like you thought I was using pre-recorded bass tones and I want to make sure, again, that I'm not damaging the speaker.

Thanks again for the great feedback.

[mmorse]

Originally Posted by Craftmatic

mmorse -

What do you mean by "flub out in the bass?" I have an Emi Legend GB12 (based on the Greenback) that gets quite buzzy on the low E string when I crank it in an open back combo - the Peavey Classic 30. When I have the volume somewhere between 10 O'Clock and noon it gets buzzy. The rest of the strings have a nice speaker breakup going on but the bass buzziness bothers me. I'm used to a G12H30 in that amp (with a 50 oz. magnet) and the bass remains more controlled at high volumes although the low E string still gets a bit buzzy, but nowhere as loose and indistinct sounding as the GB12.

I am worried that I might have caused this by breaking in the GB12 too hard with bass-ey CDs played through it and damaging the speaker. However, the speaker sounds lush, beautiful, clean and controlled at a fairly-loud-but-not-ear-splitting-volume at about 9 O'Clock - and and the low E string/bass register is full and rich. BTW, the speaker has been described on one dealers website as having fast break-up. I just can't tell if the "flub-out" is normal for this speaker. (The Classic 30 experiences tube saturation clipping at the volume mentioned above as well - I can't tell how much is the speaker and how much is the preamp).

What I mean by flub out is the bass gets loose and uncontrolled or poorly defined. In extreme cases the bass actually diminishes as cone excursion exceeds the speaker's safe limits.

[Craftmatic]

Originally Posted by mmorse

What I mean by flub out is the bass gets loose and uncontrolled or poorly defined. In extreme cases the bass actually diminishes as cone excursion exceeds the speaker's safe limits.

Thank you for getting back to me. It makes sense to me now.