Is there anything other than cool factor to be gained by multiple cabs on a single amp?

[rlmfire288]

In particular I have a SVT Classic and matching 8x10 fridge and several people tell me I can run 2 of the same cabs off this. I found that was how Ampeg originally meant for the large stage stups to be done with the SVTs back in the day. No one really does that from what I've seen. It would look cool, but take up soooo much space. Why would I? Why should I?

As far as my very limited electrical and speaker knowledge goes I feel I'd have great clarity of sound underdriving the speakers but have much less volume to work with. Lots of headroom with reduced volume potential? Or is there a better reason to dedicate that much more space to a giant cab?

Sorry if it's been covered before. I searched but ran out of desire to keep digging and just thought I'd ask.

 

[agedhorse]

More volume, slightly better low frequency extension.

 

[Downunderwonder]

Depends where you aim them and how much tolerance there is for hearing damage. A whole lot of real estate is going to be swamped in boom if you put in a big square 8x8 .

The title is rather misleading as it could include stacking little cabs sensibly like JimmyM does with his AV210 vertical rig.

 

[rlmfire288]

So I'd actually get more volume? Where's my logic off? And again I don't know much about the how and why of amps and electrical stuff so I won't be insulted by very basic amp speak.

My mind says 8 speakers powered by 300W becomes less by becoming 16 speakers at the same 300W. But it becomes more? Is this an effect of dropping the impedance by half?

 

[Wasnex]

In particular I have a SVT Classic and matching 8x10 fridge and several people tell me I can run 2 of the same cabs off this. I found that was how Ampeg originally meant for the large stage stups to be done with the SVTs back in the day. No one really does that from what I've seen. It would look cool, but take up soooo much space. Why would I? Why should I?

As far as my very limited electrical and speaker knowledge goes I feel I'd have great clarity of sound underdriving the speakers but have much less volume to work with. Lots of headroom with reduced volume potential? Or is there a better reason to dedicate that much more space to a giant cab?

Sorry if it's been covered before. I searched but ran out of desire to keep digging and just thought I'd ask.

You basically get +3dB in the low end form mutual coupling between the cabs, so the sound will be fuller and slightly louder. I believe the horizontal dispersion will be negatively impacted at higher frequencies. This could be a problem if you roam around the stage. Some people recommend cross-firing the cabs to broaden horizontal dispersion.

Early cabs were only rated for about 240W, so you needed two if you were going to really crank the amp. I believe modern 810Es will take way more power than an SVT can dish out.

 

[Wasnex]

So I'd actually get more volume? Where's my logic off? And again I don't know much about the how and why of amps and electrical stuff so I won't be insulted by very basic amp speak.

My mind says 8 speakers powered by 300W becomes less by becoming 16 speakers at the same 300W. But it becomes more? Is this an effect of dropping the impedance by half?

Two identical cabs will generate +6dB from mutual coupling. This only occurs for frequencies where driver to driver spacing is within 1/4 wavelength.

With a tube amp, the power remains the same when you add the second cab because of the output transformer. I.E. the amp makes 300W at either 4 or 2 ohms.

So when you add the second cab the power is distributed equally at 150W per cab.

When you cut power by half you lose 3dB (300W to 150W). Then you get +6dB from mutual coupling. The net gain is +3dB with a tube amp.

 

[rlmfire288]

You basically get +3dB in the low end form mutual coupling between the cabs, so the sound will be fuller and slightly louder. I believe the horizontal dispersion will be negatively impacted at higher frequencies. This could be a problem if you roam around the stage. Some people recommend cross-firing the cabs to broaden horizontal dispersion.

Early cabs were only rated for about 240W, so you needed two if you were going to really crank the amp. I believe modern 810Es will take way more power than an SVT can dish out.

The current 810 cabs from Ampeg, including mine, are 800W capable. But get driven by 300W? And the same 300W would drive twice the quantity better? I'm so confused. Inspired but confused.

 

[Blues Bass 2]

Intsead of having 8 speakers driven with 300 watts you would have 16 driven by 300 watts . Of course it would be louder . 16 trumps 8 for volume every time with the same power . Tube SVTs are crazy powerful anyway .

 

[rlmfire288]

Huh. Ok. I kinda get it, kinda not really but I'm willing to accept it as fact. The Amp output is 300W going to each speaker regardless of quantity. Be it 8 or 16, or even just 1? My little mind said it's 300W/# of speakers. Not so? Then the amperage going out increases and the impedance drops by half as well then?

 

[ThisBass]

Two identical cabs will generate about +3dB of SPL from improved radiation impedance.
This means that electrical input power will be +3dB better transformed into acoustical output.

In first place that's totally independent of acoustical coupling of sources.
In second place we might consider some average loss off axis IF the sources don't couple anymore.

btw we have got 100% of acoustical coupling for sources which are not more apart than 1/4 of wavelength. At the other hand side we will get comb filter effects if the sources distance equals 1/2 the wavelength.

So you may ask a question what might happen between 1/4 and 1/2 of wavelength?
Good point.

Its nothing but a "transition" bandwidth where there is coupling and comb filter effect just "side by side". As usual there is no free lunch yet trade offs.

 

[DoctorZee]

Huh. Ok. I kinda get it, kinda not really but I'm willing to accept it as fact. The Amp output is 300W going to each speaker regardless of quantity. Be it 8 or 16, or even just 1? My little mind said it's 300W/# of speakers. Not so? Then the amperage going out increases and the impedance drops by half as well then?

No, you were right. The wattage is divided evenly to each speaker. But that doesn't affect the volume output. What does affect it is total speaker area. Basically you have twice as many cones pushing air.

 

[Normando Neto]

To me, seems that cone area matters. More air being pushed, more sound. Am I right, fellas?

EDIT: Ops! Posted at the same time. ^^^

 

[sawzalot]

Yes. You can gain either 1) chiropractor expenses, 2) roadie expenses, or 3) the ire of your bandmates. I personally would rather invest in PA subwoofers and power amps than bass cabinets, but that's just me.

 

[bassicmike]

It would look cool. No. It would look unbe-effing-lievabley COOL!!

Say. no. more.

 

[Coolhandjjl]

No one wants to lug two ‘fridges around.
No one...

 

[Happy Face]

In general I prefer to have two single speaker cabs than a pair of drivers in one cab when playing out. That way if you blow one speaker out, you still have one working cab. Or one to lend to a knuckleheaded keyboard player or gitard who blows out their cab.

If you guys have the muscle and play venue sized to accommodate two SVTs, why not? Otherwise...

 

[_Some Dude]

No one wants to lug two ‘fridges around.
No one...

I would if I could get the gigs to support it...

 

[ThisBass]

More volume, slightly better low frequency extension.

This ^^^

 

[agedhorse]

So I'd actually get more volume? Where's my logic off? And again I don't know much about the how and why of amps and electrical stuff so I won't be insulted by very basic amp speak.

My mind says 8 speakers powered by 300W becomes less by becoming 16 speakers at the same 300W. But it becomes more? Is this an effect of dropping the impedance by half?

Yes, the total electrical power will be 300 watts split between either 8 or 16 drivers.

The acoustic power will be greater though, because of acoustic coupling, increased linearity (especially with the short voice coil overhang that Ampeg used to use), and the low frequency will increase.

These are real gains, not just something made up. Maybe a total of ~3dB plus maybe 5-8Hz greater extension.

 

[rlmfire288]

I think I can actually understand this a little. A very little, but enough that it makes sense. It's now clear to me that this has actual advantages. It's not just a visual gimmick. Thanks for the help.

Last question on this then - I promised my wife I'm done buying more amps and basses. I have plenty - BUT!! I am allowed to upgrade what I have, exchange one for one for better, for improvements, for that better sound, feel, etc., without getting prior approval. Soooo I'm thinking this isn't a new amp, it's a cab extension for - "better low frequency extension, linearity and acoustic coupling" & let us not forget "unbe-effing-lievabley COOL!!"

Can I convince her it's not an additional piece, but an improvement on existing stock?