2x12 drowning out a 4x12 ?

Voxman

Hi all you clever techies.  A facebook friend has a Vox Valvetronix AD120VT combo that has two stock 'Vox own' Celestion Seventy Eighty speakers, rated at 97dB.  He's just got himself a Vox V412BL extn cab that has 4 x 30w 16 Ohm GSH12-30 Wharfedale speakers (rated at 95dB I believe) - 16 ohm wired in parallel pairs to give Left and Right separate inputs of 8 ohms rated at 60 watts per side.

When running the extn cab together with the on-board Celestions, he said the Celestions are completely over-powering and drowning out the 4x12, so he's done a mod that lets him bypass the internal speakers so that he can enjoy the 4x12. He's put in a pair of breakout banana plug female connectors to access the amp outputs and put banana plugs on the internal speaker tails - so they remain plugged in and work as normal - but can be switched out by merely plugging other speakers in as required

Now, I appreciate that there's a 2dB sensitivity difference but nevertheless with 4 speakers pushing more air I'm still a little surprised that the 4x12 extn cab is being so overpowered.

Does this seem right to you guys? 

ecc83

Voxman said:

Hi all you clever techies.  A facebook friend has a Vox Valvetronix AD120VT combo that has two stock 'Vox own' Celestion Seventy Eighty speakers, rated at 97dB.  He's just got himself a Vox V412BL extn cab that has 4 x 30w 16 Ohm GSH12-30 Wharfedale speakers (rated at 95dB I believe) - 16 ohm wired in parallel pairs to give Left and Right separate inputs of 8 ohms rated at 60 watts per side.

When running the extn cab together with the on-board Celestions, he said the Celestions are completely over-powering and drowning out the 4x12, so he's done a mod that lets him bypass the internal speakers so that he can enjoy the 4x12. He's put in a pair of breakout banana plug female connectors to access the amp outputs and put banana plugs on the internal speaker tails - so they remain plugged in and work as normal - but can be switched out by merely plugging other speakers in as required

Now, I appreciate that there's a 2dB sensitivity difference but nevertheless with 4 speakers pushing more air I'm still a little surprised that the 4x12 extn cab is being so overpowered.

Does this seem right to you guys? 

Yes because there are so many variables.

Firstly you cannot be sure that the two speaker companies used identical conditions to measure sensitivity.

2) Sensitivity is subject to a tolerance as is everything and could be awry by + or -2dB.

3) Speakers of an identical sensitivity can vary in their subjective loudness because of response differences i.e. one speaker can be 'shoutier' than the other AKA 'harsh and middly'.

4) A 4 by 12 DOES have an intrinsic 'gain' over a single 12 (of the same type) but it only amounts to 3-4dB and against a 2x12 even less. In any case the extra whallop of a 4by is really only appreciated at some distance.

Dave.

ICBM

The Seventy/80 is actually 98dB - OK that's only 1dB more, but Celestion also typically rate their speakers quite conservatively, and (although I'm not a huge fan of its tone) it is not a quiet speaker. I wouldn't be surprised if the Wharfedales are *less* sensitive than their rating too.

If the 4x12" is closed-back it probably won't sound as loud in the room as the open-back combo either.

snowblind

If I'm reading the schematic correctly ( which I may well not be) the extension speakers are series'd with the internal speakers. In other words what's happening here is the two Wharfedales (which are in a parallel arrangement) are in line with with the 70-80 of each channel. Is that going to make a difference to the respective current delivery?

ICBM

snowblind said:

If I'm reading the schematic correctly ( which I may well not be) the extension speakers are series'd with the internal speakers. In other words what's happening here is the two Wharfedales (which are in a parallel arrangement) are in line with with the 70-80 of each channel. Is that going to make a difference to the respective current delivery?

You’re correct, but the internal speakers are 8 ohm, so if the extension cab is also 8 ohms per side then the power will be equally split between the internal and external speakers.

That does mean that the individual speakers in the extension cab are each receiving half the power that the ones in the combo are, but that should still mean that overall, the 4x12” has about a 1-2dB advantage since there are double the number.

So I think the difference is down to speaker sensitivity, voicing (a more middy speaker sounds louder), and the cabinet type.

roberty

How can less be more? It's impossible

https://youtu.be/QHZ48AE3TOI?si=Nkkew93hA8WO4stK