# Speaker sensitivity question???



## Stratin2traynor (Sep 27, 2006)

Let's see if I can explain this properly: from what I understand speaker sensitivity (Spl) will make a huge difference in perceived loudness (101 db speaker sounds twice as loud as 98 db speaker). Also a 16 ohm speaker in an 8 ohm tap will not be as loud as an 8 ohm speaker in the same tap, hence the volume drop when you plug in an extension cab (8 ohm internal speaker + 8 ohm cab = 16 ohm).

So my question is...Will the volume reduction be cumulative? 

Here's the reason why I ask. Love my DRRI but it is VERY loud for this basement rock star. I swapped the stock 8 ohm speaker for a 16 ohm Tone Tubby Ceramic (SPL = 96db?? I think). Awesome tone, still gets loud but a lot more reasonable. Just for the hell of it, I swapped the TT for an Eminence RWB (Spl = 101 db) then used the same settings as with the TT. Wicked tone but it was so loud it almost ripped my face off. When I turned it down to a reasonable basement level, it lost it's magic. Obviously the speaker needs to be pushed to sound great and it sounded fantastic at what I think were gigging levels.

The second part of the reason is that I want to build or buy a 2x12 cab for another amp in which I'm going to put 2 Tone Tubby's. I'm wondering if I should buy an 8 ohm TT for the DRRI and another 16 ohm for the cab. How much louder will the 8 ohm TT be on it's own in the DRRI?????.

Hopefully what I've written makes sense. If not let me know.


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## Wild Bill (May 3, 2006)

Stratin2traynor said:


> Let's see if I can explain this properly: from what I understand speaker sensitivity (Spl) will make a huge difference in perceived loudness (101 db speaker sounds twice as loud as 98 db speaker). Also a 16 ohm speaker in an 8 ohm tap will not be as loud as an 8 ohm speaker in the same tap, hence the volume drop when you plug in an extension cab (8 ohm internal speaker + 8 ohm cab = 16 ohm).
> 
> So my question is...Will the volume reduction be cumulative?
> 
> ...


Well. let's go back to the start. 101 db is NOT twice as loud as 98 db! A 3db change is the smallest change a typical human ear can notice. So you'll notice which speaker is louder but it won't really be that noticeable.

With a solid state amp, a 16 ohm speaker will not be quite as loud as an 8 ohm speaker. Solid state amps don't have impedance taps, as a rule. They don't normally need them. The output goes up as the speaker load goes down, until you hit the design limit. Go lower and the transistors will work so hard they might blow!

Tube amps have different taps to maintain the same load on the plates of the output tubes. However, a mismatch like plugging 16 ohms into an 8 ohm tap might actually get a bit MORE power! If you looked at the data sheets for an output tube you'd see that there is no specific "best" load. Rather, there are curves over a range of load for power output and also for lowest distortion. The curves can be rather broad. Sometimes designers might go for least distortion rather than max power, or vice versa, or even a compromise.

Whatever, I guarantee there won't be enough difference either way that you can hear it!

When you wire speakers up in combinations like 2 16 ohms in a 2-12 or a 16 in an extension at the same time as an 8 ohm internal you get a combined load of less than 8 ohms. The amp sees the entire combination. Also, if the speakers are different loads then the 8 ohm speaker will hog twice as much power as a 16. If you put two 16 ohm speakers in an extension cab in parallel you get 8 ohms. Plug that in with your 8 ohm internal speaker and you'll get a total of 4 ohms but the internal speaker will be twice as loud as the extension cab, even though it has TWO speakers in it!

To make it more complicated, a brighter voiced speaker will fool your ear into sounding louder than a darker one. Also, an open backed cab sounds louder than a closed one.

Dizzy yet?:smile:

:food-smiley-004:


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## Stratin2traynor (Sep 27, 2006)

Whhoooooooaaaa. I'm spinning. Thanks for the info. So where does this 3 db perceived loudness thing come from? I've read it a few times on different forums.


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## Milothicus (May 22, 2007)

the decibel scale is a logarithmic ratio relative to 20 micropascals.

dB = pressure level
mPa = pressure

doubling the pressure leads to a change in level of 3dB.

SPL = 20*log(10^p/pref)

p = RMS of a pressure wave's amplitude
pref = reference pressure = 20 micropascals

if you double p, the result will be a change in SPL of 3.


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## Stratin2traynor (Sep 27, 2006)

Thanks Molithicus. I will try to wrap my head around that. What effect if any does that have on how loud we perceive it to be??


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## hollowbody (Jan 15, 2008)

In as plain speak as I can put it:

Every time a driver is pushed to put out an additional 3db, it requires double an amplifier's wattage.

So, your driver with a sensitivity of 96db in your DRRI that puts out 22 watts, can put out:
96db @ 1 watt
99db @ 2 watts
102db @ 4 watts
105db @ 8 watts
108db @ 16 watts
111db @ 32 watts (if the amplifier can put out this much juice at full clip)

This is what Milothicus was getting at with 


Milothicus said:


> doubling the pressure leads to a change in level of 3dB.
> 
> SPL = 20*log(10^p/pref)
> 
> ...


With this in mind, if you keep going, it's shocking to learn that a 200 watt amp is not twice as loud as a 100 watt amp. In fact, it's theoretically only 3db louder


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## Stratin2traynor (Sep 27, 2006)

Alright, F*&^ it! I quit playing guitar. This is too confusing....Just kidding. Thanks for the info people. I will put it to good use in my quest for tone.

:food-smiley-004:


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## greco (Jul 15, 2007)

Stratin2traynor said:


> Alright, F*&^ it! I quit playing guitar.
> :food-smiley-004:


I just love these threads.....nothing like a bit of math and physics to get one's neurotransmitters blowing biological "fuses" all over the place and then slowly grinding to a complete halt.....LOL

Cheers

Dave


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## Adicted to Tubes (Mar 5, 2006)

You are not losing it at all.There is a real big difference from a speaker with say 98 spl and a 101 spl.It is quite a difference indeed at basemant home levels.
Despite what Wild Bill says,it can be a huge difference.
However,getting that magic tone is not going to be achieved by changing the speaker to a lower SPL rating.It would be better to get an attenuator and get that level down to a more basement friendly level and leave the great sounding speaker alone.
By the way,that jump from a 100 watt amp to a 200 watt amp is likely to finish off whatever hearing you had left after the 100 watter ripped your ears to shreds.:rockon2:
It may be only 3dB but that 3dB is enough to make your brain bleed.

www.claramps.com


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## dwagar (Mar 6, 2006)

I had a pretty interesting experience with this.

I own an old '70 Dual Showman JBL cab (the big cab). My singer uses it for guitar with his old Bandmaster head.

I had it loaded with a single JBL E130 8 ohm. These appear to be rated at 105dB. A really nice clean, and loud, JBL.

I finally got around to loading the cab with the original D130Fs. 2x8 ohm, so it became a 4 ohm cab. Pushing twice as much air now too. So I assumed it would be louder than the 1-15". It wasn't. I think, but I'm not positive, D130F are about 97dB. Not a huge power difference, he had to turn up from about 1 1/4 to 1 1/2, lol, but there was a difference.

I was quite surprised how much power the E130 will deliver.


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## hollowbody (Jan 15, 2008)

Adicted to Tubes said:


> By the way,that jump from a 100 watt amp to a 200 watt amp is likely to finish off whatever hearing you had left after the 100 watter ripped your ears to shreds.:rockon2:
> It may be only 3dB but that 3dB is enough to make your brain bleed.
> 
> www.claramps.com


You betcha! But it really chaps my ass to hear salespeople try to convince someone that a 200w amp is twice as loud as a 100w. It's a time-honoured sale tactic that I can't stand, so I thought I would put it out there. 

Yes, a 100w amp grooving along at full clip will ruin your ears real quick, so that extra 3 db won't be hugely noticeable (as Wild Bill pointed out), but at those levels, it's elementary anyway.


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## dwagar (Mar 6, 2006)

I've read it's about 10x to double, ie, a 500 watt amp is 2x as loud as a 50 watt amp.
and a 5 watt would be 1/2 as loud as a 50 watt amp.

and then there's the tube v solid state difference too.

there's a lot more to the sound chain than just wattage.


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## Milothicus (May 22, 2007)

on a related note, if you have two sources each one producing 100 dB at a point, the sum of the two will be 103 dB.

summing two equal sources producing X dB equals X+3 dB.


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## hollowbody (Jan 15, 2008)

Milothicus said:


> on a related note, if you have two sources each one producing 100 dB at a point, the sum of the two will be 103 dB.
> 
> summing two equal sources producing X dB equals X+3 dB.


Hmm, I'd never actually looked at it that way, but it makes perfect sense! Although it seems more strange that two sources combined will only results in +3db than it does to think that doubling RMS wattage in a single source will result in +3db. I dunno, just the way my brain is wired to think, I guess.


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## Hamm Guitars (Jan 12, 2007)

If you want to just do a speaker swap then use high powered PA speaker drivers. There once was a manufacturer called 'Gauss' that you had to pump a fair amount of power through before they would start to come to life. EV's tend to be the lightest and most efficient.

Changing to a PA speaker might not give you what you are after though as the speaker is not designed to break up, they are made to deliver clean audio. Putting them in an open back cabinet would probably overcome some of this, but it still might not be what you are after.

You could mess with the suspension on your current drivers if you were going to toss them aside anyway. Silicone the surround and the spider and the efficiency will go out the window.


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## NB-SK (Jul 28, 2007)

dwagar said:


> I've read it's about 10x to double, ie, a 500 watt amp is 2x as loud as a 50 watt amp.
> and a 5 watt would be 1/2 as loud as a 50 watt amp.
> 
> and then there's the tube v solid state difference too.
> ...



I don't know if that's exact, but it seems right. 

My brother freaked out when he saw my 100 watt Traynor, "100watt? You don't need something that big. My buddy has one of those, he said it was too loud so he sold it." He's never heard my 20 watt tube amp and his friend has obviously never used the volume knob on his guitar.


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