New to the forum: 16 Ohms speaker in a 5:50 1x12"?

[GoranS]

Hi everybody.

I'm new to the forum. Some week ago I got my first Mesa Boogie, an Express 5:50. Purchased it used but it's in mint condition, the amp was originally purchased in Nov 2007. It's an awesome amp! I play mostly blues/soul and funk with clean or medium overdrive and the amp suits me real good!

Then for the question;
While changing power tubes I noticed that the single 12" speaker (A Mesa Black Shadow MC-90) is stamped 16 Ohms. Reading the manual it states that it should be an 8 Ohms speaker. Is this common, and if not has the speaker at some point been replaced?? Are there any disadvantages?

And if I would like to add an external cab will there be any negative effects? Should I be concerned?


Edited to add: When measuring the DC resistance it reads 7 Ohms. Compared to another Celestion equipped 8 Ohms cab I own which reads 6.5 Ohms DC resistance.

 

[J.J]

Hi and welcome !

With your speaker, it sounds like it was not correctly labled to me. The impedance you measured makes it an 8Ohm speaker. Most 16 Ohm speakers will measure around 12 to 13 Ohms.

If it was a 16Ohm speaker it would be about half as loud since the highest speaker output tap is 8Ohm.

 

[GoranS]

Thanks J.J

Thanks for confirming my suspicions. Some more detective work lead me to the conclusion that the speaker is actually wrongly labeled 16 Ohms instead of 8.

Over at the Celestion site they have pdf data sheets of their speakers and the one that most closely resemble the Mesa/Celestion Black Shadow is the Celstion G12-100. Give or take a couple of watts... In the downloadable pdf data sheet they notes the DC resistance of all their speakers. This 8 Ohms speaker have a DC resistance of 7 Ohms. Just as mine!

Which makes me draw the conclusion that my MC-90 speaker is the right one with the wrong label.

Thanks again J.J

 

[soundchaser59]

If it was a 16Ohm speaker it would be about half as loud

I question that assertion......

That's like saying a 50 watt amp is half as loud as a 100 watt amp, and I dont think that's true. I think it's more like a 10 watt amp is half as loud as a 100 watt amp. You need 10x the power to double the volume. My electronics and physics may be flawed, but I know from first hand side by side that a 16 ohm speaker plugged into the 8 ohm jack is not half as loud as an 8 ohm speaker. It has a bit less low end response, maybe not quite as full sounding, but it is not half as loud. At least, I wouldn't describe it that way.

 

[GoranS]

soundchaser59:

Anyway I know what he meant although not completely true. Actually:

- A 16 Ohms speaker is in theory 3 dB weaker than an 8 Ohms speakers which is equivalent of half the effect.

- If you increase the sound level to what the ear experience doubling of the sound level you'll have to increase the signal level by 9 to 11 db depending on who's ears you use for reference. This is usually approximated to 10 dB.

- If you increase the effect by the factor 100 the level will increase by 20 dB. The formula is: 10log(P1/P2) => 10log(100/1) => 20 dB

/G

 

[Newysurfer]

soundchaser59:

Anyway I know what he meant although not completely true. Actually:

- A 16 Ohms speaker is in theory 3 dB weaker than an 8 Ohms speakers which is equivalent of half the effect.

- If you increase the sound level to what the ear experience doubling of the sound level you'll have to increase the signal level by 9 to 11 db depending on who's ears you use for reference. This is usually approximated to 10 dB.

- If you increase the effect by the factor 100 the level will increase by 20 dB. The formula is: 10log(P1/P2) => 10log(100/1) => 20 dB

/G

I often run a 16 ohm cab into the 8 ohm jack on my 5:50.
Plus in my job at the EPA I deal with a lot of industrial noise issues.
I assess EIS's and apply noise limits to industries and large construction jobs.

1) I can't hear any volume difference at all when I plug the 16 ohm cab into the 8 ohm jack as compared to the 8 ohm into 8ohm.

2) 3 dB is the audible increase threshold for most people. Meaning - if you increase volume by 3 dB more that is the threshold that the average person will be able to report a very slight volume increase. At 2 dB no-one can hear any volume change. At 3 dB it's barely audible. At 5 and 6 dB it becomes slightly more noticeable etc. It's not til you hit 8 or 9 dB increase / decrease that people will notice a significant difference

 

[GoranS]

"I can't hear any volume difference at all when I plug the 16 ohm cab into the 8 ohm jack as compared to the 8 ohm into 8ohm."

Yes you're right. I do not think you (or I) would either. The volume drop depends on the transformers secondary impedance and how it performs, and the theory becomes quite complex. The volume drop is probably below the threshold of what a normal ear can detect.

Interesting to note that some sources of information (Wikipedia for one) states that it's possible to hear a difference in level by 1 dB. I do not think thats correct because I've learned and always believed that a 3 dB change in level is what the ear can detect.

If you compares two sounds on the other hand, for instance when doing a mix, it IS possible to detect a 1 dB change in one of the signal sources. But that's the way out brain works, it is great to detect differences compared to a reference for instance in sound, light or movement. But that's a whole different story.

 

[J.J]

1 dBA is the accepted minimum change that humans can detect. 3 dBA is very easy to pickup. The thing is though that our ears are very non linear across the range. Not only are we more sensitive to some frequencies than others, but the level also effects things. in audio, 1 dB doesn't really mean much it needs a reference. With dBA the reference is set to the human thesshold.

As far as power goes, doubling the speaker impedance will almost half the power going to the speaker and that will then be a 3dB loss and run half volume.

Another fact that seems to be little known is that speakers suffer from power compression. Doubling the power does not double the volume. A given speaker can easily have 6 dB of power compression between 1 watt and full power. Often when I hear people telling me that more speakers move more air I think what they are really saying is that the power compression has been reduced by using more speakers to share load. The result is that the SPL is higher, possibly 3 dB or more.

Power compression is not usually reported in speaker specs and I have only seen it in JBL data. Everyone seems to like the 1watt@1 meter measuremeant, but unless you are only playing at 1 watt that all goes out the window very quickly.

So, while the 10 times the power may double the volume percieved at one end of the spectrum, it is certainly not correct at the other.

 

[StevenL]

I'll say that a 16 ohm external 4X12 with greenbacks with a 5:25 is a wonderful thing to behold. But I don't know about perceived volume. If you "perceive" a volume drop, turn up the treble knob one millimeter. 8)