• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Sensitivity and Impedance?

mufster

mufster

Well-Known Member
I have a pair of Mordaunt Short MS208's. Rated Power 15-200watts.
Sensitivity is 91db. Impedance is 6 ohms.

Two questions I would really appreciate a little guidance on.

1. Are these sensitive or not?

2. With an amp rated with speaker impedance of 8 ohm. Is it ok to run these speakers on it because they have an impedance of 6 ohm?

Paul
 
Register to hide this ad
mufster said:
I have a pair of Mordaunt Short MS208's. Rated Power 15-200watts.
Sensitivity is 91db. Impedance is 6 ohms.

Two questions I would really appreciate a little guidance on.

1. Are these sensitive or not?
Click to expand...

They are reasonably efficient.

2. With an amp rated with speaker impedance of 8 ohm. Is it ok to run these speakers on it because they have an impedance of 6 ohm?

Paul
Click to expand...

Yes.
 
Thanks for the response. Just out of interest. Regarding the sensitivity. Is it the higher the number or lower the number which indicates the better sensitivity?

Paul
 
Higher the number, the greater the sensistivity... the number is typically expressed as db/1w 1m... that is sound pressure level in decibels with the speaker being powered at 1 watt, measured at a distance of 1 meter from the speaker. The greater the sensitivity, the less power that will be required to make the speaker play "louder".
 
2. With an amp rated with speaker impedance of 8 ohm. Is it ok to run these speakers on it because they have an impedance of 6 ohm?
Click to expand...
That depends entirely on the speakers and amplifier involved.

If the amplifier is rated for a MINIMUM load of 8 ohms, a 6 ohm speaker should be disqualified. The math should be obviously that simple.

The cruxt of the issue will really be how the speaker's 6 ohm impedance was arrived at. Said speaker could have an erratic impedance curve that dips far below 6 ohms at certain frequencies, or it may have a fairly smooth and flat impedance curve with no significant dips. An 8 ohm minimum rated amplifier might play well and safely with the second speaker example whereas the first speaker example may quickly kill an 8 ohm minimum rated amplifier.

An actual graphically represented impedance curve of the loudspeakers in question would be far more useful and conclusive than the nominal impedance rating.
 
Thanks again for the information. I don't really have any information about the MS208's other than what I provided in my initial post. I bought these off a work mate. Just the speakers with no paperwork. They don't even state the specs on the speakers. There is a label on the back that says refer to the owner manual for setting them up. That's about it. I only found out the specs from various websites. After seeing about a dozen references that matched the specs as I stated, then I was sure those must be the specs.

I have run a few amps on these speakers without issue, but that isn't to say I've simply been lucky. Nearly all of them have been 8 ohm. My Sansui AU-G90X is set at 4 ohm and works fine with them.

So am I just lucky? Am I risking damaging my amps or speakers. The thing is, amps rated at 6 ohm are like hens teeth. Surely the manufacturer wouldn't create speakers that only connect to 6 ohm amps? Maybe I should contact the manufacturer and ask if they have a manual.

Paul
 
Don't worry about it. Any decent amp can handle speakers down to at least 4 ohms. You're fine. The ohm rating is just an average anyway. Speakers don't present a constant load to the amp as music is played. Amps deal with it.
 
My Sansui AU-G90X is set at 4 ohm and works fine with them.
Click to expand...
I'd be curious to know what the switch does since the service manual quite clearly limits the amplifier section to an 8 ohm minimum. I suspect it probably adds some series resistance to the speaker outputs, but that is purely a guess.

In my limited experience with 'sui gear, it is generally underrated and overbuilt. Your amp probably has enough safety margin built in such that you'll not have any issues, particularly running it in the 4 ohm position. However, this would not be a safe practice to assume with just any amplifier.
 
Wigwam Jones said:
Don't worry about it. Any decent amp can handle speakers down to at least 4 ohms. You're fine. The ohm rating is just an average anyway. Speakers don't present a constant load to the amp as music is played. Amps deal with it.
Click to expand...
That depends entirely on the speaker in question, some amps will deal with it by failing catastrophically.

Some speakers, i'll use certain planars as an example, have a nearly ruler flat impedance curve across the audio spectrum, and are an almost purely resistive load.

Other speakers can have very complex crossover networks, and/or multiple LF transducers that offer a load to the amplifier that is capacitive(can cause some amplifiers to oscillate), inductive, and have a fairly erratic impedance curve.

I would offer this thread about a fella's receiver shutting down when driving his 6 ohm speakers as just one example.

http://www.audiokarma.org/forums/showthread.php?t=551806

Note the posted impedance curve for his 6 ohm nominal speakers drops below 4 ohms at 55hz, bottoms out at ~2.5ohms around 100hz, and does not rise above 4 oms again until it's above 400hz. That covers almost all of the fundamental bass range and well into the lower midrange.

Anyone owning vintage Infinity RS models can expand volumes on this topic.
 
Last edited:
mufster said:
So am I just lucky? Am I risking damaging my amps or speakers. The thing is, amps rated at 6 ohm are like hens teeth. Surely the manufacturer wouldn't create speakers that only connect to 6 ohm amps? Maybe I should contact the manufacturer and ask if they have a manual.

Paul
Click to expand...

I really wouldn't worry about it if I were you. As WJ has said, a drop from 8 to 6 ohms nominal shouldn't present any undue risk to your equipment. Even an 8 ohm speaker will periodically drop to half that value or even less at certain frequencies.

Only under the most extraordinary conditions (ie: prolonged sessions of pushing the amp to its limits at the precise frequencies of impedance dip) would this ever pose an issue. Also, being as the speakers are fairly sensitive, the associated risks are all the less likely.

Amplifier rating simply refers to the device's ability to deliver more current as required when load is increased.
 
Last edited:
If your speaking of tube amps with transformers then I would use the 4 ohm tap. If you asking about McIntosh amps with autoformers, it depends on the series. The older 2000 series and 7000 series with autoformers the answer is the 4 ohm tap, the 7100 and 7200 with out autoformers, have at it. The newer Century series amps, MC 302, 402, 252, 501, 601, 602, etc etc, you can use the 8 ohm tap as the amp will meet or exceed its specs with a 4 ohm load connected on the 8 ohm tap.
 
Thanks for the reassurance. I don't play my music loud. Never gone past quarter even on my 26 watt marantz 2226B so it looks like i'll be ok. Still, its great for you guys to put my mind at rest. I have emailed mordaunt short asking for a manual. If i get one, i'll post all the spec info in here.

Cheers guys!
Paul
 
fhawk618 said:
Higher the number, the greater the sensistivity... the number is typically expressed as db/1w 1m... that is sound pressure level in decibels with the speaker being powered at 1 watt, measured at a distance of 1 meter from the speaker. The greater the sensitivity, the less power that will be required to make the speaker play "louder".
Click to expand...

I hope this isn't a thread hijack, but what difference does it make when the sensitivity is expressed at 2 m? Does that mean the speakers are even more sensitive at 1 m than the db number given?

I ask because the sensitivity of my KEF 104/2s is described on the KEF site this way:

Sensitivity: 92dB at 2m on reference axis for a pink noise input of 2.83V (anechoic conditions)

Does that mean the dB number would be higher at 1 m? Or does it make no significant difference? Just curious.

Jim
 
Traditionally, 1 meter is the industry standard distance from which sound pressure measurements are taken.

The short answer is yes, SP does decrease the father the distance from the loudspeaker from which the measurement is taken. I cannot say how much the level drops from 1 meter to 2.

92 dB at 2 m should translate to a very sensitive speaker indeed.
 
Last edited:
Thanks Bowtie and Caddy for getting in with those posts... I just hadn't had time to get back to the question...
 
You must log in or register to reply here.
Back
Top Bottom