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Question Speakers and amp

antighsiothail

Active Member
Getting back into stereo after a good while with just an AVR. Got the old stuff out of the loft a Technics SL-PG440A cd player and a Technics SU-VZ220 amp. Connected them to a pair of Mission M34 floorstanders, with a rating of 25w to 150w at 8ohms.
The amp has a rotary volume knob that goes from 80 to 0, it seems the output power is 38w at 8ohms, I never thought about setting the volume before putting a cd in, damn thing nearly blew the front off the speakers, it was really really loud. When I looked at the volume as I turned it down in a panic it was about halfway round. I must be wrong somehow but I would have thought given the rating of the speakers and the amp that I could have turned it all the way up without overdriving the speakers. There is no way I could do that, most I can comfortably listen at is about a quarter of the way round, which is about 35 on the dial. Seems a bit strange to me or am I just not 'getting'it.
 

muljao

Well-known Member
The volume knob has no direct correlation to the volume on most amps, with a lot giving near or very near full power by the 12 o clock position
 
D

Deleted member 781788

Guest
Or it could be that you had connected your CD player to an input which is not for CD!
you see a CD player's output is about 3 times that of a cassette deck or a tuner.
Check your connections.
 

antighsiothail

Active Member
It is in the cd input
The volume knob has no direct correlation to the volume on most amps, with a lot giving near or very near full power by the 12 o clock position
That makes sense, it was at about the 12 o'clock position. Still surprised that a 38w amp could drive 150w speakers so loud.
 
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Joe Fernand

Distinguished Member
AVForums Sponsor
Most of your 'comfortable' listening will take place with your amp (any amp) only outputting a few Watts of power - ratings on Amps and Speakers are usually pretty meaningless as there are 101 variables in how these figures are arrived at.

The 'sensitivity' figure on the speaker spec is usually a better guide to how well they will match an Amp.

Always a good plan to have the Vol set to Zero when you power on an Amp.

Joe
 

antighsiothail

Active Member
Always a good plan to have the Vol set to Zero when you power on an Amp.

Joe
Yes do that now, just having taken it out of the loft never gave it a thought, luckily nothing seems damaged. Sooo used to remote controls which this amp doesn't have :(. The spec for these speakers say..Sensitivity SPL/m/2.83V...92dB. Not that that means much to me.
 
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D

Deleted member 781788

Guest
Yes do that now, just having taken it out of the loft never gave it a thought, luckily nothing seems damaged. Sooo used to remote controls which this amp doesn't have :(. The spec for these speakers say..Sensitivity SPL/m/2.83V...92dB. Not that that means much to me.
it means your speakers would produce 92 units of loudness if fed with 1 Watt of power into 8 ohms - which is pretty high (good).
Say another speaker with a sensitivity of 89dB (typical) would require 2 Watts to produce the same loudness (double the power adds 3dB).
to put in perspective your speakers need only 32 Watts to go to 107 dB (pretty loud)
while the other speaker would require 64 watts to go as loud.
I still suggest you check your inputs.
 

antighsiothail

Active Member
Thanks for your feedback, I did check the input, the input selector is set to cd anyway. Wouldn't play if the leads were in any other input.
Interesting about speaker sensitivity never really thought about that, given the amp will output (according to the specs) 38watts at 1khz continuous power output, both channels driven, what would that mean then in dB terms for these speakers? I should add that I have no intention of turning the amp up full, or anywhere near it, come to that.
 
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Joe Fernand

Distinguished Member
AVForums Sponsor
For most folk 103db at home would be too loud - you'll find you usually listen somewhere in the low 80's as a comfortable level.

Joe
 
D

Deleted member 781788

Guest
Thanks for your feedback, I did check the input, the input selector is set to cd anyway. Wouldn't play if the leads were in any other input.
Interesting about speaker sensitivity never really thought about that, given the amp will output (according to the specs) 38watts at 1khz continuous power output, both channels driven, what would that mean then in dB terms for these speakers? I should add that I have no intention of turning the amp up full, or anywhere near it, come to that.
well the math is easy, around 108dB per speaker, meaning about 111dB for both.
HOWEVER! (a big however) you must take the 38W power output of your amp with a fistful salt.
in reality they start to buckle at around 25W which is still OK given your sensitive speakers.
And No there is no credible app for your phone to measure sound pressure levels - a dB meter needs to be calibrated, and dB's fade geometrically with distance, so they are quoted as dB at one metre.
Don't worry about the numbers - if it gets too loud or distorted, turn that knob down!
You are there to listen to music and have fun - numbers would cut into that. ;)

Decibel-scale.jpg
 
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