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7W enough for 90dB speakers?

kacernator said:
Is 7W push-pull enough for small room cca 4x3 meters and 90dB efficient speakers?

Thank you.


IMO, 7 WPC is not enough. Paul Joppa provides a useful rule of thumb. PJ's rule tells us that an amp/speaker combo should be capable of 102 dB. SPL peaks at a 1M. distance. The rule is for a "typical" space. Adjust accordingly. 4 M./3 M. is not especially small. So, I'd go for the 102 dB. peak. 16 WPC are needed with 90 dB. sensitive speakers.
 

tubewade

Member
2007-06-03 8:54 pm
7 watts is 8.45 dBW; i.e. capable of 8.45 dB more output than 1 watt. With 90 dB/1 watt speakers a single channel should achieve 98.45 dB. With two channels, twice the power, twice the membrane area for an increase of 6dB. Total output = 104.45dB. There will be losses, of course, but this is pretty loud for most types of music. My room is about the same size and I've been quite satisfied with SE 6BQ5s and similarly inefficient speakers, but I don't like Metallica or AC/DC. I listen to Dave Grusin, Chris Botti, Brian Culbertson and Fourplay.

Wade
 
Hi,
I run 90db speakers on 110W amplifiers.
That gives a transient peak to average listening level overhead in excess of 20db.
This generally avoids clipping of any transients at the sound levels I generally listen at.

7W reduces the transient overhead by 12db.
I suspect that I would regularly hear the some degradation of the signal with a 7W amplifier.
 
helpwe woofers?

er and od?

Oh oh, the grammar police will be on the prowl...

as for a helper woofer (if that's what you're sayin' dave), how about what I'm workin on? M&K 1250VX sub/plate amp, but stereo subs and (hopefully ) aperiodic enclosure---for the real reason, to flatten the impedance, not build a smaller box.

I have to say that listening for extended periods at 100dB+ will do damage. And most folks would choose not to stay in the room to listen to it. My head-banging, still in the 60's older bro is listening to 94dB efficient FRs in a room about the same size : 3X4X2.5, with a tiny Decware SE84c (2 watts/channel). For his listening plenty loud enough.

stew
 
Nanook,
you haven't bothered to do the numbers.
110W into 90db/W/m speakers gives a maximum SPL of about 110.4db/m
For a pair of speakers at 2.4m (8feet) listening distance this is about 113db-7.6db=105.8db maximum SPL at the listening position.
Subtracting a minimum of 20db for transient peak to average listening level results in a maximum average listening level of 85 to 86db. This I would consider as turned up loud. I normally listen at about 10db lower than this, i.e. about 75db or roughly equal to conversation level. The benefit of improved overhead for transients of about 30db gives a cleaner signal.

7W will reduce the maximum level by about 12db.
Reduced transient overhead of 8db or reduced average level of 73db.
Which do you find more acceptable?
The decision to be taken by our enquirer is not whether he will risk his hearing but how often he can tolerate clipping of transient signals and the allegedly terrible listening experience that leads to.
 
AndrewT said:
maximum average listening level of 85 to 86db. This I would consider as turned up loud. I normally listen at about 10db lower than this, i.e. about 75db or roughly equal to conversation level. The benefit of improved overhead for transients of about 30db gives a cleaner signal.

7W will reduce the maximum level by about 12db.
Reduced transient overhead of 8db or reduced average level of 73db.
Which do you find more acceptable?

That is about the same as me. level wise ... that i haven't found a 50 w amp that -- let alone a 100w amp -- i find to have acceptable sound means i have to live with a smaller amp.

It is just the compromise that i find most acceptable. ie decent sonics vrs a bit of compression on dynamics, or just not able to turn things up the few times when i want to.

I'll not compromise my amp sonics -- i will find other ways to get more level & dynamics (ie add more amps)

dave
 
If it's RMS It should be enough, unless you’re a real cranker. 1m SPL, rule of thumbs are pretty much worthless. SPL decreases by 6dB each time listening distance doubles. So the power demand for a small room is much less than a moderate sized room. A listening position rule of thumb would be much more accurate. Also, people readily forget you have two channels playing simultaneous when figuring SPL. So you can calculate using 14W (2x7W) which will be 3dB more. Also, most tube amps don't clip as sudden and harsh as a SS amp so they usually don't require as much headroom.

However, if your using a 90dB full range driver. You can pretty much bet your going to add a BSC circuit if you want any bass out of it. This will leave you with 3-6dB less for the midrange and highs. In this case you may be right at the border of "not enough juice" and would probably be best off going with something in the 94dB range.
 
Jeb-D. said:
However, if your using a 90dB full range driver. You can pretty much bet your going to add a BSC circuit if you want any bass out of it. This will leave you with 3-6dB less for the midrange and highs. In this case you may be right at the border of "not enough juice" and would probably be best off going with something in the 94dB range.

So far i've only had one were i really felt the need for a BSC circuit ... and they were probably in the low 80s by the time i was done with them. With a 50W or so Pioneer they play plenty loud for their application.

dave
 

ray_moth

diyAudio Moderator Emeritus
2004-01-27 8:55 am
Jakarta
Andrew T's point about transients is well made. If you listen to dramatic or flamboyant music, you'll need good headroom. If you only ever listen to gentle music with virtually constant volume level, then it won't matter so much. But either way, IMHO, 7w is insufficient with only 90dB sensitivity, even at low listening levels.