140wpc into 8 ohms: enough for Contour 1.3SEs?

Hi Sean:

I am reading your responses with great interest and the opportunity to learn. Hopefully, you will indulge my questions.

Some background:
In my second system, which I use for 2 channel HT purposes, I have a NAD 320CEE (50 wpc) integrated amp which powers a pair of Acoustic Research 302 speakers (3 way; 10 inch; 85 db sensitivity; 35 min to 250 max recommended wpc). (Note: These speakers were AR's attempt to introduce a modern era version of a 60's AR classic. The 302's were the modern era AR5's.) My listening room is 15' X 10' X 8.5' and the speakers are each placed horizontally, on shelves inside two standalone bookcases (one speaker per bookcase and then, the two bookcases are butted together) about 5.5' high. In terms of placement inside the bookcase, if you were to look at the speakers, the woofers "kiss" and the tweeters are the furthest apart. About 8 inches of space separate the speakers, of which 3 inches are the solid pine bookcase walls.

I live in a pre-war apartment building (plaster walls; wooden floors & joists) so sound travels up & down. I am fairly considerate (lots of cranky neighbors) and so the system volume is usually pretty polite for music (volume control at 8 o'clock position ) and less polite (10 o'clock ) for movies. If the music were at the 10 o'clock position, it would be pretty loud and at 12 noon, it is not pleasant in the room.

Question(s):

Is my understanding of the math that governs the power/volume relationship correct?

1. If I understand the math that governs volume ... to get a noticeable (3db) increase in volume, you must double the wattage. Using my speaker's specs, would this mean then that ... 35 wpc gets me 85 db and I would max out my NAD to get to 88db as that would require 70 wpc. (Yes/No/Not Quite?).

I pulled a list of SPL comparisons from a power equipment site and based on this, my guess is that I am normally using less than 4 or 5 watts and am at a level of less than 80db.

dB Common Sound

140 ... Threshold of pain
135 ... Siren at 100 feet
130 ... Jet plane at 50 feet
120 ... Auto horn at 3 feet or rock & roll bar
105 ... Chain saw
100 ... Heavy city traffic
80 ... Inside a car at 50 mph or inside a busy office
70 ... Vacuum cleaner
60 ... Normal speech
50 ... Private office
45 ... Living room, suburban area
35 ... Soft whisper
25 ... Bedroom at night

In the case of Carlsaff & his Dynaudios:

30 watts has him at 86db; 60 watts has him at 89db; 120 watts would have him at 92db. (Yes/No/Not Quite?)

Many thanks, Rich

Rich, Your understanding of the application of the math is incorrect. It takes 1 watt to drive these speakers to 86dba - now start doing your multiples. I think you will find that 120 watts should produce about 106dba.

Newbee:

Thank you for the clarification ... it makes infinitely more sense. It also helps to jar my brain some, as I probably knew & forgot that it was a relationship based on 1 watt . So, my NAD at 50 wpc should produce about 102 db. My normal listening level for music is probably using up about a watt at most.

Many thanks, Rich

Bare in mind that most speakers become LESS efficient as more power is pumped into them. That does not mean that volume goes down as you put more power into them, but that power is lost in greater quantity due to thermal losses as you drive them harder. In effect, you run into what is basically non-linear dynamic compression. Combine this with the fact that many amps have a hard time dealing with increased current demands, their power supplies begin to sag and reflected EMF is increased as you drive a speaker harder. As such, one is typically best off finding the most sensitive speakers they can find that are suitable to the application. By doing so, you'll be pulling less power from the amp, so it runs with less stress and sounds better. At the same time, the speakers aren't being fed as much power, so they don't heat up as much and go into thermal / dynamic compression as rapidly or as often.

Having said that, i haven't found a lot of highly efficient speakers that i really like to listen to on a long term basis. I'm sure that there are others out there that share this dilemma, but then again, there are some folks that find low sensitivity more of a drawback. That is why there are so many different speakers and designs out there : ) Sean
>

PS... Driving in a convertible with the top down on the highway, piloting a motorcycle with stock mufflers and no helmet or driving a "Jeep" type vehicle with bigger tires in suburban areas typically clocks in at about 90 dB's. Taking a Jeep on the highway with "off-road" type tires can be amazingly loud due to the amount of air that gets trapped in the treads. The motorcycle doesn't seem as loud as most of the sound is projected behind it, but the wind whipping by your ears definitely has a similar effect.

I'm using a Rel Storm lll with my 1.3SEs. My room is 15 by 20, and I listen at moderate levels--classical and jazz. I like it. BTW, I'm driving the Dyns very nicely with 50 watts--Clayton S40.