Archived from groups: rec.audio.high-end (
More info?)
Bromo <bromo@ix.netcom.com> wrote:
> On 4/29/04 12:32 PM, in article F6akc.16637$lz5.1349697@attbi_s53, "Rui
> Pedro Mendes Salgueiro" <rps@rena.mat.uc.pt> wrote:
>> Joseph Oberlander <josephoberlander@earthlink.net> wrote:
>>> Robert Trosper wrote:
>>>> Now that we have the room size and construction, and I can look up your
>>>> receiver specs (90W per channel into 8 ohms - no mention of what happens
>>>> into 4), perhaps we can make some progress. You're going to want
>>>> something pretty efficient in a room that size with an amp that size, I
>>>> think.
>> I have the same amplifier (in a smaller room, though) with non-exotic
>> speakers (claimed sensitivity 88 dB) and I haven't yet pushed it above
>> -30 dB.
> -30dB with reference to what?
The volume control on the Yamahas is expressed in dB from -90 dB
to 0dB in steps of 0.5 dB. The -30 dB is about the highest I use
so as not to annoy the neighbours (this morning I was listening
to a music DVD (PCM stereo in 6-stereo* mode) at about that level).
Assuming that Yamaha is not lying that means I still had 30 dB
available (well, maybe a bit less, because my speakers are only
rated for 70 W). Of course, trying to estimate sound level is hard,
but I would think it was about 80 dB, which is consistent with the
speakers specification**.
* 6-stereo is a mode which the Yamahas have in which the 2 stereo
channels are spread to the 5 or 6 available. The rears don't get
much power, but the center front receives a bit, although probably
less than I thought when I wrote the calculations below.
** Order of magnitude calculations: if each front speaker produces
88 dB at 1 W / 1m and the center produces 90 dB at 1 W / 1m,
(this is 1.585 more energy than each front) all three will produce
3.585 more energy, that is 5.5 dB more than 88 or 93.5 from 3 * 1 W.
If one considers a distance from the speakers of 2 m, that is 6 dB
less, 87.5 dB. My amplifier is supposed to have somewhere between
90 W to 110 W*** . Chosing 100 W that would give 107.5 dB. So, -30 dB
would be 77.5 dB, which seems about right.
In a larger room (4 meters from speakers to listener) it would still
give 101.5 dB.
(***differents measures:
90 W is "Minimum RMS Output Power" at 0.06% THD, 8 ohms (20 Hz - 20kHz)
110 W is "Minimum RMS Output Power" at 0.7% THD, 8 ohms 1kHz
130 W is "Maximum Power" at 10% THD, 8 ohms 1kHz
140 W is "DIN Standard Output Power" at 0.7% THD, 4 ohms 1kHz
120/145/185/230 W is Dynamic Power (IHF) at 8/6/4/2 ohms, respectively.
130/160/190/235 W for USA models in the same conditions.)
>>> It will only drive 6 ohms into all channels.
>> According to the manual the two positions of the impedance switch are:
>> 1 - 8 ohms for all the speakers
>> 2 - 4 ohms for the main speakers and 6 ohms for the other 4 channels.
> Ah - the switch probably drops the voltage to the finals to keep the power
> dissipation down - it will likly reduce the amount of power otherwise
> available into those loads, and extend the life of the receiver.
Since Yamaha doesn't quote a power into 4 or 6 ohms it is not easy to guess.
Hmm, I can't remember if the reviews I read about it have some tests.
I just checked the reviews listed at ecoustics:
http
/www.ecoustics.com/Editorial/Reviews/Surround_Receiver_or_Home_Receiver_or_AV_Receiver/Alpha_Name/All/
and none of the three that worked had lab results.
Do transistor amplifiers use output transformers or only valve amplifiers ?
I thought maybe it was a choice of output voltage via a different output
coil (but there don't seem to be output transformers on the amplifier).
--
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/www.mat.uc.pt/~rps/
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