More speaker help - Ohms and Watts whats?

[macvidguy]

Thanks for all the Bose bashing you provided. With regard to speakers and assuming I win the battle for Denon 2805 which is 7X100 and has ratings for 6 and 8 Ohms (100watts). If I understand right (my conservative thinking) I need to get speakers that support at least 100 watts right? If they are below and I have it cranked way up...not so often of course...I don't want them to max out. If they are 4 Ohm though...they may overheat and shut down right?

So simply put:
If I have 100 per channel do I need to watch my min/max or both?
If my Receiver provides ratings for 6 and 8 Ohms, should I avoid 4 Ohms?

I saw a Jamo A355PDD (fronts, rears, sub, Center) normally 1200 for 800.
(http://www.jamo.com/consumer/product....php3?id=A+355)

Thanks again. Hopefully I will be able to add some value soon, rather than just absorb. Anybody need to know how crank it with an old Fisher405 boom box?
Noticed a lot of Canucks on here. I am too...just living in the Colorado right now. Bottoms up.
Mac.

[Andrew Pratt]

Mac the ohm rating of a speaker results from what and how many drivers its using. The take home message though is that ohm's is a measure of resistance so that an 8 ohm load offers more resistance then a 4 ohm load...and 0 would be a complete short (not good!). Anyway as the resistance drops the amount of power that an amp can send goes up...that is until the amps power supplies fail to provide enough juice to meet that demand. Also realize that the ohm rating on nearly all speakers (planners are the only exception) is just an average...it will actually fluctuate quiet a bit.

As for the power rating on speakers its for the most part irrelevant. As you might notice most speakers are also rated for their efficiency which is typically around 90dB/1 watt. What that means is that with only 1 watt of power your speakers will generate a tone at 90 dB at 1 meter. Now that drops when you back up to your seat but the point is that under most normal listening conditions you're only using the first 5 watts or so! So why bother with the mega watts amps? Well there's a question of headroom when an explosion happens in a movie or the bass drums start to kick in on music. During those times having more current available will improve the sound a great deal as the current demands jump very quickly.

The other point to consider with wattage ratings on speakers is that you are FAR more likely to blow up a speaker with an underpowered amp then a mega watt model. The reason for this is that you're likely to push a low powered amp much harder then a more powerful amp. During those times that the small amp is being pushed to its limits the power supply will fail to keep up and the amp will stop delivering a nice round sine wave to the speaker cones...that's called "clipping" and when it does this the speaker cone will stop moving for a brief moment even though there's still lots of current being sent to the motor...this generates a lot of heat which can seriously damage the voice coils of your speakers. For the most part with a strong amp you're likely not going to push it hard enough to make it clip before its WAY to loud to be comfortable so don't ever worry about sending too much power to a speaker.

Oh and one last point...don't beleive everything that a manufacturer says about its amps power. Take a look here and see just how low some amps have tested vs what they claimed.

[macvidguy]

Great info...thanks a ton. Have tackle some Apple G5 stuff for my boss. Maybe I'll be able to throw some video stuff in the game in a month or two. We just got a Steady-cam, HD editor, and ordered the new Sony HD Camera. Apparently we are going to shoot our corporate videos this year. Woohoo.

[Adz]

Ditto
Great info Andrew!
Why not start a sticky on Frequently Asked Technical Questions?

[brendon]

Hi Andrew thanks for the link.
That chart made very interesting reading.I was gratified to see that the Marantz 5400 or (6400 not in chart) that I was looking at was just about the only entry level amp to exceed its rated power 5 chanels driven along with the denon 2800 which was close as well.Does any body know how the current Yamaha amps that are equivelant stack up .I hear they are closer to their rated figures now 5 channels driven but have not seen any independant test figures.
I see that as usual fror those with a few more bucks the Rotel 1056 also delivered as promised.
Thanks brendon

[Andrew Pratt]

The only test I've seen on the newer yamaha's was very dissapointing.

[purplepeople]

Andrew has it about right. Since you're asking about speakers and amps, there's one thing I look for in a speaker before I bother to listen and that's...

Frequency response +/- 3dB or less. +/- 1.5dB is very expensive, but don't accept anything higher than 3dB. This is very realistic spec for how low or high the speaker will go. This is usually a graph but often just a spec such as 60-20kHz +/- 3dB for my Tannoy Proto-Js.

I also won't bother with it if that mfg won't publish the +/- db part. Anything else is usually a lie by omission.

With amps, preamps and receivers, I look for a few things before I will even listen:

1) THD must be <0.1% at maximum power output. Anything higher and it better have tubes inside it. I prefer <0.08% or lower.

2) SNR should be >90dB at 1kHz. Anything lower and the it will add noise to any clean digital source.

3) Power should be rated in watts RMS per channel. Not total power of 600W (5x100W). RMS is based on the energy level of a sine wave signal being amplified continuously. This is usually easy to determine by making certain of #4 below.

4) The amount of electrical power drawn from the wall is greater than the output power of the amplifier (circuit). For analog amps, this should be at least double since transformer efficiencies are around 40% or so. Even for Class D amps, this should still be true, but the DC/DC conversion creates efficiencies that can approach 90%. So for a 500WRMS amp, the power supply should be at last 550W. Anything less and the you cannot continuously drive all channels at the max RMS power.

If the salesperson can show me these kinds of specs (#4 is easy, just look on the back of the demo unit), then I will do one more thing before playing any test discs... that is to set the input to some source, like a CDP, make sure the source is idling, crank the volume to max, then put my ear to the speakers. Any hiss and I walk.

ensen.

[Andrew Pratt]

Doesn't #4 also depend on the number and size of capacitors inside the amp?

[macvidguy]

Good numbers

Schnikes! Well I am armed with some pin the tail on the salesguy stuff now.
Thanks again for all the help. Going listening in about 20 minutes.
Mac.

[purplepeople]

Doesn't #4 also depend on the number and size of capacitors inside the amp?

Usually.

[Cowanrg]

"pin the tail on the salesguy"?

i hope he charges you full price :roll:

its not like he can screw you over (it seems like that's what you are afraid of), if YOU listen to them and they sound good to YOU. people always forget that little fact...

[macvidguy]

Isn't Bose always full price?

Well at a TV and film shop in Denver while buying a steadycam and green screen, the editing guru who was happy to ring up lights and mic booms for me had the quote "no highs, no lows, must be Bose".
Also I don't mind paying full price...err...ok ...yes I do.

But when you crank finding Nemo so my kids are engulfed, then call my wife a "Bose Customer", you are pushing your luck. I grew up in Canada...eh...time for a mouth fulll of chicklets.

Also in my own research from the install guide, component video from the bose is considered a special cable that has RCA and S-vid on one end and component on the other. Page 26 or 27 of Lifestyle installation guide.

Can anyone tell me what resolution that would give me? Is is capable of high def...and what is better 1080i or 720p.

Anyhew, everybody is a help...no digs on salesguys if they come clean and work their magic sans fromage.
Mac.

[Adz]

I understand Bose has an interesting setup (at least in one Maryland store). You go into the home Theater "Room" and its all dark and very commerical theater like. There's a widescreen Plasma TV on the wall and very large Tower speakers in the front with a large center and large surround shelf type speakers. Then they put in Nemo and crank the volume. After the presentation, and everyone is like Wow, that sounds great. They turn up the lights, and remove the speaker enclosures to reveal their tiny tiny little speakers behind those big fake boxes!!!