Any amps that "double-down" into 4 ohms in a magazine/lab tests? (1 Viewer)

[Saurav]

Hard to say. In SPL terms, should be do-able if your Yamaha has adjustable volume for all channels, I would think. However, I don't know how the sound would match up.

I don't have any experience with SS pre and tube power. I've used the opposite combination, and it worked quite well. I got the tube sound which I liked, and at the same time had the SS damping factor and consequent bass control over difficult speakers.

 

[Duke H]

That's cool. While we're on the subject, do you know of any sites that explain things like speaker sensitivity, in PRACTICAL (as opposed to theoretical or technical) terms? Specifically, I'm looking for a chart of some kind or a formula that will allow me to match up speakers with amps, to get maximum volume with minimum distortion. I'd also like to find out exactly what causes distortion. I know various ways that distortion is caused, but I'd just like to have a handy little print out of the most common ways.

 

[Drew Eckhardt]

What about amps that have the same power ratings for different ohms? The only example I have seen is McIntosh.

McIntosh transistor amps and all traditional (as in not OTL) tube amps use output transformers which allow the drivers to see the same impedance for a variety of loads.

This is necessary with tubes because they're low current devices (although you can get big voltage swings). The iron used in a tube amp contributes to the sound; perhaps McIntosh is attempting to capture some of this in their solid state designs.

 

[Saurav]

While we're on the subject, do you know of any sites that explain things like speaker sensitivity, in PRACTICAL (as opposed to theoretical or technical) terms? Specifically, I'm looking for a chart of some kind or a formula that will allow me to match up speakers with amps

That isn't so hard to do. Here is the information you need for this:
* SPL falls off at 6dB/meter as you move further away from a speaker. This is the only number that I'm not sure of, I think it's 6dB/meter for regular speakers, and 3dB/meter for planars. Of course, 1 meter is around 3 feet
* You need to double the power to get a 3dB increase in SPL.
* If a 4 ohm speaker has a sensitivity figure which is in dB/2.83V/m, you need to reduce it by 3dB to get the 'real' sensitivity. All sensitivities should be dB/W/m. If this one confuses you, I can explain it further, or you can just ignore it for now.
* Sensitivity is measured at 1m from the speaker. That's what the dB/W/m means - you get so much dB at 1m for 1W of power.
Anyway, here's how it works:
* First, how loud do you listen? If you have an SPL meter, set it to 'Slow' and get some idea of the SPL at which you normally listen to music. For me, it's between 80 and 90 dB.
* Next, how big is your room, how far away are you from your speakers? I'm about 2m away from my speakers. So, if I have 80dB at my seat, my speakers are producing 83dB at a distance of 1m (3dB for every meter).
* Next, what's your speaker's sensitivity? Assuming mine are 89dB/W/m, which means if they're fed 1W of power, they'll produce 89dB at 1m. Since they're producing 83dB, that's 6dB down. Since every 3dB means half or double, that means they're using 1/4 of a watt of power to do that.
So, there you go - for an average 80dB of volume, I need 0.25W of power. As your average goes up, your power requirements go up, doubling for every 3dB increase. That takes care of average power, you need more power for dynamic transient peaks. I'm not sure what the peak:average ratio is, I think 10:1 is reasonable. So, multiply the wattage number you get by 10 (or 20, or whatever).
In my 15x20' room, my 8W amps can drive my 88dB speakers as loud as I need. I get 80dB+ at below 9 o'clock on my preamp's volume control.
Anyway, what you need to do is figure out how much SPL you need 1m from your speakers, based on your room size and your listening volume preferences. Then, this SPL is a combination of speaker sensitivity and amplifier power, increasing either one will increase the SPL. You can easily make a chart which tells you how much power you'd need for how much sensitivity.
Hope that helps more than it confuses

 

[Duke H]

Thanks! It makes a lot of sense. A lot of people are under the false assumption that wattage is king. When I tell them that the difference (volume-wise) between an 80-watt amp and a 100-watt amp is pretty much insignificant, I get some very strange looks! I can see where this is you're coming from, from a receiver/amp view point, but speaker sensitivity boggles my mind (or it did, until 5 minutes ago ). What I'm trying to find is a good rule of thumb as far as matching speakers and amps goes. If you don't mind here are a few questions:
(1) Is there a ratio that works when comparing a speaker's wattage rating to that of the amp? I've always assumed that your speakers should be rated as being capible of handling at least 25% more wattage (RMS and Peak) than your receiver can put out. Of course, I've always looked at it from a guitarist's POV, and guitar amp speakers aren't known for their quality...most guitarists will base their speaker cab selection on whether or not it can handle as much or more power than the amp can put out. (Ironic, isn't it?...The people who make the music usually know less than their listeners when it comes to what makes it sound good)
(2) What is the primary cause of SPEAKER distortion? What made me curious about that is the fact that if you hook up a pair of 300 watt KLH's (ie-sucky campus party speakers) to a Yamaha Htr-5280 (110 watts, peak), they begin to distort at around 3 o'clock (75% volume). It's not the receiver clipping, an the distortion is from the woofer. The mid, tweeter, and super tweeter all sound fine (if you go by KLH's definition of "fine"...shrill, brittle, and compressed to Hell).
Also, could you explane the following (you were right...it's Greek (or any foreign tounge, save Espaniol) to me:

* If a 4 ohm speaker has a sensitivity figure which is in dB/2.83V/m, you need to reduce it by 3dB to get the 'real' sensitivity. All sensitivities should be dB/W/m. If this one confuses you, I can explain it further, or you can just ignore it for now.

Thanks a lot for all the help: As I said in the "salesman" tread, I don't know everything...I'm just trying to keep my head above the water in the great ocean that is "HT" (poetic, eh?--didn't think so). Also, to answer your post in that thread, I know the whole ego think wasn't neccessarily refering to me-I just felt like I'd use it as a spring board to reinterate my previous point (ie, I don't know everything, but I don't ride the short bus, either).

 

[Saurav]

Also, could you explane the following

There was a thread about this a while back, but I can't find it any more. Anyway, I'm assuming you don't want to go into the maths behind this. Basically, here's what I was trying to say. The "unit" in which sensitivity is measured, is decibels per watt per meter, or dB/W/m. What this tells you is how many dB the speaker can produce when fed how many watts of power and measured at how many meters distance from the speaker. 90 dB/W/m means it can do 90 dB when fed 1W and measured from 1m distance.
OK so far?
Now, for an 8 ohm speaker, 1W power is equal to 2.83V. This is easy to prove, if you want to go into the math behind it. In other words, if an amp is driving an 8 ohm load, when it's producing 1W of power, it's producing 2.83V output voltage. So, 2.83V and 1W are one and the same thing, if you have an 8 ohm speaker. So, sometimes you'll see sensitivity number that say 90 dB/2.83V/m. On the face of it, it looks like the same thing, because 2.83V and 1W both represent the same amount of power output from the amp.
Again, OK so far?
Now comes a speaker that's not 8 ohms - here, 2.83V does not represent 1W of power. For a 4 ohm speaker, it represents 2W of power. For a 6 ohm speaker, it's somewhere between 1W and 2W. So, now if you see a speaker that says 90 dB/2.83V/m and you know it's a 4 ohm speaker, you know it's not really an apples-to-apples 90 dB sensitive. That's because it produces 90 dB with 2W of input power. 2W is double of 1W, so in reality, this speaker is 87 dB/W/m sensitive (doubling/halving goes up or down by 3 dB). So, if you want to compare the sensitivity of 2 speakers, you should see how loud they play with the same input power. Sure, every amp will put out more power into 4 ohms than 8 ohms, so you'll have a bit more power available to play a little louder, but that's not really comparing the speakers on the same platform.
Did that make more sense?

 

[Duke H]

Yeah, thanks. That helps out a lot, actually. Sorry I might seem a bit slow to catch on, but to honest, I've never really been a "spec" guy. More an "ears" guy. Now, I'm just trying to get the tecnical side down, without loosing the "if it sounds good, it is good" mentality. If you think drunken friends cranking stereos are bad, try this out: When my girlfriend isn't lecturing me about how I should sell/stop buying my guitars and Home theater stuff to pay for school, my Ferret is chewing on my $90 Monster Z-series wire and stealing my remotes to hide behind various artifacts (ie, furniture). My solution(s): (A) Point out, "I get along just fine, even with my slightly odd "investments," and (B) get the ferret a million toys and an Olympic-sized cage. If only I could kill two birds with one stone: Get my girlfriend to lecture the ferret, while the ferret steals my girlfriend and hides her behind furniture!

 

[Saurav]

LOL!!! That's the funniest post I've read in a long time.

Now, I'm just trying to get the tecnical side down, without loosing the "if it sounds good, it is good" mentality.

That's my mentality too when it comes to audio. Else I wouldn't be listening to scratchy old records on tube gear I think balance is a good thing though, so I don't completely throw out my college education, or pretend that the laws of physics somehow don't exist. However, I'm always open to the possibility that there are things out there that we don't yet know, and usually go by my senses and my gut feeling in such situations.

 

[Duke H]

Hey Saurav, while we're at it, here's a REALLY stupid question: It seems like speaker sensitivity is key. That being the case, how does wattage relate in the following senario:

Say you have a 100 watt amp, and two sets of speakers, both with the same SPL. One set is rated at 300 watts, RMS, and the other at 140 RMS. The amp is rated at RMS, as well.

Would the 140 watt speakers be louder, as they require less power? If so, wouldn't you want to go with the 140 watt speakers? They wouldn't work the amp as hard, right?

 

[Saurav]

No, loudness is controlled only by the speaker's sensitivity. The power handling rating is just that - how much power can they handle before they start smoking.

So, if you use the same 100W amp, they'll both play at exactly the same SPL. If you had a 500W amp, again, at a fixed position on the volume control, they'd both play at the same SPL/volume. However, as you start turning the volume control up, the 140W speaker will smoke before the 300W speaker. Until that 'smoking point' though, they will both play at exactly the same volume. So, 'power handling' is 'how much power can I feed it before I break it', not 'how much sound power can it make from the electrical power I feed it'. That's sensitivity - the amount of acoustic output for a given electrical input.

 

[Duke H]

Humm...very interesting. That's basically what I thought, but I just wanted to check.