amplifier DB meters
Hi Al, I dont think anybody did actually answer why no meters, except for the fact that they may not be totally accurate. Why not make accurate meters then?! I use on my woofer system two stereo amps (a 200wpc stereo amp for both the left and right bank of woofers, 32 eight inch drivers, yep 16 drivers per side!) and I have both VU and LED meter types of the same amps. I do find them very useful regardless of what others say here, But as of yet I have never had anyone agree with any of my postings on Audiogon, so definitly dont go by anything i say! Again, I do find meters to be a great tuning instrument and important for for setting up ones system. And yes they do look cool, the only "bells and whistles" in my system. Hello Atmasphere, I just received word that the Laverda V6 will be at Mid Ohio this year for the vintage event in July. This is not to be missed! Piero Laverda along with the "factory race team" Agusto Brettoni, Pieros son and others will be there also. Along with the V6 we will be allowed to run our Laverdas on the track with the V6. I will most likely bring my '74 750 SFC. Hope to see you there. Bob |
So nobody really answered with a "why"? I was wondering the same thing. Is it cost? Can't be. The newer (90's - 00's) mega amps I see here on A'gon put out tons of w/rms per channel. I have a 1970's vintage Son of Ampzilla, and I love watching the meters. I would not have an amp without them. I just like the looks. It must my 70's radio/DJ background with VU meters that keeps me interested. Any sound issues I have missed? AC cord replacement and power conditioning are things I have not seen before lurking on A'gon. Could the bulbs in the meters change the sound? (I took a leave of absence to raise kids). Oh I have a computer with a noisy fan in my listening room, I know THAT effects the sound. AL-- |
Hi Atmasphere, I will be there if the V6 shows up, though I will be there no matter what. I am also going this year, dont know what I will bring this year (perhaps my Bimota SB2) but I will definatly have the SFC there next year. Here is a link to a party I had a few years ago at my house with the SFC as the featured bike, we had 7 SFCs there. Also fotos of my Laverda and other bikes if you are interested. Bob http://rides.webshots.com/album/10045837YaZlbTdAGB |
Hi Atmasphere, I heard it through the motorcycle/audio grapevine that you are a Laverda-phile. I have a '72 SF, '74 SFC and a RGS Corsa. I have owned the SFC since the early 80s. Great bikes any chance you make it to Mid Ohio for the vintage races? Next year the rumor is that Laverda will be there with the V6! Bob |
Hi Bob, if you're using a VU meter, the thing to do is to calibrate it against the load you're using- in this case your 4 ohm speakers. To do that you'll have to measure the output voltage of the amp and then calculate the current to then get to the power level. Then, using a variable resistance, set the level of the meter to a point that makes sense for you- for example 0VU = 100 watts, so +3db will then be 200 watts. That way you will have a nice relative level for your speakers. It won't be completely accurate, but it will be close. BTW, yes, I do have a couple of Laverdas that are both riders, a '73 SF2 and a '79 Jarama (3CL). |
HI Shadorne, I believe each bank is wired in just that- parallel groups in series. I have the wiring diagram and paramaters somewhere but I did this 8 years ago so I kind of forgot the details. I needed to keep it 4 ohms where my friends are wired to 2 ohms owing to the different amps we are using. I also believe it is the way Marshall stacks are wired. An internet friend designed the speaker system and had enough custom drivers made for 3 sets (96 drivers, plus 4 to make an even 100 which was required for a price discount). He and a friend are using them with the big Soundlabs. Bob |
One more thing- if you listen to pop/rock, there will be no peaks and you will never need more power than you see on your meters. Why? Because the mastering engineer has basically compressed the recording to have less than 5dB of dynamic range. Play a CD on your computer with a sound program and watch the "peaks" and you will see that 90% of the song is at the maximum volume you can have. Classical is different- lots of dynamic range there. |
Hello, Atmasphere and Shadorne, thanks for your responses. Meters are good and useful I believe, just perhaps we should have better ones on our amps. My woofer system is wired - parallel groups in series. There are 32 drivers in total. 8 forward facing and 8 rear facing per channel, each bank gets its own channel from one amp. This way one stereo amp drives the front 8 with the "left" channel and the rear bank is driven by the "right" channel. Each bank is then 4 ohm. So am I actually seeing double the power than on the meters? If the meter is reading 4 watts it is actually 8 watts, is that correct? I am using two 200 watt per channel amps. Also FYI after really studying the meters since I wrote my original post the most I see is quite a bit more than 4 watts I originally cited, it is actually 18 watts. Going by Atmaspheres example of 4X and then doubling that, I need 144 watts to be safe. Guess I need to have my 200 watt amps. Though I could get away with 100 to 150 watt amps perhaps. The interesting point also is just how small the excursion is at each driver, just a few millimeter at the most. The sound is also quite different due to this, ultimately giving great bass detail and no room shaking. Atmasphere, I understand that you have/like Laverda motorcycles is that correct? I have a few and have ridden them since the early eighties. Bob |
When my system is playing and I only ever see 4 watts on the meter with the loudest peak, I can figure that the amp is using more watts, than the meter is reading, but how much more? 4 watts metered power (referenced to an 8 Ohm load) is; 1) is actually 60 watts into a 0.5 ohm load. In this case, the limiting factor, however, will NOT be the watt rating of the amplifier but the current limitation (11 amps of current is required at 60 watts when driving a 0.5 ohm load and most amps will not deliver anything close to this level of current unless they are rated 1000 watts or more and designed to handle very low impedance loads and high current output...so basically your amp will be current limited at some point ...usually around 7 amps for a 200 watt amp and the meters on the display will, of course, never exceed 4 watts) 2) is actually 15 watts into a 2 Ohm load. The above is a hypothetical example but it illustrates how power meters can be completely misleading. Are your woofers in parallel or series or a mixture of both? |
Hi Bob, VU meters usually have averaged response and don't show the peaks. LED-style units exist that do show the peaks; having watched a lot of these it appears that your typical peak is 3-6 db above the reading on an averaging meter, IMMV (definitely not cast in concrete) 6 db is 4x amplifier power, in your case 16 watts, to be safe in this case I would allow for at least double that. Since our ears operate logarithmically, that's not a huge increase and is the root of the term 'gold plated decibels'. This is why speaker efficiency is such a big deal. |
Helio, When my system is playing and I only ever see 4 watts on the meter with the loudest peak, I can figure that the amp is using more watts, than the meter is reading, but how much more? Assuming that the meter is correct - a big assumption I gather - I know I would need a more powerful amp than 4 watts. I know that this is one of those impossible to answer questions when you figure in the variables ; probably impedances, speaker type etc. I can be pretty well assured though a 400 watt amp can handle the peaks, but what about 100 watt or 40 watt? Any ideas of how much headroom is needed? Bob |
Arthur, nice answer. To expand on that, when listening at 2 watts, if you want to double your perceived volume, you need to increase volume by approximately 10db. Each 3db required a doubling of power. That translates into about 18-20 watts continuous to just double from "mellow" to more. That's why we need 100/200/300 watt amps just to handle the dynamic peaks which can be much louder... |
I guess I need to clarify "logarithmic." Basically, this means that our ears require multiplicative power consumption to hear louder sound - not additive. Not to mention that the same goes for different frequencies. Bass notes require more power than treble notes. If you are listening to a violin solo, you only need a couple Watts. If you are listening to a concert, you will need hundreds more Watts to get the dynamic range right. You can use less power but when the tympani hits, you will get distortion. If you can live with that, then you don't need much power. :) When I had my MC7200 playing classical, the meter needles could bounce between 0.1W and 150W every couple seconds without ever touching the volume knob. Also, I already said that to measure real power, you need voltage AND current. Some meters base it only on voltage which is correct if the impedance is constant but as we all know, speaker impedance is all over the map. The McIntosh meters from the 1980s up to the most recent amplifiers are true power meters and are accurate if their calibration isn't out of whack. They may be off a few Watts but that isn't a big deal. However, the recent integrateds like the 6500 and 6300 have volt meters and not power meters. This was probably done to lower costs and will not be very accurate unless your speakers are a relatively flat 4 ohm load. You really need to watch an amp with meters one day. You would find it very instructive - I sure did and often I wish I still had a McIntosh with big blue meters. Arthur |
Hi, So most of the meters are inaccurate? Though they give a reasonable indication of power, is that correct? As I originally stated I use mine for tuning my system, I can see more or less power being used when setting crossover, EQ or listening level. Yes I can hear the changes but seeing them is also a good confirmation and it is repeatable as I freq write notes. Also I guess it is kind of fun to watch them, I will admit to that! If most of us "only listen at 1 or 2 watts" why such big amps? I know that is true with myself, but how do you know you are only using 1 or 2 watts when you really dont know that without a meter? Arthur says that you need peak power which is understandable but how much more power do you need if you are only using those 1 to 2 watts.? The reason I ask is my subwoofer amps at the most use less the 4 watts or so on the loudest bass I have seen and indeed 90 percent of the time much less than 1 watt as indicated on the meters, with my 200 watt per channel amp, can I use a much less powerful amp? Bob |
All the recent McIntosh and some of the new Cary have them. You need an amp capable of producing your PEAK power demands and not average power demands. There can be hundreds of Watts difference between the two. Don't forget that power is logarithmic. To measure Watts, you need to have voltage and current readings. Voltage is easy since it is parallel but current has to be done in series so you must "break" the power path. Nice hand-held meters have current clamp probes that wrap around a wire so you don't have to cut it but those get into some money. Arthur |
Bob, Music is dynamic. An amplifier meter is only indicative of clipping/power. Power is a function of load (resistance/reactance) and load is a function of frequency. More expensive amplifiers will have a high speed soft clipping circuit to protect speakers (often with a clipping warning light) - this is all that is really necessary to assure good sound. A clipping meter is only a ball park device. If an amplifier does not have meters can you hook one up or use a test meter to find out how many watts you are using? You can - but measuring power is quite complex - very few test meters can measure this correctly. A device to measure power accurately would probably cost more than the amplifiers. Yokogawa Power Meters Most power meters (common in the 70's) are just estimates of power - they measure voltage (easy to do) assume an RMS conversion (using a a fixed load factor and sinusoid waveform type) such as 8 Ohms....all very inaccurate and only indicative). You need to measure current very accurately as well as voltage to get power. |
