AVI ADM woofer power amp rated @ 250W. BS or not?

[Phileas]

But I think many people are just tired of many of the claims about AVI (especially about technical superiority), hence we end up in relatively petty debates about specs.

Actually, I don't think many posters mention the specs of the ADMs. Most people simply make big claims about sound quality. IMHO the OP was just trying to re-ignite a tired old debate to discredit AVI.

We all know that all manufacturers can be selective about how they quote specs.

 

[andyjm]

Audio power amp measurement is not a black art. As I posted earlier, with a defined set of criteria, amplifiers can be compared on an apples to apples basis. The generally accepted criteria are 1KHz sinewave into 8 ohms with total harmonic distortion below 0.1%

To be clear, this does not capture every aspect of amp performance, there are many other parameters that can be measured, but it does provide a ready comparison.

In the US, claims of amplifier performance for home audio became so daft that the federal trade commission implemented the 1974 'amplifier rule' which mandated certain aspects of the testing process and required these parameters to be disclosed. It would be helpful if there was a similar standard adopted in the uk and used by hifi manufacturers.

 

[pauln]

So there we have two completely opposite opinions on the effectiveness or otherwise of "Naim" watts.

Maybe some people really do prefer the sound of an amplifier clipping?

It has been suggested that hearing the full dynamic range of a piece of music can provoke our "fight or flight" response and that can make certain personality types uneasy and uncomfortable while others revel in the scale and drama of the music.

Is peoples varying tastes in gear linked in some way to being a "thrill seeker" personality type for instance?

You make an interesting point here pauln.

It does seem that there might be some people who actually prefer the sound of a clipping amplifier. Not that there's necessarily anything wrong with that, although personally I don't like the sound of an amplifier when it's clipping.

I wonder if anyone has ever done any sort of reasearch into this?

Not to be rude and argumentative but he actually doesn't have a point. He has a very large assumption. You can't conclude that the amp was clipping just because it is rated at 25 watts. We don't know how efficient the speakers he used were, nor the listening distance or volume levels.

"what I thought was tape saturation was the Naim amp running out of headroom on a sudden dynamic peak, and distorting."

Is that not the same as clipping?

Anyway, the first point I was making was how this is all so subjective and not worth arguing about, secondly I remembered something I'd read and wondered if there was some physiological reason that would explain this variation in taste - and which would also explain why many people go mad for low powered valve amps rather than AVI's. They sound so different (apparently; I've heard neither) that both can't be high fidelity in the true sense of the word because there can be only one accurate reproduction of the original sound.

Sorry for veering off topic slightly.

 

[Covenanter]

It seems to me that there are two issues here:

1 - Are AVI making false / insufficiently well-defined claims about their equipment?

2 - Does what they say effect how the kit sounds?

On the first of these I have no idea what the situation is. If they are they need smacking.

On the second the answer is clearly no. As others have said, if they sound good and produce the volume you want then who cares what the wattage is? I've no idea of the wattage of my kit, although I could look it up if I wanted to. It sounds good, is as loud as I want it and I rarely have it higher than 10 o'clock and I've never heard any clipping.

Chris

 

[JMacMan]

It seems to me that there are two issues here:

1 - Are AVI making false / insufficiently well-defined claims about their equipment?

2 - Does what they say effect how the kit sounds?

On the first of these I have no idea what the situation is. If they are they need smacking.

On the second the answer is clearly no. As others have said, if they sound good and produce the volume you want then who cares what the wattage is? I've no idea of the wattage of my kit, although I could look it up if I wanted to. It sounds good, is as loud as I want it and I rarely have it higher than 10 o'clock and I've never heard any clipping.

Chris

Sensible post, and I agree.

JMac

 

[oldric_naubhoff]

you're in a way correct because I know the answer. there's no way in this world that a pair of transistors could produce 250W into 8 Ohms at reasonable THD level into sinewave for longer than a microsecond.

May I ask what you base your calculations on?

250 watts into 8 ohms is a little over 5amps. Any self respecting power transistor will be able to carry that level of current with ease.

simple. (250*8)^1/2=~45V

do you realisticaly believe the rails in there could sustain this level of voltage supply? I don't.

 

[BigH]

you're in a way correct because I know the answer. there's no way in this world that a pair of transistors could produce 250W into 8 Ohms at reasonable THD level into sinewave for longer than a microsecond.

May I ask what you base your calculations on?

250 watts into 8 ohms is a little over 5amps. Any self respecting power transistor will be able to carry that level of current with ease.

simple. (250*8)^1/2=~45V

do you realisticaly believe the rails in there could sustain this level of voltage supply? I don't.

Who said they were 8ohms?

 

[oldric_naubhoff]

you're in a way correct because I know the answer. there's no way in this world that a pair of transistors could produce 250W into 8 Ohms at reasonable THD level into sinewave for longer than a microsecond.

May I ask what you base your calculations on?

250 watts into 8 ohms is a little over 5amps. Any self respecting power transistor will be able to carry that level of current with ease.

simple. (250*8)^1/2=~45V

do you realisticaly believe the rails in there could sustain this level of voltage supply? I don't.

Who said they were 8ohms?

who said they weren't? it's not clear from spec on the web site. and 8 Ohm rating is univerally used for comparing amplifier performance. so I guess I'm not causing an abuse here supposing the rating was calculated into an 8 Ohm load.

P.S. rapid reply! I didn't even have a chance to edit my reply to remove the 8)

 

[John Duncan]

Like I said, they claim it into 5.1 ohms (the actual driver impedance). No @THD figures AFAIK. I found this with a quick search of the manufacturer's forum.

 

[andyjm]

Oldric,

I am afraid I don't quite understand your post. Assuming your post is questioning whether it is possible to build a power supply that will produce 250W (45V, 5.55A) and fit it into a speaker?

http://www.cui.com/Product/Power/Ac-Dc_Power_Supplies/Internal/120~499_W/VF-S250-XXA_Series

 

[BigH]

The problem is you are comparing amps for passive speakers with active speakers.

 

[oldric_naubhoff]

Oldric,

I am afraid I don't quite understand your post. Assuming your post is questioning whether it is possible to build a power supply that will produce 250W (45V, 5.55A) and fit it into a speaker?

http://www.cui.com/Product/Power/Ac-Dc_Power_Supplies/Internal/120~499_W/VF-S250-XXA_Series

yes, this one looks quite small. but it's a switching one. AFAIK AVI uses toroids.

 

[oldric_naubhoff]

The problem is you are comparing amps for passive speakers with active speakers.

like there is a difference between them.

 

[oldric_naubhoff]

Like I said, they claim it into 5.1 ohms (the actual driver impedance). No @THD figures AFAIK. I found this with a quick search of the manufacturer's forum.

that would mean some 150W into 8 Ohms. nothing near 250W.

 

[chebby]

AFAIK AVI uses toroids.

(Clicky)

 

[BigH]

Like I said, they claim it into 5.1 ohms (the actual driver impedance). No @THD figures AFAIK. I found this with a quick search of the manufacturer's forum.

that would mean some 150W into 8 Ohms. nothing near 250W.

It is what the speaker produces that counts. As for distortion there is generally much lower distortion with active speakers than passive ones.

 

[altruistic.lemon]

Speaker driver unitss are what determines the load for any speaker. Most are either 8 ohm or 4 ohm, but, if you look at the graphs, you can see some dip well below their average rating.

The ADM 40 uses Scanspeak Revelators, apparently, so you should be able to find the info from their website. Fine speakers, by the way.

 

[Dan Turner]

Oldric - If you're quoting power stats for an integrated amp then it makes sense to have a baseline such as quoting the power into an 8ohm load, so different amps could be compared, but why on earth would the manufacturer of an active speaker quote the power of the amp in those speakers as being anything other than what it is into the load presented by the specific driver it is (and only ever will be) connected to?

I have to confess I'm not entirely sure what you're accusing AVI of. Are you saying that you think they have quoted the figure in to 8ohm but that they must be lying because it's so high? Or are you saying that they have quoted the figure into the load presented by the driver, but you think they should have quoted the figure into 8ohms? Or are you saying that they have quoted the figure into the load presented by the driver, but you think they are deliberately hoping that people will assume that it is into 8ohm and therefore think it's more powerful than it actually is?

I will agree that AVI could be more explicit about the conditions under which the power figures were obtained. However rather than assume that they have done one of a multitude of stupid or dishonest things, why don't we assume instead that they the figures they have quoted have been taken on the only logical basis for the power rating of an amp in a pair of active speakers - that the power figure for the mid/bass amp is based on the actual performance when connected to the mid/bass driver that it is permanently connected to. It's the only figure that it makes any sense to quote, so I think it's a pretty safe assumption. There is no real basis to doubt that the figure given is genuine.

Please stop trolling, but you may permit yourself a wry smile at my expense for making me feel like I needed to write this post.

 

[Phileas]

Speaker driver unitss are what determines the load for any speaker. Most are either 8 ohm or 4 ohm, but, if you look at the graphs, you can see some dip well below their average rating.

The ADM 40 uses Scanspeak Revelators, apparently, so you should be able to find the info from their website. Fine speakers, by the way.

Illuminators.

 

[altruistic.lemon]

Yeah, thought it might be them after I'd posted. Fine speakers, nonetheless!

 

[oldric_naubhoff]

AFAIK AVI uses toroids.

(Clicky)

thanks Chebby. decent trafo and decent enough smoothing caps. I guess it could wrestle out that 150W when deeply biased into class B. no way it could put out 250W though. here's an example of a 250W/ 8 Ohm, 500W/ $ Ohm AB amp for comparison. note 3 pairs of transistors/ channel. it's an integrated amp so a preamp is included here as well.

 

[oldric_naubhoff]

Or are you saying that they have quoted the figure into the load presented by the driver, but you think they are deliberately hoping that people will assume that it is into 8ohm and therefore think it's more powerful than it actually is?

BINGO!

now this:

but why on earth would the manufacturer of an active speaker quote the power of the amp in those speakers as being anything other than what it is into the load presented by the specific driver it is (and only ever will be) connected to?

and this:

why don't we assume instead that they the figures they have quoted have been taken on the only logical basis for the power rating of an amp in a pair of active speakers - that the power figure for the mid/bass amp is based on the actual performance when connected to the mid/bass driver that it is permanently connected to. It's the only figure that it makes any sense to quote, so I think it's a pretty safe assumption. There is no real basis to doubt that the figure given is genuine.

do you really believe a dynamic driver presents a constant load for the amp? this is not a ribbon or a planar magnetic driver which genuinely acts as resistor. dynamic driver has inductive load imbedded into its construction. remember voice coil? plus putting a driver into a box will change its load characteristics even further. plus adding a bass reflex loading will change those characteristics further more. so no. I don't really agree with you saying that giving only one convenient figure in case of active speakers gives the whole picture.

just for the reference; an open baffle load characteristic of a Scanspeak 6,5" midbasss driver (I chose Scanspeak because graphs were readily available and AVI is using Scanspeak?), follow clicky to open a pdf. note how the impedance is wildly changing from some 40 Ohm @ 40Hz (must be resonance freq) than rapidly drops to reach minimum @ 5 Ohm between roughly 100-200Hz and then steadily rises again to above 8 Ohms in xover region. so as you can see that reference 5 Ohms load is hardly there over the covered spectrum.

Please stop trolling

ohhh, how I wish AVI fans stopped trolling too

 

[oldric_naubhoff]

Like I said, they claim it into 5.1 ohms (the actual driver impedance). No @THD figures AFAIK. I found this with a quick search of the manufacturer's forum.

that would mean some 150W into 8 Ohms. nothing near 250W.

It is what the speaker produces that counts. As for distortion there is generally much lower distortion with active speakers than passive ones.

maybe you mixed threads mate. AFAIK this is not a thread about speaker distortion but manufacturer's trustworthiness when submits specification data for public to asses product's performance.

 

[the record spot]

So long as it can reproduce the dynamic peaks of music at the desired volume level that's all that matters.

...and as long as you don't push the amp too hard, then you're fine. Applies across the board no matter what. Yes, you can have 200wpc, but you can as easily use a 30-watter with a pair of Mission 752s, say, and it'll work a treat. I have done and it did.

 

[Craig M.]

Oldric, I have just had a look at the websites of ATC, PMC, Barefoot, and Quested. All very big hitters in the active speaker world. None of them give any more info about amp power than AVI, none of them give figures into 8ohm. Nor do Mackie, nor do Genelec. AVI are quoting their amps inline with the other manufacturers I've looked at - they are quoting into the nominal impedance of the driver they are attached to. Let me know if you find an active speaker manufacturer who quotes power figures in the way you think they should.