how many "A" watts to drive 802d 75dbs

[misterdoggy]

This might be a stupid question, but does anyone know how many "A" watts it would take to drive a pair of 802D's to 75 decibels.

Is there a scientific formula ?

Im trying to figure out how big an amp can do the job in the "A" watt arena

[Paul H]

Start with the speakers sensitivity rating - whatever decibel rating per 1 watt they have - I don't know what these are but probably 80-something for 1 watt.

Double the wattage for each 3 decibel increase.

And it doesn't matter if its A, B or G class for that calculation.

[misterdoggy]

Start with the speakers sensitivity rating - whatever decibel rating per 1 watt they have - I don't know what these are but probably 80-something for 1 watt.

Double the wattage for each 3 decibel increase.

And it doesn't matter if its A, B or G class for that calculation.

Paul you are saying all watts are the same ? AB whatever

I don't think so

[sikoniko]

Paul you are saying all watts are the same ? AB whatever

I don't think so

He is saying it doesnt matter what type of watts. This is how you figure out how many watts the speakers are pushing, then you look at your amp and see what range it is in.

Sensitivity 90dB spl (2.83V, 1m)

So I am guessing 1W for 90db?

[sikoniko]

He is saying it doesnt matter what type of watts. This is how you figure out how many watts the speakers are pushing, then you look at your amp and see what range it is in.

Sensitivity 90dB spl (2.83V, 1m)

So I am guessing 1W for 90db?

not sure how that works out. I never listen at that volume. Does that mean we only need 10w amps?

[DM3000 Owner]

He is saying it doesnt matter what type of watts. This is how you figure out how many watts the speakers are pushing, then you look at your amp and see what range it is in.

Sensitivity 90dB spl (2.83V, 1m)

So I am guessing 1W for 90db?

A few more things need to be added to the equation (rules of thumb from speaker builders). subtract 3 db for every meter that you are away from the speaker (after the first one). Ex. if you are three meters away, subtract 6 db.

Subtract 2 db from the manufacturer's specification to account for different room treatments, etc.

Finally, the dynamics of the music. if you listen at 75 db but there are peaks that are 6 db above the steady 75 db you need power to cover that too.

These are very general rules of thumb that I have learned from speaker builders, so take it for what it is worth. Also remember, for every 3 db increase, you must double the power. Go out and pick up a Radio Shack db meter for $40 and experiment.

Finally, Class B amplifiers are "in their realm" after the first few watts, so you really do not need that much true class a power if the amp transitions well. If you try to play a true Class A amp at volume you will heat the entire room (and the amp will be huge and put out maybe 10 or 20 watts).

As an aside, I have used 3.5 watt SET (Single Ended Triode) amps to drive horn speakers rated at 103 db 1W/1M and my wife has had to tell me to turn it down because the floor was shaking upstairs. But these are extremely efficient speakers. Horn Speakers are fun.

[Joey_V]

Paul you are saying all watts are the same ? AB whatever

I don't think so

As for sound, watts from a different class (bearing the same amplifier topology/design) will sound a bit different. However, the amount a power a speaker draws is the same at a given SPL.

[dknightd]

Yes there are formulas for these things. Unfortunately I'm not fluent in them.

First the speaker sensitivity has to be considered. Note that db/2.83V at 1 meter is only useful for an 8 ohm speaker (perhaps partially explaining why speakers are lower impendance than they used to be - it makes them appear more efficient - but you better have an amp that can deliver current as well as voltage), you need to convert that to db/watt at 1 meter. Unfortunately speaker impedance varies with frequency - which complicates things.

Then you need to consider that you don't listen 1m away from your speaker. Again, there are formulas for that. Complicated only by room gain.

Then you need to consider that you probably don't listen to test tones, so, you have
to allow for peaks. How much to allow depends on what you listen to, and how its dynamic peaks compare to the RMS.

For 75db, at typical distances, speakers, and music I'd guestimate 10-20 watts should be fine. The RMS will probably be around 1 watt, but you need to have adequate headroom. 5 might be enough, 50 would be better just in case you want to listen to more dynamic music, or turn it up to 80 db

There must be web sites out there that lead you through these calculations, but a quick search didn't find one. Maybe you could find one, or, maybe somebody else could find it for you. Unfortunately whatever you find will be an approximation - unless you find somebody who has done the analysis for your speakers and your music - if you find such a site, double what they recommend to be on the safe side.

[misterdoggy]

So back to the original question restated:

If I have a Pass labs X5 which is 125 watts a channel and the first 15 watts are "A" watts, would this be enough to drive the 802D's efficiently. (enough bass)

[dknightd]

If you have it, try it, and let us know. If memory serves you've got kick-ass amps already, do they deliver less "class A" watts? I'd be suprised. To answer your question, I think 15 watts with 125 watts in reserve should be plenty to give you a nice sound at 75db, just don't try to use them to get 100db and you'll be fine. I've read good things about that pass labs amp, you may like it just fine.

[misterdoggy]

I've been downsizing and have found I didn't need to have a 100$k in audio equipment to have great sound. Pass Labs makes great amps and the sound is great and for a lot less.

It sounds good. I'm just wondering about the next model up the X250.5 which is 250 watts and the frist 35 A watts

[sikoniko]

Thats what I like about classe... 1/3 power is class A. 1/3 of 200W is 66W.

[Kobus]

I've been downsizing and have found I didn't need to have a 100$k in audio equipment to have great sound

Hi doggy, I trust we will hear more about this.

Kobus

[misterdoggy]

Yeah, I went the whole route to the top.

Got one of the best systems money could buy. Then realized that the difference might not be that much.

Sold off all the Mark Levinson 2x436 @ 19,000 euros and 1x433 @ 14000 euros and replaced them with a Pass Labs X5 for 3000 euros and you kow what. Still sounds outstanding.

So when they ask which components are the most important in the chain, I would say good quality cables (not crazy prices) and the most important are at the beginning and the end. The source (CD) and the Speakers. Cause if the speaker isn't up to the task, and its the final voice for the system to perfrom, then nothing before it matters. Amps and Preamps should be transparent.

So I aint dumpin my 802D's so fast............

[DM3000 Owner]

Yeah, I went the whole route to the top.

Got one of the best systems money could buy. Then realized that the difference might not be that much.

Sold off all the Mark Levinson 2x436 @ 19,000 euros and 1x433 @ 14000 euros and replaced them with a Pass Labs X5 for 3000 euros and you kow what. Still sounds outstanding.

So when they ask which components are the most important in the chain, I would say good quality cables (not crazy prices) and the most important are at the beginning and the end. The source (CD) and the Speakers. Cause if the speaker isn't up to the task, and its the final voice for the system to perfrom, then nothing before it matters. Amps and Preamps should be transparent.

So I aint dumpin my 802D's so fast............

That is quite a journey!

As far as the watts, impedance plays a big role, but look at what the rated power is at the load presented. Most very accurate speakers dip way low in impedance at certain points. This is avoided in other speakers so that most amps can drive them. In any event, you seem to be looking at very high quality amps. FWIW, I used a 200 wpc amp with my N801's and it drove them just fine for the loads that you are talking about.

As for your experience, I have noticed that when you A/B and listen closely, you can hear a difference, but you will never notice most of the difference if you do not A/B compare (after you are up there in quality as far as equipment).

You will probably be happy for years with whatever you buy, as long as you do not get the upgrade bug.

I spoke to someone who was extremely satisfied with IcePower amps running 802's. They are based in europe.

http://www.acoustic-reality.com/

Let us know what you decide on.

[ChrisssB]

I hope this helps:

http://www.myhometheater.homestead.com/splcalculator.html

Regards
Chris

[Joey_V]

So back to the original question restated:

If I have a Pass labs X5 which is 125 watts a channel and the first 15 watts are "A" watts, would this be enough to drive the 802D's efficiently. (enough bass)

15w can drive it well... but you will easily run out of headroom depending on the dynamics of said track. Say the 802D is 90db efficient with 1watt at 1meter. Then at your listening chair, you're probably getting about 80-84db or less of actual sound. So, lets play devils advocate and play it safe at 80db... you're using 1watt, regardless of class.

Now, say you're listening to a piece of jazz by Miles Davis. Though the baseline track is at 80db, lets just say that Miles Davis pulls out his trumpet and has a dynamic peak that hits about 89db at listening position.

So, that's about a 9db swing, which is very possible with well recorded/mastered recordings. That's 9/3 = 3... meaning that you need 3 doublings of your initial 80db watt usage. So at 89db, you're looking at using 8w.

You're probably saying, well that's fine.

Now what if you werent getting 80db at listening position with 1w? What if you were getting only about 77db? Now, to get to 89db, your amp has to use up 16w!

Now what if the piece you are listening to has a transient peak that hits 92db and you're at a baseline of 77db at listening spot? Now you require 32w!

Just to hit 101db with a speaker that hits 77db at the sweetspot requires quite a bit of power... now we're looking at about 256w of power consumed!!

And you think those Kilowatt amps are bottomless? Hah... a peak that hits 107db will bring a killowatt amp down to its knees (impedance not withstanding).

[misterdoggy]

Okay, then heres another question. How do we know we are getting the bass of of the amp, or that we are driving the speakers and hearing everything compared with more power. I'm not talking about to the point of clipping, but would we hear better bass at lower listening levels with a more powerful amp.

[Kobus]

This can get interesting.

I doubt that there are specs for this question, maybe the doubling of watts with the halving of Ohms will be an indication.

Not sure though where pure "A" fits into this.

Kobus

[RebelMan]

Okay, then heres another question. How do we know we are getting the bass of of the amp, or that we are driving the speakers and hearing everything compared with more power. I'm not talking about to the point of clipping, but would we hear better bass at lower listening levels with a more powerful amp.

MD, why does "Class A" power matter to you? If your reasons are like most, then perhaps you should consider driving the HF with a Class A amp and the LF with a Class AB amp to achieve the best price/performance ratio. This is how I have seen and heard most Pass Labs (XA and X) amplifiers used and the results have been delicious.

[misterdoggy]

MD, why does "Class A" power matter to you? If your reasons are like most, then perhaps you should consider driving the HF with a Class A amp and the LF with a Class AB amp to achieve the best price/performance ratio. This is how I have seen and heard most Pass Labs (XA and X) amplifiers used and the results have been delicious.

Its the LF I'm looking to get more of. I don't listen at high decibels, but woudl like to hear more bass at low decibels.

[Nick M]

Not sure how many watts from Krell amps are actually Class A, but man do I love 'em!

The FPB-300cx (300Wx2) sounds amazing hooked up to large bookshelves/small towers. I do notice that having massive reserves of power makes dynamics sound fuller, and the music just seems tight and effortless. I also notice when using Krell's preamp/integrated amp with Krell juice that the midrange sounds natural and fluid (but not warm or glossed over). I like the clarity of solid state amps (get that out of the way). My A/B rotel 200Wx2 sounds great, but the Krell's just seem more natural (best word to describe it)... almost as if my Rotels are a touch artificial (hate to use that word because it's really not representative of the quality I get from my Rotel gear).

Anyhoo, try experimenting with something like the Krell 700cx to get an idea of what serious power does for control and dynamics. I could never afford an amp like that with what I make (unless I ditched every other hobby), but it doesn't hurt to listen... unless you like it...

[sikoniko]

Not sure how many watts from Krell amps are actually Class A, but man do I love 'em!

The FPB-300cx (300Wx2) sounds amazing hooked up to large bookshelves/small towers. I do notice that having massive reserves of power makes dynamics sound fuller, and the music just seems tight and effortless. I also notice when using Krell's preamp/integrated amp with Krell juice that the midrange sounds natural and fluid (but not warm or glossed over). I like the clarity of solid state amps (get that out of the way). My A/B rotel 200Wx2 sounds great, but the Krell's just seem more natural (best word to describe it)... almost as if my Rotels are a touch artificial (hate to use that word because it's really not representative of the quality I get from my Rotel gear).

Anyhoo, try experimenting with something like the Krell 700cx to get an idea of what serious power does for control and dynamics. I could never afford an amp like that with what I make (unless I ditched every other hobby), but it doesn't hurt to listen... unless you like it...

Nicholas,

Are you using the Krell CAST? That is supposed to make a difference as well for an all Krell setup.

I have heard the 700cx with the CAST pre and a pair of 802d's.

It sounds great for about a half hour, then i get fatigued... I hear their new EVO stuff is the best of the best with no fatigue, but it is really expensive.

[misterdoggy]

Not sure how many watts from Krell amps are actually Class A, but man do I love 'em!

The FPB-300cx (300Wx2) sounds amazing hooked up to large bookshelves/small towers. I do notice that having massive reserves of power makes dynamics sound fuller, and the music just seems tight and effortless. I also notice when using Krell's preamp/integrated amp with Krell juice that the midrange sounds natural and fluid (but not warm or glossed over). I like the clarity of solid state amps (get that out of the way). My A/B rotel 200Wx2 sounds great, but the Krell's just seem more natural (best word to describe it)... almost as if my Rotels are a touch artificial (hate to use that word because it's really not representative of the quality I get from my Rotel gear).

Anyhoo, try experimenting with something like the Krell 700cx to get an idea of what serious power does for control and dynamics. I could never afford an amp like that with what I make (unless I ditched every other hobby), but it doesn't hurt to listen... unless you like it...

Nicholas,

I used to run a FBP 400CX with the 802D's. I found krell too bright with the 802D's and let it go.

My question is not about too much power like 700mx's, but how much is enough to drive them properly

[Kobus]

how much is enough to drive them properly

You surely do not expect a conclusive answer on that.

Before all this started, I would have looked at you for this type of answer.

Kobus

[Joey_V]

MD, why does "Class A" power matter to you? If your reasons are like most, then perhaps you should consider driving the HF with a Class A amp and the LF with a Class AB amp to achieve the best price/performance ratio. This is how I have seen and heard most Pass Labs (XA and X) amplifiers used and the results have been delicious.

Regardless, I think that using two amps to biamp a speaker still draws the exact same amount of power from each of the amps (because this results ina a parallel circuit) so in essence, I think the best value configuration is going Class A single amp for the entire speaker rather than going Class A amp for the tweeter and a Class A/B amp for the bass woofers. Not to mention the logistical problem when it comes to preamplification for amplifiers with different power specs and different topologies/design.

I think that you are asking whether there is a certain amount of power required to produce good bass. Well, the woofer will move as per the spec sheet on the BW802D at whatever efficiency it is. At 1w, the entire speaker is 90db loud at 1m.

[DM3000 Owner]

Regardless, I think that using two amps to biamp a speaker still draws the exact same amount of power from each of the amps (because this results ina a parallel circuit) so in essence, I think the best value configuration is going Class A single amp for the entire speaker rather than going Class A amp for the tweeter and a Class A/B amp for the bass woofers. Not to mention the logistical problem when it comes to preamplification for amplifiers with different power specs and different topologies/design.

I think that you are asking whether there is a certain amount of power required to produce good bass. Well, the woofer will move as per the spec sheet on the BW802D at whatever efficiency it is. At 1w, the entire speaker is 90db loud at 1m.

I have not examined the 802's crossover, but it must be really unusual. I tri-amped (active crossover) a fully horn loaded speaker and used 30w, 30w and 200w for the tweeter, midrange and woofer respectively. if the midrange and tweeter are using the same amount of power as the woofer, B&W is doing something very different than most other speakers.

I'm not sure that I understand the parallel circuit reasoning. In the most simple example, assume a first order network.

The woofer's amp will be fed into an inductor that acts as a low pass filter.

The midrange and tweeter's amp will be fed into a capacitor that acts as a high pass filter then parallel to an inductor as a low pass for the midrange and again from the original high pass filter to another capacitor which will "shave off" lower frequencies and pass very high frequencies to the tweeter.

This ignores any efficiency compensation, but the midrange and tweeter will use less power because they do not move very much compared to the woofer and are usually more efficient.

In any event, the 802's crossover must be compensating somehow.

[Joey_V]

I have not examined the 802's crossover, but it must be really unusual. I tri-amped (active crossover) a fully horn loaded speaker and used 30w, 30w and 200w for the tweeter, midrange and woofer respectively. if the midrange and tweeter are using the same amount of power as the woofer, B&W is doing something very different than most other speakers.

I'm not sure that I understand the parallel circuit reasoning. In the most simple example, assume a first order network.

The woofer's amp will be fed into an inductor that acts as a low pass filter.

The midrange and tweeter's amp will be fed into a capacitor that acts as a high pass filter then parallel to an inductor as a low pass for the midrange and again from the original high pass filter to another capacitor which will "shave off" lower frequencies and pass very high frequencies to the tweeter.

This ignores any efficiency compensation, but the midrange and tweeter will use less power because they do not move very much compared to the woofer and are usually more efficient.

In any event, the 802's crossover must be compensating somehow.

Capacitors for higher frequencies and inductors for lower frequencies are all inherent in almost any crossover, I'm not sure if the amp's power consumption will change due to this. From what I know, regardless of whether you're trying to power a tweeter or the woofer, the speaker's sensitivity will tell you exactly what you need in terms of power to get it to a certain preset value (i.e. SPL). So regardless of what amp you use, you're still going to use 1watt from the amp or 1 watt from each of the amps in a biamp or triamp system.

I'm hoping Kal Rubinson will see this thread a respond as I would like to be corrected or be supported in this dilemma.

[RebelMan]

Regardless, I think that using two amps to biamp a speaker still draws the exact same amount of power from each of the amps (because this results ina a parallel circuit) so in essence, I think the best value configuration is going Class A single amp for the entire speaker rather than going Class A amp for the tweeter and a Class A/B amp for the bass woofers. Not to mention the logistical problem when it comes to preamplification for amplifiers with different power specs and different topologies/design.

A loudspeaker is not a simple circuit with a fixed resistance, it is reactive. The impedance, or load, that a power amplifier sees is comprised of resistance, inductive reactance and capacitive reactance both of which are functions of frequency in an AC circuit. As the frequency varies so will the demands placed on the power amplifier also vary. It’s possible that the amount of power would be similar in both cases but the amount of current will be different given that power is a product of both voltage and current. Class AB amplifiers generally have much larger power (current) reserves than do their Class A bretheren.

The 802Ds are not internally wired for a reason and that reason is to facilitate biwiring or biamping. Whether or not these benefits are audible to the listener is debatable, but what isn’t debatable are the physics behind the design. Impedance restricts current flow. As frequencies increase impedance will increase placing less demand on the source of power. As frequencies decrease impedance will decrease placing more demand on the source of power. Although, the amplifier is “capable” of amplifying the entire frequency band it will only deliver the amount of power necessary to satisfy the needs of the (primarily) inductive circuit (tweeter/midrange) when frequencies are high and (primarily) capacitive circuit (woofer) when frequencies are low. A bi-amped configuration splits the loads between amplifiers with the lions share going to the low frequency driver(s).

The impedance curves and phase plots of the 802D show it to be somewhat demanding at the low end and un-wielding in the upper midband. This would suggest that an amplifier with sufficient current reserves be considered. While a fully Class A amplifier with sufficient power will suffice it may not be the optimal alternative. Such an amplifier will likely be large, heavy, hot and expensive. A lesser Class A amplifier for the top end buttressed with a sufficiently capable Class AB amplifier for the bottom end maybe a better alternative and is a plausible reason why the arrangements that I have seen using Pass Labs amps are configured in this manner.

I do agree that careful gain matching would be in order and utilizing a front end that supports a bi-amped configuration would easy the implementation. However, a greater price/performance ratio can be realized using a mix of Class A (or perhaps one of the SET variety) and Class AB amplifiers in a bi-amped configuration than could be achieved with a Class A amplifier alone, provided that a methodical approach is taken and the advantages for implementing a fully Class A (SET) power source for the midrange and high frequencies and a Class AB power source for the low frequencies is fully understood. Having said that, some well designed push-pull amplifiers are built with the ability to handle large bias current and thus operate in a wider Class A band before switching eschewing the need for a fully Class A device.

[DM3000 Owner]

A loudspeaker is not a simple circuit with a fixed resistance, it is reactive. The impedance, or load, that a power amplifier sees is comprised of resistance, inductive reactance and capacitive reactance both of which are functions of frequency in an AC circuit. As the frequency varies so will the demands placed on the power amplifier also vary. It’s possible that the amount of power would be similar in both cases but the amount of current will be different given that power is a product of both voltage and current. Class AB amplifiers generally have much larger power (current) reserves than do their Class A bretheren.

The 802Ds are not internally wired for a reason and that reason is to facilitate biwiring or biamping. Whether or not these benefits are audible to the listener is debatable, but what isn’t debatable are the physics behind the design. Impedance restricts current flow. As frequencies increase impedance will increase placing less demand on the source of power. As frequencies decrease impedance will decrease placing more demand on the source of power. Although, the amplifier is “capable” of amplifying the entire frequency band it will only deliver the amount of power necessary to satisfy the needs of the (primarily) inductive circuit (tweeter/midrange) when frequencies are high and (primarily) capacitive circuit (woofer) when frequencies are low. A bi-amped configuration splits the loads between amplifiers with the lions share going to the low frequency driver(s).

The impedance curves and phase plots of the 802D show it to be somewhat demanding at the low end and un-wielding in the upper midband. This would suggest that an amplifier with sufficient current reserves be considered. While a fully Class A amplifier with sufficient power will suffice it may not be the optimal alternative. Such an amplifier will likely be large, heavy, hot and expensive. A lesser Class A amplifier for the top end buttressed with a sufficiently capable Class AB amplifier for the bottom end maybe a better cost effective alternative and is a plausible reason why the arrangements that I have seen using Pass Labs amps are configured in this manner.

I do agree that careful gain matching would be in order and utilizing a front end that supports a bi-wired configuration would easy the implementation. However, a greater price/performance ratio can be realized using a mix of Class A (or perhaps one of the SET variety) and Class AB amplifiers in a bi-wired configuration than could be achieved with a Class A amplifier alone, provided that a methodical approach is taken and the advantages for implementing a fully Class A (SET) power source for the midrange and high frequencies and a Class AB for the low frequencies is fully understood. However, some well designed push-pull amplifiers are built with the ability to handle large bias current and thus operate in a wider Class A band before switching eschewing the need for a fully Class A device.

I just remembered that a B&W engineer told me that they usually use the same power for the top and bottom end when bi-amping. Home amps, unlike pro amps, do not have gain controls, so maybe they anticipate people using the same power for each and design accordingly. Hmmmm...

[misterdoggy]

I just remembered that a B&W engineer told me that they usually use the same power for the top and bottom end when bi-amping. Home amps, unlike pro amps, do not have gain controls, so maybe they anticipate people using the same power for each and design accordingly. Hmmmm...

They biamp at Abbey road Studios with a pair of the same CAM400's top and and bottom.

Kobus,

I got sucked in to the more amps is better. Quality Amps are better than lower quality amps, but quality amps cost more. better to have less amps of quality than more amps of a lesser quality. Therefore the question is how much A watts are enough.

I know 1000 A watts would do it, but what is the least amount that would do it efficiently. In any case I have a 250 watt X250.5 where the first 35 watts are A coming. I am going to A/B and will try to get some answers.

The learning curve is a long and winding road

[sg2]

Hi all,

The answer to your wonder is simple : biamping is not bypassing the filters.

- it is the role of the filters to extract from the full band signal fed at a given power point, the right amount of frequency filtered signal, for each speaker. Sounds obvious, but note the "right" : the tweeter only takes a fraction of the electrical power required by the woofer, to generate the same amount of SPL, thus it is the filter which is in charge of this power "reduction" by adequate impedance matching

- also note the "s" at the end of "filters" above. In the B&W 80x, there is not a single filter, but rather two, a low pass filter for the woofers, and a mid+high pass filter for the medium & tweeter. In regular mono amplified configs, you just have those two filters working in parallel, thanks to the wire jumpers that effectively wire in parallel the two filter/speaker combos.

- To illustrate the "power to SPL" reasoning above, say your amp sends 100 W of white noise (a random signal with a flat power/frequency spectral density) to a mono amplified 80x. The low pass filter, essentially made of an inductive coil in series with the woofers (both of them being wired in parallel, thus the low impedance dip of the 80X) will send most of the sub-350 Hz spectrum to the woofer, without any power attenuation below the crossover frequency. The med&high pass filters, essentially made of capacitors & resistors in series with the speakers, will pass only the right frequency ranges to each of med & tweeter, but the construction of the med/hi filter will also eat part of the power, so that all in all, the more efficient med & high speakers produce the same SPL as the woofer.

- When you bi amp a loudspeaker like the 802D, you don't bypass the filters (you rather feed independantly the low pass filter for the woofers, and the med/high pass filter for the med/tweeter). And you do feed them with the same signal, at the same power. Thus, each of the two filters will do the exact same job as if mono amplified : extract the right part of the spectrum, and do the impedance / power adaptation.

- Thus, say you have a mono amped 100 W configuration ; if you bi-amp without bypassing the filters (which is the only option with loudspeakers with internal filters), then you need 2 100W amps, sending the full band to the speakers (otherwise you will unbalance the power-to-SPL efficiency of each speakers). Coincidently, this is also why you send the same input signal at the same level to the amps when you biamp like that (and why you absolutely need identical gain amps).

- Subsequently, the *only* benefit of bi amping is that the amplifier allocated to the "med & high" speakers, is not strained by the huge current demand by the woofer (the amp will output the low frequency *voltage*, but because of the high pass nature of the med&high filter, there will be no *current* drained for this part of the spectrum). Thus, you would expect a better med & high definition in a bi amped setup.

- This situation cannot be compared to when you triamp an unfiltered speaker combo with pre-amp active filtering. In this case, the bandwidth selection and power-to-SPL work is done at the active filter level (before the amps), thus you can get away with different gain amps, and it is obvious that in this case you can have a dedicated high power but low resolution amp for the woofer, and fine but less powerful amps for the med & high.

Regards,
--
Stéphane

BTW, MrDoggy, I see you are living in Annecy, I'm also a 802D'er, I'm living in Lyon, and I'm also pondering on my next amp setup (IcePower ? Gemincore ? Classe 2200 ? Advance Acoustic MAA705 ? McIntosh ? choices are so open...)

[misterdoggy]

Stéphane

BTW, MrDoggy, I see you are living in Annecy, I'm also a 802D'er, I'm living in Lyon, and I'm also pondering on my next amp setup (IcePower ? Gemincore ? Classe 2200 ? Advance Acoustic MAA705 ? McIntosh ? choices are so open...)

Hi Stephane,
Glad to see a fellow 802Der not far from me. You have much more possibilities to visit and see top audio stuff. Here there are "slim pickings". Even in Geneva there isn't much.

I have had the chance to live witht the 802D's with the following amps, Krell FPB400CX, Rotel 1090RB, Mark Levinson ML436, and Now Pass Labs X5 but awaiting delivery of a X250.5. The Rotel was not remarkable, The Krell was too bright and you fatigued too quickly, the Mark Levinson was understated with a beautiful timbre, nice sound stage, and overall great performer, but at 19,000 euros list price they had better be.

I had a Pass Labs preamp X1 and was so impressed with Pass products that I decided to give their amps a chance. Now I can tell you that the X5 is a great amp, lots of detail, lacking a little bit in the bass and mid, but this could be that the X5 is not up to the task of driving the 802Ds, therefore this thread.

I will let you know how it works out. I have a great contact for Levinson if you are looking for anything, right here in france.

[DM3000 Owner]

--
Stéphane

BTW, MrDoggy, I see you are living in Annecy, I'm also a 802D'er, I'm living in Lyon, and I'm also pondering on my next amp setup (IcePower ? Gemincore ? Classe 2200 ? Advance Acoustic MAA705 ? McIntosh ? choices are so open...)

I'd be interested in your review of an icepower amp if you try one.

[misterdoggy]

I'd be interested in your review of an icepower amp if you try one.

icepower im not familiar with it. I'll check it out

[gerardhn]

Doggy
Dont do so difficult: x1 /250.5 is perfect. You know that!
My wondering to you: why do you deny Classe?
You can buy it blindly, or is it too expensive in your current minimalistic approach? Pass is qua price on the same level i think....?

[RebelMan]

I just remembered that a B&W engineer told me that they usually use the same power for the top and bottom end when bi-amping.

…

They biamp at Abbey road Studios with a pair of the same CAM400's top and and bottom.

From a technical standpoint, that is, with respect to impedence matching and voltage gains, etcetera, it is irrelevant that Abbey Road chose to bi-amp their monitors with the same amplifier. Any one of the Classe’ Delta Series amplifiers could have been selected to bi-amp the HF of the 800D in concert with the CA-M400 bi-amping the LF.


One watt of power in does not equal one watt of power out. That is why efficiency is never stated on the specification sheets the speaker manufactures provide. Instead we have SPL because it is a much easier quantity to measure. The problem with SPL is that it doesn’t care weather power is Class A or Class B. When you consider that dynamic speakers like the 802D are notoriously inefficient, on the order of 1%, gauging how much Class A power would be necessary to achieve the desired 75dB SPL from the listener’s position is an uneasy task at best.

B&W recommends that the 802D be feed a minimum of 50 watts, but why? Could it be to overcome the inherent inefficiency of the speaker itself? Or could it be that it is the amount required to achieve the necessary 90dB SPL at 2.83V/1M stated on their specifications? Let’s assume for a moment that both are true. Knowing that for every doubling of power the perceived loudness is measured to be 3dB we can say that at 25 watts of Class A input the rated SPL will drop to 87dB. Given that for every doubling of distance we loose 6dB of SPL our figure will drop to 75db at a distance of 4M. Because we want listen to stereo not mono we add another speaker to bring the SPL up to 78dB.

Okay perfect, we can achieve our goal with a 50 watt amplifier. But wait, musical signals are not a steady source of current but rather dynamic inputs of varying amplitude and speed. Assuming the typical dynamic spread of 6db we find that our comfortable 78dB SPL has just climbed to 84dB. This jump in SPL will require that an amplifier have the necessary headroom to compensate, but not many have more than about 1.5dB on tap to supply. If we assume headroom on the order of 3dB (atypical of most amplifiers) the amplifier will still need to have double the continuous power output available from its reserves. This puts our once pleasing 25 watts of Class A power into Class B territory, and thus circumventing the benefits of using the first X watts of Class A power.

It would appear that misterdoggy wants to utilize only the Class A part of a Class A/B amplifier. If the first X number of Class A watts were sufficiently high enough then this might be doable, but the reality is very few Class A/B amplifiers can offer this and as the above example shows it would unlikely meet his needs in practice. Unless of course he prefers to listen to music so low that the effects of the Fletcher-Munson curves become prevalent. If I recall he is looking for more bass at low levels not less!

So the question remains, why is Class A power crucial to misterdoggy’s enjoyment? If its like most, that is, a linear output stage that is free from switching distortion and feedback noise the results of which audibly manifests itself in midrange air and high levels of sweetness, then only a fully Class A device will do. Unfortunately, fully Class A devices, when used with moderately sensitive speakers like the 802D, are not very adept to producing deep, powerful bass and are usually lacking as impedances drop, conversely what the 802D needs at low frequencies. For instance the fully Class A Pass Labs XA160 amp loses half of its output power when the load drops to about 4 ohms. Not the most compatible marriage between it and the 802D which makes frequent visits into sub 4 ohm territory and less.

The only other economically viable alternative would be a passively bi-amped configuration. This is precisely what speaker engineers like TAD’s Andrew Jones has done with his Reference 1’s (among others) and Pass Labs amps. I have had the pleasure of meeting Mr. Jones and hearing his speakers (which aren’t too dissimilar from the B&W 800s) in such a configuration. The results of which have left their indelible mark on me, twice and counting.

[DM3000 Owner]

From a technical standpoint, that is, with respect to impedence matching and voltage gains, etcetera, it is irrelevant that Abbey Road chose to bi-amp their monitors with the same amplifier. Any one of the Classe’ Delta Series amplifiers could have been selected to bi-amp the HF of the 800D in concert with the CA-M400 bi-amping the LF.


One watt of power in does not equal one watt of power out. That is why efficiency is never stated on the specification sheets the speaker manufactures provide. Instead we have SPL because it is a much easier quantity to measure. The problem with SPL is that it doesn’t care weather power is Class A or Class B. When you consider that dynamic speakers like the 802D are notoriously inefficient, on the order of 1%, gauging how much Class A power would be necessary to achieve the desired 75dB SPL from the listener’s position is an uneasy task at best.



.

Here is the area that I am having a problem with. If the 802's are balanced when 1 amp drives them, say a 400 wpc amp, they must be balanced when 2 amps drive the now divided crossover.

So say for a particular passage, the preamp puts out 0.25 v at 100 hz and 0.25v at 4,000 hz for a balanced sound both calling for maybe 1 watt on a particular 100 wpc amp. If one amp is hooked up, them 1 watt is delivered at 100 hz (corresponding to an ultimate spl in the room) and 1 watt is delivered at 4,000 hz (also corresponding to a certain spl) (a crazy example but nice round numbers).

Now lets bi-amp with a 100 wpc amp for high frequency and a 500 wpc amp for low frequency. So now the preamp puts out 0.25v at 4,000 hz calling for 1 watt and it also puts out 0.25v at 100 hz, but on the 500 wpc amp, the output that corresponds to 0.25v is, say 3 watts. The sound is no longer is balance.

This is one big reason that pro amps have gain controls on the front. It is also a reason the dividing networks and active equalizers have gain control (a little different, but the theory).

It just seems unusual that a speaker will require the same size amps for high and low to be balanced. It appears that you will always have wasted headroom on the upper frequency and it is a strange way to balance a speaker.

[sikoniko]

Doggy
Dont do so difficult: x1 /250.5 is perfect. You know that!
My wondering to you: why do you deny Classe?
You can buy it blindly, or is it too expensive in your current minimalistic approach? Pass is qua price on the same level i think....?

It would seem he wants something noone else has (at least on this board).

Theres a really cool thread on AVS by Zissou about pre/pro's and whats the most musical.. he evaluated pre/pros in the various price levels and reports back. perhap doggy will do the same for us in regards to amps.

[Kal Rubinson]

Now lets bi-amp with a 100 wpc amp for high frequency and a 500 wpc amp for low frequency. So now the preamp puts out 0.25v at 4,000 hz calling for 1 watt and it also puts out 0.25v at 100 hz, but on the 500 wpc amp, the output that corresponds to 0.25v is, say 3 watts. The sound is no longer is balance.

What you describe has nothing to do with output power of the amps but with their different input voltage sensitivities. A 100w amp and a 500w amp with the same sensitivity will output the same power at all input voltages until the former runs out of steam.

Kal

[misterdoggy]

What you describe has nothing to do with output power of the amps but with their different input voltage sensitivities. A 100w amp and a 500w amp with the same sensitivity will output the same power at all input voltages until the former runs out of steam.

Kal

Kal,

The "Grand" question is when do we sense "running out of steam". How do we sense when you have enough power for the 802D's. I'm not talking about obvious like clipping.

[Kal Rubinson]

Kal,

The "Grand" question is when do we sense "running out of steam". How do we sense when you have enough power for the 802D's. I'm not talking about obvious like clipping.

Probably as we approach clipping. :W

Kal

[misterdoggy]

Kal,

Do you think that more "A" power would present more mids and bass at lower decibels.

[Kal Rubinson]

Kal,

Do you think that more "A" power would present more mids and bass at lower decibels.

Depends on the amp. Frankly, I have not had to deal with that phenomenon in years since a good amp has little change in tonal balance throughout its usable power range. My problem is with wimpy class A-only amps that are often clipping when asked to do the job.

Kal

[misterdoggy]

Depends on the amp. Frankly, I have not had to deal with that phenomenon in years since a good amp has little change in tonal balance throughout its usable power range. My problem is with wimpy class A-only amps that are often clipping when asked to do the job.

Kal

Kal,

Wimpy Class A ???

Can you be more specific