What is best attenuation rat for power attenuator

[kldguitar]

The four components are #1 preamp tube distortion, #2 power tube distortion, #3 speaker distortion and #4 the physical movement of air that your speakers produce at high volumes.An attenuator can only simulate two out of the four components that are involved when you crank up an amp. So the two components missing are speaker distortion and the physical movement of air and these are VERY BIG components! Some attenuators have built in EQ to help modify the tone but if you are looking to get the exact tone and feel of your amp at higher volumes, you can't get all the way there from here...
The harder you work a speaker the better it sounds until you reach the point where the voice coil is out of travel so players using a 4/12 cab will find that when attenuated down to a low volume their sound will be particularly thin. If you want a better sound at lower volumes try running a single 12 where you can work the speaker a little, this will make a lot of difference over using four speakers that are barely working.
when attenuation is more than -12dB through attenuator, the sound will become thinner, So the better way is select right power amp and good attenuation.
what is right power of amp?

[Chuck H]

This isn't going to help much... But... Speaker distortion can be ignored. Most distorted amps, classic or otherwise, do not actually drive the speaker hard enough to cause speaker related distortions. There are a few. But it's rare enough that adding this parameter to your criteria only complicates your problem. So that leaves one more parameter. Air movement. Which is to say, how the human ear percieves frequency balance and compression at different volumes. This is certainly something that can be simulated with frequency response, BUT... It's frightfully hard to emulate all the nuances with a device as crude as a power attenuator. That's why most only offer a simple bright switch. The HotPlate has a lamp circuit that offers some compression. But it's my understanding that most players only use it until the novelty wears off. So we're left with only EQ> The Weber MASS unit has adjustments for high, low and mid. But IMHE players become confused by this. It just seems to get more lost the more they mess with it. Looking at the schem for that unit I can see why. There isn't much isolation possible for the band specifics and this just makes it hard to dial in. The average musician would be much happier with one knob that makes things sound acceptible. You can search for the magic formula if you like. Others are doing it too. It's commendable that you want to make a higher performance product. I just don;t think there is an economical way to do it in this case. The Ho, or Ultimate attenuator uses an impedance that is somewhat nominal to speaker impedance over a large bandwidth and then re amplifies with a solid state circuit. This allows much better EQ control. Food for thought. The Ho/Ultimate attenuator is considered by many to be the best sounding unit on the market. And it should be for the price. But consider that the human ear s perceptions change with sound pressures. So any EQ adjustment would need to be controled logarithmically simultaneaous with the amount of attenuation. That's my two cents. Good luck in general. And good luck with the translation of all the vocabulary I've included.

P.S. I failed to mention that you neglected one more parameter that affect attenuation performance. That is, speakers have a complex impedance. Resistors do not. An amplifier playing into a complex impedance performs and "feels" different from an amp playing into a purely resistive load. Since a reactive load that matches every speakers impedance curve is impossible, it is therefor impossible to create an attenuator that truely sounds accurate at high levels of attenuation for every amp. Not to mention the much greater expense of including reactive circuitry in such a design. There will always be a compromise.

[Steve Conner]

I beg to differ on ignoring speaker distortion.

Celestion specified some of their guitar speakers with an Xmax of 0. That means the voice coil is the same height as the pole pieces, so as soon as the cone starts to move at all, the motor becomes non-linear. I believe this is representative of many guitar speakers. They probably generate lots of distortion on loud, low notes. Designs that started out as PA woofers, like the EV and JBL ones, would be an important exception.

My favourite "attenuator" is a crappy back room in an industrial estate with no neighbours.

[kldguitar]

I failed to mention that you neglected one more parameter that affect attenuation performance.
We compare THD Hot plate, Dr.z air Brake, and KLDguitar PB1, we selected different amps include Marshall DSL2000 , THD BiValve-30™, and mesa boogie Marke II.
we found, all attenuators were good connecting with Marshall's amp, but all are bad connecting with mesa boogie. The reason is different speaker and amp have different impedance which is not pure resistor.It is impossible to let one reactive load matching every speakers. It is why some people like this attenuator, some like others.

[Chuck H]

Chuck H says "thank you" for this useful post.

[kldguitar]

Thanks Chuck H. I agree with you "It's frightfully hard to emulate all the nuances with a device as crude as a power attenuator." . In fact, distortion of speaker is no-line of speaker. Speaker is almost no-line component, almost all its working area is no-line . It is difficult to emulation only by Cap, Resistor . The attenuator can be used in two ways.
1.Protecting your hearing and not noising your neighbor when you practice in home .Below is chart of Volume of guitar.
50dB-60dB volume of electric guitar without power.
70dB-80dB the volume of watching TV and wood guitar
80-90dB Volume of solid guitar amp, this volume don't noise your neighbor on day.
90dB-100dB The volume of ROCK ,you can start feeling cool ,although it still need more headroom. It is only one fifth of full volume of 30w-50w amp damaging your hearing. Not face to speaker.
100dB-110dB The volume is very cool. half of volume of 50w amp, good headroom, damaged hearing serious .
110dB-120dB It is limit of amp.
so if you want hear good sound and protecting your hearing same time. It is better use one attenuator which has smaller atttenuation rating.
2.Silence recording in your home studio,which cann't afford of expensive recording gears. There are many soft wares in studio which can compensate last two components we talked upwards. It is complicated and expensive to many guitarist ,recording music by Microphone .It will reduce cost and let their works easy,recording sound by attenuator which has DI out ,then deal with it by computer.

[kldguitar]

The function of attenuator is consuming additional power . The safe and best way to consume power is through resistor net. Electric power changed to heat which is directly dissipated. Inductance and Capacitance net stored power not consume power. If the power stored in L-C net cann't discharge right, it is easy damaged speaker or amp. In fact, some artists have noticed this problem.

[Chuck H]

Yes. Some players have had amp problems due to the use of attenuators. But I think it may have more to do with the abuse of the amps. After all, when do they get to crank up their amp for six hours straight unless their using an attenuator? Also, when unplugging speakers and plugging in attenuators and then unplugging attenuators and plugging in speakers... There is a lot more opportunity to accidentally run the amps output into an open load by mistake. The best attenuators simulate a typical guitar speaker impedance for the alternative load. Marshall's power break goes so far as to adjust the attenuation through a variable inductance. But their alternative load is less than ideal. A lot of designers have opinions on the matter. But be sure that no amp ever blew up because it was playing into a rated load. Attenuators, when designed and used properly, pose no threat to amplifiers any more than cranking them up to ten with actual speakers does. In fact, many attenuators are less prone to cause failure as a load. The biggest issue is that players don't generally run their amps wide open with actual speakers but commonly do it with attenuators. When do you suppose an amp is most likely to fail? when it's being played on two, or when it's being played on ten?

[Leo_Gnardo]

Yes. Some players have had amp problems due to the use of attenuators.

AND HOW! There's also those who don't pay attention which is the input, and which is the output. In other words, they plug the amp into the attenuator's output (thinking that's the side that receives the amp's output). Then hearing not much signal (since the amp's output is driving practically a short circuit) dial the amp up to 10, 11, 12... I've seen it done by stage techs who ought to know better, working for world class bands. (Think CSN for instance) As well as local club & home-recording guitarists.

As far as loss of tone at dialed-down volume, think about Fletcher-Munson curves. The ear-brain interface tends to discount high and low frequencies when listening to lower volume signals. So there's that to contend with, as well as physical explanations. Some attenuators try to overcome this by passing extra high & low frequencies as you dial in more attenuation. I've seen built in attenuators in THD amps that have a brightening capacitor between the hot lug & wiper of the wire-wound pot.

I'm not a big fan of power attenuators, but there's always someone who will use 'em, so we gots to deal with 'em.