No, an attenuator is not just a resistor - it would be hopelessly inaccurate if it was. Even when an attenuator is a well-conceived potential divider it is affected by the source impedance and the load impedance to some extent. The source impedance is usually so low that it isn't an issue but the load impedance can be a nuisance if you need accuracy. It is possible to minimise the effects of the load impedance by making the impedance of the attenuator much lower, but doing that puts an unnecessary load on the source so I don't recommend it. The truth is that without knowing the load impedance that the attenuator will work with (ie the input impedance of the amplifier) it is difficult to get accurate attenuation within 1dB or so. It gets worse the lower the level of attenuation you're aiming for.
In short, in-line attenuators can work to even out the sensitivity discrepancy between amplifiers, but you can't really rely on the nominal value of the attenuator when you're aiming for accuracey of 2dB or better.
Location: Middlesex, UK
Posts: 4,482
I'm Alex.
Not sure if anyone has mentioned this before, apologies if they have. Perhaps one needs to consider if the two amps are phase inverting or not.
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I understand what you’re saying. I guess the only way to make these inline attenuators work would be to have a wide selection, and use trial and error to find the one that works best? Even if it’s just car audio, it’s still it’s hit and miss. An active crossover is the best option.
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Given accurate figures for the amps' sensitivities and input impedances it's possible to use attenuators to match them. Assuming that the speakers have passive crossovers with elements to match the drivers' sensitivites, all should be fine. However, if you're starting from scratch and using amps with different sensitivities and drivers with different sensitivities then yes, you would have to make measurements to get them to work well together.
Location: London/Durham
Posts: 6,883
I'm Lawrence.
I did this quite simply in a previous set up of mine with kef reference model 2s which were a beast to drive in the bass. I used a valve integrated on the mid and treble, it had a pre amp out so I took that into a Nad 370 integrated line input. I could use the volume of the Nad to adjust the bass output, having a second pre in the path had no obvious deleterious affect as it was only going below about 150hz. This was a cheap solution that probably drove the Kefs as well as a very expensive valve or hybrid amp. In fact I found that for some recordings it was useful to adjust the bass output (obvious examples being 80s pop/rock albums with not enough bass, but also a few recordings that had too much).
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Location: Birmingham, UK
Posts: 394
I'm Phil.
A big thank you to everyone who has responded with suggestions and advice , my bass speaker crosses over at 200hz so not to bad , the plate amplifiers from hypex and going active on the bass only seems the way to go , i have 3 sets of banana plugs on the drivers so it would be easy to plug
back in the passive crossover to the bass and compare with the active crossover . £350 ish 200w rms into 8 ohm , out of stock at the moment so i cant pull the trigger at the moment , me phil.
Phil.