Active speaker - orginal bass driver vs. modern

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I have old active 3 way speakers with one of best mids&highs i have ever heard.

The bass is not so good.

Crossover section for the bass is 45hz to 400hz.

If i play them loud (the max) the bass gets distorted& muddy. Also the bass woofers are so old (40 years) that they breakdown every now and then. They simply cannot handle the power.

I want to replace the bass with modern woofers using the original active amp. There is three separate amps for bass, mid&highs.

Everytime its said that if you replace the original driver with another one, you need to change the crossover too.

So first, if i use l-pad attenuator for getting the levels right

And secondly make a new enclosure for the new bass driver according to its specs and for adjusting the time delay.

Why wouldnt it work in this case?
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The original is late seventies 8" peerless woofer. Theres no info about it in the net. The amp in the active speaker for bass is quad 405 style 50w transistor amp.

I want drive 10" Phl driver in a new enclosure. Completely different specs, sensitivity etc.

So using l-pad for levels and new enclosure for the driver/delay

What will be the problems?
Potential problems....

An L-Pad on a woofer may have to absorb quite a lot of power - so may need quite a high power rating. It will also introduce extra series resistance between the amp and driver, so will reduce damping factor - you'll be unlikely to get really nice tight bass from such an arrangement.

The amp plus active crossover combination may already have EQ built in to get the specific frequency response that the manufacturer wanted out of the original driver.
A new driver in a different enclosure will almost certainly not have the same FR, thus that EQ built in to the system will now be wrong.

At the very least you'd need to measure the FR of the output of the amp to check this, and if there is EQ, be prepared to add extra EQ upstream of the amp to counteract it if your new woofer has differing tone shaping needs.

If you're experienced enough at component level electronics, you may be able to ID the relevant parts of the circuitry and adjust them instead of putting extra EQ upstream.

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