Trying to make sense of the rules for matching amps to speakers

[jronnquist]

I would suggest setting the amp to 50w using the dmm method at 1khz sinewave

V(ac)=√(watt×ohm)
14.14(Ac)=√(50×4)
1. Set the dmm to v(ac) on the output terminals

2. Set the radio to the desired max volume usually 75% of the volume

3. Play a 1khz tone recorded at -3db

4. With the tone playing turn the gain up until the dmm reads 14v. +/- .5v

5. Remove the dmm and set the crossovers

6. Plug in the speakers

7. Starting with the volume low turn the volume up to the desired level without passing the previously selected max point.

8. Adjust time alignment and eq (try and cut more than boost)

Having more power on hand isn't really a bad thing since it will more than likely go unused anyway. Even with 50w you will likely have to turn the highs down or the subs up relative to one another since a lot more power is needed to match the efficiency of higher frequency speakers.

90db subs need 2x the power of 93db mids and 2x more to match 96db tweeters

500sub, 250mid, 125tweet

But it's more like 87db subs and 93db mid and 96dbtweeter
500w sub, 125w mid, 62.5w tweeter

thats just for flat response. Most people want subs and midbass 10db higher than everything midrange which means a lot more power is used in the lower frequency low efficiency subs.

It's easy to see why you would use significantly less power for highs once you consider efficiency and then the target response curve.

Just out of curiosity, when you say turn up the gain, are we talking about the input sensitivity?

 

[winkychevelle 10+ year member]

Just out of curiosity, when you say turn up the gain, are we talking about the input sensitivity?
View attachment 46484

Yes, and don't use any bass boost.

 

[jronnquist]

Yes, and don't use any bass boost.

Got it.

 

[nauc 10+ year member]

what car? what deck? any subs?

 

[jronnquist]

what car? what deck? any subs?

2012 Seat Alhambra

Deck: Grundig GX-3800 (already unhappy with this and planning to switch it out for a Kenwood unit)

Door speakers: Kenwood X302-4 paired with Focal ASE165 on front doors and ASE130 on rears.

Sub: Rockford Fostgate PBR 300X1 paired with a custom built enclosure containing 2 x Earthquake Sound SWS 6.5X drivers.