This is what you guys are talking about:
http://www.circuitcity.com/ssm/Pioneer-4-T...roductDetail.do
Go to bestbuy.com and circuitcity.com and search for 4" speakers. Around six months ago these stores only carried 1-2 kinds of 4", now they have added more varieties. These retail stores are a little expensive when it comes to car speakers. If you don't mind ordering online, I recommend online audio merchants:
http://www.crutchfield.com/
{When searching their catalog skip the crutchfield car selector step, because they have incorrect size for LS400 in their lists.}
Here is their line up of 4” speakers:
http://www.crutchfield.com/S-mGf0WN9KxVB/c...=Y&skipvs=T
Here is a tutorial made by a Lexus enthusiast on “How to fit a 5.25" Speaker in a 4" Location”
http://www.lexls.com/tutorials/audio/fspeaker.html
In his pictures you can see that the speakers fit into a plastic box. If the holes on any 4” speakers do not match the original holes than you can simply drill new holes with a hand screw driver, nothing complicated there.
As for as selecting the correct speakers while NOT upgrading the original amplifier [if you have one] you should select speakers based on their sensitivity. Because you want speakers that are the most “efficient.”
"For the first example, a speaker that is 3 dB more sensitive than another will produce double the sound pressure (or play 3 dB louder) for the same power as the other. Thus a 100W speaker (call it A) rated at 92 dB/(W.m) sensitivity will be twice as loud as a 200W speaker (call it "b") rated at 89 dB/(W.m) when both are driven with 100W of input power. For this particular example, when driven at 100W, speaker A will produce the same SPL or loudness that speaker B would produce with 200W input. Thus a 3 dB increase in sensitivity of the speaker means that it will need half the power to achieve a given SPL, and this translates into a smaller power amplifier and some cost savings."---wikipedia
Originally I did purchase the Pioneer TS-G1041R from circuit city but after installing just one speaker, I returned both pairs and purchased Audiobahn AS40Q from crutchfield.com
However, the Pioneers are great speakers, in my opinion, just as good as the originals if not better. But I wanted to upgrade a little bit more.
Here is a link to my old thread about my speakers with pictures of the original Nak speakers and Pioneer TS-G1041R side by side.
http://us.lexusownersclub.com/forums/index...25116&st=15