Why would you optimize height WRT bass response? In almost all instances speakers are voiced on the tweeters axis or between the mid and tweeter.
Speaker height should always aligned and be placed be on the designed listening axis so it coincides with seated listening height.
In addition there are nulls in the vertical axis due to crossover and driver physical distance.
You go too high or too low and you will be listening in one of the nulls.
So in all cases you should adjust height where the listening axis is. I almost all cases except for the largest systems this will automatically raise the speaker off the floor higher than what spikes alone can do.
2-3 mm WRT bass response? A foot OK not 2-3mm we are talking wavelengths is feet.
Rob
Hello Rob,
The "why" is because it works. Why it works I don't know but here is some attempt. The closest boundary to the woofer is likely the floor. In some speakers about a foot away. The boundaries in a room are extremely high pressure zones and as we move away from the boundary the pressure drops rapidly. We all know this from the front wall as we all pull our speakers away from it. The most common reason to pull the speaker away from the boundary is boomy bass. The floor is the exact same thing. Because the speaker is so close to the floor moving the speaker a few mm away from the floor is changing the way the speaker interacts with it. I don't know any other or better explanation than this.
Being on the tweeter axis depends on how the speaker is designed. But lets assume your speaker was designed for listening to occur on axis. If the tweeter is below your ear level then you could always raise the speaker up in some way (e.g. put books under it) to get the tweeter up to your ear level. What about speakers where the tweeter height is above your ear height when seated? I suppose you could raise your sofa by several inches and again be on the tweeter axis. But there is a different way.
If the tweeter is low then you simply rake the speakers back until the tweeter points at your ear. You are still listening on axis. You can still adjust speaker height independent of rake.
The effect of raising the speaker height is very obvious in the bass. All I ask is that you try it. We need to move past the stopping thought of "bass waves are measured in feet so how could moving the speaker up 2-3 mm matter?". It is a simple experiment that would take maybe 30 minutes. Here are the steps:
1. pick a track with bass that is played relatively fast. Electric bass or stand up bass. You could use the stereophile test CD that has the bass guitar.
2. Listen to this track several times with your speakers the way they are. Make notes if necessary. Pay close attention to how articulate the bass sounds. Is it muddy or murky sounding in certain areas.
3. Go over to the speakers and get each speaker as level as you can. Both front to back and side to side.
4. Come back and listen to the track again. Note any differences.
5. Go over to the speakers and give each of the spike 1/2 of a turn. You can go full turn if you want.
6. Listen again and note any changes.
7. Keep raising the spikes and noting changes. Assuming you have enough thread you should run into a spot where the bass starts to sound too lean. This is usually within a few turns of the spike but it depends on the speaker. sometimes there is so much bass you can not get it to really lean out until you are already out of thread.
7. if you hit the too lean part then go back down 1/4 turn and reassess.