The JBL 305P MkII has three small switches on the back: input sensitivity, Boundary EQ, and HF Trim. The 306P MkII and 308P MkII have the same three. JBL's manual says to pick the Boundary EQ setting that gives you the most natural bass, and that mostly comes down to how close the wall is.
The short answer
| Where your monitors sit | Boundary EQ | HF Trim |
|---|---|---|
| On stands, well away from walls | 0 dB | 0 dB |
| On a desk, near a wall | -1.5 dB | 0 dB |
| Right against a wall or in a corner | -3 dB | 0 dB |
Start there, then check by ear (below).
Boundary EQ
A wall or desk close to a speaker adds bass. Boundary EQ turns the deepest bass down by 1.5 or 3 dB to make up for it.
On the 305P MkII it matters more, because the port is on the back. Push the speaker against a wall and the port fires bass straight into it. Before you touch the switch, pull the speakers away from the wall as far as your desk allows. Our post on rear-ported monitors near a wall has more on spacing.
HF Trim
HF Trim turns the treble up or down by 2 dB. It has nothing to do with bass. Try -2 dB if a bare room makes cymbals and vocals harsh, +2 dB if a soft, heavily furnished room sounds dull. Otherwise leave it at 0.
Input sensitivity
This switch matches what you plug in, not your room. It ships at -10 dBV, which JBL says suits most setups, including a computer or phone. Move it to +4 dBu if your audio interface or mixer is rated for +4 dBu output (its manual will say), or if the sound distorts even with the speaker's volume knob turned low. Set both speakers the same.
Placement
JBL's manual gives a short list, and every item affects the bass:
- Stand the speaker upright, tweeter on top.
- Aim each tweeter straight at your ears.
- Stands are better than the desk. A speaker sitting on the desk shakes it, which muddies the bass. On a desk, stick the four rubber pads from the box on the bottom corners.
- Keep the two speakers symmetrical, each the same distance from the walls next to it.
- Sit so you and the two speakers form a triangle with equal sides. JBL notes that moving the speakers closer together or further apart changes the bass you hear, so try a few spacings.
The free Monitor Placement tool works out these distances for your room.
Check it by ear
- Play a song you know well with a steady bass line, at your normal working volume.
- Listen to each bass note. Do some boom while others fade?
- Move Boundary EQ one step on both speakers and play the same part again.
- Keep the setting where the bass line sounds most even, not the one with the least bass.
The free Room Bass Test makes this easier. It plays a slow bass sweep in your browser, so you can hear exactly where the bass swells.
Check the desk before the switch
JBL's troubleshooting page has a quick test for a boomy speaker. While music plays, lift one speaker off the desk. If the boom drops, the speaker is shaking the desk. Pads or stands fix that better than any switch. If nothing changes, go back to Boundary EQ and try -1.5 dB and -3 dB.
When the boom stays
Boundary EQ fixes the extra bass from a wall, which spreads across the whole low end. It can't touch the boom from your room's size, where one or two notes get much louder where you sit. At -3 dB those notes still stick out, because the switch turns them down by the same amount as everything else.
Unboom is for that note. It plays a quiet sweep, listens with your Mac's microphone (or lets you pick the boom by ear), and turns down just that note in your music and video apps. It only cuts, never boosts, and one switch turns it off so you can compare.
FAQ
Are 305P MkIIs good for a small room?
Yes. Small monitors suit small rooms, and Boundary EQ helps when they sit on a desk near a wall. Expect a note or two to still boom. That's the room, and new speakers in the same spot would boom at the same notes.
Should both monitors use the same Boundary EQ setting?
Usually, yes. If one sits in a corner and the other doesn't, try one more step on the corner speaker.
Does this work for the 306P MkII and 308P MkII?
Yes, they have the same three switches. The 308P plays deeper bass, so it's more likely to bring out your room's boomy notes.