Open baffle (dipole) bass problem

[Volenti]

I've just recently finished my dipole speakers, I'm very impressed with the sound (as are my friends). I used Peerless HDS tweeters (810653) and a pair of Phillips PRS 602 6 1/2'' mids ,a cast frame 4 ohm ex-car audio speaker (don't laugh)

The mids were extremely co-operative in dipole and needed no x-over what so ever, and the Peerless tweeters got away with a single series 2.2uf poly cap.

I'm getting a +-3db response from 80hz to 20k, pretty stoked with that, so I decided to add some active bottom end, and that's where the problems started.

I have an 8'' sub in a TL (can just be seen behind the electronics and under the telly in the attached pic) that's powered by a plate amp with switchable 0-180 phase (as well as gain, freq ect) but no matter which position phase switch is in I get a huge chasm at 50hz (response pics will follow)

I initally thought it was some weird interaction between the TL and the dipole speakers so I quickly rigged up a 12'' in one of my sealed test enclosures but ended up with the same result.

Now granted with just the sub alone the "room" is a bit weak at 50hz but no where near the dip that happens with the dipoles running.

Thoughts?

[Volenti]

response of dipole speakers alone.

[Volenti]

response with sub presumably in phase

[Volenti]

response with sub out of phase

[ronc]

The response curve is typical of a wave re-enforcement/cancellation.Its primarly a room condition, but a phase change should (<--keyword) solve the problem.
ron

[Erik]

I think Ron's right about the room interaction.

Have you measured the sub by itself to see what the in-room response is?

[Guss]

Originally posted by Volenti
a cast frame 4 ohm ex-car audio speaker (don't laugh)

lol, don't worry, many car woofers are just some 4ohm version of common home woofers. Max pentivent subs are suitable for both. I've built a pair of MaxPent subs and I was pleased in my room and in ''the'' car, not mine btw I still can't drive !

[Volenti]

Originally posted by Erik
I think Ron's right about the room interaction.

Have you measured the sub by itself to see what the in-room response is?

I have measured the sub (both sub setups) and while there is a dip at 50hz the dipole speakers seem to make it worse, regardless of phase.

So to try and get around the room problem I try some different sub postions? or listening positions? the layout of the listening area is pretty flexable (I live by my self so I can do whatever I want )

[ronc]

Depends on the room dimensions.There are 3 normal different possible phase (high peaks or low peaks) in an in-room response.If you divide all 3 room dimensions(x,y.z) by 1/2 wavelength (of the problem frequencies) i would bet that some or all of the peaks/nulls fall within those numbers.
In my room i have bass traps in the corners, mid traps high on the wall between the horns, and high traps behind the listening position.This helps some with in room response but will not eliminate it totally.
ron

[ronc]

Yea, i looked again at the curve.The peaks appear to be almost 1/2 octave (first peak x 1.414) to the bottom of the adjacent null.Without exact numbers its hard to calculate.
ron