Open baffle speakers

@coltrane1 I have been designing and building subwoofers for 40 years, https://imgur.com/gallery/building-resonance-free-subwoofers-dOTF3cS I have no idea about bass and I have been an audiophile for 70 years. My mother had to put a table radio in the crib with me to shut me up. None of this means that I know what I am listening to. This is a matter of experience. To know what proper imaging sounds like you have to have heard a system that images correctly. I did not hear that system until I was 24 years old and I was not able to reproduce that feat for another 10 years in my own system. 

Unless you have measured your system in your room you have no idea what you are listening too. You like what you hear, but you cannot say exactly what that is.

@coltrane1 Sorry friend, but I have made and measured open baffle subwoofers and there is no mystery here. If you think what your listening too sounds good you have a lot left to experience, which is a good thing.

@jaytor @coltrane1 Low bass, below 100 Hz is handily the most difficult part of the audio spectrum to evaluate by ear and even measurement can be tricky. The first tell that there are problems is the baffle shaking or vibrating with low notes. That vibration is distortion. The best way of measuring what is happening is comparing free air response to t in room measured response with short sinewave sweeps measuring at various locations. Regular enclosed subwoofers are bad enough, but Open baffle versions are all over the map. If you think you are getting anything below 30 Hz. Take a pair of subwoofers and put them across the room from one another. Flip one in and out of phase while playing a 25 Hz test tone. Please tell us what happens.

@ozzy62 Frequency response measurements are taken at 1 meter. The frequency response below 50 Hz of an open baffle woofer in a residential room at a 12 foot listening position is at best unpredictable and more than likely horrendous. An open baffle speaker makes a lot of sense if you were going to cross over to subwoofers at 100 Hz. It is easier to avoid enclosure resonances and you get the advantage of dipole behavior when it comes to room interaction. 

@jasonbourne71 My very best friend in Miami, a Jewish journalist two decades my elder had DQ 10s. We met at Sound Components, Peter McGrath's high end store. I had just moved down there for med school and I was a fish out of water. Leo and his wife took me under their wing. I already had a pair of Acoustat Xs with their built in high voltage amp which had the most amazing image compared to what I was use to at the expense of bass and volume. Since I lived in the Nurses Dorm (don't ask) I couldn't play them loud anyway. So, I'm over Leo's for the first time sitting in front of his DQ 10s and I mean right in front. Leo listened to speakers like most of us listen to headphones. My response when he asked me what I though was, "Very transparent. I can't tell where anything is but they are very transparent." Thus began my career trying to fix other people's systems. I could never get them to image properly and at that point I had not been exposed to the high school teacher's system that permanently warped my brain, or the HQD system that came next. I did not achieve that level of performance until I got my first pair of Acoustat 2+2s some five years later. The DQ 10s downfall was undoubtedly it's crossover. Within a year Leo had moved over to Acoustat Monitor 4s on top of RH Labs subwoofers controlled by the Dalquist LP1 crossover. Biggest set of headphones you'll ever see. There was no way they were going to perform to their potential in that room, but they did image better than the DQ 10s. 

@invalid I owned Divas for 6 years. I had just moved back to New England in 1987 and picked up my pair directly from the factory in Mass. My previous speakers were Acoustat 2+2s with Tympany 3s before that and several models of Acoustat before that going back to 1978. All dipoles. The Divas chased me right back to Acoustat 2+2s.  I use Sound Labs 645-8s now, 8 foot 645s. All dipoles without exception, but only two full range line sources, the 2+2s and the current Sound Labs.

The reason you have to dampen the front wall behind dipoles that have thin membranes or ribbons is the sound reflected off the front wall at full volume comes right back at the speaker and is transmitted back through the diaphragms causing severe comb filtering. This creates response irregularities and really messes up imaging. In some cases the effect can be euphonic especially if you have not lived with a system that images properly. It can create a false sense of ambience at the expense of image specificity. At worse it can make things shrill and sibilant. 

If you go to my virtual system page you can see a device called a SALLIE (Sound Attenuator of Low Level Interference Effects) These are sitting directly behind my speakers and are way more affective than the usual fare. Roger West of Sound Labs only makes them 1 foot wide and I needed them 2 feet wide. Left to my own devices I made them out of Walnut, god forbid someone should look behind the speaker. I had been using plain 4" acoustic foam tiles behind the speakers, but the remaining comb filtering was tying a new digital signal processor up in knots, so I had to do something more drastic. Fortunately it worked.

The DQ10 was not an open baffle speaker in the purest sense. It was a speaker with numerous time aligned baffles. It was a beautiful sounding speaker that could not image.

One has to be specific about what they are calling open baffle speakers. The are bipolar speakers, both sides radiating in phase and dipolar speakers, the sides radiating out of phase. Most open baffle speakers are dipoles and most are planar speakers of one sort or another, ESLs, Ribbons and Planar Magnetics. Trying to do this with multiple dynamic speakers has never worked well. This brings us to line source speakers. Line source speakers project sound more effectively than point source speakers. Acoustic power drops off at the cube of the distance with point sources, but at the square of the distance with line sources which is why you see them at large concerts. Due to their construction, planar speakers fall naturally into the line source category, with some irregularity. For a speaker to project as a line source it has to be longer than the wavelength of the lowest frequency it is to reproduce. For a free standing speaker to project 20 Hz as a line source it would have to be 60 feet long! There is one major caveat. If the line source terminates at a barriers, a walls, floors or ceilings it will maintain line source behavior down to 1 Hz. Dipolar line sources, like any dipole does not like making bass below 100 Hz. This is particularly true of full range dipoles like ESLs. They will do it, but it creates distortion with everything else the speaker is doing. Even if the speaker ends at barriers. typically the floor and the ceiling, it is best to cross over to subwoofers at 100 Hz, but it can not be any old subwoofer. In order to maintain balanced amplitude behavior with distance it has to be a line source subwoofer. Even two subwoofers will get lost under line source speakers. The major problem is most "line source" speakers really are not line sources. A speaker that is 6.5 feet tall in a room with 8 foot ceilings looses it's line source behavior under about 250 Hz. As you move away from these speakers they will become progressively brighter or tinny. 

Line source, dipole speakers have one huge advantage in residential size rooms. Because they do not radiate sound to the sides, up or down there is way less room interaction. Only the front wall is a problem and this can be easily dampened behind the speaker.  Only Horn loaded speakers have dispersion controlled at this level. 

The OP is right to question the bass performance of "open baffle" speakers. The baffle has to be so large you enter the realm of infinite baffle loudspeakers. People including Linkwitz have tried it, tongue in cheek and they will provide the illusion of bass, but it is far from accurate. What most people are listening to under 100 Hz is a mess anyway. Don't believe me? Measure it for yourself. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DQ10s are not open baffle speakers. They are a bunch of separate, time aligned baffles mounted in a cage with mass insanity for a crossover. They could not image to save their lives. They hold a place in HiFi history next to Bose 901s.