If you have a loudspeaker that have flat frequency response in free field an put it in a room you get interaction with walls. This gives non flat response. Further, different positions gives different response.
My take on this is that Sig Carlsson turned it around, and chose a position in a room and designed the loudspeaker to have as flat response that you can get for that position.
For a 3way, bass close to two boundaries ( front and floor ) and a certain distance to the side wall. For midrange close to one boundary ( front ) and away from the others, remember wavelength shorter for midrange.
He had a room built at KTH where 3 wall were reflecting and the other 3 were absorbing, so he could measure this.
For reading; Richard V Waterhouse, Interference Patterns in Reverberant Sound Fields ( JASA 1955 ) and Roy F Allison, The influence of Room Bounaries on Loudspeaker Power Output ( JAES 1974 ).
I think he wanted direct response and reverberant response to match, thus an omnidirectional loudspeaker.
/örjan
My take on this is that Sig Carlsson turned it around, and chose a position in a room and designed the loudspeaker to have as flat response that you can get for that position.
For a 3way, bass close to two boundaries ( front and floor ) and a certain distance to the side wall. For midrange close to one boundary ( front ) and away from the others, remember wavelength shorter for midrange.
He had a room built at KTH where 3 wall were reflecting and the other 3 were absorbing, so he could measure this.
For reading; Richard V Waterhouse, Interference Patterns in Reverberant Sound Fields ( JASA 1955 ) and Roy F Allison, The influence of Room Bounaries on Loudspeaker Power Output ( JAES 1974 ).
I think he wanted direct response and reverberant response to match, thus an omnidirectional loudspeaker.
/örjan
I think we're all aware of this fundamental approach. It's why I'm on this path.
Good point.
Yeah, I did read this.
Not sure if that defines an omni, but for sure his focus is on sound power -- total acoustic energy into the room -- rather than FR at any given point or even average hemispherical.
At this point, I'm thinking of assembling a tweeter + mid on top baffle angled as in the Larsen 4 (or maybe the 6) + a side firing 8" or 10" woofer on the inside panel, near floor/wall intersection. The 4 presents less of a challenge for my woodworking skills.
I would probably position the mid driver to clear the flange around the top of the tower -- if only to reduce diffraction effects. Thick felt or similar around the sides/back of the drivers might also be useful.
A triangular cross-section tower might make the construction simpler. The top baffle would then tilt away from the inside panel of the tower without discontinuities. (Just thought of it so no drawings...)
With these Larsen designs, the mid/treble directivity is reduced nearly to just 1/8 sphere, focusing most of the total acoustic energy toward the central area between L & R speakers. I suspect the steep upward angle is to compensate at least partly for the low height of the tower. Height, including the top driver assembly, is just 73.5cm or 29". Of course, there's also the benefit of reduced floor bounce effects.
With only one tweeter angled this way, I expect the measured on-axis FR has to have an upward till to compensate for higher freq. beaming.
The ceiling is also brought into play more prominently as a late reflection boundary. It probably explains part of the spatial performance the reviewers all refer to. My studio has a ceiling of "50% absorbent" tiles + 12" of fiberglass insulation. IE, considerably more absorbent than in most rooms. I wonder how that will affect the overall sound.
Thanks Dave.
Interesting but weird, and very dated looking web site. The designs look like they haven't been changed for years, too. The smaller models look similar to the Larsens, and the Compass & Starter models are similar to what I described in my last post in a rectangular tower. I'd be leery of the bigger ones. I am not seeking to make an omni.
Compass -- no mention of placement, though the web site shows them far from walls. If that's the way they're meant to be placed, not what I'm looking for here.
Stigs OA-52 sounded very spacious in his last listening room (very high ceiling) driven by ML amps and and a Bremen Licience No1 D/A - I heard it numerous times and it all sounded really good.
I also owned a pair of OA-52 for more many many years. Stig Carlsson was a somewhat mysterious man but it was always very interesting to visit his apartment where he also did the development of the OA--5x series. Strange 4-way prototypes loomed behind curtains ;-)
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I also owned a pair of OA-52 for more many many years. Stig Carlsson was a somewhat mysterious man but it was always very interesting to visit his apartment where he also did the development of the OA--5x series. Strange 4-way prototypes loomed behind curtains ;-)
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Not me. An omni would radiate in 360 deg if placed out in the room - like a Walsh. Only one Carlsson do that and it would be the OA-14 as I see it.
114 and 2212 has arrays of tweeters directed in a certian way...
MBL yes!
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I beg to differ, like TNT: It doesn't radiate 360 deg. It's much more directed than that -- except for <150Hz or so.
Since no one here seems have have any significant hands-on experience with the Larsens, I've decided to forge ahead on my own.
I studied the idea of a triangular cross section tower for a while --
This idea has been set aside, because the end result will be too much like a corner speaker. I don't intend for it to be in a corner or address questions about why the sharp 45 corner edge is sticking out into the room. 😛
Instead, I will copy the look of the Shahinian Acoustics Compass (I posted a pic above) and make the lowest corner of the diamond-shaped top baffle the inside corner of each mirror-image pair. It took a little puzzling to figure out how to cut the 4 side panels to make a 45 degree angle across the top starting with a corner. I realized that it's actually a 22.5 degree cut across the top end of each side panel. Haven't drawn it yet but I'm pretty sure this works. (LMK if you think this won't work!) (Just in case, will try with carboard first.)
Max height at the top will be 36~40", with the tweeter centered a few inches below, which seems about right. If an 10" square cross-section tower is used, the widest portion of the top baffle will be 14.14" -- more than enough for any mid driver. It might be better to go smaller -- perhaps 8", though this might make the enclosure volume too small if I'm going to make it a 3-way with anything bigger than 7". Assuming at least 5/8" thick panels, a 36~40" tall 8" square tower = 25~28 liters or about a cubit foot. This should be enough for the right 7-8" woofer. But then some space is needed for the mid driver. I haven't thought much beyond the 6.5" Seas driver I used in the last project. Hmmm.
It might mean just staying with a 2-way for this implementation. Go for something more ambitious next time. The close-wall reinforcement should make its bass better than in the pentagon LXmini tower anyway.
One question is whether the panel that rises up beyond the drivers in the Larsen 8 and 9 is absorbent or reflective? I refer to the portion of those speakers that go up against the front wall. My hunch is that it is partly or mostly absorbent to reduce diffractive reflections off that wall...?
Any suggestions or thoughts?
I studied the idea of a triangular cross section tower for a while --
This idea has been set aside, because the end result will be too much like a corner speaker. I don't intend for it to be in a corner or address questions about why the sharp 45 corner edge is sticking out into the room. 😛
Instead, I will copy the look of the Shahinian Acoustics Compass (I posted a pic above) and make the lowest corner of the diamond-shaped top baffle the inside corner of each mirror-image pair. It took a little puzzling to figure out how to cut the 4 side panels to make a 45 degree angle across the top starting with a corner. I realized that it's actually a 22.5 degree cut across the top end of each side panel. Haven't drawn it yet but I'm pretty sure this works. (LMK if you think this won't work!) (Just in case, will try with carboard first.)
Max height at the top will be 36~40", with the tweeter centered a few inches below, which seems about right. If an 10" square cross-section tower is used, the widest portion of the top baffle will be 14.14" -- more than enough for any mid driver. It might be better to go smaller -- perhaps 8", though this might make the enclosure volume too small if I'm going to make it a 3-way with anything bigger than 7". Assuming at least 5/8" thick panels, a 36~40" tall 8" square tower = 25~28 liters or about a cubit foot. This should be enough for the right 7-8" woofer. But then some space is needed for the mid driver. I haven't thought much beyond the 6.5" Seas driver I used in the last project. Hmmm.
It might mean just staying with a 2-way for this implementation. Go for something more ambitious next time. The close-wall reinforcement should make its bass better than in the pentagon LXmini tower anyway.
One question is whether the panel that rises up beyond the drivers in the Larsen 8 and 9 is absorbent or reflective? I refer to the portion of those speakers that go up against the front wall. My hunch is that it is partly or mostly absorbent to reduce diffractive reflections off that wall...?
Any suggestions or thoughts?
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I haven't started studying for my project but some early thoughts based on shallow knowledge. The OA-52 appears a better designed speaker than the Larsen based on existing measurements. It is also closer to what you seem to be proposing in terms of geometry. It may be a better reference.
The panels around the tweeter are waveguides for the high and mid frequencies. They are likely to be important in balancing w.r.t. frequency the relatively weak direct and relatively strong indirect sound to get a reasonable balance. This cannot be addressed with equalization and will need to be done with geometry. It is also likely to be pretty tricky to get close, will be significantly room dependent and will fall short of what can be achieved with direct radiating speakers. The enhanced sense of space will need to compensate if the design is to be successful.
A single tweeter directed largely upwards is almost certainly not going to be successful because the direct sound will be nigh on impossible to balance and it is the side walls that are going to contribute most to a sense of space.
My guess is that a fair few commercial "omnis" have a poor overall performance. Measurements like those in Stereophile do not provide information on how well "omnis" may enhance a sense of space that is weak with conventional speakers (stereo not multichannel) but they do show if a speaker has significant issues with frequency balance.
Given how much the “omni’s” overall performance depends on the room it is in. And the “waveguides” andy mentions, means a lot of cut & try to find your way.
These can be quite enjoyable to listen to, room filling, music everywhere, but the image/soundstage becomes quite diffuse, FR is all over the map.
My c=microTower II clones are just such, a lot of fun, work well in my workshop.
dave
These can be quite enjoyable to listen to, room filling, music everywhere, but the image/soundstage becomes quite diffuse, FR is all over the map.
My c=microTower II clones are just such, a lot of fun, work well in my workshop.
dave
That must be one of your early creations, Dave?! Looks kinda fun. Was it best out away from the wall? Did you toe-in as dramatically as the Larsens & Carlssons?
The trouble with the Carlsson designs is that they're >20 decades out of production, they don't appear to be well documented by the makers, and the current websites dedicated to them also lack real technical details.
Also, existing measurements of all the Carlsson speakers are suspect, imho: None that I've studied documented the measurement conditions well enough.
After scanning & reading through many of the pages at https://www.carlssonplanet.com/en/ I'm coming to the position that none of the Carlsson or Larsen products are likely to be ideal references for my goals. Not hearing any of them -- or having discussions with people who have -- isn't helpful either.
Yes, the PDF doc Carlsson Ortho- Acoustic Loudspeakers: Design and Performance Principles is wordy but there are some specific notes there, such as this. Note point #2.
Also:
Since I haven't found any original spec sheets, I cannot comment on the "wall reflex absorbers" but would venture to say whatever was used is likely long degraded by time.
The above citations from the Carlsson Ortho-Acoustic principles paper makes it clear that their speakers were not really omnidirectional. There was a distinct & concerted effort to direct the upper frequencies in a way quite different from the usual omni. The focus on maximizing direct sound while controlling reflections strikes me as a modern approach; perhaps they were ahead of their time. Though again, I have tov repeat that the use of multiple tweeters is counterintuitive to me.
All this makes me wonder if waveguide domes would be more suitable than bare domes for this application.
This is a comment I don't understand the reasoning behind:
What exactly does this achieve?? Off-axis for much of the listening area? Less reflections from floor? What about the ceiling reflections -- maybe this is why they are so short -- to keep the distance to ceiling longer?
Again, I doubt standard SPL measurements are particularly useful for multi-direction speaker systems like these. Larsen & Carlsson both refer to sound power measurements. At least Stereophile did some off axis measurements, which is more than you can say about earlier tests of the Carlssons.
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Is there a way to model the wall-adjacent 45-degree rotated/tilted baffle in any of the usual loudspeaker designs apps popular among accomplished DIYers here? (I refer to vituixCAD and the like). Please chime in if there's some existing method to do this.
I found little if anything of substance on the Larsen and CarlssonPlanet sites but the CarlssonKult and the forum chat linked earlier had enough for me to pick up the gist of what Carlsson was likely trying to do. Not enough to design a speaker but enough to have an idea of what to look for in some simulations.
The CarlssonKult site provides information on how he is measuring and why. Seemed reasonable to me.
Your objectives may be different to mine. I have heard both Sonab and MBL speakers deliver the enhanced spaciousness which is my objective. This was at the cost of imaging and tonal balance particularly in the case of the Sonab. If I can get enhanced spaciousness, an OKish tonal balance and modest imaging that would meet my objectives. If I hadn't heard speakers deliver enhanced spaciousness in the past I doubt I would have an interest in the project.
This seems to be basic boundary reinforcement reducing/removing "baffle step correction". This is fairly common and, indeed my first DIY speaker from a magazine in the 70s used the same principle for an against the wall transmission line speaker. I don't think it is particularly relevant to using the side wall and possibly ceiling to increase a sense of spaciousness.
Not sure about ahead of time. In the days of mono an increase in spaciousness that didn't come at the expense of tonal balance was a win which is likely why it received the attention it did in the 50s and 60s. With the advent of stereo imaging became important and increasing the indirect sound relative to the direct sound is going to inevitably degrade it. This is likely why such speakers became less common.
They are used to remove the perception of peaks and troughs at higher frequencies created by correlated signals summing and cancelling. Given my objectives it is hard to see a design being successful without them but I am placing little weight on imaging.
It will depend on what it takes to balance the indirect and direct sound over the frequency range. This will require some simulations (or measurements) to quantify what is going on and hence what can be done to achieve a reasonable performance. I don't think either of us is in a position to address this yet.
I would suggest that what is heard/measured at the listening position is useful. Of course this need to include both direct and indirect sound which isn't particularly difficult plus one needs to be aware that we don't perceive peaks and dips in the way it is measured by a microphone at a fixed point in space so an appropriate form of averaging is likely to be useful even if only done mentally.
To simulate the summing of direct and indirect sound I will likely use a BEM or FEM code possibly with a geometrical acoustics code for higher frequencies. Acousto is an open source BEM code I have used in the past but people on the forum seem to favour AKABAK which is a fairly expensive proprietary Windows program which I think is available for free in a limited evaluation form which I haven't tried myself (not a Windows user for work/simulation).
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I made my surrounds like that. I place them slightly under ear hight, slightly behind my ears. They work much better than speakers placed on the wall above my ear hight and even with my ears, like Sony said to do.
They work well as mains too providing lots of space and air. Unfortunately, I already built my WTW front speakers.
Nice thread. Some of these speakers remind me of the Allison loudspeakers.
Just to add a PS to my comments earlier on the measurements of the Larsen 8 in stereophile. I missed that the speaker had been placed against the sidewalls, as noted here, and not the front wall when measured. A strange thing to do which, of course, breaks how the speaker is designed to work. The manufacturer's response doesn't comment on this which is also strange. The delay in the early reflections in normal rooms (but less so the huge room I heard the Larsens in) will bring the big hump down. To what extent will be room dependent but the perceived response will almost certainly be substantially better balanced than that suggested by Figure 7 in the measurements.
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