mustang guy Posted March 12, 2015 Share Posted March 12, 2015 (edited) Check out the ports in the reference stuff in this picture. I think they may have been tuned using the same technology. The RB-81 is 97db efficient, which is very high compared to like sized speakers. They would be expected to be around 91db efficient. Look at the round ported Paradigm Signature S2. Edited March 12, 2015 by mustang guy Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 12, 2015 Share Posted March 12, 2015 (edited) So why don't they make all acoustic guitars with F holes instead of round ones if it is that superior, generally speaking? Check this out from Kramer Studios. http://www.kramershimmy.com/studios.html "My 1938 Epiphone Olympic Archtop, the loudest acoustic guitar I've ever heard." Edited March 12, 2015 by mustang guy 1 Quote Link to comment Share on other sites More sharing options...
DrWho Posted March 14, 2015 Share Posted March 14, 2015 Are the f holes really the dominant source of output in a string instrument? If I cover the holes on my viola, it still makes a lot of sound because the "sound board" is still vibrating. Sure, all the body / fullness goes away, but that's expected. I'm not convinced the flow velocity of the hole is the dominant factor in the loudness of the instrument. And I'm certain that these principals don't apply to loudspeaker design...I don't want the sound of a wood panel vibrating, or the sound of a box resonance to increase SPL. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 14, 2015 Share Posted March 14, 2015 (edited) I don't think they are implying the f holes are the dominant source of output. I would have to go back and re-read it. I believe they are saying it sets them apart from earlier versions. The amplification is on the lowest of notes, so that would be where the sound stands out the most. I think you are misreading the study. They were not talking about panel vibrations or resonances. They were talking about the Helmholtz resonance. That is more akin to a flute than a wood instrument. Actually, a beer bottle comes to mind. It's about oscillations caused by air pressure equalization. Edited March 14, 2015 by mustang guy Quote Link to comment Share on other sites More sharing options...
Mallette Posted March 15, 2015 Share Posted March 15, 2015 (edited) I am pretty weak in this area, but think from experience that some experiments would be worthwhile with speaker cabinets. Jack Frazier's slots and the rounded ones in the RB-81 shown above obviously did a lot to improve efficiency, and that appears to be exactly what the Cremonese school was doing. Dave Edited March 15, 2015 by Mallette 1 Quote Link to comment Share on other sites More sharing options...
Marvel Posted March 15, 2015 Share Posted March 15, 2015 So why don't they make all acoustic guitars with F holes instead of round ones if it is that superior, generally speaking? F holes are almost always used on arch top instruments, with carved tops, while round/oval or other single hole shapes have been used in flat top guitars or other stringed instruments. You will find round sound holes in some carved top instruments in the mandolin family of instruments, mandolin, mandocello, cittern, and even on some carved top guitars like the early 20th century Martin C1 (they changed to F-holes in 1933). I believe the thicker carved top may be able to handle the weakening of the structure better than the thinner flat top guitar, but I don't know that as a fact. Bruce Quote Link to comment Share on other sites More sharing options...
DrWho Posted March 19, 2015 Share Posted March 19, 2015 (edited) They were not talking about panel vibrations or resonances. They were talking about the Helmholtz resonance.Ya, I'm the one talking about the panel vibrations because they dominate the acoustic output of the instrument. I think the shape of the f holes have a larger effect on the vibration of the instrument's 'panels'. I don't think you can discuss loudness of the port without the context of the rest of the instrument when trying to explain the reason for the changes over the years.When it comes to speakers, I'm very much in the camp of not adding resonance to a system.....except for ports, but only because nearly every low frequency system uses ports and that affects what ends up on the recordings. Edited March 19, 2015 by DrWho Quote Link to comment Share on other sites More sharing options...
Schu Posted March 19, 2015 Author Share Posted March 19, 2015 well then... someone build a bass horn tuba with two enlarged "f" hole openings and lets test this theory. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 20, 2015 Share Posted March 20, 2015 (edited) They were not talking about panel vibrations or resonances. They were talking about the Helmholtz resonance.Ya, I'm the one talking about the panel vibrations because they dominate the acoustic output of the instrument. I think the shape of the f holes have a larger effect on the vibration of the instrument's 'panels'. I don't think you can discuss loudness of the port without the context of the rest of the instrument when trying to explain the reason for the changes over the years.When it comes to speakers, I'm very much in the camp of not adding resonance to a system.....except for ports, but only because nearly every low frequency system uses ports and that affects what ends up on the recordings. Perhaps the shape of the f slot is more rigid than a straight slot would be. It seems like the outside curves of the f would be more rigid while the inside ones would be more prone to vibrations. Maybe you are right, and the increased velocity at the edges of the longer perimeter hole is simply vibrating the panel more than a circle with lower perimeter velocity. That makes a lot of sense to me. In that case, would the Helmholtz frequency and the resonance frequency have to be different, or all hell would break loose? If you had no ports in a violin, the sound would be less than with them, but probably not by half. I agree the panel vibrations are dominant, and I bet the attached study proves that. I'm not intellectually up to the task of figuring that out from the study. I think the gist of it is the lowest frequencies are amplified by the f slots particularly if they have an area necessary to make the Helmholtz equal to the lowest frequency the instrument can play. In fact, it is saying any port with the area tuned to Helmholtz will do this, but the longer perimeter one does it better. Edited March 20, 2015 by mustang guy Quote Link to comment Share on other sites More sharing options...
Mallette Posted March 20, 2015 Share Posted March 20, 2015 well then... someone build a bass horn tuba with two enlarged "f" hole openings and lets test this theory They're playing your song, Carl... Dave Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 28, 2015 Share Posted March 28, 2015 This subject kinda fizzled out, but I have some new information. We were discussing the slot ports of the Fraziers and the newer Klipsch speakers. Check out this Frazier ad for the Frazier Black Box. "Frazier modified Hemholtz direct radiator type tuned box speaker system..." Quote Link to comment Share on other sites More sharing options...
Schu Posted March 28, 2015 Author Share Posted March 28, 2015 (edited) So why don't they make all acoustic guitars with F holes instead of round ones if it is that superior, generally speaking?They do make acoustic guitars with f holes... they sound very unique. The main reason this has changed is because flat top acoustic guitars use a very unique bracing configuration that notonly precludes using an f hole layout, it accentuates the placement, size and shape of the modern acoustic soundhole.There are also other guitar makers that use unique placement and shape of soundhole, but the holy grail for guitar makers is the Martin sound... that requires a bracing and placement similarity Edited March 28, 2015 by Schu Quote Link to comment Share on other sites More sharing options...
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