I built a u frame woofer sample to test with open baffle configurations. I choose to get the Eminence 15A and the plan is to EQ and biamp. I have some options for the mids and highs that I want to test and see which one makes it to my permanent setup (if I like OB). For testing I have some Greencone Sabas, AN 12 cast frame, FE126E, RS 40-1354, oval coral alnico fullrange and others. The picture shows a RS 40-1384E 5 inch fullrange.
I have already played with the woofer non eq'd just biamped and there is definitely much better bass that any other speaker I have. I have been using the recommended crossover from the Endorphin P17 OB speaker.
I have also been reading the NAO site that talks about the damped U frame cardioid setup. I want to test this as well. Since I currently do not have any damping material available, I would like to get an idea of how much I need to make it a cardioid. Do I need to fill he thing up with pollyfill? Will a breatheable sheet (or layers) of wool felt do the trick?
The interior dimensions are: 14.4Dx16Wx24H
Any assistance is appreciated.
Alfredo
I have already played with the woofer non eq'd just biamped and there is definitely much better bass that any other speaker I have. I have been using the recommended crossover from the Endorphin P17 OB speaker.
I have also been reading the NAO site that talks about the damped U frame cardioid setup. I want to test this as well. Since I currently do not have any damping material available, I would like to get an idea of how much I need to make it a cardioid. Do I need to fill he thing up with pollyfill? Will a breatheable sheet (or layers) of wool felt do the trick?
The interior dimensions are: 14.4Dx16Wx24H
Any assistance is appreciated.
Alfredo
An externally hosted image should be here but it was not working when we last tested it.
A damped U-frame may not be the appropriate way to approximate a cardioid. At low frequencies it tends to behave as a dipole, while it's upper frequency is limited by the U-frame resonance.
Theoretically, a cardioid could be constructed with a resistance box with a specific volume which should behave as an acoustical compliance, and an acoustical flow resistor. The output of the rear wave would then be delayed by T=RC. See Frontiers for theoretical considerations.
See also Kimmo Saunisto's archive for cardioid bass experiments. I suggest you simply experiment with different amounts of damping material (preferably mineral wool).
Theoretically, a cardioid could be constructed with a resistance box with a specific volume which should behave as an acoustical compliance, and an acoustical flow resistor. The output of the rear wave would then be delayed by T=RC. See Frontiers for theoretical considerations.
See also Kimmo Saunisto's archive for cardioid bass experiments. I suggest you simply experiment with different amounts of damping material (preferably mineral wool).
The mineral wool is not so easy to find, it is not a hardware store item. Home Depot carries something called denim insulation that may work. Anyone use it before?
I made test baffles with driver inserts so i can test various drivers. I can accommodate up to a 12 inch driver.
Tomorrow i will listen to the Sabas.
I made test baffles with driver inserts so i can test various drivers. I can accommodate up to a 12 inch driver.
Tomorrow i will listen to the Sabas.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
FIY NaO II U-frame woofer design
The damped U is an acoustic resistance enclosure. One thing to realize that it is much beeter to use a U-frame with cross sectional area on the order of the driver Sd, or at least restrict the exit area at the rear to approximately Sd.
The damped U is an acoustic resistance enclosure. One thing to realize that it is much beeter to use a U-frame with cross sectional area on the order of the driver Sd, or at least restrict the exit area at the rear to approximately Sd.
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Thanks John, i have been reading the excellent information on your site. Base on your Sd reccomentation it will be a lot harder to dampen my box. If i put a back panel with a circle the same dismeter as the driver cutout, and dampen that, it would no longer behave as a u frame, correct? Or should i just install two shelves, on top and below the driver, then dampen that?
Currently listening to the Sabas... I like what I am hearing 
. I am currently using the Endorphin P17 crossover. But... I am just listening at low/mid level, 8 feet from speakers and in my garage that is full stuff everywhere. The next step is to move them temporarily to where I have my main setup. In order to do that I need to minimize the crossover spaghetti as seen in picture. The main setup also has my MiniDSP that I can use to biamp them.
So far what I can tell is that the speakers sound effortless. The standup bass stands out, never heard it as good.
I will get some of the Denim Insulation from HD, it is inexpensive enough to give it a try.
. I am currently using the Endorphin P17 crossover. But... I am just listening at low/mid level, 8 feet from speakers and in my garage that is full stuff everywhere. The next step is to move them temporarily to where I have my main setup. In order to do that I need to minimize the crossover spaghetti as seen in picture. The main setup also has my MiniDSP that I can use to biamp them. So far what I can tell is that the speakers sound effortless. The standup bass stands out, never heard it as good.
I will get some of the Denim Insulation from HD, it is inexpensive enough to give it a try.
An externally hosted image should be here but it was not working when we last tested it.
Some more progress.... I buiit the temp crossover on a proto board and placed the speakers on my main listening room. These things are too tall. 50 inches. I may need to chop the top baffle down a bit.
I am now listening to them with a pp 7591a amp. From the listening position the sound appears to come from behind the speakers with excellent imaging.
I need to play with the placement from the back wall, they are now around 4 feet. This is where playing with the damping may allow me to place them closer to the back wall.
More to come.
I am now listening to them with a pp 7591a amp. From the listening position the sound appears to come from behind the speakers with excellent imaging.
I need to play with the placement from the back wall, they are now around 4 feet. This is where playing with the damping may allow me to place them closer to the back wall.
More to come.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Prepared a few more removable baffle inserts. Next up RS 40-1354A with 1.5" ribbon tweeter and a pair of TB W4-930SF.
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I have been playing some more. Now I am using a minidsp crossover and biamping. For level control I am using a Sansui QS-1. It is a Quadraphonic unit but allows the control of 4 external channels. The minidsp is fed from a rec out output from my preamp, the 4 channels out from the minidsp go the the 4 channel tape PB IN on the Sansui. The lows go to a Hifimediy T2 and the highs to the 7591 tube amp.
So far I have tested (with no measurements) the Sabas, the TB, some cheapo Kenwood I "tried" ENABL'ing and the Radio Shack's. The Radio Shacks I added from behind the baffle and added a second tweeter.
The TB sound good but are missing sparkle on top. The Kenwoods surprisingly sound very good but undoubtedly the larger speakers sound more open. The Sabas sound really good but they cant really be cranked up high. The RS 40-1354A sound very good with the ribbon tweeters. The Sansui has a convenient Front/Rear balance pot that makes balancing the bottom and top quite easily.
The Minidsp is a breeze to use and sounds better than the generic passive crossover I was using.
I have done no stuffing test yet as I need to setup a measuring rig to try and follow JohnK technique. The last driver I will test is the AN 12 Cast Frame. From what I have heard now, the larger the driver the better it appears to sound. Lets see.
So far I have tested (with no measurements) the Sabas, the TB, some cheapo Kenwood I "tried" ENABL'ing and the Radio Shack's. The Radio Shacks I added from behind the baffle and added a second tweeter.
The TB sound good but are missing sparkle on top. The Kenwoods surprisingly sound very good but undoubtedly the larger speakers sound more open. The Sabas sound really good but they cant really be cranked up high. The RS 40-1354A sound very good with the ribbon tweeters. The Sansui has a convenient Front/Rear balance pot that makes balancing the bottom and top quite easily.
The Minidsp is a breeze to use and sounds better than the generic passive crossover I was using.
I have done no stuffing test yet as I need to setup a measuring rig to try and follow JohnK technique. The last driver I will test is the AN 12 Cast Frame. From what I have heard now, the larger the driver the better it appears to sound. Lets see.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Audio Nirvana Super 12 Cast Frame
I like these the best! They sound really open and big, as if the back wall is one large speaker.
I need to measure and equalize the system. Right now I am running the crossover at LR4 120hz, 6db boost at 20, 3db cut at 213. For sure it is not the ideal setting but it sounds good. Looks ugly!
My space has been invaded this morning for the placement of our Christmas tree in the far end corner of the room. Don't think there will be much progress today.
I like these the best!
They sound really open and big, as if the back wall is one large speaker. I need to measure and equalize the system. Right now I am running the crossover at LR4 120hz, 6db boost at 20, 3db cut at 213. For sure it is not the ideal setting but it sounds good. Looks ugly!
My space has been invaded this morning for the placement of our Christmas tree in the far end corner of the room. Don't think there will be much progress today.
An externally hosted image should be here but it was not working when we last tested it.
Hi SAC,
I did not continue with the cardioid experiment as I was happy with the UFrame sound with equalization. Although it sounds very good I am moving away from it do the placement requirements of the speakers. They need to be away from the back and side walls which completely screws up my furniture and listening arrangement. I have been asked "nicely" to keep the speakers close to the wall. I am now gathering the parts to build an Econowave style speaker that I can put against the back wall.
I did not continue with the cardioid experiment as I was happy with the UFrame sound with equalization. Although it sounds very good I am moving away from it do the placement requirements of the speakers. They need to be away from the back and side walls which completely screws up my furniture and listening arrangement. I have been asked "nicely" to keep the speakers close to the wall. I am now gathering the parts to build an Econowave style speaker that I can put against the back wall.
An undamped U-frame is a dipole at low frequency. Whether a true dipole, undamped U, or correctly damped U, such woofers can be placed against a side wall provided the axis of the system is parallel to the wall. Such arrangement will increase the bass output level. A correctly damped u-frame or a true cardioid can also be placed so that the rear output is fairly close to the back wall without negative impact other than how that position affects the modal response. A true dipole can not be position close to the back wall as the image source will cancel the real source at low frequency, reducing low bass output.
Thanks Alfredo for your update. I too have close rear wall issues, hence I am looking to go from flat baffle to damped u-frame. However, I asked how much stuffing and what eq was necessary on your alpha 15 u-frame, which if I understand correctly that is what you are using now. For example, was strong eq necessary? I use a pllxo so would have to forgo this. Also, was the whole u-frame stuffed or was quite light damping sufficient?
Edit; Wait, now I understand you did not damp your u-frame! How much eq was necessary in that set-up. I will aim to eq using damping therefore.
Edit; Wait, now I understand you did not damp your u-frame! How much eq was necessary in that set-up. I will aim to eq using damping therefore.
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Thanks John. This is useful feedback. Joining to the side walls would suit my set-up, but making a good join would necessitate some ugly and unworkable solution. The walls in British brick houses are rarely straight! The skirting board will get in the way. I imagine a rubber seal would be necessary unless there is some simple solution I am not thinking off!? It needs to be an air tight join to the wall right?
P.S.
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