Rudolf said:
Brilliant! Thanks Rudolf.
I had read John’s paper last year and sort of had it in the back of my mind. Just didn’t remember the details. He makes a good case. Because the dipole (open baffle) woofer can not pressurize the room, response will fall off under the room fundamental. Here is a quote from the 2nd page of John K’s paper to show that I was wrong.
"If a dipole woofer system with a corner frequency of 20 Hz is placed in a room with a fundamental frequency of 40 Hz, the response will drop off below 40 Hz. Very little can be done to alter this situation. Application of additional equalization will just result in further taxing of the driver and amplifier with little gain."
Of course he is talking about a sealed or mostly sealed room. Mine never is as I live in Hawaii so all doors and windows are open 24/7/365.
A great subject to explore, but I will let CLS continue if he wants so as not to thread-jack.
Thanks for the responses🙂
At first, with 40hz xover, and without further EQ, I found the mid-high bass (50~100Hz) was too strong. Among other things, maybe it's simply because these 18s are born to be like this. Before this OB, I used BR cabs with them, at that time the response is also strong in this region.
So later I pushed it lower to 26Hz, to further suppress the middle bass. And it seemed good to do so.
I didn't read that <JohnK'... > article yet (and surely will do), I guess maybe it's because the OB can not pressurize the room to get to the lowest octave.
However, it dose sound good without pressurizing the room. There is no boom at all. My previous corner BR cabs need massive attenuations at several particular frequencies, as much as 30~40dB! Now these OB needs none! I can feel the sound is now more complete, more coherent without those high Q and deep attenuations.
Last night I changed the bass amp from modded Altec 1568A to 300B SE. And it turned out very good.
I'm not sure it's the "w/ vs w/o NFB" or the "SE vs PP" thing. I found the sound from PP 1568A was kind of muffled, or laid back. I could tell the SPL was high enough comparing with conversations, but it just felt not so dynamic. With 300BSE, the bass is jumping around, more energetic. I got satisfied overall listening pleasure with lower SPL.
😀
At first, with 40hz xover, and without further EQ, I found the mid-high bass (50~100Hz) was too strong. Among other things, maybe it's simply because these 18s are born to be like this. Before this OB, I used BR cabs with them, at that time the response is also strong in this region.
So later I pushed it lower to 26Hz, to further suppress the middle bass. And it seemed good to do so.
I didn't read that <JohnK'... > article yet (and surely will do), I guess maybe it's because the OB can not pressurize the room to get to the lowest octave.
However, it dose sound good without pressurizing the room. There is no boom at all. My previous corner BR cabs need massive attenuations at several particular frequencies, as much as 30~40dB! Now these OB needs none! I can feel the sound is now more complete, more coherent without those high Q and deep attenuations.
Last night I changed the bass amp from modded Altec 1568A to 300B SE. And it turned out very good.
I'm not sure it's the "w/ vs w/o NFB" or the "SE vs PP" thing. I found the sound from PP 1568A was kind of muffled, or laid back. I could tell the SPL was high enough comparing with conversations, but it just felt not so dynamic. With 300BSE, the bass is jumping around, more energetic. I got satisfied overall listening pleasure with lower SPL.
😀
Good to see a project with the Audiom7k being used,I have two pairs one in a three way Onken and a spare pair awaiting in a 14 litre IB enclosure.I hadnt thought of horn loading them,by the way how much do the horn bits themselves cost roughly?
Before the horn, I also used Audiom7k on small OB (with folded back wings) above 200Hz. They did pretty good on OB, too. Very open and fast.
The horns were bought long ago, maybe in '99 or '00, forgot. I spent about US$750 for the horn kit, and very costly shipping (they are big! and I'm far away). I remember my total cost was more then US$1000 (for a pair of "plastic" stuff)
Now they seem obsolete, BD design is now selling smaller version with 2" throat....
Actually the Audiom7k doesn't fit the horn perfectly, because the throat is designed for 8" Lowther. Directly fitting the 7" Focal on the horn, I can even see the metal part of frame through the throat, not to mention the whole suround area. So later I extended the throat to another 1" on the depth along axis. This makes the throat slightly smaller. But this extension is not precise, I just made the cut by bare eyes and unstable handheld tool, oh well...
So, I think it's good to bring down the range of this mid combination.
The horns were bought long ago, maybe in '99 or '00, forgot. I spent about US$750 for the horn kit, and very costly shipping (they are big! and I'm far away). I remember my total cost was more then US$1000 (for a pair of "plastic" stuff)
Now they seem obsolete, BD design is now selling smaller version with 2" throat....
Actually the Audiom7k doesn't fit the horn perfectly, because the throat is designed for 8" Lowther. Directly fitting the 7" Focal on the horn, I can even see the metal part of frame through the throat, not to mention the whole suround area. So later I extended the throat to another 1" on the depth along axis. This makes the throat slightly smaller. But this extension is not precise, I just made the cut by bare eyes and unstable handheld tool, oh well...
So, I think it's good to bring down the range of this mid combination.
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