Afaik, the diaphragm has a phenolic ring that the main diaphragm is permanently affixed to. Like the cheap phenolic tweeters or the phenolic diaphragms in those cheap horn loaded tweeters.
I wrote up a comment on the K-55 mod that got lost in internet space on posting... but the gist of it is/was that by drilling the holes in the phase plug the compression ratio is dropped somewhat. The uneven path length between the original path and the path through the holes doubtless has an effect at some high freqs, but that may be above the usable top end of the driver anyhow.
So, putting a space above the phenolic mounting ring, and below it will indeed reduce the compression as well as providing some extra space for diaphragm excursion.
That doesn't explain the apparent improvement in frequency response... unless the extra (stock) compression creates a highish Q condition. Also I would expect a drop in sensitivity with the increased volume due to the spacers?
_-_-
I wrote up a comment on the K-55 mod that got lost in internet space on posting... but the gist of it is/was that by drilling the holes in the phase plug the compression ratio is dropped somewhat. The uneven path length between the original path and the path through the holes doubtless has an effect at some high freqs, but that may be above the usable top end of the driver anyhow.
So, putting a space above the phenolic mounting ring, and below it will indeed reduce the compression as well as providing some extra space for diaphragm excursion.
That doesn't explain the apparent improvement in frequency response... unless the extra (stock) compression creates a highish Q condition. Also I would expect a drop in sensitivity with the increased volume due to the spacers?
_-_-
The only effect that the holes in the phase plug has is a bit stronger hf.
Important only for those who want to be able to get by with just a bullet
tweeter above the K55. There is no ill effect that we can see. Neither in the
response nor in the distortion department.
Noteworthy here is the fact that the compression ratio has almost no effect on
the frequency response from 100hz to 3khz. With that many holes we are
talking about a compression ratio variation of at least 30% .
In the picture I attached you see two identically modified units
only comparing holes vs. non holes.
Attachments
Although we seemingly have found a more suitable driver, I think the lessons we
can glean from the modified K55 are very valuable for us:
1. Compression ratio has very little effect in the frequency
range the K55 should be used in. At least on big horns.
2. Qtc on some of these drivers is way to high, therefore a back chamber
increase exhibits great gain in the lower region
3. Softening the surround (be it by making holes in it or by clamping it more on
the outside) lowers fs, exhibiting, in the right relationship with the back
chamber volume, a further low frequency extension.
can glean from the modified K55 are very valuable for us:
1. Compression ratio has very little effect in the frequency
range the K55 should be used in. At least on big horns.
2. Qtc on some of these drivers is way to high, therefore a back chamber
increase exhibits great gain in the lower region
3. Softening the surround (be it by making holes in it or by clamping it more on
the outside) lowers fs, exhibiting, in the right relationship with the back
chamber volume, a further low frequency extension.
Afaik these compression drivers are operating below Fs. Fs tends to be somewhere in the upper mid frequencies.
By making the surround more compliant Fs might be lowered somewhat, but it's not down at 100Hz I would not expect.
Lowering the Q of the system would indeed tend to flatten the shape of the response. (assuming Fs at the mid point of the peak of the stock curve) But I would expect an attendant reduction in the SPL measured for the highest part of the curve, IF the Q reduction was the cause of the apparent LF extension. But for the LF to lift up implies another mechanism at work.
An impedance curve on the Plane Wave Tube would show the Fs of the driver.
Most compression drivers are limited at LF by the stiffness of the surround, which forms a mechanical limitation, afaik. (at very very low levels, they'll pretty much all move at LF, but as the level goes up they still are excursion limited by the suspension)
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Bear,
I don't have any real figures to go by but I would suspect that the resonant frequency of these devices is higher than the low frequency range that is being desired here. That being the case you could operate below the resonant frequency as long as you had a reasonable upper frequency cutoff which in my eyes questions the use of a compression driver to produce these low frequencies in the first place. As far as a reasonable output down to 100 hz with a compression driver even on a horn sounds like you are asking for device failure due to suspension failure or coil burnout from over powering the device.
On another subject entirely if these compression drivers are using a composite phenolic surround material drilling round holes in that material is a known failure mode in composite construction. The edge of the hole between holes will propagate cracking over time and this will be a failure mode, a standard miss application of composite construction known very well in the aircraft industry and composites in general.
I don't have any real figures to go by but I would suspect that the resonant frequency of these devices is higher than the low frequency range that is being desired here. That being the case you could operate below the resonant frequency as long as you had a reasonable upper frequency cutoff which in my eyes questions the use of a compression driver to produce these low frequencies in the first place. As far as a reasonable output down to 100 hz with a compression driver even on a horn sounds like you are asking for device failure due to suspension failure or coil burnout from over powering the device.
On another subject entirely if these compression drivers are using a composite phenolic surround material drilling round holes in that material is a known failure mode in composite construction. The edge of the hole between holes will propagate cracking over time and this will be a failure mode, a standard miss application of composite construction known very well in the aircraft industry and composites in general.
Certainly, they will operate down there, but one would have to restrict the max SPL to modest levels as found in a typical home environment. Also there is no reason not to use multiple drivers on a manifold to get higher SPL since this is for LF applications and the phase/path length issues that might happen if ur interested in full HF response seem to not apply.
I'm still trying to understand how or why the LF response became improved over the stock unit, other than a change to the rear volume (load).
_-_-
I'm still trying to understand how or why the LF response became improved over the stock unit, other than a change to the rear volume (load).
_-_-
Bear,
It would seem to me that you would be changing the compliance by changing the air volume that the diaphragm would have to work against. It would seem that increasing the air volume both in front of and behind the diaphragm would change the loading it would see, not the same as changing the ratio of open to closed area of the phase plug, but the distance between the diaphragm and the phase plug usually is at a minimum causing refraction of the air waves.
It would seem to me that you would be changing the compliance by changing the air volume that the diaphragm would have to work against. It would seem that increasing the air volume both in front of and behind the diaphragm would change the loading it would see, not the same as changing the ratio of open to closed area of the phase plug, but the distance between the diaphragm and the phase plug usually is at a minimum causing refraction of the air waves.
This is exactly what I will be doing, multiple drivers on a manifold. At home levels distortion should be low in the 100Hz region where the driver is operating below Fs.
Okay, speed trials of the un-modded K55-V!
Setup 1:
¤ JBL 12" 2204H 60Hz-200 Hz.
¤ K55-V in a wooden 1.75m deep horn with 75cm diameter, inspired by the Goto S-150, that has 200 Hz as its lowest crossover point, hence the bandpass 200-650 Hz.
¤ JA6681B 650-4000 Hz.
¤ Beyma 1" above and beyond.
Versus
Setup 2:
¤ JBL 12" 2204H 50Hz-650Hz.
¤ JA6681B 650-4000Hz.
¤ Beyma 1" above and beyond.
No ribbon supertweeter today. Too few amps are operational.
K55-V
+ The K55 gives me a feeling that Sinne Eeg, in the song "Brief Hesitation" is in the room , and not just in a speaker.
- The K55 sounds a little strained, compared to the JBL 12". Is this what could be horn honk? I suspect the culpret to be strange aerodynamical anomalies caused by a 1.75 meter cushion of air in front of the diaphragm.
- I was expecting the sound to be clearer, but maybe I am used to metal diaphragms and shorter horns. The deepest horn I have heard before today is the 40cm deep horn I use with the JA6681b. Do I dare to use the JA-6681b in the Goto horn? Naah.
JBL 2204H 12"
+ The 12" sound effortless. It does not have 1.75 meters of air to push against.
- The 12" JBL sound pretty boxy. As if was a speaker, and not a live performance. Go figure!
My room is too small to really assess it properly. I should really wait until after I have cooked lunch, because I get a way better, and very different sound walking into the kitchen, six meters away from my listening room, while still standing in the straight, and rather narrow beam of sound coming from the horns.
I doubt having a doorway between me and the system is the best way judge its performance. Still, it is slightly more enticing than the JBL 12" was before. It is a keeper!
I posted some pictures, as there are only some minor details left to fix. The horn needs some more sandpaper, another paint job, and a new appartment.
Setup 1:
¤ JBL 12" 2204H 60Hz-200 Hz.
¤ K55-V in a wooden 1.75m deep horn with 75cm diameter, inspired by the Goto S-150, that has 200 Hz as its lowest crossover point, hence the bandpass 200-650 Hz.
¤ JA6681B 650-4000 Hz.
¤ Beyma 1" above and beyond.
Versus
Setup 2:
¤ JBL 12" 2204H 50Hz-650Hz.
¤ JA6681B 650-4000Hz.
¤ Beyma 1" above and beyond.
No ribbon supertweeter today. Too few amps are operational.
K55-V
+ The K55 gives me a feeling that Sinne Eeg, in the song "Brief Hesitation" is in the room , and not just in a speaker.
- The K55 sounds a little strained, compared to the JBL 12". Is this what could be horn honk? I suspect the culpret to be strange aerodynamical anomalies caused by a 1.75 meter cushion of air in front of the diaphragm.
- I was expecting the sound to be clearer, but maybe I am used to metal diaphragms and shorter horns. The deepest horn I have heard before today is the 40cm deep horn I use with the JA6681b. Do I dare to use the JA-6681b in the Goto horn? Naah.
JBL 2204H 12"
+ The 12" sound effortless. It does not have 1.75 meters of air to push against.
- The 12" JBL sound pretty boxy. As if was a speaker, and not a live performance. Go figure!
My room is too small to really assess it properly. I should really wait until after I have cooked lunch, because I get a way better, and very different sound walking into the kitchen, six meters away from my listening room, while still standing in the straight, and rather narrow beam of sound coming from the horns.
I doubt having a doorway between me and the system is the best way judge its performance. Still, it is slightly more enticing than the JBL 12" was before. It is a keeper!
I posted some pictures, as there are only some minor details left to fix. The horn needs some more sandpaper, another paint job, and a new appartment.
Attachments
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I realize that just highpassing the compression drivers works well, except for the 12" 2204H, that is doing a rather poor job as subwoofer. Sound is even more alive/live now. At lest on singer song writer music, like Tony Joe White - Lazy.
Video:
https://www.facebook.com/photo.php?v=10151493772301198&l=2444485153912794167
Video:
https://www.facebook.com/photo.php?v=10151493772301198&l=2444485153912794167
Attachments
Seems like it was the 200-650Hz bandpass that made the K55-V go muddy. 200 Hz highpass works better.
Drop it, no. The wooden glue is not as solid as I expected. I will have to drench it in liquid plaster to make it not deform in the next years to come.
It is more sturdy, than you think, with a rim of oak on the outer edges of the horn. The first 50-60cm of the horn, starting from the driver, is in very solid wood, and I belive this to be the most important part of the horn, so I took great care to carve and grind it to exact specifications. Took me the two first days of vacation. Third day is for wine and re-listening to all my records.
Narrow bands are strange. I have been fiddling a lot the Minidsp 4x10HD lately. When it comes to really intense music, usually a strange phenomenon called "popular music", you have to do something to constrain the chaos, and narrow bands are a necessity. Like during parties when people put on anything.
It is more sturdy, than you think, with a rim of oak on the outer edges of the horn. The first 50-60cm of the horn, starting from the driver, is in very solid wood, and I belive this to be the most important part of the horn, so I took great care to carve and grind it to exact specifications. Took me the two first days of vacation. Third day is for wine and re-listening to all my records.
Narrow bands are strange. I have been fiddling a lot the Minidsp 4x10HD lately. When it comes to really intense music, usually a strange phenomenon called "popular music", you have to do something to constrain the chaos, and narrow bands are a necessity. Like during parties when people put on anything.
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Great entrepreneur work.
Don't judge the K55 on this horn to early. There are just to many variables in a setup like this. Especially when it comes to small rooms.
When the SD-370 is bolted on this horn I expect a more authoritative output.
Klaus
Don't judge the K55 on this horn to early. There are just to many variables in a setup like this. Especially when it comes to small rooms.
When the SD-370 is bolted on this horn I expect a more authoritative output.
Klaus
Thank you, Radian!
More about the K55: Without measuring, I notice by ear, an okay output down to 120 Hz, 180 Hz is more okay, and 200 Hz is safe, as in I am pretty sure it is not too low for the driver. I tried crossing the JBL 12" midwoofer and the K55 at 250Hz, but I could not decide if that sounded better than 200Hz, or not. I am tempted to modify the K55, but the FS100W is arriving soon.
Not heard the Goto drivers, but the Goto SG-505 seem actually pretty bad around 100Hz on le cleach 140 Hz horn, see fig. I think Goto recommend 200Hz as the S-150 horn's limit, more because of the limitations in the driver they intended to use it with, i.e. the SG-505. If the FS100W sounds good to the ear, it has the ability to surpass the Goto SG-505, since it has good output down to 100Hz.
More about the K55: Without measuring, I notice by ear, an okay output down to 120 Hz, 180 Hz is more okay, and 200 Hz is safe, as in I am pretty sure it is not too low for the driver. I tried crossing the JBL 12" midwoofer and the K55 at 250Hz, but I could not decide if that sounded better than 200Hz, or not. I am tempted to modify the K55, but the FS100W is arriving soon.
Not heard the Goto drivers, but the Goto SG-505 seem actually pretty bad around 100Hz on le cleach 140 Hz horn, see fig. I think Goto recommend 200Hz as the S-150 horn's limit, more because of the limitations in the driver they intended to use it with, i.e. the SG-505. If the FS100W sounds good to the ear, it has the ability to surpass the Goto SG-505, since it has good output down to 100Hz.
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Rewind it is definitely ok to use the 6681b down to 250Hz. I do it all the time. Probably 200Hz is ok too.
The curve you put up seems to show the horn is only going down to >~300Hz. Maybe more like 400Hz.
_-_-
The curve you put up seems to show the horn is only going down to >~300Hz. Maybe more like 400Hz.
_-_-
It is just a curve I found from the Hifi Heroin blog, as a hint of the Goto SG-505 drivers performance.
Some day, I may try it. Right now, I am pretty satisfied. Things will probably just improve with the SG-505.
Some day, I may try it. Right now, I am pretty satisfied. Things will probably just improve with the SG-505.
When it comes to low frequency, 99.9% of the people are used to paper cones moving air.
Only very few natural instruments actually move allot of air at producing low frequencies. It's not about moving air it's about exiting air.
Horns move very little air to reproduce a grand tone.
Until our ears are retrained we will miss something that hasn't even been there to begin with. What we actually miss is the awfully slow attack and the slow decay of the moving
mass. wooff, wooff.
Only very few natural instruments actually move allot of air at producing low frequencies. It's not about moving air it's about exiting air.
Horns move very little air to reproduce a grand tone.
Until our ears are retrained we will miss something that hasn't even been there to begin with. What we actually miss is the awfully slow attack and the slow decay of the moving
mass. wooff, wooff.
It is getting increasingly more difficult to move back to the cone driver. I asked my gf and she said the difference was more noticable in kitchen. Sitting next to the horn does not do much. But if we put some distance between us and the horn it is so musical!
Except for low-res netflix. Then a cone driver and the ribbon tweeter are perfect. An XO@2500Hz is perfectly adequate. We just saw Tremors 2, (enjoyable Texas monster hunting movie, based on cult classic 90's monster hunting movie) and the sound was very okay. Luckily I have everything hooked on, so I can just switch settings in a Minidsp plugin without changing a thing physically.
Except for low-res netflix. Then a cone driver and the ribbon tweeter are perfect. An XO@2500Hz is perfectly adequate. We just saw Tremors 2, (enjoyable Texas monster hunting movie, based on cult classic 90's monster hunting movie) and the sound was very okay. Luckily I have everything hooked on, so I can just switch settings in a Minidsp plugin without changing a thing physically.
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