As I mentioned in post #118 the very long, slowly flaring horn throat required for LF reinforcement also increases distortion due to air non-linearity at high SPL.
Looking at Dietmar's Sato horn driven at .15 watts it reaches 100 dB at .7 meters with second harmonic distortion at only about 4% at 100 Hz.
At 110 dB at .7 meters (presumably 1.5 watts), the D2 rises to around 11% at 100 Hz, generally a linear increase of around three times the distortion, but the more objectionable third harmonic distortion has not risen in a linear fashion, probably due to air non-linearity rather than diaphragm break up.
It appears with the nature of the non-linear distortion, if the power input was raised to 15 watts, D3 would rise over 100%. The diaphragm would also likely be hammering on the phase plug at that level.
Raising the crossover point would reduce distortion somewhat (and eliminate the problem of the diaphragm hammering on the phase plug), but the air non-linearity would still present a problem with such a long throated horn.
If one wanted to reduce third harmonic distortion at high SPL, a better choice would be a more rapidly expanding horn, which would not go as low.
Or one could simply use larger diaphragm drivers, which don't require such extreme throat pressures (or excursion) to achieve greater SPL with less distortion.
Art
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weltersys,
You seem to be speaking to the choir. I understand what you are saying and have been there enough times to see banks of phenolic diaphragms broken when excursion limits are reached. These drivers were never intended to be used this way, yes you may get them to work at low output but the first large transient and you can kiss the diaphragm goodbye. The excursion of the phenolic diaphragms were never intended for much at all and can be found quite easily by measuring the actual clearance from the diaphragm to the phase plug. Increase that distance and the high frequencies will go with the increased distance and you still have the mechanical limit of the phenolic surround. The only way this can work at all is with a third device to fill in above one of these very large horns that will go as low as 100hz and then your center to center distance is just stupidly large at those mid frequencies. I know I will get an argument here but reality just doesn't track what I am seeing written here by others.
You seem to be speaking to the choir. I understand what you are saying and have been there enough times to see banks of phenolic diaphragms broken when excursion limits are reached. These drivers were never intended to be used this way, yes you may get them to work at low output but the first large transient and you can kiss the diaphragm goodbye. The excursion of the phenolic diaphragms were never intended for much at all and can be found quite easily by measuring the actual clearance from the diaphragm to the phase plug. Increase that distance and the high frequencies will go with the increased distance and you still have the mechanical limit of the phenolic surround. The only way this can work at all is with a third device to fill in above one of these very large horns that will go as low as 100hz and then your center to center distance is just stupidly large at those mid frequencies. I know I will get an argument here but reality just doesn't track what I am seeing written here by others.
Interesting, though I have seen (and paid for) dozens of shattered aluminum diaphragms, I have never before heard of any "broken" phenolic diaphragms.
I have seen many phenolic diaphragms with burnt voice coils, but if someone builds a horn/driver combination like Dietmar's Sato, the driver's output will be quite audibly distorted before burnout will occur.
What types of drivers were used that resulted in "banks of phenolic diaphragms broken"?
Any pictures?
weltersys,
It was years ago for sure and they were Altec drivers, very large format ones at that. They were mounted on sectoral horns, don't remember the part # but the very large multicells. Don't forget this was PA application, so you can imagine when this happened at an outdoor festival back in the day.
It was years ago for sure and they were Altec drivers, very large format ones at that. They were mounted on sectoral horns, don't remember the part # but the very large multicells. Don't forget this was PA application, so you can imagine when this happened at an outdoor festival back in the day.
The "large format" Altecs used 3" diaphragms, aluminum were more common for rock and roll PA as they did not require a HF driver above.
If used for a speech only sporting event, phenolic diaphragms may have been used.
Did you actually see "banks of phenolic diaphragms broken", or are you simply assuming they were phenolic, and broken rather than burned?
weltersys,
In that instance it was more likely that the voice-coils were burned but yes I have seen plenty of old phenolic diaphragms that would crack around the joint between the dome section and the attachment of the former. These things were old to say the least and probably had seen more than their share of max excursion, they do fail. Most of the time they were aluminum but believe me the phenolic was tried and not particularly liked for live music PA. This was in the days when we were still moving around large A2 enclosures and even some old RCA W-bass bins along with plenty of Altec multi-cells and 311 horns with large honking Altec drivers. I still remember Altec power amps in racks and Ampex 3 track tape recorders, so just call me old.
In that instance it was more likely that the voice-coils were burned but yes I have seen plenty of old phenolic diaphragms that would crack around the joint between the dome section and the attachment of the former. These things were old to say the least and probably had seen more than their share of max excursion, they do fail. Most of the time they were aluminum but believe me the phenolic was tried and not particularly liked for live music PA. This was in the days when we were still moving around large A2 enclosures and even some old RCA W-bass bins along with plenty of Altec multi-cells and 311 horns with large honking Altec drivers. I still remember Altec power amps in racks and Ampex 3 track tape recorders, so just call me old.
Ok guys,
I spoke to Dietmar last night and he discovered a fault.
The third harmonics are not what you see on the pic.
His mic pre was clipping but he did not notice it.
It dawned on him when he measured the SD-370 and found
an unusual rise in H3. He did not remeasure the K55 but
he indicated that it behaves in a normal manner with the
harmonics at 110db compared to 100db.
The SD-370 is better yet with lower distortion. The only limitation is
that it just goes up to 1.2khz so it needs another driver on top.
I wouldn't go above that range with a phenolic dia. anyway as those
start to miss some detail in the higher range.
The SD-370 has been modified about the same way the K55 was.
No back chamber change yet though, if I remember right.
Klaus
I spoke to Dietmar last night and he discovered a fault.
The third harmonics are not what you see on the pic.
His mic pre was clipping but he did not notice it.
It dawned on him when he measured the SD-370 and found
an unusual rise in H3. He did not remeasure the K55 but
he indicated that it behaves in a normal manner with the
harmonics at 110db compared to 100db.
The SD-370 is better yet with lower distortion. The only limitation is
that it just goes up to 1.2khz so it needs another driver on top.
I wouldn't go above that range with a phenolic dia. anyway as those
start to miss some detail in the higher range.
The SD-370 has been modified about the same way the K55 was.
No back chamber change yet though, if I remember right.
Klaus
Oops. I just ordered fours Atlas FS. Goto recommends two in each horn, and I don't think it is (just) a marketing ploy to sell more drivers. It would increase sound pressure which must be important for midbass. The Y adapter I am getting angles the drivers. If I was to angle two drivers I would want to do it later in the horn. That will be another project.
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No, just the stock magnet.
He did discover though that the holes in the diaphragm surround work
as I envisioned to lower FS. The first time he tried it the back chamber
was not nearly big enough so the compliance was dictated by the air pressure
buildup instead by the surround.
I forgot to ask how many holes he drilled into the surround and what drill size
he used.
That was done on the K55 mod. I don't even know if he reopened them
after he discovered that it had a posive effect with the bigger back-chamber
and if he did it on all the other K55 also.
I will ask him.
Klaus
I should contact him myself also. Until my horn is finished I am left guessing. But soon I can conduct my own experiments.
I am having trouble getting the beginning of the throat right. I tried plaster, but it was too soft, so I will try scultping out a 50cm wooden log. I want it solid, but to have a nice tone. How about a complete birch tree, with bark and all.
Maybe it is time to take that long romantic walk in the forest that my gf is nagging about.
- Why did you bring a saw?
- Don't ask questions.
Could the lowest frequency at 200Hz of the Goto S-150 be extended if I made the horn mouth larger but kept the curvature? I was thinking of just adding on the existing horn, so it would look more like a 2 meter deep, stretched version of the Avantgarde Trio midbass, with ~110cm mouth instead of 75cm.
I am having trouble getting the beginning of the throat right. I tried plaster, but it was too soft, so I will try scultping out a 50cm wooden log. I want it solid, but to have a nice tone. How about a complete birch tree, with bark and all.
Maybe it is time to take that long romantic walk in the forest that my gf is nagging about. - Why did you bring a saw?
- Don't ask questions.
Could the lowest frequency at 200Hz of the Goto S-150 be extended if I made the horn mouth larger but kept the curvature? I was thinking of just adding on the existing horn, so it would look more like a 2 meter deep, stretched version of the Avantgarde Trio midbass, with ~110cm mouth instead of 75cm.
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Full range Western Electrics were only adequate in the earliest days of talkies for voice reproduction (narrow band voice reproduction at that). As soon as sound tracks improved W.E. added 15" woofers to deal with LF power inadequacy and tweeter horns to deal with limited HF output from coiled horn and compression driver rolloff.
W.E. ran into the same problems that are being discussed here: you can't make a full range system from a horn/compression driver. (Nice midrange , yes.) That is why everyone jumped on the Shearer designs when they came out.
David
If you run the drivers on the Goto horn I would not do anything to them.
What for if the Goto goes only down to 200hz.
Dietmar pointed out that the SD-370 is really well build. No surprise, they where
mostly installed as security sirens, on Government buildings and cars. Reliability
was first on the list.
Klaus
What for if the Goto goes only down to 200hz.
Dietmar pointed out that the SD-370 is really well build. No surprise, they where
mostly installed as security sirens, on Government buildings and cars. Reliability
was first on the list.
Klaus