ReliaBill Engineer
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Posts posted by ReliaBill Engineer
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Really? Are you just trying to be difficult and defensive? Or am I misunderstanding you?
So….I guess after I get these sounding smooth, I’ll have to buy a pair of 4X speakers in which to install them. But even then you’ll be skeptical, regardless of what I say, show, or even record.
Likely I’ll have to send them to you for auditioning. But I’m very hesitant to do that.
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37 minutes ago, RoyC said:
Hmmm, I'm sure it will be interesting, but it is hard to see how it will be relevant to the 4x. Impedance is only one parameter. You are proposing using it with a different woofer, different cabinet, different crossover...and conclusions reached based on your listening impressions?
Relevant to the 4X? Aren’t these PRTs being used to replace original AR tweeters in the 4X? Haven’t you yourself, and others tried to make them more suitable as a replacement? Or did I misunderstand?
Listening is always the final test. Test equipment has its place, but the final test is in the listening. Right?
The Polk RTA-8T speakers I’ll be auditioning these tweets in are also 2-ways. They’ll make for a good test case for these tweeters. Sink or swim.
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6 hours ago, RoyC said:
So you have experience using this tweeter in the 4x? What crossover and cabinet changes did you make to accommodate this tweeter?
Not in the 4X. 1988 I restored a pair of McIntosh XR7 speakers.
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4 hours ago, RoyC said:
4 or 8 ohm. Are you installing them in 4x's? What kind of changes do you have in mind?
I said this in an earlier post:
“I bought 2 of the 8 ohm PRTs to play around with. I don’t know if I’ll have any more luck than you did smoothing them out. But it will be a fun learning experience.
I’ll test them using my Polk speakers, since it’ll be easy to adjust the mounting, and I have impedance adjusting resisters, and I’m very familiar with the original sound of these Polks. Also, the efficiency matches as well as useable FR.”
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Just got these in. Hopefully I’ll have time tonight to make a few changes. I bought 2. One will remain unmolested.
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There were extensive tests done in the early ‘80s on tweeter pistonic motion. Laser interferometry was used to analyze various cone and dome tweeters, design and materials. Cone tweeters tended to have the highest distortion caused by vibration nodes; different velocities and phase from center to outer edge. Domes had much less; even less depending on material and surround used.
Paper cone tweeters just cost less than well designed domes. Paper cone tweeters tend to be used on the bottom tier speakers of any given mfr, 1950 to now. (The paper cone mid on the 2ax is another example of price point compromise.) There are exceptions, of course. The paper cone tweeter I showed above in the wharfdale W70C was replaced with a modified dome in the W70D, but the W70C was an expensive iteration of the paper cone tweet. Even that didn’t work well. Poor dispersion and a harsh character to its sound.
The 4X was not AR’s flagship model. Not by a long stretch.
The below tweeter, while not paper, is a very good design for a cone tweeter. It’s actually smooth and well behaved.
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14 hours ago, RoyC said:
I disagree. No speaker system (or individual driver) has ruler flat frequency response...so are those departures considered to be "distortion"? The 4x replacement tweeter referred to as "harsh" by some people has been found to be satisfactory others. Earlier in this thread a forum member stated "I actually like the Parts Express replacements". Are you going to tell him he prefers "distortion"? If so, based on what?
"Distortion" is usually considered to be something that should not be present such as noise, static, rattles. clipping, etc. I think you are actually referring to frequency response and tonal balance, not distortion. The crossover integrates presumably properly functioning drivers to produce a desired response. There will always be variations and preferences on the part of the designer and the listener.
I disagree.
Distortion usually arises from lack of pistonic motion from the driver. It can be coloration, or most often from resonance(s) in the cone or dome. It’s a lack of faithfulness of the driver’s output compared to input. 2nd and 3rd harmonics produced in addition to the fundamental signal.
Cone breakup is common from paper cone tweets. The outer edge of the cone can’t keep up with the center motion driven by the VC. Out of phase output from the outer edge compared to the center of the cone often results.
That’s why AR used dome tweeters in its upper line speakers, so the outer edge IS the driven part where the VC is mounted. The PRT has an outer edge restrained and a center free to move by the VC.
Can you imagine a woofer with a secured outer edge instead of a surround, trying to reproduce low frequencies? Or lower mids? Or upper bass?
I remember the paper cone tweeter used on the ‘66 Wharfdale W70C. It had similar issues of harshness and beaming. It was a paper cone mounted on its outer edge to a grey felt ring. I wound up replacing it with a dome tweeter back in 1982 on my father’s speakers. I couldn’t get that Wharfdale tweeter to sound good.
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On 3/7/2024 at 5:16 PM, RoyC said:
Not necessarily. In this case it probably has more to do with its inherent frequency response and behavior with the existing crossover.
Inherent frequency response and behavior *is* the distortion, if it’s in the pass band. A crossover can limit distortion if it occurs below or above the XO frequencies.Even with the crossover, there shouldn’t be distortion. Rather, it should have a smooth roll off at both ends of the FR. And an inherently smooth pass band.
The AR-2ax mids are harsh. AR really liked using fiberglass batting to damp distortion.
I bought 2 of the 8 ohm PRTs to play around with. I don’t know if I’ll have any more luck than you did smoothing them out. But it will be a fun learning experience.
I’ll test them using my Polk speakers, since it’ll be easy to adjust the mounting, and I have impedance adjusting resisters, and I’m very familiar with the original sound of these Polks. Also, the efficiency matches as well as useable FR.
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Duplicate post…
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Which I guess speaks well for the durability of the woofer mechanics. The voice coil can’t shed heat fast enough, and 30-1000 Hz is where the majority of music power is.
Looking at the suggested wiring of the fuses, it doesn’t protect the tweeters by themselves. The fuse is seeing the total current fed to the loudspeaker. So is it going to protect the tweeter? Kind of doubtful. It’s a crapshoot whether enough current still passes to the tweeter to blow its VC before the fuse blows.
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On 3/6/2024 at 3:58 PM, tourmax said:
Thanks gents.
I’ll get on those caps.
I’ve seen the scans of AR recommendations for fusing in the library section. I’ve also seen the “signal loss” argument on the internet in places. I’m more concerned with protecting these old speakers than I am loosing any signal. It’s not like I’m building some competition sound system or anything like that. It’s just a simple home system, so I’m willing yo give up a little something in order to possibly save them this type of damage if it ever happens again in the future.
whats the difference between the suggested brand fuses and a commonly available “fast blow” fuse?
I don’t think a fuse would have protected your tweeters from the sudden *thump* of a mic input:
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I’m thinking of buying a pair to play around with. Harshness comes from distortion. So have to reduce the distortion.
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IMO, yes, those caps need to be replaced if original. A fuse could be added, but putting inside the cab would be a pain to replace if you blow it. I’d put it outside on the terminal plate with a fuse holder clip. Some audiophile purists would say to never use a fuse in a tweeter circuit; but these aren’t $100,000 Wilson Audio speakers, either.
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Last pair of 4x tweeters I worked on had the same issue. I used an Exacto knife, new blade, to cut the glue holding the paper cone edge. Then removed the solder from both terminals. Desoldering braid worked for me. Then I cut one remaining lead. Lifted out the cone+ voice coil. Checked coil condition and continuity. Both were good. I soldered extension wires onto the originals. Threaded the extensions into the terminals. No solder yet. I then ran a small bead of thinned black RTV under the edge of the cone, centered it. While still moveable, I used a 1.2 volt battery cell to energize the leads, to center the VC. Then pressed the cone edge into the glue all around. I rechecked the centering by using the battery cell. No scraping sound. I let the glue cure. Then soldered the wires to the terminals.
Pretty much what I do for repairing dome tweeters also.
I like using thinned RTV because it’s reversible. If I find that I goofed, an Exacto blade can be used to cut the glue and start over.
AR was fond of using fiberglass batting to damp mids and tweeters.
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I’ve been comparing a new pair of KLH 5s to my fully refurbished 1965 AR-2ax speakers. Hands down, the 2ax’s are preferable. The 5s do have slightly lower bass. But in other areas of imaging, “air”, realism, FR “balance”, smoothness and extension of treble, vocals, the 2ax’s really shine!
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Did you have the original diaphragms and voice coils? If not, what did you use as replacements?
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On 12/27/2023 at 2:22 PM, RoyC said:
It is not unusual for the DC resistance of AR drivers to measure appropriately, yet subjectively exhibit distortion due to mechanical degradation.
True. But it’s difficult to address distortion from mechanical degradation issues when the VC windings are bad, reading discontinuity from being fried or severed. Mechanical degradation becomes secondary to a bad voice coil.
This mid driver read “open circuit”:
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I usually remove the drivers from the circuit, then test the drivers using a DMM set to 200 ohms. This tells me if the VC has continuity and at what DC resistance. The DC resistance tells me what impedence range the driver is in, 2/4/6/8 ohms nominal. All necessary to repair or replace the driver.
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One of the mids, after arrival:
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On 12/4/2023 at 12:38 PM, Aadams said:
Do you have them in working order?
Alas, no. Neither mid has the dome+VC. I wound up getting a “forced” refund from the seller. I asked him prior to purchase what the DCR was of each. He said “open circuit”. But he failed to say that neither one has any wires to measure from! eBay agreed with me, that the seller was deceptive in his description and communications with the buyer (me).
Since then I have the raw domes, but need the VCs. I may wind up having to make my own VC formers, and winding them myself. I have kapton. I have various spools of wire, 24-36 AWG. But not sure I want to go that route.
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I’ll be rebuilding these early AR/3a dome midranges. Open circuits, per the seller. Once complete, I’ll use them to compare sound to the 2” hard dome midranges above.
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Great news!!
I have a pair of AR-3a dome midranges coming my way. They need repair work done. I’ll document the repair. Then I’ll compare to my dome midrange “mod” for the 2ax. This will be my 3rd pair of 1965-1969 3a dome mid repairs. The other 2 pair got sent back to their owners locally (in state). This pair is mine.
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The light beige looks just like my original cloth grill on my 2ax. Very difficult to see any difference.
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Sound deadening. Acoustic damping inside the speaker cabinets.
I’m working on an interesting project at work that pertains to this. Artemis IV has a “hollow” tubular section 33 feet in diameter, 40 feet high, 34,194 cubic feet volume, where computer modeling shows it to have destructive levels of acoustic resonance. In essence a huge bell, or a volume that will build up acoustic vibrations from air passing over the outside of the volume at very high velocity. Modeling shows the acoustic vibrations to build to a level shown to be a structural hazard both to the section as well as to the avionics and structures within the volume. The solution has to be low mass, low volume, and fire proof. Frequencies 10 Hz to 10 kHz. 30 dB of damping.
Blown AR4x tweeters and a repair attempt…
in Acoustic Research
Posted
“I bought 2 of the 8 ohm PRTs to play around with. I don’t know if I’ll have any more luck than you did smoothing them out. But it will be a fun learning experience.
I’ll test them using my Polk speakers, since it’ll be easy to adjust the mounting, and I have impedance adjusting resisters, and I’m very familiar with the original sound of these Polks. Also, the efficiency matches as well as useable FR.”