Why not 4th order crossovers?

[Swerd]

I get that, but two of my all-time favorite speakers, the Salon2 and the KEF 207/2, both use 120Hz low-pass frequencies. Perhaps I just like the sound of problematic designs.

I don't know whether passive crossovers at such low frequencies actually produce poor sound. It's only that there are difficulties in designing them properly and large expenses in building them.

 

[yepimonfire]

@shadyJ

I’ve actually pulled apart one of my speakers to find a massive heat sink on one of the tweeters, not sure how effective it is by itself.



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[Swerd]

I’ve actually pulled apart one of my speakers to find a massive heat sink on one of the tweeters, not sure how effective it is by itself.

Interesting. Got a photo?

 

[yepimonfire]

I didn’t get one unfortunately, but the service manual for the speaker has one http://support.klipschgroupinc.com/kb/faq.php?id=80

I know several other Klipsch tweeters have had mounted heat sinks on them also. For whatever reason, unlike the II series, the premier series doesn’t have them.


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[yepimonfire]

On a more practical level than using plasma drivers, what can a speaker builder do to minimize or alleviate thermal compression?

• If cheap tweeters are the problem, would it be better to use tweeters with more robust voice coils? Does a tweeter with a low Fs, such as 500 Hz instead of 1500 Hz, mean that the voice coil/motor assembly is more robust and therefore less prone to thermal compression?
  
  
• Do ribbon or planar tweeters avoid this problem? They lack voice coils as seen in typical dome tweeters – their diaphragm also functions as the voice coil.
  
  
• If thermal compression varies with insertion loss, would it help to use inducters of lower DCR (larger gauge wire or iron/steel core)? Usually, this seems to be done only for large inducters for a woofer network. If the ADS guy was right, this may not matter.
  
  
• Would using an active crossover avoid thermal compression? Or is it still a problem due to driver voice coils?

I have to wonder if horn loading is also a solution, and that’s why they often sound so dynamic. I don’t remember off the top of my head how much efficiency you gain from a horn, but I do know that it has the effect of limiting excursion and properly matching the impedance to the air. IIRC a horn loaded tweeter should have a constant level of excursion down to the cut off frequency of the horn, that’s one reason you can cross a 1” tweeter over at 1500hz which would normally destroy it.

Just because a tweeter has a low fs doesn’t meant it can handle lower frequencies. It’s still excursion limited.


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[shadyJ]

@shadyJ

I’ve actually pulled apart one of my speakers to find a massive heat sink on one of the tweeters, not sure how effective it is by itself.



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Not uncommon to see heatsinks on tweeters. For example, the back of the tweeter on the Hsu CCB-8 coaxial driver. Remember its not just about preventing thermal compression, these cooling methods are also there to stave off destruction from abuse.

 

[killdozzer]

I didn’t get one unfortunately, but the service manual for the speaker has one http://support.klipschgroupinc.com/kb/faq.php?id=80

I know several other Klipsch tweeters have had mounted heat sinks on them also. For whatever reason, unlike the II series, the premier series doesn’t have them.


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I'm trying to follow this topic but it goes over my head all the time. Could you please tell me where is the heat sink in the linked pic?

 

[Swerd]

I'm trying to follow this topic but it goes over my head all the time. Could you please tell me where is the heat sink in the linked pic?

You have to download one of the pdf files linked at the bottom of that page. See page 7 of this link: http://support.klipschgroupinc.com/...ture=3ec8e6683c688913882f29a6ffbf3dff84bf928b

The topic is about voice coils of tweeters, the moving part of the driver. These coils are very light thin aluminum or copper wires wound in a coil and attached to the back of the tweeter's dome diaphragm. This coil is also surrounded by a magnet shaped into a circle around the coil. As the musical signal passes through the voice coil, it causes an electromagnetic field to form around it. The surrounding magnet forces the coil and the attached dome to move back and forth, generating acoustic waves. It works like a spring that responds to the electrical music signals.

Because the coil has to be made of very thin, lightweight wire, it also can easily overheat. When it grows warm enough, it's ability to conduct electrical signals gets noticeably weaker, especially at higher frequencies, resulting in less output. This loss of response is called thermal compression, because the driver's dynamic range get smaller or compressed.

Tweeters apparently are more prone to thermal compression than larger woofers or mid range drivers. Several things are done to help dissipate the heat.

• Immerse the voice coil in ferrofluid, a light oil with small iron particles immersed in it.
• Build a ventilation path into the tweeter's electromagnet-voice coil assembly.
  
• Use large magnets that can soak up and dissipate heat. This involves using large iron ferrite magnets instead of smaller neodymium magnets. Ferrite generates a less potent magnetic field, so more of it must be used than neodymium.
• Attach a heat sink at the back of the tweeter's magnet. Shadyj pointed out that such heat sinks probably have the primary purpose of delaying failure due to overheating instead of preventing thermal compression.

 

[killdozzer]

See it now:

Funny, it's not in the pic above in this manual.

 

[Swerd]

Not uncommon to see heatsinks on tweeters. For example, the back of the tweeter on the Hsu CCB-8 coaxial driver. Remember its not just about preventing thermal compression, these cooling methods are also there to stave off destruction from abuse.

I've seen heat sinks on the back of some ribbon tweeters such as those made by Fountek. https://www.madisoundspeakerstore.c...3.0m-blk-3-ribbon-tweeter-round-flange-black/

If I understand correctly, ribbon tweets have large transformers to convert the amp's signal to a high voltage low current signal that drives the aluminum ribbon. Other ribbon tweeters I've seen do not have these heat sinks, but all of them have large heavy transformers.

 

[yepimonfire]

You have to download one of the pdf files linked at the bottom of that page. See page 7 of this link: http://support.klipschgroupinc.com/...ture=3ec8e6683c688913882f29a6ffbf3dff84bf928b

The topic is about voice coils of tweeters, the moving part of the driver. These coils are very light thin aluminum or copper wires wound in a coil and attached to the back of the tweeter's dome diaphragm. This coil is also surrounded by a magnet shaped into a circle around the coil. As the musical signal passes through the voice coil, it causes an electromagnetic field to form around it. The surrounding magnet forces the coil and the attached dome to move back and forth, generating acoustic waves. It works like a spring that responds to the electrical music signals.

Because the coil has to be made of very thin, lightweight wire, it also can easily overheat. When it grows warm enough, it's ability to conduct electrical signals gets noticeably weaker, especially at higher frequencies, resulting in less output. This loss of response is called thermal compression, because the driver's dynamic range get smaller or compressed.

Tweeters apparently are more prone to thermal compression than larger woofers or mid range drivers. Several things are done to help dissipate the heat.

• Immerse the voice coil in ferrofluid, a light oil with small iron particles immersed in it.
• Build a ventilation path into the tweeter's electromagnet-voice coil assembly.
  
• Use large magnets that can soak up and dissipate heat. This involves using large iron ferrite magnets instead of smaller neodymium magnets. Ferrite generates a less potent magnetic field, so more of it must be used than neodymium.
• Attach a heat sink at the back of the tweeter's magnet. Shadyj pointed out that such heat sinks probably have the primary purpose of delaying failure due to overheating instead of preventing thermal compression.

Back to the question I asked previously, is thermal compression an issue in home audio? In pro audio, speakers have to deal with dissipating 100s to 1000s of watts on a near constant basis, a typical direct radiating tweeter in a two way bookshelf more than like is about 3-5dB more sensitive than the woofer. Let’s assume a soft dome 1” tweeter has a sensitivity of 91dB, regular music contains less and less energy as frequency increases, compared to 100hz-4khz, content above the typical 2500hz xover frequency is significantly lower, a tweeter may only be responsible for playing signals that are about -10dB or lower in comparison to the midrange. If we assume one listens to music at 80dB, with 95dB peaks, and sit 3m away, that’s only about 1w of power to the tweeter max.

If it isn’t power compression, what else could explain the difference between speakers dynamic range?


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[MrBoat]

The topic is about voice coils of tweeters, the moving part of the driver. These coils are very light thin aluminum or copper wires wound in a coil and attached to the back of the tweeter's dome diaphragm.

New diaphragm of an RS28A. I was surprised how loosely it was placed and traveled in it's package, considering how fragile it appears. I'll certainly be more careful with it and make sure I remove 'their' dust specks from it.

 

[everettT]

Back to the question I asked previously, is thermal compression an issue in home audio? In pro audio, speakers have to deal with dissipating 100s to 1000s of watts on a near constant basis, a typical direct radiating tweeter in a two way bookshelf more than like is about 3-5dB more sensitive than the woofer. Let’s assume a soft dome 1” tweeter has a sensitivity of 91dB, regular music contains less and less energy as frequency increases, compared to 100hz-4khz, content above the typical 2500hz xover frequency is significantly lower, a tweeter may only be responsible for playing signals that are about -10dB or lower in comparison to the midrange. If we assume one listens to music at 80dB, with 95dB peaks, and sit 3m away, that’s only about 1w of power to the tweeter max.

If it isn’t power compression, what else could explain the difference between speakers dynamic range?


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This link starts on page two measurements but should provide the answer your looking for with measurements. Page 1 will give you technical info

https://www.stereophile.com/content/hot-stuff-loudspeaker-voice-coil-temperatures-page-2

 

[Irvrobinson]

Back to the question I asked previously, is thermal compression an issue in home audio? In pro audio, speakers have to deal with dissipating 100s to 1000s of watts on a near constant basis, a typical direct radiating tweeter in a two way bookshelf more than like is about 3-5dB more sensitive than the woofer. Let’s assume a soft dome 1” tweeter has a sensitivity of 91dB, regular music contains less and less energy as frequency increases, compared to 100hz-4khz, content above the typical 2500hz xover frequency is significantly lower, a tweeter may only be responsible for playing signals that are about -10dB or lower in comparison to the midrange. If we assume one listens to music at 80dB, with 95dB peaks, and sit 3m away, that’s only about 1w of power to the tweeter max.

If it isn’t power compression, what else could explain the difference between speakers dynamic range?


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I'm far from a speaker design expert, but even I can tell your analysis is incorrect. If the tweeter really does have a higher sensitivity than the woofer, in your example, the tweeter will have to be padded down to achieve a flat system-level frequency response. Also, your assumption that the content reproduced by the tweeter will always be 10db down compared to the midrange is not true for some acoustic instruments, like cymbals and violins. Your assumption about 95db peaks is also incorrect for instruments reproduced in a small venue. Again, TLS Guy was referring to accurate reproduction of live music, not some 80db rendition. Mark is correct IMO - power compression is a real factor in reproducing live music.

 

[Swerd]

Back to the question I asked previously, is thermal compression an issue in home audio? In pro audio, speakers have to deal with dissipating 100s to 1000s of watts on a near constant basis, a typical direct radiating tweeter in a two way bookshelf more than like is about 3-5dB more sensitive than the woofer. Let’s assume a soft dome 1” tweeter has a sensitivity of 91dB, regular music contains less and less energy as frequency increases, compared to 100hz-4khz, content above the typical 2500hz xover frequency is significantly lower, a tweeter may only be responsible for playing signals that are about -10dB or lower in comparison to the midrange. If we assume one listens to music at 80dB, with 95dB peaks, and sit 3m away, that’s only about 1w of power to the tweeter max.

If it isn’t power compression, what else could explain the difference between speakers dynamic range?

That's a good question. (I always say that when I don't have a good answer .)

Your point is true. Typical home audio speakers tweeters are more sensitive than woofers. Therefore tweeters in home audio don't seem to suffer from the heating problems of pro audio.

Is there a way to measure dynamic range, or thermal compression? The only way I can think of is to run many sweeps of SPL vs. frequency at different volume settings. Plot them in a way that shows the range of volume settings in which the speakers have a wide & flat frequency response, and at what volumes (high or low) the speakers loose that ability. It would look for a range of SPL over which the speakers respond to changes in volume in a linear fashion while keeping a wide & flat frequency response. Is there a simpler way?

I've always assumed that differences in dynamic ranges are caused by differences among drivers themselves. Some drivers deliver it in spades, and others cannot, even though they do perform well within a narrower range of SPL. Some speakers sound good at moderate SPL, but cannot handle louder sound. And other speakers, those designed for loudness, tend to perform less well (IMO) at lower SPL. In that sense, they need to be loud to sound good.

But I haven't taken that idea beyond an assumption. And I cannot explain what design feature(s) of drivers generates greater dynamic range.

Independent of speakers, I do find that a wider dynamic range is possible with good recordings on less noisy media, and more powerful and quieter amplification, combined with speakers capable of a wider range of SPL.

The problem I have with my idea is, if true, speakers with a large dynamic range will always sound better than speakers without it. And, in my experience, that isn't always the case.

Anyone else have ideas directed toward Yep's question?

 

[Swerd]

I'm far from a speaker design expert, but even I can tell your analysis is incorrect. If the tweeter really does have a higher sensitivity than the woofer, in your example, the tweeter will have to be padded down to achieve a flat system-level frequency response.

That is very often the case, if not always. I can't think of a DIY home audio design where the woofer(s) are more sensitive than the tweeter.

 

[Swerd]

That is very often the case, if not always. I can't think of a DIY home audio design where the woofer(s) are more sensitive than the tweeter.

An example to illustrate my point. Compare two speakers, Salk SongSurround I and Salk SongTower.

The SongSurround I uses one Seas ER15RLY midwoofer (sensitivity of 87.5 dB) and one Hiquphon OW1 tweeter (sensitivity 88 dB). Their sensitivities are close enough to require little or no tweeter padding to achieve a neutral sound balance.

The SongTower uses two identical Seas ER15RLY midwoofers, wired in parallel, arranged as an MTM. The tweeter is a Hiquophon OW2x almost identical in sound and characteristics to the OW1, but with a sensitivity of 90 dB instead of 88. Using the OW2x tweeter in the SongTower keeps the sensitivities of the two midwoofers and the tweeter as close as possible without requiring significant padding.

 

[ski2xblack]

Anyone else have ideas directed toward Yep's question?

Re dynamic range of tweets? Direct radiator vs horn loaded. The latter will have higher sensitivity, lower distortion, much more dynamic range, and far better transient response.

(YIOF has horns, I figured he would appreciate that.)

 

[Swerd]

Also, your assumption that the content reproduced by the tweeter will always be 10db down compared to the midrange is not true for some acoustic instruments, like cymbals and violins. Your assumption about 95db peaks is also incorrect for instruments reproduced in a small venue. Again, TLS Guy was referring to accurate reproduction of live music, not some 80db rendition. Mark is correct IMO - power compression is a real factor in reproducing live music.

I don't really know how to comment on your other point. I certain cannot disagree with it.

 

[Irvrobinson]

I don't really know how to comment on your other point. I certain cannot disagree with it.

In retrospect though, I wonder how power compression compares as a factor to a tweeter just reaching its output capability limits.