Why not 4th order crossovers?

[Swerd]

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

Thanks for that link . It was interesting to read.

The author found that little or no changes in resistance of a woofer or a tweeter occurred during the repeated music passage. Although it is possible that he chose a music passage and a speaker that were not good representatives, he concluded that thermal compression is not a significant problem in home audio speakers.

"So I strongly suspect that, for most hi-fi users—those who don't habitually wind the volume control to its highest position and indulge in PA listening levels—thermal compression is a paper tiger."​

Irv's intuition may be closer to the truth, that power compression due to heating in a voice coil is minor compared to other factors that limit a tweeter's SPL output.

 

[Johnny2Bad]

Whatever works ... the crossover is a key part in a loudspeaker and must be designed specifically to work with the system.

One reason a 4th order isn't popular in a 2-way is the sharp rolloff might mean crossing over to the HF driver at too low a frequency, or running the LF driver too high in the passband. Less of an issue in a 3-way where you can cross the mid / HF drivers with a 4th order without those issues.

But in the end, and it can't be said enough, the loudspeaker is a system and the right crossover slope is part of that system. There is no hard-and-fast prohibition against 4th orders, but you don't want to fall into the trap of holding on to a technology or configuration just because you are married to it.

The loudspeaker, with our current level of technology, is a massive set of compromises. Choosing where to compromise in order to get this or that performance criteria is, in essence, the sum of what making speakers is all about. Get this, give up that. Speaker designers either make good choices or not so good ones, but they all have to compromise somewhere.

 

[yepimonfire]

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

Yeah, I’ve seen that article before, which led me to believe it isn’t really. Of course, this is with music, movies OTOH are much more demanding. 100dB-105dB is just too damn loud for music playback, but during movies, I’ve frequently measured LC fast max peaks of 110dB during intense scenes, and it doesn’t sound objectionable at all.

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.)

Based on the Stereophile article above, going to assume that power compression isn’t a huge factor in dynamic range. The low distortion in horns is obvious, since above the cutoff frequency of the horn the impedance matching controls the excursion of the diaphragm, making it fairly constant from the lowest to the highest frequency. In addition, the ability to use a lower xover point greatly reduces IM distortion and Doppler distortion, which is way more objectionable than harmonic distortion.

If you want to get an idea of just how jarring IM distortion sounds, use REW to generate a 4:1 ratio dual tone signal of 50hz, or the lowest possible considering the f3, and 2500hz/3000hz depending on the xover point of the speaker.

What I don’t get is what factors into dynamic range capabilities from one speaker to the next? I am not sure what a standard xmax is for a typical 1” dome tweeter, but even at 2500hz, 105dB @1m only requires 0.3mm of excursion from a 1” driver, so what determines dynamic range (or lack of), transient response?

What about dynamic range with woofers? Even at the midrange and midbass/upper bass frequencies, the dynamic range of the RP-150m would put some smaller tower speakers to shame, from 60hz-1500hz, THD measurements @100dB/1m show a maximum of ~3% THD (centered at 89hz), with the numbers reaching fractions of a percent above 200hz. No horn loading on the woofer obviously.

It does appear the speaker was design more for efficiency rather than small size with deep bass (Hoffman’s iron law comes to mind). The cabinet is quite a bit larger than average for a typical 2 way 5.25” bookshelf, ceramic anodized aluminum allows a very thin, light diaphragm, in comparison to poly composite materials or paper, aluminum isn’t very “lossy”, and from what I’ve heard, they’ve begun using titanium for the VC formers instead of aluminum. Being poorly conductive, it offers most of the benefits of aluminum (heat dissipation, since it is attached to an aluminum cone) without the power wasting eddy currents that plague aluminum.

I’m not entirely sure on this, but wouldn’t a speakers sensitivity rating be limited to the sensitivity of the box loaded woofer (since the tweeter would just be turned down with an L-pad to match)? Since Klipsch measures sensitivity in room, you can subtract 3dB from their rating(this usually matches with third party measurements). Even at 90dB anechoic, that’s still pretty efficient for a 5.25” bookshelf speaker. Many speakers in that category measure anywhere between 85dB-87dB. That translates to being either double or almost 4x as efficient.



Sent from my iPhone using Tapatalk

 

[Johnny2Bad]

Power Compression is real. The more you run a driver the more the voice coil heats up. It's really a problem most often found in Pro Audio, but it can happen in the home.

 

[yepimonfire]

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.

If only recorded music actually contained the full dynamic range of music. Unfortunately, it doesn’t more often than not. I actually have a “full dynamic range” release of a heavy metal album, you have to crank the volume knob up about 18dB, but looking at the waveform peaks in Reaper, each kick drum beat is a 20dB swing, snare is similar, in total the music has peaks and valleys of over 36dB. Most modern recordings are compressed somewhere between 12-9dB on a “good” mastering, and at the worse end of the scale 6-3dB. I believe classical music has a range from about 65dB during quieter passages to 100dB at its loudest, so I suppose it depends on whether or not your speakers are capable of achieving 97dB a piece at your listening spot.

Unfortunately, plenty of common consumer speakers (your average direct radiating 2 way slim tower) may be able to handle 100w without blowing, but start sounding seriously strained above 10w, hence my preference for horn loaded speakers. It does not make any difference if I listen at 80dB, or 100dB (which I’ve actually done when trying to fill the house with music), the sound is just as clear and dynamic. The only time I’ve heard speakers capable of reproducing such unhindered dynamics at high volumes was in PA setting, or at an IMAX theatre. I haven’t had the privilege of hearing or owning some very large high end speakers (which I am sure can perform much better), but I can confidently say that 95% of mid and upper mid priced home audio designs I’ve either owned or heard myself fail to faithfully reproduce that kind of dynamic range cleanly.

This is less of an issue with larger speakers with 3 way designs using dedicated midrange drivers, since, in my experience, it’s usually the midrange that starts crapping out at high volume (I’m also a firm believer that midbass and midrange is the most taxing on a speaker, and I know @tlsguy agrees with me).

Most “space friendly” home audio speakers suck at truly reproducing the full dynamics of music and movies. I don’t think it’s power limited as much as it is mechanically limited.

 

[everettT]

As a note using heavy metal as reference to dynamic range seems odd. In music classical, jazz, Bluegrass and Opera would be better than HM for testing dynamic range. I came from the origins of HM in the late 70s , enjoyed it, still listen to it, but wouldn't use it to demo my systems ability. If one is getting 110db out of their system without distortion and with smooth FR, I'd say you are doing quite well.

 

[KEW]

If one is getting 110db out of their system without distortion and with smooth FR, I'd say you are doing quite well.

...aside from hearing damage.

 

[Irvrobinson]

If only recorded music actually contained the full dynamic range of music. Unfortunately, it doesn’t more often than not. I actually have a “full dynamic range” release of a heavy metal album, you have to crank the volume knob up about 18dB, but looking at the waveform peaks in Reaper, each kick drum beat is a 20dB swing, snare is similar, in total the music has peaks and valleys of over 36dB. Most modern recordings are compressed somewhere between 12-9dB on a “good” mastering, and at the worse end of the scale 6-3dB. I believe classical music has a range from about 65dB during quieter passages to 100dB at its loudest, so I suppose it depends on whether or not your speakers are capable of achieving 97dB a piece at your listening spot.

Unfortunately, plenty of common consumer speakers (your average direct radiating 2 way slim tower) may be able to handle 100w without blowing, but start sounding seriously strained above 10w, hence my preference for horn loaded speakers. It does not make any difference if I listen at 80dB, or 100dB (which I’ve actually done when trying to fill the house with music), the sound is just as clear and dynamic. The only time I’ve heard speakers capable of reproducing such unhindered dynamics at high volumes was in PA setting, or at an IMAX theatre. I haven’t had the privilege of hearing or owning some very large high end speakers (which I am sure can perform much better), but I can confidently say that 95% of mid and upper mid priced home audio designs I’ve either owned or heard myself fail to faithfully reproduce that kind of dynamic range cleanly.

This is less of an issue with larger speakers with 3 way designs using dedicated midrange drivers, since, in my experience, it’s usually the midrange that starts crapping out at high volume (I’m also a firm believer that midbass and midrange is the most taxing on a speaker, and I know @tlsguy agrees with me).

Most “space friendly” home audio speakers suck at truly reproducing the full dynamics of music and movies. I don’t think it’s power limited as much as it is mechanically limited.

As usual, you’re not a good listener. This portion of the discussion refers to recordings intended to be realistic, on systems thought to be capable of realistic reproduction. You’re also being too vague talking about “listening at 100db”. Just what does that mean? An average level of 100db or peaks at 100db? The other numbers you bandy about are just as out of context. I get the feeling that you really don’t know what you’re posting about.

 

[everettT]

...aside from hearing damage.

WHAT?

 

[TLS Guy]

I have been away from this for a while. It seemed like winter was on the wing up here, despite 72 degree temps 8 days ago. However forces have been changing on the Pacific and North Atlantic.

I woke up to this yesterday morning.

Anyhow it is still all there and it has not been above freezing since.

I have been working hard to get all the fall work done. I just my neighbors boat lift repaired with about two hours to spare before the snow started coming down, Thursday afternoon. I have been unpaid maintenance man on this part of Benedict Lake for years. I was fixing a couple of small problems with the Christmas lights as the snow started to fly.

I had just a few minor jobs left which I did today in my shop with the heat on. So I'm now ready for winter pretty much, which by all accounts looks here to stay most likely. Also i'm on the slate for a left total hip replacement Thursday. So I will be confined to base for six weeks or so. I have been forbidden to get on a tractor for at least 6 weeks after surgery.

Anyhow thermal compression is real in classical music, but only in certain repertory. Most of the time spl is low, but there are works with extended passages, where there are a couple of choirs, a large orchestra at full forte and a huge organ thrown in. Dynamic range of classical recordings since the advent of digital audio is not restricted.

The problem is manifest by a muddling and loss of detail as the intense passage progresses as well as volume reduction. The heating of VCs and passive crossover components changes the crossover points and L-pads.

This current rig is free of it and effortless.

Now a fourth order crossover will not necessarily limit power to a tweeter. With lower order crossover roll off will start higher for a tweeter and there will be more power sharing with the driver below.

As I have said before sustained power demands are high out to 2.5 KHz. I think low tweeter crossover points are the wrong approach. I like mine 2.5 KHz or higher.

I don't like passive crossovers in the high power demand regions. For a reference speaker the lower crossover points at least should be active.

In my main speakers BSC for the 7" drivers is given to the upper 10" drivers. This helps power sharing. In the center one driver handles the BSC. In active designs it is easy to get BSC just right for location. Avoiding more BSC than required is good for fidelity and helps reduce driver power demands.

I like two drivers handling the power range. That is just one of the reasons I'm keen on MTM.

This seems to have solved the issues very well. The system stays effortless and relaxed even in the most demanding passages, and yes, even the brass remains true and powerful.

I think this is the first rig I have never run out of gas so to speak.

 

[Alex2507]

Initially I clicked on the thread to see what TLS had to say. Good luck with the hip, Mark.

Then I find this:

I get the feeling that you really don’t know what you’re posting about.

It's like you're channeling Banned Mark. My thanks to you for that.

Now I suppose I'm going to have to read the article that Swerd said was interesting. More coffee should help with that. Edit: The article lost me on the first paragraph due to not understanding output and load impedance. Ima go back to my bananas.

 

[Irvrobinson]

Initially I clicked on the thread to see what TLS had to say. Good luck with the hip, Mark.

Then I find this:



It's like you're channeling Banned Mark. My thanks to you for that.

Now I suppose I'm going to have to read the article that Swerd said was interesting. More coffee should help with that. Edit: The article lost me on the first paragraph due to not understanding output and load impedance. Ima go back to my bananas.

I agree - I hope you have the best outcome possible, Mark, on that hip replacement.

Who is Banned Mark?

 

[Alex2507]

I agree - I hope you have the best outcome possible, Mark, on that hip replacement.

Who is Banned Mark?

Markw, he and TLS both had a habit of not suffering fools.

 

[Johnny2Bad]

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?

Fire the system up, set a relatively high volume, and measure. You could use a smartphone Sound Pressure Meter app and I would expect also a multimeter measuring the voltage at the speaker terminals would also work.

For consistency, you could use a test tone (1 KHz should be fine, you don't really want to be throwing too much power into the tweeter alone) to set your level, play music, then re-test with the tone. Don't alter your level control, obviously, between test tone level measurements.

Run the system for a half hour and re-measure. If there is thermal compression it should show in your results. The voltage measurement would indicate if the resistance of the system has increased because of playing music (measured voltage would fall), so would be just as effective, maybe more (more sensitive) than an SPL comparison. Increased resistance is essentially the definition of thermal compression.

Generally speaking you have to run a speaker pretty hard to get thermal compression, so use your good judgement. You are actually pushing the system near or even at the limit of heat damage, so maybe only for the adventurous and those willing to deal with possible damage.

 

[Swerd]

@TLS Guy – good luck with the hip replacement surgery. I hope you're as good a patient as you are a home audio DIY builder! Best wishes for a speedy recovery.

Speaking of dynamic range… Last night I was at my local concert hall (it has the pretentious sounding name of The Music Center at Strathmore) and saw my first Baltimore Symphony Orchestra concert of the season. As an encore at the end, they played Bernstein's Overture to Candide. I've played that brief (~4 minutes) but exhausting piece myself in a high school concert band, but I've never heard it done live by a first rate symphony orchestra in a proper concert hall. WOW ! That piece of music is a good example of what large dynamic range is.

Note to self: I should look for a good recording of that.

In contrast, this talk about the dynamic range of heavy metal music does make me laugh, just a bit.

 

[KEW]

Markw, he and TLS both had a habit of not suffering fools.

I always considered Markw and TLSGuy the "resident curmudgeons" and they had that in common, but a key difference is that TLS will explain to you in no uncertain terms (and in meticulous detail) why you are a fool, while Markw usually considered it "self evident".
On the occasions that it is my turn, I appreciate that TLS gives the time and care to "educate" me! That display of respect softens the blows to the ego!

 

[Swerd]

Now I suppose I'm going to have to read the article that Swerd said was interesting. More coffee should help with that. Edit: The article lost me on the first paragraph due to not understanding output and load impedance. Ima go back to my bananas.

I’ve already had an extra cup of coffee this morning, so I’m ready to walk through this.

https://www.stereophile.com/content/hot-stuff-loudspeaker-voice-coil-temperatures-page-2. (The first page gives some back ground, but you can skip the first page, and go directly to page 2 for the details of the test.)

Everyone agrees that a speaker voice coil heats up when used. The louder the playback, the more it heats up. It is also known that a speaker voice coil, when hot enough, conducts electricity less well than if cool. This is said to result in a loss of output, especially in tweeters, and is called thermal compression or power compression. Apparently this is a known problem in auditorium PA loud speakers. Many people also believe that thermal compression occurs in home audio speakers.

The question is, do home audio speakers suffer the same loss of output to voice coil heating? Does the resistance of woofer or tweeter voice coils increase with use?

Keith Howard, the author of the Stereophile article, measured the voice coil resistance in a B&W CDM1NT speaker that he owns. He used them as an example of compact 2-way speakers of lower than average sensitivity, in which you might expect to find thermal compression problems. He also had physically removed the speaker’s crossover board from the cabinet, allowing him to measure thermal behavior downstream of the crossover.

He had to build some test equipment so he could directly measure the voice coil temperature (did he mean resistance?) of both the mid-woofer and the tweeter.

As program material, he wanted a music passage that was likely to heat the speaker’s voice coils. He quoted a good authority (Bob Stuart of Meridian) that Metallica tracks make for good power-testing material, as they have negligible dynamic range and quite a wide frequency spectrum. As he didn’t have any Metallica, instead he chose a passage from the song Heartbreaker from Led Zeppelin II. He claimed, the instrumental section in the latter half of that song was just what he was looking for, with a paucity of dynamic range, and quite a wide acoustic spectrum (fig.2). Because this passage lasts about 47 seconds, he stitched seven repeats (329 seconds) end to end in a WAV file to create a single track of over five minutes long.

This graph (figure 2) shows two traces of dB full scale (dBFS) vs frequency of peak (red) and average (blue) audio spectra of the 47 second passage. The author claims the wide frequency range and close spacing of the red and blue traces confirm the low dynamic range of the passage. I’m glad he at least tried to document the dynamic range. Without anything to compare to this, we have to take his word. If anyone cares enough, they can do a similar measurement with another musical passage.

Playback was done with a Townshend TA565 universal disc player and a Rotel RA-1062 integrated amplifier rated at 60 Wpc continuous into 8 ohms. The volume control was set to about 2 o'clock, at which the sound-pressure level at 1 meter driving the CDM1NT's mid woofer driver read between 100 and 104 dB. The author described the mid-woofer’s cone as “undergoing sufficiently large excursions to threaten the end-stops had the volume been much higher”. He also measured the tweeter at the same volume setting.

If the author directly measured voice coil temperature, he didn’t show those results. Instead, all his results show voice coil resistance in ohms over a time of 500 seconds, where the seven back-to-back repeats of the music took place during the first 329 seconds.

The results (figures 3 and 4) were something of a surprise. Despite what he thought was a high playback level, the increases in voice coil resistance were even less than he expected in the mid-woofer and barely detectable in the tweeter.

Figure 3 – mid-woofer
The trace began at 3.9 ohms before the music passage began, rising to about 4.2 ohms while playing the test program, and rapidly returned to 3.9 ohms afterward.

Figure 4 – tweeter
Same test as in figure 3, but with the tweeter. Note that the vertical scale is different than in figure 3. It shows the range of 2.5 to 3 ohms, over the same vertical distance as the 3.5 to 5 ohms in figure 3. It is ‘zoomed in’ or magnified. Here the change in resistance during the test program was barely distinguishable, amounting to about 0.01 ohm.

Conclusion: Under these test conditions, thermal compression is barely detectable, and is not considered a problem.

 

[Alex2507]

I actually read Page 1 in an effort to get some bearing on the terms that I didn't understand. I'm going to go through the article again and then your post as well. Thanks. Hoping to get through some painting and baseboard installation here before all that though. More later. Seriously, thanks for going through the effort.

 

[Swerd]

I actually read Page 1 in an effort to get some bearing on the terms that I didn't understand. I'm going to go through the article again and then your post as well. Thanks. Hoping to get through some painting and baseboard installation here before all that though. More later. Seriously, thanks for going through the effort.

Read my post first . I thought the article was kind of thick and hard to read. I had to read it several times just to get to the take home message.

I figured if I ran into that problem, so will others. There are too many articles in rags like Stereophile where the author gets way off-topic and apparently likes to hear himself talk. In my opinion they need some serious editing. Of course, if that happened the article would be a whole lot shorter .

As Banned Mark would say, "If you can't dazzle them with brilliance, baffle them with bullshirt."

 

[shadyJ]

Read my post first . I thought the article's wording was kind of thick and hard to read. I had to read it several times just to get to the take home message.

I figured if I ran into that problem, so will others. There are too many articles in rags like Stereophile where the author gets way off-topic and may like to hear himself talk. In my opinion they need some serious editing. Of course, if that happened the article would be much shorter .

As Banned Mark would say, "If you can't dazzle them with brilliance, baffle them with bullshirt."

I don't know why he wouldn't just use a pink noise to test compression like everyone else. Or, better yet, use something that has a tilt to higher frequencies. Low frequencies aren't good for inducing thermal compression because the large movements of the coil actually help it cool off. Higher frequencies see a lot of current dumped into the driver but not much relative motion to cool it off. Were I to conduct the tests, I would have measured the effect on frequency response by using pseudo random noise. Testing resistance is interesting, but I would be more interested in the end result on the response.