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Linkwitz LX521.4 - new build and impressions

Joecarrow

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I will try to reply to a few of your specific points.

Thanks for a response from someone who actually owns these speakers. The comments I've seen from different users over the years, with both this speaker and its predecessor, is that the deep bass is probably not adequate to satisfy people who want home theater level of bass, but adequate for people who listen to music. I would be in the latter category, however I do sometimes listen to music where the deep bass is an important part of it and it wouldn't sound very satisfying if the deep bass wasn't fully present and accounted for..

In my room I do hear satisfying bass well into the high 20s, which for non-theater content is sufficient for most all music that I listen to. In my use of the LX521 for theater content, I was able to cause extreme (and disturbing) cone movement from exposure to LFE, and of course the speakers did not successfully produce the infrasonic content in any tangible way.


For anyone who isn't thoroughly familiar with the history, the predecessor of this speaker, the Orion, first came into prominence thanks in large part to the praise heaped on it by Peter Aczel, the publisher/editor of The Audio Critic. Criticisms of any speaker design are often based in the understanding of the theoretical distinctions between the given design and more conventional designs. As such, the criticisms of the Orion and the LX521 are generally twofold, and are essentially the same as with any other dipole radiator (or any speaker that approximates a dipole radiator). Some people question whether it is desirable to have so much acoustic energy reflecting from the wall in back of the speaker. Linkwitz obviously believed that this is to be desired, and while he did also mention that the radiation pattern avoided much of the side wall reflections, this benefit seemed sort of secondary, at least less important than the strong desirability of the late reflections from the rear wall, and he emphasized the importance of tonality match of those reflections to the direct wave.

I think that it is widely understood that the match in tonality between the direct and reflected sound is desirable. I see it frequently mentioned on this site with other speakers. There are a couple of points that I think you need to consider though. First, the overall polar area of radiation for a dipole speaker will be less than a typical speaker, and there will be a greater proportion of direct sound for the dipole at the same distance. More on that here: Listening_room (linkwitzlab.com)

Almost any box speaker will send sound to the rear, but in general it is a lowpassed version of the sound that wraps around the box at the baffle transition frequency, generally around a few hundred hertz.

The other criticism that is based in the theoretical understanding of the design approach is with the fact that as frequency moves lower and wavelengths get longer, the cancellation between the front and rear wavefronts increases. I recall that he wrote that the cancellation yields a bass rolloff that increases at -6dB per octave. But I suspect this is fully correct only for a middle region where the wavelength is not a whole lot shorter than the baffle width and not a whole lot wider than the baffle. At frequency high enough to where the tweeters are highly directional, there will not be appreciable cancellation between the front-facing tweeter and the one facing the rear. For upper treble the dipole pattern is achieved merely by virtue of a pair of highly directional tweeters aimed in opposite directions.

As it turns out, the -6db per octave is a predictable behavior that can be corrected in the filtered signal sent to the amplifier, just at the expense of increased excursion. You are correct that the dipole radiation cancels to different degrees based on wavelength and baffle size, but it does not have to show up in the sound produced once the filters are taken into account.

At the other end of the spectrum, I think there must be a point where the wavelength is so great that cancellation between the front and the rear is essentially perfect, such that the effect would not become appreciably worse as the wavelength increases further. The only way I would expect to hear much deep bass from any dipole radiator would be if I were sitting close enough to the speaker that the wavefront coming directly at me, from the two woofers, will be greater in strength than the wavefront that reaches me by propagating around the baffle from the other side. The wavefront that comes from the far side of the baffle has a slightly longer distance to travel, and spreads out more, and is thus slightly weaker than the wavefront that travels a shorter distance to reach me. But when you listen from a distance where the difference between the two distances is minor in relation to the distance, this effect goes away. For any listener a reasonable distance from the speaker and for wavelengths at least a few times greater than the baffle width, it seems likely to me that the wave cancellation would be essentially complete. I would not expect to hear much of anything below 100 Hz unless I were sitting within a few feet of the speaker and directly in front of it, not off to either side. It need not be said that Linkwitz understood this perfectly well. This was the reason that he designed and built the subwoofer, the Thor (if my memory is correct he did the Thor when he was still focused on the Orion, prior to the LX521).

The Thor was produced when the Orion was still using some Peerless woofers that had limited excursion capability. Linkwitz worked with Seas to produce the L26RO4Y woofers, and once those were in place the Thor became (other than for theater) obsolete. The LX521 can produce bass just fine at a distance, and inside a typical room the bass does not fall off noticeably as you move side to side. It is true that the woofer equalization has in excess of 20db of correction from the high end of its range to the low end, and this compensates for the acoustic cancellation.

The reason I have just now written all of this is not to disparage the speaker. I was curious about whether people who own the speaker are satisfied with the deep bass, and the answer from one person suggested an absence of understanding of the unique characteristics of the design. So I thought I would take the time to write a few words about it. For what it's worth I'm a great admirer of Linkwitz partly because of his independent spirit. But I suspect that if I owned either the Orion or the LX521, I would also be an owner of either Thor or some other subwoofer that I thought would do justice to the Orion or LX521. In the Orion/Thor crossover he designed, the handoff point was surprisingly low, around 50 Hz or 60 Hz. I would be inclined to do this differently, choosing a subwoofer known to give a flat response to somewhere up around 200 Hz. For this particular application I would be inclined to use shallow, 1st-order slopes, so that the Orion or LX521 gradually yields to the subwoofer starting where the wavelength is already several times greater than the baffle width, because at this wavelength (about 5.5 feet at 200 Hz), the excursion of the drivers will already be much greater than it will be for the same woofers in a conventional enclosure (greater excursion is needed to make up for the front/rear cancellation and is accomplished by way of equalization).

Experimentation is wonderful, and I think that if you were to use these speakers you would greatly enjoy the iteration towards a subwoofer implementation that worked for your room. In my experience, though, the 40hz operation is quite satisfactory. If I had a larger theater room that would allow me to use the LX521 I would certainly use them down to 80h or below. Reaching maximum excursion at 40hz would be very loud, and I think that it would take quite a lot of amplifier power.

In writing this it was certainly not my intent to step on anyone's toes and I hope that I've not done that. I just got the sense that some of this is not very well understood and I thought that it might be appropriate to sort of rehash some of it. With every unconventional approach to speaker design, there are fundamental questions that cannot be overlooked by anyone who is naturally curious about loudspeakers and acoustics. With the Orion and the LX521, one of these fundamental questions is concerned with dipole speakers generally, and the question is whether, given that the dipole pattern is inherently unachievable in bass frequencies where the wavelength is several times greater than the width of the baffle, it is nevertheless desirable for the radiation pattern in the midrange and treble to be dipole. I don't have an answer to this question. I only know that it is a meaningful question that wouldn't be overlooked by anyone who is fully objective, and that conventional wisdom strongly suggests that any attempt to achieve the dipole pattern in bass, especially deep bass, would very likely yield a compromised result that is neither dipole in radiation pattern nor satisfactory in the more obvious respect.

I do think that you are approaching this with a spirit of curiosity, and so I have expanded my replies. I hope that this has been helpful.

One thing that is complicated that could use more examination is how dipole bass behaves in a room. As I turn the bass modules in my too-small room, the bass does change somewhat. It changes a lot less than you may expect, though, and I think this is likely due to excitation of the room. I hope to move the speakers into a larger more suitable room (again) some day, and perhaps I'll find something new in the bass when I do.
 

Adam_M

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I'll add on to the chorus of replies that speaks to the quality and quantity of bass coming from unaugmented LX521's. In my room, which is about 24x16x9, they are essentially flat to 20Hz at and near my main listening position per my Omnimic. It's overused, but I can tell you that the canons in Telarc's 1812 overture provide a more than satisfying punch and at a volume where I no longer care to be in the room. The woofers put on quite a show doing it too. I've actually never REALLY let loose on that because I don't want to bottom out the woofers.

I will add a caveat - I do use a sub for HT, but not really for SQ reasons - I don't want to bottom out the big 10"s. The drivers will clip before the amp does so some measure of protection is warranted.

And yes, they are as good as everyone else has described beyond the bass. Kind of finicky to place though.
 

AudioJester

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For about 6 months i tried incorporating a sealed sub (hypex - 18inch Dayton) with my Lx521. The rationale being more bass sources etc. Lots of positions, setiings etc. In the end I realised in my room to my ears the best option wss to take out the sub. The Lx woofers are nt only adequate but sound terrific and tespond to eq, low shelf if needed
 

Joecarrow

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It just occurred to me that there's another feature worth noting on this design; it's possible to create significant changes to the stereo image by rotating the top sections to point the dipole nulls at the first reflection points. Depending on your room geometry you can arrange this so that the sound directed at both the front and side walls are down by 6db or more. It's kind of subtle, but it's some time to try it.
 

JimB

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It just occurred to me that there's another feature worth noting on this design; it's possible to create significant changes to the stereo image by rotating the top sections to point the dipole nulls at the first reflection points. Depending on your room geometry you can arrange this so that the sound directed at both the front and side walls are down by 6db or more. It's kind of subtle, but it's some time to try it.
I do. It doesn't have to be perfect to be significant. You don't have to design the room around it.
 

Burning Sounds

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Welcome to the LX521 club @suttondesign! I have absolutely no doubt you will get much enjoyment from them and I think the way you have finished the baltic birch really suits the design. Regarding the looks of the LX521 I guess you could say it's of the "Marmite" flavour. (FWIW I like Marmite)

I built mine about 7 years ago after looking for something to replace my aging but still fully functional Magneplanar MG2.5Rs. I have also built LXMinis now, too. I guess you could say I like dipoles. :)

music_room_speakers.jpg


Regarding the bass of the LX521 - I find it one of the real strengths of the speaker. If you want to use it for home theatre then yes, I would add a sub, but for music it is quite exceptional. IIRC the bass driver was designed (modified?) by SEAS specifically for this project. In my experience the speaker needs a solid floor as it sits directly on the floor (no spikes allowed!). I tried mine once on a springy wooden floor and the bass was very uneven.

Yes, this speaker requires space, but you can rotate the top baffle which helps in narrow rooms. @jeffbook has created a very useful calculator to get the optimum toe in for the top baffle. I think it is on the OPLUG forum where there is lots of support for anyone thinking about building these.

IMO this speaker is in the same league as the D&D8c, Kii3 and the Grimm LS1 - I have heard all three - the 8c several times. To my ears all these speakers are more similar than dissimilar. The 8c has an advantage in that it still sounds excellent in a small room - the LX521 can't do that. But at the price the LX521, even including the required 8 channels of amplification is a bargain. All in my subjective opinion, of course.

Here's a distortion measurement I posted on another thread some time ago. I'll let those more expert than me decide if it is valid or not.

1khz dist 23042018-1mtrlt2000.jpg
 

dc655321

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Here's a distortion measurement I posted on another thread some time ago. I'll let those more expert than me decide if it is valid or not.

At at a glance, you are showing a 230dB range and using A-weighting, and say nothing of how the measurement was performed.
Not so useful, IMO.
 

Burning Sounds

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At at a glance, you are showing a 230dB range and using A-weighting, and say nothing of how the measurement was performed.
Not so useful, IMO.

Thanks, that's why I asked about its validity as the original thread was about the best way to get valid distortion measurements. I think it was taken at the LP.
 

Juhazi

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That's 1kHz sine wave at 82dB at listening spot (distance unknown)

With REW and obviously UMIK-1, best way to measure a full loudspeaker's distortion is to drag speaker in the middle of the room, turn it 45deg so it points to the corner, put mic at 1m distance, height between mid and tweeter. Then play sweep 10-22 000Hz, length 256k and set spl level so that you get 86 or even 100 dB at 1kHz. Then toggle Distortion window and save the image (you can add text) - like I did for my 4-way dipole which has closed box bass module. The response graph is not valid be cause it shows all reflections and modes, as well distortion shows every rattle in the room... but thats's best we can do at home. One can toggle which harmonics etc. to show. Best is to show spl instead of percentage, in my opinion.

Remember to download and activate he calibration file of the mic!

https://www.roomeqwizard.com/help/help_en-GB/html/index.html

My examples were even higher spl and longer distance, because lower spl is just room/ambient noise
ainogneo83 due11 100db disto.jpg
ainogneo83 v4a disto 96dB 1,6m.jpg
noise.
 

Burning Sounds

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The distance would have been about 2.5m. Yes, I'm pretty sure the mic calibration file was used. Recalling the original thread as best I can - (I can't find it unfortunately - I think it was about 3 years ago) I think we were discussing distortion at the listening position, so slightly different from distortion of the actual speaker itself, which is what I unintentionally implied in my post. Hence the measurement at approx 83dB, my typical listening level. Perfectly understand about using SPL rather than percent, but I think other measurements in that thread were using percent, so it was easier to do the same. As you rightly said my measurement would include any room rattles etc. And yes, LX521s can rattle things in the room. They can play far louder than I find comfortable, but of course in the bass they are restricted by cone excursion - 96db @30Hz is the max I think. What distortion is at that level I don't know.

Which brings me to something that @suttondesign said describing the bass of these speakers "In a concert hall with live instruments, bass doesn't thwack and pump like box subwoofers do; it sort of shoots across you and then is just gone. I think the Linkwitz open-baffle woofers do a better job of recreating that more natural feeling, but it's a lot more fleeting and less conspicuously boomy than boxes." My music room (converted stables) is a room within a room if you will. The floor is isolated from the walls. When I measure these speakers using REW the initial low frequency measurement causes the inner walls to creak for a moment so there is major pressure being created, but it is only fleeting. Perhaps this is what contributes to my perception of a very articulate speaker in the bass.
 

oivavoi

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My Orions had adequate bass, for sure, and the LX521.4 do too, but what Siegfried emphasized, and which I find to be true in spades, the sound quality of the bass is different than that from box speakers, and it can be deceiving.

In a concert hall with live instruments, bass doesn't thwack and pump like box subwoofers do; it sort of shoots across you and then is just gone. I think the Linkwitz open-baffle woofers do a better job of recreating that more natural feeling, but it's a lot more fleeting and less conspicuously boomy than boxes. Until I heard the Orions back in ought-seven, I had never heard realistic-sounding bass from a speaker system. The V-frame, open-baffle of the LX521.4 is the same. There's a solid foundation, but it doesn't sound forced or boomy. I think you have to adjust the expectations you've built up about what bass from a speaker system is supposed to sound like, not in quantity terms, but qualitative terms.

I agree with this sentiment - having never heard the LX521.4s. But I have always felt that reproduced subwoofer-bass (or speaker bass in general) is often different from the bass from acoustic instruments, be it big drums, double bass or church organs. I used to think that it was about resonances in small rooms etc, until I started noticing that the same thing applies to subwoofer bass in open air PA-systems. Most subwoofer bass has always felt more bloated and boomy than acoustic bass sounds. Acoustic bass is just there, it doesn't call attention to itself. Reproduced bass through subwoofers often calls attention to itself.

Have never heard dipole bass, but my experience is that it's possible to get closer to the experience of acoustic bass if using critically damped sealed subwoofers and taming the room resonances with eq. Plan to audition the LX521.4 when I get the chance.

Would love to know if there are any measurable properties of the bass reproduction which can account for these subjective experiences...
 

hex168

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I agree with this sentiment - having never heard the LX521.4s. But I have always felt that reproduced subwoofer-bass (or speaker bass in general) is often different from the bass from acoustic instruments, be it big drums, double bass or church organs. I used to think that it was about resonances in small rooms etc, until I started noticing that the same thing applies to subwoofer bass in open air PA-systems. Most subwoofer bass has always felt more bloated and boomy than acoustic bass sounds. Acoustic bass is just there, it doesn't call attention to itself. Reproduced bass through subwoofers often calls attention to itself.

Have never heard dipole bass, but my experience is that it's possible to get closer to the experience of acoustic bass if using critically damped sealed subwoofers and taming the room resonances with eq. Plan to audition the LX521.4 when I get the chance.

Would love to know if there are any measurable properties of the bass reproduction which can account for these subjective experiences...
One factor:
http://musicanddesign.speakerdesign.net/roomgain.html
 

Burning Sounds

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I agree with this sentiment - having never heard the LX521.4s. But I have always felt that reproduced subwoofer-bass (or speaker bass in general) is often different from the bass from acoustic instruments, be it big drums, double bass or church organs. I used to think that it was about resonances in small rooms etc, until I started noticing that the same thing applies to subwoofer bass in open air PA-systems. Most subwoofer bass has always felt more bloated and boomy than acoustic bass sounds. Acoustic bass is just there, it doesn't call attention to itself. Reproduced bass through subwoofers often calls attention to itself.

Have never heard dipole bass, but my experience is that it's possible to get closer to the experience of acoustic bass if using critically damped sealed subwoofers and taming the room resonances with eq. Plan to audition the LX521.4 when I get the chance.

Would love to know if there are any measurable properties of the bass reproduction which can account for these subjective experiences...

You may already have seen it but in his 1998 AES paper (Presented at the AES 105th Convention, 1998 September 26-29, San Francisco, California) Siegfried Linkwitz used tone bursts to investigate the differences between dipole and monopole woofers. He states:

"It is difficult to show pictorially and quantitatively the perceived differences when listening to the reproduced multi-burst test signal from a monopolar and a dipolar low frequency radiator in a room. After examining the two steady-state frequency responses with the multi-burst signal over the whole frequency range under investigation and in small 1 Hz frequency increments, it was concluded that the dipolar radiator has fewer and less pronounced regions of loss in articulation, on average, than the monopolar radiator. The strong 73 Hz resonance excited by the monopole is a major factor in its subjectively degraded performance. This might be correctable by electronic equalization but the dipole would require less of such remedy since it inherently couples to fewer room modes."

He concludes:

"The investigation showed that measurable and audible quality differences exist between monopolar and dipolar woofers due to differences in their respective interactions with the room. The degree of these differences is difficult to predict and will depend upon the specifics of a room and the placement of woofer and listener. However, the dipolar source can be expected to interact less strongly with the room and will, therefore, on average convey greater detail and resolution of complex low frequency material."

I've highlighted the text that I think is very important - I've had my LX521s in three different rooms. In my own room which is long, but relatively narrow the bass is excellent. I've taken the speakers to two hifi enthusiasts get togethers. At one, with a very large room the bass was again excellent - in fact the speakers sounded the best I've ever heard them. At the other get together in a small room with a springy wooden floor the bass was awful. I knew the room was going to be difficult so I took REW and sure enough below the transition the FR was very uneven and while I could correct the peaks, the dips were impossible, no matter where or how the bass units were positioned. Above transition the speakers were fine.

So, as much as dipoles can be shown not to interact with the room as much as a monopole, they are certainly not immune to the room.
 

Plcamp

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I don't know about that- my Spatials have 2 15" woofers too but definitely need a sub. I know there is dsp on the linkwitz, but still...
Same here with PAP Trios.
 
D

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I don't know about that- my Spatials have 2 15" woofers too but definitely need a sub. I know there is dsp on the linkwitz, but still...
The Spatials have a very short front/back distance, so it's not surprising. It doesn't matter how big of drivers are used in that application, you can't beat the physics. :)

The Linkwitz scheme utilizes an approach with nominal trade-offs in driver size, floor footprint, equalization, etc, etc, such that a subwoofer is not required for anything.......excepting dinosaur footsteps.

Dave.
 

Piranesi

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Sorry to hijack the thread, but I figured this would be a good place to ask. I'm thinking of building a pair of these as a sort of follow up project to a Linkwitz Pluto-inspired 3-way speaker I recently attempted.

Would it be okay to construct the LX521 baffles out of transparent acrylic, polycarbonate or even glass?
As far as I can tell, nobody's done that. I think it would improve the appearance of the speaker tremendously, at least for those of us who prefer a more conventional design.
 

peanuts

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Same here with PAP Trios.
there is also a world of difference between seas long throw low Fs sub drivers and spactial/pure audio midbass eminence drivers. size doesnt help with anything.
 

preload

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Would it be okay to construct the LX521 baffles out of transparent acrylic, polycarbonate or even glass?
As far as I can tell, nobody's done that. I think it would improve the appearance of the speaker tremendously, at least for those of us who prefer a more conventional design.

Without a doubt, doing so will improve the transparency of your speakers.
 

JimB

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Sorry to hijack the thread, but I figured this would be a good place to ask. I'm thinking of building a pair of these as a sort of follow up project to a Linkwitz Pluto-inspired 3-way speaker I recently attempted.

Would it be okay to construct the LX521 baffles out of transparent acrylic, polycarbonate or even glass?
As far as I can tell, nobody's done that. I think it would improve the appearance of the speaker tremendously, at least for those of us who prefer a more conventional design.
Definitely take this one over to their User Group:
https://oplug-support.org/index.php
 
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