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Review of JBL LSR305

Discussion in 'Computer Audio' started by germanium, Aug 30, 2015.
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  1. germanium
    I purchased a set of JBL LSR305 monitors after comparing them with several others at guitar center. Things that I liked about them in the store was their smooth & extended bass for there size & solid dynamics in the bass especially for their size. They sounded like much bigger speaker than they were. It sounded like they had 6-7inch bass drivers instead of 5 inch. Even the bass extension was suggestive of a larger driver that was not far off of what most 8 inch drivers are capable of. Most 5inch drivers start to roll off in the mid to upper 50Hz range these go down to 43 Hz but die very quickly afterwards. Most 8 inch monitor speakers only go down into the upper 30HZ range as in for example the LSR308's only go down to 37Hz.
    While these may be analog input speakers but internally they do all processing & amplification digitally. The crossover & any driver EQ is done in the digital domain. I looked up the major chips that I found on the board.
    There is an STA350 capable of up to 50 watts per channel in stereo mode in to a 6 ohm load. This chip handles all the crossover & EQ functions as well. It also can do anti-clipping limiting as well as compression though this last capability is not used here only the anti-clipping limiter is used.
    There is a Cirrus Logic 5341 ADC on board as well which handles the analog to digital conversion.
    There is also an STM8S0 chip that is a BIOS chip that has a serial interface for storing the parameters used by the STA350. This chip also contains a small 16MHz CPU.
    The woofer cone is made of a plasticized paper with a soft plastic dust cap & a rubber surround, The magnet structure is good size for this driver & contains a secondary magnet to contain stray magnetic field so you can use the close to older style CRT monitor displays.
    The tweeter is a 1 inch soft dome  made of tightly woven fabric & mounted in a horn like wave guide that controls dispersion. The magnet structure is quite small but seems quite powerful so the must be using neodymium magnets.
    The output power in this case is about 50 watts to the woofer & about 30-35 watts to the tweeter giving a total of 80-85 watts. Most review sites list the power to each driver as 41 watts but this is definitely not the case given the impedance characteristics of the driver which are not the same. The woofer is clearly a 6 ohm unit & the tweeter appears to be a 10 ohm unit.
    Well the real question is how do they sound in my own home. In a word astoundingly good, far beyond what I imagined a small speaker is capable of doing. The bass is robust & smooth & lacking any kind of noticeable distortion a any kind of reasonable volume & even when pushed to somewhat more than reasonable volume. The crossover & EQ are impeccably handled resulting in a very smooth sound signature. The tweeter is some what larger than some tweeter drivers used on speakers that have 5 inch woofers, such as the BX5's, that combined with the horn like wave guide allows the tweeter to handle a lower frequency cross over than most tweeters can used with 5 inch woofers, this improves the detail near the crossover  quite a lot. The body you hear from the tweeter matches that of the woofer at the cross over frequency very well. dispersion is also well matched between the 2 drivers.
    These speakers are said to have a broader sweet spot for listening off axis. In my situation they show excellent frequency response across a broad listening area. Image still moves though when you move closer to one speaker than the other which is to be expected. 
    Depth of soundstage in recordings is quite good, some of the best I have heard. The amount of detail within that soundstage is also excellent, far beyond what one would expect to have from such inexpensive speakers & it's not a hyped detail gotten through hyped up treble. List price of these is 149 dollars for each speaker, basically 300 dollars for a stereo pair
    I have yet to play some music that contain places where there is intentional imaging beyond the outer edges of the speakers but will provide that info in a later update.
    Update; The speakers do image beyond outer edges of the speakers well indeed.
    The only fly in the ointment with the speaker is really one to be expected given the size of the bass driver & part of this is due to the steep subsonic filter. That is on 90-95% of the music is not a problem but on 5-10% of the music the bass drops like a rock below 43Hz like as in nothing there after being so strong up to that point. Consequently you will need a sub if you have any music at all that goes lower than 43 Hz as the effect can be somewhat jarring if there are lot of notes near that cutoff frequency, otherwise you will get strong notes then nothing & then right back to loud bass notes with extreme suddenness. A subwoofer can fix this though you need one that can crossover below 50Hz. Most can not do so at least not from the factory.
    Speakers are very quiet, Only a very faint hiss from the tweeter on both channels but I have to put my ear right up to the tweeter to hear it.
    Here are some pictures of the JBL LSR305's inside & out.
    This is the main amp board. As you see there only is a relatively small chip near the speaker outputs though it is the largest chip on the board. This chip does everything except the analog to digital conversion & can provide up to 50 watts per channel in stereo into a 6 ohm load. If used in mono mode it can provide up to 90 watts into a 3 ohm load. It even does the crossover digitally & any EQ as well.
    Here you can see the paper like backing of the bass driver.
    Here you can see how large the magnets are
    The back side of the front panel with drivers.
    The panel showing the adjustments available.
    This is the JBL's in my computer sound setup.
    Letm, MisterMudd and NoOneLt like this.
  2. germanium
    Bump, added pics & some comments.
  3. pigmode
    Great review. Came close to ordering an LSR310S today, but the idea popped up of replacing my LSR305 with LSR308, and needed to be looked into first before finally being rejected. If If there was more space in from of the desk, the 308 might have worked. Imo 5" monitors are borderline acceptable in terms of size for desktop mounting, but the JBL's sound so-o-o good. 
  4. cel4145
    Good review

    My understanding is that the wave guide is what gives the speakers great imagining. Not an effect on the crossover.
  5. germanium
    I listened to the 308's & was considering buying them but were way over kill on the bass. Some reviews mentioned the same. The 305's were better balanced through their spectrum than the 308's. midrange was still quite good on the 308's though in spite of the overdone bass. I would only go with the 308's if you quite a large room to soak up some that bass. not good for smallish rooms, even guitar centers somewhat large room was rather over powered by the 308's
  6. germanium

    Both contribute & the crossover is in fact lower than most 1 inch dome tweeter crossovers. Normal is between 2000 & 2500 Hz. The 305"s crossover at 1500 Hz & the horn like wave guide contributes to the tweeters low range body which helps it blend sonically with the woofer. this all helps the midrange detail. It is all important not just the presence of the wave guide but what the wave guide allows as well.
  7. cel4145

    My understanding is that it has to do with the tweeter itself, and not the wave guide. To be accurate, it's not a horn. It's a wave guide.
  8. germanium

    To be accurate a horn is in fact a wave guide. My friend which is in fact an audio engineer & physicist pointed that as soon as he seen these speakers not that I didn't already know. This friend of mine has run some rather large multinational audio companies.
  9. cel4145

    Glad your friend is a competent company manager. My "friends" who are actual speaker designers have pointed out to me that this is not a horn tweeter. So yes. A horn tweeter uses a wave guide, too, but it is more accurate to describe this as a wave guide.
  10. germanium
    Once my friend got the companies going stayed largely in the background designing equipment except for marketing. He is semi retired now but is very well respected in the audio industry as a very inovative designer of audio gear which he still does though now he is designing vacuum tube gear with design features that allow high output power without excessive distortion all the while sparing the tubes from rapid decline & death from excessive idle currents. These circuits have never been used in tube audio amps before
  11. cel4145
    Here you go. An introduction to what a horn speaker/driver is: https://en.wikipedia.org/wiki/Horn_loudspeaker.
  12. germanium

    I already know what horns look like. I used to own a set of Altec Lansing A7-500's voice of the theater speakers. Horns do not need to be rectangular. There are many styles of horns. There is folded horns, reflex horns. Some horns are very short & some are very long. There is exponential horns & tractrix horns. Many horns are round such as the Edgar horn. Many horns use regular drivers normally used in direct radiator speakers, most use specialized compression drivers. I really don't need a lesson what horns are. I tried to avoid such arguments by just saying horn like but I guess that didn' work.
  13. cel4145

    I didn't offer it for pictures. I offered it to point out that horns have particular function that is more specific than a wave guide alone.
  14. germanium
    The term "waveguide" is used to describe horns with low acoustic loading, such as conic, quadratic, oblate spheroidal or elliptic cylindrical horns. These are designed more to control the radiation pattern rather than to gain efficiency via improved acoustic loading. All horns have some pattern control, and all waveguides provide a degree of acoustic loading, so the difference between a waveguide and a horn is a matter of judgement.
    Note that wave guides are still horns. The above was taken straight from the article you linked. I do hear the mild-moderate effect of acoustic loading with the tweeters. Not nearly as much as on the A7-500's though. That to me makes these  definite horn though with only light- moderate increase in acoustic loading the effect being mostly heard near the crossover frequency though it helps all frequencies reproduced by the tweeters.
  15. cel4145

    Note that some idiot added that to the article in its recent history. Probably the company website that is used as a reference for that section because they wanted to call their waveguide a horn, and none of the people that wrote the article to begin with picked up on that change. The first paragraph of the article quite clearly defines the purpose of a horn.

    And I don't how you can "hear" to know that the waveguide is adding any significant acoustic loading. You'd have to measure the tweeter with and without the waveguide to determine if that's happening. Note that JBL makes no claims of that in their description of their waveguide technology.
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