LSi25 needs more power then LSi15 why?

chrisfromalbany
chrisfromalbany Posts: 41
edited October 2009 in Speakers
I think title say it all. Now with the LSi15s you need to power the 8' woofer as well. On the LSi25s need more power but don't need to power the 10' woofer because that is all done (correct me if I am wrong) by the plate amp. With everything else between the two speakers being the same(on the top part), why does the LSi25 need more power. Are the crossovers any different for the mids and tweeter. I am just not understand how it could be possible that LSi25 would need more power with so much being the same.

Thanks,
-Chris
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  • Face
    Face Posts: 14,340
    edited October 2009
    Who said they "need" more power?
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    the specs on the polk website..

    http://www.polkaudio.com/homeaudio/lsi/specs.php

    LSi15 Recommended Amplifier Power 20 - 250 w/channel
    LSi25 Recommended Amplifier Power 20 - 300 w/channel
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  • megasat16
    megasat16 Posts: 3,521
    edited October 2009
    LSi25 can handle more power but not necessarily requires more power to run. LSi25 would be less power hungry than LSi15 since LSi25 subs are powered by the plate amps. You really need more power for LSi15 than LSi25.
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone. :redface::biggrin:
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    when I was talking to the sale associate they were saying that the Lsi25 would need the same or more power. I am wondering if the 500uf in the LSi25s is part of the reason.

    So basically your theory is these speakers have the ability to be played louder then the LSi15. So I am guessing there are differences in the Xcross of the LSi25s compared to the LSi15s.
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  • megasat16
    megasat16 Posts: 3,521
    edited October 2009
    chrisfromalbany wrote: »
    So basically your theory is these speakers have the ability to be played louder then the LSi15. So I am guessing there are differences in the Xcross of the LSi25s compared to the LSi15s.

    Yes and Yes! The XO of LSi25 is different from that of LSi15. LSi25 has adjustable XO setting between lower bass and the upper bass on the plate amp. You can adjust the contour frequency of the lower bass or mid-bass.
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone. :redface::biggrin:
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  • pmckeealaska
    pmckeealaska Posts: 808
    edited October 2009
    I got a Rotel 1080 power amp and it has been all I ever needed to make my 25's sing. Love it!
    Music and Movie Rig

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  • comfortablycurt
    comfortablycurt Posts: 6,745
    edited October 2009
    A lot of that could be due to the increased cabinet size too.


    That being said...the LSi25's don't really "need" more power than the 15's.
    The nirvana inducer-
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    Now I thought the adjustable XO would only be used for the plate amp and wouldn't effect the sound or take the power of the two mids and tweeter? Where does the "500uf" fit into the network for this speaker and how that effects the performance?
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    comfortablycurt wrote: »
    A lot of that could be due to the increased cabinet size too.


    That being said...the LSi25's don't really "need" more power than the 15's.

    when you say increased cabinet space are you talking about the upper portion or the lower portion. I know there is more space in the lower section but I thought the upper portion of the LSi25 was smaller then the LSi9s. And the upper portion of the LSi25 is close to the same size as the LSi15s. I mean being that the lower sub is power totally by the plate amp, all we are talking about is the differences with the top portion of the speaker and the crossovers.
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  • Face
    Face Posts: 14,340
    edited October 2009
    The 500uf is part of a 2nd order high pass for the mids, to prevent them from playing low bass and adding distortion.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    Face wrote: »
    The 500uf is part of a 2nd order high pass for the mids, to prevent them from playing low bass and adding distortion.

    any idea at what point that crossover starts maybe 12Ohz?
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  • Face
    Face Posts: 14,340
    edited October 2009
    80hz: http://www.polkaudio.com/homeaudio/lsi/specs.php
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • megasat16
    megasat16 Posts: 3,521
    edited October 2009
    http://www.polkaudio.com/homeaudio/lsi/specs.php

    There are three parts in LSi15 XO plus LPF of 150Hz.
    Driver 1: HPF at 150Hz 6dB/oct, LPF at 800Hz 12dB/oct. (Mid Bass)
    Driver 2: HPF at 150Hz 6dB/oct, LPF at 2.4kHz 12dB/oct. (Mid Bass + Vocals)
    Tweeter: HPF 2.4kHz 18dB/oct.

    I believe the components values are based on driver T/S parameters plus compensation for lobing, and front baffle width.

    It's easy to figure out the rest if you know the drivers T/S parameters but I don't know polk supply them.

    Edit : Face beat me to the LSi spec sheet. :D
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone. :redface::biggrin:
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    ok so then the LSi25 you need more power for the two mids because they start in at 80Hz compared to 150 Hz for the LSi15s.

    I have the active XO set at 60 Hz on my Onkyo 807 for the LSi25s because I have a large 15 inch sub doing the down and dirty below that. I then have volume on the LSi25s turn up to about 3/4 power to get response out of the subs.. Seems anything over 3/4 tends to get on the boomy side.
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    megasat16 wrote: »
    http://www.polkaudio.com/homeaudio/lsi/specs.php

    There are three parts in LSi15 XO plus LPF of 150Hz.
    Driver 1: HPF at 150Hz 6dB/oct, LPF at 800Hz 12dB/oct. (Mid Bass)
    Driver 2: HPF at 150Hz 6dB/oct, LPF at 2.4kHz 12dB/oct. (Mid Bass + Vocals)
    Tweeter: HPF 2.4kHz 18dB/oct.

    I believe the components values are based on driver T/S parameters plus compensation for lobing, and front baffle width.

    It's easy to figure out the rest if you know the drivers T/S parameters but I don't know polk supply them.

    Edit : Face beat me to the LSi spec sheet. :D

    So this is part of the reason some people prefer the sound of the LSi15 but then others prefer prefer the LSi25s. This XO would make a noticeable difference in the sound characteristics of the mids.
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  • F1nut
    F1nut Posts: 50,836
    edited October 2009
    LSi15 Recommended Amplifier Power 20 - 250 w/channel
    LSi25 Recommended Amplifier Power 20 - 300 w/channel

    You are reading that wrong. All it's saying is that the LSi25 will handle more power, not that they need more power. Big difference.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • megasat16
    megasat16 Posts: 3,521
    edited October 2009
    chrisfromalbany wrote: »
    So this is part of the reason some people prefer the sound of the LSi15 but then others prefer prefer the LSi25s. This XO would make a noticeable difference in the sound characteristics of the mids.

    People prefer the speakers for many reasons. If you can setup LSi25 and LSi15 properly, it should sounds very close to each other. I have two pairs of LSi25 and one pair of LSi15 but I don't prefer one over the other.

    The seating position (ear height when seated) has to do with the speaker choices too. Some people may find their height to be more ideal for the LSi15 tweeter level and LSi25 may be a bit too high. Some people may find it exactly the opposite.
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone. :redface::biggrin:
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    Thanks..

    I now know alot more which is good..
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  • megasat16
    megasat16 Posts: 3,521
    edited October 2009
    Check out this LSi15. This one belongs to Face and he has upgraded the entire XO of the LSi15. I think he puts the XO outside of the speaker? Under any case, I definitely prefer that LSi15 over my LSi25. :)

    http://www.polkaudio.com/forums/showpost.php?p=1172568&postcount=5
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone. :redface::biggrin:
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  • Face
    Face Posts: 14,340
    edited October 2009
    I did the work, but they weren't mine. ;)

    I also managed to fit everything inside. The stuff on the floor belongs to the ugly speakers behind them.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • megasat16
    megasat16 Posts: 3,521
    edited October 2009
    Hell, I want those Ugly Speakers with Big A$$ Outboard XO. :D
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone. :redface::biggrin:
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  • Systems
    Systems Posts: 14,873
    edited October 2009
    chrisfromalbany wrote: »
    With everything else between the two speakers being the same(on the top part), why does the LSi25 need more power.....

    ....the specs on the polk website..
    LSi15 Recommended Amplifier Power 20 - 250 w/channel
    LSi25 Recommended Amplifier Power 20 - 300 w/channel


    These are guidelines as to the minimum and maximum power requirements.The 20 watt minimum rating stated for both would indicate they are about equal as far as sensitivity is concerned.
    Testing
    Testing
    Testing
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  • Bernal
    Bernal Posts: 991
    edited October 2009
    GV#27 wrote: »
    These are guidelines as to the minimum and maximum power requirements.The 20 watt minimum rating stated for both would indicate they are about equal as far as sensitivity is concerned.

    Indicates that 20 watts are equal? Explain a little more to understand.
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  • Systems
    Systems Posts: 14,873
    edited October 2009
    Bernal wrote: »
    Indicates that 20 watts are equal? Explain a little more to understand.

    Hi Bernal:)To clarify I meant the sensitivity of the two speakers is about equal.According to Polk's' recommendation both the 15 and 25 can be driven to reasonable levels with a minimum of 20 watts.
    Testing
    Testing
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    Face wrote: »
    I did the work, but they weren't mine. ;)

    I also managed to fit everything inside. The stuff on the floor belongs to the ugly speakers behind them.

    if you went that far why not upgrade the woofer in the Lsi15s then? I am guessing it is close in build quality of the lsi25s. After taking my Lsi25 apart fix a burned out plate amp when i got the speakers, I got a good look at the 10' woofer and magnetic size.
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  • megasat16
    megasat16 Posts: 3,521
    edited October 2009
    Replacing a driver in a speaker is more than just swapping in and out. Not all 8" drivers or 10" drivers have the same T/S specs and will not perform the same if you don't follow the T/S parameters closely. It'll do more bad than good if you just simple pull the old 8" out and put in a bad **** new 8" woofers in. The enclosure size is already limited and you can't tune for the best possible performance. It'll upset the frequency response of the lower bass region if you don't have a comparable replacement.
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone. :redface::biggrin:
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  • chrisfromalbany
    chrisfromalbany Posts: 41
    edited October 2009
    Face wrote: »
    I did the work, but they weren't mine. ;)

    I also managed to fit everything inside. The stuff on the floor belongs to the ugly speakers behind them.

    so what are the speakers behind the LSi15s and where you get the sound panels from you used in the pic?
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  • Face
    Face Posts: 14,340
    edited October 2009
    chrisfromalbany wrote: »
    so what are the speakers behind the LSi15s and where you get the sound panels from you used in the pic?
    The speakers are custom, I'll post a build thread when I'm done with their new cabinets.

    The panels are Monster Bass traps and 244's from http://www.gikacoustics.com/products.html
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • McLoki
    McLoki Posts: 5,231
    edited October 2009
    As already stated the difference was max power it can take (sustained, not peak) not what it needs. The volume difference between 250watts and 300watts would be only about 1db or less so that is comparable as well.

    The crossover in both speakers is only a 6db slope, so it actually plays quite a bit of sound above and below the crossover point. I prefer the sound of the 15's over the 25's although I think the 150hz crossover seems high. (I was not on the listening tests when they were deciding it though, so maybe that is what sounded best)

    Supposedly from talking to some Polk engineers - the T/S specs for the Db series 8" sub would work very well in the LSi15. (This was the older style Db series though I don't know if that translates to the new style or not)

    Regarding cabinet size, the 25 is a little taller (that may be mostly in the bass section as you say, I am not sure) but it is also 4" deeper (front to back) and that would be in the top and bottom section of the cabinet.

    I still need to do the crossovers in my 15's, but will probably purchase some 8" DB drivers and try them in there as well. If it does not work out - they will make it over to my cars or be sold to other polkies who want to try it out.

    Michael
    Mains.............Polk LSi15 (Cherry)
    Center............Polk LSiC (Crossover upgraded)
    Surrounds.......Polk LSi7 (Gloss Black - wood sides removed and crossovers upgraded)
    Subwoofers.....SVS 25-31 CS+ and PC+ (both 20hz tune)
    Pre\Pro...........NAD T163 (Modded with LM4562 opamps)
    Amplifier.........Cinepro 3k6 (6-channel, 500wpc@4ohms)
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  • Face
    Face Posts: 14,340
    edited October 2009
    McLoki wrote: »
    The crossover in both speakers is only a 6db slope, so it actually plays quite a bit of sound above and below the crossover point. I prefer the sound of the 15's over the 25's although I think the 150hz crossover seems high. (I was not on the listening tests when they were deciding it though, so maybe that is what sounded best)
    Since the woofer is side firing, the distance from the mids to the woofer dictates the crossover frequency between the two.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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