Polk Lsi15 Subwoofer upgrade to mid bass driver

I started this discussion in another thread but didn't want to derail it further so I thought I'd start a new one.

I've replaced the sub in my Lsi15s with the Polk DB840 as recommended on this site. It was a worthwhile upgrade. However like a lot of people I run my Lsi15s as mains in a 5.1 setup so I really don't need these speakers to play that low. I have them crossed over at 80Hz and my 15" subwoofer plays below that. The problem is that neither the 8" sub built into the Lsis or my larger external sub play mid bass frequencies with any kind of authority. From around 80Hz to 250Hz. Although these speakers do well for movies and sounds like gunfire and action scenes they really lack when watching concert videos or rock music with a lot of mid bass drums.

I was considering getting a mid bass module such as the HSU MBM-12 to fill in that mid bass range but I really don't want to add more equipment. Neither do I want to replace all of my Lsi speakers (Lsi15, Lsic, and Lsi9s. I really like the upper mids and highs from my setup.

These mid bass modules use a larger subwoofer sized speaker but the speakers used have cones that are made of a lighter material such as paper. Similar to the old 3 way speakers that were popular in the 70s-80s.

My thinking is that I could replace the Lsi15s 8" subwoofer with a mid bass driver with a lighter paper cone and possibly get more snap and impact in the mid bass frequency. This speaker would be crossed over from 80Hz to 150Hz.

Being that it is side firing that could cause problems. Also it would be hard to level match this new driver with the rest of the speaker. I've been looking at a few cheap speakers to try for this experiment. I found a couple with similar efficiency ratings that look like they could be direct drop in replacements.



Can anyone with speaker building knowledge offer any advice on this. Tell me if I'm just wasting my time. The speakers I mentioned are very cheap so it's not an expensive experiment at all. I know this is a total crap shoot. Maybe someone else has tried this, who knows


  • F1nutF1nut Posts: 44,481
    Upgrading the crossover components will result in cleaner, snappier mids.
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  • Inspector 24Inspector 24 Posts: 1,306
    What is your room like? Have you tried moving the speakers around? Experimented with crossover, eq, level settings etc? Need more power?
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  • mrhydemrhyde Posts: 4
    What is your room like? Have you tried moving the speakers around? Experimented with crossover, eq, level settings etc? Need more power?

    Thanks for your responses.
    I have good power going to them. I use a denon AVR989 with preouts going to an emotiva xpa-5 outboard amp.

    I have experimented with crossover settings, placement, and different settings in the processor. I've covered just about every tuning solution I believe and I get a pretty decent frequency response graph in room eq wizard when measuring.

    The room is not ideal. It's a big room with too many windows. I know that the room itself is important and that I have a lot of work to do there. It could be a big part of my problem but I don't feel that it's entirely to blame.

    I know that I'm not the first person to comment on the low quality bass from the Lsi15s so maybe there is more of a problem than tuning and room treatments when using these speakers.

    Also a lot of people are happy with the bass from these speakers. Could it be that they all have perfect rooms? It could also be that people have different preferences on what they consider good sounding bass or different musical tastes. I could listen to certain types of music all day on these speakers and it's perfect but as soon as I play some type of rock or pop music with a lot of mid bass I get very aware of their weaknesses. Even a cheap set of 3 way box speakers will outdo the mid bass performance of these Lsis.

    I just don't believe that the 5 1/4" mid bass speakers in these are capable of reproducing mid bass with any authority. Also the 8" sub is not much help in that range. The sub needs something to build upon. That's what led me to ask the question of possibly replacing this sub with a speaker designed for mid bass instead of sub output.

    After rechecking the dimensions on some of the speakers I linked earlier I see now that the outside dimensions may be too big to fit the Lsi enclosure. I may have to do some more searching

  • sk88sk88 Posts: 158
    F1nut wrote: »
    Upgrading the crossover components will result in cleaner, snappier mids.

    This is the first step I’d take. Upgrade the capacitors and inductors in the crossover can help move the driver (pushing and pulling the cone) with more power and efficiency. Whether if it’s all you need is up to your room size. Then you can try a new different driver if this doesn’t help enough, but the crossover upgrade won’t be a waste in anyway. There are enough information in the forum about Lsi crossover upgrades. Good luck and enjoy.

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