LSI15 upgrade at 2020

I just replaced my woofers with these: https://www.amazon.com/Audio-db840-8-Inch-Single-Subwoofer/dp/B0016GX21G/

Had a very hard time getting the grills off:
https://forum.polkaudio.com/discussion/192868/cant-remove-woofer-grills-from-my-polk-audio-lsi15-speakers#latest

Sounds better. I am running them off an Emotiva XPA-2 & XMC-1with a Velodyne SPL 1200 Sub. I cut the sub off and the LSi15s are now producing a little bass but still not much. I have them set to large. The new woofers are not at all boomy and the upper lows sound, perhaps, a little more snappy.

Looking to pick up some LSiM 707s if I can find a good deal. Man I wish I knew about the Polk sale on those.

skrol wrote: »

You may be able to find a close match based on the small parameters. From the owners manual that came with my DB840svc

Diameter 8
Freq Resp 30-200 Hz
Impedance 4 ohms
Efficiency 85 dB
Pwr RMS 180W
Pwr Peak 360W
VC Diameter 1.5 in
fs 42 Hz
Xmax linear 0.24 in / 6.1 mm
SD 35.65 in^2 / 230 cm^2
VAS 0.54 f^3 / 15.4 L
QTS 0.56
QES 0.58
QMS 13.4
RE 3.5 ohms
LE 2.3mH

However, there is some inconsistent info. From the old Polk Audio site for the DB840SVC:
Diameter 8
Freq Resp 30-200 Hz
Impedance 4 ohms
Efficiency 85 dB
Pwr RMS 180W
Pwr Peak 360W
VC Diameter 1.5 in
fs 49 Hz
Xmax linear 0.51 in / 13 mm
MMS 67g
BL 10.3 TM
CMS 157.6 um
SD 35.65 in^2 / 230 cm^2
VAS 0.42 f^3 / 11.9 L
QTS 0.6
QES 0.6
QMS 14.1

Then from the DB840svc sales literature:
Diameter 8
Freq Resp 30-200 Hz
Impedance 4 ohms
Efficiency B 85 dB
Pwr RMS 180W
Pwr Peak 360W
VC Diameter 1.5 in
fs 47 Hz
Xmax linear 0.24 in / 6.1 mm
SD 35.65 in^2 / 230 cm^2
VAS 0.42 f^3 / 11.9 L
QTS 0.61
QES 0.67
QMS 7.5
RE 3.25 ohms
LE 1.11mH

I tend to believe the owners manual.

For the MM840:
Diameter 8
Freq Resp 26-200 Hz
Impedance 4 ohms
Efficiency B 90 dB
Pwr RMS 250W
Pwr Peak 500W
VC Diameter 1.5 in
fs 35 Hz
Xmax linear 0.75 in
SD 35.65 in^2 / 230 cm^2
VAS 0.54 f^3 / 15.4 L
QTS 0.6
QES 0.7
QMS 5.5
RE 3.3 ohms
LE 2.3mH

I measured 840 SVC and from memory, believe it was very close to 42Hz. So you are correct, the other numbers seem to be wrong.


The biggest issue with finding a similar woofer, is the Vas measurement is very small, and most woofers that are 8", have a far larger Vas, and when used in the very small box of the Lsi15 bottom section (about .75 cuft) they will lack deep bass totally.

I have only seen a few woofers similar to what Polk used, and they are mostly Car audio woofers. Normal Hifi woofers, usually have a Vas that is far larger and meant to be used in boxes about 1.5 cuft or so,

critical_gp wrote: »

Would these woofers work? Vas is .95

https://www.parts-express.com/Dayton-Audio-DCS205-4-8-Classic-Subwoofer-4-Ohm-295-200?gclid=Cj0KCQjwtMCKBhDAARIsAG-2Eu-OAj2V9rH64Qt-xM6XYyOpyRSUuKTe_lwTqMTGWfDPKmqPYLPn_xYaAneqEALw_wcB

Yeah for sure would "work", but even without plugging the numbers into my box calculator, I doubt they would be (in the SMALL lsi15 box) be any real improvement.

The lsi15 has a TINY bass box. I believe it is right around .7-.75 cubic feet of volume at best.

So even though the dayton would "work", its Vas number is .95 cuft, and that would raise the resonant frequency, even though it is rated in free air at 32hz, you would be right back to what the stock woofer does.

You may hear some variance in sound for sure, but the box is just too small, to get any really deep bass.

The box volume is more along the lines of what most 6.5" woofers would need.

Cheap upgrade 2021 and worth it.... I used the Boss CXX8 as the specs were very close to the above, and ported box volume recommendation were perfect. I was concerned about the sound level as the efficiency is only 83db/W. But they turned out perfect.

I am very very happy with the results. I was torn between these and some Dayton Audio. But it all came down to price as I am in New Zealand and shipping is the killer. The Boss were really well priced, in fact so cheap I wasn't worried if they didn't work out.

I made up a test CD with about 6 tracks from Classic Rock, Pink Floyd Time (my fav test track), through to some hip hop and Drum and bass. I listened and measured using an app on my phone, with screenshots. Then did the speaker swap, very very easy, grills popped out easily and I was done in about half an hour. Then listened again.

To me the bass is fuller (not even broken in yet) and less flabby down low, it feels like slightly more bass. According to the app (yes the phone mic is limited but I am comparing apples with apples here) the levels were identical in the lower frequency, but I gained a tiny bit more low bass it seems.

This was a great time to do an upgrade as I have been trying a few bookshelf units for my office. So I've listened to these same test tracks a lot. My ears are very sensitive to upper mids (I've bene this way since a kid) and it's really hard to find a bookshelf unit that is not harsh. I'm now thinking of getting some old LSim 703's or LSi7's and paring with a sub. My only complaint with my LSi15's now is I wish there was a little more detail in the tweeter range, but I'd rather it be laid back than have it in your face like the Klipsch, I lasted 10 mins with those.

critical_gp wrote: »

So I guess I'm a little confused as to what exactly vas is a measure of (will look it up).

Dayton specs out optimum cabinet size for that sub as .19ft³ sealed and .48ft³ vented.

Their idea of optimum, does not really calculate out to best. Their box size models at -3db at 48 hz.
Which means basically flat to about 50hz.

That is not deep bass truly.

With a decently bigger box, that woofer can do far deeper bass, if you plug in the numbers into a box calculator.

My calculations show......

reviving an old thread. I put in MM842's in my LSi15's. They were on sale for only 10 bucks more than the DB's. rolled the dice and won. Anyone worrying about the higher VAS being a problem......it aint. Bass is deep....and tight as a Pope's **** shoot. No more boomy muddy bass. Shockingly night and day. Why the frikkin hell did Polk use that garbage woofer?