Replacement Woofers for existing cabinets

[GanjaMax]

I recently had some Pioneer speakers blow out and attempted to replace the woofers myself. They were old 3 ways. The cabinets say 32-20Khz, 150W, 8ohm (CS-G5000). I couldn't find the specs on the drivers. They live in 2.43 cu ft cabinets with a single 3" diameter 4" length port. I "plugged" a few drivers in my price range into these cabinets in WinISD and ended up buying some Audiobahn drivers that I think should work fine. They are AudioBahn AWC12Q 12" Dual 4 ohm Voice coil 500W rms woofers. 92.8dB spl1w@1m, Fs 21.7 Hz, Qms 4.22, Qes 0.38, Qts 0.35, 5.5 Cu ft Vas, 7mm xmax, (14 peak to peak). I hooked up the voice coils in series to yeild a 8ohm load and poped them in the cabinets. They don't seem to produce as much bass as the flimsy drivers that were there originally. The booklet that came with them recommends an enclosure volume of 0.7-1.4 cu ft sealed or 1.4 cu ft vented to 30 Hz. This confuses me as I thought an enclosure volume equal to Vas is ideal. I was considering putting a couple basketballs in each of the cabinets to get a box size closer to recomended. Any help or suggestions on what is wrong here would be awesome and appreciated. I am pushing these speakers with a newish yamahaa 85w/channel surround receiver. I can make the cones move alot so I think there isn't a power issue. I can hear really low bass 30-35 hz but 80-100hz stuff is disappointing. I can give more info about anything if someone could help, Thanks Again, Max

[sreten]

Have you tried using one 4 ohm coil ?

sreten.

[Thunau]

Originally posted by GanjaMax
I recently had some Pioneer speakers blow out and attempted to replace the woofers myself. They were old 3 ways. The cabinets say 32-20Khz, 150W, 8ohm (CS-G5000). I couldn't find the specs on the drivers. They live in 2.43 cu ft cabinets with a single 3" diameter 4" length port. I "plugged" a few drivers in my price range into these cabinets in WinISD and ended up buying some Audiobahn drivers that I think should work fine. They are AudioBahn AWC12Q 12" Dual 4 ohm Voice coil 500W rms woofers. 92.8dB spl1w@1m, Fs 21.7 Hz, Qms 4.22, Qes 0.38, Qts 0.35, 5.5 Cu ft Vas, 7mm xmax, (14 peak to peak). I hooked up the voice coils in series to yeild a 8ohm load and poped them in the cabinets. They don't seem to produce as much bass as the flimsy drivers that were there originally. The booklet that came with them recommends an enclosure volume of 0.7-1.4 cu ft sealed or 1.4 cu ft vented to 30 Hz. This confuses me as I thought an enclosure volume equal to Vas is ideal. I was considering putting a couple basketballs in each of the cabinets to get a box size closer to recomended. Any help or suggestions on what is wrong here would be awesome and appreciated. I am pushing these speakers with a newish yamahaa 85w/channel surround receiver. I can make the cones move alot so I think there isn't a power issue. I can hear really low bass 30-35 hz but 80-100hz stuff is disappointing. I can give more info about anything if someone could help, Thanks Again, Max

First, basketballs will not really make the enclosure look smaller to the driver. After all they are filled with air and the shell is not stiff. Think solids. Bricks, wood blocks or even solid styrofoam blocks will work.
As to the low end problem. Below you see how lspCAD models your driver in your cabinet.


As you can see you are getting a huge bump around 45Hz which corresponds with what you are hearing. Your box is tuned too high for this driver. But, if you tune the box to low 20's the bump will go away. See the image below



Just extend the port lenght to about 11" or 28cm and things should even out dramatically.

As to the stated efficiency of your woofer. It is a bit lower than the claimed 92.8. LspCAD calculates 88dB from the parameters supplied by you. It is possible that the midrange and tweeter will play a bit louder than the woofer. You can't gain efficiency you can only turn other drivers down. You might have to pad the mid and the tweeter by a few dB to bring things back in focus. You should measure your mid and tweeter resistance and compute L-pads accordingly, otherwise your crossover slopes will get out of whack.
Hope this helps a little or at least get you started in the right direction.

[sreten]

It is a bit lower than the claimed 92.8. LspCAD calculates 88dB from the parameters supplied by you.

Which is why I suggested trying a 4ohm coil on its own.
(I suspected 93dB is @1.83V into 2ohms, coils in parrallel)

Though depending on the complexity of the crossover, adding
L-pads or padding resistors may be the proper way to do it.
Or adjusting the value of the bass unit crossover components
if the bass unit is used as a 4 ohm unit.

Just extend the port lenght to about 11" or 28cm and things should even out dramatically.

11" may not fit your cabinet, it may be easier to to find
a tube that fits inside your port, around 9" to 10" long.
Line your port with felt to get a snug fit.

sreten.

[Thunau]

Originally posted by sreten




11" may not fit your cabinet, it may be easier to to find
a tube that fits inside your port, around 9" to 10" long.
Line your port with felt to get a snug fit.

sreten.

I would use an elbow before using smaller port. The smaller diameter is easier to tune low but port noise becomes a problem at much lower SPLs.

And yes, if he uses the driver with the coils in any other setting than 8 Ohm the LP filter will have to be adjusted accordingly.

[GanjaMax]

I tried running just one coil from each woofer, that made a huge difference by itself. 4ohm load now. I'd like to try running both coils in parralel as a 2ohm load but I'm not sure my amp could take that... (Yamaha Natural Sound AV receiver HTR-5450) Has selector switch on back for impedance level... Setting 1 is 4ohm or higher pair of main speakers 8ohm or higher 2 pairs of main speakers. Setting 2 is 8ohm or higher pair of main speakers, 16ohm or higher 2 pairs. I just accidently hooked up the speakers for 4ohm operation with out changing the switch to the corresponding 4ohm min per speaker and everything went fine. (My amp didn't shut off or break Does this mean I could run a 2ohm load if I selected 4ohm min?
I have a set of JBL 8ohm Northridge bookshelfs with 8in woofers that I'd like to run as a second pair of main speakers for their mid-high freq clairity. Does anyone have any thoughts on this?
About the 5.5 cu ft Vas rating, Why would the manufacturer suggest using a 1.4 cu ft enclosure. I assumed from what I've read that drivers perform best in enclosure sizes matching their Vas rating. Is this not true? Should I buy a small box for these and get different drivers for my 2.4 cu ft enclosures. If I have to use these Audiobahn car speakers as car speakers that is acceptable. If that ends up being the case how do I go about finding a good replacement 12" driver for my 2.4 cu ft box.

[sreten]

I'd like to try running both coils in parallel as a 2ohm load but I'm not sure my amp could take that...

Severely not recommended.

Does this mean I could run a 2ohm load if I selected 4ohm min?

Not IMO.

I assumed from what I've read that drivers perform best in enclosure sizes matching their Vas rating. Is this not true?

It is not true, you have been misinformed.

Should I buy a small box for these and get different drivers for my 2.4 cu ft enclosures.

Not IMO.

sreten.

[JC-21]

Reducing the cabinet volume sounds OK,

That will push some of the lower output more up into the 60Hz range.

I guess with the cabinet tuned to ~30Hz and stiffer (less compliant) drivers it all makes sense. They are fighting each other.

Tune the lower cabinet resonance a few notes higher via shortening the port, and leave the cabinet volume where it is, or take up some volume to raise the cabinet resonance frequency.
Or maybe both eventually. One at a time though. I guess volume adjust first, since lengthening the port later could be tricky.

There is most likely a lower resonant frequency for the replacement drivers because of the added mass of the extra voice coil. I guess that the blown drivers probably had much smaller magnet structures on them as well, which also lend themselves to less control - therefore more compliant. So more bass (to a limit). - you know, until they jump the gap.

Well that is my input, I am new at this.