Lowering Fs.

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I have a pair of discontinued Dayton 15" PA woofers I would like to use in a pair of home subwoofers: Dayton Audio PF385-8 15" Cast Frame Driver 4" VC 295-080

38 Hz seems a little high for a subwoofer, and the sensitivity is high so I though adding mass to the woofers might be the way to go. I know some of the classic British manufacturers used to use something that looked like epoxy and sand to add mass to their woofers, and JBL adds lead mass rings to the top of the voice coil assembly.

Opinions, ideas, comments?
 
Hi,

In theory you can add about 100g to the 100g cone to drop
Fs to 27Hz and bump up the Qts to 0.5. AS Vas remains
the same due to higher Qts the ideal box size increases.

How the suspension and surround would cope with
the extra mass I'm not sure, probably would be OK.

rgds, sreten.
 
I don't see any advantage in adding mass. Just use EQ like LT or PEQ.

The only help you could get by adding mass is if the suspension is very non linear and swamping the cone motion, and the added mass pushes the mass controlled region down enough to limit the distortion, assuming the electrical motor is linear enough. Although by that point it's better to get another driver. IMHO.

Fs is an outdated way to look at subwoofers from an age where passive crossover was the only option and EQ was unheard of. IMHO of course.

I would take advantage of the relatively low Qes and large box and go with it. Fair amount of stuffing too.
 
Ex-Moderator R.I.P.
Joined 2005
with 100gr added to 100gr cone, your 95db SPL will dump to 88db
but is it really only 100gr ?

had it been at around 20hz I would say fine, but considering its around 30hz, I would say its a bit on the low side
also consider the lowish Xmax is made to match the higher 38hz Fs

sounds like they could be very nice bass guitar woofers :D
 
with 100gr added to 100gr cone, your 95db SPL will dump to 88db
but is it really only 100gr ?

had it been at around 20hz I would say fine, but considering its around 30hz, I would say its a bit on the low side
also consider the lowish Xmax is made to match the higher 38hz Fs

sounds like they could be very nice bass guitar woofers :D

Had what "been around 20hz?"

I really don't like the way it sounds now in the 3^ft cabinet, sealed or vented, boomy and thumpy, so I'm going to give it a shot. I can keep one cabinet stock and listen to the difference. They will be used in a multi sub (five) system for smoothing in a low sensitivity setup, so the sensitivity cut doesn't matter to me.
 
Last edited:
Ex-Moderator R.I.P.
Joined 2005
clamshell would be closed as well....it just means it halfs the box volume
from your describtion I suspect your present closed boxes are too small
relatively speaking, it would make your present boxes twice as big
it should be easy to try with additional attached front baffle
 
Hi,

The current 3cuft boxes with the original drivers should be vented
to about 40Hz, which will add about 5dB to 40Hz over sealed.

If they are sealed, Q is about 0.6 and they are ideal for adding
bass boost, ideally with a peaking 2nd order high pass.

Adding significant mass means they would need to be sealed.

Doubling mass and 3cuft well stuffed would work quite well.
Q would be about 0.8, less mass you add the lower the Q.

Personally rather than sand and epoxy I'd spray car
underseal onto the cone, masking off the surround.
Use a digital scale to measure the added mass, if
that's possible, or monitor Fs changes for the same.

Tetroseal car plan Black 500ML BLACK UNDERSEAL AEROSOL - LIMITED OFFER | eBay

I'd guess is enough to do both.

rgds, sreten.

Investigate / review spraying techniques if you are not sure.
Something you can spin the driver on can help a lot.
 
Last edited:
Thanks again streten. The boxes are currently tuned to 35 Hz and I don't like the sound. It's great for rock but other music makes it sound thumpy and resonant. I'll pick up a can of undercoating and give it a shot. My scale is not accurate at those weights so I'll just keep spraying until I get to my desired Fs.
 
Last edited:
Thanks again streten. The boxes are currently tuned to 35 Hz and I don't like the sound. It's great for rock but other music makes it sound thumpy and resonant. I'll pick up a can of undercoating and give it a shot. My scale is not accurate at those weights so I'll just keep spraying until I get to my desired Fs.

Hi audiomagnate,

Why chase fs..IMO,you should consider other options:

b:)
 

Attachments

  • DaytonPF385-8.JPG
    DaytonPF385-8.JPG
    594.7 KB · Views: 162
I already have a pair of very nice cabinets, 3^ft in size.

Your cabinets are too small to achieve low bass with 15-inch pro drivers. You can either build larger boxes or step down to twelves or tens.

Even if you lower the fs with mass on your 15-inch drivers, your cabinets may raise the fs right back up. If the box was very big, the fs of the driver would be lower in the box than residing in free air.
 
That makes no sense to me at all.

The fs of the loudspeaker in the cabinet usually shifts downwards if the cabinet is optimum sized or larger than the loudspeaker's requirements.

The link below offers the TS Parameters of one of my older Beyma 18-inch drivers.

Beyma Speakers - Beyma 18LX60 speaker - Beyma 18LX60 1200 watt 18" woofer for all bass applications. Beyma 18LX60 and other Beyma 18" speakers here.

This is the measured impedance curve of the loudspeaker in the box.

yKvHOi8.png



As you can see, the loudspeaker offers an fs of 27 Hz in free air and, 19.04 Hz in the box. A 3 cubic foot box for a 15-inch pro driver is not going to give you low bass for the limiting factor is the enclosure size.
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.