Vintage PA Subs

Gwho

Member
2008-10-14 10:51 am
I recently picked up a pair of vintage PA subs for cheap from someone that was moving and obviously did not want to lug these around. They are model Peavey 118-Sub HC with an 18" Black Widow driver and a slot port. They have the following specs:
42Hz -3dB point
35Hz -10db point
350W continuous power
700W peak
100dB 1 Watt/Meter
Maximum Sound Pressure 127db
Fbox 42Hz

Would it be possible to change the -3dB point to a lower frequency (for example 35hz) by equalization, port change, or both? I won't be going anywhere near 127dB as I will be using this in a home/garage environment for music (not home theater) with a compression driver/horn. I do not want to replace the drivers (at least not now). Thanks for any wisdom or help you may provide.

Regards,
gwho
 

TBTL

Member
2013-10-08 12:26 pm
Yes, that is possible. The only thing to keep in mind is that the woofer should not receive a strong signal below the vent tuning frequency. Then there are two options: (1) closing off the vent or (2) tuning it at the lowest frequency you want to play. Then use an equalizer or DSP to bring the response back to shape.


If you use a vent and play loud, use a second order high pass filter set at the tuning frequency, to protect the woofer from overexcursion. The vent can be 'downtuned' by shoving pieces of wood into the vent, to decrease its cross section (along its full length). Alternatively, the vent can be lengthened. WinISD or similar software can be used to calculate the required change in cross section or length. A box with a low tuned vent will be louder than a closed box, though with a steeper roll off and slightly more ringing.
 
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Gwho

Member
2008-10-14 10:51 am
I got the winsd simulation program and tried to run a sealed and ported simulation. I also found the paramters for the driver (although it did not have all the parameters for the boxes that winsd provided).
Re - 6.5
Fs - 40.2
Qts .61
Qms 8.4
Qes .63
Vas 321 liters
Xmax +- 4.8mm
The cabinet is a approx 9 cubic feet (26.25 x 37 x 20.25)

The simulation did not seem to work for the ported version as it gave me a Qes/Pe error in red.

The sealed version does seem good. It is about 3db down at 50hz and 12db down at 30hz. I did not see any feature for determining if I have an Xmax issue. From your help though, it would seem that adding about 12db of boost would be within the realm of reason since I won't be going anywhere near (127db max - 12db) 115db in using the driver.

I've got to read up a little more on how to simulate but this gets me in the ball park. From what I can tell sealed seems the way to go with some EQ.

Regards,
gwho
 

conanski

Member
2013-03-31 3:53 am
The sealed version does seem good. It is about 3db down at 50hz and 12db down at 30hz. I did not see any feature for determining if I have an Xmax issue.
You do without a doubt. A 12db deficit requires over 10 times the amp power to make flat which means the SPL that can be achieved with 70w at 80hz would require over 700w at 30hz, and this driver simply does not have the xmax to handle that kind of power at that frequency.

How much power do you have to drive this box? If it's only 100-150w then you will be better off just using the box as it is, the ported box will produce more low frequency output than if it is sealed.
 
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Gwho

Member
2008-10-14 10:51 am
TBTL, Jag768, and conanski

Thank you all for your knowledge. I obviously was not thinking about the power required. I do have amps that can provide that kind of power (crown k2s) but clearly the driver in the 118-Sub HC was not designed for being operated with that much equalization. I would assume that I would be hearing a lot more distortion because of the higher power operation (due to the increase in lower frequency). Clearly, Peavey optimized the design for the speaker. Using it as is makes sense. My guess at the levels I will be listening at the 118-Subs won't even be using a few watts. It will then be operating very linearly with minimal cone movement in relation to Xmax. I've learned a lot from this exercise. Thank you
 

Gwho

Member
2008-10-14 10:51 am
GM / TBTL,

I guess that you are saying that the 118-Sub HC specs (I posted) are wrong when viewed against the simulation data? Moreover, are you saying that the Sub has almost no low frequency output below 60hz. Why call it a sub. Thanks for the information.

TBTL yes, I was just looking at using the 118-Sub HC with a horn/cd that I have in my garage and trying to determine if I could improve it to sound as good as possible. They did not cost much so it is no loss if they are not useful. Once again, I am learning a lot and thank you both for the help.

Regards,
gwho
 
Correct, though the driver specs you posted are close enough to others I'm aware of, just the published response is way off WRT to how flat it is, i.e. much more 'humpback' like HR sims due to being a too high Qt driver for this cab alignment [too small, too high tuned].

It's only a 'sub' by vintage prosound requirements as up until fairly recently, prosound was ~flat from 80-300 Hz, -12 dB/60 Hz, -24 dB/40 Hz simply because the music didn't have much bass to the point where 'sub' bass was below 40 Hz, with 'infra' bass below 20 Hz till THX became the cinema norm, so reclassified as 'sub' bass below 20 Hz in recent decades.

With a 40 Hz Fs, the only way it will get anywhere near 20 Hz at a reasonably loud output is with a small room size BLH, so think of this 'sub' as one for a low B bass guitar.

GM