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Old 9th October 2019, 06:32 PM   #1
Gwho is offline Gwho  United States
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Default Vintage PA Subs

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
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Old 9th October 2019, 07:44 PM   #2
TBTL is offline TBTL  Germany
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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.

Last edited by TBTL; 9th October 2019 at 07:55 PM.
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Old 9th October 2019, 09:21 PM   #3
Gwho is offline Gwho  United States
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Thank you for the help. I will find the parameters of the woofer to try to simulate. Your guidance will be helpful. I assume the tradeoff is reduced SPL for increased low frequency.

Best Regards,
gwho
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Old 9th October 2019, 09:28 PM   #4
Jag768 is offline Jag768  Netherlands
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Exactly, that's the trade off. Another thing to keep in mind, is that port velocity increases and thereby port lossen, when you decrease it's cross section.
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Old 9th October 2019, 10:53 PM   #5
Gwho is offline Gwho  United States
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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
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Old 10th October 2019, 01:29 AM   #6
conanski is offline conanski  Canada
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Quote:
Originally Posted by Gwho View Post


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.

Last edited by conanski; 10th October 2019 at 01:50 AM.
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Old 10th October 2019, 03:19 AM   #7
Gwho is offline Gwho  United States
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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
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Old 10th October 2019, 06:31 AM   #8
GM is offline GM  United States
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What a joke! The response here is nothing like this driver's specs will look like without significant EQ: https://assets.peavey.com/literature...s/118subhc.pdf

Hornresp says it's limited to 13 W/Xmax/60 Hz. Can't handle 350 W till > 100 Hz and from ~38-50 Hz.

GM
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File Type: txt PV1801-8SubHC.txt (1.0 KB, 7 views)
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Old 10th October 2019, 12:43 PM   #9
TBTL is offline TBTL  Germany
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What output are you looking for exactly? Something like that of a decent hifi loudspeaker?
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Old 10th October 2019, 03:47 PM   #10
Gwho is offline Gwho  United States
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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
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