54L Sealed DPL12 Test Results (1 Viewer)

[Peter DeWitt]

Last night I tested my DIY Down Firing 54L DPL12 w/ 16oz of polyfill. The results were encouraging and frustrating.

Parameters:

Sine waves from 20-70 @ 5 Hz intervals until 40 Hz
In corner of room with SPL meter @ 1 meter away
Phase set to 0
Crossover set to ~90 Hz
Sub Volume @ 40-50%
Amp PE 250W
Yamaha RX-V2300 set to -44 (Found 30 Hz started to bottom out at -40.5)
Pioneer DV-440 for movie and test signals

Results:

dB Freq
95 20
104 25
102 30
102 35
111 40
112 50
103 60
103 70

DPL12 bottomed out at 30-35 Hz before any other frequency. A little strange since it played 20 Hz well. Played several tracks on Avia and calibrated the sub. I had to turn it down a little during the asteroid chase in Episode 2. The second sonic charge hits the 30-35 Hz range while breaking asteroids and sub was bottoming out.

Conclusions:

Probably should have tested this in the center of the room or outside to try to match the response curves. In addition, the strange shape and size of the room (as seen in attachment) makes me think the ported might give me a better response. However, for best results, I think a second sub might do a good job of pressurizing the room. Budget does not allow for this, however. Sub volume must be set at 25-30% for audio calibration. Receiver cannot exceed -30 without affecting sub performance. This is the Avia calibrated volume for my system. However, actual listening will not exceed -35. I may attempt to move sub to a different location, but this corner has always been the best location.

What do you think? Should I expect more? Why would it bottom out at 30-35 Hz?

 

[Dan Wesnor]

DPL12 bottomed out at 30-35 Hz before any other frequency.

This is simply not possible. A sealed woofer will always bottom at lower frequencies first. How do you know it's bottoming? If you are hearing something, perhaps you are hearing something else and assuming it's bottoming. Possible causes are loose parts rattling (rattling parts do not need to be in the sub - you could be rattling the TV and air blowing through gaps around the woofer or amp. If the amp doesn't have a closed back, the air could be blowing through the space around the control knobs.

 

[Peter DeWitt]

There is definitely a thumping sound coming from the box. I can only assume by the violent nature of the sound it was bottoming out. I couldn't imagine it is air escaping. This sound was too loud.

To add to the problem description. It was not there for about 0.5-1 seconds and then it would ramp up to this "noise" and be continuous.

Perhaps a brace is rattling? Or maybe the loose wires are slapping? These are wild guesses but this is a bit frustrating to diagnose.

I would assume that if it was actually bottoming out it would also do this at frequencies below 30Hz.

A real mystery. Any help would be greatly appreciated.

 

[Hank Frankenberg]

You describe the sound as "thumping". Bottoming I've heard has been a higher frequency "crack". You may indeed have something else going on inside your cabinet. Also, overly long voice coil tinsel leads have been know to slap against cones.

 

[Dan Wesnor]

Something bouncing off the cone can be surprisingly loud. Air leaks sound like rattles. First time I had a sub rattle, it took me few disassemblies to figure out it was air coming out.

 

[Peter DeWitt]

It is hard to represent the sound correctly with just words. Think of it as slapping. It isn't like a rattle at all.

I took it apart and could not find anything that stands out.

Here is my first thought after some time to think about it:

The polyfill I used was the type for stuffing pillows. I then secured it, so it did not fall, with ¼” thick roll polyfill. I stuffed this between the braces and made a “floor” out of the roll polyfill. Hence, the polyfill sits on top of the roll style. I suppose it is possible that this is negatively affecting the volume of the box. If I model the box so that it gives a net volume of 25 L I get a response curve that matches that of my readings. Then I check the power response and @ 30-40 Hz it shows the displacement being limited by the driver instead of the thermal limit. This would account for the driver bottoming out at the louder levels.

If you model a 25 L box you would see a response curve with a large hump in the response. Exactly as the data taken shows.

I’ll try it without the polyfill and see what the response is then.

If any of this sounds crazy, please slap me upside the head and knock some sense into me. If I did not hear it, I would not believe it either.

 

[Kyle Richardson]

Exactly. If it bottoms at 30-35Hz it will be bottoming from that point down.
Check all possibilities pointed out above such as wires inside, leaks, enclosure, etc. Also make sure you are not overdriving the LFE output on the Yahama.
In your parameters above you mention: "Sub Volume @ 40-50%" Are you referring to the volume control on the PE plate amp? If so then that is actually quite high for that amp and you usually want to be about 25-30%. Try readjusting it there and using the LFE out to control the volume and see if it helps.

 

[Kyle Richardson]

The way you have the poly really shouldnt reduce the volume of the box unless its REALLY packed into that part of the enclosure. Dont worry, it can touch the driver so just distribute it evenly through the entire enclosure. Try not to pack it too tightly around the driver though.

 

[Thomas J. Coyle III]

Hi Peter

Looking at your SPL response numbers, I noticed that you have a pretty big room induced peak of +10db around 45 Hz which is not unusual. I would recommend installing a Behringer BFD to tame your peak in the response curve and then work on improving your lower end. The DPL12 has a very long linear travel so are you sure that you are really bottoming out?
Regards,
TCIII

 

[Peter DeWitt]

As I said, I wouldn't believe it unless I was there. Maybe this will help solve the mystery.

Here is the procedure I used:

Set receiver to calibrated volume for other speakers (-30) and sub amp to 50% played 20Hz and recorded the readings. Then I moved up to 25, 30, ect.

When I reached 30Hz, the sub made a “slapping” sound. I turned down receiver until it went away. Then turned the receiver up slowly until slapping sound came back (-41) then decreased 3dB to (-44). Then I took all of the readings from there starting over again at 20Hz.

 

[Peter DeWitt]

BTW with a sag % of 6.5, am I in trouble if I leave this down firing.

I plan on making a second box (ported 85L) and comparing, so now would be the time to change the design on that box if the sag % is to high.

 

[ThomasW]

To add to the problem description. It was not there for about 0.5-1 seconds and then it would ramp up to this "noise" and be continuous

This certainly isn't the driver bottoming. It's more likely something wrong with the amp or it's being grossly overdriven.

 

[Scott Simonian]

Having a similar amp, my advice would be to turn the amp down just a tad.

Good luck.

 

[Peter DeWitt]

I was able to play a 20Hz test tone at 100% volume on the amp knob. There was some rattling, but it sounded like a rattle in the box (I'll discuss this latter). Then 25Hz was also no problem. The readings for these two were 112 and 115 respectively. However, when I played the 30Hz signal, the rattling was louder, of course, but the violent thwaping, slapping sound came at a mere 30% of volume knob turn. It was definitely bottoming out.

So I took the driver out and played the 20Hz signal and noticed that one of the voice coil leads was touching the spider. Rattling mystery solved. However, the 20Hz signal bottomed out at about 40% in free air. Makes sense. Then when the 30Hz signal was played 20% volume bottomed the speaker out. Seems strange to me.

Something I noticed that might be common place:

When I watch the cone move as I inch up the volume, there is a point where the cone moves substantially from one position to another closer to the driver. It reminds me of a DC offset. This movement is about ½ or more of the Xmax. I would guess that it is moving at least ¼”. Like I said, maybe this is normal but it seams a little strange.

 

[Geoff L]

You said your driving the 12 with a PE-250.
By some (strange chance), did you get a boosted model?
About 6db at 30-35Hz...

That might clip the amp at those freq's and not down lower quite "possibly"...

Also the amps gain at 45-50% is rather high to "what most" usualy need to set their PE-250's gain at.

I have 3-plate powered DIY's 12" subs running off my Yamaha, and all plate amps are set around 20% on the gain pots. Certainly all of Yamahas receivers sub outs are not exactly the same, but try turning the plate amps gain down and the receivers sub level up as mentioned, if you have tried it already.

Your discription of the drivers sound, dose not sound like bottoming of the driver. No question about how that sounds, CLACK, simalar to the sound of snapping a larger stick of wood in half!!
You won't forget it once you here it!

Hope you figure it out...

Regards
Geoff

 

[Brian Bunge]

Peter,

That is not a volume knob on the amp. It is a gain knob. With it turned all the way up you be driving the amp into clipping. Eventually you will damage the driver if you leave it like this. I've never been able to properly calibrate a sub using that amp with the gain set even as high as 50%. Set it around 1/4-1/3 of the way up and then adjust the sub out in your receiver accordingly.

 

[Peter DeWitt]

To put to rest on whether or not it is bottoming out-

The sound is like two large magnets slamming into each other. I am 100% positive that it is bottoming out. I can not emphasize enough that I can tell it is bottoming out.

Brian-
I understand that when calibrated the amp level should not need to be turned very high. Probably between 20-30%. However, if it doesn't bottom at 20Hz it shouldn't bottom out at 30Hz.

I apologize for calling it the volume knob. From now on I will refer to it as the gain knob.

I don't mean to sound unappreciative. This is a great resource and you have all been a lot of help. I would hate to wear out my welcome so soon. So if I have forgotten to say it or my message sounds a bit course, I want to say thank you to all who respond.

 

[Brian Bunge]

Peter,

If it sounds like two pieces of metal slapping together then that definitely sounds like it's bottoming out.

No need to apologize for calling it a volume knob. I just wanted to make sure you understood that it was not and that there is a difference.

Also, Geoff makes a good point. What was the actual model# of the amp you bought. Maybe you do have the amp with the 6dB boost.

 

[Peter DeWitt]

Brian-

I was very encouraged by Geoff's post also. This could be the root of the problem.

The model number was PE 250W 300-794. I read the instructions about the base boost adjustment. However, I would hate to take apart a new amp and do something that would void the warranty or make it look like I abused it. I can be careful, but you never know. When I ordered it, I assumed I was getting the non base boost model. The base boost model number is 300-796.

If I have to take it apart to check the resistors I can, I just prefer not to.

Perhaps I have unrealistic expectations, I just assumed that there was something wrong when it did not follow the models. In other words, the "This is not possible" post is exactly what I thought.

Again, thank you all for your help

 

[Brian Bunge]

How long have you had the amp? Did you buy it recently? Originally the amp came with the boost. Only in about the last year did they start selling both models.