Hi,
I was playing with my new sub last night. Specifically, I was watching excerpts from Minority Report to tweak the sub's gain and phase.
Imagine my surprise when the DTS "splash screen," or whatever the correct name for it is, caused my new toy to let out a most unmusical noise. It happened at the end of the clip, which to jog your memory features lots of yellow-tinged closeups of piano strings and hammers and so forth. It ends on quite a crescendo.
If I didn't know better, I would say that someone had dropped a golf ball onto a concrete floor about four inches from my ear during that crescendo. I am assuming this was the sound of the driver's voice coil being rudely introduced to the back of the motor.
Volume levels were on the high side, but not ear-bleeding. I had the gain on the sub set to about half. The sub is a Shiva Mk.III with a PE 250W plate amp, in Adire's standard EBS enclosure, which is 142l, vented and tuned to about 16Hz, I believe.
Is there anything I can do to prevent this from happening again? Apart from the obvious "turn it down" answer, of course. I am a little sad that this expensive (to me) hardware is having trouble meeting my listening requirements.
Could a box leak be causing it? I believe the box is sound, but it's not out of the question that there is a small leak somewhere. Or could it be a bad driver?
The driver otherwise seems OK, except that it makes a faint rubbing sound when driven hard -- not enough to be heard over the rest of the system. The noise goes away when the vent is plugged.
Any suggestions?
I was playing with my new sub last night. Specifically, I was watching excerpts from Minority Report to tweak the sub's gain and phase.
Imagine my surprise when the DTS "splash screen," or whatever the correct name for it is, caused my new toy to let out a most unmusical noise. It happened at the end of the clip, which to jog your memory features lots of yellow-tinged closeups of piano strings and hammers and so forth. It ends on quite a crescendo.
If I didn't know better, I would say that someone had dropped a golf ball onto a concrete floor about four inches from my ear during that crescendo. I am assuming this was the sound of the driver's voice coil being rudely introduced to the back of the motor.
Volume levels were on the high side, but not ear-bleeding. I had the gain on the sub set to about half. The sub is a Shiva Mk.III with a PE 250W plate amp, in Adire's standard EBS enclosure, which is 142l, vented and tuned to about 16Hz, I believe.
Is there anything I can do to prevent this from happening again? Apart from the obvious "turn it down" answer, of course. I am a little sad that this expensive (to me) hardware is having trouble meeting my listening requirements.
Could a box leak be causing it? I believe the box is sound, but it's not out of the question that there is a small leak somewhere. Or could it be a bad driver?
The driver otherwise seems OK, except that it makes a faint rubbing sound when driven hard -- not enough to be heard over the rest of the system. The noise goes away when the vent is plugged.
Any suggestions?
It's interesting that this occured in an Adire alignment. I experienced the same phenom with the Shiva MkIII in an unstuffed tube. Obviously acting the same way it would in free air. This makes me wonder if the driver has enough internal damping (is that the right term?) to function the way you would like. If it's a leak it would have to be a big one. You may want to consider leaving the port stuffed unless that makes it sound worse.
So this behaviour is not normal, then?
Leaving the port stuffed is not really an option, as with such a large enclosure it looks to have a F3 of about 50Hz, and I plan to cross it at 40.
Leaving the port stuffed is not really an option, as with such a large enclosure it looks to have a F3 of about 50Hz, and I plan to cross it at 40.
I should've been more specific. I had mounted the Shiva in the end of a long tube as I was preparing to do a simple TL app. The driver was sitting in essentially free air. No cap on the end of the tube. I inadvertently fed it a signal and it made an unusual noise like the one you described. It surprises me that it would happen in a finished enclosure. That DTS track can really push your LFE reproduction system to the edge!
With only 250W set at half gain it sounds like you clipped the amp. To get max power from the amp, set its gain to max and dial in the level at the receiver. If there's still too much gain at the sub when the receiver is set at its minimum, then fine tune it with the sub amp's gain control.
Still, with only one Shiva and 250W I seriously doubt you'll get DD/DTS reference level unless you're near the sub and there's lots of room gain. The one Shiva sub I built required two Mk1s in a stuffed 8ft^3 tuned to 16Hz with dual 15" PRs driven with 350W each to reach reference in a semi-open ~16 x 24 x 8ft room.
GM
Still, with only one Shiva and 250W I seriously doubt you'll get DD/DTS reference level unless you're near the sub and there's lots of room gain. The one Shiva sub I built required two Mk1s in a stuffed 8ft^3 tuned to 16Hz with dual 15" PRs driven with 350W each to reach reference in a semi-open ~16 x 24 x 8ft room.
GM
GM said:
I'll try this. Thanks!
Reference level isn't necessary -- I have neighbours. 😉 Just loud enough to be exciting is all I really need.
I have a pair of woofers that are, as far as I can tell, the absolute minimum amount of engineering you can put into a woofer and have distortion figures <10%. That said, I took an absurdly long time putting them into boxes. When I fired them up sitting on something soft, they made a very similar sound to what you describe, and as far as I could guess, it was the VC bottoming out on the back plate. It happened at depressingly low SPLs and anytime there was any bass deeper than ~30hz. I could get the sound reliably by playing Daft Punk.
I'm running them open-baffle now, and I've put fully 100 watts through them of organ music (whoah baby they're fun to watch!) and haven't recreated the sound since. So, my guess is, the sub basket is being allowed to move. Don't let it! 😀 The only thing that should move is the cone/VC assembly and suspension.
Other ideas? Lemme know. 😀
I'm running them open-baffle now, and I've put fully 100 watts through them of organ music (whoah baby they're fun to watch!) and haven't recreated the sound since. So, my guess is, the sub basket is being allowed to move. Don't let it! 😀 The only thing that should move is the cone/VC assembly and suspension.
Other ideas? Lemme know. 😀
Nappylady said:
That sounds plausible. It is, I admit, not as well fixed down as it could probably be. I only have four of the eight bolts in (I don't want to fit it permanently until I have the enclosure veneered) and they are also holding a grille frame, so probably don't have much direct pressure on the basket frame. I'll find a better way to mount it.
I appreciate the help. =)
Not that you would want to, but can you make it happen again maybe at a lower volume (the same track). Just to be sure sure that someone didn't drop a golf ball. Sometimes, I've found that if you are picking out tracks, individually, that they will come to an abrupt end. Is this what happened? I have a 125 watt Velodyne, and I typically set the volume on it to between 9:00 and 10:00 for most DVD material. Maybe it's just plain too loud at 1/2 volume.
4 bolts instead of 8? Why didn't you say so!
Veneer the box, bolt the thing down properly, and make sure the gill is far enough away that the woofer is not schmaking it when it hits those high transients, and watch your troubles disappear! 😀
Veneer the box, bolt the thing down properly, and make sure the gill is far enough away that the woofer is not schmaking it when it hits those high transients, and watch your troubles disappear! 😀
Well I have a 15" Tumult and if I push it too hard, I too will get that "golf ball on concrete" sound. 34 mm excursion my ***! I havent had much time to play with it but this driver's goin on ebay soon.
Nappylady said:
I had some "issues" with my T-nuts. I drilled the holes for the bolts before realising that if I put the driver in how I was planning, the bracing would be EXACTLY where the back of the bolt needed to be. =(
I'm going to use standard drywall screws for those four, so that's why they're not in yet. I think I'm going to find some other way to mount the grille or do away with it completely, because I think it's stopping the bolts getting clamped down well onto the frame. It's only there to stop the cats messing with it, and they don't seem too interested in crawling under the box.
I just did a quick simulation on the free version of lspcad you can download from the Adire site. I think you could be bottoming out your driver. You can't know how much power you are delivering to your sub by just knowing your volume setting. At half volume setting on the know, you can probably still feed it an audio signal that will cause it to max out power.
With you box an port you will be at XMAX (32mm p-p) at 25hz at ~210 watts (assuming voice coils in parallel). That should make a very loud noise, but if you feed it a signal below your port tuning frequency (I don't know if the DTS demo does that low, but it might very well do that) you would excede XMax at much lower power levels.
You should be able to look at the driver and see if it is getting close to XMax (32mm p-p should look pretty dramatic). If it makes the noise without dramtic cone motion you can look for other things. If you see the cone moving a lot (even if you don't hear a sound - 16hz would not "sound" loud, you should feel it though) then you might look to get some kind of subsonic filter that will filer out stuff much below 20hz.
With you box an port you will be at XMAX (32mm p-p) at 25hz at ~210 watts (assuming voice coils in parallel). That should make a very loud noise, but if you feed it a signal below your port tuning frequency (I don't know if the DTS demo does that low, but it might very well do that) you would excede XMax at much lower power levels.
You should be able to look at the driver and see if it is getting close to XMax (32mm p-p should look pretty dramatic). If it makes the noise without dramtic cone motion you can look for other things. If you see the cone moving a lot (even if you don't hear a sound - 16hz would not "sound" loud, you should feel it though) then you might look to get some kind of subsonic filter that will filer out stuff much below 20hz.
dhenryp said:
This is a good point. I don't think I should have been pushing anywhere near 200 watts through it at the time, but I'll investigate this some more. Thanks.
I have the same sub in the same alignment and just tried out the DTS opening on Minority Report at what I would call a very loud level. The sub did vibrate a few things, but there was no clicking. I thought there may be sub-bass sound there that could over-extend the driver below the port frequency but it appears not.
So the explanations above are your best bet, or the driver is faulty. Adire are very good about faulty drivers.
Steve
So the explanations above are your best bet, or the driver is faulty. Adire are very good about faulty drivers.
Steve
Use all those Shiva screw holes. Make sure the basket-baffle seal is good.
Play a sine wave signal at the box's tuning frequency to check for leaks. There should be no chuffing noises.
Disable the sub amp's bass boost (if there is any).
Make sure the driver itself is still ok after that unusual noise. There should be no rubbing noises inside the driver motor assembly.
It's very unlikely, but check if you received a defective driver to begin with. Who knows, your voice coil former could be longer than spec. 😀
Check that the sub is at the optimum room placement so that you needn't turn the volume up so loud.
As was already mentioned, it's unfair to ask for DTS reference levels out of just one EBS Shiva; especially if the room is relatively large compared to the sub.
To set my EBS Shiva's amp volume, I used a Pink Noise signal. Cool Edit Pro generated and normalized the signal to 100% and the resultant signal was burnt to disk. With my DVD player's Audio Attenuation turned off, I slowly wound up my sub amp's volume just before the Shiva's mechanical limit.
Enjoy 🙂
Isaac
Play a sine wave signal at the box's tuning frequency to check for leaks. There should be no chuffing noises.
Disable the sub amp's bass boost (if there is any).
Make sure the driver itself is still ok after that unusual noise. There should be no rubbing noises inside the driver motor assembly.
It's very unlikely, but check if you received a defective driver to begin with. Who knows, your voice coil former could be longer than spec. 😀
Check that the sub is at the optimum room placement so that you needn't turn the volume up so loud.
As was already mentioned, it's unfair to ask for DTS reference levels out of just one EBS Shiva; especially if the room is relatively large compared to the sub.
To set my EBS Shiva's amp volume, I used a Pink Noise signal. Cool Edit Pro generated and normalized the signal to 100% and the resultant signal was burnt to disk. With my DVD player's Audio Attenuation turned off, I slowly wound up my sub amp's volume just before the Shiva's mechanical limit.
Enjoy 🙂
Isaac
Mike, eRic:
Here's a test.
First, download a freeware sinewave generator. Here is a nice one by David Taylor:
http://www.david-taylor.pwp.blueyonder.co.uk/software/audio.html
Don't forget to both download and install the vBrun300. dll! Very simple installation, just don't forget the dll.'s.
Run a cable from your sound card to your stereo. That is a stereo 1/8" plug to RCA plug. Or Walkman to stereo. Radio Shack should have them-just tell the salesman what you want to do.
Put your volume up to where this sound occurs. Start out with a sine wave of around 150 Hz or so.
Go down the scale until you either hear the noise, OR you hit your port tuning frequency. I believe you said that yours was 16 Hz. If you hit your port tuning frequency without hearing the noise, then you know that the problem is that your program material contains tones that are below your Fb, below which point your excursion starts going out of control.
Answer-some kind of electronic way to cut off the frequencies below the box tuning frequency. That is another question.
Here's a test.
First, download a freeware sinewave generator. Here is a nice one by David Taylor:
http://www.david-taylor.pwp.blueyonder.co.uk/software/audio.html
Don't forget to both download and install the vBrun300. dll! Very simple installation, just don't forget the dll.'s.
Run a cable from your sound card to your stereo. That is a stereo 1/8" plug to RCA plug. Or Walkman to stereo. Radio Shack should have them-just tell the salesman what you want to do.
Put your volume up to where this sound occurs. Start out with a sine wave of around 150 Hz or so.
Go down the scale until you either hear the noise, OR you hit your port tuning frequency. I believe you said that yours was 16 Hz. If you hit your port tuning frequency without hearing the noise, then you know that the problem is that your program material contains tones that are below your Fb, below which point your excursion starts going out of control.
Answer-some kind of electronic way to cut off the frequencies below the box tuning frequency. That is another question.
One thing you're forgetting! The PE amp has a subsonic filter! You're either clipping the amp (possible) or something is up with the driver.
nobody special said:
Right you are. However, the subsonic filter cuts output under the specified frequency-in this case, 19 Hz-by 12 dB/octave.
However, under the port tuning frequency, the cone excursion goes up much greater than that. Even with a subsonic filter, your subwoofer still will have much greater excursion for tones a little below the tuning frequency.
- Status
- Not open for further replies.