My First Sub

[---k---]

Just a quick update, I got RoomEQ up and running, attached is what it is showing me for both subs located under the speakers. Big null at 43hz. : I got a lot better extension than I previsouly thought. Not sure why I wasn't hearing this as well, may have been I didn't have the sub level correct. I'm not quite sure how to attack this with the BFD. Add a little boost down at 20hz, but other than the incorrectable null, I'm not sure if it is worth messing with. Any thoughts, suggestions?

I think I need to measure at the other two seating locations, and maybe experiment a bit with placement, see if I can eliminate that null. Unfortunatly, with my room, seating is pretty much locked, and now because of the subs size and shape, they can either be tight to the tv or under the speakers.

[ThomasW]

Wow, you have the dubious honor of having the biggest null I've seen in 40yrs of speaker building..... 8O 8O 8O

Try rotating the subs so they face any other direction and measure again. Other than that major bass traps are in your future if the wife approves...

Now the bottom end roll-off looks like it should. You've got plenty of amplifier power so dial in boost at 20Hz. Try various filter widths to see what works best.

[Dennis H]

Edit: missed the part where you said the seating was locked. Moving the subs (feet not inches) or bass traps are the only choices. Try running just one at a time to see if that null gets better.

[---k---]

Wow, you have the dubious honor of having the biggest null I've seen in 40yrs of speaker building..... 8O 8O 8O

I'm Honored! When do I get my certificate?

I moved the mic forward and back about a foot or so, and it just got worse. I almost cried when I placed the mic on in the other locations where my wife normally sits. In the other chair which is slightly off center, it was nearly perfect! I then placed the mic on the sofa, which is way off center, again it was almost perfect, nothing that the peq couldn't fix! Take a look.

My wife got home while I was crying. To cheer me up, she suggested moving around bass traps and building more. We stumbled upon another solution, that appeared to work really well. Unfortunately, I didn't save it, because we had to leave for dinner shortly there after. But, it was opening the door to the utility closet/crawl space at the back of the room. It changed the null to a smooth, wide dip. I plan to do more testing tomorrow, and will post the graph. There has to be a downside to this solution, but I'm not sure I care. My room is already leaky, with a staircase on the other side. Is there a downside to this solution?

After we got back from dinner, we watched a stupid chick flick (with the door open), and the sound track sounded great. Had real nice bass guitar that made me get up at one point to turn off the subs to just check the effect.

Just for reference, this is approximately how my room is laid out:

Image not available



The plants are the speaker, but they are spaced out a bit more, and the big long table is treadmill. There is the wonderful basement pole in the middle of the room where the P3 is.

[Dennis H]

Cheer up! An open door is like a big bass trap the size of the door. Sound goes through and doesn't come back (sorta, kinda, blah blah.)

[steve nn]

Hey that's looking better Ryan. I've seen much worse than that I assure you. You have allot to work with there.. with the closet door open. Another thing you might try is to put a sheet of plywood right behind your recliners as to act as a boundary. If you find it helps (I think it would) you could possibly go with some sort of oriental folding wall or something to that effect??

[ThomasW]

Sometime fate steps in and hands us the answer...... :B

[steve nn]

Sometime fate steps in and hands us the answer...... :B

Yeah! The sub Gods are shining on him now. :clap:

[---k---]

Well, the movie that the wife and I were watching last night had some cool thunder in it, and I just thought to myself, "hhehehe God has subwoofers too. "

[J-Dub]

My wife got home. To cheer me up, she suggested moving around bass traps and building more.

Looks like God has blessed you with a heck of a wife as well!

[Mark Seaton]

Ryan,

If you found the open door to work well, there's no reason you couldn't cut out say 2-4 larger panels from the door which you could then frame with molding and use a fabric of your or your wife's choice to hold some compressed fiberglass in the windows created. This would make the opening a little more resistive, and probably serve to smooth things out similar to what opening the door did. Just an idea...

The other option would be to do a little more experimentation with placement. Just for a bit more knowledge of what is going on in the room, you might want to try moving one of the subs to the midpoint of the side wall, or one to the rear wall to at least observe what the changes are to the response. I'm a little fuzzy on what might be caused by what interaction as it isn't clear to me in your diagram what are the front speakers vs. the subs. I presume the subs are P1 & P5?

[---k---]

I played with REQW and the BFD a bit today. REQW is really slick! Wow, it has a little bit of a learning curve, but once you get it, it is easy. Anyway, here is what I came up with, just optimizing for my chair. Pretty impressive for minimal effort:







It ate up quite a bit of amp. I had to turn it up quite a bit, and started to get the red clip lights on the amp to flicker during Incredibles. I think it is way hot though. I need to do some more experimentation.

I'm listening to DMB right now, and the bass sounds a little stronger. Watched Incredibles briefly. The EQ was very noticeable. There was so much more bass. It wasn't necessarily louder, just fuller and a lot more impressive. A little bit more boomy, but I think that is the room, and starting to hit those low frequencies, where I don't have enough absorption - yet.

I'm also having problems with the bolts holding the driver down, or the foam gasket keeps compressing. During Incredibles, again the it sounded like the bass was breaking up. There was a small crackle. I got out a screw driver, and was able tighten the bolts. An explosion or two later, and I could again tighten the bolts. Odd.

Mark,
the speakers are in the same spot as the subs, directly under. I need to put up some photos. I'll think about modding the door.
When you coming over?

[SteveCallas]

Your chair, EQ, door open looks great and it stays pretty good for the other seating positions as well. Nicely done :T

[---k---]

Some of those waterfall plots obviously arn't correct. I'm trying to fix it.

Edit- fixed graphs above.

[MDJones]

I'm also having problems with the bolts holding the driver down, or the foam gasket keeps compressing.

I'm not sure what type of gasket you are using, but the typical foam strips from Lowes/HD will indeed permanently compress. Thomas suggested for me to use a rubber foam instead to solve this problem. I ended up using 5/16" x 3/4" x 10' Sponge Rubber Weather-strip available at Autozone for $7. If you use this, you will have to use a soldering iron to melt holes for the driver bolts since it doesn't tear easily (do it in a well ventilated area). I haven't had any problems at all sealing my sub using this.

[---k---]

Well, I watched martix Revolution today. Wow, what an experance. It was amazing. I also listened to a couple of CDs. I found the bass very strong and blended very well.

But, I'm still getting that crackle out of the subs once in a while when pushed. I thought it was the driver being loose, but I checked, and it was tight. The last time I saw it happen, I saw the red clipping lights just starting to barely flash. So, I'm guessing it is the amp clipping, as someone suggested previously. The receiver is set to 0 and the amp probably 80% up. The meter on the BFD was only going about half way up. Do I just not have an enough amp, or am I set up wrong.

Or could the crackle be something else?


Edit: The sub level on the receiver was set to 0, the dial was -12, and the sub amp was at 80%.

[Curly Woods]

Are both subs making the noise? It would be a good idea to find out this as one of the drivers maybe defective.

[---k---]

Are both subs making the noise? It would be a good idea to find out this as one of the drivers maybe defective.

Good question. I don't know. It seems like it is always the one on the left. But, it is probably 1' closer to me and it is really really hard to tell when both are running. When it happens, my eyes and ears are immediately tuned to one sub. It was difficult to pull my eyes away to look at the amp to see the clipping lights. I guess I could run only one sub, and push it until I hear the sound, but I'm not sure I really want to keep pushing it -these things are expensive!

What could be defective about the driver that it would make a small crackling sound only when pushed really hard?

I was really hoping it was just the foam compressing, because while I could tighten the bolts every hour or so of listening, that seams to have stopped and I still got the sound.

[ThomasW]

Given you've got about 950 watts available, I doubt that it's the amp clipping.

Run a couple of low frequency sine waves and listen for the noise. It could be....

1) the input terminals are vibrating
2) the internal wiring is vibrating against the cabinet walls
3) there are leaks through the screw holes
4) the sheet metal isn't completely tight against the cabinet walls and is flexing.

[---k---]

Thanks Thomas,

I will try and run some sine waves and listen more closely. I probably should also pull the drive and stick my head inside and see. It could be the wiring or the steel I guess. I didn't do anything special to tie it down. It's not the sound I would expect from the wiring though. I'm trying to talk Chris into comming down to my place this weekend and do some speaker listening, so maybe he can help me get it figured out.

I need to read up more on amp setup, what causes them to clip, and how to avoid. I know it is too much input signal, but I'm not sure I understand it fully. I did see the clip lights on my amp flicker, so I must have something wrong.

So much reading and testing, so little time to listen and enjoy!

[ThomasW]

It's not unusual for the lights to flicker a little bit at high output levels. My guess is that you're driving these subs quite a bit louder than you think....

[---k---]

I've been enjoying listening for the past couple of weeks, but now it is time to finish all the little details.

I still need to do some more sanding of my excessive bondo work and paint the exterior. I also need to drill in the spikes, make a grill cover, and clean up the wiring inside the sub.

Right now, I am using 14ga speaker wire for the hookup wire inside the box (and the run to the sub). I got bare copper at the driver, and at the terminal end I wrapped the wire around and terminal and soldered. I'm a little embarrassed by my soldering, it looks quite ugly. Obviously, I need to pratice some more, before taking on other projects. I seemed to have trouble getting the wire to heat up enough to make the solder flow.

So I need to place an order with PE, and I'm thinking of ordering some crimp on or something terminal clips or whatever for the inside of the box at both the driver end and the terminal cup end. I just want it done as right as possible, and not have to worry about something I did maybe holding me back.

So is something like this what I want, or is there something better, or should I just work on my soldering skills and forget about the connctors?

female connectors : http://www.partsexpress.com/pe/showd...number=095-810

Pins: http://www.partsexpress.com/pe/showd...number=099-310

12ga O free speaker wire: http://www.partsexpress.com/pe/showd...number=100-150

And have I missed it, does Thomas or anyone else have any pictures of how they connects their drivers and terminals together?

[ThomasW]

I use banana plugs for all my speaker wires.

I solder the wire from the driver to the input terminals, that way there's no chance of them vibrating loose.

Any 12 ga or larger wire is fine for the run from the amp to the sub.

[---k---]

Just an update for anyone who might be copying. I'm using my subs as speaker stands. Because of this, I'm wishing that I would have increased the thickness of my top layer. I've noticed that if I put my hand on the top, I can feel vibrations. I'm not sure how to quantify how big the vibrations are, or if they are a problem.

When I had the driver out for painting, I decided to add a brace inside across the top, under where the speaker sits. I used some nice pine 1x3 that I had in the garage, and glued it in with a liquid nails type glue.

Image not available

This should have stiffened up the top. I don't really have anyway of testing to see if it did any good. I gave it my best shot though, and placed two glasses half full of water on top of one of the subs - one near the front, over the new brace and one near the back. I then turned the sub way up and listened to Blue Man Group. Then I sat in front and stared at the glasses (Pass flapping bass isn't quite the word for it when you are that close. I had to move to the side 8O ) When the bass really hit, I could hear the front glass vibrating. I also noticed it rotate slightly a few times, and the water would splash slightly every so often. The glass in back didn't seem to do much.

Oddly, the vibrations don't feel as strong in the side panels. It could be either be the bracing, or it could just be that my hand isn't that accurate.

I got poster putty (Blue Tac) under the speakers to isolate them. Putting it under the glass seemed to do the trick. I'm considering my options and time commitments. One of these days, I might totally sand down the top and add another layer of 3/4" MDF.

Edit:
Here's a photos with them in Lowes Semi-Gloss Acrlic Paint - New Black, with a 3/8" nap roller, I get a nice textured look. Wife is happy, except she wants a grill cover.


Also, the inserts for the spikes are installed, but until I settle on placement I just have 3 small wood blocks under each.

[---k---]

I continue to get the slight crackling sound when I really push my subs. I have confirmed that I get it from both subs. The red amp clip lights aren't solid red, but they are flickering when I hear this sound.

I've looked for leaks, and didn't see any. I'll check again though, maybe I missed something. I intend to do more testing tonight to see if I can confirm it is clipping. Somone suggested that back on page 8, and I'm at a lost otherwise. Tonight, I intend to bypass the BFD and see if that illiminates the problem. I also intend to bridge the amp and see if I can drive just one sub with twice the power and if it still occurs. If I hear the crackling with the amp bridged, I know it isn't a clipping problem.

I might have things hooked up wrong, or miss-configured. That is why I'm posting this before doing the above testing.

Originally, I had the BFD in Pro mode. With it in this setting, I had to increase the sub level in the receiver to around 5 or 6 to get the BFD signal level to not quite reach red. The subs were then set to just shy of 2/3. This seemed to be pretty well calibrated at 85db. Throwing in the above filters would cause me to raise the subs to 3/4. Watching War of the World at about -14 on the dial, I got the crackling. It stayed there until I turned it down to about -20. Same thing with watching Black Hawk Down with a friend.

I played with the BFD more, and realized that I had it in Pro mode. I tried switching it to Home. Now, I had to back off on my receiver sub level to about -8 to avoid clipping the BFD and set the sub level to about 85% of the way up to be properly calibrated at 85db. This is with a some differnt filters. I added a +2/16 at 20hz, and not as big and fewer cuts. When I tested with War of the Worlds, listening at around -14 to -18 on the receiver, and I didn't hear the crackling - thought my problem was solved and was happy for a week.

Last night, the wife got home late, so I decided to really see how much sub I had. I didn't change my settings on either the receiver or amp, just turned it up to -6 while watching Incredibles. The bass was AMAZING, but I got the crackling on the THX ball explosion demo and in a couple of other scences. Each time the crackling occured, the clip lights were flickering. Also, beleive it or not, but -6 wasn't painfully loud. I had to go pick my wife up from the train station, or I would have kept testing to see what volume level it stopped occuring at. But, I don't want hold back and contuine to fear this happening and always be watching with the remote control in my hand out of fear.

So, could this be amp distortion? Could it be my BFD filters? Or something else? Crappy soldering on my wiring causing too much resistance?
Do I need to give a better description of the sound?
Is there a method to adjusting the settings to lessen the stress on an amp?
Other than the above mention tests, what else should I try?
Should I be worried while testing this about frying my drivers? If I keep playing the same scene over and over that causes the sound, trying differnt things, am I at risk?

[ThomasW]

If the amp lights are flickering then yes the amp is clipping. Clipping is starts out as a slight crackling sound.

I doubt that it's your soldering.

Just to check, you have the drivers wired as 4 ohm loads and one going to each channel of the amp?

How loud is it when this is happening?

Since the amp clip lights are coming on, each driver is getting 475+ watts. That should be VERY VERY loud.

The bass was AMAZING, but I got the crackling on the THX ball explosion demo and in a couple of other scences. Each time the crackling occured, the clip lights were flickering. Also, beleive it or not, but -6 wasn't painfully loud.

I'm getting this feeling you think you should be able to run this setup with the dial turned to "11" and have nothing untoward occur. That's just not realistic.

If the amp is driven into gross clipping meaning the red lights are glowing red continuously you certainly can damage if not destroy the drivers. Having the lights flicker isn't going to hurt anything.

If you want to invest in something more accurate than the RS meter and take some readings then we can diagnose this further. But the meter simply isn't accurate enough at low frequencies to tell us what we need to know.

I also intend to bridge the amp and see if I can drive just one sub with twice the power and if it still occurs.

Be VERY careful doing this!

[chasw98]

I continue to get the slight crackling sound when I really push my subs. I have confirmed that I get it from both subs. The red amp clip lights aren't solid red, but they are flickering when I hear this sound.


So, could this be amp distortion? Could it be my BFD filters? Or something else? Crappy soldering on my wiring causing too much resistance?
Do I need to give a better description of the sound?
Is there a method to adjusting the settings to lessen the stress on an amp?
Other than the above mention tests, what else should I try?
Should I be worried while testing this about frying my drivers? If I keep playing the same scene over and over that causes the sound, trying differnt things, am I at risk?

Ryan:
Is the sound mechanical or electrical?
Crappy soldering will not cause this unless a lead is flopping around inside the enclosure (mechanical)
Method to adjusting settings? Start at ground zero with as little as possible in the signal chain to eliminate major factors, i.e. preamp to amp to sub. If crackling goes away, then problem is in component removed, more troubleshooting. (During troubleshooting, don't worry about SQ, that will be fixed once problem has been identified)
Reasonable caution should be taken while recreating the "crackle" so you don't damage drivers. Playing the same scene over and over in and of itself will not put your drivers at risk, but see previous statement.
When troubleshooting, be like Mr. Spock, logical and methodical. If need be, put the actions taken on a piece of paper so that as you take a step and the problem occurs, you can take a step backwards to the previous step and see if the problem is not there.

[steve nn]

Tonight, I intend to bypass the BFD and see if that illiminates the problem. I also intend to bridge the amp and see if I can drive just one sub with twice the power and if it still occurs. If I hear the crackling with the amp bridged, I know it isn't a clipping problem.

Mmm?? I guess before you go any further, it would be good to rule the amp out. -6 on the THX Ball is pretty loud though. You figure it's around 4-6dB hot! The thing is, in all the drivers I've bottomed out, I have never heard the crackling sound you speak of...including the RL-p. I guess you ruled your mains out...

Should I be worried while testing this about frying my drivers? If I keep playing the same scene over and over that causes the sound, trying differnt things, am I at risk?

Yeah you need to be careful. WOTW at -6 in a typical room is quite aggressive.

Have you done any testing on the amount of fill your using? Anyway, it'll be nice to rule your amp out if that's the case?

[steve nn]

I'm getting this feeling you think you should be able to run this setup with the dial turned to "11" and have nothing untoward occur. That's just not realistic.

That's been in the back of my head also. Take some of the super-duper supped up movies now-adays, and try to run them at reference (settings), is asking for big time trouble. 8O

[---k---]

I'm getting this feeling you think you should be able to run this setup with the dial turned to "11" and have nothing untoward occur. That's just not realistic.

ops:
Actually, yeah I did think this. I thought we had come up with something that would make my ears bleed before the subs did. I know I don't have enough amp power to bottom the driver, so I'm safe there. And, I didn't think the amp would run out of gas unless I had it at 10, or 11 as the joke goes. I've never gone above probably 8.5. I guess I still don't understand fully what causes an amp to clip. I thought it was when the amp was working too hard, but how can it be working to hard if I can make the the clip lights flicker when it is at 60% because I have the receiver level up. I know it probably isn't true, but in the back of my head I hear all those people who told me that I should be getting a QSC or Crown amp because the Nady was poor quality, garage band junk.

The drivers are definitely wired for 4ohm. I can change the volume to each sub individually. Inside the box, I have one lead going to the plus, the other lead to the opposite VC minus, and a single peice of 12ga going from the remain plus to the remaining minus.

Thanks for ruling out my solder job. I don't think it is that bad. The wires took a lot of solder to tin, but the solder is shiny. I just want blame myself for something, because I can't beleive that design plan is bad.

When you ask, "How loud is it?" Are you refering to the crackling or the total volume? I had my SPL out when doing this, but it is hard to look at a meter and the clipping lights at the same time. So, I don't know. All I can tell you is the receiver volume levels. I have taken the time to calibrate it so that 00 is 85db pink noise to all channels. Music sounds correct and not like it has too much bass (and I typically don't like overwhelming bass with music). I'm not running it any hotter than when Chris was here a couple of weeks ago. We didn't do much listening with the subs, but when we did he was either nice or didn't hear it as being off. My wife and I normally watch movies at -12 to -16. By myself, I usually listen at -10 to -12.

I'm hearing you when you said that 475W per driver should be very very loud. Without having more experance, I can't say if I'm there. I would say it is loud, but not very very loud.

The crackling itself isn't super loud. It is very obvious that it is there, but it doesn't dominate the bass or is louder than anything else. It is probably about half as loud as everything else going on, but still very audiable. I hope crackling is the right word. It is similar to wadding up a piece of paper and then cruching it a few times, but a little more cruchy. Got that?

One of the problems I have, I keep thinking that I solved my problem only to have it occure again later. Originally, I thought it might be the drive loose - fixed that and didn't hear it for a while. Then, I thought it might be the wiring inside hitting the bracing - hot glued a twist tie wire to the back of the driver and to the bracing and tied the wiring down, and again didn't hear it for a while. Then, I thought it might be the clipping due to having the receiver channel level at +5, and reducing this to -10 would fix it, and again didn't hear it for a while.

I am using less fill than I was before. I don't think this makes any differance and not sure how it could affect anything that would make a crackling sound.

I think Chris is going to come over next weekend, so maybe he can give me a second opinion. It will be good to get two more eyes, ears, and hands. In the mean time, I was hoping that I could get some advice on what to check, how to test, and any precautions I might need.

[steve nn]

I am using less fill than I was before. I don't think this makes any differance and not sure how it could affect anything that would make a crackling sound.

No no, I was just wanting to rule out to much fill in regards to headroom is all. Curiosity got the best of me which lead me to over stuffing one of my units, and it must of reduced the output by 50%..

I feel your pain Ryan..I to would be quite bothered!

[ThomasW]

Play your a DVD (where you hear the crackling) and note the output level setting on the receiver/pre-pro.

Then play a 50 Hz sine wave at the same output level. With the RS meter sitting 2" from the dust cap of one sub what's the SPL reading? (Hint, I think you'll be really surprised ...:wink: ) Note don't run this tone for more than about 15 sec..

Steve is correct, too much damping can greatly reduce the efficiency of the sub.

[Bent]

My blueprint 1503 made a similar sound - I havn't determined what it was, but I got so irritated by it that I bought the RL-p.

(My nearest guess is it was voicecoil de-lamination, but I can't say for sure. And I can no longer re-cone it thanks to UPS)

[---k---]

First, I was mistaken. My speakers are calibrated to 75 db at 0, not 85. I verified that the Pio software does levels well enough a while ago, so usually I just use it. I've check it and tweaked it from time to time, but usually it is not more than .5 db off. This probably changes some of your opinions, slightly.

I just verified with my SPL at my seat, and all my speakers are at 75db when the master volume is 0 using the receivers pink noise. The sub bounces between 68 and 72. So with correction factors, it is probably about right. When I've looked at the sub and speakers in REQW, it looks pretty level.

Play your a DVD (where you hear the crackling) and note the output level setting on the receiver/pre-pro.

Then play a 50 Hz sine wave at the same output level. With the RS meter sitting 2" from the dust cap of one sub what's the SPL reading? (Hint, I think you'll be really surprised ...:wink: ) Note don't run this tone for more than about 15 sec..

Steve is correct, too much damping can greatly reduce the efficiency of the sub.

I can't play burned CDs on my player, it is a "Feature". So, I plugged the cumputer into the receiver. This probably causes level problems. I used the NHT tone generator to generate tones. The NHT software changes the output level each time it runs, so I can't adjust my output level to match anything. So, I put the receiver master volume at -6 like I had it the other night. Amp unchanged and levels unchanged.

The edge of the SPL meter is 2" away, so the center of the mic is probably 2.75".

Image not available


Uncorrected:
a 1000hz tone, at my seat: 80db.
w/o EQ:
Right sub, 50hz tone: 97db
Left Sub, 50hz tone: 99db

w/ EQ:
Right sub, 50 hz tone: 97db
Left sub, 50hz tone: 98db

[ThomasW]

Uncorrected:
a 1000hz tone, at my seat: 80db.
w/o EQ:
Right sub, 50hz tone: 97db
Left Sub, 50hz tone: 99db

w/ EQ:
Right sub, 50 hz tone: 97db
Left sub, 50hz tone: 98db

This is causing the crackling?

I'm trying to get a reference for what SPL is causing the crackling. How about using the test tone (pink noise) in your receiver/pre-pro, at what SPL does the crackling occur?

[Mark Seaton]

Ryan:
Is the sound mechanical or electrical?
Crappy soldering will not cause this unless a lead is flopping around inside the enclosure (mechanical)

I think many are surprised to hear what some electronics sound like when they briefly go into hard clipping. It is also surprisingly easy to do this with more recent soundtracks, even more so when you start applying EQ. Different amplifiers clip more or less abruptly than others, but early when I started working at ServoDrive I was quite surprised to hunt down noises that sounded like a woofer bottoming that were in fact the amp or some upstream electronic device clipping.

Hi Ryan,

We can chat about your problem more on Sat if you make it to the G2G, but there are some quick tests you can do to help narrow down the source of the clipping. From the bits of posts I have scanned, it sounds like you have your amp set to 60-85% of full level. First, this is just an attenuator for the input signal. It does not in any way limit the amount of power the amp can put out. With the level set lower, it just takes a bigger signal on the input to produce the same output. While it sounds like the amp is clipping, you can check to see it's the output of the amp and not something upstream like the receiver or BFD.

With the amp level set less than full level (your 60-85% range should be fine), find a scene and main volume setting that just starts to make the clacking noise. This would probably be more easily done with your main speakers disconnected or off. Now increase the level of the amplifier to max, and lower the main volume. Listen to this scene again and note at what level the clacking is heard. This should be a lower level setting than the first case. You can also then try lowering the sub-out level by say 5dB. Now check that the main volume setting to produce the clacking raised by the same amount you lowered the sub level. The above should confirm that their aren't problems upstream of the amplifier. I would recommend the bridged test, but ONLY using program material. You are fairly unlikely to damage the driver with program peaks, but test tones and sine waves could certainly do damage if left on too long.

Many look at a excursion prediction for a given power input and incorrectly presume that you can't put more power to use than would result in max excursion. For 95% of the time with real program content, there is a spectrum of bass content that the amplifier must deliver. Remember that simultaneously delivering 100W at 20Hz and 100W at 80Hz requires 200W from the amplifier, while the excursion of the driver with this 200W input will effectively be the result of the 20Hz signal. The complication is then that you also have to account for the rare cases when some low frequency effect allows most all of the amplifier to be used at those low frequencies. It's not uncommon to be able to use as much as 4x (+6dB) the power required to reach max excursion on real program material without getting near the excursion limits.

Of course the safest and best (albeit more costly) route is to limit power to only reach max excursion with a test tone and just add more subs to get the level you want.

[---k---]

I must be doing something wrong. I've torn apart my system. Pulled the amp and the BFD out and have them sitting on the floor. I've removed the cable going from BFD to the amp for one of the subs. I've removed the speaker wire for the right sub. I've set the amp to bridged. Turned the amp volume all the way down on the b channel. Un hooked the BFD entirerly. Turned the amp on and off. But everything seems the same.

Watching Incredibles, the scene where the plan has just blow and then is falling into the water, 1:10

With only one sub hooked up, and the amp in parallel mode, and all the front speakers disconnected so I can better judge the sub. I put the amp volume at about half way, and it sounds good. Slowly moving it up, and when I get just past 3/4 of the way, I get the sound. With this scene (and probably all the rest, just never listened without the other speakers), I'm not sure if crackle is the right word. It is more a gurgle sounds? I guess it is the sound that if I put my hand on the aluminum cone so it doesn't resonate and then hit it a few times. Measuring at my seat, it happens when I hit about 96db.

Now, I turn the amp off and switch it to bridge mode. Exact same thing. But the wierd thing is that the signel light for the B channel is still flickering. It seems like the amp is in parallel mode, but it isn't. The switch is up.

So I'm a bit of a failure tonight.

[---k---]

I put the ear plugs in and did that scene with the spl about 2" from the cone. It was hitting 120db. So, maybe I am at the max and am expecting too much?

[SteveCallas]

120db from one sealed sub? Yeah, I'd say you are expecting too much :B

So are you saying the output at 2" is 120db and at your seat it drops to 96db?

[ThomasW]

Sound attenuates at a rate of 6dB for every doubling of distance from the source.

Exposure to 120dB results in permanent ear damage in 1 minute. So yes 120dB is what one would call ......

LOUD

Now if your subs are in phase your 120dB is actually 126dB when the second sub is running.

So yes I'd say your expectations are a bit unrealistic....

Oh and BTW if that 120dB is uncorrected, then the real output is 3 or more dB higher ......

[---k---]

Steve, I beleive so, yes. This is pretty simple stuff. Just rechecked it. Have the meter sitting on my chair, set to 100db, and it reads -4. Put the meter in front of the sub, set the meter to 110db, and it maxed it out. Bumped the meter up to 120 db, and the needle just was hitting 0. I don't know if that means that I'm at 120, or that is as high as the meter goes.

I just read Mark's post. I got the amp at ~90%, no BFD in the chain, the sub channel level on the receiver is -10. Setting the receiver to -12, no clack, gurgle, whatever you want to call it. Master volume at -10, I get the sound. Oddly, the amp clip light doesn't start flickering until about -8.

I just don't understand if I only have 475W to feed the sub, and the models show that I need around 750W to reach max excursion, I can't be hearing the sub bottom, right? It has to be the amp clipping, or something else?

[---k---]

We could use a chat room

Yeah, I know. I'm usually pretty good on jobsites about having ear protection. I'm very familar with:

Duration Without Hearing Protection Sound Level dBA
24 Hours 80
16 Hours 82
8 Hours 85
4 Hours 88
2 Hours 91
1 Hour 94
30 Minutes 97
15 Minutes 100
7.5 Minutes 103
3.75 Minutes 106
1.88 Minutes 109
0.94 Minutes 112

Okay, so maybe I got two problems here:
1) I'm running my subs a lot hotter than I think, and should get out the Avia disc and really make sure they are calibrated correctly.
2) I'm either bottoming the sub or clipping the amp. Which, if I fix #1 above, I probably won't have the problem. I just don't like that it can and is happening.

I probably should stop reading AVS and all the threads about "Referance Level" and having dynamic peaks in the range of 110db.

Mark,
Really looking forward to Saturday and hearing that Contra and your prototype.

[ThomasW]

"0" with the meter setting at 120 means it's hitting 120dB. And thats insanely loud!!

Yes the amp is clipping. That's certainly not surprising when you're running 120dB uncorrected.

For some reason you're equating amp clipping with running out of excursion. That's not going to happen with 2 drivers and that amp. That's your safety valve, you can't destroy those drivers with that amp unless you run it into gross clipping and that will destroy both the amp and the drivers.

So turn it down. Reference level for a sub is 105dB and that's loud by most people's standards.

I seriously doubt that you're bottoming the driver, doing that makes a mechanical noise that you'll never forget. Crackling is usually the sound of the amp clipping.

[SteveCallas]

Exactly how far away from your subs are you sitting? 120db to 96db seems like a huge drop to me, esepcially since your 2" measurement shouldn't be showing any room gain. 96db at the seats entirely from bass though is nothing extreme, so I can see why you want more. Anyway to maybe place the subs closer to your seat?

[Mark Seaton]

"0" with the meter setting at 120 means it's hitting 120dB. And thats insanely loud!!

Yes the amp is clipping. That's certainly not surprising when you're running 120dB uncorrected.

As I read Ryan's post, that's at only 2 INCHES from the dustcap. That's not quiet, but it's hardly insane.

So turn it down. Reference level for a sub is 105dB and that's loud by most people's standards.

The LFE channel alone can be recorded to a theoretical 115dB level at the listener, presuming it is set to a flat level. It's quite rare for a soundtrack to hit 0dBFS, but add the typical lift people put into the low end of 3-6dB and that's certainly possible. Now add in the signal from the high passed mains and you have a potential of 3-6dB more.

I seriously doubt that you're bottoming the driver, doing that makes a mechanical noise that you'll never forget.

I agree, especially with the "gurgling" comments. A bottoming former usually sounds much more offensive, and a bottoming spider has more of a beating sound (I'm not familiar with how the RL-p15 bottoms).