Confused how I bottomed my sub

[Ricci]

FOH,

 

I must have missed your post...

 

Way off topic but here are a few replies...

 

So far I really like the BMS 18n862. It has enough displacement to be a serious subwoofer but with the triple shorting rings in the neo motor and a very light cone it also does excellent midbass. It isn't the most sensitive driver but it is still respectable at 95-96dB above 100Hz. It extends up high pretty well but after about 2khz or maybe a little higher it is pretty much done. It is of course beaming like crazy up that high as well. Also it weighs like 25 lbs. Very lightweight for what it offers and one of the better all around bass drivers I have used due to its versatility. I did have the one TD18H+ long enough to get some subjective observations on the differences between the two, but since I now know that driver was flawed from the beginning I hesitate to put too much stock into it. My casual observations so far are that the BMS probably handles high power a little better due to the much greater venting and the 4" vc. It may also have a slight advantage in deep bass output. The TD18 seemed to be more sensitive, which wouldn't be surprising with it's very lightweight MMS. Also the TD18 sounded like it extends noticeably higher in frequency past the BMS and the BMS is already very good for an 18" in this regard. Both start beaming like crazy up past 1kHz but the TD18 seems to beam a little less than other 18's but perhaps that is due to the much more extended upper range response to begin with. I am not sure on that yet. In a nutshell it is a more fullrange sound than most any other 18 I have heard yet which is exactly what I was looking for. Additionally the 14mm claimed xmax is the real deal so it can push out some bass fundamentals with ease. Xmech is 40mm or something huge like that. John says there is virtually no chance of hard bottoming the TD drivers you will simply stretch the suspension tight first. My question mark with the TD 18 so far is how does it handle high power for long periods with a 2.5" coil.

 

The bass guitar rig currently is the 2 single 18" cabs that I built which are tuned a little under 30Hz. Each 18 gets a channel of a Crest 8002. A Sansamp RBI rack mount provides extra color. Additionally the bass player/s usually have a plethora of other stomp boxes and tone makers at their disposal in front of that. We do not use any extra mids or tweets for the high end. I have not determined whther that will be added down the road or not. I don't play bass btw I am the drummer. Truthfully with a bit of top end EQ there is a plenty of midrange bite and upper mids just from the 18's. They beam off axis of course but I do not consider this worth worrying about for a musical instrument cab. Guitar and bass cabs usually have multiple drivers, resonance issues and tons of comb filtering, etc and pay no attention to that sort of thing.  Actually keeping some of the energy out of other mics and things can help out. There is a BIG difference between a cab made to produce sounds that the artist and an audience find pleasing and one made to reproduce anything put into it accurately. The typical hallmarks of a good measuring system mean about jack squat in the case of the former system. We play friggin LOUD and very dynamically. I am a crusher with a very loud drumset and big cymbals. My experience with off the shelf bass guitar rigs is they don't have enough balls for the gig and are made cheaply. The amps are bouncing off of the clip limiters and/or the cones are farting out horrible noises on the lowest notes while the bass is just trying to keep up. We have none of those problems. This rig is too much for the gig and is effortless the whole time. The clip lights never show up on our rig in actual use. We quite often have other guys ask to use whatever we are using at the time and they usually end up asking a lot of questions afterwards. The lows are really there unlike fake there like with most cabs. You will hear all of these stories about how you don't want to really reproduce the fundamentals anyway cause it causes feedback issues and bleeds too much and muddles up the bass line. We haven't had that experience. Typically we are not playing in concert halls with thousands of people and nice EAW or JBL rigs. We play rooms of anywhere from 100-500 capacity and some real dive shit holes, with no PA to speak of quite often so there is no turning down and allowing the PA to carry the weight. Our gear needs to be able to carry a large space without PA support. Hell I turn down the "sound guy" when he asks to mic my kit at a lot of these places...There is simply no need. This type of scenario is much more common than a larger place which actually does have a good PA and sound crew. Those sure are nice when we get them though.

 

The GH's are the bottom of the PA in our practice space. They do not travel. They get plenty of music, live kick drum, keyboards/synth, samples and even movies though. Those are run off of a Crest 8002 up to 65Hz. Above them is the JBL 4675C's which I replaced the 2226J's with TD15M Apollo's those are cut at 70-660Hz and get the recently repaired inuke 6000 which blew up on the GH's. The top of the 4675C's are still running the JBL 2446H CD's with JBL's reccomended EQ settings. Those run off of an old Mackie m1400i. A DCX does all of the manipulation and routing.

 

Next time we come up your way to play I will let you know. Bring your earplugs.

 

 

 

[FOH]

Thanks for the response, far too much to address here, suffice it to say .. a few of your lines made me smile ear to ear, I mean damn! That's got to be the sweetest practice rig around, hands down!

 

Those speakers; groundbreaking, way, way ahead of their time butt cheeks from DB Keele, on top of superb, world class LF drives, on top of the quite likely the finest "pro" sub cabs in existence! Damn, damn .. damn nice!  

 

"We play friggin LOUD and very dynamically. I am a crusher with a very loud drumset and big cymbals."  Love this, period.

 

Question;

"Our gear needs to be able to carry a large space without PA support. Hell I turn down the "sound guy" when he asks to mic my kit at a lot of these places...There is simply no need."

I fully understand, been there. However, what about the kick? Even though the snare cuts all the way thru the crowd, the kick typically needs support.

 

 

I'll dispense with the typical drummer jokes, as there can't be a more savvy drummer in the country, wrt the audio side of the equation. 

 

Thanks for taking the time, a wonderful read.

I'm down for a road trip.

[Infrasonic]

Thanks for the response, far too much to address here, suffice it to say .. a few of your lines made me smile ear to ear, I mean damn! That's got to be the sweetest practice rig around, hands down!

 

Those speakers; groundbreaking, way, way ahead of their time butt cheeks from DB Keele, on top of superb, world class LF drives, on top of the quite likely the finest "pro" sub cabs in existence! Damn, damn .. damn nice!  

 

"We play friggin LOUD and very dynamically. I am a crusher with a very loud drumset and big cymbals."  Love this, period.

 

Question;

"Our gear needs to be able to carry a large space without PA support. Hell I turn down the "sound guy" when he asks to mic my kit at a lot of these places...There is simply no need."

I fully understand, been there. However, what about the kick? Even though the snare cuts all the way thru the crowd, the kick typically needs support.

 

 

I'll dispense with the typical drummer jokes, as there can't be a more savvy drummer in the country, wrt the audio side of the equation. 

 

Thanks for taking the time, a wonderful read.

I'm down for a road trip.

 

+1 on all this. I would also like to hang. Gotta see Josh play them drums like a monster!

[Ricci]

FOH yeah more often than not it would be just the kick, but some of these "venues" have no subs to speak of and just mains or monitors so it would just be a distorted mess. We really have no clue what we may be walking into at any random venue! I kick a lot harder than most and mine is a 24x18 so it is loud enough to be heard in a small room though. 

[deepthoughts]

tuxedocivic, on 16 Apr 2013 - 2:03 PM, said:

 

So you think maybe my amp lost control an the cone bottomed. Wouldn't something need to drive the cone to the limit of the suspension? I don't have a good sense of the ins and outs of amplification. But it sounds pretty unanimous that what ever happened is the amps fault. I'll upgrade it as soon as I can and see what kind of improvement I get.

 

BTW, subwoofer trim was set to 0 and MV set to -13db when this happened. I thought I would have been ok. Even though that wasn't calibrated, I figured I was still a ways away from reference levels. But I suppose directing the bass from the other channels into the LFE can increase the subwoofer demand quite a bit.

While I see the original issue was resolved, as an FYI, if you have 2 boxes around or can series the drivers (if they currently aren't) when anyone encounters such a problem, you can always set up a less efficient load that can't be bottomed with the same power and run the same scene. If you get the same sound, you know its the amp. If not, then it's possible it's the driver complaining or the amp having different clipping behavior at low impedance.

[maxmercy]

That.....is a good idea.

 

JSS

[deepthoughts]

Ricci, interesting ... that sucks but thanks for sharing.

 

As you said, that's the way a well executed amp design should act; basically immune to whatever is thrown it's way. Yeah, it's a shame he got some bad coils (I immediately think of Kevin Haskins issues), but this may illustrate the difference between a small one man operation like AE, and other build houses that may uncover such failures prior to the drivers leaving the facility, via some type of simple sweeping, or full burn in. But I've really no idea how LF driver mfrs operate in this regard. I don't buy very many drivers, but I do know that the set of four Fi-IB3-18s I purchased, seemed as if they hadn't ever had any voltage swung thru them. The subtle scent during my own burn in was evidence, as was the incredible stiffness, thet really took some time to loosen up. So I've no idea what's the norm with either the small owner/operator businesses, or the big build houses.

 

Hi FOH,

 

The way such things typically work is that when an issue like this is discovered an inspection or process change is implemented to reduce the chance of it happening again.  Since John mentioned there are some visible indicators, they will likely start giving a quick visual inspection when received and before setting them up.  If something is suspect, they pull one and beat on it to check.

 

I've seen even Eminence have VC issues due to an out of spec machine.  Even with my own cabinet shop, they run a set of test cuts in a sample on the CNC before running a batch of miter folded cabinets to insure depth and other details are still in spec.  Not all take such extra steps, but those doing the most and the least volume tend to be the most on top of such things for simple economic reasons.  Small shops can't afford to be replacing 100pcs from a bad batch of parts when the majority of the cost is labor, and big shops have to catch errors before they copy an error 10,000 times.  Such process also comes from experience and time where having dealt with mistakes is the fastest way to learn to reduce their impact.

 

So far as I know, almost no driver build house does any sustained power testing.  They may test to a known excursion for rubs, buzzes or noises, but testing of duration really isn't practical unless you are at Skanning type prices.

 

Certain details like steel/gap dimensions and cone mass can be very consistent.  Voice coils and suspension stiffness have much wider variations.  Even trickier is that some parts like voice coils and spiders often are very precise within a batch, but can vary significantly one run to another.  Such variations are why driver development is best done looking at the determining parameters of Mmd, BL vs. Re and Cms.  Chasing exact matching T/S parameters will drive the anal retentive audiophile nuts.

 

-Mark

[Ricci]

John did test the woofers that I had with the bad coils. They operated seemingly fine with a simple free air tone test. I would not have known anything was wrong without capturing an impedance sweep prior to them burning up.

[tuxedocivic]

While I see the original issue was resolved, as an FYI, if you have 2 boxes around or can series the drivers (if they currently aren't) when anyone encounters such a problem, you can always set up a less efficient load that can't be bottomed with the same power and run the same scene. If you get the same sound, you know its the amp. If not, then it's possible it's the driver complaining or the amp having different clipping behavior at low impedance.

 

I'm not sure I follow. I have 4 subs. You're saying I could have wired them in series. Ok. Then when the problem occurs again...? I'm dense today, I'm sure this is a simple thing.

[deepthoughts]

I'm not sure I follow. I have 4 subs. You're saying I could have wired them in series. Ok. Then when the problem occurs again...? I'm dense today, I'm sure this is a simple thing.

Determine the level it makes the noise in original config.  Now wire 2 subs in series (or just switch drivers in the box from parallel to series).  You now are giving the drivers 1/4 the power.  If the clipping happens at the same level, it isn't the drivers, as the overload should happen at 6dB higher drive level while keeping the gains the same.  #troubleshooting 201

 

This and similar type of comparisons while changing the load and sensitivity allow you to see if you are running into current, Voltage or driver limits by way of relative comparison.  This is the type of troubleshooting that lets us determine when say a Dayton SA-1000 amp is going into current protection rather than input clipping as some blindly assumed.

[tuxedocivic]

Oh ok I see what you mean.

 

Wouldn't that be a much easier load (series, say 8ohms instead of 2) for the amp, so it might not clip. Which would then lead the troubleshooter to think the drivers did bottom when they were fed 4x power.

[maxmercy]

Amps clip at a certain voltage, so the amp should give out sooner than the Xmech/Xmax of the drivers

w/ the higher impedance load.

 

JSS

[tuxedocivic]

Ah, got it.