Damaging Your Expensive Ported Cab?

[Chienmortbb]

[quote name='Passinwind' timestamp='1481902298' post='3196148']
Yep. And as usual, there's no free lunch.
[/quote]Designing speaker cabinets is what I call squeezing a balloon. You squeeze out something you don't want and something else squeezes out somewhere else. Charlie (passinwind) has designed an HPF and we have had many happy hours emailing back and forth about it. The real issue with speakers like anything else in life is that whatever you do, the laws of physics apply. Any designer or manufacturer that says otherwise is either kidding himself, you or having his balloons squeezed by the Marketing department.

As for the HPFs built into most amps, they are not right for bass. Most PA amps have the HPF set too high and the HPF needs to have a very sharp slope to avoid affecting your bottom end. Let hope everything we open this Christmas is not like this thread (a can of worms).

[Chienmortbb]

[quote name='Bill Fitzmaurice' timestamp='1481925481' post='3196418']
For you to approach xlim with most drivers they'd sound really bad. It's ignoring the warnings of impending doom that often result in it.
[/quote]Bill at some gig volumes the death clank of the voice coil is lost amongst the general cacophony.

[Chienmortbb]

[quote name='Downdown' timestamp='1481918748' post='3196349']
Fair enough, but without going into the techie stuff, is it a real problem with ported cabs and if so why are there no warnings about it in the manuals - or have I missed them over the years?

Perhaps only some cabs are susceptible, but even so, I'd have thought that the ones that are would have a pretty clear warranty disclaimer in their manuals, as they do regarding power handling limits. I doubt I could return a cab under warranty if I'd blown a driver with too much power so why should blowing one by driving with too-low frequencies be any different?
[/quote]The problem is there are many problems associated with the super low frequencies. Phil has outlined the most extreme. That is where the speaker/cabinet combination is no longer under the control of the amplifier. It may be only in very extreme conditions that this is a real problem but it is a problem nonetheless. The other issues are, subsonics that steal you amplifier headroom, and a room boominess that you cannot dial out with EQ (although neither of these (except maybe excessive use of EQ) are damaging to the speaker).

[molan]

As a retailer I've been involved in the sale of a huge number of cabs from people including:

Aguilar
Bergantino
Hartke
Carvin
tks Engineering
MarkBass
Bag End
ATS
Gallien Krueger
Phil Jones
Warwick
Mesa
Genzler
Plus lots of other pre-owned cabs

The designs have been hugely varied with porting front & rear and fully enclosed cabs.

Prices have ranged from as low as about £50 up to £1,300.

In all this time, across all these products and all these price points and cabinet designs I can only ever remember one returned with a blown driver.

Maybe our customers don't push their cabs hard or maybe, with modern designs and construction, this isn't really much of an issue any more. . .

[bazzbass]

+1 for a HPF set at 30Hz or 40Hz

[Guest bassman7755]

[quote name='Phil Starr' timestamp='1481811037' post='3195341']
Nowadays it is rare to see any bass cab around that isn't ported, but they all have a basic flaw which isn't widely advertised. If you don't know about it then you could end up with a large repair bill.

Ported cabs for bass are generally tuned to 40, 50 or 60Hz , or somewhere in between. the way they work is simple. They are tuned to the frequency where the speaker starts to cut out as it's impedance rises. As the speaker cuts out it's output is replaced by the output from the port giving you very roughly a 3dB boost over the lowest octave. BUT you don't get something for nothing and the cost is what happens below 40Hz (or 50,60 or whatever, depending upon the make and model you use) .

Below the resonance of the port the port just becomes a big hole in the cab. Down to that frequency the air acts like a weight and damper on the cone, suddenly that is all removed and the cone is free to move with little resistance. as a result any signal below 40Hz is likely to make the cone move way beyond the limits the speaker is designed for, even with just a few watts going through the speaker. With the coil outside of the magnet it rapidly heats up and it may even start drumming on the back of the magnet, either way complete failure won't be far away.

Don't believe me? Try going to the Eminence website [url="http://www.eminence.com/pdf/Beta_12A-2_cab.pdf"]http://www.eminence....a_12A-2_cab.pdf[/url] and have a look at the designs they have for the Beta 12" speaker which is a 250W speaker. Have a look at the design for the large bass cab, they recommend only 75W into their 250W speaker and even so the graph shows the cone moving beyond its 4mm limit at 40Hz. this is a speaker widely used in Eminence equipped bass cabs.
[/quote]

Personally I always make sure there some sort of HPF in the signal chain (generally guilt into the power amp). As I've said many times in various posts, if you can see your speaker cone moving when you play as opposed to just going blurry then youve got a potentially speaker damaging subsonics problem.

Edited December 17, 2016 by bassman7755

[Phil Starr]

[quote name='alexclaber' timestamp='1481900888' post='3196140'] You can't filter out these frequencies with passive speaker level components, it has to be done at line level with active components. Most bass amps have some kind of high pass filtering and most power amps have switchable filters.
[/quote]

The trouble is that this information isn't shared by a lot of manufacturers or is buried in a lot of other information

[quote]The strange thing about this issue, is that the worst problems I've had with cone over-excursion were with cabs which were tuned to 31Hz, so you were never driving them with frequencies below the tuning frequencies. You'd think from reading Phil's original post (which is broadly correct) that these low tuned cabs could never suffer such problems. That experience set me down the road of finding out what really matters with the inputs bass guitar cabs can handle and also the sounds they're expected to generate. It's much more complicated than you think! [/quote]

That's fair comment, I've admitted up front that this is moderately complex and I'm avoiding being too technical so I am simplifying. Tuning to low frequencies does exactly what Alex says, with my own recent design lowering tuning sends excursion way up elsewhere and reduces power handling unacceptably in frequencies which a bass is much more likely to produce.

[Guest bassman7755]

[quote name='Downdown' timestamp='1481895423' post='3196063']
I'm struggling to understand all the details, but surely if a manufacturer designs a ported cab in which the driver could potentially be damaged by frequencies below x (or above y) then it would be sensible for the manufacturer to include the appropriate filters within the cab to ensure that these frequencies cannot be present at levels that could cause damage?
[/quote]

Its much more practical and efficient to do it in the amp, even if the speaker is able to handle subsonics the fact that the amp is producing them is probably seriously eating into the amps headroom.

Edited December 17, 2016 by bassman7755

[Passinwind]

[quote name='Chienmortbb' timestamp='1481925934' post='3196420']
Designing speaker cabinets is what I call squeezing a balloon. You squeeze out something you don't want and something else squeezes out somewhere else. Charlie (passinwind) has designed an HPF and we have had many happy hours emailing back and forth about it. [/quote]

Indeed, and I've now done several alternative versions. But for me the utility is more in tone control and feedback suppression than speaker protection.The cabs I use work just fine with my tube preamp that measures flat to 20Hz or so.

The generalizations about "typical" spectral content of bass signals are maybe open to further discussion. There are a ton of variables and I found little commonality as I measured more and more basses. The long thread on Talkbass quickly devolved in a very contentious affair. My current take: measure it yourself, draw your own conclusions, and don't assume.

[Bill Fitzmaurice]

[quote name='Passinwind' timestamp='1482001187' post='3196930']
The long thread on Talkbass quickly devolved in a very contentious affair.
[/quote]Doesn't everything? A goodly percentage of members there suffer from advanced cases of Dunning-Kruger effect.
[quote]Its much more practical and efficient to do it in the amp, even if the speaker is able to handle subsonics the fact that the amp is producing them is probably seriously eating into the amps headroom. [/quote]That fact isn't lost on amp designers, so most have low pass filtering in the pre-amp as part of the pre-voicing EQ. Where you're most likely to have an issue is with a separate pre-amp/power amp configuration, and then only if the pre-amp designer didn't high pass for whatever reason.

[Phil Starr]

[quote name='Bill Fitzmaurice' timestamp='1482005633' post='3196969']
Doesn't everything? A goodly percentage of members there suffer from advanced cases of Dunning-Kruger effect.
That fact isn't lost on amp designers, so most have low pass filtering in the pre-amp as part of the pre-voicing EQ. Where you're most likely to have an issue is with a separate pre-amp/power amp configuration, and then only if the pre-amp designer didn&'t high pass for whatever reason.
[/quote]

I had to look up Dunning -Kruger, part of the human condition I suspect

I think your point about the pre-power combination is really important. There are a few people out there using a PA power amp with some sort of pre. Most PA amps are engineered to be flat down to the limits of hearing sometimes with switchable filters. Often users are attracted by the almost unlimited power of the PA amps so they are using kilowatt amps which may go down to 20Hz with a pre amp which may have little or no filtering. Fine if you know your technical stuff but not safe for speakers if you don't.


I'm sure you are right about most bass amp designers being aware of the problem and having a little HPF intrinsic to their designs. Like most of us I've owned a series of amps, I always read the manuals and download them when I buy a used amp. I've never seen any information given on low frequency response given in the way it is routinely for hi fi and PA amps. It must be there as you say, otherwise we'd be seeing a lot more blown speakers but I couldn't tell you if there is any HPF filtering in my MB Tube or my Hartke for example.

Wouldn't it be great if all bass and pre amps came with a switchable filter?

[sratas]

Markbass uses a HPF in its line of amps, a gentle slope if 6 db/octave at a frequency well below 40 hz...the vast majority of manufacturers use HPFs, some don't. I'm not sure, but I guess some old fashioned tube amp may not use it, think about svt, bassman of old, maybe even contemporary

[Guest bassman7755]

[quote name='Phil Starr' timestamp='1482058061' post='3197209']
I think your point about the pre-power combination is really important. There are a few people out there using a PA power amp with some sort of pre. Most PA amps are engineered to be flat down to the limits of hearing sometimes with switchable filters. Often users are attracted by the almost unlimited power of the PA amps so they are using kilowatt amps which may go down to 20Hz with a pre amp which may have little or no filtering. Fine if you know your technical stuff but not safe for speakers if you don't.
[/quote]

The good thing about PA amps is that you have much more info available - frequency response, THD ratings, generally realistic power ratings (with certain notable exceptions) and what if any HPF is available. For the reasons you cite I'd never use a PA without a HPF for bass.

[quote name='Phil Starr' timestamp='1482058061' post='3197209']
I couldn't tell you if there is any HPF filtering in my MB Tube or my Hartke for example.
[/quote]

Place a finger on a string over the pickup and push it towards the pickup, if you can see the speaker cone move in sympathy then you definitely have no HPF.

[Beer of the Bass]

[quote name='bassman7755' timestamp='1482061481' post='3197252']

Place a finger on a string over the pickup and push it towards the pickup, if you can see the speaker cone move in sympathy then you definitely have no HPF.
[/quote]

I have never seen this happen on a bass guitar with magnetic pickups - I'm not sure that most pickups go low enough for it to be a useful test, but I have observed it when using a piezo bridge pickup on double bass with certain amps. Going by visible cone movement with double bass, it would appear that my GK MB200 does have some form of subsonic filtering going on, but it would be nice if the manual mentioned this.

[Chienmortbb]

[quote name='sratas' timestamp='1482059210' post='3197225']
Markbass uses a HPF in its line of amps, a gentle slope if 6 db/octave at a frequency well below 40 hz...the vast majority of manufacturers use HPFs, some don't. I'm not sure, but I guess some old fashioned tube amp may not use it, think about svt, bassman of old, maybe even contemporary
[/quote]6dB per octave below 40 Hz is as much use as a trap door in a canoe.

As for the old (thermionic) valve amps, the output transformer cost and size rises almost exponentially with low frequency response. The transformer itself will limit low frequency output, and the inherent compression of a valve output stage will also help.

As for a previous comment about guitar speakers, this has almost become thing of the past as the old 25W speakers used in the 60s have been replaced by higher powered speakers.

I could build a shed from the chassis log Goodmans, Celestion, Fane and Jenson speakers I have replaced in my early days as a guitard.

Edited December 18, 2016 by Chienmortbb

[sratas]

[quote name='Chienmortbb' timestamp='1482066708' post='3197307']
6dB per octave below 40 Hz is as much use as a trap door in a canoe.
[/quote]


now that you made me think about it more, i may be wrong...somewhere in my mail there is the conversation between me and a Markbass engineer, where he (or she) refuses to confirm the technical details of the built in HPF, but he admitted that an HPF was used in every amp. I may be wrong in the details, like the slope, it could be 12 db/octave, it was long time ago. 12db/octave is not much more, in fact, but not lacking too.

Anyway, with my markbass, now sold because in my opinion it sucked, I used my micro thumpinator with great results. I use it with other amps as well, but the thumpinator is conceived to be much more radical in the cut action below 30 Hz.

[pete.young]

I said earlier that I use a Thumpinator, but I've just remembered that the Ac Bs Pre preamp in the Zoom range (B3, MS-60B and B1on) can be used as a HPF.

[Balcro]

I think I can see an additional function here for my cheapo but worthy Behringer BEQ-700 graphic equalizer (A Boss GEB-7 clone) . I bought it last Christmas for the fun of it and hovered back & forth for days between it and the Caline CP-24 (a clone of MXR 108 10 band equaliser). In the current discussion I would have been better off buying the Caline (circa £30), but since I only play in "the den" I saved about £12.

The Behringer and the Boss have a cut & boost slider centred on 50Hz. With full cut, that will take out some of the electronic low level nasties between 40-60Hz and will probably make for a crisper sound without sounding tonally much different. The MXR and the Caline have 31.25Hz (that 0.25 of Hz is so important) slider, so at full-cut will possibly remove 10-12 dB of electronic & acoustic rumble between 20 & 40Hz. That's much more effective and a possible speaker saver. It would also seem to make sense if the equaliser were first in the pedal or rack-mount chain. Clean-in, clean out.

That's all good but there may be more. After searching on "Microthumpinator" and "Fdeck" I read (in the other place) an interesting observation from a Mike Arnopol -

"Put in the HPF (High Pass Filter) and dialed it up at the highest setting. The clack was gone. As I expected, but so was the low bass. Kept dialing it down. I wasn't a whole lot past the lowest setting when I didn't really notice the missing bass. But no more voice coil smack. The interesting thing---the C8 actually got LOUDER. I think it was because I was no longer using my amp's recources amplifying crap I didn't want to amplify anyways. The C8 as well as the 88 go substantially louder with the HPF. Substantially louder."


PS. Search for "Behringer" directs you to "music-group.com", but click on the links & Norton Security pops up with a warning of an unsafe site!! The detail indicates there's a Trojan in the "downloads" section?!

[Chienmortbb]

The canoe remark was a bit off but you do need a very steep cutoff to avoid cutting wanted frequencies.

In my opinion at least 18dB per octave and I prefer 24dB from about 35Hz. If you play a 5 you may want to go to 30 but for most useable bass speakers there is little output that low anyway.

Edited December 18, 2016 by Chienmortbb

[Bill Fitzmaurice]

[quote name='sratas' timestamp='1482059210' post='3197225']
Markbass uses a HPF in its line of amps, a gentle slope if 6 db/octave at a frequency well below 40 hz...the vast majority of manufacturers use HPFs, some don't. I'm not sure, but I guess some old fashioned tube amp may not use it, think about svt, bassman of old, maybe even contemporary
[/quote]Strictly speaking virtually all pre-amp cicuits, valve or SS, incorporate high pass filtering. The most common form of a high pass filter is a series capacitor, and every amp configuration that I'm aware uses series capacitors between stages, so it's not like a designer has to add anything to the circuit, by default it's already there. All one has to do to realize a desired high pass knee is to use the correct cap value. As for achieving more than a 6dB slope, which is what you get from a single cap, since there are series caps between each amp stage every one of them can be configured as a high pass, and their slopes are cumulative. Where valves are concerned they add another source of high passing via the output transformers. Fender in particular was well known for cost cutting wherever possible, and they did so with their output transformers. They never could have gotten away with the output transformers they used in the hi-fi world, where 20Hz response was demanded, but they can, did and do get away with them in musical instrument amps.

[Chienmortbb]

[quote name='Balcro' timestamp='1482069883' post='3197339']
I think I can see an additional function here for my cheapo but worthy Behringer BEQ-700 graphic equalizer (A Boss GEB-7 clone) . I bought it last Christmas for the fun of it and hovered back & forth for days between it and the Caline CP-24 (a clone of MXR 108 10 band equaliser). In the current discussion I would have been better off buying the Caline (circa £30), but since I only play in "the den" I saved about £12.

The Behringer and the Boss have a cut & boost slider centred on 50Hz. With full cut, that will take out some of the electronic low level nasties between 40-60Hz and will probably make for a crisper sound without sounding tonally much different. The MXR and the Caline have 31.25Hz (that 0.25 of Hz is so important) slider, so at full-cut will possibly remove 10-12 dB of electronic & acoustic rumble between 20 & 40Hz. That's much more effective and a possible speaker saver. It would also seem to make sense if the equaliser were first in the pedal or rack-mount chain. Clean-in, clean out.

That's all good but there may be more. After searching on "Microthumpinator" and "Fdeck" I read (in the other place) an interesting observation from a Mike Arnopol -

"Put in the HPF (High Pass Filter) and dialed it up at the highest setting. The clack was gone. As I expected, but so was the low bass. Kept dialing it down. I wasn't a whole lot past the lowest setting when I didn't really notice the missing bass. But no more voice coil smack. The interesting thing---the C8 actually got LOUDER. I think it was because I was no longer using my amp's recources amplifying crap I didn't want to amplify anyways. The C8 as well as the 88 go substantially louder with the HPF. Substantially louder."


PS. Search for "Behringer" directs you to "music-group.com", but click on the links & Norton Security pops up with a warning of an unsafe site!! The detail indicates there's a Trojan in the "downloads" section?!
[/quote]Mike knows a thing or two about speakers and he is right about the HPF. That is why I prefer a variable and switchable one.

Mike's describes just why an HPF is important and it has the added benefit of protecting the speaker and probably reducing power compression.

[Guest bassman7755]

[quote name='Beer of the Bass' timestamp='1482062577' post='3197264']
I have never seen this happen on a bass guitar with magnetic pickups
[/quote]

When I used a separates rig I could do this on my status when the HPF was disengaged. Being an inductor, a magnetic pickup acts as a LPF not a HPF, lows are more likely to be filtered by the preamp input capacitance. Your right though that its a negative test rather than a positive one in that it can prove the absence of a HPF but not the presence of one .. if this does happen though youve definitely got a problem.

Edited December 18, 2016 by bassman7755

[Beer of the Bass]

[quote name='bassman7755' timestamp='1482074018' post='3197394']


When I used a separates rig I could do this on my status when the HPF was disengaged. Being an inductor, a magnetic pickup acts as a LPF not a HPF, lows are more likely to be filtered by the preamp input capacitance. Your right though that its a negative test rather than a positive one in that it can prove the absence of a HPF but not the presence of one .. if this does happen though youve definitely got a problem.
[/quote]

I've seen some sources suggesting that a magnetic pickup has something closer to a bandpass response due to the capacitance of the coil, albeit with a much steeper slope on the high end than on the low. I've mostly had high impedance pickups similar to Fender types, and amps of no more than 300 watts, so I suppose it's not surprising that a different style of pickup through a more powerful amp might produce enough subsonic content to observe this effect. But a double bass bridge piezo did have enough subsonic response for me to push on the strings and watch the cone move if I turned off the HPF on my old Acoustic Image amp.

[Phil Starr]

First of all thanks to so many people for adding to this thread and being so constructive. I hope people are enjoying it and finding it informative.

I'm going to throw in another issue. the positioning of the pickup. The only place on the string which shows the full movement of the fundamental (deepest) note is at the 12th fret. Nearer the bridge you get more of the harmonics which is why bridge pups are always less bassy than neck pups. Somebody has just put up a link to an app that models this. you can move the position of the pup and see how this affects the output of the pup. I'm pretty sure the app doesn't allow for any frequency irregularities in the pup.

Set the neck to 34", the string frequency to 31 ( and the pup position to 17" (yes I know that's in the middle of the neck) now slide it down to a practical 6" position and you can see the bass output drop off. That's showing a significant drop in output of the deepest note. 3db drop means half the excursion.

[quote name='ikay' timestamp='1482356646' post='3199907']
Pickup position is a significant factor as well. Have a play with this app and test a few positions and multiple pickup combinations etc. Switch on the 'fundamental frequency marker' as a reference point.
[url="http://www.till.com/articles/PickupResponseDemo/index.html"]http://www.till.com/...Demo/index.html[/url]
[/quote]

[LukeFRC]

[quote name='Bill Fitzmaurice' timestamp='1482005633' post='3196969']
Doesn't everything? A goodly percentage of members there suffer from advanced cases of Dunning-Kruger effect.

That fact isn't lost on amp designers, so most have low pass filtering in the pre-amp as part of the pre-voicing EQ. Where you're most likely to have an issue is with a separate pre-amp/power amp configuration, and then only if the pre-amp designer didn't high pass for whatever reason.
[/quote]

Part of the problem is that there's a large amount of bass players who think the answer is more bass.
I play at a church, big stone building, modern glass wall at the back and massive resonance down low. We have no backlineand a IEM system and the FOH.
PA folk often end up with a massive mush in the bottom end. Its taken me a year and demonstrating that turning on the desk's HPF on the bass guitar cleans up the sound no end. I only have to suggest they do the same on the acousitic guitars, keys and kick drum and we may one day get it sounding good!