Jump to content


Damaging Your Expensive Ported Cab?


78 replies to this topic

#31 bassman7755

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,688 posts
  • Gender:Male
  • Location:Swindon
  • Interests:Heavy rock, russian language, computers/software, exotic sports cars

Posted 17 December 2016 - 10:58 AM

View PostPhil Starr, on 15 December 2016 - 02:10 PM, said:

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 http://www.eminence....a_12A-2_cab.pdf 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.

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 by bassman7755, 17 December 2016 - 10:59 AM.


#32 Phil Starr

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,990 posts
  • Gender:Male
  • Location:Chard,Somerset

Posted 17 December 2016 - 11:04 AM

View Postalexclaber, on 16 December 2016 - 03:08 PM, said:

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.

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!

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.

#33 bassman7755

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,688 posts
  • Gender:Male
  • Location:Swindon
  • Interests:Heavy rock, russian language, computers/software, exotic sports cars

Posted 17 December 2016 - 11:06 AM

View PostDowndown, on 16 December 2016 - 01:37 PM, said:

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?

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 by bassman7755, 17 December 2016 - 11:08 AM.


#34 Passinwind

    Fully fledged member

  • Members
  • PipPipPip
  • 343 posts
  • Gender:Male
  • Location:Columbia River Gorge, Washington, USA

Posted 17 December 2016 - 06:59 PM

View PostChienmortbb, on 16 December 2016 - 10:05 PM, said:

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.

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. Posted Image
--Charlie Escher

#35 Bill Fitzmaurice

    Hyper elite member

  • Members
  • PipPipPipPipPip
  • 2,225 posts
  • Gender:Male
  • Location:New Hampshire US

Posted 17 December 2016 - 08:13 PM

View PostPassinwind, on 17 December 2016 - 06:59 PM, said:

The long thread on Talkbass quickly devolved in a very contentious affair.
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.
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.
The laws of physics aren't swayed by opinion.
www.billfitzmaurice.com
www.billfitzmaurice.info/forum

#36 Phil Starr

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,990 posts
  • Gender:Male
  • Location:Chard,Somerset

Posted 18 December 2016 - 10:47 AM

Quote

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.

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?

#37 sratas

    No longer a newbie

  • Members
  • PipPip
  • 34 posts
  • Gender:Male

Posted 18 December 2016 - 11:06 AM

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

#38 bassman7755

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,688 posts
  • Gender:Male
  • Location:Swindon
  • Interests:Heavy rock, russian language, computers/software, exotic sports cars

Posted 18 December 2016 - 11:44 AM

View PostPhil Starr, on 18 December 2016 - 10:47 AM, said:

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.

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.

View PostPhil Starr, on 18 December 2016 - 10:47 AM, said:

I couldn't tell you if there is any HPF filtering in my MB Tube or my Hartke for example.

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.

#39 Beer of the Bass

    I ought to be practicing really...

  • Members
  • PipPipPipPipPip
  • 2,976 posts
  • Gender:Male
  • Location:edinburgh

Posted 18 December 2016 - 12:02 PM

View Postbassman7755, on 18 December 2016 - 11:44 AM, said:


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.

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.

#40 Chienmortbb

    Fully fledged member

  • Members
  • PipPipPip
  • 726 posts
  • Gender:Male
  • Location:Poole, Dorset

Posted 18 December 2016 - 01:11 PM

View Postsratas, on 18 December 2016 - 11:06 AM, said:

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
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 by Chienmortbb, 18 December 2016 - 01:23 PM.


#41 sratas

    No longer a newbie

  • Members
  • PipPip
  • 34 posts
  • Gender:Male

Posted 18 December 2016 - 01:22 PM

View PostChienmortbb, on 18 December 2016 - 01:11 PM, said:

6dB per octave below 40 Hz is as much use as a trap door in a canoe.


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.

#42 pete.young

    Hyper elite member

  • Members
  • PipPipPipPipPip
  • 2,818 posts
  • Gender:Male
  • Location:Ipswich

Posted 18 December 2016 - 01:47 PM

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.
Feedback: http://basschat.co.u...-for-peteyoung/
"Just another crouton, floating on the bouillabaisse of life"

#43 Balcro

    Fully fledged member

  • Members
  • PipPipPip
  • 610 posts
  • Gender:Male
  • Location:Stevenage, Hertfordshire

Posted 18 December 2016 - 02:04 PM

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?!

#44 Chienmortbb

    Fully fledged member

  • Members
  • PipPipPip
  • 726 posts
  • Gender:Male
  • Location:Poole, Dorset

Posted 18 December 2016 - 02:13 PM

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 by Chienmortbb, 18 December 2016 - 02:15 PM.


#45 Bill Fitzmaurice

    Hyper elite member

  • Members
  • PipPipPipPipPip
  • 2,225 posts
  • Gender:Male
  • Location:New Hampshire US

Posted 18 December 2016 - 02:15 PM

View Postsratas, on 18 December 2016 - 11:06 AM, said:

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
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.
The laws of physics aren't swayed by opinion.
www.billfitzmaurice.com
www.billfitzmaurice.info/forum

#46 Chienmortbb

    Fully fledged member

  • Members
  • PipPipPip
  • 726 posts
  • Gender:Male
  • Location:Poole, Dorset

Posted 18 December 2016 - 02:19 PM

View PostBalcro, on 18 December 2016 - 02:04 PM, said:

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?!
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.

#47 bassman7755

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,688 posts
  • Gender:Male
  • Location:Swindon
  • Interests:Heavy rock, russian language, computers/software, exotic sports cars

Posted 18 December 2016 - 03:13 PM

View PostBeer of the Bass, on 18 December 2016 - 12:02 PM, said:

I have never seen this happen on a bass guitar with magnetic pickups

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 by bassman7755, 18 December 2016 - 03:14 PM.


#48 Beer of the Bass

    I ought to be practicing really...

  • Members
  • PipPipPipPipPip
  • 2,976 posts
  • Gender:Male
  • Location:edinburgh

Posted 18 December 2016 - 04:31 PM

View Postbassman7755, on 18 December 2016 - 03:13 PM, said:



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.

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.

#49 Phil Starr

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,990 posts
  • Gender:Male
  • Location:Chard,Somerset

Posted 22 December 2016 - 08:49 AM

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 (B) 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.

View Postikay, on 21 December 2016 - 09:44 PM, said:

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.
http://www.till.com/...Demo/index.html


#50 LukeFRC

    Needs to get out more

  • Members
  • PipPipPipPipPipPipPipPipPip
  • 6,769 posts
  • Gender:Male
  • Location:Leeds

Posted 22 December 2016 - 10:31 AM

View PostBill Fitzmaurice, on 17 December 2016 - 08:13 PM, said:

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.

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!

'91 Streamer
'85 Thumb
Mesa Walkabout


feedback


#51 Dan Dare

    Fully fledged member

  • Members
  • PipPipPip
  • 756 posts
  • Gender:Male
  • Location:The Smoke
  • Interests:Music, Watersports, Bikes, Beer

Posted 23 December 2016 - 10:14 PM

View PostLukeFRC, on 22 December 2016 - 10:31 AM, said:



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!

+1 Luke. Relatively few appear to realise that less often equals subjectively more when dealing with low frequencies. Quantity vs quality and all that. And as others say, little point in wasting amp headroom on subsonic mush/rumble.
Not getting any younger

#52 Chienmortbb

    Fully fledged member

  • Members
  • PipPipPip
  • 726 posts
  • Gender:Male
  • Location:Poole, Dorset

Posted 11 January 2017 - 03:15 PM

I have just done a plot of the cone excursion of a well known, well loved driver the Eminence Kappalite 3012HO. The box is 50L and the tuning frequency is 50Hz

The power is 400 watts, the stated power of the 3012HO. The red line is Xmax, the maximum excursion at which the voice coil is under the influence of the magnet. It is not dangerous to exceed XMax by a small amount. However the Xlim or XDamage (12.5mm) , the point at which the voice coil is in danger, is exceed at 36.7Hz, 5 Hz above low B on a 5 string. Indeed you have to reduce the power at 31Hz to under 200W to avoid exceeding XDamage.
Posted ImageKappalite3012HO Cone excursion 400W by chienmortbb, on Flickr

Edited by Chienmortbb, 11 January 2017 - 03:32 PM.


#53 lowhand_mike

    general whipping boy

  • Members
  • PipPipPipPip
  • 1,405 posts
  • Gender:Male
  • Location:bexleyheath, sort of sarf eeest larndarn

Posted 11 January 2017 - 08:01 PM

ow my head :blink:

interesting read though even if i dont understand some of it
https://soundcloud.com/the-misguided

Ibanez SR1805 NTF
Ibanez SR500
Ashdown Rootmaster RM 800
Ashdown Mag 300 EvoIII head (poorly)
Ashdown Mag 4x10 deep cab

"Its ham and eggs, we could have ham and eggs if we had some eggs. If only we had some ham."

#54 Phil Starr

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,990 posts
  • Gender:Male
  • Location:Chard,Somerset

Posted 12 January 2017 - 09:34 AM

View PostChienmortbb, on 11 January 2017 - 03:15 PM, said:

I have just done a plot of the cone excursion of a well known, well loved driver the Eminence Kappalite 3012HO. The box is 50L and the tuning frequency is 50Hz

The power is 400 watts, the stated power of the 3012HO. The red line is Xmax, the maximum excursion at which the voice coil is under the influence of the magnet. It is not dangerous to exceed XMax by a small amount. However the Xlim or XDamage (12.5mm) , the point at which the voice coil is in danger, is exceed at 36.7Hz, 5 Hz above low B on a 5 string. Indeed you have to reduce the power at 31Hz to under 200W to avoid exceeding XDamage.
Posted ImageKappalite3012HO Cone excursion 400W by chienmortbb, on Flickr
Thanks for putting this up. The point for those that don't know about all this is that the curve is the same for all speakers in a tuned cab. Excursion rises steadily as the frequency falls but the tuning of the cab dampens the cone movement at the tuning frequency. You can see the dip in excursion at 50hz really clearly on the graph. At this point the port is doing all the work and the cone movement is damped because it is working hard to pump air through the port.

The Kappalite was chosen because it is about as good as a driver gets, and has been recommended by several designers or used in their cabs. There's every chance your speaker wont behave as well unless you use very expensive cabs.

Now moving beyond Xmax/the speakers limiting point doesn't mean instant destruction any more than running a cars revs into the red means the engine will blow up. It does mean you are taking a risk though. What happens next depends upon the exact circumstances but at this point the built in safety designs aren't necessarily going to protect you, and there is no red light on most speakers.

More later, I have to practice :)

#55 MoonBassAlpha

    Hyper elite member

  • Members
  • PipPipPipPipPip
  • 2,234 posts
  • Gender:Male
  • Location:Didcot, Oxfordshire
  • Interests:Bass, Guitar, Drums (a bit), Squash

Posted 12 January 2017 - 01:57 PM

Does anyone know if the Genz Shuttle 3.0 AND 6.0 have h.p. filtering, and if so, at what slope?
Cheers, MBA
U.S. Masters EP42 trans blue-- U.S. Masters EP42 lacewood fretless-- Sei Flamboyant headless 4
Genz-Benz Shuttle3.0 & Shuttle6.0--Ashdown CTM15 - Barefaced Super Midget G3, Midget G2-- 1x12 cab with EVM12L-- 1x10 baby cab with Celestion BN200-10X

My feedback Music by Charms Against The Evil Eye: https://soundcloud.com/the-new-moon
For sale: Celestion Greenbacks

#56 Passinwind

    Fully fledged member

  • Members
  • PipPipPip
  • 343 posts
  • Gender:Male
  • Location:Columbia River Gorge, Washington, USA

Posted 12 January 2017 - 03:50 PM

View PostMoonBassAlpha, on 12 January 2017 - 01:57 PM, said:

Does anyone know if the Genz Shuttle 3.0 AND 6.0 have h.p. filtering, and if so, at what slope?
Cheers, MBA

They have quite a bit (more than I like TBH) but I've never measured the exact response, which probably changes quite a bit depending on settings, as many amps do.
--Charlie Escher

#57 Lw.

    Fully fledged member

  • Members
  • PipPipPip
  • 845 posts
  • Gender:Male
  • Location:Reading
  • Interests:Basses & Bikes.

Posted 12 January 2017 - 04:16 PM

Whilst the numbers & that graph look great - I don't understand what any of it means. So - are we damaging our expensive ported cabs or not?

#58 Bill Fitzmaurice

    Hyper elite member

  • Members
  • PipPipPipPipPip
  • 2,225 posts
  • Gender:Male
  • Location:New Hampshire US

Posted 12 January 2017 - 05:42 PM

View PostLw., on 12 January 2017 - 04:16 PM, said:

So - are we damaging our expensive ported cabs or not?
When's the last time you had to replace a driver due to mechanical damage?
The laws of physics aren't swayed by opinion.
www.billfitzmaurice.com
www.billfitzmaurice.info/forum

#59 Beer of the Bass

    I ought to be practicing really...

  • Members
  • PipPipPipPipPip
  • 2,976 posts
  • Gender:Male
  • Location:edinburgh

Posted 12 January 2017 - 09:42 PM

View PostBill Fitzmaurice, on 12 January 2017 - 05:42 PM, said:

When's the last time you had to replace a driver due to mechanical damage?

While I've never had to replace one myself, I've played a lot of rehearsal room or venue house rigs with damaged drivers, presumably from over-excursion. It either shows up as individual dead drivers in a multi-driver cab, or just that distorted voice coil rub kind of sound. Sometimes that's from outright abuse, sometimes it's from simply not having enough rig for the room and running it night after night, but someone out there is doing it.

Edited by Beer of the Bass, 12 January 2017 - 09:43 PM.


#60 Phil Starr

    Very Advanced Member

  • Members
  • PipPipPipPip
  • 1,990 posts
  • Gender:Male
  • Location:Chard,Somerset

Posted 13 January 2017 - 08:56 AM

View PostLw., on 12 January 2017 - 04:16 PM, said:

Whilst the numbers & that graph look great - I don't understand what any of it means. So - are we damaging our expensive ported cabs or not?

That deserves a serious answer.

This was the whole reason I started this thread. Some people are damaging speakers, usually people who can ill afford it, others are using their gear well within their limits and won't ever have a problem. Some of us probably sail nearer the wind more than is sensible but get away with it. We get quite a few questions on BC about matching amps to cabs and sometimes the advice is better than others. There is an inherent problem with all ported cabs and most bassists will be unaware of it. If you know the problem of subsonic over excursion is there then it's easy enough to avoid. Basschat discussions tend to be pretty measured and by sharing information most people on here get to know their technical side pretty well. As a result the advice newbies get on BC is usually pretty spot on. Simply if there is a point beyond which you shouldn't go it is better to know where it is.

It's also true that an educated customer will ask questions when making purchases and the makes manufacturers cough up more information about the design compromises they inevitably make. I'm sure the whole lightweight movement has been sped up by BassChat and TalkBass. Wouldn't it be great if amp manufacturers published details of any high pass filtering in their manuals and then started making a feature of it. That'll only become a selling point if we all start asking questions.

So, the simple answer is a few people are blowing cabs, but it is easily avoided if you know what you are doing. I'd be pretty happy if I thought even half a dozen people avoided the heartbreak of a blown speaker as a result.





1 user(s) are reading this topic

0 members, 1 guests, 0 anonymous users