dannybuoy Posted February 27, 2011 Share Posted February 27, 2011 I've heard on numerous occasions that valve amps 'like' sealed cabs. Why is this? Do valve amps behave differently when connected to sealed/ported cabs? Just investigating new cab options to go with an AD200B and slightly less extended lows traded in for a more punchy vintage tone sounds good to me. I've played through the Orange OBC410 and like it, it has a horn but doesn't sound too harsh when using fuzz. I think I would really prefer no horn though, or at least have a switch that defeated the entire crossover circuit and not just turn the horn off. Guess you could always mod one! The other option I was looking at is a Marshall VBC412, there are couple going for stupidly low prices at the moment... There's also the Berg NV series which I'd love but they are rather pricey. Any others out there I should know about? Quote Link to comment Share on other sites More sharing options...
Chimike Posted February 27, 2011 Share Posted February 27, 2011 Hiya, Trace Elliot did a great 4 x 12 sealed cab, to go with their Valve series amps. Superb sound, and go for peanuts ! Did one without a tweeter, Heavy cabs, though . Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted February 27, 2011 Share Posted February 27, 2011 I think the low end roll off on sealed cabs is the main thing valve amps 'like', but there is probably some impedance thing too that I don't understand yet (see other thread discussing impedance curves). You can get some messyness in the bottom end of some valve amps, that a sealed cab will clear up or something, not something I've experienced, been happily using ported cabs with valve amps, I don't really think it is an issue with well designed cabs, I suspect it is the 'boomy' cab tuned too high that gets loads worse with the valve amp's drive meaning a lot of content in that area. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 27, 2011 Share Posted February 27, 2011 [quote name='dannybuoy' post='1143155' date='Feb 27 2011, 06:37 AM']I've heard on numerous occasions that valve amps 'like' sealed cabs. Why is this? Do valve amps behave differently when connected to sealed/ported cabs?[/quote]It's not the sealed cab per se, it's the high Q drivers used in them. The result is a lower peak impedance than low Q drivers in vented boxes, which keeps the circuits happy. From a response aspect a high Q sealed cab tends to be more sensitive in the midbass than a vented cab, and that makes the rig subjectively sound louder, a plus with the generally lower power of valve amps. A very high Q speaker is how one can gig with 25-35 watt Ampeg Portaflexes. The downside to high Q sealed cabs is a thin low end compared to vented cabs. Quote Link to comment Share on other sites More sharing options...
dannybuoy Posted February 27, 2011 Author Share Posted February 27, 2011 Thanks for the explanation Bill! Quote Link to comment Share on other sites More sharing options...
alhbass Posted February 27, 2011 Share Posted February 27, 2011 [quote name='Chimike' post='1143250' date='Feb 27 2011, 01:07 PM']Hiya, Trace Elliot did a great 4 x 12 sealed cab, to go with their Valve series amps. Superb sound, and go for peanuts ! Did one without a tweeter, Heavy cabs, though .[/quote] They did indeed. And they did, indeed, sound superb.. And yes, I did indeed let mine go for peanuts - I'm not going to admit for exactly how little because it's embarassing. Here is pic of the pair I had - one with and one without tweeter.. I loved standing in front of these. But I didn't love getting them to gigs on anything other than the ground floor. I still miss them - but then remind myself about how easy gigging life is now, with a Markbass NY604 in each hand! Quote Link to comment Share on other sites More sharing options...
chris_b Posted February 27, 2011 Share Posted February 27, 2011 [quote name='alhbass' post='1143430' date='Feb 27 2011, 03:43 PM']....Here is pic of the pair I had.... [/quote] Are you trying to keep the bailiffs out? Quote Link to comment Share on other sites More sharing options...
Lozz196 Posted February 27, 2011 Share Posted February 27, 2011 I think any bailiff that could move that lot - well give them whatever they want! Quote Link to comment Share on other sites More sharing options...
dannybuoy Posted March 1, 2011 Author Share Posted March 1, 2011 So, for old skool sound that won't break my back, how about a pair of Ampeg SVT 210 AV cabs side by side supporting my tube head? Sounds good in theory... Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted March 1, 2011 Share Posted March 1, 2011 [quote name='dannybuoy' post='1146245' date='Mar 1 2011, 07:05 PM']So, for old skool sound that won't break my back, how about a pair of Ampeg SVT 210 AV cabs side by side supporting my tube head? Sounds good in theory...[/quote] Stacked so all speakers in a row is better. Quote Link to comment Share on other sites More sharing options...
dannybuoy Posted March 1, 2011 Author Share Posted March 1, 2011 I know, but with an AD200B perched on top? I don't think so! Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted March 1, 2011 Share Posted March 1, 2011 [quote name='dannybuoy' post='1146355' date='Mar 1 2011, 08:23 PM']I know, but with an AD200B perched on top? I don't think so![/quote] Just put it somewhere else. The purpose of cabs is to put sound into a room first, amp stand second. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted March 2, 2011 Share Posted March 2, 2011 [quote name='Mr. Foxen' post='1146515' date='Mar 1 2011, 05:19 PM']Just put it somewhere else. The purpose of cabs is to put sound into a room first, amp stand second.[/quote] +1. Worrying more about how the rig looks or stacks instead of how it sounds should be left to guitar'd players. Quote Link to comment Share on other sites More sharing options...
Lfalex v1.1 Posted March 2, 2011 Share Posted March 2, 2011 [quote name='Mr. Foxen' post='1146515' date='Mar 1 2011, 10:19 PM']Just put it somewhere else. The purpose of cabs is to put sound into a room first, amp stand second.[/quote] [quote name='Bill Fitzmaurice' post='1146681' date='Mar 2 2011, 03:19 AM']+1. Worrying more about how the rig looks or stacks instead of how it sounds should be left to guitar'd players.[/quote] Amen, brethren! Longer speaker cable/s is all you need... Another factor to consider with valve amps/ ported cabinets may be the way in which the system behaves as it reaches its resonant frequency and (shortly thereafter) LF extension limit. There may be a peakier modulus of impedance (how impedance varies with frequency) than a sealed system. A smoother modulus of impedance would be kinder to a valve amp - fewer/less dramatic changes in current demands from the output tubes. Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted March 5, 2011 Share Posted March 5, 2011 firstly I don't believe this to be a universal truth, I am sure a lot of valve amps work perfectly happily with a lot of ported speakers. If there is a grain of truth in this I would suspect the interaction between the amp and speaker at low frequencies. The underlying reason for the impedance changes in the post above is that the speaker creates electrical currents as it moves in the magnetic field, these are in the opposite direction to the original signal. The biggest back EMF is created in a sealed cab at the bottom resonance but the sealed air in the cab controls the movement of the cone and hence the back EMF below resonance, in a ported cab the resonance peak is reduced but there is very little to control the movement of the cone below resonance and the back EMF can be quite large. Solid state amps differ from valve amps in three ways which would interact with this back emf. They usually have much larger amounts of negative feedback designed into the circuits which (sort of) compares the output of the amp with the input and corrects for any distortions. Secondly they usually have lower output impedances than valve amps and hence better damping factors. Thirdly the output transformers of valve amps are going to react in a fairly complex way with the back emf which will already be out of phase with the signal. A lot of this can be got rid of by filtering subsonic signals and most amps do this either by accident or design anyway. At a practical level this is not something I would worry about. Your ears will tell you if a particular amp and speaker work well together. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted March 5, 2011 Share Posted March 5, 2011 [quote name='Phil Starr' post='1150718' date='Mar 5 2011, 11:56 AM']firstly I don't believe this to be a universal truth, I am sure a lot of valve amps work perfectly happily with a lot of ported speakers. If there is a grain of truth in this I would suspect the interaction between the amp and speaker at low frequencies.[/quote] This impedance chart shows a vented low Qts ten loaded cab, the red trace, versus a sealed high Qts ten loaded cab, the green trace. Both are 8 ohm rated cabs. Believe what you will, but the red trace is a very unhealthy load for a valve amp, and cabs of this sort are well known to blow valves and output transformers. That's not to say that all valve amps and low Qts vented cabs don't get along, but when's the last time you saw a manufacturer post an impedance chart? Quote Link to comment Share on other sites More sharing options...
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