sreten,
Thanks again. It's nice to have someone to bounce ideas off of. My wife has zero patience for this kind of thing. 🙂 And it's educational for me, too. Socratic method and all that.
Yes it is much bigger than it needs to be to fit the speakers. This is not just to be an amp stack, it's going to be a piece of furniture and there are certain functional and aesthetic choices I'm making in addition to making a good guitar tone. The height of the cabinet will put the combo at a convenient height to reach the knobs. Also, when I'm sitting, it'll put the combo speakers at about ear level. The width will make it a couple inches wider than the combo. Depending on the size of the speakers I get, I may be able to shrink this dimension by a couple inches. I'm attaching a picture of my sort-of-to-scale drawing to give an idea of what I'm aiming for at this point.
I do understand that a baffle or frame member that is too long/large, may resonate sympathetically with the driver causing unappealing "boominess" at certain frequencies. If I run into this, I will add some bracing to damp that resonance.
If I really need to, I can always cut it apart and rebuild everything smaller. That's no big deal. I like tinkering.
These are the parameters I've been trying to match when I look at hi fi drivers, and I figure since guitar speakers with Qts around 1 can be used in either a closed or open back cabinet, the same should apply to a hifi driver with Qts around 1. But I admit, my analysis here may be lacking some important details.
Regardless, it's really easy to swap (for example) a 2/3 open partial panel to a fully closed back to a 1/3 open oval cutout back etc. That's the easiest thing to change so I'll probably play around with it until I get a sound I like.
Now, not to beat a dead horse, but if there's a good reason that the hivi M3N driver would not be suitable at all, I'd like someone to please tell me what it is. Otherwise, on paper, it looks like the best match to a guitar-type driver that I've seen. Thanks again for the advice and the back and forth. It's very informative.
Thanks again. It's nice to have someone to bounce ideas off of. My wife has zero patience for this kind of thing. 🙂 And it's educational for me, too. Socratic method and all that.
Yes it is much bigger than it needs to be to fit the speakers. This is not just to be an amp stack, it's going to be a piece of furniture and there are certain functional and aesthetic choices I'm making in addition to making a good guitar tone. The height of the cabinet will put the combo at a convenient height to reach the knobs. Also, when I'm sitting, it'll put the combo speakers at about ear level. The width will make it a couple inches wider than the combo. Depending on the size of the speakers I get, I may be able to shrink this dimension by a couple inches. I'm attaching a picture of my sort-of-to-scale drawing to give an idea of what I'm aiming for at this point.
The picture should address this. The combo is actually going to contain two separate speaker enclosures. One for the original 6" speaker and one for the low sensitivity/low volume speaker/speakers. Each speaker compartment will have it's own back so I can experiment with different back panels for each side individually. I will be making it switchable between these two speaker configurations.
I do understand that a baffle or frame member that is too long/large, may resonate sympathetically with the driver causing unappealing "boominess" at certain frequencies. If I run into this, I will add some bracing to damp that resonance.
If I really need to, I can always cut it apart and rebuild everything smaller. That's no big deal. I like tinkering.
I think it's actually not optimized for 16 ohms. I'm not an expert on circuit design, but I saw this: Cool Information About The Vox AC4TV Series and the explanation therein made sense to me. I've also seen some anecdotes that support the idea.
This is something I'm still trying to figure out. I see a couple things consistently when I'm looking at guitar speaker specs. 1) Resonance frequency usually between 70 - 140 Hz. 2) High end roll off between 5kHz and 10kHz. 3) Qts greater than 1, as high as 2.
These are the parameters I've been trying to match when I look at hi fi drivers, and I figure since guitar speakers with Qts around 1 can be used in either a closed or open back cabinet, the same should apply to a hifi driver with Qts around 1. But I admit, my analysis here may be lacking some important details.
Regardless, it's really easy to swap (for example) a 2/3 open partial panel to a fully closed back to a 1/3 open oval cutout back etc. That's the easiest thing to change so I'll probably play around with it until I get a sound I like.
Now, not to beat a dead horse, but if there's a good reason that the hivi M3N driver would not be suitable at all, I'd like someone to please tell me what it is. Otherwise, on paper, it looks like the best match to a guitar-type driver that I've seen. Thanks again for the advice and the back and forth. It's very informative.
Attachments
Okay, on the M3N....
Guitar speakers roll off the highs, starting roughly about 1.5K, due to their diameter. You will see more highs on a graph, but those are in the dreaded "beam" everybody hates to listen to. The small size of the M3N means it will be spreading those highs around the room. I'd suggest a high filter (crossover to nowhere) to keep the closer to a "real" guitar speaker.
The other thing is, we love the antique tech of our speakers because those paper cones distort the signal in a harmonically pleasing fashion. The speaker acts as a final filter for the amp which is often passing on some nasty, brittle overtones from either stomp boxes or preamp tubes. So, even with a high filter, the M3N might still be more revealing than you wish.
On the other hand, my headphones suffer the same problems, and it's not that bad, just different. (though, the SE100 I use does have filters to mock a guitar cab, a well as filters to emulate the mic position off-axis)
Keep in mind, most guitar players prefer the comb filtering of multiple speakers, they like the early reflections of a solid frame protruding around the baffle, and they tend to prefer rear mounting to the baffle which makes for even earlier reflections and more comb filtering. You need to forget just about everything you know from hifi to build a decent guitar cab. 😉
Guitar speakers roll off the highs, starting roughly about 1.5K, due to their diameter. You will see more highs on a graph, but those are in the dreaded "beam" everybody hates to listen to. The small size of the M3N means it will be spreading those highs around the room. I'd suggest a high filter (crossover to nowhere) to keep the closer to a "real" guitar speaker.
The other thing is, we love the antique tech of our speakers because those paper cones distort the signal in a harmonically pleasing fashion. The speaker acts as a final filter for the amp which is often passing on some nasty, brittle overtones from either stomp boxes or preamp tubes. So, even with a high filter, the M3N might still be more revealing than you wish.
On the other hand, my headphones suffer the same problems, and it's not that bad, just different. (though, the SE100 I use does have filters to mock a guitar cab, a well as filters to emulate the mic position off-axis)
Keep in mind, most guitar players prefer the comb filtering of multiple speakers, they like the early reflections of a solid frame protruding around the baffle, and they tend to prefer rear mounting to the baffle which makes for even earlier reflections and more comb filtering. You need to forget just about everything you know from hifi to build a decent guitar cab. 😉
Keriwena,
Thanks that helps a lot. For the past ten years or so I had two amps in my house: a 70W fender roc pro and a smokey cigarette pack amp. Since my band broke up 8 years ago, the fender amp was languishing and the smokey was the only amp I used. The fender was just too loud to use in the house. That's why I finally sold it and bought my little ac4.
My point here is that I'm used to the tinny sound of a small speaker. That doesn't bother me much at all when I'm trying to play softly. And I'll have a nice cabinet to play through when I want a bigger sound, so I think I'll do alright with either the M3Ns or maybe this: Goldwood GW-204/8S 4" Shielded woofer - 8 ohm: Madisound Speaker Store replacement woofer. If I put a pair of either of these in a decent box, I think they'll probably sound better than my old lil' smokey.
But just in case, if I find there's just too much high end, how would I go about filtering the highs? If I wire the drivers in series and I run 1 ft of 24 AWG wire (should have impedance of about 25 milliohms) from the jack to the positive terminal of the first driver then put say... a 3300 ufarad capacitor parallel to the load running to ground, will that give me a low pass filter with cutoff around 2kHz? Is there a better way to do it?
Thanks again!
Thanks that helps a lot. For the past ten years or so I had two amps in my house: a 70W fender roc pro and a smokey cigarette pack amp. Since my band broke up 8 years ago, the fender amp was languishing and the smokey was the only amp I used. The fender was just too loud to use in the house. That's why I finally sold it and bought my little ac4.
My point here is that I'm used to the tinny sound of a small speaker. That doesn't bother me much at all when I'm trying to play softly. And I'll have a nice cabinet to play through when I want a bigger sound, so I think I'll do alright with either the M3Ns or maybe this: Goldwood GW-204/8S 4" Shielded woofer - 8 ohm: Madisound Speaker Store replacement woofer. If I put a pair of either of these in a decent box, I think they'll probably sound better than my old lil' smokey.
But just in case, if I find there's just too much high end, how would I go about filtering the highs? If I wire the drivers in series and I run 1 ft of 24 AWG wire (should have impedance of about 25 milliohms) from the jack to the positive terminal of the first driver then put say... a 3300 ufarad capacitor parallel to the load running to ground, will that give me a low pass filter with cutoff around 2kHz? Is there a better way to do it?
Thanks again!
Last edited:
Build it and try it and learn heaps as you go, then tell us. It's all good fun. I'm waiting to hear what finally works for you.
Cheers
JimG
Cheers
JimG
Jim - thanks. I'll definitely post pics when I'm done, but considering I get about an hour or two to play in my shop each week, it's gonna take a while...
Keriwena - I thought that's how an RC low-pass works. It pushes low frequency signal through the load and sends high frequency to ground. I haven't done much of this myself, so maybe I'm missing something. I just did a little reading here and there to try to figure it out. Regardless, if the inductor works I can use that. Thanks!
Keriwena - I thought that's how an RC low-pass works. It pushes low frequency signal through the load and sends high frequency to ground. I haven't done much of this myself, so maybe I'm missing something. I just did a little reading here and there to try to figure it out. Regardless, if the inductor works I can use that. Thanks!
Hi, Sorry but this is heading towards the clueless advised by the ill-informed, rgds, sreten.
That is just my opinion, feel free to make up your own version of reality, and then test it.
That is just my opinion, feel free to make up your own version of reality, and then test it.
Or maybe you could call it a know-it-all making pronouncements from on high and pouting because the noob dares to question his authority.
I've got a design in mind. I have no reason at this point to believe that it won't do what I intend it to when I'm done. I'm very receptive if someone wants to explain why an aspect of my design isn't feasible. It's not very helpful to me though to just dismiss my ideas and offer no rationale.
Likewise, if I see some contradictory information and, being curious, attempt to discover the truth through simple inquiry, I don't see any reason for anyone to get huffy about it.
Whatevs... you certainly have no obligation to be helpful... or respectful...
I've got a design in mind. I have no reason at this point to believe that it won't do what I intend it to when I'm done. I'm very receptive if someone wants to explain why an aspect of my design isn't feasible. It's not very helpful to me though to just dismiss my ideas and offer no rationale.
Likewise, if I see some contradictory information and, being curious, attempt to discover the truth through simple inquiry, I don't see any reason for anyone to get huffy about it.
Whatevs... you certainly have no obligation to be helpful... or respectful...
Hi,
Sorry, I shouldn't have said that. Yes there is no reason why your proposal
won't work as such, its just massively bigger than it needs to be. A series
inductor with a resistor in parallel will cut treble levels without completely
killing them, but your likely problem will be the lack of the "presence" band
boost built into most drivers for guitar.
rgds, sreten.
Sorry, I shouldn't have said that. Yes there is no reason why your proposal
won't work as such, its just massively bigger than it needs to be. A series
inductor with a resistor in parallel will cut treble levels without completely
killing them, but your likely problem will be the lack of the "presence" band
boost built into most drivers for guitar.
rgds, sreten.
sreten - I really appreciate that. It's big of you. I apologize, too. I don't want to come off as harsh. I can tell that you know your stuff.
I definitely understand that a hifi speaker with a flat response will sound kind of thin compared to a guitar speaker that is designed to be peaky in the low-mids. I think I'll try it out anyway and if I hate it I'll try something different.
I've just got one more question about a low-pass filter. There are an infinite number of inductor/resistor pairs that would yield the same cut-off frequency. Am I correct in thinking that I want to use a resistor that has a much higher impedance than the 16 ohm impedance of the speakers? Otherwise I'd be losing a lot of power to the parallel resistor, right? Then that would necessitate a rather large inductor to get the cutoff frequency into the range I want (say somewhere between 2-4kHz)?
Thanks for the info.
I definitely understand that a hifi speaker with a flat response will sound kind of thin compared to a guitar speaker that is designed to be peaky in the low-mids. I think I'll try it out anyway and if I hate it I'll try something different.
I've just got one more question about a low-pass filter. There are an infinite number of inductor/resistor pairs that would yield the same cut-off frequency. Am I correct in thinking that I want to use a resistor that has a much higher impedance than the 16 ohm impedance of the speakers? Otherwise I'd be losing a lot of power to the parallel resistor, right? Then that would necessitate a rather large inductor to get the cutoff frequency into the range I want (say somewhere between 2-4kHz)?
Thanks for the info.
Hi,
a 16ohm resistor in parallel with the inductor would limit treble cut to ~ 6dB,
but doesn't the amp have a treble knob anyway ? presumably it works ?
I don't like the look of that goldwood at all, but that is me.
Aurasound NS3-194-16A 3" Paper Cone 16 ohm: Madisound Speaker Store
fits your criteria and you only need one.
One other issue is the amplifiers output impedance interacting with the driver Q.
Its possible this is the reason Vox went for 16ohm drivers rather than 8 ohms.
rgds, sreten.
a 16ohm resistor in parallel with the inductor would limit treble cut to ~ 6dB,
but doesn't the amp have a treble knob anyway ? presumably it works ?
I don't like the look of that goldwood at all, but that is me.
Aurasound NS3-194-16A 3" Paper Cone 16 ohm: Madisound Speaker Store
fits your criteria and you only need one.
One other issue is the amplifiers output impedance interacting with the driver Q.
Its possible this is the reason Vox went for 16ohm drivers rather than 8 ohms.
rgds, sreten.
Can you explain how you arrived at this? It seems like the kind of formula I might be able to use some day.
The amp has a tone knob that cuts treble. Chances are I won't be adding a filter, but I like learning about this stuff. 🙂
Definitely. And the price can't be beat! That might be the winner.
I'm not sure what you mean by this. Isn't Q a measure of the electromechanical damping of the driver (or something like that)? High Q gives more power, less damping, low Q means less power and tighter response?
Last edited:
Hi,
Regarding attenuation refer to some basic electronics site, not that I don't
want to explain, but a fully correct explanation is very long winded. The
short version (of many) is if you double the series impedance you half
the amount of current and as P= Isquared*R, quarter the power, -6dB.
High feedback transistor amplifiers have miniscule output impedances,
(again refer to some electronics site or book, I can't explain here),
whilst valve amplifiers, especially guitar ones with low overall feedback
can and do have significant output impedance, often 4 to 8 ohms.
This increases the effective Qts of the driver quite drastically.
rgds, sreten.
Regarding attenuation refer to some basic electronics site, not that I don't
want to explain, but a fully correct explanation is very long winded. The
short version (of many) is if you double the series impedance you half
the amount of current and as P= Isquared*R, quarter the power, -6dB.
High feedback transistor amplifiers have miniscule output impedances,
(again refer to some electronics site or book, I can't explain here),
whilst valve amplifiers, especially guitar ones with low overall feedback
can and do have significant output impedance, often 4 to 8 ohms.
This increases the effective Qts of the driver quite drastically.
rgds, sreten.
Hi,
Some further thought suggests the following :
Split the top of your cabinet into 3 enclosures (around 9" deep for the whole
thing, not 15" which is ridiculous) and install the 16 ohm 6.5", the 8 ohm 5"
I keep banging on about, and the 16 ohm 3" I recently posted.
If you can't beat them, join them, so add more options 😉.
Build it it and then tell me the 5" sounds like crap 😉. IMO the 3" only needs
say 5" cabinet width and the split the rest of the width with the 6.5" and
the 5", as it does need plenty of volume for what it is, a very different
driver to the the other two, an extra option for $4, maybe less with the
combined shipping with the 3". Really though what about the big driver ?
The latter perhaps you take your amplifier along to a store and audition
lots of extension cabinets, note which you like and then emulate them.
rgds, sreten.
Some further thought suggests the following :
Split the top of your cabinet into 3 enclosures (around 9" deep for the whole
thing, not 15" which is ridiculous) and install the 16 ohm 6.5", the 8 ohm 5"
I keep banging on about, and the 16 ohm 3" I recently posted.
If you can't beat them, join them, so add more options 😉.
Build it it and then tell me the 5" sounds like crap 😉. IMO the 3" only needs
say 5" cabinet width and the split the rest of the width with the 6.5" and
the 5", as it does need plenty of volume for what it is, a very different
driver to the the other two, an extra option for $4, maybe less with the
combined shipping with the 3". Really though what about the big driver ?
The latter perhaps you take your amplifier along to a store and audition
lots of extension cabinets, note which you like and then emulate them.
rgds, sreten.
Last edited:
I can definitely be persuaded as far as the depth of the combo cabinet. That means I only have glue up 4 boards instead of 6. That's 2/3 the number of edges to be jointed. I think I'll probably stick with wider stock, somewhere around 15", for the extension cabinet.
As far as speakers for the combo, it's not that I think the 5" speaker would sound bad. Let me try to summarize what I read in the link I posted earlier and you can tell me if you think it makes sense. The author of that thread measured the reflected load on the input of the output transformer with both 8 ohm and 16 ohm loads on the secondary. With a 16 ohm load on the secondary there was 10k impedance on the primary. With 8 ohm load on the secondary there was 5k impedance on the primary. He says that this indicates that the amp and OT are optimized for an 8 ohm load, and will put out about double the power through an 8 ohm speaker as through a 16 ohm speaker.
The caveat according to this article is that the power resistor in the attenuator circuit is only 2W, and that it should be replaced with at least a 5W if one wants to use an 8 ohm load and use the attenuator. OR replace the whole attenuator circuit with a VVR.
So I'm just leery of using an 8 ohm speaker on this amp without making some other modifications.
I'd love to hear your take on that.
For the big cab I'm definitely going to do some experimenting. I'm not positive what speaker configuration I'll go for first, but I'm leaning towards 2 weber signature series alnico 10s, one ribbed and one smooth. That should be a decent quality, but not too expensive, point of entry. Then I can play around from there.
Hi,
You haven't posted a link to that thread. Single ended amplifiers cannot
provide more current for lower impedance loads and power will drop into
8 ohms, unless it really is a 8 watt 8 ohm amplifier giving 4W into 16 ohms,
which it isn't, one would assume Vox know what they are doing.
AFAIK an EL84 would provide more power into 5K than 10K only if the
standing current was optimised for 5K, and the output transformer
is big enough such that current is in the middle of the BL curve.
I really cannot see 8ohms being an issue on the lower power settings.
Probably isn't on full power either, but for maximum volume you should
use two 8 ohm drivers in series.
IMO using two different drivers you don't get the best of both.
You might as well go for the louder 12's with all that space.
rgds, sreten.
You haven't posted a link to that thread. Single ended amplifiers cannot
provide more current for lower impedance loads and power will drop into
8 ohms, unless it really is a 8 watt 8 ohm amplifier giving 4W into 16 ohms,
which it isn't, one would assume Vox know what they are doing.
AFAIK an EL84 would provide more power into 5K than 10K only if the
standing current was optimised for 5K, and the output transformer
is big enough such that current is in the middle of the BL curve.
I really cannot see 8ohms being an issue on the lower power settings.
Probably isn't on full power either, but for maximum volume you should
use two 8 ohm drivers in series.
IMO using two different drivers you don't get the best of both.
You might as well go for the louder 12's with all that space.
rgds, sreten.
I did post the link in my post #21, but here it is again: Cool Information About The Vox AC4TV Series The author of that post believes precisely that the AC4TV is an 8W, 8 ohm amplifier. If you can tell me how to test it I'll get to the bottom of it. 🙂 I've got an 8 ohm speaker lying around that I can use for the experiment.
According to the guy I'm citing, the OT is robust enough to handle around 15 W.
Also, after reading that link a little more deeply and investigating VVR circuits, I'm starting to think I may scrap the small, low-sensitivity speaker idea altogether and try swapping the amp's attenuator for the VVR circuit from Hall Amplification here: http://www.hallamplification.com/main.html?src=%2F#2,2 I may or may not build a new combo cabinet. If I do it'll primarily be for looks, but I might build it big enough to accept a larger speaker. Also, the amp currently has a closed back. The amp chassis actually is the back panel. If I build a new combo cabinet, I'll arrange it so the controls are in front and I'll have the option of an open back in case I want to try out different speakers with different back configurations.
I'm a little nervous about messing with the guts of the amp, but I saw a video of the installation and it doesn't seem all that difficult. It's three wires, B+ in, B+ out and ground. Two things I'm not sure about 1) When I remove the attenuator do I need to connect anything in it's place? (i.e. a jumper? a resistor?) 2) Not sure I'll be able to locate the circuit points I need to use to wire in the VVR. I'm not that worried about #2. Next chance I get I'm going to open up the amp again and see if I can sort out what's what.
As far as speaker choices go, I've solicited opinions in a few different forums, and I've never seen the same answer twice. This seems to be entirely a matter of taste. That's why I'm planning to build the cabinet to be flexible. Large enough to carry 2x12's if I want to try that, and built so front and back baffles are easy to swap.
You're not the only person who's recommended the "testing lots of cabinets and build the one you like" route. That makes sense, but 1) I have been to all the music stores in my area and none of them have what I would call a "wide variety" of cabinets to audition certainly not any of the more exotic configurations like detuned cabs and 2) I have a much better time tinkering than I do shopping. I really am the type that can't leave well enough alone. There's no getting around it. 🙂
According to the guy I'm citing, the OT is robust enough to handle around 15 W.
Also, after reading that link a little more deeply and investigating VVR circuits, I'm starting to think I may scrap the small, low-sensitivity speaker idea altogether and try swapping the amp's attenuator for the VVR circuit from Hall Amplification here: http://www.hallamplification.com/main.html?src=%2F#2,2 I may or may not build a new combo cabinet. If I do it'll primarily be for looks, but I might build it big enough to accept a larger speaker. Also, the amp currently has a closed back. The amp chassis actually is the back panel. If I build a new combo cabinet, I'll arrange it so the controls are in front and I'll have the option of an open back in case I want to try out different speakers with different back configurations.
I'm a little nervous about messing with the guts of the amp, but I saw a video of the installation and it doesn't seem all that difficult. It's three wires, B+ in, B+ out and ground. Two things I'm not sure about 1) When I remove the attenuator do I need to connect anything in it's place? (i.e. a jumper? a resistor?) 2) Not sure I'll be able to locate the circuit points I need to use to wire in the VVR. I'm not that worried about #2. Next chance I get I'm going to open up the amp again and see if I can sort out what's what.
As far as speaker choices go, I've solicited opinions in a few different forums, and I've never seen the same answer twice. This seems to be entirely a matter of taste. That's why I'm planning to build the cabinet to be flexible. Large enough to carry 2x12's if I want to try that, and built so front and back baffles are easy to swap.
You're not the only person who's recommended the "testing lots of cabinets and build the one you like" route. That makes sense, but 1) I have been to all the music stores in my area and none of them have what I would call a "wide variety" of cabinets to audition certainly not any of the more exotic configurations like detuned cabs and 2) I have a much better time tinkering than I do shopping. I really am the type that can't leave well enough alone. There's no getting around it. 🙂
Last edited:
- Status
- Not open for further replies.