John,
I was very blunt,but not rude.
You're angry at the wrong things.
A guitar speaker WILL see frequencies lower than 80hz, so unloading can be an issue, since it occurs BELOW resonance.
Hand plant on strings....at full volume anyone?
Point being, by down tuning the port frequency, and forcing a high Q driver to work in a ported cab, you are reducing its power handling, and reducing the excursion limiting benefits of reflex design, so unloading is more likely. Not less.
But at moderate volume porting is reasonable. I wouldn't lug a 4x12 cab around, which is why I have 4x10. One person lift. Simple. And if anything, most times i dial the bass down...really cant say ive heard any 4x12 that was bass shy, even open backed ones.
Single driver combo.....sure they could often do with bass, or even just a back panel...
Basically what I'm saying is that you have tuned a naturally very high q driver to flatten the bass response until its reasonable and not crazy 10 db peaking in the bass. Should sound good and flat, if you want it that way, BUT you are reducing the power handling by doing so, and that deserves proper consideration. I say that as most instrument speakers that are ported are tuned to maximise power handling and not vice versa.
To clarify,my frankencab is ported......albeit with a roll of foam blocking the port. If i want to switch back to ported, its simple.
I was very blunt,but not rude.
You're angry at the wrong things.
A guitar speaker WILL see frequencies lower than 80hz, so unloading can be an issue, since it occurs BELOW resonance.
Hand plant on strings....at full volume anyone?
Point being, by down tuning the port frequency, and forcing a high Q driver to work in a ported cab, you are reducing its power handling, and reducing the excursion limiting benefits of reflex design, so unloading is more likely. Not less.
But at moderate volume porting is reasonable. I wouldn't lug a 4x12 cab around, which is why I have 4x10. One person lift. Simple. And if anything, most times i dial the bass down...really cant say ive heard any 4x12 that was bass shy, even open backed ones.
Single driver combo.....sure they could often do with bass, or even just a back panel...
Basically what I'm saying is that you have tuned a naturally very high q driver to flatten the bass response until its reasonable and not crazy 10 db peaking in the bass. Should sound good and flat, if you want it that way, BUT you are reducing the power handling by doing so, and that deserves proper consideration. I say that as most instrument speakers that are ported are tuned to maximise power handling and not vice versa.
To clarify,my frankencab is ported......albeit with a roll of foam blocking the port. If i want to switch back to ported, its simple.
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Exactly. To be precise, there can't be an optimal solution covering every speaker response, SPL, cab size and combination. I had posted a question in response to a previous comment (not yours). Apparently there is a font of knowledge which we may not be privy to, so I am curious to hear about it. I'd leave optimal out of the picture for an instrument speaker system, and go with personal preference.
Its all ok - thanks for your post!
I agree about the issues of unloading below the port frequency, and it is a fair point that there could be low frequency transients that go way below the musical frequencies. I wonder how big an issue this is? My gut feeling is that this is not worse than for an open-backed guitar cab. Also, tuning the ported cab to a higher frequency does not help the unloading issues at low frequencies, therefore, if ported cabs work at all, tuning them as I do is not particularly worse. I have certainly blasted mine at gigs and rehearsals with no problem, its a 60W speaker, but in its loudest use, its an extension cab, so its only getting half the output of a 40 valve amp.
As an experiment, I once used the DI output of my guitar amp to plug in to the sub-woofer channel of a big PA system. The sub-woofer channel included a graphic equalizer with a roll-off curve starting from 40Hz and completely rolled-off at 100Hz.
I was not really expecting to hear much through it, but I was surprised by the amount of 'thumping' and 'clunking', especially when 'palm muting'.
I think it could be useful for heavy metal, or if there is no bass player, but for most styles I think it would just be muddying things and getting in the way of the bass player.
after following this thread for a while i can't stop thinking about trying something like an RJ enclosure(floating baffle) and servo motors to reposition/retune the enclosure at will...
i understand that bass tuning is the objective but doesn't the difference in midrange tonality come into play ? or is this not a problem?(in my experience open backed vs closed back are two vary different animals not only with respect to bass but how the midrange sounds)
i understand that bass tuning is the objective but doesn't the difference in midrange tonality come into play ? or is this not a problem?(in my experience open backed vs closed back are two vary different animals not only with respect to bass but how the midrange sounds)
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John,
I agree, openbacked cabs are probably the worst in a power handling sense. But then most ive heard get rather muddy when really pushed, as opposed to the typical Marshall cab buzz at high volumes.
I'm still not sure porting is necessary, but its only an opinion.
I know a few guys who prefer a open back combo, over a cab. Mainly, because the drummer gets the rear wave, and not bass mud from the cab back panel. Good mic tech will be able to mike up even a tiny boogie and make it sound larger than life. Porting a cab probably only satisfies the guitarist, otherwise its a similar job to more 'conventional' cab.
If i were a 7 string player for example, id just play with a bright bass cab. (i used to use a fender bassman cab ;-) which was bright enough and yet bottom heavy too! All my mates had HH amps, which were pretty poor, and ported. Driving the bassman cab using the HH was immense.)
So long story short...maybe a good bassdriver and cab would work for you better?
I agree, openbacked cabs are probably the worst in a power handling sense. But then most ive heard get rather muddy when really pushed, as opposed to the typical Marshall cab buzz at high volumes.
I'm still not sure porting is necessary, but its only an opinion.
I know a few guys who prefer a open back combo, over a cab. Mainly, because the drummer gets the rear wave, and not bass mud from the cab back panel. Good mic tech will be able to mike up even a tiny boogie and make it sound larger than life. Porting a cab probably only satisfies the guitarist, otherwise its a similar job to more 'conventional' cab.
If i were a 7 string player for example, id just play with a bright bass cab. (i used to use a fender bassman cab ;-) which was bright enough and yet bottom heavy too! All my mates had HH amps, which were pretty poor, and ported. Driving the bassman cab using the HH was immense.)
So long story short...maybe a good bassdriver and cab would work for you better?
(by using a ported cab at some frequency or another).
I guess that is right in general, but in the very narrow field of specifically made guitar speakers, that's not an issue, for the very good reasons that guitar speaker designers consider their products may be used in the worst unloading cabinet of them all: an open back combo.
So they don't count on air compliance to keep excursion in control, they do so by already providing very low compliance edge and suspension.
That alone is equivalent to being in an "X" sized closed cabinet 🙂
That's the main point of diminishing returns in way too large cabinets, not because of unloading but because increasing air compliance beyond a certain point doesn't mean that much comparing it to stiff speaker compliance, remember both are in series and add up.
As in having 2 resistors in series, lowering one of them (air) won't lower the combination value that much if the other (speaker itself) is a relatively high and fixed value.
FWIW there are a few special cases where speakers have been built high compliance (i.e. "soft"/low Fs) , most known ones are the 6" speakers used in very small metal cabinet GK 250ML , with foam edges 😱
and ZT Lunchbox 200 with a single cloth edge 6"speaker.
In both cases, closed cabinet loading is paramount ... but these are exceptions, not the rule.
FWIW I have made cloth edge 10" and 12" speakers, to be used in very compact closed back combos, but had to handmake the cones, by cutting the paper edge of a normal guitar cone and fitting a spare cloth edge (which later had to be impregnated) because commercial offerings are meant as woofer cones, very thick and heavy, and kill all bite and sparkle.
Will post a couple pictures when I build another.
Hi,
You teach ? And make up your own theories about stuff
you don't understand ?* Nothing gives insight like the
correct theory, and wrong theory gives no insight at all.
BTW what is your alleged Vas and Vbox adding insight ?
Might be a "rule of thumb" that works in a given parameter
space, but TBH I very much doubt it, as its the ratio that
is the reality, and adding values of ratios is meaningless.
Whatever, your box will work a lot better tuned to 80Hz
than 50Hz if its ~ 2 cuft, and the driver is ~ 1cuft Vas,
~ 100Hz Fs and ~ 1.0 Qts. A guaranteed insight.
Vented boxes do unload the driver with Vbox < Vas,
but unloading does not apply with ~ Vbox > 2 Vas.
rgds, sreten.
* Not that the real theory is an any way complicated.
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I was about to give up on this conversation, then I saw the above edit. Yes that is exactly what it is, and no more than that.
Why tune to 50hz not 80hz?
At 80hz Id get a very significant boost right there. My cab designs are not going for mimimum dimensions, so if judged to need a bass lift, its only a couple of db that is wanted. With the usable range 80hz and above, dropping the tuning frequency lower seems to provide a way to transition the response from the full bass boost down towsrds being more similar to fully closed.
Why not make a smaller cab and port for 80hz?
When i investigated that, it seem to usually leave too much low mids, more than in a lower-tuned but larger cab. Its probably a good strategy with certain drivers though.
Whats my point about Vas plus Vb?
Just an observation I was curious about, based on trying to find port dims to tune response to a certain frequency. Its all based on using WinISD, so subject to any limitations there. I noticed first that the bump in the low response due to the porting was less than the calculated box frequency. Eg, box resonance at around 60hz gave an apparent peak at around 50hz. (more an upward bump in the slope). The box frequency in WinISD matches standard formulae. I found adding Vas to Vb in the formula then matched the 50hz observed, to within a hz or two.Just to explore, Ive tried a few cases, with box volumes from 40 to 80l and frequencies 50 to 80hz and it seemed to remain true in that range.
ps to the above post:
why would I think this Vb+Vas may even be slightly valid?
I think, it may be reasonable at frequencies significantly below the natural resonant frequency of the speaker itself, so the dynamics of the speaker are not really significant, and it is just responding passively as a compression/spring element, moving in and out in response to relatively slow changes in pressure at this low tuning frequency. And that is where I thought the Vas parameter may be relevant to capturing the effect and combining it with box volume, being the equivalent volume of air with the same compliance.
OK, so shoot if you want. The above is an honest, even if uninformed thought
why would I think this Vb+Vas may even be slightly valid?
I think, it may be reasonable at frequencies significantly below the natural resonant frequency of the speaker itself, so the dynamics of the speaker are not really significant, and it is just responding passively as a compression/spring element, moving in and out in response to relatively slow changes in pressure at this low tuning frequency. And that is where I thought the Vas parameter may be relevant to capturing the effect and combining it with box volume, being the equivalent volume of air with the same compliance.
OK, so shoot if you want. The above is an honest, even if uninformed thought
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You can combine them, what you can't do is add them .
Consider them as capacitors in series .... now they don't exactly add, do they?
In fact what you can add is their inverse, roughly :
1/Veq=1Vb + 1/Vas
I call Veq the new "volume equivalent' for lack of a better word, and it will be smaller than either Vb or Vas, so the combination will be stiffer than any of them, so resonant frequency will rise .
As you see it describes what happens when you mount a speaker in a sealed cabinet.
Consider them as capacitors in series .... now they don't exactly add, do they?
In fact what you can add is their inverse, roughly :
1/Veq=1Vb + 1/Vas
I call Veq the new "volume equivalent' for lack of a better word, and it will be smaller than either Vb or Vas, so the combination will be stiffer than any of them, so resonant frequency will rise .
As you see it describes what happens when you mount a speaker in a sealed cabinet.
It would be instructive to plot the cone excursion in your simulations if the software can compute it. Even if the cone moves too far at low frequencies, it might sound good by adding higher harmonics.
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But, per the sims, the resonant frequency falls rather than rises. I don't think the capacitor analogy is right.
My simplistic mental picture is like masses on springs. The air in and around the port , which is moving most, is the mass, and it is supported by the spring which is the rest of the air in the cab. This has a resonant frequency which reduces if the air in the box gets softer. In this mode, I picture the speaker as a spring in series with box air, adding softness to the air system. This applies to the low frequencies that im considering.
Hi,
For somebody who teaches your full of self justifying
recalcitrent nonsense about something you know little.
There is nothing honest about pig-headed thoughts,
your the typical nightmare pupil, insisting whatever
they think is the only thing worth thinking about.
This isn't a conversation you can "give up" on,
as you haven't engaged in a conversation.
You just want to make out whatever you are
doing is right, if that is the way you teach
god help your students, first principles
are not your forte in getting them right.
Port tuning essentially is the port and box.
Driver tuning is essentially the driver and box.
They interact but not but not in the way you
imply, Vas does not add to Vbox in anyway
when it comes to the effective port tuning.
Adding Vas to Vbox is pretty meaningless,
and useless as a concept of understanding.
Anyway I'm fed up with discussing a subject
on cluelessly biased terms. Your box would
work better tuned to 80Hz, and I've no real
interest anymore in why you think it won't,
because that is because you want to, you
simply don't know that it won't, or why
I think it will (already described).
rgds, sreten.
FWIW anyone who knows their mechanics usually
gets on with equivalent circuits much better than
most*, and a fine introduction to those is the
manual of the Basta! speaker simulator.
http://www.tolvan.com/basta/Basta!TechDoc.htm
* Why ?
SPICE can model nearly all mechanical systems,
by transforming them into an electrical analogy.
For somebody who teaches your full of self justifying
recalcitrent nonsense about something you know little.
There is nothing honest about pig-headed thoughts,
your the typical nightmare pupil, insisting whatever
they think is the only thing worth thinking about.
This isn't a conversation you can "give up" on,
as you haven't engaged in a conversation.
You just want to make out whatever you are
doing is right, if that is the way you teach
god help your students, first principles
are not your forte in getting them right.
Port tuning essentially is the port and box.
Driver tuning is essentially the driver and box.
They interact but not but not in the way you
imply, Vas does not add to Vbox in anyway
when it comes to the effective port tuning.
Adding Vas to Vbox is pretty meaningless,
and useless as a concept of understanding.
Anyway I'm fed up with discussing a subject
on cluelessly biased terms. Your box would
work better tuned to 80Hz, and I've no real
interest anymore in why you think it won't,
because that is because you want to, you
simply don't know that it won't, or why
I think it will (already described).
rgds, sreten.
FWIW anyone who knows their mechanics usually
gets on with equivalent circuits much better than
most*, and a fine introduction to those is the
manual of the Basta! speaker simulator.
http://www.tolvan.com/basta/Basta!TechDoc.htm
* Why ?
SPICE can model nearly all mechanical systems,
by transforming them into an electrical analogy.
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'K sreten. Enough. I'm outa here.
I really hope you do not have to teach.
/John
I really hope you do not have to teach.
/John
Hi,
I don't have to but I have, I'm quite good at it.
Toys out of the pram is not very mature,
but you didn't come here to learn, you
came here to pontificate on your musings.
rgds, sreten.
There is no sound reason to do this, if I understand what you are doing. Show us a worked example calculation so we know exactly what you are talking about.
Please reread my post, I was talking about a sealed cabinet. and specifically to simplify the concept and concentrate on those variables only , so you understand 1) stifness are in series and 2) they are inversely proportional to volume.
That is similar enough for me to explain them like capacitors in series.
If you tune one of them (a tuned cabinet) basic concept does not change but new resonance clouds understanding.
As of simulators, you'll see that I consider them a very powerful and useful tool, but often (specially here in DIY) they can be a double edged sword because they will only simulate whatever you feed them ... and ignore what you don't.
Remember I asked you for a couple extra simulations, which you kindly did 🙂
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