Tannoy Enclosure
#16 Re: Tannoy Enclosure
This is a very interesting discussion. And all the necessary components are in the mix like critical damping, room interaction, speaker behavior at resonance frequency, DF of amp, historic development of speaker-amp-relation etc.
The only thing this discussion is still missing IMO is to draw the right conclusions for getting the best possible SQ.
I am in the middle of fact finding myself as I have started to build the OB subs with servo control. I went through a similar process in my efforts to get some clarity about what to do but with different results.
I started with measurements (impedance, looking at the CSD diagrams and connection to impedance/amp and listening experience) in order to verify my listening impressions and everything points in the direction that the most/maybe only really critical area is the bass and its room response (even acoustically treated) and the best cure is to disconnect the main speakers just a little above the resonance frequency and reproduce the bass with something that doesn't act like a heavy mass driver in a boxed enclosure. Smaller sized closed speakers might be the only exception.
Everything in the process to reproduce real and realistic bass creates some "stored energy" in the bass driver (the more the heavier the mass of the cone) that interacts with the room and has the tendency to "smear". Can even sound nice but it's not real. An array of smaller drivers for reproducing the bass or OB sub with servo control seemed to be the only practical solutions for this problem.
The only thing this discussion is still missing IMO is to draw the right conclusions for getting the best possible SQ.
I am in the middle of fact finding myself as I have started to build the OB subs with servo control. I went through a similar process in my efforts to get some clarity about what to do but with different results.
I started with measurements (impedance, looking at the CSD diagrams and connection to impedance/amp and listening experience) in order to verify my listening impressions and everything points in the direction that the most/maybe only really critical area is the bass and its room response (even acoustically treated) and the best cure is to disconnect the main speakers just a little above the resonance frequency and reproduce the bass with something that doesn't act like a heavy mass driver in a boxed enclosure. Smaller sized closed speakers might be the only exception.
Everything in the process to reproduce real and realistic bass creates some "stored energy" in the bass driver (the more the heavier the mass of the cone) that interacts with the room and has the tendency to "smear". Can even sound nice but it's not real. An array of smaller drivers for reproducing the bass or OB sub with servo control seemed to be the only practical solutions for this problem.
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#17 Re: Tannoy Enclosure
I don't have much time, but a few visual examples.
Three different sealed boxes; I used the MA Alpair 12PW as the example drive unit. The three system alignments are the ones mentioned above:
Qtc = 0.707 (Butterworth). Maximally flat response, lowest possible F3*
Qtc = 0.577 (Bessel). Maximally flat group delay
Qtc = 0.5 (Critically damped). Optimal transient response / 'transient perfect'
As you can see, the bigger the box, the lower the system Q (Qtc), and the higher in frequency the roll-off begins, but at a shallower slope. No surprises there, since it's derived from electrical filter theory.
*As noted above, Toole & others have shown F3 is relatively meaningless as a guide to practical in-room response but it's essentially built into filter theory, so we use it for the academic purpose.
Three different sealed boxes; I used the MA Alpair 12PW as the example drive unit. The three system alignments are the ones mentioned above:
Qtc = 0.707 (Butterworth). Maximally flat response, lowest possible F3*
Qtc = 0.577 (Bessel). Maximally flat group delay
Qtc = 0.5 (Critically damped). Optimal transient response / 'transient perfect'
As you can see, the bigger the box, the lower the system Q (Qtc), and the higher in frequency the roll-off begins, but at a shallower slope. No surprises there, since it's derived from electrical filter theory.
*As noted above, Toole & others have shown F3 is relatively meaningless as a guide to practical in-room response but it's essentially built into filter theory, so we use it for the academic purpose.
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#18 Re: Tannoy Enclosure
And some vented.
-Top is a flat alignment. Basically, again, the lowest possible F3. There are a couple of ways of doing it, this is just one. In most practical situations best avoided unless the room is well-damped and the speaker well away from walls.
-Middle is a [relatively] well-damped alignment. In this particular case achieved by using a smaller enclosure volume tuned a little lower than the above to damp the knee around the bottom end and also provide a relatively broad vent tuning (the pale blue line). The downside here is a slightly longer settling time (not shown). You balance compromises; there's no such thing as a perfect speaker, just a selection of options; you go with whatever is the least evil balance according to your needs.
-Lower is one EBS type alignment. Large box, tuned low. You can see the LF has an initial rolloff, flattens to a lower shelved down response before the final rolloff. Good option for subwoofers if tuned low enough, not always ideal for more ordinary speakers.
-Top is a flat alignment. Basically, again, the lowest possible F3. There are a couple of ways of doing it, this is just one. In most practical situations best avoided unless the room is well-damped and the speaker well away from walls.
-Middle is a [relatively] well-damped alignment. In this particular case achieved by using a smaller enclosure volume tuned a little lower than the above to damp the knee around the bottom end and also provide a relatively broad vent tuning (the pale blue line). The downside here is a slightly longer settling time (not shown). You balance compromises; there's no such thing as a perfect speaker, just a selection of options; you go with whatever is the least evil balance according to your needs.
-Lower is one EBS type alignment. Large box, tuned low. You can see the LF has an initial rolloff, flattens to a lower shelved down response before the final rolloff. Good option for subwoofers if tuned low enough, not always ideal for more ordinary speakers.
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#19 Re: Tannoy Enclosure
The best I have heard these sound was mounted in a wall to another room as an infinite baffle. In this case Thiele/Small becomes insignificant, there are no audible reflections from inside the cabinet coming back through the speaker cones and the most AWESOME low end extension imaginable.
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#20 Re: Tannoy Enclosure
Well, under those conditions, and assuming a voltage source amplifier with the usual minor series R for wire, connections, the behaviour of the driver using the published T/S data is akin to free air / true IB conditions where in effect Qtc = Qts, Fb = Fs, F3 = 115Hz [nearly] and F6 = 70Hz [nearly]. F10 is about 40Hz. Depending on what filter is used, some compensation for step-loss may be built in, though this is a bit open to question, and that may help the balance a little.
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#21 Re: Tannoy Enclosure
Thanks Scott. I've been doing a lot more reading and fiddling about with winisd after your examples.Scottmoose wrote: ↑Sun Feb 23, 2020 6:06 pm I don't have much time, but a few visual examples.
Three different sealed boxes; I used the MA Alpair 12PW as the example drive unit. The three system alignments are the ones mentioned above:
Qtc = 0.707 (Butterworth). Maximally flat response, lowest possible F3*
Qtc = 0.577 (Bessel). Maximally flat group delay
Qtc = 0.5 (Critically damped). Optimal transient response / 'transient perfect'
As you can see, the bigger the box, the lower the system Q (Qtc), and the higher in frequency the roll-off begins, but at a shallower slope. No surprises there, since it's derived from electrical filter theory.
*As noted above, Toole & others have shown F3 is relatively meaningless as a guide to practical in-room response but it's essentially built into filter theory, so we use it for the academic purpose.
I can see why the first example is desirable but maybe not practical.
Group delay I've read is something some people are sensitive too, some not so much. It depends on where it occurs in the frequency spectrum. And as long as it's not too terrible and low in frequency it might not be terrible. But I also imagine if you were sensitive to it or had exposure to it at low levels, higher levels might be a problem. Have I got that right?
Optimal transient response also is a tempting thing to chase but I'm guessing that will be at the expense of group delay and earlier roll off but isn't it the end more extended? Is this where you rely on room gain?
So although there's compromises with all of them, short of building all 3, how would you know where your own compromises lie?
Were those graphs you produced from winisd or something else?
I was hoping to put my current cabinet into winisd but some parameters like the port length is calculated I'm guessing to produce the alignment first entered at the start of the project. I get some weird results.
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#22 Re: Tannoy Enclosure
No, the two go together.izzy wizzy wrote: ↑Mon Feb 24, 2020 10:22 pm Optimal transient response also is a tempting thing to chase but I'm guessing that will be at the expense of group delay
Also tone is very much associated with low group delay , in my books.
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#23 Re: Tannoy Enclosure
Scott had two examples where one was maximally flat group delay and the other optimal transient response.IslandPink wrote: ↑Mon Feb 24, 2020 10:44 pmNo, the two go together.izzy wizzy wrote: ↑Mon Feb 24, 2020 10:22 pm Optimal transient response also is a tempting thing to chase but I'm guessing that will be at the expense of group delay
Also tone is very much associated with low group delay , in my books.
My aim with this was not to turn it into a 10 year search for the perfect speaker
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But I can see trying to understand this isn't going to be easy given the time I have and especially as I have no idea what my preferences are in relation to what I have, what I think I want and the tradeoffs involved in sticking them in a box.
This initially was going to be easy. Make another box. Stick them in. Done. It worked before. What was I thinking?
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#24 Re: Tannoy Enclosure
Are the old cabinets going to be scrapped ?
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#25 Re: Tannoy Enclosure
Tannoy Amesbury cabinet?
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#26 Re: Tannoy Enclosure
A Bessel alignment (Q[tc] = 0.577) has the fastest settling time to rest after an impulse, but also slight overshoot. Anything over 0.5 overshoots -the higher the Q, the greater / longer it is. Critically damped (Q[tc] = 0.5) settles almost as quickly & has no overshoot to an impulse. That's why it's also sometimes called 'transient perfect' -some argue whether this latter is a slight misnomer or not as they rightly point out context is critical. However, 0.5 has no overshoot so providing we accept it's just one factor, it's a reasonable enough description.
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#27 Re: Tannoy Enclosure
Yes. I'm amazed they lasted this long.
Didn't know that one until you mentioned it. It seems a version of the Lancaster. In some respects, that's where I'm headed but hopefully with some knowledge or something that might help me make it work, possibly a bit better coz we know more stuff these days?
I was hoping to be able to put these older cabinet dimensions into a sim to see what happens especially the cabinet I've lived with and see if some things can be moved around to make it a bit better.
Thanks Scott. More info to digest. Can I get my cab into a sim to see what it does without defining an alignment?Scottmoose wrote: ↑Tue Feb 25, 2020 10:24 am A Bessel alignment (Q[tc] = 0.577) has the fastest settling time to rest after an impulse, but also slight overshoot. Anything over 0.5 overshoots -the higher the Q, the greater / longer it is. Critically damped (Q[tc] = 0.5) settles almost as quickly & has no overshoot to an impulse. That's why it's also sometimes called 'transient perfect' -some argue whether this latter is a slight misnomer or not as they rightly point out context is critical. However, 0.5 has no overshoot so providing we accept it's just one factor, it's a reasonable enough description.
Edit:
Having just said that above, I put in the Arden dimensions in and it came out fairly good response wise with my speaker parameters when it was designed for another; a later model. So more work to do.
Last edited by izzy wizzy on Tue Feb 25, 2020 12:39 pm, edited 1 time in total.
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#28 Re: Tannoy Enclosure
Correct. At lower frequencies the audibility threshold of GD is a little longer than for the midband. Some are a little more suseptible than others, but the basic principle holds.izzy wizzy wrote: ↑Mon Feb 24, 2020 10:22 pmThanks Scott. I've been doing a lot more reading and fiddling about with winisd after your examples...
Group delay I've read is something some people are sensitive too, some not so much. It depends on where it occurs in the frequency spectrum. And as long as it's not too terrible and low in frequency it might not be terrible.
No, as Mark notes they tend to go hand in hand here. With a lower box Q the rolloff starts at a higher frequency but with a very shallow (low Q) curve and the outright extension is greater, albeit at a lower level, so it's a question of balancing what you need off against room gain. People can spend a little too much time worrying about system Qtc -the fact is, our hearing acuity is poor in the LF and the room will foul things up anyway, so there is a modest amount of leeway here. Lower system Qs are generally thought to sound 'tighter' as you would expect, but the price is reduced output.Optimal transient response also is a tempting thing to chase but I'm guessing that will be at the expense of group delay and earlier roll off but isn't it the end more extended? Is this where you rely on room gain?
That's where you have to make a judgement call based on your own experience, what you know you value in presentation, how the speakers are to be used, what the rest of the system will be, and make what is in essence an educated guess based on that.So although there's compromises with all of them, short of building all 3, how would you know where your own compromises lie?
Duct length for a given tuning frequency is a function of box volume and vent CSA; typically with WinISD once you've got your driver data entered into the database, you'll enter your box volume & tuning frequency; you can then adjust the number and diameter of the vent[s]; it will calculate the duct length required from that.I was hoping to put my current cabinet into winisd but some parameters like the port length is calculated I'm guessing to produce the alignment first entered at the start of the project. I get some weird results.
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#29 Re: Tannoy Enclosure
Well, as far as a sealed box goes, the alignment comes from the driver's electro-mechanical characteristics (i.e. what are described by the T/S parameters) and the box volume. So if you put it in any box it will always have an 'alignment' -nature of the beast. The particular Q value may not have a name, but names don't mean much in themselves.izzy wizzy wrote: ↑Tue Feb 25, 2020 12:01 pm Thanks Scott. More info to digest. Can I get my cab into a sim to see what it does without defining an alignment?
Just play with it. Sealed boxes are quite straightforward. For a given drive unit as box volume decreases, so the system resonant frequency (aka 'tuning frequency') increases, and you will start to see peaking at that frequency. As the box volume increases, so the system resonant frequency decreases and the low end response will become increasingly well-damped. The lowest system Q (Qtc) possible is = driver Qts.
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#30 Re: Tannoy Enclosure
So far I put in what I knew and then wiggled tuning frequency to get the duct length that are in these older cabinets. And that gave the wildest LF peak. Not only for mine but a couple of the other older cabinets. Either I have something wrong or that's what I actually have and that's an issue with these older cabinets? Chris did measure a great hump at Owston last year but of course couldn't be sure what it was down to: room, mic position or speaker or combinations of any of it.Scottmoose wrote: ↑Tue Feb 25, 2020 12:05 pm Duct length for a given tuning frequency is a function of box volume and vent CSA; typically with WinISD once you've got your driver data entered into the database, you'll enter your box volume & tuning frequency; you can then adjust the number and diameter of the vent[s]; it will calculate the duct length required from that.
I suppose it might be time to wind up the IMP analyser to see what happens here. Would that be a good next move?