rabstg said:
exactly
Here is a crude overlay of Fat Thor (red), Short Thor (purple) & Small Thor (green). (don't know why Small Thor is offset upwards 3 dB.
But these support Scott's contention that ShortThor is best. Then i'd say Small Thor -- it gives up a small amount of bass to Fat Thor but has way less ripple.
dave
Attachments
jgwinner said:Maybe I've just sipped instead of drinking deep of the draughts of knowledge, but it looks like a vented box to me
Rather specifically done, mind you
Download and read Martin King's ML-TQWT paper. Using ANSYS he clearly shows that the behaviour of a bass reflex box is quite different from a mass-loaded transmission line.
Take a bass reflex box with a dimension ratio that is not extreme, then keeping the volume the same, start increasing the height (while keeping the port at the bottom. As the height increases the box will morph from a clearly bass reflex box into an ML-TL with quite different behaviour. There is no clear line where it stops being one and becomes the other, but at the "ends" they are definitly different beasts.
Another term for an ML-TL is a transmission line with restricted terminus.
dave
Short Thor port is fine Dave. You can increase the width somewhat to roll things off if bass gets too heavy, which is where I remember some of the confusion crept in a few months back -entierly my fault. Small Thor's response is too high because of an error I made when entering the data, but the curve shape and F3 don't change, so it's still useful. Many thanks for all you've put into this with drawings, overlaid graphs etc. Above and beyond that is, considering you've no interest in building a pair.
If I was all-out to build a Thor version (no, I'm not going to either, but don't let that stop you), and I had a cathedral, I'd build Fat Thor. If I had a big house, Short Thor. A 'normal' sized house, Small Thor.
Oh yes: nice little illustation about why MLTLs are not BR boxes by Bob Brines: http://www.geocities.com/rbrines1/Pages/QWR_not_BR.html
Regards
Scott
If I was all-out to build a Thor version (no, I'm not going to either, but don't let that stop you), and I had a cathedral, I'd build Fat Thor. If I had a big house, Short Thor. A 'normal' sized house, Small Thor.
Oh yes: nice little illustation about why MLTLs are not BR boxes by Bob Brines: http://www.geocities.com/rbrines1/Pages/QWR_not_BR.html
Regards
Scott
What Bob Brines has shown is that a poorly chosen vented analogy to a TL does not fit very well, this should be obvious. What one has to consider is that a good portion of the line in a TL, roughly the last half toward the port, is analogous to the port in a vented system. This means that the vented analogy should have a box volume of about half that of the TL. Brines used the entire volume which provides about 6 dB more output at Fb, just as his simulation shows.
He also uses equal port area in the comparison when the correct analogy would adjust port area to match Fb to Fl/4.
A valid analogy, would size the box to match output level at Fb, and size the port area so that Fb = Fl/4. One system is distributed, the other roughly lumped there is no reason to expect the behavior to match at f >> fl/4, it would be erroneous if it did.
It is well known that undersized ports in vented systems are nonlinear and exhibit dynamic compression with level increase. TLs have the advantage of very large port area and should not exhibit much compression, however the penalty is significantly increased box volume and higher resonant modes. A vented system with a large port, or a properly designed passive radiator vent substitute is worth considering as an alternative to a TL.
Pete B.
He also uses equal port area in the comparison when the correct analogy would adjust port area to match Fb to Fl/4.
A valid analogy, would size the box to match output level at Fb, and size the port area so that Fb = Fl/4. One system is distributed, the other roughly lumped there is no reason to expect the behavior to match at f >> fl/4, it would be erroneous if it did.
It is well known that undersized ports in vented systems are nonlinear and exhibit dynamic compression with level increase. TLs have the advantage of very large port area and should not exhibit much compression, however the penalty is significantly increased box volume and higher resonant modes. A vented system with a large port, or a properly designed passive radiator vent substitute is worth considering as an alternative to a TL.
Pete B.
Scottmoose said:
Astonishing! ;-)
Sigh. I don't want to sound unpleasent here, because that's honestly not my intent, but I couldn't care less whether the alignments Bob used in his little article were optimised or not. That's not the point.
Pete, nobody's arguing that a properly designed BR box can produce similar results, but you seem to have missed the object of the exercise a bit, which was to show that an MLTL enclosure like, for example, Bob's FT1600MK2 is not a BR box. That's it. It was written for the many people with less knowledge than yourself, who think that because an MLTL looks like a reflex box, it must be one, and is simply there to illustrate that a BR cabinet of the same Vb as an MLTL, using the same port area, does not produce the same results. Therefore they are not the same thing, as you yourself point out.
Sigh. I don't want to sound unpleasent here, because that's honestly not my intent, but I couldn't care less whether the alignments Bob used in his little article were optimised or not. That's not the point.
Pete, nobody's arguing that a properly designed BR box can produce similar results, but you seem to have missed the object of the exercise a bit, which was to show that an MLTL enclosure like, for example, Bob's FT1600MK2 is not a BR box. That's it. It was written for the many people with less knowledge than yourself, who think that because an MLTL looks like a reflex box, it must be one, and is simply there to illustrate that a BR cabinet of the same Vb as an MLTL, using the same port area, does not produce the same results. Therefore they are not the same thing, as you yourself point out.
planet10 said:
What I am saying, just as I have stated previously, is that there is a very strong analogy between a resonant transmission line and a vented box around Fl/4 and Fb, just as microwave engineers have known for years. The analogy does not apply for frequencies far above Fl/4.
The details cannot be swept under the rug and blanket statements made based on simplifications. What Brines' page suggests is that Vented systems are in no way similar to TLs, when that is not the case.
Pete B.
You choose to not care about how Brines optimises the vented analogy, however, the failure to do so offers a conclusion in support of yours and perhaps his wishful thinking - that they are in no way alike. The fact is that they are alike in some ways, and different in others, this leads to a better understanding of TLs and not just to prove a premise at will. It would seem that you don't care because you only wish to support a particular premise, valid or not.
Brines makes a claim, a sarcastic one at that, which by the way clouds the issue, "Yea, that looked just like the measured data. Yea, right!"
Yes, sigh, Brines' work suggests that they are entirely different when in fact there is a very strong analogy between the two. His discussion clouds the facts.
Pete B.
Brines makes a claim, a sarcastic one at that, which by the way clouds the issue, "Yea, that looked just like the measured data. Yea, right!"
Yes, sigh, Brines' work suggests that they are entirely different when in fact there is a very strong analogy between the two. His discussion clouds the facts.
Pete B.
Scottmoose said:
Pete, I don't choose to take offense at every imagined slight, but as a professional historian I take the accusation of my being selective with data extremely gravely indeed. I realise no offense was intended, but that is highly insulting, not to mention innacurate, because you seem to be looking at something different. You're also putting words into both my, and Dave's mouth.
I really, really did not wish to begin yet another technical debate on MLTLs with this. All I did was post a useful link which demonstrates that MLTLs (or two summed resonant structures, one a 1/2 wave, the other a 1/4 wave, creating a non harmonic summed sytem in its passband) and BR boxes are not the same thing, as you yourself have noted several times. They share some similarities of course. Just as most trunkated horns and BR enclosures do. And some variations on dipoles if it comes to that. They're all singing variations from a songsheet, to major or minor extents. I am perfectly aware of this, you might be astonished to learn. But that doesn't make them exactly the same thing though, which is all I'm saying -we are actually in agreement you know.
I don't fall-in with everything Bob writes. However, if I'd known you were going to make such a big deal over a fairly simple article intended only to demonstate to beginners that an MLTL variation of vented type enclosures produces a different response to a more regular type of reflex enclosure with the same Vb and port area (and therefore they cannot be exactly the same thing, despite their similarities in some respects), I'd never have bothered posting the wretched thing. But that's why I wasn't fussed about if the BR alignment was optimal or not, which I probably didn't make too clear. It wasn't the issue in question, and indeed, would negate the point of the comparison; i.e. newbie to speaker design spots what looks like a de rigure floorstander with a vent, and assumes it is a normal BR box, which are relatively forgiving of alterations, within reason. He then changes the cabinet shape to suit himself, whilst being careful to retain the same volume, and subsequently wonders why the response is different to the original, unless further changes to the vent area / length are made.
Dave -I guess I'm headed for the sin-bin now, right?
Best regards (honestly meant)
Scott
I really, really did not wish to begin yet another technical debate on MLTLs with this. All I did was post a useful link which demonstrates that MLTLs (or two summed resonant structures, one a 1/2 wave, the other a 1/4 wave, creating a non harmonic summed sytem in its passband) and BR boxes are not the same thing, as you yourself have noted several times. They share some similarities of course. Just as most trunkated horns and BR enclosures do. And some variations on dipoles if it comes to that. They're all singing variations from a songsheet, to major or minor extents. I am perfectly aware of this, you might be astonished to learn. But that doesn't make them exactly the same thing though, which is all I'm saying -we are actually in agreement you know.
I don't fall-in with everything Bob writes. However, if I'd known you were going to make such a big deal over a fairly simple article intended only to demonstate to beginners that an MLTL variation of vented type enclosures produces a different response to a more regular type of reflex enclosure with the same Vb and port area (and therefore they cannot be exactly the same thing, despite their similarities in some respects), I'd never have bothered posting the wretched thing. But that's why I wasn't fussed about if the BR alignment was optimal or not, which I probably didn't make too clear. It wasn't the issue in question, and indeed, would negate the point of the comparison; i.e. newbie to speaker design spots what looks like a de rigure floorstander with a vent, and assumes it is a normal BR box, which are relatively forgiving of alterations, within reason. He then changes the cabinet shape to suit himself, whilst being careful to retain the same volume, and subsequently wonders why the response is different to the original, unless further changes to the vent area / length are made.
Dave -I guess I'm headed for the sin-bin now, right?
Best regards (honestly meant)
Scott
Guys:
I am so, so sorry that I in a sense started this. I should have scrolled back and done some reading before posting my question.
I'm having some severe personal issues this week and I'm just not terribly intellectual.
It's my fault for not understanding that an ML-TL was, what threw me was the lack of an internal brace like the regular TL Thor has, I was expecting a longer line.
I am truly sorry to have sparked this off.
I am so, so sorry that I in a sense started this. I should have scrolled back and done some reading before posting my question.
I'm having some severe personal issues this week and I'm just not terribly intellectual.
It's my fault for not understanding that an ML-TL was, what threw me was the lack of an internal brace like the regular TL Thor has, I was expecting a longer line.
I am truly sorry to have sparked this off.
Hi John,
This subject probably would have come up sooner or later, and I actually believe it is best to discuss it because TLs are not very well understood. People are going to disagree at times this is how we come to a better understanding. I have made comments to the effect that some modified TLs are moving closer to something similar to a vented system, and I've pointed out the TL to vented analogy on the web for many years. This is why I responded.
Hope your other issues work out.
Best Regards,
Pete B.
This subject probably would have come up sooner or later, and I actually believe it is best to discuss it because TLs are not very well understood. People are going to disagree at times this is how we come to a better understanding. I have made comments to the effect that some modified TLs are moving closer to something similar to a vented system, and I've pointed out the TL to vented analogy on the web for many years. This is why I responded.
Hope your other issues work out.
Best Regards,
Pete B.
jgwinner said:
I could also point out my professional credentials also, however people can find them if they're interested.
The point is that if you refer to a site and in a sense endorse at least that particular discussion on the page, and I point out a flaw that you then dismiss as unimportant I have a right to comment. The fact is you avoided the point, and instead dismissed it, as you have done again below. I don't see it as an accusation, I made a point and you dismissed it, I don't call that an accusation - I call them as I see them. I don't see it as putting words in anybody's mouth, in fact in a sense you both seem to be demanding an answer to the question are they the same or different, when you're asking the wrong question. The answer is that there is an analogy over a limited frequency range that offers some insight into the behavior of the system. That is my answer.
You are corrrect no offense was intended, just wanted to clarify the situation because it is something that I've addressed several times on the net. This analogy was pointed out to me by a professor of audio, electrical engineering, and acoustics at the university level.
If you wish to dismiss this important analogy, that is your choice and we can agree to disagree.
On another subject, I'd like to hear listening impressions of these Thor variants since this is what matters in the end, enjoying the process and the music.
Best Regards,
Pete B.
The point is that if you refer to a site and in a sense endorse at least that particular discussion on the page, and I point out a flaw that you then dismiss as unimportant I have a right to comment. The fact is you avoided the point, and instead dismissed it, as you have done again below. I don't see it as an accusation, I made a point and you dismissed it, I don't call that an accusation - I call them as I see them. I don't see it as putting words in anybody's mouth, in fact in a sense you both seem to be demanding an answer to the question are they the same or different, when you're asking the wrong question. The answer is that there is an analogy over a limited frequency range that offers some insight into the behavior of the system. That is my answer.
You are corrrect no offense was intended, just wanted to clarify the situation because it is something that I've addressed several times on the net. This analogy was pointed out to me by a professor of audio, electrical engineering, and acoustics at the university level.
If you wish to dismiss this important analogy, that is your choice and we can agree to disagree.
On another subject, I'd like to hear listening impressions of these Thor variants since this is what matters in the end, enjoying the process and the music.
Best Regards,
Pete B.
Scottmoose said:
John, you have nothing whatsoever to apologise for.
I'm sure your credentials are impessive Pete. I refered to my own day job simply as an explanation as to why some of your perhaps less well-chosen remarks can cause severe, though unintended offense. I actually abandoned posting on this thread for a while due to some other comments you made a while back. And I'm not alone. Sorry if that's a shock to you -as I say, I like to be on friendly terms with everyone. Life's too short for anything else.
So, Dave, Bob and I are asking 'the wrong question', which is apparantly 'are MLTLs and BR boxes the same or different?' Whilst you are pointing out that they are related. But we know that -you're reading far too much into selective sentences and phrases and drawign incorrect conclusions regarding out own background, knowledge and experience. We do all have a certain amount of these regarding speaker enclosure design and the physical principles of their operation, believe it or not. You say you've posted regarding this similarity between the various types of vented enclosures many times? Great. You might not realise this, but so has Dave. And Martin. And Greg Monfort. And Rick Schultz. And me. And quite a few other people. We have all done just that on this board and elsewhere, both electronically and in print -to borrow your own phrase, you can find them if you're interested.
You state that I am deliberately evading your point, which is, I believe, that MLTLs and BR enclosures are variations on a common, vented theme, correct? But I've gone out of my way to agree with you that they have similarities. Didn't you reads my posts? We know they do. If that means I've dismissed your point, then what in the name of prognosticating pelicans is an acceptance?
Now, I shall repeat ours, of which Bob's article provides a useful illustration. Take 1 MLTL style of vented enclosure. Now, retain the Vb and port dimensions, and alter the HxWxD dimensions. Astoundingly enough, the response changes. That is the only point I, and Dave, were making. No more, no less. We weren't talking theory, we know perfectly well without being told that we can make further alterations to the new enclosure by adjusting the port dimensions to optimise the alignment. But the very necessity for doing so is the perfect illustration of what we're talking about -that the two variations on a commen enclosure theme don't behave in entirely the same way. They have similarities, fine, we accept that, but they are not identical, as we all know and are accepting. My Peugeot has the same engine and floor plan as a Citroen, but that doesn't mean it's the same car.
Regards
Scott
I'm sure your credentials are impessive Pete. I refered to my own day job simply as an explanation as to why some of your perhaps less well-chosen remarks can cause severe, though unintended offense. I actually abandoned posting on this thread for a while due to some other comments you made a while back. And I'm not alone. Sorry if that's a shock to you -as I say, I like to be on friendly terms with everyone. Life's too short for anything else.
So, Dave, Bob and I are asking 'the wrong question', which is apparantly 'are MLTLs and BR boxes the same or different?' Whilst you are pointing out that they are related. But we know that -you're reading far too much into selective sentences and phrases and drawign incorrect conclusions regarding out own background, knowledge and experience. We do all have a certain amount of these regarding speaker enclosure design and the physical principles of their operation, believe it or not. You say you've posted regarding this similarity between the various types of vented enclosures many times? Great. You might not realise this, but so has Dave. And Martin. And Greg Monfort. And Rick Schultz. And me. And quite a few other people. We have all done just that on this board and elsewhere, both electronically and in print -to borrow your own phrase, you can find them if you're interested.
You state that I am deliberately evading your point, which is, I believe, that MLTLs and BR enclosures are variations on a common, vented theme, correct? But I've gone out of my way to agree with you that they have similarities. Didn't you reads my posts? We know they do. If that means I've dismissed your point, then what in the name of prognosticating pelicans is an acceptance?
Now, I shall repeat ours, of which Bob's article provides a useful illustration. Take 1 MLTL style of vented enclosure. Now, retain the Vb and port dimensions, and alter the HxWxD dimensions. Astoundingly enough, the response changes. That is the only point I, and Dave, were making. No more, no less. We weren't talking theory, we know perfectly well without being told that we can make further alterations to the new enclosure by adjusting the port dimensions to optimise the alignment. But the very necessity for doing so is the perfect illustration of what we're talking about -that the two variations on a commen enclosure theme don't behave in entirely the same way. They have similarities, fine, we accept that, but they are not identical, as we all know and are accepting. My Peugeot has the same engine and floor plan as a Citroen, but that doesn't mean it's the same car.
Regards
Scott
As I underestand, - it's basically the length ( or height ) that sets the response for the lower end of an MLTL, as with a"normal" TL. Moving the units to the broad side, or changing the W and D , without changing WxD shouldn't alter the response too much....some to be expected though......One could even make a curved front.......
Am I totally astray here, or what??
Am I totally astray here, or what??
Quite right, so long as the driver height along the line remains the same. The baffle-step response will alter of course, given the change in area / dimeter, but that's nothing per-se to do with the enclosure's (internal) response.
I like wide baffles. They can produce some very interesting results -not a little of the dipole effect without actually being diploes themselves. Being sneaky, if you get the width right, you can push the baffle-step issues below the all-critical midrange, so a nice midrange driver working from ~400 upwards isn't being clobbered by a filter, and you only need to apply it to the less-critcal bass drivers. Troel's most excellent site and speaker projects has an interesting discussion and prototype here:
http://www.troelsgravesen.dk/Acapella_WB.htm
The larger pdf file covering the project in full and linked to on the page is also well-worth a read.
Best
Scott
I like wide baffles. They can produce some very interesting results -not a little of the dipole effect without actually being diploes themselves. Being sneaky, if you get the width right, you can push the baffle-step issues below the all-critical midrange, so a nice midrange driver working from ~400 upwards isn't being clobbered by a filter, and you only need to apply it to the less-critcal bass drivers. Troel's most excellent site and speaker projects has an interesting discussion and prototype here:
http://www.troelsgravesen.dk/Acapella_WB.htm
The larger pdf file covering the project in full and linked to on the page is also well-worth a read.
Best
Scott
Actually....that's exactly what I had in mind.....
I've been following Gravesens work for quite some time
I'm a sucker for deep bass ( not necessearly DEEP ), as I play mostly orchestral music these days, and I like to keep the low end too...............So a WB , curved front version of Short Thor has been playing in my head for some weeks now...
BTW -- thanks, Scott
I've been following Gravesens work for quite some time
I'm a sucker for deep bass ( not necessearly DEEP ), as I play mostly orchestral music these days, and I like to keep the low end too...............So a WB , curved front version of Short Thor has been playing in my head for some weeks now...
BTW -- thanks, Scott