I simply asked what makes you think the ripples are caused by resonant frequencies? There has to be reason to interpret these as resonances other than stating that they are (and sending us you work biography). To that end, there should be some science behind it. Resonance occurs at linear divisions and multiples of the fundamental resonant frequency. It doesn't look that way to me on the graph. Particularly as this is impedance measurement, not frequency!
Second, those graphs are not from an anechoic chamber and are real in-room measurments and subject to room reverberation. I therefore cannot see how you can be definitive in your assertion. But I am open to a more thorough explanation if you can give it.
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Hey,
First of all, can we agree that there are multipiple resonances? What would you call the "resonance looking" peaks if its not a resonance?
If they are there becourse of a poorly designed unit, or the bassdrivers. Its still a bad construction. They should not be there.
But... If it was the big bassdrivers.. why is the resonances not missing on the project only with the troels units? JA8008
The impedance plot i showed is from the small project without the eminence drivers.
First of all, can we agree that there are multipiple resonances? What would you call the "resonance looking" peaks if its not a resonance?
If they are there becourse of a poorly designed unit, or the bassdrivers. Its still a bad construction. They should not be there.
But... If it was the big bassdrivers.. why is the resonances not missing on the project only with the troels units? JA8008
The impedance plot i showed is from the small project without the eminence drivers.
Hey,
Ofcourse I cant be sure that its the cone/susprension that is the problem. But its my best guess. If i had a impedance plot of the units in free air, i could be sure. The Eminence unit has the problem, as seen here :
http://www.troelsgravesen.dk/JA8008_10inch_files/eminencedeltaliteii2510.pdf
Look at 250Hz, 550Hz and alot at 2KHz. Luckly the unit is not used at high frequencies.
Maby Troels will post a impedance plot of his unit. If there is nothing there, it has to be the enclosure. Im not 100% sharp on DTQWT enclosures. But an enclosure should not introduce resonanses other then those planned.
Ofcourse I cant be sure that its the cone/susprension that is the problem. But its my best guess. If i had a impedance plot of the units in free air, i could be sure. The Eminence unit has the problem, as seen here :
http://www.troelsgravesen.dk/JA8008_10inch_files/eminencedeltaliteii2510.pdf
Look at 250Hz, 550Hz and alot at 2KHz. Luckly the unit is not used at high frequencies.
Maby Troels will post a impedance plot of his unit. If there is nothing there, it has to be the enclosure. Im not 100% sharp on DTQWT enclosures. But an enclosure should not introduce resonanses other then those planned.
Frequency resonance? Not quite in the manner you allude to. I believe there is impedance variation due to the fact it is a loaded horn design. The internal pressure of the cabinet isn't going to be in equilibrium with the outside world at all frequencies and on occasion we will have positive/negative pressure within the cabinet which will affect the measured electrical impedance. However, that does not mean the JA8008 driver is performing poorly.
Also the TQWT can act like a combfilter causing impedance peaks due to line resonances which require lots of damping as in this design. If over damped, certain frequencies may show the dips as on the graph.
I think that is the proper explanation. The JA8008 in free air does not exhibit these impedance anomalies, so it's not the driver as you suggested:
http://www.jantzen-audio.com/download/PD_JA8008_Oct07_v1-f.pdf
However, I've never built or measured such a design. Only briefed over theory and DIYers comments after building them.
Line resonance, as above, but not attributable to the driver.
This is not necessarily true. If a design is a TQWT horn, then the internal pressure will never be perfectly stable and subject to changing pressures variation causing impedance changes of a small amount when measuring the drivers in the cabinet - as in this case. As it's based on a TQWT, there will be combfilter effects that cause impedance variations that are dealt with (usaully through damping). I don't know if the shown measurement is damped or undamped - I suspect overdamped. The important thing is whether we achieve good frequency and phase response, but more than that (since phase is not as critical as we are led to believe, for that speak to Earl Geddes work on perceived distortion, he's GedLee on this site).
The graphs in question only show the JA8008 and TW034 or "the Troel's units". You're talking about the graph from the TQWT not the DTQWT, so no bass drivers to speak of. As for the tweeter, it's in a sealed waveguide and is physically shielded from the varying pressure in the cabinet. It should behave as if in it's own cabinet, which I believe it does. Even if it was, the internal air displacement of the tweeter compared to the 8" driver are non-comparable and only the 8" would shift enough air to affect internal pressure enough to set up line resonances causing impedance variation.
True, but the above holds true for this type of design, and as such, will alter impendance and not have a perfect smooth driver response curve in the graph. Of course, you can keep playing with damping arrangements until it is perfectly sorted, but I doubt anybody has that time. Remember, when Troels measures the JA8008 in the cabinet, if undamped, you are hearing the driver and the cabinet. The impedance dips are likely from overdamping the cabinet to remove audible line resonances, but the effect on electrical impedance on the driver will remain, so when measuring the electrical impedance of the JA8008 in the cabinet, it will look like the driver has some 'issue' when in fact it does not.
Overall, it is only important to keep impedance above a certain point to maintain an easy load for our amps, particularly the lower powered ones like SETs. Providing the frequency response is fairly flat, and the drivers aren't having fits of uncontrolled resonance there should be no issue with this design.
Hi,
Thanks for the link to the driver. I have never seen that document.
Well, i was wrong. The reason that i thought it was the driver, was that i came across this page :
Tapered Quarter Wave Tube - TQWT. Anyone built one here? - Home Theater Forum and Systems - HomeTheaterShack.com
Normaly i would be shure that it was the driver, but i did not know alot about the enclosure. So i found the above and could not see any "ripple". Naturally i thought i was the driver.
You say it doesnt affect the frequency domain? With a filter on the unit, the filter will act on the "ripples", making it visible on the frequency respons, if we had more resolution. Im i right?
The link i found (theres not alot of thouse cabinets on the internet with impedance messurements) has no ripples. Why is that compared to the design by Troels?
Thanks for the link to the driver. I have never seen that document.
Well, i was wrong. The reason that i thought it was the driver, was that i came across this page :
Tapered Quarter Wave Tube - TQWT. Anyone built one here? - Home Theater Forum and Systems - HomeTheaterShack.com
Normaly i would be shure that it was the driver, but i did not know alot about the enclosure. So i found the above and could not see any "ripple". Naturally i thought i was the driver.
You say it doesnt affect the frequency domain? With a filter on the unit, the filter will act on the "ripples", making it visible on the frequency respons, if we had more resolution. Im i right?
The link i found (theres not alot of thouse cabinets on the internet with impedance messurements) has no ripples. Why is that compared to the design by Troels?
Syncro,
I think we use positive air pressure in the cabinet to not push the drivers as such, but certainly make pushing them easier, or more efficient. After all, we're trying to get large dyanmic drivers to work with SETs. This increased air volume is then also used with the tuned horn to increase bass response when the 10" drivers come in to play. It should not be possible to pressurize the cabinet beyond a certain point as increasing the pressure just causes air to flow out the horn like a port. We can only 'pressurize' very briefly. Hence, fast dry bass!
I could be wrong, but that is how I understand it. Horns use compression drivers and here we are using somewhat compressed air in the cabinet. The majority of the cabinet needs to be damped and spongy to not affect the drivers. We don't have the 10" drivers directly hooked to a housing to compress air as in a compression driver, so we have to achieve that another way - through transmission line! This is why damping is only shown where Troels has put it, because we do need some reflective surfaces around the drivers and at the top of the cabinet to help us complete this transmission line.
If the cabinet is not damped you would get significant influence on frequency response as you thought. The point is, this negative affect on frequency is almost completely dispelled as to not be audible if suitably damped. So in a DTQWT or TQWT design, damping is good, whereas in most designs, damping is bad.
I think we use positive air pressure in the cabinet to not push the drivers as such, but certainly make pushing them easier, or more efficient. After all, we're trying to get large dyanmic drivers to work with SETs. This increased air volume is then also used with the tuned horn to increase bass response when the 10" drivers come in to play. It should not be possible to pressurize the cabinet beyond a certain point as increasing the pressure just causes air to flow out the horn like a port. We can only 'pressurize' very briefly. Hence, fast dry bass!
I could be wrong, but that is how I understand it. Horns use compression drivers and here we are using somewhat compressed air in the cabinet. The majority of the cabinet needs to be damped and spongy to not affect the drivers. We don't have the 10" drivers directly hooked to a housing to compress air as in a compression driver, so we have to achieve that another way - through transmission line! This is why damping is only shown where Troels has put it, because we do need some reflective surfaces around the drivers and at the top of the cabinet to help us complete this transmission line.
If the cabinet is not damped you would get significant influence on frequency response as you thought. The point is, this negative affect on frequency is almost completely dispelled as to not be audible if suitably damped. So in a DTQWT or TQWT design, damping is good, whereas in most designs, damping is bad.
Look, if you play with horns and transmission lines you have to think about acoustic impedance.
But that doesn't mean there is trouble ahead. And "audible" depends on your definition. If it's used to tune something to give a flat frequency response with good phase alignment, good transient response, low distortion, then that's good as we are not listening to the box make noise (resonate and 'boom'), rather the box tunes how the combination of drivers work synergistically so the box seems to disappear sonically.
Acoustic impedance, other than being part of physics, like all of physics, is also a tool. You cannot throw something that can be used productively and constructively in to the 'bad' bucket because you choose it as a 'bad' way to design speakers. I would remind you that all the wind instruments you listen to in an orchestra are using acoustic impedance.
If the maths has been done right for this design, then there isn't trouble ahead. There are lots of TL, Voigt Pipes, TQWT that are successful and most people who seem to have heard one don't go back to normal ported boxes.
Why do you think it 'trouble'?
But that doesn't mean there is trouble ahead. And "audible" depends on your definition. If it's used to tune something to give a flat frequency response with good phase alignment, good transient response, low distortion, then that's good as we are not listening to the box make noise (resonate and 'boom'), rather the box tunes how the combination of drivers work synergistically so the box seems to disappear sonically.
Acoustic impedance, other than being part of physics, like all of physics, is also a tool. You cannot throw something that can be used productively and constructively in to the 'bad' bucket because you choose it as a 'bad' way to design speakers. I would remind you that all the wind instruments you listen to in an orchestra are using acoustic impedance.
If the maths has been done right for this design, then there isn't trouble ahead. There are lots of TL, Voigt Pipes, TQWT that are successful and most people who seem to have heard one don't go back to normal ported boxes.
Why do you think it 'trouble'?
Since speaker design is tradeoff, much of the bad that we may have to deal with to get something good come down to personal decision about what one is looking to achieve with the design.
"Perfect sound forever" maybe? But even that we did not get with CD!
I also expect any design to show some evidence of what design it is in a driver plot. For example, an F2 similar to Fb and a big dip at F3 would suggest the measured driver being used in a double/dual chamber reflex design (DCR).
The same is true with Troels design. There are clues to it. How well he deals with them in the final analysis I do not know, but the design is
a) very creative
b) very technical in being feasible at all and requires the person doing it knows a lot to pull it off
c) has been implemented favorably by people
I don't care if he gets paid for the kit. I would care if those favorable reveiwers were receiving money for those reviews.
"Perfect sound forever" maybe? But even that we did not get with CD!
I also expect any design to show some evidence of what design it is in a driver plot. For example, an F2 similar to Fb and a big dip at F3 would suggest the measured driver being used in a double/dual chamber reflex design (DCR).
The same is true with Troels design. There are clues to it. How well he deals with them in the final analysis I do not know, but the design is
a) very creative
b) very technical in being feasible at all and requires the person doing it knows a lot to pull it off
c) has been implemented favorably by people
I don't care if he gets paid for the kit. I would care if those favorable reveiwers were receiving money for those reviews.
Hi,
We are all different. I would prefer to know wether a private DIY'er eans money or not on a product. Thats just me i guess. Not that theres anything wrong with that. But i would like to know, so i would know how much i could rely on his recommendations.
Personally i still think ripples on the impedance and phase is bad. It simply should not be there. If its possible to remove, then i belive that troels is not finished with the kit. Thats my opinion. I showd you another mass-loaded project alike, with no ripples, so i guess its possible.
We are all different. I would prefer to know wether a private DIY'er eans money or not on a product. Thats just me i guess. Not that theres anything wrong with that. But i would like to know, so i would know how much i could rely on his recommendations.
Personally i still think ripples on the impedance and phase is bad. It simply should not be there. If its possible to remove, then i belive that troels is not finished with the kit. Thats my opinion. I showd you another mass-loaded project alike, with no ripples, so i guess its possible.
Well I would disagree with your assertions. (including the impedance, phase worries).
I think anybody who does extra-curricular speaker building since 15 and is now 58 obviously loves doing it. However, it is a pricey thing to keep doing and if you have a family, they don't want to sacrifice their holidays or other niceties in life so you can indulge in a hobby at their expense. To that end, if I was consistently building speakers all the time, I would hope to recuperate some money somehow, so if I made those designs available in kit form it would enable me to pursue that passion without limitation and allow me to reward my family for putting up with me.
Of course, there are a lot of lonely single men in audio who earn money and don't have any other responsibilities. Many of those lonely men once had wives who lost them because hifi turned out to be their first love and acquired all the income until the wife had her revenge in court!
I've seen it happen. I used to go to a gym with a man who had hundreds of thousands of dollars worth of Mark Levinson equipment and super expensive top of the line Martin Logans. He lost it all when his wife divirced him. He had regrets over losing his hifi, but not his wife. If he had the money again, he said he would rebuy all the Mark Levinson he lost. Other than that, he was quite a lonely old man.
So I think for these reasons: to be able to pursue an expensive hobby without sacrifices to family life, and to be able to reward a family for all the time you spend in a workshop and money spent in self-indulgence, it is important to be able to gain an income from it.
I think anybody who does extra-curricular speaker building since 15 and is now 58 obviously loves doing it. However, it is a pricey thing to keep doing and if you have a family, they don't want to sacrifice their holidays or other niceties in life so you can indulge in a hobby at their expense. To that end, if I was consistently building speakers all the time, I would hope to recuperate some money somehow, so if I made those designs available in kit form it would enable me to pursue that passion without limitation and allow me to reward my family for putting up with me.
Of course, there are a lot of lonely single men in audio who earn money and don't have any other responsibilities. Many of those lonely men once had wives who lost them because hifi turned out to be their first love and acquired all the income until the wife had her revenge in court!
I've seen it happen. I used to go to a gym with a man who had hundreds of thousands of dollars worth of Mark Levinson equipment and super expensive top of the line Martin Logans. He lost it all when his wife divirced him. He had regrets over losing his hifi, but not his wife. If he had the money again, he said he would rebuy all the Mark Levinson he lost. Other than that, he was quite a lonely old man.
So I think for these reasons: to be able to pursue an expensive hobby without sacrifices to family life, and to be able to reward a family for all the time you spend in a workshop and money spent in self-indulgence, it is important to be able to gain an income from it.
Syncroniq,
This thread was started to discuss the technical aspects of some well known DIY 3 way speakers, not to attack someone's motives or integrity. Can we please stay on the technical aspects? If you have concerns please contact Troels directly. His email is posted and he will respond. I believe in confronting someone directly, rather than disparaging their name when they are not present. No more trolling. Please no more posts about whether a designer receives profits, let's get back on topic.
This thread was started to discuss the technical aspects of some well known DIY 3 way speakers, not to attack someone's motives or integrity. Can we please stay on the technical aspects? If you have concerns please contact Troels directly. His email is posted and he will respond. I believe in confronting someone directly, rather than disparaging their name when they are not present. No more trolling. Please no more posts about whether a designer receives profits, let's get back on topic.
Well, gentlemen I must be nuts because I am shopping for materials for my next project before I've even bought the drivers. I am thinking of using solid hardwood for the the baffles and a pretty distinct veneer for the sides. I think I will use sapele, which is similar in strength and appearance to mahogany. Here is a link to the sapele:
Sapele Ribbon Stripe 4/4 Lumber Shipped to You! Lowest Price, Highest Quality for your wood working needs from Woodworkers Source
and to the veneer:
AAA Sapele Quilted Veneer Sheet - VeneerSupplies.com
What do you think?
Sapele Ribbon Stripe 4/4 Lumber Shipped to You! Lowest Price, Highest Quality for your wood working needs from Woodworkers Source
and to the veneer:
AAA Sapele Quilted Veneer Sheet - VeneerSupplies.com
What do you think?
Well, I keep researching. I can make the entire cabinet out of ribbon stripe sapele hardwood for the same amount as buying the veneer. The veneer will have a much more intricate design, but be much more labor intensive. The hardwood only requires a filler and then a lacquer finish. Here is a picture of a guitar that was built from sapele in the finish I want.
M.A.D.D CHARITY GUITAR - Woodworking Project Picture Photo Gallery with Furniture, Cabinetry, Musical Instruments, and More
The total cost of the wood for both cabinets will be $320. But no additional finishing costs. Plus routing will be very easy. Any opinions from more experienced builders?
M.A.D.D CHARITY GUITAR - Woodworking Project Picture Photo Gallery with Furniture, Cabinetry, Musical Instruments, and More
The total cost of the wood for both cabinets will be $320. But no additional finishing costs. Plus routing will be very easy. Any opinions from more experienced builders?
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