Extra thoughts.....
In answer to some of your questions.....
Transmission lines give DEEEEEEP sinewave bass really, really well (my old KEF TL cabinets flap your trousers big time), but don't do kick drum quite like a more normal cabinet, and they take a whole cycle or something before they deliver serious low end.
Some reading I have done extolls an undersized, slightly overdamped bass cabinet, driven by its own amplifier with frequency EQ and phase EQ.
According to the author this gives transient fast and clean, and totally non resonant lows that work really well.
This performance is reliant on the phase EQ though.
One downside of this technique of course, is that the cabinet/driver system is non resonant, and therefore lower efficiency, but highish power amplifiers are relatively cheap nowadays, so this ought not to be an obstacle.
Regards, Eric.
In answer to some of your questions.....
Transmission lines give DEEEEEEP sinewave bass really, really well (my old KEF TL cabinets flap your trousers big time), but don't do kick drum quite like a more normal cabinet, and they take a whole cycle or something before they deliver serious low end.
Some reading I have done extolls an undersized, slightly overdamped bass cabinet, driven by its own amplifier with frequency EQ and phase EQ.
According to the author this gives transient fast and clean, and totally non resonant lows that work really well.
This performance is reliant on the phase EQ though.
One downside of this technique of course, is that the cabinet/driver system is non resonant, and therefore lower efficiency, but highish power amplifiers are relatively cheap nowadays, so this ought not to be an obstacle.
Regards, Eric.
Re: Very interesting
there are a number of reasons. Up until very recently, with Martin King's TL software (and George Augspurger's -- much harder to get your hands on), there were no analytical design tools available*, so TL design was the realm of Rules-of-Thunb and Cut-and-Try. Turns out that some of the R-o-T were not in the ballpark of optimum. So getting a good design was a lot of work and since there is a huge spectrum of possible lines, with only a small percentage that are close to optimum there were many BAD TLines built and many people formed their opinion of TLs are based on these bad examples.
*(and while fairly accurate, are still somewhat cumbersome)
A good TL also tends to be big (Hoffman's Iron Law) and more complex than your plain-jane box, so cost of construction is higher. And because it is bigger and heavier, shipping costs go up. All this conspires to push the end dollar cost of a TL up so high that the TLs advantages are most often swamped in a commercial product.
In DIY-land, particularily now that we have some design tools, big only plays into WAF, and heavy -- well me & a buddy can lug the thing from the workshop into the living room.
The spectrum of possible good TLs is only starting to be explored. From straight lines straight lines to ML-TQWTs (same link) to lines with curved taper, the results of analytically designed boxes are just starting to creep onto the scene.
dave
jmiyake said:
there are a number of reasons. Up until very recently, with Martin King's TL software (and George Augspurger's -- much harder to get your hands on), there were no analytical design tools available*, so TL design was the realm of Rules-of-Thunb and Cut-and-Try. Turns out that some of the R-o-T were not in the ballpark of optimum. So getting a good design was a lot of work and since there is a huge spectrum of possible lines, with only a small percentage that are close to optimum there were many BAD TLines built and many people formed their opinion of TLs are based on these bad examples.
*(and while fairly accurate, are still somewhat cumbersome)
A good TL also tends to be big (Hoffman's Iron Law) and more complex than your plain-jane box, so cost of construction is higher. And because it is bigger and heavier, shipping costs go up. All this conspires to push the end dollar cost of a TL up so high that the TLs advantages are most often swamped in a commercial product.
In DIY-land, particularily now that we have some design tools, big only plays into WAF, and heavy -- well me & a buddy can lug the thing from the workshop into the living room.
The spectrum of possible good TLs is only starting to be explored. From straight lines straight lines to ML-TQWTs (same link) to lines with curved taper, the results of analytically designed boxes are just starting to creep onto the scene.
dave
How about the little wedgies
What do you all think of Bill F.s idea of varying sized wedgies lining the walls? I guess you could get by with 3 walls, bottom, back and one side. Since the dimensions are constantly varying, wouldn't it eliminate the resonance caused by the air tuning to a particular dimension of the speaker interior?
How much size variance would be required to make this work?
James
What do you all think of Bill F.s idea of varying sized wedgies lining the walls? I guess you could get by with 3 walls, bottom, back and one side. Since the dimensions are constantly varying, wouldn't it eliminate the resonance caused by the air tuning to a particular dimension of the speaker interior?
How much size variance would be required to make this work?
James
Re: about your 8 s
No real science or math here just pure experimentation, I built three different tapered octagons and 4 different baffles and did extensive listening tests and some measurements before I settled on this design, I must admit the sphere I tried (from US Enclosure) did very well in the listening test and measured very well also, but the logistics of mounting the tweeter close enough to the Mid/Woofer was too difficult and wouldn't look very good. As far as parallel surfaces are concerned, the taper takes care of that.
jmiyake said:
No real science or math here just pure experimentation, I built three different tapered octagons and 4 different baffles and did extensive listening tests and some measurements before I settled on this design, I must admit the sphere I tried (from US Enclosure) did very well in the listening test and measured very well also, but the logistics of mounting the tweeter close enough to the Mid/Woofer was too difficult and wouldn't look very good. As far as parallel surfaces are concerned, the taper takes care of that.
Regarding the wedgies,
Just keep in mind, the secret is to rotate each wedgie 90 deg. from its neighbors to prevent parallel wedgie surfaces. The idea is to bounce that backwave around in so many random directions and get is so confused that it simply dispairs of ever pulling itself together and finding its way back out through the cone.
Think of it in terms of wave psychology--try to become the wave.
Bill
Just keep in mind, the secret is to rotate each wedgie 90 deg. from its neighbors to prevent parallel wedgie surfaces. The idea is to bounce that backwave around in so many random directions and get is so confused that it simply dispairs of ever pulling itself together and finding its way back out through the cone.
Think of it in terms of wave psychology--try to become the wave.
Bill
Wedges vs waves
Ok, I am trying to think like a wave...
so the higher frequencies have smaller waves that are more broken up by small wedgies. As you go lower the waves are less affected by small wedgies. So what are the larger waves doing? Specifically what are the waves roughly the size of the cabinet dimensions doing? They would be ringing like a bell but what happens as the waves crash onto the little wedgies?
I think I am getting a headache.
james
Ok, I am trying to think like a wave...
so the higher frequencies have smaller waves that are more broken up by small wedgies. As you go lower the waves are less affected by small wedgies. So what are the larger waves doing? Specifically what are the waves roughly the size of the cabinet dimensions doing? They would be ringing like a bell but what happens as the waves crash onto the little wedgies?
I think I am getting a headache.
james
To help me think like a wave, I like to play dress-up and do interpretive dances, but that's not for everyone.
Anyway, that's enough for your first time, you can stop thinking like a wave now.
The bigger waves don't crash, they sorta ooze. And they don't give a rat's hiney about wedgies. Darn them, they are nearly impossible to spread out or damp in a closed box, (chalk one up for open transmission lines). This is one reason why it's a good idea to enclose bass and mid drivers in their own boxes--the fundamental air mass resonance in each compartment can be pushed out of the passband.
You do have the option of effectively clipping LF waves with a vario-vent, which some would argue is no longer a closed box.
Bill
Anyway, that's enough for your first time, you can stop thinking like a wave now.
The bigger waves don't crash, they sorta ooze. And they don't give a rat's hiney about wedgies. Darn them, they are nearly impossible to spread out or damp in a closed box, (chalk one up for open transmission lines). This is one reason why it's a good idea to enclose bass and mid drivers in their own boxes--the fundamental air mass resonance in each compartment can be pushed out of the passband.
You do have the option of effectively clipping LF waves with a vario-vent, which some would argue is no longer a closed box.
Bill
Bill F. said:
The vario-vent is an interesting beast. Developed by EJ Jordan when he was at Goodmans (ARU -- Acoustic Resistance Unit). I think of these as a poor mans TL since well done, one of their prime features i a very flat impedance curve. Bill Perkins has done a lot of work on this kind of loading (he calls it DAMPS) on his PR-2. It can work quite well.
dave
Vacillating
Still trying to think like a wave...
So I have a box 32" long. The wavelength would be about 400hz, right.
I have wedges that range up to 5" long let us say... that takes us to 27" or 500hz. So our semi oozing wave is now trying to bounce back and forth...
In this example what is happening?
Also what is happening at 800hz?
What about 200hz?
I will keep bouncing off the walls until you tell me. I think I bruised my elbow.
James
Still trying to think like a wave...
So I have a box 32" long. The wavelength would be about 400hz, right.
I have wedges that range up to 5" long let us say... that takes us to 27" or 500hz. So our semi oozing wave is now trying to bounce back and forth...
In this example what is happening?
Also what is happening at 800hz?
What about 200hz?
I will keep bouncing off the walls until you tell me. I think I bruised my elbow.
James
>I will keep bouncing off the walls until you tell me. I think I bruised my elbow.
I fear I have brought you to a resonant high-Q state of wave empathy. Quick, everyone, grab your butterfly nets and lets damp this poor chap before he hurts himself further!
Basically, it would be useful to picture things thusly: long waves in a short box don't bounce, they pressurize. Since their cycles occupy relatively large chunks of time, they create pretty uniform levels of fluctuating pressure throughout the box.
By saying they ooze, I refer to the fact that they are no longer effected by the geometry of the surfaces they encounter, only the springiness of the air load in the box. So, basically, you gotta vent 'em or lump 'em and design for them.
If you want to think in elecrical terms (I won't ask you to become the electron), a speaker wall represents a virtually infinite impedence to a LF pressure wave. A vario-vent is a somewhat lower-impedence shunt that damps the amplitude by its turbulent nature.
Bill
I fear I have brought you to a resonant high-Q state of wave empathy. Quick, everyone, grab your butterfly nets and lets damp this poor chap before he hurts himself further!
Basically, it would be useful to picture things thusly: long waves in a short box don't bounce, they pressurize. Since their cycles occupy relatively large chunks of time, they create pretty uniform levels of fluctuating pressure throughout the box.
By saying they ooze, I refer to the fact that they are no longer effected by the geometry of the surfaces they encounter, only the springiness of the air load in the box. So, basically, you gotta vent 'em or lump 'em and design for them.
If you want to think in elecrical terms (I won't ask you to become the electron), a speaker wall represents a virtually infinite impedence to a LF pressure wave. A vario-vent is a somewhat lower-impedence shunt that damps the amplitude by its turbulent nature.
Bill
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