Probably a long shot, but maybe I should have or should just make a thread asking if any one who lives in New Hampshire or Massachusetts, would let me come listen to their TL and/or ported enclosure.
Hmmm . . . maybe I can go to a local store around here that has good speakers, but I don't think such a place exists
Maybe I'll just go to Best Buy for fun 
Hmmm . . . maybe I can go to a local store around here that has good speakers, but I don't think such a place exists
Maybe I'll just go to Best Buy for fun A BR enclosure will also have peaks at higher frequenies generated by standing waves in the enclosure. People tend not to recognize this because the modeling tools they use to design BR enclusres are based on lumped parameter models, they are not sophisticated enough to include any standing wave effects.
A TL and a BR enclosure are very similar. My definition of a TL is very broad, any enclosure geometry that relies on standing wave resonances to augment the bass output is in my opinion a TL. This covers a wide range of cabinets from almost all back loaded horns to many tower style BR designs. A classic BR enclosure is one where the air inside is compressed uniformily to produce the spring that is reacted by the slug of air mass in the port. If the air in the box is not compressed uniformily and there is a standing wave then I would consider the enclosure to be more like a TL. Those are my personal definitions and may or may not agree with other people's (like Scott, Dave, or yours) which is OK. It just gives you a reference baseline for understanding my statements.
I think we would both advocate adding stuffing to the inside of an enclosure, I think there are advantages even for a classic BR design. A minimal amount of stuffing can be very effective at contolling unwanted standing waves which can have a negaitve impact on the system SPL response above the tuning frequency. I noticed in reading your article on Rod Elliot's site that you are using results from Bradbury as part of your position, I think that you will find in the past 10 years Bradbury's model for the interaction of air moving through a fiber tangle is incorrect (see Bullock and Augspurgers AES preprints if my work is not credible enough for you). It is an interesting and elegant mathematical solution to a partial differential equation, but not correct. I beat my head against the wall with Bradbury's method for almost 10 years and never got good correlation with any test data I could find, I guess I am a slow learner.
In my opinion, lightly stuffing a TL should be the goal. Solve as many of the standing wave issues with the geometry of the box and only use the stuffing to clean up the remainder of the ripples. A heavily stuffed TL is in my eyes a non optimized TL design, you are throwing away potential acousitc output.
Not the TL's I design. I think that the advantage of a well designed TL (keep in mind my definition) is that you can control the response to augment the bass output over a wider range of frequencies and then cut off the terminus output at a prescribed frequency. You can design an expanding TL to produce a significant amount of bass energy to help compensate for the roll off of a low Qts driver, not so easy for a BR enclosure design. There is a tremendous amount of flexibilty in the geometry design to use drivers that might not work so well in a standard alignment table generated BR enclosure. A classic BR design will only augment the bass output over a narrow range of frequencies associated with the tuning frequency.
Another advantage of the TL is a lack of port noise sometimes associated with the tube typically used as a port in a BR box. I believe this is due to the typically larger size of the terminus opening in a TL and the lack of internal acoustic reflections in the BR tube created by the sudden geometry changes at the entrance and exit of the tube.
Personally I do not look at pipe resonces as flaws, I see them as just a different design challenge. If you don't see the point, or any advantage, of designing a TL then stick to BR designs. I do not believe there is an optimim enclosure type, there are good and bad examples of each, so building one that you are confident in designing and supports the trade-offs that produce the sound that appeals to your taste in your system/room seems like a reasonable approach. It makes no difference to me.
How would the difference be for a sub?
I have spent some time simulating a fairly small sub (95L) using a 15" midbass driver in hornresp.
Having a 160cm pipe going from 800cm2 to 400cm2 yields loading down to 40Hz or so.
Doing a BR with the same dimension (90L + 5L for the port) gives virtually the same response (except a bunch of peaks and dips +120Hz with the TP)
Same cone excursion and similar impedance.
GD for the BR it larger at resonance though.
Having listen to the impulse response generated by hornresp I prefer the TP over BR.
On a side note doing a TH with the same taper provides about the same response as the TP but with slightly worse cone control (at the peak) but with slightly more output at loading (due to narrower excursion null) Also worse IR as all resonance peaks have a negative copy from the driver firing into the pipe. Could be a benefit in real life from it though. Not sure.
I have spent some time simulating a fairly small sub (95L) using a 15" midbass driver in hornresp.
Having a 160cm pipe going from 800cm2 to 400cm2 yields loading down to 40Hz or so.
Doing a BR with the same dimension (90L + 5L for the port) gives virtually the same response (except a bunch of peaks and dips +120Hz with the TP)
Same cone excursion and similar impedance.
GD for the BR it larger at resonance though.
Having listen to the impulse response generated by hornresp I prefer the TP over BR.
On a side note doing a TH with the same taper provides about the same response as the TP but with slightly worse cone control (at the peak) but with slightly more output at loading (due to narrower excursion null) Also worse IR as all resonance peaks have a negative copy from the driver firing into the pipe. Could be a benefit in real life from it though. Not sure.
Actually Martin, I reckon your definition of a TL (as in in terms of a damped pipe) is pretty much exactly in line with what Bailey created. 🙂 I know I set a very rigid definition & if I'm honest, I don't always stick to it in practice. I do rate the 'purist' (for want of a better phrase) TL though, albeit within specific circumstances & no more or less than any other type of cabinet in other situations. Horses for courses.
It is true that I refered to Bradburies paper in the article, but only to his published data regarding measurements of the attenuation verses frequency of various types and densities of stuffing.
These have nothing to do with his proposed mechanism.
In the compliance scaling article, also on Rods site, I outlined various methods of using scaling plus filters and output impedance modification to achieve a desired result.
The advantage of this is that it is always possible to put the driver in a box that optimises energy transfer between it and the Helmholtz resonator, and use the other filters to taylor the responce to that required.
This is the approach used in professional monitoring, p.a. etc, with good reason, from a given driver you get the most output, with the least power input and cone excursion.
It does have the disadvantage that you need to do some electronics, and treat the speker box and electronics as one system.
Speaker builders in general seem to steer clear of this for various reasons, and it is understandable that in general people who build speakers would rather do it all acoustically.
If you do however it has disadvantages of the sort that I have outlined, that people seem to ignore or discount because the TL has some mystical other property not possesed by the humble BR, it dosen't, and that's my overall point.
rcw.
These have nothing to do with his proposed mechanism.
In the compliance scaling article, also on Rods site, I outlined various methods of using scaling plus filters and output impedance modification to achieve a desired result.
The advantage of this is that it is always possible to put the driver in a box that optimises energy transfer between it and the Helmholtz resonator, and use the other filters to taylor the responce to that required.
This is the approach used in professional monitoring, p.a. etc, with good reason, from a given driver you get the most output, with the least power input and cone excursion.
It does have the disadvantage that you need to do some electronics, and treat the speker box and electronics as one system.
Speaker builders in general seem to steer clear of this for various reasons, and it is understandable that in general people who build speakers would rather do it all acoustically.
If you do however it has disadvantages of the sort that I have outlined, that people seem to ignore or discount because the TL has some mystical other property not possesed by the humble BR, it dosen't, and that's my overall point.
rcw.
If it isn't a foolish question, what exactly are these famous 'mystical properties' you are refering to supposed to be? I mean, you're stating that other people claim TLs possess 'mystical properties', but where and what these are is currently elluding me. 😕 Last I checked, there wasn't a whole lot that was mystical about them. The physics is rather well defined, largely thanks to Augspurger, Schultz, and particularly Martin.
For the above (I know I'm not the brightest even when I'm not waiting for half a dozen pain-killers to kick in), you seem to be suggesting that a BR, or perhaps one should say an overall system designed with this ability in mind can ~mimic XYZ characteristics via a variety of electrical filters &c. Correct? Fair enough. I know plenty of systems not dissimilar. However, not everyone wishes to do this, can do it, or regards it as being optimal or even benefical. Personally, I sit on the fence; I can see the potetianl benefits & problems of both takes. YMMV as ever.
For the above (I know I'm not the brightest even when I'm not waiting for half a dozen pain-killers to kick in), you seem to be suggesting that a BR, or perhaps one should say an overall system designed with this ability in mind can ~mimic XYZ characteristics via a variety of electrical filters &c. Correct? Fair enough. I know plenty of systems not dissimilar. However, not everyone wishes to do this, can do it, or regards it as being optimal or even benefical. Personally, I sit on the fence; I can see the potetianl benefits & problems of both takes. YMMV as ever.
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I don't see anything mystical about a TL, it is pretty well understood and can be designed very accurately. No mysticism at all. Sometimes treating a "ported box" purely as a classic BR is a gross oversimplification of what is really going on in the box and can lead to unexpected results.
For the sake of historical interest, Bailey's original Wireless World article actually put quite an emphasis on just that. Great way of doing it too; he used exploding wires to generate a suitable pulse with which he could measure the transient response of various systems -some have suggested this might have been one of the first times it had been done with reasonable accuracy. Whether that's true or not I don't know, but it certainly wasn't common practice in wider speaker-building & design circles back in 1965. Anyway, contemporary BRs (pre the T/S vented box alignments generally used these days) were found to be ringing past 5ms; the TL was critically damped within 1. No, I wouldn't read too much into that, but the fact remains that a critically damped TL inherently possess a very good impulse response.
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Hi Jimmy154,
I have a lot of trust in the simulation program LEAP by LinearX. Chris Strahm, the owner, wrote an excellent paper on the differences between BR, IB and TL's as shown in this link -
http://www.linearx.com/files/pdf/EncShopApp_01.pdf
Well worth reading IMO.
Regards
Peter
I have a lot of trust in the simulation program LEAP by LinearX. Chris Strahm, the owner, wrote an excellent paper on the differences between BR, IB and TL's as shown in this link -
http://www.linearx.com/files/pdf/EncShopApp_01.pdf
Well worth reading IMO.
Regards
Peter
It was.
Here's one on group delay
http://www.geocities.com/cc00541/group_delay.html
This group delay might be what I and most people who don't like BR designs are hearing.
The Author writes: In researching this dissertation, I was unable to ascertain a finite limit for acceptable group delay in speaker design. It appears to be relatively indiscernible, especially when listening to musical content (as opposed to test tones), and some studies indicate its effects to be partially masked by the reverberant field of the room.
Why purchase low distortion drivers in the first place then? Why build your own speakers? Why not buy some speakers from guys in a white van? Your listening to reflected sound with plenty of distortion anyway.
Or just think of your room as your own funny shaped "horn" you live in. It must sound better because it makes your drivers louder. Just adds a little delay and timbre to the sounds you're listening to, but you can't hear that well anyway and if you think you can, then you're
I would really be surprised if people all had the same perception when it comes to hearing or any sense. Some people visually perceive something moving before others do. Maybe something similar applies to sound.
Maybe people with big ears don't hear group delay as well because their ears create a lot of group delay before the sound hits their ear drums anyway
IF that's what you're hearing then it's a bad design. It's relatively easy to design a BR box so that the max group delay occurs at freqs low enough that it doesn't matter.
One reason people cite as an advantage of a two way system is that it ts easy to keep group delay within the Blauert and Laws curve limit.
An AES paper I have indicates that tests show that people cannot hear the difference between second and higher order roll off for frequencies above 50Hz.
If this is due to group delay or faster roll off is not clear but in the average room with normal music signals I doubt if it is much of an issue.
With a three way system there is a crossover with a large group delay in an area in which the ear is sensitive to this effect, and this is where the satellite plus subwoofer system has an advantage in that the crossover frequency can be moved down to the 80-100Hz. Region.
As I pointed out in my article however now the typical nominally five or six inch driver will be overdriven even at modest levels in a sealed box with a cut off in this region, and you can avoid this by using the filter in a 5.1 receiver as part of a scaled QB5 filter assisted alignment, this then having the group delay of a sixth order Q=0.5 filter.
You can also use an eight inch driver in a sealed box, with a high pass bi-quad filter if you are really worried about group delay.
My references to transmission lines are based upon many web pages I have seen and forum submissions I have read that proclaim the magical properties of transmission lines, such as a six inch driver that goes down to 30Hz. for instance.
When I point out that it may go down that far but a simple calculation will show that the driver will have to make impossible excursion for you to hear it, I usually get replies of the sort that you can't measure everything and I obviously haven't heard a good TL, or the implication if not the statement that since there were particularly good omens on the day they made theirs, that the spell they cast worked so well it enables their gadget to defy the laws of physics obeyed by lesser creations.
It is good that in this forum it is possible to have robust discussion with out things degenerating into a slanging match, although it's a close thing sometimes.
Rcw.
An AES paper I have indicates that tests show that people cannot hear the difference between second and higher order roll off for frequencies above 50Hz.
If this is due to group delay or faster roll off is not clear but in the average room with normal music signals I doubt if it is much of an issue.
With a three way system there is a crossover with a large group delay in an area in which the ear is sensitive to this effect, and this is where the satellite plus subwoofer system has an advantage in that the crossover frequency can be moved down to the 80-100Hz. Region.
As I pointed out in my article however now the typical nominally five or six inch driver will be overdriven even at modest levels in a sealed box with a cut off in this region, and you can avoid this by using the filter in a 5.1 receiver as part of a scaled QB5 filter assisted alignment, this then having the group delay of a sixth order Q=0.5 filter.
You can also use an eight inch driver in a sealed box, with a high pass bi-quad filter if you are really worried about group delay.
My references to transmission lines are based upon many web pages I have seen and forum submissions I have read that proclaim the magical properties of transmission lines, such as a six inch driver that goes down to 30Hz. for instance.
When I point out that it may go down that far but a simple calculation will show that the driver will have to make impossible excursion for you to hear it, I usually get replies of the sort that you can't measure everything and I obviously haven't heard a good TL, or the implication if not the statement that since there were particularly good omens on the day they made theirs, that the spell they cast worked so well it enables their gadget to defy the laws of physics obeyed by lesser creations.
It is good that in this forum it is possible to have robust discussion with out things degenerating into a slanging match, although it's a close thing sometimes.
Rcw.
Don't know why people care about that sort of thing really. I'm kind of embarrassed at how much time I spend thinking about this silly hobby. I just want to build some descent speakers and not have to think about them for the next three or four lifetimes. That's right I'm taking them into my afterlives!
That's right, with an "s" When I started this thread. I went from thinking I was going to build a TL with 1 woofer per enclosure and I only considered going ported because I wanted to use 2 woofers per enclosure, but now I am think the best design for me is 1 woofer in a ported enclosure.
I'm going to use the kx project drivers/software as my pc controlled active crossover. Do I need to measure the specs for my 21W/8555-01 ScanSpeak drivers? I already tried and it did not go too well. Specs were not repeatable. I think the Fs of 22 Hz is too low for my sound card to get accurate specs, but I did not calibrate it. Other drivers with higher Fs' measured fine I think. I can double check; I use Speaker Workshop.
I also have to reread that rear vs front firing port thread.
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Ah, well, I entirely agree with you from the POV of excessive claims & that kind of nonsense, although in fairness, I suppose I should mention that an appropriately selected 6in driver can in fact offer useable output down to 30Hz without excessive travel in various forms of QW box, although if we're sticking purely with heavily damped pipes (i.e. what is generally called a TL) then it's certainly very uncommon.
In a hermetically sealed Northern hemisphere shoe box perhaps.
But down here we have open plan flow through ventilation etc. to suit a sub tropical climate, and you might as well set your sound system up in a paddock for all the room gain you get.
rcw.
But down here we have open plan flow through ventilation etc. to suit a sub tropical climate, and you might as well set your sound system up in a paddock for all the room gain you get.
rcw.
Not particularly, ~flat to 30Hz anechoic with a suitable 6in driver isn't difficult to achieve with a QW / TL style cabinet, but if you need lots of LF dynamic BW in a large & acoustically dead space (which was not previously specified), then short of the largest bass horn you can manage, it's not going to cut it & multiple 15in HE woofers would certainly be my prefered option. Which frankly, they usually are anyway if space permits.
I need help!
I don't know how close I should put the bass and midrange drivers. I would like to keep the woofer about 6-12" away from the midrange, but these speakers are going to be about 1 meter away from my head and I'm looking for a closest to one point source sound. I don't think this woofer-midrange distance will be a problem if I use a 24 dB/octave cross-over at 100 Hz, but I would like to use more of a 6 dB/octave cross-over at around 300 Hz. Do I need to keep the woofer and midrange close if I do this? Is it necessarily bad to have a "stretched" image, if that's the right term?
The speakers are 48" tall and I kind of want to keep the center of gravity low and I want to get some floor gain by putting the woofer closer to the floor. Should I just go with a 24 dB/octave cross-over between the midrange and bass driver at 100 Hz, so I won't stretch the image, since the speakers will be 1 meter away from my head?
I don't know how close I should put the bass and midrange drivers. I would like to keep the woofer about 6-12" away from the midrange, but these speakers are going to be about 1 meter away from my head and I'm looking for a closest to one point source sound. I don't think this woofer-midrange distance will be a problem if I use a 24 dB/octave cross-over at 100 Hz, but I would like to use more of a 6 dB/octave cross-over at around 300 Hz. Do I need to keep the woofer and midrange close if I do this? Is it necessarily bad to have a "stretched" image, if that's the right term?
The speakers are 48" tall and I kind of want to keep the center of gravity low and I want to get some floor gain by putting the woofer closer to the floor. Should I just go with a 24 dB/octave cross-over between the midrange and bass driver at 100 Hz, so I won't stretch the image, since the speakers will be 1 meter away from my head?
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Ideally they would occupy the same space, though in practice a c-t-c spacing of < 1/4 WL of the XO point is close enough, so for 300 Hz = ~13560"/4/300 = ~11.3". WRT 'stretching', I find it very distracting, especially if the XO is > ~500 Hz, but some folks are fine with up to a WL apart = ~45.2". Still, considering your near-field app, closer is better.
1st order XOs are desirable, but textbook ones typically don't sound good unless the XO points are very low/high, so I prefer using active >24 dB/octave in our acute hearing BW to minimize overlap and even these need the drivers physically aligned for best performance if digital delay isn't used.
GM
1st order XOs are desirable, but textbook ones typically don't sound good unless the XO points are very low/high, so I prefer using active >24 dB/octave in our acute hearing BW to minimize overlap and even these need the drivers physically aligned for best performance if digital delay isn't used.
GM
Hmmm . . . sounds like I should go with ported
Here's what have. The one on the left is an Usher 8955a in a 10:1 tapered TL with a start area of 5 Sd and length of 90 inches. The middle one is a ScanSpeak 21W8555-01 in the same TL and the one on the right is a Usher in an enclosure half the volume of the TLs, so I can use two for my design. However, for the ported box, I get a different result using MJK's ML TQWT spreadsheet with same dimensions, I believe. The one in the picture is his standard "ported" spreadsheet.
Check out some of my posts on diyaudio... I've built and measured a ton of horns, tapped horns, and a few transmission lines.
I would discourage you from building a transmission line with a ration of 10:1. With a ratio like that, there is virtually zero output emanating from the end of the line.
What you end up with is a response which is virtually equivalent to a sealed box, and a design that's a lot of hassle to build. What works better is to use a big mouth, ideally twice as big as the woofer itself. Don't fret if there's ripple in the simulated response; the simulations always exaggerate ripple.
Check out some of the designs from Bob Brines or Terry Cain - these guys know how to deliver real dynamics from a line. Designs like that are particulary exciting with low powered amps.
Could I interest you in a tapped horn? 😀