Yeah, that one doesn't seem to compute. FWIW, I just used PE's additional specs to calc BL and arbitrarily used 7" for its effective diameter as it's close enough for a sim since there's no measured specs:
5.7 ohms Re
0.5 mH Le
7.9583 N/A BL
248.3 cm^2 Sd
GM
I either forgot or neglected to mention that, forget which it was. 8955A specs at usheraudio.com don't match partsexpress.com specs on the pdf. Le I got off the partsexpress description not the pdf at the site. I figured the specs at usher were closer to the correct specs for those woofers. It is problem. I was able to measure some specs correctly using speaker workshop on my 21W855-01 drivers recently, but most of the specs were wrong and inconsistent.
Which specs are you going by, other than the ones you mentioned?
FWIW I believe that the published specs are good enough to model a TL as the TL alignment is more forgiving than the bass reflex design. For BR I measure the T/S specs for each driver then average them to work up the box design. I wouldn't rely on the published specs for a BR.
Also, I have built both TL and BR - I prefer a well designed BR.
Also, I have built both TL and BR - I prefer a well designed BR.
Jimmy,
The important thing is to have a coherent set of specs; mixing and matching from two different sheets is not as reliable as taking a known good, coherent (but incomplete) set of specs and deriving the missing ones from the good data. If you go from two different sheets, you might be looking at a production change. A change to the motor would really throw you off in this way since your two different spec sheets might actually be for two different motors, model number identicality notwithstanding. In this case, the specs would likely be 'incoherent' or mathematically impossible. The DPC program (among others) would alert you to this problem. Changes to suspension compliance or cone mass are not as bad because the specs would likely remain coherent.
I used 235 Cm^2 for Sd as this is what you get when you use the published baffle cutout dimension for effective diameter, which in my experience, is usually pretty close to the real thing. The rest were Fs=25Hz, Vas=133l, Qm=2, Qe=.376, Le=.3mH, Re= 6.5 Ohms, BL=8.1.
At any rate, this is what I got when I modeled it with a 70" tapered line, 2.5 Sd to .3Sd, ~12" driver offset, and lightly stuffed:
That's the same TL as I am using. Mine is folded into a box with outer dimensions of 21" X 11" X 12" or a little less than 50 l gross volume, likely competitive in size with a ported box for that driver.
And look at that F10!
Jimbo
The important thing is to have a coherent set of specs; mixing and matching from two different sheets is not as reliable as taking a known good, coherent (but incomplete) set of specs and deriving the missing ones from the good data. If you go from two different sheets, you might be looking at a production change. A change to the motor would really throw you off in this way since your two different spec sheets might actually be for two different motors, model number identicality notwithstanding. In this case, the specs would likely be 'incoherent' or mathematically impossible. The DPC program (among others) would alert you to this problem. Changes to suspension compliance or cone mass are not as bad because the specs would likely remain coherent.
I used 235 Cm^2 for Sd as this is what you get when you use the published baffle cutout dimension for effective diameter, which in my experience, is usually pretty close to the real thing. The rest were Fs=25Hz, Vas=133l, Qm=2, Qe=.376, Le=.3mH, Re= 6.5 Ohms, BL=8.1.
At any rate, this is what I got when I modeled it with a 70" tapered line, 2.5 Sd to .3Sd, ~12" driver offset, and lightly stuffed:
That's the same TL as I am using. Mine is folded into a box with outer dimensions of 21" X 11" X 12" or a little less than 50 l gross volume, likely competitive in size with a ported box for that driver.
And look at that F10!
Jimbo
Jimmy,
The important thing is to have a coherent set of specs; mixing and matching from two different sheets is not as reliable as taking a known good, coherent (but incomplete) set of specs and deriving the missing ones from the good data. If you go from two different sheets, you might be looking at a production change. A change to the motor would really throw you off in this way since your two different spec sheets might actually be for two different motors, model number identicality notwithstanding. In this case, the specs would likely be 'incoherent' or mathematically impossible. The DPC program (among others) would alert you to this problem. Changes to suspension compliance or cone mass are not as bad because the specs would likely remain coherent.
I used 235 Cm^2 for Sd as this is what you get when you use the published baffle cutout dimension for effective diameter, which in my experience, is usually pretty close to the real thing. The rest were Fs=25Hz, Vas=133l, Qm=2, Qe=.376, Le=.3mH, Re= 6.5 Ohms, BL=8.1.
At any rate, this is what I got when I modeled it with a 70" tapered line, 2.5 Sd to .3Sd, ~12" driver offset, and lightly stuffed:
View attachment 140773
That's the same TL as I am using. Mine is folded into a box with outer dimensions of 21" X 11" X 12" or a little less than 50 l gross volume, likely competitive in size with a ported box for that driver.
And look at that F10!
Jimbo
I got the same graph for the Usher TL with your specs as I did with my specs. I modeled it as 80" long tapered from 5 Sd to .5 Sd, with .45 lb/ft^3 stuffing the first 57" and driver offset by 29" and in an odd shaped enclosure, which looks like this:
An externally hosted image should be here but it was not working when we last tested it.
Also the TL will contain a Scan Speak 21W/8555-01, not an Usher. I shouldn't have posted a picture with the Usher modeled in a TL. My decision is between two 8955a Ushers per ported enclosure or a Scan Speak in the described TL, but actually more like 87" long.
Right now I'm leaning towards a ported enclosure. I mean even Dennis Leary prefers a BR over a TL. While I don't really care for him or his "comedy" or "acting", I do respect him as an audiophile. I might even put a single ScanSpeak per ported enclosure. After all, I am building computer speakers here
I really like the build quality of the ScanSpeaks and I kind of don't want to give that up. But two Ushers per ported enclosure will have much less excursion at a given SPL. And even the posters that like TLs over BR aren't criticizing ported designs as having poor group delay, whatever that means in practice
I've built a pair of ported enclosures that didn't sound that great, but I think they were tuned at a constant SPL to the point where they roll-off or just mistuned and maybe placed too close to a wall.
You know what? Since every one is being so helpful, I should take a picture of my computer area and give a description of my equipment and some one could just tell me what to do
Last edited:
No it isn't. I seem to be repeating myself here but you are not describing a Transmission Line. You are describing an undamped, or lightly damped quarter-wave line. That is not, repeat not, a Transmission Line.
FYI, a Transmission Line is technically an untapered line, damped to provide the flattest possible impedance load to the amplifier. That's it. End of story.
Admittedly, a lot aren't that extreme. A negative taper is often employed, and many people don't damp them quite so heavily, in order to obtain some gain from the line. Strictly, they're not TLs, although they're often called it & are fairly close to being one. Augspurger & Schultz for e.g., essentially stipulate no more that a 1dB null at F3 & no more than 0.5dB lift / response ripple above that & preferably less. That's acceptable; it's a damn site less than most drivers inherently possess.
Nonsense. You're ignoring the different characteristics of the boxes again. A principle design object of a pure TL is to provide the flattest impedance / most unreactive practicable load to the amplifier. I don't seem to recall that being a renowned characteristic of a sealed box, excellent though they can be in other fields. I might add, I can't quite see how, in it's simplest form, leaving the base off a box & adding the requisite amount of stuffing makes it 'over-complicated', while adding a single (or even two or three) internal panel is hardly likely to cause an outbreak in mass-hysteria, with women and urchins weeping in the streets about how difficult the build has suddenly become.
Your experience I fear, is not one that has been shared by most of the rest of us. Quite the reverse as it happens. Perhaps you haven't heard a decent Transmission Line yet.
OK, I found the manufacturer's specs and they calc a larger T/S max flat alignment than PE's which is surprising since it's usually the other way around and using your 'corrected' shorter line length/driver offset, the specs I used now yields an audibly matching sim.
Regardless, as your SS measurements imply, I'd be very surprised if either sets of specs are accurate, but whichever set yields the largest cab is the better choice, so you're right in this case.
GM
all of what I have said Scottnmoose is backed up by theoretical and measured data, all you have is the usual handwaving pontification that charicterises the transmission line brigade.
The fact is that most of the music you listen to is monitiored on bass reflex systems and if the transmission line was so superior it would have long ago suplanted the bass reflex by demand of the enginners and artists in the buisness.
It hasn't with good reason, simply the transmission line in all of its manifestations is a sub optimal design, all of its supposed benefits are illusory, and no amount of supercilious pontification will change it.
rcw
The fact is that most of the music you listen to is monitiored on bass reflex systems and if the transmission line was so superior it would have long ago suplanted the bass reflex by demand of the enginners and artists in the buisness.
It hasn't with good reason, simply the transmission line in all of its manifestations is a sub optimal design, all of its supposed benefits are illusory, and no amount of supercilious pontification will change it.
rcw
You'll have me in tears at that rate. I have simply stated what a Transmission Line is, the statements being supported by theoretical and measured data; I even cited some sources and provided a set of illustrative models of proven accuracy. If you don't like it, that's not my problem. Doesn't square too well with the 'all I have is handwaving pontification' remark does it? Incidentally, I wasn't aware that I was part of some form of 'transmission line brigade.' If you had read my posts, you might have noticed that at no time in this thread have I advocated any specific means of loading over another. I even went out of my way to point out that all different methods have their positive and negative aspects.
Frankly, I couldn't care tuppence what it was monitored on, providing it was of reasonable quality. And who said anything about a TL being automatically 'superior' to anything else in all times & all places? Recognise this phrase? 'They all have their advantages & disadvantages. Superior to a BR? Not necessarily. Inferior? Again, not necessarily. Back to design goals.'
In your opinion, but your opinion is only that, not fact. Incidentally, I don't think your attempt at personal insults is going to help your position a great deal.
Last edited:
BRs only sound bad if they're badly designed or implimented, otherwise you can't beat the solidity of bass a good BR gives. TLs (semantics aside) may go lower, but IMHO, any output below the low 30s is pointless.....;-) I think their strength is in getting output below Fs (not explored much here). I have a 4" in 2M TL, Fs 80Hz, and it goes really low (but runs out of Xmax way too soon :-( . MLTLs are probably the best of both worlds.
They certainly have their uses (as in MLTLs / ML QWRs / whatever you like to call them). I've got a pair here at the moment actually. One of my favourite box types.
Generally, for the really low stuff, I tend to like sealed boxes, a really low-tuned EBS BR, DSL style tapped horn, or a big TL. Any would make me happy; which would depend on the circumstances / exact requirements of course. Name your poison.
Generally, for the really low stuff, I tend to like sealed boxes, a really low-tuned EBS BR, DSL style tapped horn, or a big TL. Any would make me happy; which would depend on the circumstances / exact requirements of course. Name your poison.
It would be interesting to see that. I've had my nose in the literature for nigh on 40 years and have never seen anything that would be as conclusive than that. As for TLs, with reasonably accurate modeling only having been available for 10 years now, not much more than anecdotal research has been done on TLs.
dave
As Martin King has shown a transmission line with no stuffing has a double hump electrical impedance just like a reflex, but in addition has other peaks at higher frequencies due to the pipe modes in the line.
In other words we start out with a basically flawed reflex and then attempt to fix it by stuffing it.
By the time we end up stuffing it sufficiently we end up with what is tantamount to a sealed box that has the disadvantage that since its impedance peak is lower than that of a straight sealed box it needs more power input for the same acoustic output.
We might note that we have done all this to remove the flaws we inherantly get from using a pipe in the first place, that's why a reflex is the optimum TL, i.e., just get rid of the pipe.
I completely fail to see the point of all of the rigmarole of the TL when we can save ourselves a lot of time and effort by simply make the whole thing a reflex box in the first place, and by so doing get superior performance.
rcw.
In other words we start out with a basically flawed reflex and then attempt to fix it by stuffing it.
By the time we end up stuffing it sufficiently we end up with what is tantamount to a sealed box that has the disadvantage that since its impedance peak is lower than that of a straight sealed box it needs more power input for the same acoustic output.
We might note that we have done all this to remove the flaws we inherantly get from using a pipe in the first place, that's why a reflex is the optimum TL, i.e., just get rid of the pipe.
I completely fail to see the point of all of the rigmarole of the TL when we can save ourselves a lot of time and effort by simply make the whole thing a reflex box in the first place, and by so doing get superior performance.
rcw.
You must try listening also, measurements doesn't always tell the whole story.
I agree with you both. Science does not know everything. Since the beginning of time people have thought they know all there is too know. I've been interested in theoretical physics since I was a teenager. It's all really funny. Many physicists or scientists treat science like a religion. It's quite interesting psychologically and scientifically; that's right the former is not a science or "soft" science at best.
With that being typed, I might agree with rcw slightly more
In reality it comes down to listening. Blind A-B tests and even that can be flawed. It's hard to say what humans perceive and do not perceive. I could be totally wrong though
For example: to paraphrase the almighty Zaph: "the sound of wires come down to Inductance, Capacitance and Resistance, that's it. Makes me laugh when people claim otherwise." This is true (and I agree with it a great deal, as best I can imagine even accepting the rest of this sentence as truth), if you know all there is too know about electromagnetism, but you don't, and that's the real lol in such a statement. There's always a probability you're wrong with any statement you make, even this one
Anyway, I think I'm building a ported box
Hawking's writings were the most hilarious when I was a Teenager. Black hole, white hole, singularities, oh really and just how do you know this? Oh, is that how, lo freakin l. Too bad you can't bang you're hot wife
Damn it that was mean 
Last edited:
Okay, so I should elaborate. My friend says that I can't know that copper coins can't make you pass a breathalyzer, but I do know this with my basic knowledge of science. Does this make sense to any one. Dang it I shouldn't have written this I must be slightly more intoxicated than I though Where are my smileys!? I can't find my smileys
And another thing why does every audiophile enjoy Dianna Krall (spelling?). I don't. I think I'm going to listen to some Dianna Krall. I only like "fly me to the moon" and temptation to a lesser extent. But she is not that good
You know I'm glad you can only edit your post for 30 minutes, otherwise I would make even less sense than I already do
I must be slightly more intoxicated than I though Where are my smileys!? I can't find my smileys And another thing why does every audiophile enjoy Dianna Krall (spelling?). I don't. I think I'm going to listen to some Dianna Krall. I only like "fly me to the moon" and temptation to a lesser extent. But she is not that good
You know I'm glad you can only edit your post for 30 minutes, otherwise I would make even less sense than I already do
Last edited:
The double-hump impedance curve / creation of two new system resonances in a pipe &c. is not an especially remarkable fact; as you point out Martin illustrated it in the various papers on his site some time ago, as did Augspurger, and many others right back to Olney. But here we are talking about a QW pipe, not a transmission line.
Leaving aside the question of helmholtz or QW behaviour, what do you mean 'fix it?' For certain, damping in a pipe attenuates the unwanted harmonic modes, but a TL is a specific sub-set of enclosure design which does not share the same goals of providing output; it's entire object / definition is to be damped. It's not a question of 'fixing' things, although granted, if you're employing a lightly - modestly damped pipe to support the LF then the goal of supressing line harmonics while preserving as much of the fundamental as the design goals dictate is true enough. I can't see why that's suddenly meant it has become 'flawed' though, any more than a supposed BR box that required some damping (as 99.999% do) to suppress any unwanted eigenmodes etc. present.
Disadvantage? You're presenting the amplifier with an essentially unreactive load, while also providing a shallower roll-off slope than a vented alignment & one that does not unload below Fb (or Fp in this case) until well below any audible frequency. If you wish to regard that as a disadvantage, fair enough, but don't expect everyone else to.
In your opinion. Once again, you appear to be implying that the same objectives are present for each cabinet type.
Obviously (as in that you fail to see the positive attributes of a TL or of a damped QW pipe). And again, in your opinion. But it remains your opinion, not fact.
It doesn't work. A lot of Herberts ('erberts?) in the UK try that when pulled over. It gives the coppers something to laugh about, but not much more. The breathaliser works just the same, and if they have any reasonable doubt, they'll haul someone back to the station anyway for the evidential breath-tester, where the likelihood of your having a coin in the mouth is about, oh, zero squared.
A great man. I had the honour of meeting him a few years ago.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.