Not at all GM, it was just that due to my lack of familiarity with the concepts I ended up spending a lot of time reading articles and forum threads that were confusing, partly because people were arguing about why one method was better than another, or they had misleading titles and didn't address the question. One of the challenges of being a novice is not knowing what to throw out so it's inherently inefficient. Please don't mistake my lack of experience here for lack of respect. I'm reading my *** off in the constricted time I have at the moment due to work/life circumstances.
If I'm getting the Toole article right, the overall driver characteristics and the driver/enclosure alignment are more important than amplifier output impedance. I read another article (can't find it now to link) that seemed to be saying the same thing.
If I'm going to set up and measure the actual output impedance of this amp, it might be a few weeks away. Honestly it's a bit of a reach at this point but if it's necessary step I'll do what it takes.
Got it, yes I finally read the Pearl article correctly🙄
But I continue to read how tube amps in general have much higher output impedance, 4ohms not being out of the question. Isn't this the often cited reason for them (especially SETs) having "flabby bass"?
This sounds like a great idea GM.
Setting aside the impedance testing for a minute, and knowing that I'm dealing with a small single ended amp with no NFB and "no ability to control output impedance" according to its builder, is it safe to assume we're dealing with high output impedance?
I saw a banner recently in a photo from a friend. It said "we don't do this because we think it's easy, we do it because we thought it would be easy when we started". Haha that about says it. I truly appreciate all the input here, if I seem unresponsive or slow it's only because I have a full plate outside of this arena. But I'm permanently bitten with this and trying to learn, at 60 this month, and wishing I'd discovered this fascinating and rewarding passion. Thanks so far to everyone.
Yes good observation. What is flabby to one listener might be warm and bouncy to another. The same laws at play can also produce some subtle or not so subtle response changes in the midrange and treble due to the fact most speakers do not present a flat load impedance.
I'm sure Toole and myself would tell you to stop faffing about with these under-designed amplifiers that can not exert proper control over the sepaker. But this hobby is not always about doing what is logical or technically correct. The path you are taking here is not the one for me, but I can recognise it suits some people. I hope my experiment will help you learn where you sit on that gradient.
OK, understood, but me n' others have been repeatedly posting many of the same things for decades now and frankly I for one am pretty much burned out on many 'fronts' and in a continuous 'time crunch' nowadays.
Re Toole, you need to read others' following responses as he's posting during a transition in speaker/amp design of increasing DF/lower output impedance where we eventually concluded > 80 was just wasting $$$.
Right, the lower the DF where a matching impedance = 1.0/unity was the pioneer's goal for max eff., then the more the driver must be over damped, i.e. a 0.1 Qts in T/S parlance, which until recently could only be achieved using a field coil driver or suffer 'flabby' bass and elevated highs, i.e. sometimes referred to as a 'smiley face' EQ since it tracks the speaker's impedance, hence the need for Fs box tuning for max bass, otherwise you get varying degrees of 'one note' bass, though the pioneers often did just this to act as an acoustic TT or tape machine 'rumble' filter tuned below a typical recordings lowest audible signal.
To improve design flexibility, performance, a tapped output impedance coupling transformer was added and later, variable DF tone controls, so SOTA circa '53 was this preamp/amp combo and their integrated amp variants that to some of us that was weaned on these type systems still represent the best overall compromise for an analog playback "is it live, or is it Memorex" experience when coupled to appropriately designed speakers.
You're welcome!
Wow 25 'crossover combinations' on the 440B preamp and adjustable output impedance on the 340A, now you're talking! Knowing what I'm beginning to know these last few days about damping/impedance, I'm surprised this isn't a feature on any modern amp I've ever seen. Seems like it would make speaker compatibility far less of an issue. But hell, it seems doable in a speaker, to match different amps, why not? Why isn't something like this more common, with all the money people are spending on shiny components nowadays?
I'm going to reach out to someone I know and ask for a little help with measuring the impedance of the 45. Now that I know about this, I kinda can't un-know it, as much as I'd like to just punt.
I'm going to reach out to someone I know and ask for a little help with measuring the impedance of the 45. Now that I know about this, I kinda can't un-know it, as much as I'd like to just punt.
Things are lot different than 1953. It cost a lot of money then in the output transformer & output tube to control the voltage out the speaker terminal effectively. Now we have SS amps that can accurately produce an output voltage at a fixed gain to the input whatever back emf the speaker produces: - high damping factor. If you want one note bass or resonance at a particular frequency, we have digital effects that can emulate a room with defined reflective characteristics and any defined echo time to suit your taste.
I don't quite understand the desire for "speaker warmth" or "flabby bass". One test I put to my last speaker+amp combo on day of purchase was the bass drum of ZZ Top track Woke up with Wood. I've marched on a football field 10' from a 30" bass drum. When the head is tight, a real bass drum produce a WHAP not more than a quarter second long. Inaccurate repro systems will sound more like Boog or scoop in frequency. The ZZ Top drum hit is so clean, the source might be digital. I have owned a digital effect between preamp & amp that would simulate various room echos & treatments. Perhaps people that like SET amps are not listening to tracks for accurate sound. I listen at 1/8 watt on 15" woofer with 98 db sensitivity for hours, but my lowest damping factor amp is 9 with 35 w/ch.
I have a 1961 vacuum tube + transformer amp, the dynaco ST70. While classic and great sound compared to the RCA garbage my Mother bought with Top Value Stamps in 1966, I much prefer the sound of my nineties CS800s. If I want to modify the sound, I have graphic equalizers and effect units.
Last edited:
Another great post jo! I think 'accurate' can be defined in different ways, though I assume for the most part it means the ability to deliver power with low distortion through the system etc, good measurements and all. But sometimes a system just sounds so real, and it's not always on systems that measure well. I never measured the systems that started me on this quest of low power tubie/high sens speakers, but I'm sure they wouldn't have measured all that well and weren't very 'accurate', and probably had pretty high odd order distortion. But each to their own, I've had super duper measurement amps and I hated them! Sometimes I walk in the house and my GF is sitting there playing Mal Waldron through the butt end of her iphone, having a great time, makes me laugh.
Anyway, I spoke with my guy Al at US Speaker yesterday, we played with a bunch of drivers. Up late reading about damping and flea watt power. I'm seriously considering ditching this effort solely because I don't think I can achieve the sensitivity I need for this 2 wpc amp. So I've got to consider another option. Maybe I just go grab some of those Peaveys for now and build some nicer boxes for them! But I'm working with constraints from all sides - low power, smallish space, yada yada, it's a tough one. If I'd just gottn a 2A3 at least I could get away with it (4-5 wpc), but I really thought I could make something work with the 45. Maybe not. I have to be realistic. I could definitely make this work with 15" drivers, or maybe some kind of more complicated enclosure for the 12", but as it's plain to see I haven't even gotten up to speed with BR cabs yet!
Anyway, I spoke with my guy Al at US Speaker yesterday, we played with a bunch of drivers. Up late reading about damping and flea watt power. I'm seriously considering ditching this effort solely because I don't think I can achieve the sensitivity I need for this 2 wpc amp. So I've got to consider another option. Maybe I just go grab some of those Peaveys for now and build some nicer boxes for them! But I'm working with constraints from all sides - low power, smallish space, yada yada, it's a tough one. If I'd just gottn a 2A3 at least I could get away with it (4-5 wpc), but I really thought I could make something work with the 45. Maybe not. I have to be realistic. I could definitely make this work with 15" drivers, or maybe some kind of more complicated enclosure for the 12", but as it's plain to see I haven't even gotten up to speed with BR cabs yet!
A 15" two way with a CD/Horn will get you there but not exactly small.....you'll need at least an 18" baffle and 12" of cabinet depth. If you can spare the space, then the Faital pro 15pr400 is the driver for you.....ruler flat to 3.5kz and can easily cross to a CD at 1.2khz without too much beaming. With baffle step compensation and ported to 35hz frequency, that's a 96db speaker all day long...........expensive though.....you're gonna go $1k in parts all in with CDs and horns
That’s exactly the driver I’m looking at! I don’t know how I’m going to fit 18” baffles in my 12’x13’ room (10’ ceilings), but damned if I’m not about to try. I think Faital also makes a 15” coax too? I’ll have to look into it when I’m done work. Good call mayhem thanks.
I like very much!!!!!!!!!!!!!!! The 15PR400 is a fantastic driver. Bass wont be very deep, but mid-bass and mids will be excellent.
If I go with a horn on top that's the driver I'm most likely to go with, would just have to find the right CD/horn. Buuuut, I'm still not giving up on the coax fixation, and Beyma and Faital both make excellent coaxes. I'm going to do some modeling tonight, just to see where they land, I've already got the PR400 in my files.
The big question right now is about power, considering this is still a 2wpc amp, no matter the sensitivity. So it seems like I should be going for a smaller box/higher tuning, max flat as GM calls it, does that make sense? Or, I could do a slow first order rolloff that starts higher and tapers down more slowly. I'll have to see them on the screen. Any suggestions? I guess another way of approaching the question is whether it's best to use the Fr or tune higher?
The big question right now is about power, considering this is still a 2wpc amp, no matter the sensitivity. So it seems like I should be going for a smaller box/higher tuning, max flat as GM calls it, does that make sense? Or, I could do a slow first order rolloff that starts higher and tapers down more slowly. I'll have to see them on the screen. Any suggestions? I guess another way of approaching the question is whether it's best to use the Fr or tune higher?
Last edited:
http://www.troelsgravesen.dk/Faital-3WC-15.htm
Troels has used it in two designs and is Gaga over the low end extension…….it digs down to 30hz in room at 97db efficiency in its passband with BSC.
Troels has used it in two designs and is Gaga over the low end extension…….it digs down to 30hz in room at 97db efficiency in its passband with BSC.
The 15PR400 is one of those unicorn drivers that balance mids with lows very well. My only complaint with it is that it doesn't stay composed in the lower mids at higher SPLs and Its picky about amplification. When you stay within the limits of this driver, its one of the best woofers for a large 2 way.
Everything is a compromise in a two way……too many octaves to cover for each. Tune the 15pr400 to 80hz and watch that midbass tighten right up……..or use two in a .5 configuration and all of the issues are solved……….unless a SET amp is part of the equation…………that’s like asking for cholesterol free ice cream…..sorry
Well, all this talk about the 15PR400 is enough to make me seriously reconsider the coax idea, but for now I'm staying with it. At just over 2m listening distance I think it will give me something a separate horn several inches away from the woofer will not. Tonight I modeled a few 15" coax drivers, and the Beyma 15CXA400ND is looking like the top candidate https://usspeaker.com/beyma 15CXA400nd-1.htm
One of the things I'm keeping an eye on is Mms. Tomorrow I'll chat with Al at US Speaker and compare notes, he has much more experience with the actual sound o, f these drivers as well as a lot of feedback. I've got a fresh sheet of 3/4" plywood on top of my van as I speak, and will finish modeling an enclosure and build the test cab this weekend in preparation for the arrival of the drivers, whatever they end up being.
Although these speakers will inevitably be used with bigger amps, the whole point of this excursion is to design a pair of speakers that will play paired to my SET amp. So I want to ask again the same question I did earlier - given the very slim margins I'm working with, and since lower frequencies use proportionately more power, what kind of tuning would people suggest? Although I can model the Beyma to an F3 of 34hz and it looks fantastic, might it not be better to tune it higher, above Fr (40hz), as mayhem was saying above? It's a bummer because this driver can go pretty low and stay relatively flat by the looks of it, but conserving power seems to be a good idea.
One of the things I'm keeping an eye on is Mms. Tomorrow I'll chat with Al at US Speaker and compare notes, he has much more experience with the actual sound o, f these drivers as well as a lot of feedback. I've got a fresh sheet of 3/4" plywood on top of my van as I speak, and will finish modeling an enclosure and build the test cab this weekend in preparation for the arrival of the drivers, whatever they end up being.
Although these speakers will inevitably be used with bigger amps, the whole point of this excursion is to design a pair of speakers that will play paired to my SET amp. So I want to ask again the same question I did earlier - given the very slim margins I'm working with, and since lower frequencies use proportionately more power, what kind of tuning would people suggest? Although I can model the Beyma to an F3 of 34hz and it looks fantastic, might it not be better to tune it higher, above Fr (40hz), as mayhem was saying above? It's a bummer because this driver can go pretty low and stay relatively flat by the looks of it, but conserving power seems to be a good idea.
The Eminence KL3012CX is still on the top of my list for a 12" coax. It goes down to low 40s in an extended shelf ported alignment in 95 liters. It has a very smooth FR too. Just add a Faital HF108 and you can cross at 1.3k.
Again, with a low DF tube amp you've no choice but to tune to Fs for max bass since it 'tracks' the driver's impedance and if wanting max cab alignment acoustic efficiency, then vb = Vas/1.44, but does not mean it's max flat or any other specific T/S alignment, hence the variable DF tone controls, though of course you can use DSP and/or passive frequency shaping filters to correct any unacceptable in room responses or my inline pot and use a by-pass cap to 'let through'/'lift up' any HF that's too rolled off/'depressed' (AKA CD horn EQ).
2m listening distance to a 15” coax on axis isn’t something I can recommend……..the fwd lobe through the beaming and right at the phase overlap of the xo????????…….things will get messy. I’d wanna be at least a meter out from the side and back walls with an EQ triangle of 3m…….that’s a listening space no smaller than 5m square
15”+horn will not change anything or solve the amp problem not the listening distance so I don’t see why you should abbandon coax if you still want it, it’s a good approach for many reason.
If anything my experience is that a coax as a point source is less sensitive to listening distance and for the most sounds coherent. I use my Celestion 12” coax as studio monitors both nearfield and far field. The only difference is the room bass modes where I sit.
FYI the Celestion coax is also a 15” option. With a bigger HF it looks very interesting. Still need a close attention to crossover but why not just use the company designed? It’s rather cheap too.
If it will work with tubes I have idea. Why not get a solid state amp.
https://celestion.com/product/ftx1530/
https://celestion.com/wp-content/uploads/2019/09/FTX1530-Crossover-datasheet.pdf
If anything my experience is that a coax as a point source is less sensitive to listening distance and for the most sounds coherent. I use my Celestion 12” coax as studio monitors both nearfield and far field. The only difference is the room bass modes where I sit.
FYI the Celestion coax is also a 15” option. With a bigger HF it looks very interesting. Still need a close attention to crossover but why not just use the company designed? It’s rather cheap too.
If it will work with tubes I have idea. Why not get a solid state amp.
https://celestion.com/product/ftx1530/
https://celestion.com/wp-content/uploads/2019/09/FTX1530-Crossover-datasheet.pdf