Yeah, me even young, most folks, can barely hear a 3 dB difference except up in our peak hearing BW (~2 - 6 kHz) and virtually every inexpensive speaker system I did for folks wound up with at least +6 dB built in, otherwise it didn't have that 'toe tappin' quality and with the few systems tuned below a recording's BW (<40 Hz) they had more peaking at Fb to act as a turntable (TT) 'rumble' filter, so wound up extending a recording a bit with basically noise to the pleasure of some.
I 'preach' T/S max flat because that's what folks have been brainwashed with and as good a place as any to start with, but the room acoustics combined with mass quantities of cheap EQ typically makes the in room response look more like a Rocky Mountain Range profile than anything remotely 'HIFI', not to mention one usually needs at least some form of baffle step compensation (BSC).
I 'preach' T/S max flat because that's what folks have been brainwashed with and as good a place as any to start with, but the room acoustics combined with mass quantities of cheap EQ typically makes the in room response look more like a Rocky Mountain Range profile than anything remotely 'HIFI', not to mention one usually needs at least some form of baffle step compensation (BSC).
While I'm trying to decide whether to just go with the Ferrite version of this driver, there's two things I'm curious about.
The first is that the Qms of the Fe is 16.4, vs 4.4 for the neo. From all the reading I've done on mechanical Q, I think the higher Q would be preferable IF it weren't for the low damping factor of my SET amp. My reasoning is that high Qms means lower damping at the driver, and combined with the high output impedance of the amp, this seems like it could be a mudbath. Is my thinking correct here, or are they not directly related?
The second concern is that the Fe definitely want to extend further in the bass department, and because I'm limited to about 5.5 ft^3, maybe I'm restraining this driver and it will impact performance? I mean, the WinISD plot looks great, it's just that if I had a chance I'd build the enclosure cloer to 7 ft^3, maybe 180L. That's for max flat though. Should I be concerned about this?
The first is that the Qms of the Fe is 16.4, vs 4.4 for the neo. From all the reading I've done on mechanical Q, I think the higher Q would be preferable IF it weren't for the low damping factor of my SET amp. My reasoning is that high Qms means lower damping at the driver, and combined with the high output impedance of the amp, this seems like it could be a mudbath. Is my thinking correct here, or are they not directly related?
The second concern is that the Fe definitely want to extend further in the bass department, and because I'm limited to about 5.5 ft^3, maybe I'm restraining this driver and it will impact performance? I mean, the WinISD plot looks great, it's just that if I had a chance I'd build the enclosure cloer to 7 ft^3, maybe 180L. That's for max flat though. Should I be concerned about this?
Let me put it to you this way........the pioneers were only interested in effective motor strength (Qes) and the late Dr. Leach told me in '68 that he ignored Qm, Qt in his personal designs, but these were early T/S days, so may have changed his mind.
From here:
From here:
Qts
Also called total Q – The damping made by Qms and Qes combined. They don’t literally add up, instead use this formula : 1/Qts = 1/Qms + 1/Qes . This is the Q you should look for if you plan to use it in free airGood article, concise, thanks GM.
Yeah the arguments about Qm seem to go on and on, but a lot of people do say higher Qm trades off linearity for "liveliness" or better transient response and more realism. it makes sense logically. I've never measured an old Altec or Tannoy, but I'd bet good money the best sounding of them, not to mention the not-best sounding, would send the objectivists running away and forgetting their mics.
Edit - maybe less true for some of the xovers I've seen with lots of correction parts in there, but I really want to keep it on the lighter side unless I have to put out a fire, which might happen.
Yeah the arguments about Qm seem to go on and on, but a lot of people do say higher Qm trades off linearity for "liveliness" or better transient response and more realism. it makes sense logically. I've never measured an old Altec or Tannoy, but I'd bet good money the best sounding of them, not to mention the not-best sounding, would send the objectivists running away and forgetting their mics.
Edit - maybe less true for some of the xovers I've seen with lots of correction parts in there, but I really want to keep it on the lighter side unless I have to put out a fire, which might happen.
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On the topic of DMMs and analog meters, I prefer to use my tried and true fet input meter. The fet input stage provides a very high input impedance and gives a wider frequency range at lower voltages, so the rectifier doesn't dictate your low voltage cutoff limits as much. I've used this meter for just about everything not requiring a scope. It was used for everything from calibrating tape machines to measuring TS parameters of speakers before there were dedicated computer setups. Its very accurate up to 30 kHz AC signals, so it can deal with any audio task you throw at it.
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Altec drivers typically have very low Qms (<3) though their woofer horn drivers are very high (>7) to handle its compression of sealed back chamber or the lack thereof in a low tuned vented back box, so another way of showing that it's mostly irrelevant except at the extremes of box 'loading' ('squeezed' tight or open air).
That makes total sense GM, I appreciate your thorough knowledge tying several decades of speaker design together. I'm going back to basics in large part because of this thread and some of the references you've posted. Just got a copy of Cohen's Hifi Loudspeakers and Enclosures, almost as old as me (1968 edition), and a joy to read, unlike some of the more complicated modern writings, which I'll tackle with time. Even the LDC is pretty difficult, definitely not a novice resource although the info is there if needed, just wish there was an index!
I ordered the 15CXA400Fe drivers last night, and will finish bracing and making some holes in the test enclosure this weekend, so I'm ready to hit it when the 50 lb box arrives!
I ordered the 15CXA400Fe drivers last night, and will finish bracing and making some holes in the test enclosure this weekend, so I'm ready to hit it when the 50 lb box arrives!
Doing the sim for the 15cxa400Fe in WinISD, everything looks peachy, except the impedance spikes are a bit scary to me. Should I be concerned about these (below, compared to the neo version)
The one impedance peak is below where the drivers will operate. Amp will not see naked impedance, it will be blocked off by the passive crossover. I believe you were saying 40 hz for the box tuning? Woofer impedance peak is 26 hz. Additional impedance peak at 70 hz. Infinite baflle frequency response is - 4db to 60 hz, only 2 db down at 80 hz. despite the impedance peaks so balancing mechanical & electrical damping is what designers do to make that happen.
I'm surprised you bought Fe magnet. According to post 124 link, lower Qm means better damping. If I read the understood the audiojudgement artical. With Fe model at Qm 16, I thought this model would be possibly more buzzy with an underdamped fleawatt amplifier. At least more than Qm 4.4. I suppose Qt matters more to out of control buzzes than Qm alone. I didn't download the 15cxa400fe datasheet since I'm not going to buy one.
I'm surprised you bought Fe magnet. According to post 124 link, lower Qm means better damping. If I read the understood the audiojudgement artical. With Fe model at Qm 16, I thought this model would be possibly more buzzy with an underdamped fleawatt amplifier. At least more than Qm 4.4. I suppose Qt matters more to out of control buzzes than Qm alone. I didn't download the 15cxa400fe datasheet since I'm not going to buy one.
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Thanks jo. Yeah it was the 72Hz peak I was worried about, not as much now.
You are right about the lower damping with the high Qm, but after exhaustively reading up on how much it matters, I didn't give this as much weight. In the end the difference in total Q is .06, very small.
Two other factors nudged me toward the Fe magnet - $240 less cost, and possibly a slightly juicier bass response, which Al agreed on with hearing them both. Oh, third factor - the neos won't be here for at least two months, the Fe's will be here in a few days!
Like I've said though, if the 45 can't handle these speakers, I've got a 35w P-P that sounds fantastic and probably will be a very good match. Most likely the P-P would be my daily driver either way, since I listen to a variety of music and not just the stuff that's more likely to shine with the SET. Sure would be great if this ends up working out though. A week from now I'll have dont the first round of sweeps in REW, I should have something tangible to work with from that point.
You are right about the lower damping with the high Qm, but after exhaustively reading up on how much it matters, I didn't give this as much weight. In the end the difference in total Q is .06, very small.
Two other factors nudged me toward the Fe magnet - $240 less cost, and possibly a slightly juicier bass response, which Al agreed on with hearing them both. Oh, third factor - the neos won't be here for at least two months, the Fe's will be here in a few days!
Like I've said though, if the 45 can't handle these speakers, I've got a 35w P-P that sounds fantastic and probably will be a very good match. Most likely the P-P would be my daily driver either way, since I listen to a variety of music and not just the stuff that's more likely to shine with the SET. Sure would be great if this ends up working out though. A week from now I'll have dont the first round of sweeps in REW, I should have something tangible to work with from that point.
Seeing your test boxes made me wonder if you listen on the floor. Or will you build stands for them to get the tweeter up in ear height?
Cheers!
Cheers!
I'll build plinths for the final version. They won't be the full 20-25cm high, but will have a bit of an angle to aim them slightly upward. Pretty common solution to a lot of boxes this size range. If I really can't stand the source coming from below ear height, I'll build stands, I've never been a fan of music coming from much above or below the ear-hole horizon 😉
Touché. But.....a cinema isn't the same thing at all, there are speakers surrounding the listener, some of which are at or below ear level (unless you sit in the front row) and others above. It's big and loud, not the same at all!
True, but you're old enough to enjoy cinemas that only had 1-3 channels with the mids/HF centered at 2/3 screen height where the folk's heads are 'framed', which is still the spec for the mains and ideally for HT w/acoustically transparent screens. Regardless, we like what we like, so should have added some smilies. 😈 😉
Oh for sure. I live in a small vermont village, which for some reason is blessed with a golden era cinema and one of the, if not the largest screens in New England, complete with balcony! There are two others within 30 minutes, both splendid.
I do remember when the sound in theaters started becoming “surround-y” and very loud, dynamic, and boomy, and cineplexes started popping up in the blighted landscape of modern America. Wish I’d been out back with a giant rental van as they were removing all those glorious, dust covered plywood bins! If Only I knew then what I know now……
I used to run the audio at home through my 2.1 system, but really didn’t think it was worth burning tubes over, so went and dropped $120 on a vizio soundbar and baby sub a year ago. Surprisingly good sound I have to say, and I can actually understand the dialogue now! Good enough for movies and whatnot, where I’m more engaged visually. When I listen to music I have my eyes closed half the time, really different experience for me and I’m sure lots of people around here.
Since I’ve been reading the older texts lately, nostalgia aside, I’m struck by how much common sense drove things back in the day, before everything had a price tag attached and got spun for some profit angle, it’s very refreshing 😉😌
All good GM, apologies for wandering OT!
I do remember when the sound in theaters started becoming “surround-y” and very loud, dynamic, and boomy, and cineplexes started popping up in the blighted landscape of modern America. Wish I’d been out back with a giant rental van as they were removing all those glorious, dust covered plywood bins! If Only I knew then what I know now……
I used to run the audio at home through my 2.1 system, but really didn’t think it was worth burning tubes over, so went and dropped $120 on a vizio soundbar and baby sub a year ago. Surprisingly good sound I have to say, and I can actually understand the dialogue now! Good enough for movies and whatnot, where I’m more engaged visually. When I listen to music I have my eyes closed half the time, really different experience for me and I’m sure lots of people around here.
Since I’ve been reading the older texts lately, nostalgia aside, I’m struck by how much common sense drove things back in the day, before everything had a price tag attached and got spun for some profit angle, it’s very refreshing 😉😌
All good GM, apologies for wandering OT!
Alrighty, finally got the Beyma 15CXA400Fe drivers in this Thursday, and mounted them in the 145L (net) boxes, and ran sweeps in REW and took the free air parameters with my DATS. Not horrible but I'm going to have to do some fancy footwork with the crossover. I had hoped to be able to cross these 2 drivers at 1000 if possible, but it's looking like I'll either have to go to 1500 to get past the huge dip (coinciding with an impedance spike at 1250), or brute force that imp. spike with a filter. So I'll post a couple of shots, and I'd like any input or feedback anyone has.
The first pic will be nearfield woofer and port. Nearfield on this woofer is difficult because there's a giant horn blossoming out from the concentric CD.
The second pic is the CD and woofer both at 1m, and gated at 6.2ms. That little blip at 130hz is from a box resonance, I know this because I cut it way down with some extra damping on the top and sides around the woofer.
I'd wanted to try to keep the xover to simple 2nd order but I don't know if I'll be able to do it unless I cross on the higher side?
The first pic will be nearfield woofer and port. Nearfield on this woofer is difficult because there's a giant horn blossoming out from the concentric CD.
The second pic is the CD and woofer both at 1m, and gated at 6.2ms. That little blip at 130hz is from a box resonance, I know this because I cut it way down with some extra damping on the top and sides around the woofer.
I'd wanted to try to keep the xover to simple 2nd order but I don't know if I'll be able to do it unless I cross on the higher side?
Okay, now I have finally figured out how to sum and splice the gated 1meter, nearfield, and port responses. I've also included the gated 1M CD response.
The Y axis indicator is at 1.5k, which is how Beyma crosses these. I think that dropout at 1.3k is just a feature of the horn, diffraction/cancellation? But does anyone have any thoughts, ie could it work to cross lower than 1.5k? And does anyone have any good starting points as far as order, etc? This is my first from scratch build so any pointers are welcome. I was going to use Vituix but it's pretty intense, I think I'm going to use WinPCD, partly because I'm an admirer of Jeff Bagby, and also because it looks less intimidating.
The Y axis indicator is at 1.5k, which is how Beyma crosses these. I think that dropout at 1.3k is just a feature of the horn, diffraction/cancellation? But does anyone have any thoughts, ie could it work to cross lower than 1.5k? And does anyone have any good starting points as far as order, etc? This is my first from scratch build so any pointers are welcome. I was going to use Vituix but it's pretty intense, I think I'm going to use WinPCD, partly because I'm an admirer of Jeff Bagby, and also because it looks less intimidating.