I totally agree with Lynn, that 15 Watt is high power region
A good loudspeaker only needs a few hundred mW (MilliWatt) for satisfactory listening levels.
For the average (RMS) level, maybe.
But each +10dB dynamic swing requires 10x the power, and good recordings have 20+ dB of crest factor.
So even starting with "a few hundred mW" = say, 0.5W, you quickly end up with a peak demand for 50+ Watts. Then, you either have those clean Watts, or you run into amplifier clipping = heavy, nasty compression. Even though the "soft" clipping of a DHT amp may not sound particularly objectionable, it still is significant distortion of the original signal, i.e., not "Hi-Fi" anymore.
M.
I agree that efficiency is a key aspect of any design, my preference being for high efficiency and low thermal compression. But I am not of the "tubes rule" clan.
In elaborate tests done decades ago I showed that "soft clipping" was barely audible while hard clipping was seriously offensive. Both sources had the exact same max-voltage (rails). Everyone thought that the soft clipped amp sounded louder and better. But, of course, if the signal never went to the rails then both amps sounded the same.
That the mid-bass was seriously compressing at a mere 100 dB SPL is very disturbing to me and not at all what I would expect from a 15" driver.
OOPs I may have read the charts backwards. Still that's more compression than I would expect.
Some years back I tried a similar test but using short term pulses of ever-increasing magnitude. I was unable to detect any changes. Hence, the question becomes how much time does the signal have to spend at the higher level before this compression takes hold. That, to me, becomes the key factor as music is seldom a constant high level.
I think that dynamics can be reproduced in an absolutely satisfactory amount with an 5-10W amplifier and an high efficiency loudspeaker.
If 1Watt and about 100dB efficiency would rock the furniture in the room then we Do not need +20dB to reach the level of an starting airplane with 120dB. Look upwards down from 100dB with respect to dynamics. 100-20dB.
If 1Watt and about 100dB efficiency would rock the furniture in the room then we Do not need +20dB to reach the level of an starting airplane with 120dB. Look upwards down from 100dB with respect to dynamics. 100-20dB.
Respect! An all-field coil loudspeaker system!!! That goes a lot further than anything I've been discussing.
Field coils have the interesting ability to change BL product on the fly ... of course, that changes not just efficiency but Qt as well. The mechanical system (Qms, HF resonances, etc.) stays exactly the same, but the electrical system is profoundly altered.
So if I'm reading your letter correctly, the residual overlap between the lower and upper woofer had no harmful consequences, and you've been using the lower woofer to shape the overall system response to correct for BSC and assorted other LF errors that are inherent to a single-point woofer in a cabinet. It does confirm my intuition that the response and level adjustments for the lower woofer need to be rather fine-grained, so the overall impression at the listener's position is subjectively flat (with most recordings).
P.S. I am puzzled why field coil loudspeakers are priced as high as they are. They should be much cheaper to make than Alnico or Neodymium magnets (which are brittle and difficult to machine), and not much more than molded ceramic magnets. True, they are aimed at a very narrow specialist market these days, but all loudspeakers used field coils back in the Twenties and Thirties, and they weren't anything special back then. (Yes, that includes the famed Lansing Iconic, which set the pattern for all 15" paper-cone woofer + MF/HF horn + 700~800 Hz crossover studio-monitor systems that followed.)
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At least the music I listen to isn't.
But that got me thinking; "How often does music hit the peaks?" I looked a a few dynamic recordings, 1812 Overture, Jupiter from the Planets and some others.
Answer: It depends - a lot. It depends on what is defined as a peak and it depends on the music and recording. What I found was that during loud, dynamic passages the signal is peaking 8 to 20 times per second. Those peaks are brief, between 4 and 12 samples each.
It really depends on where you set the threshold for the peak.
Knee jerk question from somebody who doesn't know much : Could the M-ray sides be extended or would the reflections from woofer cone then become the problem?
Lynn, as you showed deeper interest here are some more infos...
The woofers were already entirely tested and documented in german Hobby HiFi 4/2015. I will show the parameters only for two field coil currents here and additionally my measuremnts for frequency response at these (1.5A and 3.0A):
[A] --Qts -Rms --dB ---BL
1,5 0,499 1,59 83,5 13,68
3,0 0,164 1,48 88,5 26,22
Here are my own measurements in the open baffle (job_for_lower_woofer.gif).
The red line is the resonse for 3.0A and the black line at 1.5A up to 700Hz. Normally, one would say, hey the woofer has a more flat response for 1.5A and has a slightly better extension to LF. But in this way you give away 4-5 dB effiency in the upper region. Ok, let's go to 3.0A with slightly rising response from about 80 Hz on. I hope you clearly see that the baffle step (baffle is about 1m width) coming from 20 Hz with about 6bB per octave is turning around 70-80 Hz in a slightly rising response. And that's where the blue curve is coming into the game. It is the cross-over function for the lower woofer. A big sereis coil is doing the job to bring the woofer down but a parallel arrangement of an resitor in series with a much smaller coil resembles the curve to fill up to a nearly flat response. After that all, a parallel capacitor is doing it's job to resemble the roll-off of the middle woofer. I thought that is is a good idea that the the lower woofer shows the same acoustic roll-off where the compression driver comes into the game as the middle woofer but at much lower in level. In this way it works for me. Maybe because both woofers have comparable properties even with different field coil current. And the best thing is that you can lift up or down the woofers using the field coil supply to flat response.
Just to mention that it was a hard job to measure the responses as comb filter effects with the floor are horrible. I used all damping material on the floor that could be found. But comb filter is a good point. At the listening position every speaker shows these effects most often with the floor. The lower woofer is at another height with respect to this and should make these comb filter effect smaller. Where the middle woofer shows a comb filter to the listeners ears the lower does not and vice versa.
Attachments
Not the stand alone Mantas you are thinking of. The little horns in the center of the 604 coaxial driver.
Attachments
Got you Pano. Whether that was an improvement over the original multi-cell horn is the question or just different. That horn is just to small to cover the top end of a 15" cone and have a chance.
I was thinking of the standalone big Manta's that is what I was around when I was working on horns, Manta's, Bi-radials, EV's CD horns, Community, EAW, saw it all.
I was thinking of the standalone big Manta's that is what I was around when I was working on horns, Manta's, Bi-radials, EV's CD horns, Community, EAW, saw it all.
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At least the music I listen to isn't.
But that got me thinking; "How often does music hit the peaks?" I looked a a few dynamic recordings, 1812 Overture, Jupiter from the Planets and some others.
Answer: It depends - a lot. It depends on what is defined as a peak and it depends on the music and recording. What I found was that during loud, dynamic passages the signal is peaking 8 to 20 times per second. Those peaks are brief, between 4 and 12 samples each.
It really depends on where you set the threshold for the peak.
Just curious, is that 1812 overture from Telarc?
LP or CD?
There is a big difference.
Thanks John, that makes sense and is what I would expect. I was just hoping that maybe it was a feature I had missed in some off the shelf software.
I liked your measurements enough to take a serious look at them, and try to get an idea of what they might tell us. Earl Geddes is correct, music isn't loud all the time, so pink noise may not be the best way to test this, it being a rather continuous level. Noise like that also is not a good match for the spectral content of music.
Pink and Brownian noise contain much more energy below 100Hz than most music does. I've run spectral analysis on many recording and genres before, and did again. A good approximation of big classical recording would be Brownian noise high passed filtered at 52 Hz, 2nd order. Some like Pink Floyd also fit that shape, with other rock and Pop - ACDC, Metallica, Black Eyed Peas, Green Day, the Eagles and others - rolling off faster under ~52Hz, perhaps 4th order. Testing with the heavy bass content of pink or brown noise may be showing more compression in your 15" sub than you are actually getting.
Looking at your graphs shows that with pink noise your sub starts compressing 10dB before your 15" mid bass. That made me wonder how much your subs would be into compression for various types of music, if your mid-bass is just at the onset of compression. Looking at various recordings, I'd say that the sub is into your compression zone about 2% of the time when the mid-bass is just touching that region. But on Pink noise? The sub would be into the compression zone 25% of the time. A major difference.
I made some graphics to show the compression differences of the sub in music vs pink noise. I can post them if anyone is interested.
