In speakers, large is not necessarily heavy, and small is not necessarily light. Depends on the type of speaker. Generally, high efficiency speakers have low, and compression woofers high Mms, relative to their size.
I am beginning to think that . . .
The speaker part of this thread should be moved to Loudspeakers.
And the amplifier part of this thread belongs in Tubes / Valves.
Then, if and after you solve each of those two parts, perhaps they can be brought together again.
Just my opinion
The speaker part of this thread should be moved to Loudspeakers.
And the amplifier part of this thread belongs in Tubes / Valves.
Then, if and after you solve each of those two parts, perhaps they can be brought together again.
Just my opinion
In my small and humble opinion, splitting the thread would make it way less interesting and interacting between the two arguments.
The amp and speaker are an unicum that rarely is treated as it should, and I would not split an argument just because the site has different closets.
On the opposite, I think that this thread is very useful because it talks about both sides of the final parto of music reproduction in one single thread, and can attract people experienced in both fields.
Just my two small cents.
The amp and speaker are an unicum that rarely is treated as it should, and I would not split an argument just because the site has different closets.
On the opposite, I think that this thread is very useful because it talks about both sides of the final parto of music reproduction in one single thread, and can attract people experienced in both fields.
Just my two small cents.
So? How that invalidates a single word of what I wrote so far? And I mean - anything, starting with my post #199 and backward?
"ALL mid-bass drivers tested have bad waterfall". OK. Compared to what? To tweeters???
Perhaps a new thread Category needs to be created for diyAudio:
something like? . . .
Speaker / Vacuum Tube Amplifier interactions
something like? . . .
Speaker / Vacuum Tube Amplifier interactions
OK. But, in a view of your
will you care to answer this simple question:
6A3sUMMER - maybe you are right about a new forum, but I doubt such forum would have much traffic. As to the appropriateness of speaker discussion here, I explained in post 19 that if I try to discuss current drive speakers on one of the speaker forums, it will not get traction. Given common assumptions of the members specializing in speaker building, the whole rationale of no-NFB amplifier driving some kind of exotic speaker will be vigorously challenged (as it has been challenged here). But on this forum, we at least don't need to prove to each other that a 300B SET with THD of 5% may sound better than Parts Express plate amplifier with THD of 0.01%.
I am almost done with the speaker part and will soon proceed to the amplifiers.
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Thank you, Zintolo - it is more challenging (and, to me, more interesting) to think about the interactions of the two systems. And I agree that it makes for a somewhat messy thread. But an interesting thread nonetheless ...
I should say that my participation is driven by more than idle curiosity - I have heard loudspeakers that work well when driven by low output impedance amps transformed into sub-par performers when driven by a valve amp with (relatively) high output impedance. And vice versa. In those circumstances, we tend to assume that the principle of superposition holds (both components act as independent, linear systems) and that one or the other (speaker or amp) is to blame. "The Axiom 80 is a dreadful sounding thing!" "The Axiom 80 is divine!!" "Your SET is bloated." "I have never heard a 300B amp with such extended, controlled bass!" and so on and so on. It is also possible that the two systems are dependent, affecting each other's response.
On the one hand, in this sort of circumstance it makes perfect sense for loudspeaker manufacturers to reduce the inter-dependence of the loudspeaker and amplifier and make loudspeakers that suit low output impedance amplifiers - after all, they are the VAST majority of amplifiers, for quite understandable reasons. And I want manufacturers to be able to sell their product and stay in business.
On the other hand, here on diyAudio we have the luxury of parting company with commercial necessity if we so wish. Here I can explore the idea of current drive by my preferred method within my available budget (simple pentode scrap-box amps with relatively high distortion driving very ordinary cheap drivers) and can reflect on the results and share them with others.
12" mid driver
The mid driver I want to use is the left one in post 19. It is "light" Magnavox FC, which was used from 1930s to 1960s in that company's consumer radios and consoles. It is not to be confused with the "heavy" Magnavox FC (middle driver in post 19) that was used in musical instruments.
The choice of the "light" Magnavox for this project comes naturally - it has been used with no-NFB pentode amplifiers during the pre-Hi-Fi era.
Light Magnavox FC drivers had same appearance, but quite a variety of characteristics: 4, 8, and 16 Ohm VC; 250, 600, 1000, 1200, 1600 and 6000 Ohm FC; 60 or 90 Hz main resonance; ribbed, smooth or curvilinear cone. During 60s -70 FC was replaced first with Alnico and later with ferrite magnets. Each specific driver had unique 6-digit number. My incomplete database of these drivers have over 40 entries.
I just finished measuring one particular driver for posting here, 4 Ohm/1,600 Ohm, model 232203:
Fs 61 Hz
Frequency response 60-8,000 Hz
Sensitivity 99 dB 1W/1m
Mms 11.4 g
Qms 2.85
Bl 5.4 Tm
Le 28.3 microH
Sd 182 cm2
VC diameter 25 mm
VC height 8 mm
Xmax +/- 1 mm
Magnetic circuit:
Central pole cross-section 5.76 cm2
Yoke cross-section 6.12 cm2
(central pole saturates before yoke)
FC power at the onset of magnetic saturation, approximate, 18 W.
Working FC power, 24 W. The point of saturation cannot be accurately determined because B-H curve is asymptotic.
Parameters were measured at 24 W FC power. FC runs hot at this power, approximately 60oC rise. A driver running at such power cannot be placed inside a cabinet - overheating will result.
The pictures are: driver hooked up for measurment; voltage, current, and power at the onset of magnetic saturation (no further increase in SPL of 1 kHz tone); setup for measuring Bl.
The mid driver I want to use is the left one in post 19. It is "light" Magnavox FC, which was used from 1930s to 1960s in that company's consumer radios and consoles. It is not to be confused with the "heavy" Magnavox FC (middle driver in post 19) that was used in musical instruments.
The choice of the "light" Magnavox for this project comes naturally - it has been used with no-NFB pentode amplifiers during the pre-Hi-Fi era.
Light Magnavox FC drivers had same appearance, but quite a variety of characteristics: 4, 8, and 16 Ohm VC; 250, 600, 1000, 1200, 1600 and 6000 Ohm FC; 60 or 90 Hz main resonance; ribbed, smooth or curvilinear cone. During 60s -70 FC was replaced first with Alnico and later with ferrite magnets. Each specific driver had unique 6-digit number. My incomplete database of these drivers have over 40 entries.
I just finished measuring one particular driver for posting here, 4 Ohm/1,600 Ohm, model 232203:
Fs 61 Hz
Frequency response 60-8,000 Hz
Sensitivity 99 dB 1W/1m
Mms 11.4 g
Qms 2.85
Bl 5.4 Tm
Le 28.3 microH
Sd 182 cm2
VC diameter 25 mm
VC height 8 mm
Xmax +/- 1 mm
Magnetic circuit:
Central pole cross-section 5.76 cm2
Yoke cross-section 6.12 cm2
(central pole saturates before yoke)
FC power at the onset of magnetic saturation, approximate, 18 W.
Working FC power, 24 W. The point of saturation cannot be accurately determined because B-H curve is asymptotic.
Parameters were measured at 24 W FC power. FC runs hot at this power, approximately 60oC rise. A driver running at such power cannot be placed inside a cabinet - overheating will result.
The pictures are: driver hooked up for measurment; voltage, current, and power at the onset of magnetic saturation (no further increase in SPL of 1 kHz tone); setup for measuring Bl.
Of the 11.4 g Mms, 9 g is Mmd and 2.4 g is air. Air motion index is 2.4 : 11.4 = 0.21. For comparison, 6" Scan Speak midbass AMI is 0.025. An order of magnitude worse.
Of Magnavoxe's Mmd, about half is the copper mass of voice coil. The driver may be very substantially improved by rewinding its VC with aluminum wire. More mass can be shaved off by removing felt dust cap and changing external spider with internal one (Klangfilm style). I will do these mods in the drivers for this project.
Have to apologize for the error in the previous post, Sd is 571.5 cm2, not 182. Forgot the pi.
One problem I see is disparate sensitivities of Magnavox (99 dB) and Neo-8 (91 dB). Of course, the Magnavox can be padded down, but I don't like this approach. I think the new lighter VC can be designed in a way to reduce Bl by making the"l" thing shorter (and thus VC even lighter!) Nice tradeoff of increasing the air motion index in exchange for reduced sensitivity.
All these FC drivers have countermodulation coil. This is a coil of thick wire wound, in opposite direction to VC, on top of FC. CM coil has same number of turns as VC. The purpose is to neutralize the modulation of gap magnetic flux by VC. In addition to countermodulation, CM coil reduces VC inductance. However, this only works if the magnetic circuit is below saturation. I prefer running FC magnet beyond saturation, where the effects of CM coil are lost (Le actually increases)..
Nobody remembers the hum bucker coil for some of the dynamic speakers in the old console and cathedral radios?
(not all field coils were without some ripple voltage across them)
(not all field coils were without some ripple voltage across them)
I have this saved-link related to the topic:
https://www.radiomuseum.org/forum/background_hum_with_electrodynamic_loudspeakers.html
Hum bucking could be indeed yet another beneficial effect of this contraption. FCs are quite sensitive to residual ripple of DC supply. As sensitive, perhaps, as a SE amplifier.
18Sound have that scheme in some of their PA drivers. Sadly, the concept didn't seem to stick. The real trick -- seldom exploited though -- is to drive the compensation coil with a current that is proportional to the VC current and that requires sensing of the VC current (when driven from a standard voltage source) and using it in a control loop for the compensation coil. This cures BL(i) dependancy completely.
Simply paralleling it with the VC is not fully effective as the currents are only roughly proportional to each other.
CM coil in Magnavox drivers is in series with VC, so CM and VC currents are always equal.
Concluding remarks on speakers
Magnavox and Neo-8 are close to ideal drivers to use with a no-NFB pentode amplifier. Within their proposed frequency ranges, they present resistive, frequency-independent load to amplifier output. Incidentally, these drivers are arguably among the best one can have, regardless of price. The Magnavox has the desirable very low Qms, so it should be able to handle whatever residual bass coming it's way via a shallow slope crossover.
Because the pair has broad overlapping frequency ranges, they can be crossed first order, with all the benefits of such minimalist crossover. Phase shift at the crossover frequency can be compensated by forward placement of the Neo-8.
Implementation may vary to achieve overall goals. If more low frequency capability is desired, two 8 Ohm Magnavoxe's, 60 and 90 Hz, can be connected in parallel. A parallel pair of Neo-8s (a 94 dB 8 Ohm version of Neo-8) can be used to better match the high sensitivity Magnavox and to extend the lower end of the planars.
I am thinking of round or oval open baffle with drivers eccentrically placed to mitigate edge reflections. The baffle is to be clad on both sides with sound- absorbing layers of felt.
Magnavox and Neo-8 are close to ideal drivers to use with a no-NFB pentode amplifier. Within their proposed frequency ranges, they present resistive, frequency-independent load to amplifier output. Incidentally, these drivers are arguably among the best one can have, regardless of price. The Magnavox has the desirable very low Qms, so it should be able to handle whatever residual bass coming it's way via a shallow slope crossover.
Because the pair has broad overlapping frequency ranges, they can be crossed first order, with all the benefits of such minimalist crossover. Phase shift at the crossover frequency can be compensated by forward placement of the Neo-8.
Implementation may vary to achieve overall goals. If more low frequency capability is desired, two 8 Ohm Magnavoxe's, 60 and 90 Hz, can be connected in parallel. A parallel pair of Neo-8s (a 94 dB 8 Ohm version of Neo-8) can be used to better match the high sensitivity Magnavox and to extend the lower end of the planars.
I am thinking of round or oval open baffle with drivers eccentrically placed to mitigate edge reflections. The baffle is to be clad on both sides with sound- absorbing layers of felt.
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Thinking about this backwards. Parallel connection doesn’t help the sensitivity on a current driven amplifier where gain is directly proportional to load Z. Series does, until you hit max SPL limited by the actual voltage swing. Useful for woofer/tweeter level matching, but won’t give any more max output.