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I am confused about speaker load, efficiency and tube amp's drivability. Can anyone explain me this in simple terms. I have a CJ integrated 45w/ch push-pull amp. The rating says 45 w into 8 ohm or 4 ohms. My current speakers are PSB Stratus Minis which are 88 dB efficient with a 4 ohm nominal load (I believe it drops down further at some freq). My amp drives it fine, in the sense that I do not notice any straining, but I am wondering if it drives it the best. I have to turn up the volume to almost 12 o'clock on almost all material to get listenably loud levels (I do not listen at loud levels, but do not listen to low volumes either). My room is not that big, 14'x13' with one side opening up to the kitchen and dining space. Ceiling is vaulted with 8' high on the short side and 9.5' high on the long side.
In this moderate size room is bugs me that I have to turn the volume knob up so high. Is the efficiency of the Minis causing this, or is this the impedance, or both? My previous amp was 100w/ch SS and I had to barely turn the knob up to past 8-30 before it got too loud (but did not sound better, of course)I am currently in the hunt for a good speaker and I want to find one which is a moderate load and efficient for my amp. My question is:
1) Consider two speaker with similar drivers and sonics. One is 88 dB sens and 8 ohm nominal load, the other is 91 dB sens but 4 ohm nominal load. Which one is a easier speaker to drive with my amp?
2) Please explain what governs the drivability of a speaker with tube amps and SPL levels that can be achieved. Why do I hear that with tube amps, one has to be careful about speaker matching more so than similarly powered SS amps.
BTW, i have tracked down some nice speaker kits but many of them are low in sens (but a easier impedance than my minis) and I am hesitating to go for them not knowing how my amp would drive them.
PLEASE enlighten this ignorant soul.
Follow Ups:
Don't worry about the volume control sitting a the 12:00 position. Mine does when I listen at roughly the high 80 to low 90 dB range. Granted, my speakers are rated 85dB and my power amp is solid state model at 124w/pc into their impedance. I get sufficient volume, and have even gone higher on the volume control without hearing any clipping (almost to the 3:00 position!!!)!
If you aren't hearing it clip, I wouldn't worry too much about it.
Cheers
Dman
Hi,
Most designers say that a volume control should be chosen that gives your normally prefered listening level in your room set at 12:00 position. The reason being that the 2 sections of the volume control do not "track" each other well until the control reaches mid position. Your left and right channels can have a 1db or greater difference between them at lower control settings. At 12:00, the 2 sections track each other much more closely. I wouldn't worry about the setting at all, unless your amp is straining to cleanly produce an adequate level, and the music is affected.
mg16
The laws of physics state that in order to increase sound pressures by 3 dB, you must double your amplifier power. So if your speakers produce 88 dB peaks with an input of 1 watt at 8 ohms, measured at 1 meter from the front of the speaker, it will take 2 watts to produce 91 dB peaks, 4 watts to produce 94 dB, and so on. Your 45 watt amp will produce just over 104 dB peak levels. Whether this is loud enough for you depends on your musical tastes, how far you sit from the speakers, room size, and other factors. If your speakers are 4 ohms nominal, it will take twice as many watts to produce the same sound levels. How well your amplifier will do this depends upon several factors, but mainly it boils down to how well it can keep the voltage constant into different loads. Since speaker impedance is a function of frequency, and loads can be reactive at varying frequencies, it it difficult to determine how well an amp will perform into different loads.The reason your solid state amp allowed you to use a lower volume control setting on your preamp was probably due to a higher voltage gain in the solid state amp, which required your preamp to produce less voltage gain, hence the lower volume control setting. There is probably nothing inherently wrong with using a higher volume control setting on your preamp, unless you are amplifying a lot of noise in your system.
You do have to be more careful in matching speaker loads with most tube amps due to their usual higher output impedance, which will cause more interaction with the speaker. Some speakers benefit from the lower output impedances of solid-state gear, leading to greater speaker damping, especially ones with large bass drivers. Many times you can achieve higher sound pressure levels with a tube amp with the same wattage rating because you can drive tubes into clipping with lesser harsh distortion than with a similarly rated solid-state amp, i.e. the tube distortion is more pleasing to the ear. The best way to determine whether a tube amp is a good match for your speakers is to ignore everything everyone else says and listen to the combination. If you like it nothing else matters.
rlawry, you told hondadanda:
"If your speakers are 4 ohms nominal, it will take twice as many watts to produce the same sound levels."If his amp has both 4 and 8 ohm taps, and he uses the 4 ohm tap with 4 ohm speakers, then it should still take 1 watt to produce the SPL of the speaker's rated sensitivity, and his CJ should still produce 104dB/1w/1m before clipping. If he puts a 4 ohm speaker on the 8 ohm tap, he may get even more power, but with more distortion and some risk of damage.
I don't have any 4 ohm 8 ohm taps. The specs just say 45w into 4, 8 or 16 ohm load and the amp just looks like a regular unit.
If there is only one tap (optimized for 8 ohm?) then I am surprised the rated power doesn't vary with impedance. probably the amp is conservatively rated (also conservatively built to handle the different loads.)
I was surprised about that too. Maybe I will call CJ and find out why?
If I remember correctly, CJ optimizes for 4 ohms.The reason for the discrepancy in volume knob position between the solid state and tube amp is due to a difference in gain between the two amps. Usually this is published by the manufacturer and should be on their websites.
Do not worry about your normal volume control settings. It depends on many things, including the gain of the preamp and driver stages of your integrated, the voltage output of your source(s), design of the volume control itself and speaker sensitivity. Some cheap components have "trick" volume controls where the entire useful range is below 9 o'clock, to create the illusion that there is a ton of reserve power. In reality, 45 good tube wpc is PLENTY to drive 88 dB speakers in a room like yours.If you really are concerned about this, you may be able to get inside the amp, loosen the entire volume control on its mounting, and rotate it to the left so your normal setting will seem "lower."
I wouldn't advise rotating the actual volume pot. The voltages inside a tube amp are high enough to do some damage. Based on the questions asked, I would assume that hondadonda shouldn't be poking around inside the unit.A better idea is to rotate the volume knob on the pot post so the detent or marker sits where you want it. This should be possible without opening anything up. If CJ is as quality as I've seen, there should be a set screw on the volume knob that will make this easy.
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