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Boston Acoustics A150: Sensitive Enough?

btol

btol

Well-Known Member
Hi All,

I have an 8wpc Heathkit AA-32 tube integrated that I love. I have a line on a pair of mint Boston Acoustics A150's and was wondering if they would work well with the AA-32.

Looking around, it seems that the 150's are 8ohm w/ a sensitivity of 91db/m. I currently use EPI 180's with the AA-32. They are 4ohm w/ a sensitivity of ~ 88db. These get plenty loud for my tastes so I was wondering if the A150's would work with the AA-32.

Any input would be greatly appreciated.

Bryan
 
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Well, they will be louder than the ones you are using now. A 3db difference is enough that you can hear a difference in volume at the same input power. The BA's should work well for you. Also, an 8 ohm load will cause less strain on your amp.
 
Thanks for the info HTHMAN. I was under the impression that higher resistance would mean less volume. The speakers I mentioned above - the EPI 180's are much louder at 4ohms & 88db/m than my ADSL520's wich are 6ohms with ~92db/m sensitivity. So I'm afraid that the A150's at 8ohms and ~ 91db/m sensitivity will be even quieter than the ADS. Is this line of thinking wrong?
 
Recall that current * impedance = voltage. Voltage is volume. Counter-intuitively, when speaker impedance goes down volume (voltage) does not go up. It goes down--until you turn up the volume. To maintain the same volume (voltage), the current load on the amp goes up.

If you want more voltage (volume), you increase the current (accomplished with your volume control).

Now, current * volts = watts. This is the relation between wattage and volume. If you keep adding current and thus increasing voltage (volume), you keep adding wattage at an ever increasing rate. When you reach the wattage rating of your amp, that's your limit before distortion and clipping start ruining the experience.

You'll note that amps commonly are rated at some watts at 8 ohms impedance, and some higher number of watts at 4 ohms. But few are rated at twice the watts at 4 ohms. This means most amps can get to higher voltage (volume) with 8 ohm speakers than they can with 4 ohm speakers.

Now I've been using voltage and volume as equivalent, but that's really only true when sensitivity is held constant. If speakers are more sensitive, that means they put out more volume per volt. So the more sensitive speakers are, the louder they are, until you run out of watts, which depends on your amp, and on impedance.

I've been figuring all this out as I go.... Someone check me?
 
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btol said:
The speakers I mentioned above - the EPI 180's are much louder at 4ohms & 88db/m than my ADSL520's wich are 6ohms with ~92db/m sensitivity.
Click to expand...

OK, my reasoning above says that at a given volume setting on a given amp, the ADS L520s should be louder than the EPI 180s. Otherwise, something is wrong somewhere....
 
Whoa...appreciate the thorough explanation, Don, but it's over my head. I do agree about the ADS L520's. I was expecting them to be louder than the EPI's. Maybe it's the fact each EPI 180 is essentially two EPI 100's smushed into a larger cabinet. So perhaps there's a wall of sound effect that the much smaller L520's can't match. I also hooked up some Klipsch KG2's that are 4ohm with 90.5db/m sensitivity and they were also louder than the ADS L520's.

Anyway, do you think my Heathkit AA-32 would push Boston Acoustics 150's to a reasonably loud level? Don't need earth shaking. Just enough to feel the bass in my chest.
 
Unless my theoretical musings are all wet in some way, I say yes, the BA 150s should be fine if the EPI 180s are fine. You may have to turn the vol knob higher than you are used to, but your amp should have the reserves to get to the vol you had before and then some.

I'm now thinking maybe changing the impedance load changes the relationship between volume knob position and current output, which could explain why the higher impedance speakers don't seem louder at a given vol knob position....
 
Reading a little more in a source I've been using, I see that 'tube amps are different.'

Tube amplifiers typically have a switch on the back to adjust for the speaker load impedance. Tube amps have different output characteristics than solid state amplifiers, and too low a load impedance will not normally damage them, but the total output will become weaker and muddy. So too little load impedance is still undesirable. Too high a load impedance on a tube amp can cause high voltages inside the amp that can damage power output tubes or the output transformer. link

Do you have an impedance switch on your amp? If not, is your amp documented to want a certain impedance?
 
RE: ADS vs EPI

The ADS senstivity is rated at 2.8V, and they are going to be 4Ω where it counts, so you can subtract 3dB to get the 1W/1M rating, 89dB. 88dB/1W sounds low for the EPI to me, but I can't find good specs on it with a quick search :dunno:. I also can't comment on the Heathkit's capabilities into various impedances, but yes, they will vary, as do SS amps (but in different ways). You have to consider the whole picture.

As I think was already mentioned here, you need to compare how loud you can get before clipping to know which one's getting more headroom on your amp. The volume knob won't tell the whole story for several reasons.
 
I believe that it's also true that as you approach the output limits of a tube amp, you don't run into the hard "clipped" output of a solid state amp driven to the same conditions. Tube amps will clip the output waveform, but it is a "soft" clip. In a SS amp that is clipping, it's the odd-order harmonics generated that tend to fry tweeters. It's my understanding that a tube amp driven to clipping will generate even-order harmonics as a result of the rounded edges of its clipped waveform.

Dave
 
I wish I could hang with the technical talk but it's beyond me. Sounds like the only solution is to try to audition the A150's with my Heathkit, if possible.
 
btol said:
I wish I could hang with the technical talk but it's beyond me. Sounds like the only solution is to try to audition the A150's with my Heathkit, if possible.
Click to expand...

That's far the best solution in any case!

If the seller won't give you a try-out period, see about taking your amp to his place to try them together.
 
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