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Boston Acoustics A400 - Distortion in Midrange

Marv S.

Marv S.

New Member
Hello,

I am a proud, or at least proud that I have hung on to them this long, original owner of a pair of BA A400's. I bought them new c1984 and at some point moved on to other speakers. The A400's were in climate-controlled storage for around 15 years and I recently had a reason to resurrect them. They, of course, needed reforming which I did, hooked them up and was immediately returned to my happy place. A time when I first discovered real Hi-fi. The sound was that distinctly old-school beautiful. After a few days, I noticed (might have been there all along, just not certain) a small amount of distortion in the currently-right midrange driver. Other than that they sound remarkable for 35-year-old speakers.

I could use some help in determining the problem and what might be able to be done. Could it be the crossover caps? I have read this thread from some time ago with interest. I will switch the mid-range drivers this evening and recheck. Any help from someone more knowledgeable would be much appreciated.

-M
 
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I believe the mids are similar to the woofers in that they use voice coils. Did you shim them when you put new foams in?
 
If it is just one mid, switch them from one speaker to the other. If it stays in the same speaker your driver is OK and it's time to look at other components. If it moves the mid is the problem.
 
Marv S. said:
Hello,

I am a proud, or at least proud that I have hung on to them this long, original owner of a pair of BA A400's. I bought them new c1984 and at some point moved on to other speakers. The A400's were in climate-controlled storage for around 15 years and I recently had a reason to resurrect them. They, of course, needed reforming which I did, hooked them up and was immediately returned to my happy place. A time when I first discovered real Hi-fi. The sound was that distinctly old-school beautiful. After a few days, I noticed (might have been there all along, just not certain) a small amount of distortion in the currently-right midrange driver. Other than that they sound remarkable for 35-year-old speakers.

I could use some help in determining the problem and what might be able to be done. Could it be the crossover caps? I have read this thread from some time ago with interest. I will switch the mid-range drivers this evening and recheck. Any help from someone more knowledgeable would be much appreciated.

-M
Click to expand...

Before swapping drivers, it might be easier to swap L/R speaker connections at the amplifier to determine whether the speaker or the amplifier is the culprit.

I still have a pair of Boston T1000 that I also purchased new which feature a near-identical driver compliment of the A400 which I thoroughly enjoy to this day.

Welcome to AK.
 
grillebilly said:
I believe the mids are similar to the woofers in that they use voice coils. Did you shim them when you put new foams in?
Click to expand...
I did not shim them as I was advised they were rather easy to do without. I believe that there is no rubbing of the voice coil but I will double check. Thanks!
 
grillebilly said:
If it is just one mid, switch them from one speaker to the other. If it stays in the same speaker your driver is OK and it's time to look at other components. If it moves the mid is the problem.
Click to expand...
This was exactly by planned next move. Will do so this evening and report back. - Thanks.
 
62caddy said:
Before swapping drivers, it might be easier to swap L/R speaker connections at the amplifier to determine whether the speaker or the amplifier is the culprit.

I still have a pair of Boston T1000 that I also purchased new which feature a near-identical driver compliment of the A400 which I thoroughly enjoy to this day.

Welcome to AK.
Click to expand...
I'll switch left to right before swapping mid ranges. Thanks!
 
grillebilly said:
How do they compare to the Polk RTiA9's?
Click to expand...

Quite different. RTiA9 more detailed, can absorb tremendous amounts of power, tighter, more powerful bass with deeper extension and slightly "brighter" overall.

T1000 more "polite" and very accurate, even response. Does not require a lot of power for excellent bass but it cannot be driven as loudly as the A9 without distorting. A very competent, all around performer with all types of music.
 
62caddy said:
RTiA9
Click to expand...

I was very tempted to get a pair as they are now discounted to what seems like a ridiculously low price, shipped. I am using the 400's currently and wondered if it was a sideways move.
I held off and ended up ordering Tekton Double Impacts, based entirely on reviews, which are phenomenal. They should be here in about 3 weeks.
Thanks for your reply.
 
Hi! Regretfully had to leave town right after my earlier post. I swapped the mid-ranges and can now say with certainty that the distortion is from the driver, not the crossovers as the distortion went with the swapped driver. So, now I am at a bit of a loss. Not sure of what I could do to restore/ repair the actual speaker/driver. I am certainly open to suggestions. I've searched far and wide and cannot locate any 400 parts or whole speakers for sale anywhere at the moment. So, I remain open to suggestions.
 
That was one of the first things I thought of but when I carefully move the cone in and out I don't hear any "rubbing." If you are as confident as you sounded about it though I will do that :)
Is it possible for the coil to be slightly off center causing some distortion but not so much so as to actually rub?
 
I agree, sounds like voice coil is off a little from the refoam. I had to refoam mine as well. Fortunately I didn't have issues. There is ferrofluid in the midrange voice coil gap, from what I have read. Hopefully it isn't dried up gunk in the voice coil gap causing problems. Weird though, since you said it moves freely.
 
The coil moves freely and noiselessly and so it's hard for me to see how misalignment would be the cause unless slight misalignment short of physical contact can cause distortion? The distortion is almost always present but most noticeable in male voices and piano, for what that's worth.
 
Understand. they seemed solid to me when I checked them. I even tried to jiggle them around while playing to see if I heard anything but nothing. I will, however, remove it again tomorrow and take a closer look at the leads. it does seem that i must be something simple though. I would refoam the refoaming but again, there is no audible rubbing noticeable from the voice coil. In any case, would that cause some distortion or more of a rubbing sound? (I've never experienced it before and so don't know the effect)
 
I think if you take the dust cap off you will see the two thin wire leads. At this point you have nothing to lose to remove it and look, it will also give you the opportunity to check for VC rubbing.
Look at this link and how they cut the cap. I've done this a bunch of times on BA's. Yeah, it looks a little sloppy when glued back on, but who cares. They are fantastic speakers that are worth more in your listening room than the money they bring if you sold them.
http://www.decware.com/newsite/refoam.htm

I shim every pair I do. Not that you have to but it virtually guarantees perfect VC alignment. The mid IIRC is much tighter than the woofer and that makes it even more critical.
 
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