A7 Baffle-Spacer issue

[aditya]

Hi everybody,

Season's Greetings to all !

I was away on work for nearly 6 months (April - November). So almost nil activity here in this wonderful forum. However now that I am back, I am latched on to all the old posts like a hungry man. Thanks to all those who have kept this forum humming...

My predicament ATM is that....
I have aquired a (DIY-ed) pair of A7 cabinets. They are quite nicely & sturdily built. Wt. per box is around 280/300 lbs. They are of the original (two vertical vents) design. All the measurements are perfect. So in essense...it is a nice pair of A7s without the need for any rigidising/bracing/leak-plugging etc.

But one problem is there..... the carpenter seems to have misread the design-plan, and has added (glued) an EXTRA piece of 1" ply (with a circular hole of throat dia. ) to the back of the baffle board.
As a result the LF driver seats on kind of a 1" spacer.

My question is.....how far the sound will be affected by this.....?

AFAIK, it has changed (actually reduced) the throat chamber compression, and this will definitely reduce uniformity in the effective BW.

But my point is that....though it can be done, it is also not a very easy job (at least for me) to remove the glued circular portion. Ofcourse if it is a must then I will have to remove it.


Thanks to all
Aditya

[GM]

The early cab has a spacer, but it's only 3/8" thick, so unless you have original paper surround 803s it's not needed at all. Regardless, worst case is it damps the woofer's peaking break-up modes a bit, so unless they obviously sound obviously 'duller' when mounted on the horn and driven through the XO (HF horn disconnected) referenced to a free air audition, I wouldn't bother with getting rid of them.

GM

[aditya]

Hi GM,

I was hoping you will chime in......thanks a lot.

Yes, you are very very correct in your assesment.

The woofer is sounding dull compared to its free-air performance. The low-mid & mid attack is missing. I have been trying tooth & nail to XOver it successfully, but a void somehow remains. The typical fullness is not there. That made me to suspect the spacer issue. I think I will have to remove it.

By ear I feel the FR is affected from 500Hz onwards. Also there is a crude peak around 2-2.5K which otherwise is not there in the free air performance.

My original A7 setup is gone....to my parental home. This present A7 pair (only cabs) was found with a friend.....lying unused. So I picked them up. I will get the drivers at a later time. Right now just playing with whatever is at my disposal.

Thanks a lot again.

PS:-Enjoyed your this post a lothttp://www.hostboard.com/forums/altec-users-board/196466-604-8g-big-cabinets-big-sound.html#post1850499

[aditya]

The 1" spacer board has come out. Luckily it was not glued at all ! Just 8 rusted screws !

Oh what a relief....

Yes the sound is slightly sharpish and flat-ish now. Earlier it was a tad muddled, as if too much 200-300 Hz.

Thanks
Aditya

[GM]

Saves you from having to shrink the throat.........

GM

[aditya]

yes, it was kind of both the ways.....

but trying to re-adjust the throat area compresson is also not an easy task though it can be done....

I had thought of inserting a 1" thick circular disk (ofcourse no more a disk but two cut-off sides of a disk) into the area so as to level things up again, while maintaining the curve, but was not very sure of the consequences. May be I would have done that finally.....

But my problem is that I always get too engrossed in a situation till I solve it. As it is, its not a bad thing b'coz it helps me delve deeper in to the issue and ofcourse learn a lot in the process. But it also kind of stops me from attending to other issues in life. I kind of end up shutting down everything else ! These cabs came to me around a month back, and till today I was stuck with that ! Hence the relief....

I plan to use for the time being a pair of woofers with the following parameters...

Fs-35, Qt-0.28, Vas-287 ltrs,

Any comments will be most appreciated.


Thanks
Aditya