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In Reply to: RE: Question for Satie posted by Roger Gustavsson on August 24, 2016 at 12:08:09
Thank you for your interest. I have the IIIA a mid bass panel and the low bass panel to the outside of each 3.7. Not sure about the XO issue. I have the IIIA. bass panels connected to a Marchand XM9 with a 24 db XO set at 90 Hz. as per you very helpful suggestion some time ago. Unfortunately I have not been able to implement your other suggestion for rolling off the bass from the 3.7s. My concern about the method to measure distance from a panel speaker was primarily for the 3.7s.. Presently I have tried attaching a 6" block of wood to a small laser distance finder so that I could get a perpendicular distance reading from the 3.7 ( ribbon and woofer ) to my listening position. Not sure where to aim the laser beam for the ribbon and then for the woofer panel. Right now I have each 3.7 ribbon 10'6" from a place just to the side of my head. With this orientation of the 3.7s the lateral portion of the woofer panel is 10' 1" and points to a place 10" from the side of my head. Jim Smiths book indicates that the placement of the non-panel speaker is based on the tweeter but that doesn't seem to make sense to me with Magnepans. but maybe I don't understand the issues involved. I would appreciate you guidance. Joe Fagan
Follow Ups:
Crossing over from the bass panels to the 3.7 should be 1st order symmetrical in order for the equidistant setup to work. A good starting point is 100 hz and you can go down from there, the proper freq will probably end up being about 80 hz. The measurement to the center of the 3.7 bass panel should align with the bass panels. The other drivers should be aligned to the 3.7 bass by ear with the T3 bass panels not playing but placed near the 3.7 roughly where you intend to place them. The mids and highs are not crossed over symmetrically and you can not get them to align in the equidistant arc, since they are on the same plane as the bass on the 3.7. So first thing is to get the 3.7 aligned properly as a stand alone speaker and that will determine the exact locations for the T3 bass panels.
If you want to, you can easily do the crossover passive at line level as it would be just a single cap + optional resistor for the high pass and a cap and a resistor for the low pass. The high pass cap value will depend on your top amp's input impedance and the low pass will just depend on the freq unless your preamp has a high output impedance (tube preamp for example) in which case you would need to calculate for that. You can add a level adjustment pot on the 3.7 high pass filter before the cap - assuming it is more sensitive than the T3 and the amp gains are both close to standard. You can easily get these figures from the manufacturer spec sheets.
I suggest you don't use the LR4 Marchand at all. If you want to do equidistant and can't wait for the 1st order parts to arrive and to build the filters then use both the high and low outputs of the crossover to the top and bottom amps respectively so that the drivers can be both electrically and physically aligned. The phase change on the 3.7 bass panel may bother you, if it does, you definitely will be better off with a 1st order.
Thanks for your two posts. Reading your recommendations is always a humbling experience. Unfortunately the amp for the IIIA bass panels is a 1000 W4S amp which is much less sensitive than the Bryston 7BST that I use for the 3.7s. Both are mono blocks. Don't think that I could use a passive XO for either amp as my preamp is auto former based and as such the output impedance changes with the level of the passive preamp. Given this I can try to use my existing 24db XM9 and see if the phase issues you noted is audible. If so I will ask Marchand to either send me two circuit boards set up for 6 db which I could put in my existing XM9. If that is not possible I could get a XM9 set up for 6db. Appreciate your description of your methods of setting up your Magnepans. Your method seems to make a lot of sense. One question. Why not measure the IIIA bass panels in the center of each panel? Thanks again Joe Fagan
"Why not measure the IIIA bass panels in the center of each panel? "
Obviously didn't come out clearly, You DO measure to the centers of the Tympani panels The 3.7 you are adding to them you are coordinating the bass panel outputs with the T3 panels so you are measuring to those bass panels too.
Where you don't adjust that way is with the mid and tweeter on the 3.7.
Just to be sure that we aren't talking across each other you are using a 3.7 and augmenting the bass with the bass panels from a T3a, Tell me if I got it wrong.
You have it right. Have been running the 3.7 full range and augmenting with the IIIA bass panels crossed over at 90 Hz 24 db. Bass response measured well but only with a RS SLM.
Probably will be better with a first order XO for both the 3.7 and the IIIA bass panels. Marchand can replace the 24 db circuit boards with boards for a 6db XO. Thanks again for your help. Joe Fagan
First order low pass on Tympani IIIA basses? I doubt it is a good idea, they are high mass drivers not doing that well over 150-200 Hz. A steeper cut-off will leave out the "problematic" high frequences.
The issue is that the LR4 as part of a band pass on the 3.7 bass makes for 2 octaves of phase changes which would be ok on an earlier high order maggie but would make a difference in the coherence of the 3.7. The main point for him is whether he likes the one over the other, since the replacement cards for the XM9 are not expensive and he can try it out both ways.
In my case the TIV bass is far slower than the Neo8 mids so there is a slight degree of congestion that I didn't love in the 250-500 hz range with 1st order symmetrical but the problem with LR4 is that the entire 2 octaves around the XO lose their time coherence and sound phasey. Detail is more prominent and the bass panel's contribution of congestion, however small was gone. But the harmonic structure is disrupted and the time alignment is hurt and takes away from the really great imaging performance and instrumental texture. The latter was more important to me than the sort of disconnected detail you get with the LR4 symmetrical.
I think that at the 80'ish hz XO the heavy bass wire and membrane are not going to be so much of a problem even at 150 hz since the output would be down 8db.
After I located my seating position and distance from the 1.7's,I ran tape lines from the center of the sofa to the distance the speakers would be.I used a straight edge to track along the low pile carpet to make a straight line impression in the carpet that I could see,there by marking the speaker distance line.After setting the speakers the same distance from the side walls and positioned on the line impression in the carpet,I toed them in.I used a angle gauge to toe them in at the same angle.The line impression on the carpet allowed me to use the angle gauge.Having the center marked is good way to be sure that the speakers are equally spaced at the center seating position. I hope that helps your set up.
Dave
I think that is a good idea, but I would still confirm with a mono recording that all drivers are positioned well and the tonal balance is even. If it can't be made to even out just by positioning then you need to start loading the sidewalls with "stuff" to even out the two sides. I am a firm believer in furniture and "junk" as room treatments.
I forgot about the mono listening test.I believe that you advised me to do it and it is a good idea. Best wishes,
Dave
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