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In Reply to: RE: Active bi-amping of ET LFT-8b posted by BDP24 on July 02, 2016 at 03:38:39
The B4 is probably the better choice since you alter the filters by using plug in jumpers. The Marchand required desoldering and resoldering in the components on the frequency boards. that is time consuming and an annoyance. .
Wall loading not only reduces dipole cancellation on one side but if placed about 45% into the room will capture the transverse mode of the room which has the lowest frequency of any of the major room modes. If there is one mode you do want to excite then that is the one. Since that is usually in the 30 hz range. The narrow wall mode is one you want to minimize as it is likely to fall in the 80-100 hz range and also produce nulls at that freq in various spots in the room. To do that you place the bass panels flat face forwards with no toe in.
When using the wall loaded setup and you have the panels face forwards then the bass panels will be offset from equidistant and will be out of time alignment so would have to be low passed steeply so that they don't interfere with the mid panels and smear the imaging. I am still trying to make the most out of this config so that you can get closer to the perfect imaging of the equidistant arc setup. .
Follow Ups:
So with the T-IV bass panels placed equidistant with the M/T panels, and only say 3' away from the front wall, the problems created with the 5'/straight ahead positioning can be avoided, ay? I'll try them there ofcourse, as soon as I can get going here in the new room. I'm chomping at the bit! Thanks again Satie, your advice is of great help.I looked again at the First Watt B4, and realized it was the original version (from '12) that had an input impedance of 100k. The '14 revised current version has only 10k---no input buffer. My pre-amp (EAR 868L) has a pretty healthy output at the studio-standard 600 ohms, which I guess will be okay looking at 10k, though 100k would be much better. I didn't know the XM44 required soldering in parts---don't the changeable cards do all the adjusting of frequency and slope?
Edits: 07/03/16
Yes the cards do all the changes, but you still need to solder the parts for each freq and slope into the card. And if you want to reuse the card for a different freq or slope you need to desolder the old parts out and put the new parts in. If you don't recycle them then you end up with a big pile of freq cards. I tried using micro pots (wirewound) but they were difficult to turn precisely and have no calibration marks.
If you end up with the tweeters just 3' off the front wall then you will need to do some absorption or quite a bit of diffusion over the wall.
Lots of things to try out.
I'm pretty sure I'll end up with the panels 5' off the front wall (I have JUST enough space to pull that off), all equidistant and aimed at the listening position. The M/T panel will be separated from the two bass panels of course. I'll switch out the T-IV M/T for the ET's and Quads, trying all three with the bass panels. Having the First Watt B4 will make it much easier. Is the B4 reputed to have a little better sound than the Bryston 10B? Looks like used 10B's go for about the same as a new B4.
I would go with the B4 for flexibility and Pass' voicing. I have not come across a heads on comparison, but it seems the 10B has better bass but the B4 is better in everything else. Both are regarded as transparent.Both use discreet parts rather than op amps. Marchand manages to do quite well with the op amps but they are still noticeable. Taking out an idle gain and buffer on the marchand was a relief,
Do try the equidistant arrangement on the corner to corner plane, I am curious and can't really try it in my room any time soon.
I happened to go onto Audiogon yesterday not long after a First Watt B4 x/o was listed. It's the revised 2014 version, and less than a year old. I made an offer, it was accepted, I sent payment, and it'll be on it's way to me today. What luck!
There is serendipity for you. If your preamp sags on driving it (loses the freq extremes) then you can increase the input impedance by replacing the input resistor to a 20k, most tube pres do perfectly well with that load.
Serendipity---exactly Satie! I took another look at my pre-amp's (EAR 868) specs. I thought I remembered it having an output impedance of 600 ohms, but the spec sheet actually reads "5 volts output into a 600 ohm load". Tim de Paravicini, the pre-amp's designer, does a fair amount of work in the professional recording field, designing products for the studio environment, where 600 ohms is the de facto standard. Nelson Pass told me yesterday that the EAR will have no trouble driving the B4.
Edits: 07/07/16 07/07/16
Pass and TDP know each other's equipment so I would expect you would have no problem if Pass does not expect one.
BTW I used TDP's TC4 MC trannie for a while and it does deserve its high reputation, definitely bested the internal MC trannie in the 834p, The phono stage benefited from a cap diode and resistor upgrade in a big way, made it sound more like the higher end TDP designs.
I know TDP is not a believer in boutique parts, using garden variety one's in the EAR products. The 868 sounds darn fine as is, so I'm not gonna tinker with it just yet!
Well, he tends to make the best of a price target with robust designs that can handle some component drift. That is why he is TDP. Does not mean that the end user can't mod the unit with boutique parts and obtain a significant improvement at a reasonable cost that would have multiplied the price had it been done at the OEM.
I'm going to take a look inside the 868 after I get set up and running in my soon-to-be new room. I remember being surprised by how few parts it actually has.
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