NOOB built JKim’s Peerless buyout MTM’s and MT’s for HT, need center channel help

[Vinman]

Hi, I’m a new DIYer that just finished the vented MTM’s and MT’s in this thread

http://techtalk.parts-express.com/showthread.php?t=211207&highlight=peerless+buyout

I have spent many months reading this forum (and others) and learning the freeware tools. I’m not an EE (or an ET, or anything “E”) and have kinda hit a wall. I would appreciate some help optimizing a CC crossover.

I attached some pic’s of my new family.

As for the CC.
I selected the Dayton RS52 as a mid to go with the Vifa DQ25SC and Peerless 832873. It just seemed like a good fit to my novice eye. After trying several different networks (1st/3rd order, 3rd, 4th, traps, zobels, pads) my head was spinning. I happened to come across Zaph’s ZD3C, which uses the RS52, in a google search. His topology was crossing right where I was trying and he had about half the parts I had! Needless to say, I “utilized’ it. This is where I’m at with changing values to tweak it (changed so many times, I don’t even know if I have the original crossover points anymore).

It’s been a great learning experience so far but I’m getting quite confused at what to do next so I need suggestions on changing/improving this. I think the low impedance at the high frequency is going to need to be fixed but I’m not sure how.

17L box tuned to 52Hz, baffle 10x20 (I needed the 10” width to fit the big flange on the RS52 with the Vifa stacked over it). The vifa was +2.5 offset, the RS52 is -1.75 from vertical center. Peerless truncations arranged vertically and out 5.5 from the center. Speaker Workshop file is available but I couldn't attach in this posting.

[arlis_1957@yahoo.com]

why do you want to add the rs52? whynot just another mtm on its side. im sure the x-over could be modified for this use.
by the way, that is an exellent looking family so far:)

[J.Lee]

Pretty impressive work for a newb Vinman.

[Vinman]

why do you want to add the rs52? whynot just another mtm on its side. im sure the x-over could be modified for this use.
by the way, that is an exellent looking family so far:)

Thank You. I thought the addition of the mid range would give me a kickin' CC. But your suggestion is well taken. I got "wrapped around the axle" trying to optimize the 3 way, but I think I'll try modeling the MTM on it's side. What might need to change? Vifa on axis? Less BSC?

[Vinman]

Pretty impressive work for a newb Vinman.

Thanks,
A few more pic's of the MT, MTM crossover and sealed RSS265HF subs. It's taken me quite a while to get here, but I'm very happy with the way it all sounds.

[jkim]

Excellent build, Vinman. As for the center channel, I don't think you need to add a dome midrange with your midbass drivers. Here's my suggestion. It's MTM, but not in a usual layout. On a 9.5" high baffle (or you can decide upon the baffle height with a careful layout---I guess it should be between 9" to 10"), place two midbass drivers right next to each other(that is, with truncated sides touching each other) a bit offset towards the baffle's bottom edge, and the tweeter right above the two midwoofers in the middle. This way, lobing errors will be minimized. It should be alright within +/- 20 degrees. You will have a bit different baffle diffraction effect upon the tweeter's response, but this can easily accommodated by adjusting the tweeter lower rolloff by tweaking the tweeter network's primary cap value (via listening). If the center channel is right below or above TV in a cabinet, you will also need reduced baffle step compensation. In that case, I can quickly come up with a reduced BSC version. Let me know.

jAy

[Vinman]

Excellent build, Vinman. As for the center channel, I don't think you need to add a dome midrange with your midbass drivers. Here's my suggestion. It's MTM, but not in a usual layout. On a 9.5" high baffle (or you can decide upon the baffle height with a careful layout---I guess it should be between 9" to 10"), place two midbass drivers right next to each other(that is, with truncated sides touching each other) a bit offset towards the baffle's bottom edge, and the tweeter right above the two midwoofers in the middle. This way, lobing errors will be minimized. It should be alright within +/- 20 degrees. You will have a bit different baffle diffraction effect upon the tweeter's response, but this can easily accommodated by adjusting the tweeter lower rolloff by tweaking the tweeter network's primary cap value (via listening). If the center channel is right below or above TV in a cabinet, you will also need reduced baffle step compensation. In that case, I can quickly come up with a reduced BSC version. Let me know.

jAy

Cooool. I like it! I did a quick layout and I think 9.5 wide by maybe 16 long as if it's too long with all the speakers centered in the middle it could take away from the unique look. Do you think the 16" baffle will change it significantly? It will be sitting on the table in my pic's (below the projector screen, which isn't in place yet) so I'm not sure if reduced BSC is needed. I just use the same box volume and crossover you designed and tweak C9?
Flush or surface mount?
Thanks again for your original design, they sound great!

[rogoll]

Thanks,
A few more pic's of the MT, MTM crossover and sealed RSS265HF subs. It's taken me quite a while to get here, but I'm very happy with the way it all sounds.

Looking at the quality of this work, I think we would have to officially declare you a "non-noob" or maybe it's "post-noob", whatever it is, you are definitely not a noob! Your stuff looks great! If you have more pics, please post them. We like lots of pics and lots of details (hence the numerous "build threads").

[tom_s]

Very nice job! Those look as good as anything you might find in a hifi boutique...and if they sound like the MTs I built, they sound just as good as the high dollar stuff too! This combination seems to excel in the range where the RS52 would be brought into play, probably thanks to the above average distortion profile of each driver and Jay's attention to that in the design process. I would imagine it would be a challenge to match the voicing of your other speakers, especially since you would have many more variables to consider. I also wonder how the power response would change with the dome mid.

[jkim]

Cooool. I like it! I did a quick layout and I think 9.5 wide by maybe 16 long as if it's too long with all the speakers centered in the middle it could take away from the unique look. Do you think the 16" baffle will change it significantly? It will be sitting on the table in my pic's (below the projector screen, which isn't in place yet) so I'm not sure if reduced BSC is needed. I just use the same box volume and crossover you designed and tweak C9?
Flush or surface mount?
Thanks again for your original design, they sound great!

A 16"x9.5" baffle will be just fine. Center channel speaker will benefit from slightly reduced BSC, anyway---for better clarity of movie dialogues. The following is my suggested crossover:

http://techtalk.parts-express.com/attachment.php?attachmentid=5710
http://techtalk.parts-express.com/attachment.php?attachmentid=5709

I'm pretty sure that the default value of 13 uF for C9 will work fine, but if you're willing to, you may adjust it within my suggested range. For example, using 12 uF and two 1.0 uF caps will let you try 12, 13, and 14 uF (when wired in parallel). For R9, the default value of 1.5 ohm will be alright.

By the way, did you flush mount all drivers in your build? I can't tell it in your photos.

jAy

[Vinman]

Looking at the quality of this work, I think we would have to officially declare you a "non-noob" or maybe it's "post-noob", whatever it is, you are definitely not a noob! Your stuff looks great! If you have more pics, please post them. We like lots of pics and lots of details (hence the numerous "build threads").

Thanks Rogoll, I'll officially take the "promotion".

A few more pic's. I built two prototypes out of mdf and then tweaked Jay's crossovers to my liking. You can see the "MT monster" with all the wire nuts and parallel caps. Got to come up with a better way to do that! I'm "into" wood and actually get logs and have them cut into rough boards. I dry them and work them up from there. The MT's and MTM's are 7/8" cherry boxes, with 3/4" baffles and backs. The subs are a hefty 1" cherry.

[Vinman]

A 16"x9.5" baffle will be just fine. Center channel speaker will benefit from slightly reduced BSC, anyway---for better clarity of movie dialogues. The following is my suggested crossover:

http://techtalk.parts-express.com/attachment.php?attachmentid=5710
http://techtalk.parts-express.com/attachment.php?attachmentid=5709


I'm pretty sure that the default value of 13 uF for C9 will work fine, but if you're willing to, you may adjust it within my suggested range. For example, using 12 uF and two 1.0 uF caps will let you try 12, 13, and 14 uF (when wired in parallel). For R9, the default value of 1.5 ohm will be alright.

By the way, did you flush mount all drivers in your build? I can't tell it in your photos.



jAy

Great. I wanted to tweak the BSC on the MTM's and MT;s as well to see what it does to the sound. I found it unpractical to unwind the inductors. Now I have a better understanding of how to tweak values and what to get to substitue an inductor. It looks like you just lowered the primary until you got about a 2db shift and then slightly lowered the cross point, boosted the highs and midrange.

As far as flush mounting, yes, does that dictate what I do with the CC?

[jkim]

If you already flush mounted drivers in your previous build, why not do it again for your CC? Flush mounting the tweeter is highly recommended.

[Vinman]

If you already flush mounted drivers in your previous build, why not do it again for your CC? Flush mounting the tweeter is highly recommended.

Ok, thanks again Jay. I will be posting the build as I go. If I can get it to work from a woodworking perspective, I will leave a small sliver of wood between the two 832873's because I think it will look way sharper than the two just butted up.