Possible CC rebuild reusing drivers & crossover

[Bogey]

I'm brand spankin' new to DIY speakers and would like some input. I have been reading on several center channel speaker designs in this forum and before I consider building speakers from the ground up, I would like to try my hand at what I think is a simple project to improve my existing configuration.

Groundwork
I have a complete 7.1 configuration of Eosone speakers (by Polk) including RSF 400 towers, RSC 300 center channel, RSR 350 surrounds, RSR 100 radiant surrounds, and RSP 912 subwoofer.

Project: Center Channel
The center channel speaker in this configuration is pretty weak. After running Audessey on my AVR, the crossover frequency for the center channel crossover is set to 110 Hz (far too high) and I had to bump the level up 2 dB to make dialog more intelligible. I don't think it has as much to do with the drivers as the sealed cabinet design. The angled mount of the 5 1/4" woofers is something I have not seen anywhere for center channel speakers except in this design.

What I am considering is to rebuild the center channel in a more standard enclosure in an MTM configuration, farming the drivers and crossover from an extra RSC 300 CC I have. This way, I can hopefully extend the low end frequency response and improve the overall sound stage without getting in deep on driver and crossover design issues.

Design Goals

• Driver Configuration: maintain existing MTM (front) + T (rear) layout
• Cabinet Dimensions (max): 34'W x 18"D x 8"H (7"H preferred)
• Frequency Response: <60 Hz (as low as is practical) to 22 kHz

Questions, questions...

1. Is this a reasonable project to undertake and expect decent results?
2. Can the rebuild achieve the frequency response goal of <60 Hz in a sealed cabinet?
3. Can this be achieved in a Dayton MTM 0.75 pre-fab cabinet? If not, is there an existing cabinet design that meets the design goals?

Suggestions and constructive criticism welcomed and appreciated.

Bogey

[Bear]

Read this thread, in its entirety:

http://www.htguide.com/forum/showthread.php4?t=11475

[---k---]

1. No - The existing crossover has been designed for the current box and driver layout. Change that and you need to modify the crossover. Without the T/S you can't do that.
2. No - If you're not getting less than 60 hz now, how you going to get it sealed? You likely need to go ported to get more extension with those drivers. Model it in Unibox or WinISD to prove it. But, you can't do that without the T/S parameters.
3. No - See above.


The FAQ's on this page will help you:

http://undefinition.googlepages.com/diy

If you want a fun project go forth, but I suggest you post on AVS or PE Forum. You're likely to get better help there.

If you want better results, then sell what you have on Craigslist and build a proven design such as the TriTrix.

[Bogey]

Ryan.

I thought the crossover was mostly for the drivers and to a lesser degree for the layout. Your response indicates that repositioning the drivers alone will have have a big impact, squirreling the XO works. Thx.

Wouldn't a move from a smaller sealed to larger sealed cabinet result in lower frequency response? I must've misunderstood something in my reading.

I appreciate your response. I read thru the FAQs you linked. That helped a lot.

I will give some thought to building an existing design. If I take the plunge, the CC will be the first to take on.
_________________________

Bear,

If I decide to build a proven design, I might consider the Modula MTM CC, but would first look for one that fits the dimensions I outlined in my OP. I'm not quite sure how this build thread applies to my post. It is 9" tall and doesn't reuse my existing drivers.
_________________________

Is there a newbie guide somewhere here that defines the acronyms used? (i.e. - BSC = baffle step compensation). I figured some of them out, but not all just yet.

Thx again for the input.

Bogey

[ThomasW]

A correctly designed crossover takes into consideration the drivers mounted in the baffle where they'll be used. So in most cases change the baffle, change the crossover.

Nope no n00bie guide to terms.

Might consider buying Ray Alden's book "Speaker Building 201". It's a good way to get started since the internet doesn't provide the information in a single condensed format.

[---k---]

Like Thomas says. The crossover should be optimized for the baffle layout. Generic text book crossovers don't. But, all the crossover used in designing speakers here do. I would assume any decent commercial speaker would too.

If the current box is undersized, then yes a larger box can get you more extension. But, there are points of dimensioning returns. And, it is highly improbable that you can take a speaker from 120hz to 60 hz.

I think Bear suggested the Modula MTM thread to demonstrate what all goes into designing a speaker, not as a suggestion of what to build. I would suggest the TriTrix speaker for low budget, first attempt. I think it fits your size requirements. CJD's RS150 MTM is also a good option.

Speaker Building 201 is a good reference. I have it. Very accessible read.

Also, you should note that a MTM on it's side is not really preferred for a center channel. If you sit directly in front of it, it is fine. But, it will have holes in the vocal range of the frequency response off to the sides. The MTM may be more "standard" but it isn't optimum. See designs like the RS WTMW or the Khancenter for what is better.

[Bear]

Also, you should note that a MTM on it's side is not really preferred for a center channel. If you sit directly in front of it, it is fine. But, it will have holes in the vocal range of the frequency response off to the sides. The MTM may be more "standard" but it isn't optimum.

Hence my pointer back to Jon's Modula MTM Center Channel thread...

[Undefinition]

Is there a newbie guide somewhere here that defines the acronyms used? (i.e. - BSC = baffle step compensation). I figured some of them out, but not all just yet.

I was there once, too. This helped me at least understand what the acronyms stood for.

http://www.parts-express.com/resources/speaker-building-terms.cfm

[---k---]

I was there once, too. This helped me at least understand what the acronyms stood for.
http://www.parts-express.com/resourc...ding-terms.cfm

Ahhh. Good find. I either haven't seen that or forgotten it was there.

[Bogey]

Hence my pointer back to Jon's Modula MTM Center Channel thread...

Sorry Bear. I didn't gather your intent from your first response. I understand that the MTM CC configuration isn't optimal, but I'm not prepared to build an entire set of speakers just yet.

[Bogey]

I may undertake a project to build a proven CC design, but it would have to be a first step to a complete system with matched voicing.

My original intent was to maintain the voice matching of my current set-up while improving the sound stage a bit, but it looks like a lost cause at this time.

Thx again to all of you.

Bogey

[Bear]

I may undertake a project to build a proven CC design, but it would have to be a first step to a complete system with matched voicing.

My original intent was to maintain the voice matching of my current set-up while improving the sound stage a bit, but it looks like a lost cause at this time.

Thx again to all of you.

Bogey

Depending upon your goals and content mix, a fully matched set may be a bit of overkill for your needs. If your system is predominantly home theater and/or two-channel music, then focusing on the front set (LCR) is most important. For home theater, the center channel is usually most important if you actually like to hear dialog. Other people vote with their wallets for the ".1" channel.

Assuming you are using a decent subwoofer, there are several designs around here that have gotten rave reviews for sound quality, buildability and value. The question for you is setting a budget and being honest with your woodworking skills. Oh, yeah, and the amount of time you have to devote to it. This last is where I keep getting tripped up.