A new midbass

Brian Cheney · « **on:** 12 Jan 2005, 01:48 am »

When more than one woofer share a vented enclosure they should not be identical--the result is tubby, one-note bass. For some time we have used 10" and 12" midbass woofers with different Qt's and Fs's to prevent the dreaded "one-note" bass effect. On the RM 40 this means a 10" WCf cone with a 40oz magnet, 37Hz Fs and a two-layer voicecoil.

It occurred to me that we might better stagger the TS characteristics of a woofer with incremental magnetization, while leaving the balance of the motor the same. In other words midbass and lowbass would be identical except for magnetization, which would permit use of an 80oz stacked magnet (i.e. the former cannot bottom out), 4 layer voicecoil (with its higher power handling), and identical spider and surround on both woofers.

A consult with Dan at Misco in Minneapolis, who assembles for us, yielded a process in which the incremental magnetizer produced a 90% charge for a Qt of .3 and an 80% charge yielded a Qt of .5. Voila, staggered Qt's and Fs's! An elegant solution to the problem not possible with off-the-shelf drivers. Another favorable byproduct of the process is improved power handling, to 600W rms on the RM40, and no bottoming out the system on the Telarc 1812 Overture.

The upgrade requires a crossover change (about 2% lower to the mids) so if you want to do it, you have access the crossover and solder in additional caps. The drivers are $200pr and if you have the TRT's, you need about $80pr in additional caps. For the Auricaps the extra value is about $40pr.

With this upgrade you get deeper and punicher bass and midbass. As heard at CES!

ekovalsky · « **Reply #1 on:** 12 Jan 2005, 01:53 am »

Is there an upgrade for the RM/X also, or does this just apply to the RM40?

Brian Cheney · « **Reply #2 on:** 12 Jan 2005, 02:59 am »

Applies to RM/X as well, same prices.

JoshK · « **Reply #3 on:** 12 Jan 2005, 03:03 am »

count me in...

woodsyi · « **Reply #4 on:** 12 Jan 2005, 04:13 am »

Brian,
How would this work if I disabled the coil and am actively biamping the speakers?

John Casler · « **Reply #5 on:** 12 Jan 2005, 04:19 am »

Thanks B, for explaining the "details".

All I know is that even powered with only the 100wpc of the Son of Ampzilla, the RM40 had very deep, dry, tight and defined bass with a warmth and richness that blended perfectly.

JoshK · « **Reply #6 on:** 12 Jan 2005, 03:09 pm »

I just added the midwoof upgrade to the FST upgrade I ordered before CES. So I'll be doing the upgrade soon and hopefully I can help with questions if anyone has any, but usually BC's instructions are quite good.

rblnr · « **Reply #7 on:** 12 Jan 2005, 03:17 pm »

I'm interested, but please please please include thorough instructions. Have done some factory auth. upgrades in the past w/importants items left out on the instruction sheet.

BTW, can anyone tell me how to rename the below links? Just posted some pix and my sig. is getting unwieldy.

ctviggen · « **Reply #8 on:** 12 Jan 2005, 03:20 pm »

How do we order? Contact Brian directly?

John Casler · « **Reply #9 on:** 12 Jan 2005, 03:32 pm »

Quote from: ctviggen

How do we order? Contact Brian directly?

Either through B, or a dealer.

woodsyi · « **Reply #10 on:** 12 Jan 2005, 05:13 pm »

John,

Brian confirmed that driver change and TRT mods are not affected by active biamping. I want in. How much is it and when will you ship? Can I sell back the old woofers?

Brian Cheney · « **Reply #11 on:** 12 Jan 2005, 06:01 pm »

Cal 510-222-4276 to order the upgrade. Drivers will be available end of this month.

brj · « **Reply #12 on:** 12 Jan 2005, 06:08 pm »

So is this change now standard in all dual-woofers-in-a-single-airspace speakers? (Which would be the RM30s, RM40s and RM/Xs, I believe?)

Thanks!

Brian Cheney · « **Reply #13 on:** 12 Jan 2005, 06:23 pm »

Upgrade applies to RM40 and RMX speakers. The RM30's already have this feature in that the midbass 6.5" are substantially different Qt and Fs than the lowbass.

KJ · « **Reply #14 on:** 12 Jan 2005, 06:31 pm »

So, on the RM30:

a) one 6.5" driver is for "high-bass" with different Qt/Fs than b?
b) one 6.5" driver is for "mid-bass?" with different Qt/Fs than a?
c) the 10" driver is for "low-bass?"

OR

a) one 6.5" driver is for "mid-bass" with different Qt/Fs than b?
b) one 6.5" driver is for "mid-bass?" with different Qt/Fs than a?
c) the 10" driver is for "low-bass?"

-KJ

brj · « **Reply #15 on:** 12 Jan 2005, 06:33 pm »

Quote from: Brian Cheney

Upgrade applies to RM40 and RMX speakers. The RM30's already have this feature in that the midbass 6.5" are substantially different Qt and Fs than the lowbass.

Ok, so while the 2 forward-firing 6.5" mid-bass drivers are both identical and share the same airspace, they don't need the adjustment because the 10" side-firing woofer also shares the same airspace?

Do the passives affect this somehow?

KJ · « **Reply #16 on:** 14 Jan 2005, 12:52 am »

I know CES probably back logged everyone. Brian or John, any input?

-KJ

John Casler · « **Reply #17 on:** 14 Jan 2005, 01:16 am »

Quote from: KJ

I know CES probably back logged everyone. Brian or John, any input?

-KJ

Only "BIG B" can answer your technical questions with authority.

John Casler · « **Reply #18 on:** 14 Jan 2005, 01:21 am »

Quote from: woodsyi

John,

Brian confirmed that driver change and TRT mods are not affected by active biamping. I want in. How much is it and when will you ship? Can I sell back the old woofers?

The Woofs are $200.

The TRT caps are $80

Shipping is $15

B, has not ask that the old woofs be returned and is not taking them in on trade.

KJ · « **Reply #19 on:** 14 Jan 2005, 01:22 am »

Quote

Only "BIG B" can answer your technical questions with authority.

"All hail B! All hail B!"

Just a little misquote from MIB II.

-KJ