A new midbass

JoshK · « **Reply #20 on:** 14 Jan 2005, 01:25 am »

I might be interested in buying the old midwoofs for a DIY project. PM me.

buffer · « **Reply #21 on:** 14 Jan 2005, 02:07 am »

Brian,

It seems like the FF1SRE would also be a candidate. Am I correct?

Given I have the external active crossover between the bass and mids, would there be any internal crossover changes required?

Thanks,
Brian

Brian Cheney · « **Reply #22 on:** 17 Jan 2005, 05:03 pm »

On the RM 30, the two 6.5" actives are the same. The two 6.5" passives are slightly different from one another. The 10" is lowbass only and starts to roll off by itself at about 150Hz.

KJ · « **Reply #23 on:** 17 Jan 2005, 07:14 pm »

I'll start off by stating that I am not an engineer. That said:

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When more than one woofer share a vented enclosure they should not be identical--the result is tubby, one-note bass.

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On the RM 30, the two 6.5" actives are the same.

I don't understand why an improvement wouldn't also be noticed with different magnetization between the two 6.5" mid-bass drivers. Does the smaller size of the 6.5" mid-bass drivers play a factor?

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The two 6.5" passives are slightly different from one another.

I assume this is performed to achieve a similar improvement since magnets are not used on the passive radiators? Are the passives different in density?

If the answers are revealing too many "corporate secrets," feel free to respectfully decline my questions. I'm just curious.

-KJ

KJ · « **Reply #24 on:** 19 Jan 2005, 08:52 pm »

Bump...

Tyson · « **Reply #25 on:** 19 Jan 2005, 08:55 pm »

The problem with the 40's was that the midbass and low bas drivers were the same physical size, so another method was needed to get them to have different T/S properties. However on the 30's the midbass drivers are already physically different and w/different T/S properties than the Low bass driver. So I don't see why there would be any need to "re-magnetize" either of the 6.5" midbass drivers. Of course that's just supposition on my part, so I'll defer to whatever answer Brian gives....

KJ · « **Reply #26 on:** 19 Jan 2005, 09:53 pm »

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However on the 30's the midbass drivers are already physically different...

Are they really? I guess I missed that tidbit. I thought they were both identical 6.5" WCF cones? Guess I'll wait for Brian to chime in.

-KJ

Tyson · « **Reply #27 on:** 19 Jan 2005, 10:18 pm »

In the RM30 the midbass woofers are physically a different size than the low bass woofer. The midbass woofers are 6.5 inches, the low bass woofer is 10 inches. In the RM40's the midbass and low bass woofers are all 10 inches.

The only reason to change the midbass woofer in the 40's was because it was the same size as the low bass woofer (both are 10 inches). Since the midbass woofers in the RM30's are already different than the low bass woofer, I doubt there is any need/reason to make any changes to the 6.5 inch midwoofers at all.

Again, it's just my speculation, but it makes sense based on what Brian has already stated in this thread....

KJ · « **Reply #28 on:** 19 Jan 2005, 10:32 pm »

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The only reason to change the midbass woofer in the 40's was because it was the same size as the low bass woofer (both are 10 inches). Since the midbass woofers in the RM30's are already different than the low bass woofer, I doubt there is any need/reason to make any changes to the 6.5 inch midwoofers at all.

Yup, I'm on board with that part. I am curious if the same "magnetization theory" can be beneficially applied when two identical drivers are sharing the same enclosure, AND when the intention is to produce the same frequency range of sound out of those drivers.

-KJ

brj · « **Reply #29 on:** 19 Jan 2005, 10:36 pm »

I think the confusion results from the fact that RM30 has 4 cones of identical size (2 active, 2 passive) inhabiting a single air space, just like the RM40 has 3 cones of identical size inhabiting a single air space (2 active, 1 passive).

Yes, it is clear that the RM40's identically sized 10" drivers cover different parts of the frequency spectrum (mid-bass vs. low-bass) while the RM30's identically sized 6.5" drivers do not (all mid-bass).

The question becomes: Why doesn't the RM30 need the same magnetism treatment as the RM40.

1) This "magnetism" solution only applies to identically sized drivers inhabiting a single airspace when the different drivers cover different parts of the frequency spectrum. (i.e. the RM30 uses all 6.5" drivers solely for mid-bass, and not a split between mid-bass and low-bass like the RM40's)

2) This "magnetism" solution only applies to identically sized drivers inhabiting a single airspace when no other drivers of different size are also sharing the same airspace. (i.e. the RM30 addition of the 10" driver to the same airspace avoids the problem)

3) All of the above!

Clear as mud?

KJ · « **Reply #30 on:** 19 Jan 2005, 10:48 pm »

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Clear as mud?

That's what I'm trying to ask.

Hopefully, Brian can chime in with some insight.

-KJ

Tyson · « **Reply #31 on:** 19 Jan 2005, 11:11 pm »

Quote from: brj

1) This "magnetism" solution only applies to identically sized drivers inhabiting a single airspace when the different drivers cover different parts of the frequency spectrum. (i.e. the RM30 uses all 6.5" drivers solely for mid-bass, and not a split between mid-bass and low-bass like the RM40's)

This is correct, at least based on Brian's assertions earlier, to my understanding, anyway.

Rory B. · « **Reply #32 on:** 19 Jan 2005, 11:32 pm »

What I don't understand is how the bass drivers can be properly loaded to the enclosure. Further stumping me is how the change in the magnetization of the midwoofers can prevent them from bottoming out, since that's what reflex loading does. Unless the passive radiators aren't usd for reflex loading.

Brian Cheney · « **Reply #33 on:** 20 Jan 2005, 04:16 am »

The stacked magnet 80oz driver in the RM 40 can't bottom out because the pole piece is so long the former cannot physical reach the backplate no matter how hard the woofer is driven.

By using the exact same driver as a midbass that driver too cannot bottom out, whereas the old 40oz woofer, even with a bumped backplate, could.

I discovered I could retain the virtues of the lowbass driver (longer throw and power handling, higher self-inductance) by remagnetizing it for lower Qt. This staggers the T/X parameters sufficiently to prevent one-note bass at resonance, of which there are now three (PR at 10Hz, lowbass at 26Hz, midbass at 38Hz).

woodsyi · « **Reply #34 on:** 2 Feb 2005, 09:31 pm »

Brian and/or John,

How are the midbass upgrade program going? Are you close to shipping them?

John Casler · « **Reply #35 on:** 2 Feb 2005, 09:48 pm »

Quote from: woodsyi

Brian and/or John,

How are the midbass upgrade program going? Are you close to shipping them?

B, told me he expected them at the end of Jan, so I suppose they should be here anytime, if they're not already.

John Casler · « **Reply #36 on:** 2 Feb 2005, 09:51 pm »

Quote from: KJ

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However on the 30's the midbass drivers are already physically different...

Are they really? I guess I missed that tidbit. I thought they were both identical 6.5" WCF cones? Guess I'll wait for Brian to chime in.

-KJ

Hi KJ,

The 6.5" drivers are physically different than the 10" driver they share the same space with, not each other.

KJ · « **Reply #37 on:** 2 Feb 2005, 10:05 pm »

Quote from: John Casler

The 6.5" drivers are physically different than the 10" driver they share the same space with, not each other.

So, mid-bass uses the same drivers and frequency range eliminating the need for a difference in magnetization. Low-bass is solely provided by the 10" driver. Correct?

-KJ

Brian Cheney · « **Reply #38 on:** 3 Feb 2005, 12:06 am »

You are correct.