Near field monitor project - advice wanted

[unknownuser]

I'm going to build a set of near field monitors to go alongside a computer monitor. I'm looking for something with fairly high fidelity but capable of a thin profile. It will be used at relatively low SPLs and occasionally for long listening periods.

I'm thinking the RS125 is the way to go for the woofer and am trying to choose a tweeter. Several seem like good choices based on John Krutke's tests, published designs from him and Roman Bednarek, as well as a bit of my own research:
- Tangband T25-1166S 1" neodymium
- North D2506-S
- Seas 22TAF/G
- Seas 27TBFCG
- Dayton ND20TB-4
- Aurasound NSW1-205-8A 1"

I've noted Roman's comments, on his Microbe SE, about the somewhat fatiguing nature of the 22TAF/G combination with the RS125. I really want to avoid this as I will sometimes sit in front of these speakers and listen for the better part of the day!

Any comments on the above list or other suggestions?

BTW, any thoughts on doing this, or not, as an MTM?

TIA! Jonathan



(Originally posted by: Jonathan Z)

[tommoore]

Hey, Jonathan

I built a pair using the RS125 with the rear mount dayton neo in a ported enclosure. They sound very good. I never get tired of listening to them. If you want the design details, let me know.

Tom

[unknownuser]

Yes, I would like the details. You can email me at j2468new "at" yahoo.com

Thanks!


(Originally posted by: Jonathan Z)

[romanbednarek]

> I'm going to build a set of near field
> monitors to go alongside a computer monitor.
> I'm looking for something with fairly high
> fidelity but capable of a thin profile. It
> will be used at relatively low SPLs and
> occasionally for long listening periods.

> I'm thinking the RS125 is the way to go for
> the woofer and am trying to choose a
> tweeter. Several seem like good choices
> based on John Krutke's tests, published
> designs from him and Roman Bednarek, as well
> as a bit of my own research:
> - Tangband T25-1166S 1" neodymium
> - North D2506-S
> - Seas 22TAF/G
> - Seas 27TBFCG
> - Dayton ND20TB-4
> - Aurasound NSW1-205-8A 1"

> I've noted Roman's comments, on his Microbe
> SE, about the somewhat fatiguing nature of
> the 22TAF/G combination with the RS125. I
> really want to avoid this as I will
> sometimes sit in front of these speakers and
> listen for the better part of the day!

> Any comments on the above list or other
> suggestions?

> BTW, any thoughts on doing this, or not, as
> an MTM?

> TIA! Jonathan

Do you have a CRT monitor or an LCD flat panel? If you have a CRT monitor then you will want to go with a tweeter that is shielded or has minimal stray magnetic fields. Otherwise your monitor will be distorted. Of the tweeters you selected the ones with the neo magnets will have the best chance other than a regular shielded tweeter. Of the versions I've built the original Microbe (with the TB T25-1166S) would be the best bet but my brother has a center channel using those drivers and if it is placed really close to the screen it still interferes a bit (but I suppose the improvement would only be minimal with a true shielded tweeter).

I don't recall offhand which tweeters I've used with the RS125 but there have been quite a few. I do have a version that uses the 27TDFC (the fabric version of the 27TBFC/G) and if you needed a shielded speaker you could try the 27TDFC/TV which should be close to a drop in replacement. The crossover and response for this version is shown below. I wouldn't consider the 22TAF/G version (SE) to be really fatiguing but it isn't as "laid back" as the original Microbe in the midrange.

Let me know if you have any other questions.

[unknownuser]

Thanks for your thoughts!

Yes it's a CRT and shielded or Neo should be a requirement. So, that narrows down the list.

I like the suggestion of the 27tdfc/tv for its lower fs. I wish the mounting flang was smaller though! I'm still toying with the idea of an MTM and putting active EQ on the woofers for a better low end response.

It appears you choose to cross the 27TDFC higher than it's lowest reasonable point. What drove your selected crossover point? In looking at the response, it occurs to me that a lower point might help the variability in SPL from 750-1500.

I've recently discovered the Tang Band 28-847S and 28-847SA tweeters which are shielded, have low FS points, and small mounting flangs. I'm a bit concerned though about the chamber shape and it inducing stored energy problems. I'm also now looking at the Vifa D26NC55. This has the advantage of a small mounting area and documented, by Zaph, distortion numbers that are reasonably good above 2.5.

Any thoughs on those tweeters?

Thanks!

> Do you have a CRT monitor or an LCD flat
> panel? If you have a CRT monitor then you
> will want to go with a tweeter that is
> shielded or has minimal stray magnetic
> fields. Otherwise your monitor will be
> distorted. Of the tweeters you selected the
> ones with the neo magnets will have the best
> chance other than a regular shielded
> tweeter. Of the versions I've built the
> original Microbe (with the TB T25-1166S)
> would be the best bet but my brother has a
> center channel using those drivers and if it
> is placed really close to the screen it
> still interferes a bit (but I suppose the
> improvement would only be minimal with a
> true shielded tweeter).

> I don't recall offhand which tweeters I've
> used with the RS125 but there have been
> quite a few. I do have a version that uses
> the 27TDFC (the fabric version of the
> 27TBFC/G) and if you needed a shielded
> speaker you could try the 27TDFC/TV which
> should be close to a drop in replacement.
> The crossover and response for this version
> is shown below. I wouldn't consider the
> 22TAF/G version (SE) to be really fatiguing
> but it isn't as "laid back" as the
> original Microbe in the midrange.

> Let me know if you have any other questions.



(Originally posted by: Jonathan Z)

[romanbednarek]

> Thanks for your thoughts!

> Yes it's a CRT and shielded or Neo should be
> a requirement. So, that narrows down the
> list.

> I like the suggestion of the 27tdfc/tv for
> its lower fs. I wish the mounting flang was
> smaller though! I'm still toying with the
> idea of an MTM and putting active EQ on the
> woofers for a better low end response.

> It appears you choose to cross the 27TDFC
> higher than it's lowest reasonable point.
> What drove your selected crossover point? In
> looking at the response, it occurs to me
> that a lower point might help the
> variability in SPL from 750-1500.

> I've recently discovered the Tang Band
> 28-847S and 28-847SA tweeters which are
> shielded, have low FS points, and small
> mounting flangs. I'm a bit concerned though
> about the chamber shape and it inducing
> stored energy problems. I'm also now looking
> at the Vifa D26NC55. This has the advantage
> of a small mounting area and documented, by
> Zaph, distortion numbers that are reasonably
> good above 2.5.

> Any thoughs on those tweeters?

> Thanks!

I chose the higher crossover point with the 27TDFC because it matches the natural roll off of the woofer with the simple LC notch and series inductor. I don't think the crossover point could be lowered enough to fix the issues with the woofer in the 500 to 1kHz range.

I have a design for the Vifa D26 tweeter shown below. Either the 27TDFC(/TV) or the D26 would be excellent choices.

If you stick with the ported Microbe or MIcrobe MTM cabinet design you won't want to boost the bass at all because they play very deep for their size and boosting the response below the port tuning will reduce power handling.

[unknownuser]

(Originally posted by: Jonathan Z)