My RS180 MTM Design

[greywarden]

Re: My RS180 MTM Design

Unless Jeff has the crossover worked out for a 4-ohm-in-series version, the corssover will have to be reworked. As to how do they sound? Jeff has commercially-sold designs with his name on them, I wouldn't worry too much about how they sound, haha.

http://www.salksound.com/continuum%20-%20home.htm

http://www.salksound.com/archos%20open%20baffle%20-%20home.htm

http://www.salksound.com/soundscape%2012%20home.htm

To start with... no telling how many others he's had his hand in.

[JCC]

Re: My RS180 MTM Design

It looks like Jeff did work out a crossover for a pair of 4 ohms in series (see posts 64, 68 and 69). It also looked like ontariomaximus was going to build a pair. I was wondering if he (or anyone else) did and how it worked out.

I'm also interested if anyone did a Thor-alike with different drivers.

Maybe Jeff or ontariomaximus could weigh in on this if they are monitoring this thread.

[Jeff B.]

Re: My RS180 MTM Design

It looks like Jeff did work out a crossover for a pair of 4 ohms in series (see posts 64, 68 and 69). It also looked like ontariomaximus was going to build a pair. I was wondering if he (or anyone else) did and how it worked out.

I'm also interested if anyone did a Thor-alike with different drivers.

Maybe Jeff or ontariomaximus could weigh in on this if they are monitoring this thread.

I never build them with two 4ohm drivers in series, I just scaled the crossover assuming the same basic frequency response of the woofer, adjusted for the change in sensitivity. It should be pretty close though.

Jeff

[gimpy]

Re: My RS180 MTM Design

After reading this post, I have thought about building a set of these speakers. I had originally planned on building a set of curved Nat P's, but think that these might be a little easier to build (the crossover).

But, PE does not have the tweeter Jeff used on these originally. Is there a drop in tweeter that can be used with the original crossover design? I have read this thread 3 or 4 times now and, I am sorry, but I do not understand all the talk about the substitution parts, etc. It is just over my head. I need the design to be on paper so that I can follow it point by point. Even then, I make mistakes.

Is there a printed design somewhere with current drivers and tweeters that I could use?

Sorry, for my confusion,
thx.

[Applesauce]

Re: My RS180 MTM Design

But, PE does not have the tweeter Jeff used on these originally. Is there a drop in tweeter that can be used with the original crossover design? I have read this thread 3 or 4 times now and, I am sorry, but I do not understand all the talk about the substitution parts, etc. It is just over my head. I need the design to be on paper so that I can follow it point by point. Even then, I make mistakes.

I can't help you with summarizing the substitutions. (I do know that the information is all here in this thread, because I've been following it since the beginning, and I think the RS28A was belatedly deemed a drop-in replacement for the RS28A-S, but someone else should chime in to confirm...)

That said, there are two RS28A-S still available at Solen:

http://www.solen.ca/pub/cms_nf_catalogue_fiche.php?id=2104&nobut=1

I bought mine from there (six months ago when there were four available - not exactly hot sellers!) with the sole intention of building exactly this speaker as Jeff laid it out to begin with. I haven't got around to it yet... But soon, I hope. Soon!

[Jeff B.]

Re: My RS180 MTM Design

I can't help you with summarizing the substitutions. (I do know that the information is all here in this thread, because I've been following it since the beginning, and I think the RS28A was belatedly deemed a drop-in replacement for the RS28A-S, but someone else should chime in to confirm...)

That said, there are two RS28A-S still available at Solen:

http://www.solen.ca/pub/cms_nf_catalogue_fiche.php?id=2104&nobut=1

I bought mine from there (six months ago when there were four available - not exactly hot sellers!) with the sole intention of building exactly this speaker as Jeff laid it out to begin with. I haven't got around to it yet... But soon, I hope. Soon!

Yes. I beleive it was Pau Carmody who measured both and found they had identical roll-offs. The original data indicated otherwise. From his measurements it looks like the regular RS28a would work fine. In fact, from all I have seen the RS28F should too, since I applied no response shaping to the tweeter's top end in this design.

[gimpy]

Re: My RS180 MTM Design

Thx, Applesauce. I checked that link out, but the pricing, shipping, customs (if I read/understand it correctly) is kind of cost prohibitive, especially this time of year, for me. It totals about $160 or $170, I think.

These will be used in a 50 liter, curved speaker that I started about in another thread. It was originally for the Nat P's, but I think the footprint of the curved speaker will not give me enough space for that XO; therefore, the interest in this design when I came across it. I do already have the bracing/skeleton cut out for that shape and size. (I assume I can increase the volume with no tweaking of the crossover?).

Jeff, if you think the rs28a is good for the original design you show (no audible differences), then, I think that is the way I will go and what I will get.

Please let me know if my thinking is wrong and I need to change something.

thx,

[Pete Schumacher]

Re: My RS180 MTM Design

I will second Paul Carmody's assessment of the A/F versions. I have both here, and am able to drop either one into a current build, and the response plots with XOs applied is identical, save the top octave.

[billschulte]

Re: My RS180 MTM Design

How audible would you think a difference in crossover point between 1700 on the woofers versus 1800hz on the tweeter be?...if I used a tweeter that was pre-set by design to roll off at 24db/octave at 1800 and cannot be made to go lower? This is sort of a goofy question but I have a friend who has a pair of RAAL 70xrs and we were considering repurposing some old speaker cabinets for fun. YES..RS-180s are not Seas or Scan Speak but it may be a fun experiment none the less.

[Pete Schumacher]

Re: My RS180 MTM Design

How audible would you think a difference in crossover point between 1700 on the woofers versus 1800hz on the tweeter be?...if I used a tweeter that was pre-set by design to roll off at 24db/octave at 1800 and cannot be made to go lower? This is sort of a goofy question but I have a friend who has a pair of RAAL 70xrs and we were considering repurposing some old speaker cabinets for fun. YES..RS-180s are not Seas or Scan Speak but it may be a fun experiment none the less.

If the phase is tracking well, the slight dip in summation at the XO point is likely to be inaudible.

[czag]

Re: My RS180 MTM Design

Yes. I believe it was Paul Carmody who measured both and found they had identical roll-offs. The original data indicated otherwise. From his measurements it looks like the regular RS28a would work fine. In fact, from all I have seen the RS28F should too, since I applied no response shaping to the tweeter's top end in this design.

I modeled the RS28A and RS28F using some frd files I worked up from another project. The tweeter placement is close with my model being 1.5" off center and your actual design being 1" off center. So you should attribute any differences under 5Khz to the 1/2 inch difference in offset and the diffraction caused by the woofers mounted in the baffles, but the top 2 octaves should be accurate. While it does look to be a drop in around the xover region, it is about 1.5db to 2db hotter with the RS28F from 6khz on up. The frd files for both tweeters were created from the RS28A and RS28F measurements done by John Krutke. See results below:

RS28A Vs. RS28F with xover applied


Another forum member built them and implemented a zobel to bring the top end down to match the RS28AS, you can see some measurements he did here in post #36.

Chris

[Jeff B.]

Re: My RS180 MTM Design

I modeled the RS28A and RS28F using some frd files I worked up from another project. The tweeter placement is close with my model being 1.5" off center and your actual design being 1" off center. So you should attribute any differences under 5Khz to the 1/2 inch difference in offset and the diffraction caused by the woofers mounted in the baffles, but the top 2 octaves should be accurate. While it does look to be a drop in around the xover region, it is about 1.5db to 2db hotter with the RS28F from 6khz on up. The frd files for both tweeters were created from the RS28A and RS28F measurements done by John Krutke. See results below:

RS28A Vs. RS28F with xover applied


Another forum member built them and implemented a zobel to bring the top end down to match the RS28AS, you can see some measurements he did here in post #36.

Chris

The current RS28a's are almost 2dB more sensitive than early versions. Plots I have seen of current tweeters (A and F versions) overlay each other almost perfectly except for the response above 15kHz. By the way, I don't get quite that much rise at the top of my RS28F.

[czag]

Re: My RS180 MTM Design

The current RS28a's are almost 2dB more sensitive than early versions. Plots I have seen of current tweeters (A and F versions) overlay each other almost perfectly except for the response above 15kHz. By the way, I don't get quite that much rise at the top of my RS28F.

That is what John's test showed also, this model was made from a newer unit with 91db sensitivity for the RS28A. These differences could very well be attributed to Dayton's unit to unit variability. There was about 1.5db difference in sensitivity between the batch of 5 RS28F that John tested for me. I used the one with about 91.5 sensitivity for the RS28F since that seemed to be about the average for the 5 units I have.

When I modeled it the extra top end rise seemed to come from the xover being applied.



I do not want to come off as if I am picking you design apart, it is by all accounts a great design. I just wanted to point out that these 2 tweeters may not be drop in replacements in every design due to the differences in top end and unit to unit consistency. This was just something I noticed when working on my own project with a similar tweeter xover topology , but with different woofers.

Chris

[Jeff B.]

Re: My RS180 MTM Design

That is what John's test showed also, this model was made from a newer unit with 91db sensitivity for the RS28A. These differences could very well be attributed to Dayton's unit to unit variability. There was about 1.5db difference in sensitivity between the batch of 5 RS28F that John tested for me. I used the one with about 91.5 sensitivity for the RS28F since that seemed to be about the average for the 5 units I have.

When I modeled it the extra top end rise seemed to come from the xover being applied.



I do not want to come off as if I am picking you design apart, it is by all accounts a great design. I just wanted to point out that these 2 tweeters may not be drop in replacements in every design due to the differences in top end and unit to unit consistency. This was just something I noticed when working on my own project with a similar tweeter xover topology , but with different woofers.

Chris

As I pointed out in other posts in this thread - my design was with the RS28AS. I have never built it, or adjusted it for any other tweeters, so you're not picking apart my design. Substituting tweeters is completely up to the end user. A lot of that gets discussed here too. Adustments are easy to make though, and shouldn't be a problem for anyone wanting to go down that road.

[czag]

Re: My RS180 MTM Design

As I pointed out in other posts in this thread - my design was with the RS28AS. I have never built it, or adjusted it for any other tweeters, so you're not picking apart my design. Substituting tweeters is completely up to the end user. A lot of that gets discussed here too. Adustments are easy to make though, and shouldn't be a problem for anyone wanting to go down that road.

Understood. Members are trying whatever they can to make this design work for them with a different RS tweeter because you developed such a simple but effective xover. I'm glad you decided to share it and your xover design programs, I am sure I wouldn't be nearly this deep into speaker building if you had not developed PCD.

Chris