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- Jakes_dad 1:53AM
- Tom_S 1:53AM
- tommytunes50 1:53AM
Now for something nice - and a little retro.
OK, so I scored a NOS pair of RS28 fabric dome tweeters, and a pair of NOS 7" Usher 8945A within the last year or so.
Flashback to 15 or 20 years or so ago when I was struggling financially but dreamed of doing a design using this exact combination. My situation has changed since then, and now I am going to finally build this bad boy.
I have constrained myself out of nostalgia sake - I am going to offset the tweeter despite it going against one of my primary design mantra of "symmetry is damned important in loudspeakers". I also wanted to use Bagby's Response Modeler but it won't run on the latest version of Office 
. So I best-guessed the tweeter offset. I do plan on doing most or all of the XO modeling in PCD, however. I still use AutoCAD 2002 so that portion is definitely covered.
Design objective are aligned with what I believed back then. I am targeting as flat as possible on-axis and going to shoot for a very deep reverse null. In other words, an ideal 4th order LR.
Another constraint is I am going to use a pair of cabinets that Brad had knocked together - the baffle width only leaves room for a 1/2" round-over. Since that was the largest round-over bit I owned back in the day it tracks.
Anywhoo, here is some driver porn:
Bass alignment (modeled with some series resistance) in 0.6 cubes tuned to 45Hz. F3 is 46Hz or so. Should be adequate for most music.
Excursion at 15W does not exceed Xmax until 32Hz.
15W yields ~99.5db in 2pi space. Call it 93db or so after baffle step losses and any potential insertion losses that are not accounted for in the model.
Here is my old school CAD drawing:
So anywhoo, I am going to maybe machine the baffles today already since it is supposed to tickle 70 degrees. The cabinets are already largely assembled, I am just going to add a couple more braces. If I do not get around to machining them today, I may take advantage of the CNC over at Brad's. This is going to be a special build for me, so I will take my time modeling and listening before I call them done. I am curious to see how they fare using my old school approach compared to my design goals of today.
I do not currently have a name for these, will wait for my muse (Mrs. JR) to help me come up with something. She has helped me name quite a few designs, especially "back in the day".
Curious as to your guy's thoughts on this build, as I know it might have been a similar wishlist design for others. Let me know!
and 1 other.
Comments
RUsher 3's?
I always wanted a pair of those Ushers to play with back then, but just didn't have the spare $. How bout the unobtainiums.
That should be a stellar combo!
I forget the difference between the 8945A and the 8948A, but I don't recall it being very significant. I had the ShawnA designed 8948A/9950 combo until they found a better home, and live with the RS28Fs on a daily basis. This will be good.
8948 cone had the ugly on the inside.
That said, these should be great, almost a Proac approach.
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AFAIK Response Modeler will run with all versions of Office, but you need to install the 32 bit version instead of the default 64 bit version. That's not an option for all people and I don't know if it's true for Office 365. Those are two classic drivers (I still have 2 pair of the RS28As).
I could not get RM to run on my new laptop a year ago. I used Office 2015, and tried both installs. I got others to run okay like the last edition of PCD and Unibox, but RM would not run.
Fixed...^^^
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So diffraction and boundary simulator works just fine after I fought Office to get it to let me run the fricken macros. What a pain.
Anyways, simulated diffraction signature:
Since I plan on crossing around 1500 or so, I am not too worried about things.
http://audio.claub.net/software/jbabgy/BDBS.html
Can someone help me understand this simulated response? I have run this and added BSc, but don't really understand the concepts. What exactly does this mean, What would be an optimum XO point for this, assuming the woofer can reach sky high and the Tweeter can do subwoofer duties. How much BSc should we apply and how to tame the squiggles before the -6db dump?
1500 Hz seems to be right in the middle of the big hump.
More so when starting a new design - given a tweeter/mid combo, how can I determing what would be a good baffle width/ Given the other way, for a given woofer which dictates the baffle width, what XO point hsould I choose - which would dictate the mid / tweet choice?
This is the effect the baffle has shown as basically an EQ curve. You apply this to the plots of manufacturer curves and it will show the effect of the baffle on the frequency response. The loss below 1kHz is known as the 6dB baffle step loss.
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Ani, you ask some very difficult questions. I like to take the bsc curve and merge it with a NF woofer curve, then splice it with the FF woofer curve to create a guesstimated anechoic curve down to very low frequencies. But then I can't just pound the merged squigglies flat because I also have to account for "room gain" and boundary reinforcement. And the amount and bandwidth of room gain and boundary reinforcement depends on how you intend to place the speaker in the room. It is a real guessing game to get a speaker to sound right in the room. At least for me. Others might be much better at this.
Has anyone ever attended a speaker listening event outside.
I've mixed live sound outside. Been to my share of live music events outdoors. It has its own issues, and is harder to dial things in when you don't have four walls to reinforce the bass.
I thought these are apropos. Always struck me as too expensive back in the day, but wanted to use them someday. Figure they fit right in with the theme of this build.
Fancy. You could probably get them engraved, if you wanted.
Yeah, Keith does that.
I might send them out if I decide on a name.
I'm using better drivers than Proac, and I am better at crossover design. Their approach is like mine, not the other way around.
I always thought those woofers were pretty cool looking - beauty is in the ‘ear’ of the beholder.
Comes down to your Xover, no pressure-ha
I was speaking from an aesthetic perspective as I've never heard Proacs. No offense was intended.
I'm sure Proac used the SS 18W/8545 though.
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I'm too far into this game to feel any pressure ;-)
I only described the carbon ridged side as ugly just for description sake. I also think they look cool and interesting to the eye.
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I understand that.
Baffles are machined, just gotta glue everything up then the fun part begins.
Ugh, finally glued up. Will finish router work tomorrow night.
Ok, router work instead of lunch today. Busy couple next days, possibly get to measurements on Saturday afternoon, see how weekend plays out.
Everyone needs priorities.
Ready for whoop whoops.
Might have my work cut out for me on the woofer side of things.