Blog Forums DIY Speakers and Subwoofers 3-way tower design (frustrations)

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    • #10228
      nick7676
      Member

      So I’m having trouble coming up with a 3-way tower design. I already have a new pair of (Dayton rs28f-4) 1-1/8″ silk dome tweeters and a new pair of (Dayton rs150p-8A) 6″ midranges.  What I’m having trouble with is decided what bass driver to use.

      I want the bass to be deep, 30hz or lower. I don’t plan on ever building separate subwoofers.

      Staying with the Dayron rs drivers (so they match) I’ve been thinking of using the Dayton RS270p-8A 10″ woofer. The tweeter and mid will be at the top of the baffle with the 10″ woofer placed  toward the bottom of the baffle (near the floor). 

      I was considering using two RS 8″ drivers (2 per towerl but that will put too much of a load on my amp. Any comments or ideas of using the 10″ the way I want to would be greatly appreciated. Thanks

       

       


       

    • #10231
      bjaurelio
      Participant

      The parts Express recommended vented box only has an F3 of 38Hz. For most music that’s fine. Electronic music and organ music will go lower. For home theater, you should consider a dedicated sub.

      If you really want sub 30Hz content with that woofer, you will have to model the woofer in different enclosure volumes and port lengths to see how it will work. You can also try modeling with a 15″ or two 10″ PRs.

    • #10233
      tvor-ceasar
      Moderator

      There’s discrepancy between BassBox and other software such as WinISD and my own QBasic programs (which pretty much match WinISD). For the Dayton RS270P-8A, I get an optimum box of 2.23 CuFt., a 2″ port 3.8″ long, with a tuning of around 27-28 Hz.

      If you build the box to the recommended 1.43 CuFt., your F3 will be about 38 Hz (with a slight bump of 1.45 dB) , and the 2″ port will be 4.5″ long.

      It’s a trade-off. Size vs. max. dig.

      As to the 8″ speakers, how would they be too much of a load? Two 8 ohms in parallel would be 4 ohms, and two 4 ohms in series would be 8 ohms. What is the lowest rating your amp can handle?


    • #10234
      nick7676
      Member

      Thanks for the box calculations. 27-28hz would be well within my tuning goals. 

      Running two 8″ woofers in parallel (8-ohm per woofer) would indeed give me a 4 ohm load.  However, I still have to include the tweeter and midrange to those two woofers (TMWW). I’m just not sure if everything would end up at 4 Ohms or a little bit lower than that.   My two channel amp is rated at 8 or 4 ohm loads. 

      I don’t mind each enclosure being 2.23 CuFt if I go with the 10″ (TMW). The midrange will have it’s own separate enclosure inside the main enclosure. 

      I don’t really want to build separate subwoofer enclosures. These speakers wjll only be used for two-way stereo music listening, no home theater use. 

       

    • #10235
      tvor-ceasar
      Moderator

      @nick7676

      A nice floor stander would be a good build with the 10″ woofer. It’d be possible to get the drivers high enough with that volume that you wouldn’t really need a stand. And since you plan to put the midrange into it’s own separate cavity, the box would need to grow that much more in order to keep the volume needed for the woofer, making it easier to get a taller “box”.

      Re: Impedance – that’s where the crossover comes into play. It separates out the frequencies so that the impedance the amplifier sees is more or less constant. That’s the theory anyway. The truth is that most speakers vary wildly in their impedance, depending on frequency and power level being fed to them. As long as you have your lowest Ohm rating of driver (or combination of like drivers) within your amplifier’s rating, you’ll be okay.

      For example: say you go with the (2) 8″ woofers, a midrange and a tweeter. All are rated at 8 ohms. You parallel the woofers, so they become 4 ohms. Your cross-over then gets designed for a woofer rating of 4 ohms. The cross-over then gets designed for a 8 ohm midrange and a 8 ohm tweeter. Each of these has it’s own section on the cross-over, specific to it’s apparent rating. One section does not affect the other. That way, you just have to worry about the lowest “individual” ohm rating when pairing to an amp.

      Another example is up in the Lounge area, I did a quick “napkin design” (5-minute design) and one of the tweeters I had considered was a 6 Ohm unit and all I had to do was take that into consideration when calculating the cross-over.

      That’s the “quick and dirty” of it. Hope it made sense.


    • #10237
      123toid
      Keymaster
      Posted by: @nick7676

      Thanks for the box calculations. 27-28hz would be well within my tuning goals. 

      Running two 8″ woofers in parallel (8-ohm per woofer) would indeed give me a 4 ohm load.  However, I still have to include the tweeter and midrange to those two woofers (TMWW). I’m just not sure if everything would end up at 4 Ohms or a little bit lower than that.   My two channel amp is rated at 8 or 4 ohm loads. 

      I don’t mind each enclosure being 2.23 CuFt if I go with the 10″ (TMW). The midrange will have it’s own separate enclosure inside the main enclosure. 

      I don’t really want to build separate subwoofer enclosures. These speakers wjll only be used for two-way stereo music listening, no home theater use. 

       

      @tvor-ceaser is absolutely correct. 

      Just to clarify.  You speakers nominal impedance will typically be rated at whatever your lowest frequency driver is rated.  This has to do with power dissipation and as @tvor-ceaser has mentioned, your crossover frequencies.  I’ll post a video below that may help explain it as well. But the basic premise is, since you are crossing over (or handing off) the duties from one driver to the other, the impedance remains (for the most part) unaffected.  That of course can be tailored with the crossover.   So for example we will assume you wanted to use a 4ohm woofer, and 8 ohm mid and 8ohm tweeter with crossover points of 800hz and 2500hz. The first part of your speaker (your woofer) to roughly 800hz will be considered 4ohm at that point we are crossing over or handing off the duties for the midrange.  This is playing from 800hz-2500hz, where it will be considered 8ohm.  Once again, the mid will crossover or hand off the rest of the frequencies above 2500hz to the tweeter, where this once again will be considered 8 0hm.  Now the completed speaker will be considered a 4ohm speaker, even though the majority of the bandwidth is 8ohm.  Why?  The lower frequencies are the hardest for the amplifier to push.

      THe one thing I would be concerned about with the 10″ is it looks to lack a lot of xmax.  I haven’t run any simulations yet.  But let me know what type of amplifier you plan to run, will help us with the woofer recommendation.  

      Now for the promised video 😀  https://youtu.be/MMTGDiLjsZ0


    • #10238
      nick7676
      Member

      Thanks for the info, it all made sense ( especially about how the crossover separates each driver in terms of ohms). It makes me feel a little more confident if I were to go with the (2) 8″ woofers.

      I guess I’m just torn between using the (2) 8″ woofers or just the (1) 10″ woofer.  The positive I see going with the (2) 8″ woofers would be better  sensitivity. Plus it would look pretty cool.  I just don’t know if two dayton RS 8’s can be tuned to 30hz or less. (The Dayton RS225-8 “claims” it has an Fs of 28.3hz and an overall frequency range of 28-2,400hz.)  I haven’t used any box modeling software yet to see if that truly can be done. You would have to also double the box volume

       I don’t really want the enclosures to be over 3 CuFt.

      The (1) 10″ seems to give me everything I’m looking for. (All except it would have less sensitivity). But then again, I could go with (1) 4-ohm 10″ woofer which has higher sesitivity. 

      Decisions decisions lol

       

       

    • #10239
      nick7676
      Member

      @123toid

      Thanks for the video.

      The amp is the Outlaw RR2160

    • #10240
      tvor-ceasar
      Moderator

      Looking at the 8″ & 10″ RS drivers, the XMAX is close for those available: between 6 mm and 7 mm, at least the ones I’d choose to work with. All the drives are good, but I really like the specs on the 10″ I listed above. It digs deep, has the same SPL as 2 of the comparable 8″ ones would have in the compound configuration talked about in the OP while requiring about 2/3 the box size of the twin 8’s. That’s just my thoughts on it. (Oh, btw, a 3 CuFt sealed [acoustic suspension] box with that same 10″ would be tuned to 35 Hz and have a 6 dB roll-off after that. Just sayin…) (Aaanndd, a TL would need a 1.96 CuFt chamber feeding a 12.33′ long x 63.6 sq.in. TL, but it’d be tuned to about 23 Hz and the roll-off is around 3dB. Ooofff! What a behemoth!)

      Alright, that’s enough weirdness from me tonight. Let’s hear your thoughts.


    • #10241
      nick7676
      Member

      That 10″ RS driver can go deep, wow. I’m assuming you’re talking about the 4-ohm version of the 10″ (Rs270P-4A)?  Or the 10″ Rs270P-8A?

      My midranges are the RS “paper” version so I want to stay with the paper version for whatever woofer(s) I pick.

      I want to use a regular ported box.  To keep port noise down I plan on using atleast a 3″ diameter port.

      I think the 10″ may be the way to go. 

       

    • #10242
      tvor-ceasar
      Moderator

      The 8A. The 4 has a lesser Qts which raises its in-box resonance frequency for the optimum box calculation. You can use the 4 in the same 2.2 CuFt box as the 8, and it will tune to about 30 Hz, but it’ll be dropping off slightly by 1.4 dB when it hits the port tuning frequency.

      Just an FYI when looking at the Sensitivity ratings, in case you didn’t know, whenever you see a rating of 2.83V/1m, make sure you take into account the ohm rating of the speaker. This will tell you the actual power they are using for measurement purposes. The way you calculate power is to take the RMS voltage ^2 / Ohm rating. in the cases shown for these speakers, the 2.83 is supposed to be RMS already, so:

      2.83^2/8 = 8.0089/8 = 1.0011125 Watts or 1Watt/1meter (the standard)

      2.83^2/4 = 8.0089/4 = 2.002225 Watts or 2Watts/1meter (not the same as above^^)

      Knowing this, you can make empirical adjustments to compensate by dropping a dB or 2 off the 4 Ohm unit and you’ll see they are actually pretty closely matched. Just a little tidbit to tuck away in your knowledge locker.


    • #10243
      123toid
      Keymaster

      @nick7676

      I’ll try to simulate and this weekend. That’s a really nice amplifier. In fact it might be to your advantage if you don’t want a dedicated subwoofer, to run something like the reference series subwoofer sidefirining. For that to work properly, you would want to cross it over and your omnidirectional range like by 120 hertz. But if its side firing and using just on the directional base, you could cover it with acoustic fabric.  That definitely is an option if you’re interested. The tenant reference subwoofer, would give you a lot more room filling bass at the same cost. I’ll try to run simulations on both as well as xmax limitations due to your tuning frequency.


    • #10244
      nick7676
      Member

      I drew up a quick generic sketch to give everyone a general idea of how I want my tower design to look. Instead of using a typical tall rectangular box, I want the cabinet to slightly taper inward as it rises up from the floor. All drivers will be flush mounted and centered on the baffle. (I also plan to use internal bracing, more than what my crude drawing is showing).

      If you look closely at my drawing, I would also like to incorporate a stepped baffle in my design. From what crossover knowledge I do have, I know you can acoustically align the tweeter and the midrange in the crossover (without using a stepped baffle). However, I personally like the look of a stepped baffle. I must admit, my inspiration to use a stepped baffle comes from Troels Gravesen. He is a high-end DIY speaker builder / designer and uses stepped baffles in 90% of his projects. I have never built a speaker with a stepped baffle and thought it would be fun to try it. I will probably create another topic on this when it comes to figuring out if I’m going to use it or not. But for now I just want to focus on what woofer / woofers to use for the low end.

      I would like to have the woofer somewhere on the front baffle; however, I would entertain a side or rear firing RS subwoofer as an alternative.

      I really appreciate everybody’s comments and help with my project. I also really appreciate those of you who are taking the time to model different woofer/box scenarios. I truly appreciate the time and effort you take out of your day to do such things.

      -nick

       

       

    • #10245
      luftfeder
      Member

      Dear Nick,

      I do like your design idea and coincidentally I was on Troels web site last night and really like his plans with the exception that they are all made from drivers that are 5-10X what I can afford and so I myself have been pondering the idea of making a 3-way which takes inspiration from his designs but based on Dayton Reference Series drivers.

      I was thinking of designing mine with a significant radius on the baffle (baffle has to be thick) like in one of his designs.

      One thing I had thought about is doing it as an M-T-W configuration 

      I will be interested in following how your project turns out.

    • #10246
      nick7676
      Member

      @luftfeder

      Yeah I really like Troel’s designs, too. He has several projects I’d love to build. But, like you said, he pretty much only uses high-end drivers.  I’d have to take out a small personal loan just to buy the drivers. My wife would not be too happy.

      I will be sure to post pictures of the build as it progresses. I have also been contemplating posting the build in video form as well on YouTube.  I’m anxious to figure out what woofer I want to use and wrap up the design phase so I can start building.

      -nick

    • #10248
      kevin-kendrick
      Participant

      @nick7676

      Since this applies to the design you have in mind, I’ve always been curious if there’s more than one way to determine the amount of offset a stepped baffle would require to time align the drivers. The only way I’m aware of would be to mount the drivers to a flat test baffle (no offset, no step) and take measurements. You could then use the measurements to determine the Z-offset and incorporate that into the final cabinets. If others know of another way, would love to hear about it.

      Good luck on your build Nick!

    • #10272
      nick7676
      Member

      I’m going to go ahead and just order two of the 10″ RS270P-8A. 

      Thanks again for everyone’s thoughts and help.

    • #10281
      123toid
      Keymaster

      @kevin-kendrick

      You can guesstimate off previous experience with same sized drivers.  It is typically close, but there is no sure fire way that I know of, besides testing for z-offset.  

      @nick7676 sorry I never got the simulations back to you.  My family just closed on our house on Monday (the 28th) and have been unpacking and moving.  I may have underestimated how much time that would take.  I am really excited about this build.  I love the design you came up with.  I sounds like it will look really sharp. 


    • #10289
      kevin-kendrick
      Participant

      @123toid

      Yea, I kinda figured taking measurements on a test baffle was the only way to do it accurately. Like you said, guessing based on previous experience with similar drivers would only get you in the neighborhood. I wouldn’t want to design and build an enclosure based on a guess only to find out afterwards it was a bad guess, that would be a bummer. On the other hand though, I’ve never subscribed to needing to time align the drivers on the baffle, it’s easy enough to do through the crossovers.

    • #10290
      nick7676
      Member

      I’m excited to start the build. And no worries about the simulations. Closing and moving is an exhausting event.

    • #10384
      nick7676
      Member

      I ended up making a change to my design. I ended up ordering two 8″ RS woofers instead of the 10’s. I was in the process of checking out when I realized the 10’s were no longer on sale. I was able to model the 8’s (rs225-8) to tune to 29-30Hz in winISD. I couldn’t justify spending $200 for the 10’s just to be able to tune 2-3Hz lower. 

      I also picked up 2 sheets of 1″ thick MDF.  I had to special order them from a local lumber yard.  Wow is that stuff crazy heavy lol.

      I already have the mids (6″ RS150P-8A). However, I’m debating on going with the 5″ RS’s.  The offaxis breakup on the 6″ really starts to break up at 2,000Hz. The offaxis breakup on the 5″ RS’s starts breaking up around ~2,500Hz. This would allow me to not cross my RS tweeters down so low (I know this tweeter can be crossed down as low as 1,500 – 1,800Hz). But I keep thinking to myself if I’m building a 3-way speaker why cross over the drivers to their limits if you don’t have to. It just seems the more overlap you have the better.  I would really appreciate anyone’s thoughts or recommendations on a mid. And I’m not worried about the extra expense of using a diff mid because I saved $100 by going with two 8″ RS drivers. Or should I stay with the 6″ RS’s I have?

      Thanks

       

       

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