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Midwest Audio Fest

It’s that time audio enthusiasts! Registration for the 2019 Speaker Design Competition is now open! Visit midwestaudiofest.com for details and to list your speaker project. We are excited to see all returning participants, and look forward to meeting some new designers this year, as well! Be sure your plans include a visit to the Parts Express Tent Sale for the lowest prices of the year, and the Audio Swap Meet where you can buy and trade with other audio fans. We hope to see you this summer! Vivian and Jill
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RS270P-4A and H26TG45-06 2-way

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  • RS270P-4A and H26TG45-06 2-way

    My plan is to make a center channel that has some size to it, and will fit under a front projection screen. The woofer I have chosen is the RS270P-4A. The box will be sealed, and about 1 cu-ft. My sims show that 100dB output should be a piece of cake, with excursion below 6mm. This should work well in my room. My box sims show about 10dB more output at 30hz than my other speakers. This should be plenty. I just hope it's not too much for the room. I went with the 4 ohm driver to increase the speaker sensitivity, thereby reducing the odds of clipping the amp. The sim showed that 25w can get pretty loud. Peaks may take 50w to 100w. Odds are, I'll never need that much power.

    This will be a 10" 2-way. I'm hoping that I can make the mid-range quality, and tonal balance similar to my smaller 2-ways. I may run into problems with this combination of drivers. We will see. If nothing else, it should be fun trying.

    The tweeter is going to be the Peerless H26TG45-06. It has a small wave-guide, I'm not sure how low I can cross it. It's only 4". I plan to cross at 2k if both drivers permit. I expect the acoustic centers to be off by an inch or more. I may slope the baffle eventually, but I plan to use an existing box for initial prototyping. I will tilt it as needed. The tweeter will be about 24" above the floor so that the speaker will fit under a large projection screen. I can raise it a little for my screen, but I'm hoping that it gives the illusion of voices coming from the screen even though it's down low to the floor.

    I hope to have the drivers in a few days. I'm anxious to do some distortion measurements early on to see how these drivers perform.

    The tweeter has a wave-guide that exits at the flange with a sharp edge. As a separate experiment, I plan to add onto the the guide making it deeper, and larger diameter. One of the user reviews said that it has really low distortion. I hope he is right.

    I didn't find much information on the RS270P-4A distortion. I'm crossing my fingers that it's going to be good up to 2k.

    https://www.parts-express.com/peerle...-ohm--264-1386

    https://www.parts-express.com/dayton...4-ohm--295-569

  • #2
    Looks like 22l might be ideal.

    Click image for larger version  Name:	RS270P-4A in 22 liter sealed box.jpg Views:	1 Size:	354.4 KB ID:	1401437Click image for larger version  Name:	RS270P-4A in 22 liter sealed box excursion.jpg Views:	1 Size:	308.0 KB ID:	1401438
    Last edited by rpb; 01-26-2019, 12:57 AM.

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    • #3
      Reserved

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      • #4
        I’m currently doing trial crossovers and voicing with an rs270p-8a based two way.

        The heavy cone cone needs to be crossed as low as you can, not only for directivity of course, but it gets muddy sounding. My current crossover point is 4th Bessel acoustic at 1200. I wouldn’t go higher, that’s for sure.

        Even though it is paper, plan on notching the first two big bumps. I used a tank on one and series rlc on the other.

        That tweeter is not going to be happy in that combo of crossed low enough to keep the woofer clean. The little guide will not be helpful. Your best bet to be successful will be with a tweeter with a 500-600hz fs. A large (8” or more) guide would only help from there.

        good luck!

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        • #5
          Originally posted by dynamo View Post
          I’m currently doing trial crossovers and voicing with an rs270p-8a based two way.

          The heavy cone cone needs to be crossed as low as you can, not only for directivity of course, but it gets muddy sounding. My current crossover point is 4th Bessel acoustic at 1200. I wouldn’t go higher, that’s for sure.

          Even though it is paper, plan on notching the first two big bumps. I used a tank on one and series rlc on the other.

          That tweeter is not going to be happy in that combo of crossed low enough to keep the woofer clean. The little guide will not be helpful. Your best bet to be successful will be with a tweeter with a 500-600hz fs. A large (8” or more) guide would only help from there.

          good luck!
          Do you have a build thread showing measurements? Particularly on axis response without a x-over? Distortion measurements?

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          • #6
            I dont, it’s only in the prelim stage, an osb enclosure with a nest of parts and jumpers on top of it. I just measured distortion of the setup, 4th/6th bessel at 1200, last week. At 1m, distortion was highest at -40db at around 1k. This was at 95db. I don’t have it handy but it was lower than -40 down to 500 where measurements started to become meaningless. I am a novice at measuring btw.

            i didn’t measure the rs270p distortion without the crossover. All I can say is audibly and subjectively it is makes for a muddy sounding midrange. Cone is too heavy imo. Ymmv..

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            • #7
              Found this from when I got them. Post 21. Measurement conditions are pictured so take it for what it’s worth (may not be worth much..).


              http://techtalk.parts-express.com/fo...-version/page2

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              • #8
                Originally posted by dynamo View Post
                I dont, it’s only in the prelim stage, an osb enclosure with a nest of parts and jumpers on top of it. I just measured distortion of the setup, 4th/6th bessel at 1200, last week. At 1m, distortion was highest at -40db at around 1k. This was at 95db. I don’t have it handy but it was lower than -40 down to 500 where measurements started to become meaningless. I am a novice at measuring btw.

                i didn’t measure the rs270p distortion without the crossover. All I can say is audibly and subjectively it is makes for a muddy sounding midrange. Cone is too heavy imo. Ymmv..
                Do you have a raw in box measurement?

                A muddy mid-range could be caused by the x-over. My speaker will be close to the floor, so it may be a real challenge to get the voicing right. I'm up for the challenge. If it blows chunks, I'll add a dome mid, or scrap the design.

                I believe that the Peerless tweeter will turn out to be a lot more capable than you think. Hoping so anyway. It's 96dB at 2.83v., and rated for 100w! That's really loud! I think it will be fine even crossed below 2k if I need to. I wasn't counting on the wave-guide to provide any pattern control. Mostly, I just wanted a guide type driver to help align the acoustic centers. I could have gone with an RST28 in a wave-guide, but everyone is on that bandwagon already. I have some Morel tweeters than can cross at 1.2k without a guide. Obviously, I'd give up a bit of spl crossed that low. If the RS270P simply doesn't sound very good, then there's not a lot that I can do about that.

                Here's one of the reviews.

                Outstanding
                This tweeter measures better then shown in the posted graph. The slight dip/hump at the top of the response is real, but is honestly a non issue at that frequency range, and it goes away off axis. The claimed sensitivity is also real.The real surprise is the distortion performance. This is one of the lowest distortion levels I have seen measured at 90 db 1m. This tweeter should have serious output capability, and should be able to cross at 2khz LR4 with ease.
                Last edited by rpb; 01-25-2019, 11:36 PM.

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                • #9
                  Yes but don’t have it handy at the moment.. sorry. That said I recall it appearing to match the model in response modeler fairly well if you wanted a starting point.

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                  • #10
                    Originally posted by dynamo View Post
                    Yes but don’t have it handy at the moment.. sorry. That said I recall it appearing to match the model in response modeler fairly well if you wanted a starting point.
                    I'll find out soon enough when I get the drivers.

                    Ok, just did some modeling, and it looks like the speaker will need no BSC, if the software prediction is accurate. That's both good, and bad. On the good side, I gain 6dB of output, making the speaker really efficient. On the bad side, the filter may get a bit trickier. The sim predicts a smooth response with the driver about 40" from the wall, and 10" off the floor. Closer to the wall boosts the 100hz range substantially. I can use delay to effectively move it closer to the wall. There's a bump around 800 hz that looks like it will need to be notched. The sim doesn't appear to account for listener position. I believe that my seat position reduces the 100hz range. I'll measure with an existing speaker tomorrow, and see what the room response looks like. I've measured such things before, but it's been a while,and usually, I was measuring the mains which are not in the same location as the center will be.

                    Here's the sim.
                    Click image for larger version  Name:	room effects.jpg Views:	1 Size:	377.9 KB ID:	1401456
                    Last edited by rpb; 01-25-2019, 11:40 PM.

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                    • #11
                      Ooops... My sub was on. Found out while working on a x-over for another 10" 2-way. I'll add the real measurement later.
                      .
                      Last edited by rpb; 01-26-2019, 07:30 PM.

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                      • #12
                        Here's a comparison of a smaller 12l box. The excursion levels out at 4mm, and bass from 60hz up is about the same.

                        Click image for larger version

Name:	12l sealed box comparison.jpg
Views:	1
Size:	337.6 KB
ID:	1401471

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                        • #13
                          It's not the drivers fault, but I'm loosing my motivation for this build. I had good weather yesterday, and decided to modify an old 3-way speaker. I converted it into a 2-way with a dome tweeter. The woofer is a discontinued 850146, and a Morel mdt28, which is also discontinued. The x-over came together really quick, so I gave it a listen sitting on a 24" stand. I listened to some Nora Jones, and Diana Krall, and was surprised how nice it sounded. The x-over had no BSC, but didn't sound as forward as I was expecting. I moved it into center channel position, and tried some TV type shows on Netfix that are primarily dialog. It performed very well, and sounded very natural. I then tried a dvd concert video by James Taylor. I only had time for about 15 minutes of this before I left to meet with a fiend. I think this center would be hard to beat. So... I don't really need the RS270 for a center anymore. I may test it out anyway.

                          The tweeter will fit the cutout in a box that I have, so I'll do some testing on it to see how low it might reasonably cross.
                          Last edited by rpb; 01-27-2019, 10:08 PM.

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                          • #14
                            Tweeter measurements.

                            The tweeter is mounted in a box that the woofer is missing, so there's an open hole close by, and it doesn't quite sit flush with the baffle because it is connected with jumpers that are not quite clearing the cutout notches. Sounds like a horrible way to test it. Think of it as a worse case situation. I may take better measurements later, but what I'm seeing is a very respectable performing tweeter above 2.5k. It's pretty good at 2k too I think. It seems to be relatively easy to filter from what I can tell. I'm not sure what I'll do with these tweeters, but I'm itching to try a 2nd order with some 6.5" drivers I have. As for my originally planned center with the RS270P, I'm not sure yet. If I can stretch the RS270p to 2.5k, I might have to give it a try.

                            On, and off axis response. There is a filter in use, so don't use this to generate an frd file. I tried to get the response down pretty low.

                            Click image for larger version  Name:	h26 off axis.JPG Views:	1 Size:	207.3 KB ID:	1401850

                            Distortion (3rd order) Second order is very similar, but levels out at -60dB above 5k.

                            Click image for larger version  Name:	H26 distortion.JPG Views:	1 Size:	201.5 KB ID:	1401851

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                            • #15
                              Here are measurements of what I'm working on. About 1m, pretty reflective environment.

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