Well, hello folks.
It seems that I have this sickness that makes me want to try various types of designs, getting to know them, getting bored with them, and trying something else for fun.
This time, I'm going to try open baffle. I saw a design by James Trexx called "The Gate" and the impressive looks, coupled with his listening impressions have baited me into trying something like this, WMTMW. I've got spare drivers hanging around and a MiniDSP (soon to be two) so I can pretty much try anything. Open Baffle looks intriguing, mostly because it seems extremely easy to build (I can probably rip out the two main H Frames on a table saw in the same amount of time it takes me to pencil mark where the internal pieces go in a folded horn
)
So, now we're onto driver selection. I have a supply of Peerless 831727s (4 of em) that have been gathering dust for a while and I'd like to do something with them. So, I whipped up a rather crude H-Frame 11"w 22"h 12"d and mounted them in there push-pull. Measured, they seem to be fairly well behaved from 60 hz to around 600 hz, so I'm guessing they'll work fairly well tasked with 60 - 300hz or so. The design I'm working on wouldn't have a push-pull H frame, but rather a single driver bottom and single driver top.
For a midrange driver, I'm considering something from Dayton RS, perhaps RS100s or RS150s.
For the tweeter, I'm prepared to cannibalize the B&G Neo3 PDRWs that are currently in my speakers.
I've received some input from a couple of members already from another thread that show some concern with the WMTMW layout, I.E vertical issues with the Neo3, and also some issues with it not being able to keep up with flanking H-Frame midwoofers. Perhaps I can overcome the sensitivity issue by simply lowering the gain on the midwoofers and using the extra headroom to eek out some extra low end extension with EQ.
I'm open to any and all suggestions / warnings / kicks in the chuff. Here's a preliminary sketch I did yesterday, borrowed heavily from James Trexx's Gate, and the center baffle borrowed from 2Pi's Aristoteles.
Fire your cannons!
It seems that I have this sickness that makes me want to try various types of designs, getting to know them, getting bored with them, and trying something else for fun.
This time, I'm going to try open baffle. I saw a design by James Trexx called "The Gate" and the impressive looks, coupled with his listening impressions have baited me into trying something like this, WMTMW. I've got spare drivers hanging around and a MiniDSP (soon to be two) so I can pretty much try anything. Open Baffle looks intriguing, mostly because it seems extremely easy to build (I can probably rip out the two main H Frames on a table saw in the same amount of time it takes me to pencil mark where the internal pieces go in a folded horn
)So, now we're onto driver selection. I have a supply of Peerless 831727s (4 of em) that have been gathering dust for a while and I'd like to do something with them. So, I whipped up a rather crude H-Frame 11"w 22"h 12"d and mounted them in there push-pull. Measured, they seem to be fairly well behaved from 60 hz to around 600 hz, so I'm guessing they'll work fairly well tasked with 60 - 300hz or so. The design I'm working on wouldn't have a push-pull H frame, but rather a single driver bottom and single driver top.
For a midrange driver, I'm considering something from Dayton RS, perhaps RS100s or RS150s.
For the tweeter, I'm prepared to cannibalize the B&G Neo3 PDRWs that are currently in my speakers.
I've received some input from a couple of members already from another thread that show some concern with the WMTMW layout, I.E vertical issues with the Neo3, and also some issues with it not being able to keep up with flanking H-Frame midwoofers. Perhaps I can overcome the sensitivity issue by simply lowering the gain on the midwoofers and using the extra headroom to eek out some extra low end extension with EQ.
I'm open to any and all suggestions / warnings / kicks in the chuff. Here's a preliminary sketch I did yesterday, borrowed heavily from James Trexx's Gate, and the center baffle borrowed from 2Pi's Aristoteles.
Fire your cannons!
Attachments
Well, hello folks.
It seems that I have this sickness that makes me want to try various types of designs, getting to know them, getting bored with them, and trying something else for fun.
This time, I'm going to try open baffle. I saw a design by James Trexx called "The Gate" and the impressive looks, coupled with his listening impressions have baited me into trying something like this, WMTMW. I've got spare drivers hanging around and a MiniDSP (soon to be two) so I can pretty much try anything. Open Baffle looks intriguing, mostly because it seems extremely easy to build (I can probably rip out the two main H Frames on a table saw in the same amount of time it takes me to pencil mark where the internal pieces go in a folded horn
So, now we're onto driver selection. I have a supply of Peerless 831727s (4 of em) that have been gathering dust for a while and I'd like to do something with them. So, I whipped up a rather crude H-Frame 11"w 22"h 12"d and mounted them in there push-pull. Measured, they seem to be fairly well behaved from 60 hz to around 600 hz, so I'm guessing they'll work fairly well tasked with 60 - 300hz or so. The design I'm working on wouldn't have a push-pull H frame, but rather a single driver bottom and single driver top.
For a midrange driver, I'm considering something from Dayton RS, perhaps RS100s or RS150s.
For the tweeter, I'm prepared to cannibalize the B&G Neo3 PDRWs that are currently in my speakers.
I've received some input from a couple of members already from another thread that show some concern with the WMTMW layout, I.E vertical issues with the Neo3, and also some issues with it not being able to keep up with flanking H-Frame midwoofers. Perhaps I can overcome the sensitivity issue by simply lowering the gain on the midwoofers and using the extra headroom to eek out some extra low end extension with EQ.
I'm open to any and all suggestions / warnings / kicks in the chuff. Here's a preliminary sketch I did yesterday, borrowed heavily from James Trexx's Gate, and the center baffle borrowed from 2Pi's Aristoteles.
Fire your cannons!
Here are my thoughts, from a recent endeavor involving active OB :
WMTMW layout is a potentially bad idea because of vibrations, especially from the top section, which will not be stiffly coupled to the floor because the middle is open. Move all woofers to the bottom.
Use a 4in-5in diameter true midrange driver, of as high a sensitivity as possible. For instance, in my prototype I used a pair of Seas MP12 drivers that I had around, and this worked pretty well. After extensive searching and modeling it seems the best driver out there for this purpose is the Seas 10F.
Do not use two midranges - this will definitely result in undesirable interference, because you can not cross over to the B&G until 3-4kHz IIRC.
Change to a 4-way system. You will need a driver to fill in below the small diameter midrange, which has to be crossed over somewhere around 600-700Hz, and the woofers, which can only operate up to about 100-150Hz because of the TL resonance of the H-frame.
Suggest U-frame loading for the woofers instead of H-frame. U frame has better sensitivity for given physical "size/length" and a better dispersion pattern.
You will need to EQ the woofers substantially. Sugges that you do NOT do this in the MiniDSP (except during the development phase when you are trying out different EQs) - keep in mind that the max peak output voltage of the MiniDSP is NOT very high (2V pk-pk?). The high amount of gain that is needed to extend the woofer response means that all other levels must be depressed in order to prevent internal digital levels greater than 0dB and very high and obvious distortion, etc. Instead, design and build an analog circuit for this purpose using an LT + a shelving filter.
Consider using a low noise, fixed gain stage with 10dB-20dB of gain on each MiniDSP output to better match its output to amplifier input sensitivity, or use amplifiers that have 0.707Vrms or less input voltage to reach max output power. You will appreciate the extra headroom!
-Charlie
Thanks Charlie!
A couple of additional questions, if I may.
You suggest against H frame loading, preferring U frame instead. Are there still issues with the TL resonances using the U frame that would prevent their usage past 150 hz?
As far as the output of the MiniDSP, I'm planning on using my spare HTR as an amplifier, it has multichannel inputs and offers around 100 wpc, along with a fairly substantial amount of gain, as it's really just a 7 channel integrated amplifier when used like that.
Lastly, will I need to EQ the woofers substatially? In the cheezy prototype H-Frame (and I'm guessing the U frame wouldn't be terribly different) they go down to about 90 hz without any EQ at all, and the drop off below that doesn't seem very bad. In either case, I've got a pair of OD-ML-TL subs that I can run all the way up to about 120 hz if I needed to.
A couple of additional questions, if I may.
You suggest against H frame loading, preferring U frame instead. Are there still issues with the TL resonances using the U frame that would prevent their usage past 150 hz?
As far as the output of the MiniDSP, I'm planning on using my spare HTR as an amplifier, it has multichannel inputs and offers around 100 wpc, along with a fairly substantial amount of gain, as it's really just a 7 channel integrated amplifier when used like that.
Lastly, will I need to EQ the woofers substatially? In the cheezy prototype H-Frame (and I'm guessing the U frame wouldn't be terribly different) they go down to about 90 hz without any EQ at all, and the drop off below that doesn't seem very bad. In either case, I've got a pair of OD-ML-TL subs that I can run all the way up to about 120 hz if I needed to.
Yes, both U- and H-frame have the line resonance. One main reason for using a U- or H- frame woofer is that you get near constant-directivity, but that is true ONLY when used below the first (lowest frequency) resonance of the short "transmission line" that is formed by the geometry. If you make the depth of the frame long enough to get good bass response, this also lowers the first resonant frequency, so there is a tradeoff. Do not expect to use the U- or H- frame up to 500 Hz, for instance. If you need to, then just use an open baffle, which doesn't have these restrictions.
Look up the input sensitivity in the manual. The power capability means nothing if you can not use it because the MiniDSP doesn't generate enough output voltage. Don't forget that you have to reduce all the levels in the system so that the highest output ever needed (eg at full "volume") is no higher than about 0dB digitally.
For instance, I used an Adcom GFA-2535 which has 4 channels. I bridged two channels, and spec'd power is 200W into 8 ohms. But the input sensivity for "full power" for the bridged configuration is 1.78V RMS! The MiniDSP CAN NOT reach this output voltage! So I could not "use" all 200W. Worse, the amp has a couple of dB of headroom, but you need to supply an even higher input voltage to push the amp into clipping. In short I could not use the full capabilities of the amp, which was kind of disappointing. Another 10+dB of gain would have been useful...
If you use a subwoofer, you won't need to EQ the woofers that much. But then again, because of the line resonance it doesn't make sense to use a U- or H-frame plus a subwoofer. You should change to OB for the woofers instead. If you do use a U- or H-frame, then you should operate the woofers between the line resonance (e.g. about 150 Hz) and the lowest frequency that balances bass extension, SPL capability, power requirement, and driver max excursion limitations.
Here are some links to info on U- and H-frame:
U and H Frames - Quarter Wavelength Loudspeaker Design (Martin King)
DIY-dipole-1 (Music and Design)
H-U frame woofers (Linkwitz Labs)
A comparison of OB, H-, M- and U-frame dipole
In the Linkwitz Labs link, for instance, the line resonance that Siegfried is modeling is at 143Hz (see his plots) and the woofer output needs to be already down at this point, so the crossover point should not be higher than about 100 Hz.
-Charlie
Thanks for explaining the line resonances, that makes a lot more sense. Most of those links were already greyed out from my research yesterday and today, but it would appear I should read them more carefully...my mind wanders sometOH LOOK THERES A CHICKEN.
I guess this greatly simplifies my idea, now I'm thinking just one straight open baffle, no H or U frames, crossed over to the sub around 100 hz or so, I'm guessing that'll be where f3 happens on a flat baffle with those woofers.
I'll make some sawdust here shortly and see what it gets me, at least I can get 3 or 4 design iterations out of a single piece of MDF
Thanks again!
I guess this greatly simplifies my idea, now I'm thinking just one straight open baffle, no H or U frames, crossed over to the sub around 100 hz or so, I'm guessing that'll be where f3 happens on a flat baffle with those woofers.
I'll make some sawdust here shortly and see what it gets me, at least I can get 3 or 4 design iterations out of a single piece of MDF
Thanks again!
I simulated two Visaton W250 drivers in a H-frame (red) and in OB (blue) to give a rough comparison without any EQ applied:
The H frame is 9 cm deep on both sides. If you don't intend to use the dipole woofers below 60 Hz, a shallow H-frame will not have much advantage over a simple OB of same cross area. But a shallow H-frame will be usable up to at least 300 Hz too. Note that the frame resonance is only about 4 dB.
Doubling the depth of the H-frame would give another boost below 40 Hz, but reduce the upper range to about 200 Hz:
Rudolf
The H frame is 9 cm deep on both sides. If you don't intend to use the dipole woofers below 60 Hz, a shallow H-frame will not have much advantage over a simple OB of same cross area. But a shallow H-frame will be usable up to at least 300 Hz too. Note that the frame resonance is only about 4 dB.
Doubling the depth of the H-frame would give another boost below 40 Hz, but reduce the upper range to about 200 Hz:
Rudolf
Cool, thanks Rudolf. I started cutting a test baffle just to measure the 831757 to see how usable it is and if I can get my subs crossed over high enough to meet them. Right now my baffle looks a lot like Gainphile's s19. I have to fiddle with the driver cutout a bit, so it might be tomorrow before I get the drivers mounted up. If its a complete disaster, I won't bother measuring it, but I'm anticipating that with a little eq, I should be able to get some halfway decent results.
I transfered the above posts from the other thread because I'd like to discuss the "sonic size" and the "wall of sound" in more depth.
There is nothing in the literature indicating that you can raise the vertical impression of < 200 Hz bass by lifting a bass source. Bass below 200 Hz will be dominated by room modes. And the excitation of those modes doesn't rely very much on the floor or ceiling position of the drivers.
Nevertheless I don't doubt that the visual impact of the upper woofer can feed the illusion of raised bass. Ventriloquism is a strong persuader
.Raising the midrange is a different story. Having a second midrange driver above the tweeter can help to lift the acoustic scene.
How about "lighting the whole wall up with sound"? Dipoles allow for a really impressive horizontal sound panorama. It depends on the interaction of the radiation pattern and the room and is not a "feature" of the speaker alone. Lighting the wall from bottom to top is a matter of increasing ASW. You can have the proverbial "wall of sound", but only at the expense of widened individual phantom sources. Did I mention that increasing ASW is very much a function of your room treatment (or lack of it) too?
Rudolf
My OB attempts have evolved into something like this recently. It's active 4-way and sonically is the best thing I've tried so far. An H or U frame can help boost the lower end but the resonance(s) aren't for me ... after trying it without. I have been using 3rd order bessel elect filters with spread frequencies to knock down the peaks at the various xo points. Simple enough to do.
The 15" driver has a 6db shelf w/5db boost starting @ 320hz .... his HP is 144hz or so. The 12" lower mid is rolled off @ 80hz .... varying this can allow a petty large contribution to the low end or not depending on the room or one's listening tastes.
Sorry that I don't have proper data to offer, however, I think it's worth a look see Doc.
The 15" driver has a 6db shelf w/5db boost starting @ 320hz .... his HP is 144hz or so. The 12" lower mid is rolled off @ 80hz .... varying this can allow a petty large contribution to the low end or not depending on the room or one's listening tastes.
Sorry that I don't have proper data to offer, however, I think it's worth a look see Doc.
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Oh, that looks like a big Heil, I already love it.
As far as the sonic size and having the upper driver, that was when I was considering having those drivers play a bit higher than 200 hz, my original plan was 300hz...or maybe even more, if my measurements and MiniDSP coaxing could work it out. It's really only after some discussion that some have said having them play up that high is probably a bad idea...although that was when we were talking about H frame resonances...now that they're just on a flat baffle (and going by the measurement) the first phase swing doesn't happen until quite a bit higher than 300 hz, so...now I'm wondering.
Would, say, WMTW be bad if they're all on a flat baffle? In my head I imagine something like 72" h x 18" (maybe more) w.
WAF isn't really a factor here and I don't mind if my speakers dominate the room.
Hi DrDyna,
Why don't you start with something simple ?
A 3 ways WWMT ?
WW HFrame til 100Hz
MT simple 8"+1" above 100Hz.
Something like Linkwitz Orion, simple and efficient.
I think OB is difficult to make sing right, a lot diffraction problems. Small surfaces on openbaffle is very tricky.
Just my 2cents
Why don't you start with something simple ?
A 3 ways WWMT ?
WW HFrame til 100Hz
MT simple 8"+1" above 100Hz.
Something like Linkwitz Orion, simple and efficient.
I think OB is difficult to make sing right, a lot diffraction problems. Small surfaces on openbaffle is very tricky.
Just my 2cents
Here's some info on an OB/nude prototype that I built recently, and used with a pair of the MiniDSP 2x4s. Pic:
Frequency Response on and off axis:
It's from this system that I learned the things that I wrote in post #2 of this thread.
Anyway, this was easy to build, looks ugly (it's a prototype after all) but sounds great. I used it with a pair of 12" subs and this was OK in a small room but in a large room was horrible. I am currently planning the next version that will include u-frame subs.
Drivers are the Exodus Audio Anarchy (6.5") on the baffle, Seas MP12vc midrange, and Tang-Band W2-800SL. The mid and tweeter are operated nude. The high location of the woofer helps to smooth out the ripples in the frequency response that result from the open baffle loading. The baffle is 24" wide and 30" high. I initially used a 24"W x 48"H baffle and that was also good, but I ended up not needing such a tall baffle because I crossed over the woofer to the subs at 100Hz. In the USA,I can buy sheet goods (like MDF) precut to 24x48 so mt first try was just done by mounting the drivers without any cutting of the sheet.
-Charlie
Here's what I was testing, this is what I got the measurement from yesterday (I held a piece of wood over the mid cutout and had someone else click measure
Edit: I probably won't stick with this baffle though, I really think it should be wider...and when I put in the Neo3, I was thinking of making a square cutout around 8 inches and suspending it with wire.
Edit: I probably won't stick with this baffle though, I really think it should be wider...and when I put in the Neo3, I was thinking of making a square cutout around 8 inches and suspending it with wire.
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A large u-frame properly stuffed with Bonded Logic or fiberglass (see John K) can damp the cavity resonance of the u-frame........in theory anyways. I haven't done it personally but I intend to sometime this year. More of a super-cardioid pattern but at these low freqs the room modes will dominate as Rudolph points out.
The H frame is 12" deep and - I guess - 12" from the front wall? That is way too near. Make the distance from wall to baffle at least 3-4 feet. The mic distance is ok, if it is at least 2x baffle width.
... because of ...?
A good point to start from
The H frame is 12" deep and - I guess - 12" from the front wall? That is way too near. Make the distance from wall to baffle at least 3-4 feet. The mic distance is ok, if it is at least 2x baffle width.
... because of ...?
A good point to start from
The H- Frame isn't being used atm, it's really just a stand. Right now I'm seeing if I can get just the top 3 way going, which is the reason I was thinking a wider baffle might help the 831757 go a little lower so it won't be a trapeze trick to get the subs to come up and meet it.
The mic is about 25" away, but I move it between where it is and ~ 40 inches and scoot it around to check various distances.
The H frame was only a means to guess the baffle distance from the front wall. Just make sure that your baffle is at least 3 feet from the front wall. Below that the bass response will drop severely.
Rudolf
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