On the upper end, distortion seems to limit the DMB-A to about 4500hz. Super low distortion until about 5khz, then up it goes, dramatically. Is this breakup, or is something wrong with my test set-up? There is a few dB dip in FR around 4300hz
Have others noticed the rapid rise in distortion? I wonder: Could it be my settings in ARTA? I have checked advanced Windows settings for mic and speaker through Sound blaster card, are all at16bit/96khz.
I am OK with crossing to a tweeter at 4500hz, I just wonder why I see distortion rise so quickly.
I did get it to roll-off well enough, but that was by using a parallel notch filter---1.5uF/.14mH/30ohm. For some reason, the calculator I used gave very different values than these, so these are the result of trial and error, with measuring.
For others working with the DMB-A: To tame/roll off the low end resonance/ response; here is a starting point that looks good for an 800hz high-pass: 20uFseries cap plus a series notch filter (parallel with the driver): 40uF/1.2mH/3.3ohm
This looked good after measuring/swapping parts; I did not do a simulation.
Too bad it is hard to find “acoustic suspension”(compliant suspension, Fs/Qes below .5) woofers like the vintage AR units nowadays. Seems like Dayton could sell an 8" steel frame for $40-$50 retail, if they wanted to. Maybe the cones/spiders/surrounds that are easily available overseas don't have the characteristics required?
Ported speakers are popular, but I find that sealed lets me hear the deep bass notes more clearly, even though the mid bass may not be so powerful. Dayton, and others, have drivers that work in sealed boxes without DSP, but they roll-off earlier on the low end, and most have more breakup in their upper range. Highly successful vintage 2ways, with larger woofers, tended to have woofers that rolled-off more gracefully on the top end. They did tend to have less distinct mid-range sound though, likely due to more internal damping of the cone material.
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Very interesting project! Will you work out a crossover for a widely available and not expensive 8" bass unit and tweeter? I like the idea of a sealed cabinet.
andyjevens: "Very interesting project! Will you work out a crossover for a widely available and not expensive 8" bass unit and tweeter? I like the idea of a sealed cabinet."
That is a good idea. I know that would be more useful to folks than modifying this old speaker.
I have had these speakers around a long time with a blown tweeter, and they cost very little money when I got them. I re-foamed the woofers, which is typically a very satisfying project---bringing new life to old.
Using two 8" woofers each in sealed 2.5way towers, my friend is getting great bass, but the enclosure is 2x the size of the AR-16, at least. The bass is especially clear and not boomy or boxy. His woofers are (NLA) Vifa poly cones. There should be something similar available now. He used a (to me) novel filling material to achieve lower Fc: activated carbon. It had to be enclosed in cloth bags!
I should first get these boxes working well. I hope to find the time to do it soon. The HIVI DMB-A mid-driver band-pass is the toughest part of this build. The stock AR-16 woofer is very well behaved. The woofer low-pass is not "textbook" 2nd order, it uses a large air core coil to accomplish baffle-step compensation, then has a capacitor shunt to ground near the crossover point. The response drops steeply to 1500hz.
Almost any new tweeter could work OK. I plan to use the SB Acoustics SB19ST-C000-4 3/4" Textile Dome Tweeter- 88mm- 4 ohm. It has smooth response, and generous x-max for a 19mm tweeter. It is inexpensive for what it is. I hope the directivity of the dome mid and this tweeter are similar at 4500hz crossover point. If not maybe a typical 1" dome, or even one of the small "horn loaded" dome tweeters would be good.
That is a good idea. I know that would be more useful to folks than modifying this old speaker.
I have had these speakers around a long time with a blown tweeter, and they cost very little money when I got them. I re-foamed the woofers, which is typically a very satisfying project---bringing new life to old.
Using two 8" woofers each in sealed 2.5way towers, my friend is getting great bass, but the enclosure is 2x the size of the AR-16, at least. The bass is especially clear and not boomy or boxy. His woofers are (NLA) Vifa poly cones. There should be something similar available now. He used a (to me) novel filling material to achieve lower Fc: activated carbon. It had to be enclosed in cloth bags!
I should first get these boxes working well. I hope to find the time to do it soon. The HIVI DMB-A mid-driver band-pass is the toughest part of this build. The stock AR-16 woofer is very well behaved. The woofer low-pass is not "textbook" 2nd order, it uses a large air core coil to accomplish baffle-step compensation, then has a capacitor shunt to ground near the crossover point. The response drops steeply to 1500hz.
Almost any new tweeter could work OK. I plan to use the SB Acoustics SB19ST-C000-4 3/4" Textile Dome Tweeter- 88mm- 4 ohm. It has smooth response, and generous x-max for a 19mm tweeter. It is inexpensive for what it is. I hope the directivity of the dome mid and this tweeter are similar at 4500hz crossover point. If not maybe a typical 1" dome, or even one of the small "horn loaded" dome tweeters would be good.
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The frequency response looks much like what I measured. The distortion in the HIFI Compass graph does not show the steep rise that my measurement had. There is likely something amiss in my measurement set-up. Thanks.
The dip at 4300hz seems very stubborn, so 4500hz remains a promising spot to cross.
Does anyone have experience crossing from a 2" dome around 4500hz? Generally speaking, would a 19mm or 3/4" be as good of a directivity match as a 1" dome? HIVI has a really sweet, inexpensive, 1" (or is it 28mm) dome in the Q1R. I do like the smaller faceplate of the 19mm SB, becasue it brings centers closer, and my baffle space is limited.
Looking more at the HIFI compass directivity/off-axis info, it looks like beaming sets in strongly at 4300hz. So this may be an answer to my earlier question about breakup above 4500hz. The shape of the curves do not so much look like breakup. I am not really sure if the power response does/does not rise above 4500hz, but the beaming seams responsible for the increase in the on axis response above 4500hz. Due to the increase in directivity, it does seem like 4000-4500hzwould be a good place to cross to a tweeter.
I have come up with a 3way passive crossover for my 8” AR-16 speaker rebuild, using the HIVI DMB-A dome-mid. I used the previously mentioned series-notch, but not the parallel-notch for the higher frequency hump. After many, evolving, iterations the speaker now sounds coherent and “relaxed”; or maybe I should say, I feel relaxed listening to it.
The DMB-A was the most difficult mid I have worked with, especially rolling off the top end. I usually try to pick drivers that are easy to work with. I am learning a little bit more about manipulating stubborn areas in drivers though.
Early iterations did not sound right, even when the frequency response looked basically OK. The latest sounds really coherent; and the frequency response in room at 40” is +/- 2dB bumpy, but basically flat. The baffle has some physical time alignment built in, as well as some mild wave-guiding---I am hoping that the imaging characteristic works out OK. I added lots of bracing/stiffness to the stock cabinet.
Sensitivity must be well below 85dB, but the bass is clean and solidly there, at least in my room, which has a mode-related 40hz boost at the listening position.
The DMB-A was the most difficult mid I have worked with, especially rolling off the top end. I usually try to pick drivers that are easy to work with. I am learning a little bit more about manipulating stubborn areas in drivers though.
Early iterations did not sound right, even when the frequency response looked basically OK. The latest sounds really coherent; and the frequency response in room at 40” is +/- 2dB bumpy, but basically flat. The baffle has some physical time alignment built in, as well as some mild wave-guiding---I am hoping that the imaging characteristic works out OK. I added lots of bracing/stiffness to the stock cabinet.
Sensitivity must be well below 85dB, but the bass is clean and solidly there, at least in my room, which has a mode-related 40hz boost at the listening position.
Why do you want to crossover the midrange and tweeter so high? I hardly know any tweeters that can't be separated lower.
In this case, a few reasons:
The mid dome is physically like a big dome tweeter that plays to 800hz without stress. On the upper end it has a big on-axis notch, or dip, at about 4300hz, that may have to do with the shape and height of the dome. It also starts to beam at this frequency.
I wanted to have the mid covering as wide a range as it could,until it started to beam, which looks, from a HIFI Compass article,to be about 4300hz.
Here a quote (from profiguy) from another thread,
https://www.diyaudio.com/community/threads/the-dome-midrange-thread.407105/page-52
which agrees with my design choices on this project. He likes to use an 8” cone below about 800hz for lower mid-range substantiality (my choice of adjective):
“Its important to aim for at least high 100s to 4k coverage by a smaller cone or large dome. Having this critical part of the spectrum come from one driver allows for smoother phase. I do this for all of my 3 way builds and its the main reason I don't usually build anything with a crossover point between 1k to roughly 3.5 - 5k.”
The mid-dome crosses from the woofer near 800hz (this is an approximation), so even at 4300hz cross to the tweeter, the mid is only covering about 2.3 octaves. The mid is almost acting like a "filler mid-driver", overlapping significantly with both the woofer and the tweeter in the mid's range. Also it has proven tough (for me) to get this mid to roll off on the top end with a low passive-components count---I don't like to use lots of parts if I can help it.
One other factor, that I did not anticipate, was that the SB Acoustics 19mm tweeter had a big peak 1000-2000hz (probably boosted by my wave-guide baffle) near it's resonance, when the tweeter had a 2nd order high pass. The peak was very noticeable in the overall FR around 1500hz. Crossing lower would have necessitated a steeper cross, and related to earlier comments here, it was hard to get the mid to roll off quickly to meet the tweeter for a steeper hand-off. The tweeter filter section now has 3 reactive components and a resistor.
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