Working on a project with the Vifa D75MX-41-08 / Scanspeak D7608-9200 dome midrange that I want to couple with a modified PE 8" waveguide. I don't have the part number to the WG, but it was the only 8" threaded guide PE recently sold, so that should narrow it down.
I managed to remove the throat portion with a router bit chucked in a small drill press, which worked very well. It took some patience and care not to be overly aggressive with the feed rate since the plastic wants to melt and bunch up. I'm very pleased with the results.
The opening I made is just large enough for the dome without the surround.
Now to the tricky part - building (or 3d printing) an adapter to bolt onto the dome flange. I dont want to permanently attach the WG to the mid flange so that I can still change things as I go.
The magic question is, would it be better to shade/cover the surround and only allow enough gap for dome excursion and surround movement - OR - enlarge the WG throat to fully expose the surround? My gut says shade it and allow just enough gap for dome excursion. If so, I was going to accommodate the surround profile in the adapter flange.
Obviously it would be smart to perform measurements, but I figured I'd ask here first since there are quite a few dome tweeter / WG experts on here that have done their homework on this. Please share your thoughts on how I should proceed.
I managed to remove the throat portion with a router bit chucked in a small drill press, which worked very well. It took some patience and care not to be overly aggressive with the feed rate since the plastic wants to melt and bunch up. I'm very pleased with the results.
The opening I made is just large enough for the dome without the surround.
Now to the tricky part - building (or 3d printing) an adapter to bolt onto the dome flange. I dont want to permanently attach the WG to the mid flange so that I can still change things as I go.
The magic question is, would it be better to shade/cover the surround and only allow enough gap for dome excursion and surround movement - OR - enlarge the WG throat to fully expose the surround? My gut says shade it and allow just enough gap for dome excursion. If so, I was going to accommodate the surround profile in the adapter flange.
Obviously it would be smart to perform measurements, but I figured I'd ask here first since there are quite a few dome tweeter / WG experts on here that have done their homework on this. Please share your thoughts on how I should proceed.
Attachments
BtW, waveguide will end up being roughly 1.75" deep, so it should couple well with the shallow dome profile. My goal is to get a tiny bit more sensitivity down low where there isn't much output capability to start with due to 1mm total p-p xmax. Hopefully this will help cross it over a tiny bit lower and also align acoustic center to the drivers in a large 4 way I have planned, using this dome as a mid-high driver between a 7" Scanspeak bass-mid and seas 1.5" dome also in a WG. I'm cautiously optimistic the mid will still have enough output up top to allow for a 2.5k xover point.
I think you are making a reasonable choice in a situation which doesn't have a perfect answer. I think you can take comfort in the fact that if you get close enough to the diaphragm then it can incorporate the beginning of the waveguide. Therefore, if I was in this position I'd go ahead and do polars later to discover the upper frequency limit.
That's an encouraging answer.
The next step then is the adapter. If I can design it in CAD then I'll aim for shading the surround since there's not much worry of excessive excursion. It was tricky getting the throat this close in size, so I'll just run with it now. The BL/Mms isn't very high on this dome so I'm not expecting anything amazing in terms of upper cutoff. I'm just trying to avoid an excessive blip in the FR when the surround can cause weird phasing issues in the WG throat.
Taking a closer look at the mounting flange frame, it appears there's a seam where it snaps in place around the motor assembly. They did use some kind of adhesive there, so I dont want to take the chance of ruining a 100 dollar drive unit trying to remove the flange in an attempt to make attaching the WG simpler.
The next step then is the adapter. If I can design it in CAD then I'll aim for shading the surround since there's not much worry of excessive excursion. It was tricky getting the throat this close in size, so I'll just run with it now. The BL/Mms isn't very high on this dome so I'm not expecting anything amazing in terms of upper cutoff. I'm just trying to avoid an excessive blip in the FR when the surround can cause weird phasing issues in the WG throat.
Taking a closer look at the mounting flange frame, it appears there's a seam where it snaps in place around the motor assembly. They did use some kind of adhesive there, so I dont want to take the chance of ruining a 100 dollar drive unit trying to remove the flange in an attempt to make attaching the WG simpler.
Well I'm sad to say the news isn't good. Preliminary testing shows the motor is too weak to support the added loading from the WG. I won't even bother posting any measurements because its a waste of time.
With a Qts of 1.7, this mid's low end is×w already on the loose side. I have run this driver successfully in an aperiodic damped 1.5 liter enclosire, which brings it down to a Qts of .7 but low end rolloff predictably takes a hit. Without a WG, it sounds great crossed over 900 hz @ LR2, resulting in an LR4 acoustic rolloff. It gels up top very well with the Seas T35-C002 crossed @ 2.5k LR2. Mechanical power handling really improves with an aperiodic enclosure and transforms this mid into something special. I've yet to hear a cone mid sound this open and detailed. Its inherit weakness is low end output capability, which is why I wanted to try a WG with it.
Now to the ugly part. With the WG, things go south. Qts ends up at 1.3, which isnt acceptable and just results in a sharp bump at 800 hz. This actually hurts low end extension and the dome rolls off sharper down low than without the WG in just the aperiodic enclosure. There is literally no overall usable passband gain with the WG added. At the resonance, there is a narrow bump of 2 dB and outside of that it falls off like a cliff. I tried various enclosures with the WG and they make no usable difference
Oh well, iti was worth a try.
With a Qts of 1.7, this mid's low end is×w already on the loose side. I have run this driver successfully in an aperiodic damped 1.5 liter enclosire, which brings it down to a Qts of .7 but low end rolloff predictably takes a hit. Without a WG, it sounds great crossed over 900 hz @ LR2, resulting in an LR4 acoustic rolloff. It gels up top very well with the Seas T35-C002 crossed @ 2.5k LR2. Mechanical power handling really improves with an aperiodic enclosure and transforms this mid into something special. I've yet to hear a cone mid sound this open and detailed. Its inherit weakness is low end output capability, which is why I wanted to try a WG with it.
Now to the ugly part. With the WG, things go south. Qts ends up at 1.3, which isnt acceptable and just results in a sharp bump at 800 hz. This actually hurts low end extension and the dome rolls off sharper down low than without the WG in just the aperiodic enclosure. There is literally no overall usable passband gain with the WG added. At the resonance, there is a narrow bump of 2 dB and outside of that it falls off like a cliff. I tried various enclosures with the WG and they make no usable difference
Oh well, iti was worth a try.
Uhm, no. The dome is too soft to take the loading. That's also the problem on the upper end, the center of the dome stays more or less still or even moves in the opposite direction because of the lack of stiffness of the dome and flexing with one or two zero ranges. That also leads to very odd dispersion patterns which are seemingly not explainable (well, unless you take in account the partial movements and flexing). Used in their optimum range they can sound amazing though.
That's a quite common Q of a midrange dome driver. There are also quite a bunch tweeters which got a high Q. On the other end you've got the ferrofluid damped tweeters which got a quite flat impedance response but that changes when the FF got heated up and that's why FF driver speakers got so many mixed reviews if they are crossed over too close to the fs and the xo isn't designed to minimize the effect. Just don't use them close to the fs. There are a lot of dome tweeters which sound a ton better than their FF stricken twins. There are also several of non-FF tweeters with very low fs which work great on low XO frequencies.
Just use these drivers not too close to their fs and the SQ really pays off and the Q isn't any issue then anyways.
Well, that's perfectly normal for a big dome midrange driver. They need the high q but are not suggested to use them at the fs.
Uhm, not every driver is capable to work in a WG or a horn. The first thing you need is a diaphragm which is stable enough to take the extended air load. Soft domes like silk, supronyl (like the Heco dome mids and tweeter dome drivers) and others built like that simply cannot take the air load of a horn. There are (partly) exceptions, the Mivoc XGH/HGH 258 worked nicely up to a certain level but when it was exceeded they suddenly sounded odd or even harsh.
Adding a WG or horn to everything seems to be the fad now but while it can be a great improvement when used right, not all and everything is built for that. There are also horns and drivers which - individually - are practically perfect but are a huge disappointment when combined. Be it different driver exit/throat entrance angles, steps/edges or whatever, it's not THE solution for everything. Every driver is only as good as you use it appropriately.
Aside from that, I do not have the Vifa D76MX as stellar sounding in my memory. Maybe it sounds good if it's used with the right partners above and below, I don't know but I'm not sure if it's worth to elaborate on that in a WG if it is probably not a good idea to proceed that path anyway. You could post some measurements (FR and FR under angles, distortion, impedance) and maybe someone in the forum got some ideas.
Like I already said, do not use a tweeter or midrange at its fs! The Qts is only really of interest at drivers you use at their fs or below (full-range, mid-woofer, woofer, subwoofer). If the impedance peak is a problem when designing a passive xo, you still got the option for a suction circuit, parallel resistor, enclosure modificatons or driver modifications. If that's not enough, sometimes it's worth to go from passive to a DSP as it can be a real gamechanger. But you should verify first if the driver can deliver what you are expecting. If not, all effort on it is in vain and the time spent would probably be more useful on some other solution or project.
Hello Profiguy,
Your experiment is more or less what I had in mind. Thanks for sharing your findings: this spares me a lot of trouble.
Could you do some experimenting how far below 900 Hz you can go without losing the SQ you describe and seem to like? I would like to shoot for a 700Hz HP LR4 acoustic.
Your experiment is more or less what I had in mind. Thanks for sharing your findings: this spares me a lot of trouble.
Could you do some experimenting how far below 900 Hz you can go without losing the SQ you describe and seem to like? I would like to shoot for a 700Hz HP LR4 acoustic.
Hey ICG, thanks for the input and I understand what your saying.
I don't run this driver down low at resonance. It doesn't even have the xmax to support it and it would be useless there anyways. Its not on level playing field to something like an ATC 75-150 mid dome or even the Volt 753, but not far from it if used correctly.
I'm not adding the WG just for the hell of it because its "trendy". I wanted a little more low end extension to support a slightly lower HP (mainly limited by lack of xmax). The Qts matters even though the mid is running outside of that area. Lack of damping at resonance can be heard even if the driver is crossed over 2 octaves away with steep filter slope and it compromises distortion levels at higher SPL, which is important to me. An LCR notch doesn't always fix this.
The big Vifa dome is a very good mid and will beat almost any decent small cone mid driver in terms of resolution, naturalness and speed in its somewhat limited bandwidth (its main weakness). Again, its overall not on the same level as the ATC or Volt, but it comes close when playing above 900 hz or so up to 3.5 kHz with the right filtering. PMC uses this same mid in some of their reputable 3 way designs. They run it with steep active filters which obviously helps. I shy away from anything more than passive LR2 for many reasons, so I'm stuck trying make the best of it's strengths.
I don't fully agree that the dome stiffness is the reason it falls short in a WG. I'm not treating it as a compression driver but rather using the shallow WG to increase efficiency by reducing the low end radiating angle. The Qts of this dome is much higher than any other mid I've used and unlike some smaller 2" domes ie. Dynaudio D52, Morel MDT55 (which have much lower Qts), its still useless anywhere close to its Fs because of it's puny xmax. I've run other mid domes close to their Fs with an LCR notch in power limited applications successfully, but would never dream of doing that with small dome tweeters, even if others say it's OK to do so. That's however where a WG can help alot and in most cases has multiple benefits, ie. phase alignment, power response, dynamic capabilities, etc. I don't see it as a fad, as in most cases a WG can significantly improve a small mid or HF driver's performance in many ways and help integrate it better with other drivers as well as into the listening environment.
My findings with this 3" Vifa mid coupled to a WG are on par with the way most other lower BL/Mms drivers perform in a WG. The soft dome isn't the issue here. IMO Its mostly the lack of BL/Mms ratio somewhat high Q. I've successfully used WGs on my Dynaudio D52s. The Morel Cat378 is also a great soft dome with WG and has basically the same motor as the MDT30 - both are soft domes. My Audax TW034s also work amazingly well in a WG, but they have a massive motor asy compared to most soft domes (ie. high BL/Mms). Modifying them to lower their system Q helped extend the low end towards Fs, allowing a higher electrical HP for the same linearized low end rolloff when un-modded.
I don't run this driver down low at resonance. It doesn't even have the xmax to support it and it would be useless there anyways. Its not on level playing field to something like an ATC 75-150 mid dome or even the Volt 753, but not far from it if used correctly.
I'm not adding the WG just for the hell of it because its "trendy". I wanted a little more low end extension to support a slightly lower HP (mainly limited by lack of xmax). The Qts matters even though the mid is running outside of that area. Lack of damping at resonance can be heard even if the driver is crossed over 2 octaves away with steep filter slope and it compromises distortion levels at higher SPL, which is important to me. An LCR notch doesn't always fix this.
The big Vifa dome is a very good mid and will beat almost any decent small cone mid driver in terms of resolution, naturalness and speed in its somewhat limited bandwidth (its main weakness). Again, its overall not on the same level as the ATC or Volt, but it comes close when playing above 900 hz or so up to 3.5 kHz with the right filtering. PMC uses this same mid in some of their reputable 3 way designs. They run it with steep active filters which obviously helps. I shy away from anything more than passive LR2 for many reasons, so I'm stuck trying make the best of it's strengths.
I don't fully agree that the dome stiffness is the reason it falls short in a WG. I'm not treating it as a compression driver but rather using the shallow WG to increase efficiency by reducing the low end radiating angle. The Qts of this dome is much higher than any other mid I've used and unlike some smaller 2" domes ie. Dynaudio D52, Morel MDT55 (which have much lower Qts), its still useless anywhere close to its Fs because of it's puny xmax. I've run other mid domes close to their Fs with an LCR notch in power limited applications successfully, but would never dream of doing that with small dome tweeters, even if others say it's OK to do so. That's however where a WG can help alot and in most cases has multiple benefits, ie. phase alignment, power response, dynamic capabilities, etc. I don't see it as a fad, as in most cases a WG can significantly improve a small mid or HF driver's performance in many ways and help integrate it better with other drivers as well as into the listening environment.
My findings with this 3" Vifa mid coupled to a WG are on par with the way most other lower BL/Mms drivers perform in a WG. The soft dome isn't the issue here. IMO Its mostly the lack of BL/Mms ratio somewhat high Q. I've successfully used WGs on my Dynaudio D52s. The Morel Cat378 is also a great soft dome with WG and has basically the same motor as the MDT30 - both are soft domes. My Audax TW034s also work amazingly well in a WG, but they have a massive motor asy compared to most soft domes (ie. high BL/Mms). Modifying them to lower their system Q helped extend the low end towards Fs, allowing a higher electrical HP for the same linearized low end rolloff when un-modded.
Again, the issue is the low xmax and depending on how low you push the HP, it will run out of steam accordingly and odd order HD goes up quickly when playing it louder. If you limit the volume levels, it would sound nice at 700 hz LR4 acoustic. To get the most out of it, run it = > 900 LR4 and use an LCR notch regardless. The back chamber volume matters too. I don't recommend running it without a chamber or one larger than 3 liters, as it actually makes THD rise early down low (not sure why) - maybe a pressure equalization/airflow issue in the VC gap if you look at the double impedance peak hump on the factory spec sheet. Again, just my findings. The entire back of the dome isn't exposed and only ventilated by 7 small holes, so running it dipole isn't that smart IMO. Some people say it sounds OK that way, but I don't agree.
The FR linearity depends on a few things - chamber volume/dampening is the main thing, dictating low end response and rolloff. Don't go higher than 3 kHz LP. You'll end up with 90-92 dB @ 2.8V sensitivity overall. An aperiodic rear chamber or tapered TL absorber sounds best with this driver IMO and will help linearize phase response to integrate it better with the LF. An untreated low end without a chamber or absorption will really hurt the overall sound of this driver.
Hi, I have a question on this Vifa mid dome. Many years ago, Madisound used to sell this Seas rear chamber for it. Was the chamber only needed when sharing airspace with a woofer in a vented box, or can it be omitted if mounting the Vifa within its own sealed chamber?
It's only needed if sharing airspace with another driver or if the enclosure its mounted in is too small / shallow.
Thanks for that. In earlier posts you recommended running the D7608 900hz LR4, but also said you like to run LR2 as a rule. You also mentioned it should go no more than 2.5Khz, but then also mentioned 3.5Khz...what range did you settle on in the end?
I got one bad driver in a set of 4 (weak motor). In a horn, the bad driver had exactly the same FR plot, just lower sensitivity.
More info / FR plot:
Midrange (cone driver) horns; low relevance of magnet strength and Qts
...based on this apples-to-apples comparison, it seems to me like Qts is not predictive of how well a driver copes with (midrange) horn loading.
Sorry for the confusion.
I'm very close to 900 hz electrical LR2 with an aperiodic dampened rear chamber design. That rolls off the bottom much earlier and attenuates the overshoot designed into the driver, which controls the dome better at higher levels down low and reduces THD there as well. The dome is very limited in output capability down low and its the only way to keep it from running out of coil overhang when playing louder. Its not a driver that can be crossed at 2x Fs like other domes with larger Xmax, unless you can tolerate the resulting higher THD
It will depend on your acoustic rolloff in baffle as well as your rear chamber design what HP you can get away with. The high Qts will fatten up the low end and allow for a higher electrical xover to obtain a given low end rollof curve when equalized. It also means you have to stay further away from Fs with the HP. Again, i suggest an LCR notch and reduce Qts with appropriate dampening to get the most out of this mid. Most people don't bother doing this and end up disappointed with the results. This dome is hard to implement correctly to get the best out of it. When you do get it right, the rewards are big.
For a LP point, I dont go over 3.5 k but it really depends on the tweeter what slope you need to get phase tracking right. 2.5k is a guideline for best off axis behavior as it is afterall a 3' dome. For my needs and taste I like a 3k+ mid/high xover because it ends up drooping that range off axis a bit and follows the Fletcher Munson curve, making it sound more pleasant compared to other frequency ranges being attenuated through dispersion limitations. It may sound odd to some of you, but i prefer to lose this FR (if needed) off axis to make it sound more natural. Of course I try to avoid running into this, but its the least necessary evil IMO.
Thats interesting, however the difference between your drivers in output is negligible - about 1.5 dB. I'm just going off my personal findings with various drivers in WGs. The rear chamber will for sure mess things up around Fb and low end response in the WG, when the magnetic field strength is changed. A stronger field means better dampening and less overshoot (lower Qts) and better diaphragm control. The main thing that always seems to change with a chambered driver / WG combo along with less BL is bandwidth. If the driver isn't in a smaller rear chamber (ie driver rear exposed, it may not show any significant changes when playing in a WG.
I would imagine it would run out of BL at higher levels and at a minimum make top end response fall short of the other drivers. Electrical dampening at resonance will change with lack of magnet flux
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"Thats interesting, however the difference between your drivers in output is negligible - about 1.5 dB."
That's my point 🙂
I previously had the impression that a stronger magnet (lower Qts) = more HF response. My accidental experiment indicates that is not true.
"If the driver isn't in a smaller rear chamber (ie driver rear exposed, it may not show any significant changes when playing in a WG."
The ugly speaker stack next to me disagrees.
I mounted a nominally 95dB 6" driver onto a 2" horn (using an adapter plate). It plays 300-1,000Hz. It is open backed, and there is no crossover - the response is flat, and for the levels I'm playing, it doesn't need a high pass filter.
Above it is an old JBL 1" (2425J). The levels are matched. I don't need to pad down the JBL.
That is: the 6" driver is open backed, but still gets a "significant" boost from the horn.
That's my point 🙂
I previously had the impression that a stronger magnet (lower Qts) = more HF response. My accidental experiment indicates that is not true.
"If the driver isn't in a smaller rear chamber (ie driver rear exposed, it may not show any significant changes when playing in a WG."
The ugly speaker stack next to me disagrees.
I mounted a nominally 95dB 6" driver onto a 2" horn (using an adapter plate). It plays 300-1,000Hz. It is open backed, and there is no crossover - the response is flat, and for the levels I'm playing, it doesn't need a high pass filter.
Above it is an old JBL 1" (2425J). The levels are matched. I don't need to pad down the JBL.
That is: the 6" driver is open backed, but still gets a "significant" boost from the horn.