Does having a vented / open midrange driver enclosure (3 way design) have any advantages over sealed midrange. Sealed is the "obvious choice" because of GD, however I plan to have it passively crossed at 400 and 2,5k and the GD is in sealed enclosure territory within 400 hz when modeled in software. The speaker is going to be Wilson Sabrina sized and they have what looks like a port for the midrange at the top. So what's it for? Does it improve sound quality? Does it flatten the impedance curve? I suppose it's not used for the 3dB gain.
I generally prefer bass reflex for midrange with a tuning freq. at least 2 octaves below the high-pass crossover freq.. (with port facing back of speaker). GD should be about the same as a large volume Sealed cabinet well within the crossover freq. passband.)
It typically provides better subjective depth.
The Wilson design is a design characteristic from the original WATT - when it did NOT have the "Puppy" addition: it needed that extra extension and made use of the console it was set on for extension near the average.
I suspect that after trying it sealed that they came to prefer bass reflex design and a bit more "over-lap" between drivers in a real room. (..though they are still prone to in-room "suck-out" between 100-400 Hz.)
It typically provides better subjective depth.
The Wilson design is a design characteristic from the original WATT - when it did NOT have the "Puppy" addition: it needed that extra extension and made use of the console it was set on for extension near the average.
I suspect that after trying it sealed that they came to prefer bass reflex design and a bit more "over-lap" between drivers in a real room. (..though they are still prone to in-room "suck-out" between 100-400 Hz.)
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There was a trend to do with mid transmission lines and with the aim of dispensing with the rear radiation. In those cases the result resembled closed.
Some of the best midranges that I've heard are open-back types within their own sealed enclosure.
Of course, the enclosure is lined/stuffed with polyfil etc, to cancel out reflections / backwave.
I certainly don't want to hear anything from the rear of the cone.
Of course, the enclosure is lined/stuffed with polyfil etc, to cancel out reflections / backwave.
I certainly don't want to hear anything from the rear of the cone.
The Sabrina has an aperiodic vent for the midrange (a port with some damping material in it). I'm not sure what the motivation is to do this, but perhaps they can get away with a smaller enclosure than optimal, or it makes the impedance easier to deal with in the crossover, or the extra phase shift on the low end of the mid aligns the phase between the mid and the woofer.
Normally you don't want to vent the midrange as it results in unloading at low frequencies causing more excursion (and therefore distortion) from the mid. It also makes the mid rolloff steeper (12dB/oct vs 6dB/oct) on the low end which can be seen as a pro or a con - pro being that you get an extra order steeper rolloff for 'free' without needing additional crossover components, con being that you might need to add another order of rolloff to the woofer, therefore adding more crossover components and complexity.
Normally you don't want to vent the midrange as it results in unloading at low frequencies causing more excursion (and therefore distortion) from the mid. It also makes the mid rolloff steeper (12dB/oct vs 6dB/oct) on the low end which can be seen as a pro or a con - pro being that you get an extra order steeper rolloff for 'free' without needing additional crossover components, con being that you might need to add another order of rolloff to the woofer, therefore adding more crossover components and complexity.
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The new one is (X version)..
Wilson has provided foam plugs for ports and "room-tuning" on the older models.
What's interesting with the older model is the Impedance trace: it looks like a 2-way bass reflex excepting the lowered impedance. In fact, note the magnitude (about 53 Hz) for what appears to be the woofer's impedance: it seems much lower than it should be..
Wilson Audio Specialties Sabrina loudspeaker Measurements | Stereophile.com
Wilson has provided foam plugs for ports and "room-tuning" on the older models.
What's interesting with the older model is the Impedance trace: it looks like a 2-way bass reflex excepting the lowered impedance. In fact, note the magnitude (about 53 Hz) for what appears to be the woofer's impedance: it seems much lower than it should be..
Wilson Audio Specialties Sabrina loudspeaker Measurements | Stereophile.com
I tried glass fish bowel of 6L. It needed to be damped by elastomer and a piece of wood glued on the opening to fix the driver.
Just measure 0-180deg and you'll see what vent does.
I have open back midrange with some damping and it is bit wide power response wise.
I have open back midrange with some damping and it is bit wide power response wise.
Curt Campbell / Jim Holtz used an open back mid in their Statement series of speakers, the statement monitor version also has a switchable crossover for near/far wall placement. More info on their site.
Speaker Design Works
Speaker Design Works
I have my MA Pluvia 7PHD full range in a "bread container" This is a plastic container in the shape of a standard all American mass produced and pre-sliced white bread. The driver is mounted on one end; almost zero baffle face (one of my main reasons for doing this). I few inches behind the magnet; I have polyfill. At the opposite end; I block the opening with 4 inch thick dense foam. I call this my "non-box". It has virtually no parallel internal surfaces. I suppose one might call this Aperiodic but the rear foam is so thick; very little "sound" gets through. This has a very open and non-fatiguing honesty about it. I do have it crossed fairly high but only with 1st order. It is some of the best mid band I have ever owned and when you add in my Satori MR16; very hard to beat. FWIW...
I am glad I found this thread as it may answer (or not) a problem I have run into trying to amatuerishy design my own speakers from the Wilmslow Audio Allegros and a recent aquirement the Mission M71i.
ALLEGRO
My intenton was to use the mission as midrange and possibly its tweeters to go in the Large Adagio cabinets. These have a midrange sealed enclosure of approx 7.5 litres. Slightly smaller than the Missions .
Meanwhile I have been using the Mission alone and slightly tuning the bass / treble balance along with better pp capacitors and dueland resistors, When I upted the 2.2 r to 3.3 it was a much better balance and I l know I now should be revising the xover slightly...
I could also reuse the Morel mdt31 instead..
Just NOW I tried plugging the two ports on the missions to a devastating effect. ie flat dull under dynamic vaues lost imaging etc..
It occurs that this is what may happen when I actually insert the two 5.25 midranges into the cabinet....using the same port size and length as the Missions,
I Intend? to eventually add bottom end crossover for the Volt 2208s ie 2nd order to balance out the speakers to a fuller range. ie 120hz ish.
This means I have two large cubic areas behind my (currently unconnected for now ) Volt 2208 which would be only for 150hz and below..
The question is ? Can I just port my midrange enclosure into this void ?? It is easier by far for me...? Also Would this have an effect on the existing lower port performance?
I suspect I am not going to get good news...
Just trying to keep it simpler..
Dave
ALLEGRO
My intenton was to use the mission as midrange and possibly its tweeters to go in the Large Adagio cabinets. These have a midrange sealed enclosure of approx 7.5 litres. Slightly smaller than the Missions .
Meanwhile I have been using the Mission alone and slightly tuning the bass / treble balance along with better pp capacitors and dueland resistors, When I upted the 2.2 r to 3.3 it was a much better balance and I l know I now should be revising the xover slightly...
I could also reuse the Morel mdt31 instead..
Just NOW I tried plugging the two ports on the missions to a devastating effect. ie flat dull under dynamic vaues lost imaging etc..
It occurs that this is what may happen when I actually insert the two 5.25 midranges into the cabinet....using the same port size and length as the Missions,
I Intend? to eventually add bottom end crossover for the Volt 2208s ie 2nd order to balance out the speakers to a fuller range. ie 120hz ish.
This means I have two large cubic areas behind my (currently unconnected for now ) Volt 2208 which would be only for 150hz and below..
The question is ? Can I just port my midrange enclosure into this void ?? It is easier by far for me...? Also Would this have an effect on the existing lower port performance?
I suspect I am not going to get good news...
Just trying to keep it simpler..
Dave
The way i do it. Can be quarter or half wave. Stuff until as close to aperiodic as you can get.
This creates an environiment that greatly aids in ensuring little or no time-smeared stuff coming back thru the cone. And if you are going to attempt a passive XO the greatly reduced impedance peak makes the task of getting a passive XO to work much easier. The enclosure is open so the midTweteer cone is much more capable of moving freely.
dave
I have 3 systems with an open back midrange. While all 3 drivers could be used for bass, I have them high passed, at least to a degree, and am quite happy with the results. It really does remove the boxed in sound that can be so prevalent.
Drivers:
Foster 10F3
Misco 6.5" midbass
Altec 604-8H
Drivers:
Foster 10F3
Misco 6.5" midbass
Altec 604-8H
Thnking outside the box and also inside the box
Thnaks to Cal and Dave . Slight suspension of activity whilst recovering from the Jab,
So it now looks like I have more options and may even work out a plan.
I will try to post diagrams of Allegro assembly and xover pictures and its design ? I am curious about 5.6uf and series 2.7 resistor accross the midrange in adition to its second order filter...
Not seen that before...
A previous postings advice on this site seems a bit odd but I dont think he had heard or seen a Mission M71i.
I have since remembered that the so called sealed inner box is no longer sealed as I drilled a number of random holes in its real wall after I had removed the CAW538.
I now realize that my initial impression of the caw538/mdt31 was in a vented cabinet at Wilmslow audio.
Putting a caw538 inside the Allegro was the failing. I probably realize this was why I was disappointed with the initial mk1 Allegro.(lack of midrange life or clarity by comparrison. )
Cal, I always liked open baffle sounding speakers but this cabinet has two rear walls for the midrange..ie internally sealed mid box within the outer cabinet.
Its now even possible for me to transfer the input board mounted crossover into the Allegro input. (photo will make it clearer than my description.)
Then it can connect to some decent input speaker cable..
thanks for now more when I get a photosharing place...
Dave
Thnaks to Cal and Dave . Slight suspension of activity whilst recovering from the Jab,
So it now looks like I have more options and may even work out a plan.
I will try to post diagrams of Allegro assembly and xover pictures and its design ? I am curious about 5.6uf and series 2.7 resistor accross the midrange in adition to its second order filter...
Not seen that before...
A previous postings advice on this site seems a bit odd but I dont think he had heard or seen a Mission M71i.
I have since remembered that the so called sealed inner box is no longer sealed as I drilled a number of random holes in its real wall after I had removed the CAW538.
I now realize that my initial impression of the caw538/mdt31 was in a vented cabinet at Wilmslow audio.
Putting a caw538 inside the Allegro was the failing. I probably realize this was why I was disappointed with the initial mk1 Allegro.(lack of midrange life or clarity by comparrison. )
Cal, I always liked open baffle sounding speakers but this cabinet has two rear walls for the midrange..ie internally sealed mid box within the outer cabinet.
Its now even possible for me to transfer the input board mounted crossover into the Allegro input. (photo will make it clearer than my description.)
Then it can connect to some decent input speaker cable..
thanks for now more when I get a photosharing place...
Dave
IMG_3107.JPG - Google Drive
OK I am beginning to see I created a nightmare for myself.
Firstly The volume of my internal box is a lot smaller that I expected...Probably about 3.5 litres. I pressume this will be too small even prior to decide on porting BUT I am now considering the only simple way to resolve this is by cutting a hole (or two) and going rearwards to back wall of the speaker either to outside or just rear wall or one of each. this will bring free space to near 6 litres. Enough ???
Ok this sounds like desperate thinking ?
From DIY point this is may be easy enough for me...30mm tubes ? This will only resolve the problems partly? Perhaps I should got this far and have a listen?..
The second choice is to take a similair hole just into the top inner rear cabinet and use
foam to create a vented path behind the tweeter .
Again slightly easy to do as I have access through the tweeter cut out.
This gives me a cubic space almost triple the existing design less the foam volume
This may indeed be the first option ?
c. Now the next alternative is to go downwards with a pipe of 30mm length 500m? into the bowels of the speaker.
not liking this but again easy access through main speaker hole.
again helllllllllllllllllllllllllp
Dave
OK I am beginning to see I created a nightmare for myself.
Firstly The volume of my internal box is a lot smaller that I expected...Probably about 3.5 litres. I pressume this will be too small even prior to decide on porting BUT I am now considering the only simple way to resolve this is by cutting a hole (or two) and going rearwards to back wall of the speaker either to outside or just rear wall or one of each. this will bring free space to near 6 litres. Enough ???
Ok this sounds like desperate thinking ?
From DIY point this is may be easy enough for me...30mm tubes ? This will only resolve the problems partly? Perhaps I should got this far and have a listen?..
The second choice is to take a similair hole just into the top inner rear cabinet and use
foam to create a vented path behind the tweeter .
Again slightly easy to do as I have access through the tweeter cut out.
This gives me a cubic space almost triple the existing design less the foam volume
This may indeed be the first option ?
c. Now the next alternative is to go downwards with a pipe of 30mm length 500m? into the bowels of the speaker.
not liking this but again easy access through main speaker hole.
again helllllllllllllllllllllllllp
Dave
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If the Morel CAQW538, it is has a Q of less than 0.707 in a 3.5 litre box so that is certainlty a suitable volume for use as a mid, response (for the XO choice) is in th elow 90s so typically one would choose an XO a couple octaves higher, ie 350 Hz.
The shape of an enclosure that small can be an issue, best to use something like X’s dagger mid, misTweeter enclosure.
That little woofer looks nice in a 6 litre miniOnken, response to the low 40s.
dave
The shape of an enclosure that small can be an issue, best to use something like X’s dagger mid, misTweeter enclosure.
That little woofer looks nice in a 6 litre miniOnken, response to the low 40s.
dave
Based on published specs and adding 0.5 ohms for wiring, 3.5 L sealed = ~0.73 Qtc/~89.6 Hz Fc.
https://www.parts-express.com/pedocs/specs/297-082--morel-caw-538-spec-sheet.pdf
https://www.parts-express.com/pedocs/specs/297-082--morel-caw-538-spec-sheet.pdf
