Andy Graddon said:
The tweeter I have has a 90mm faceplate. It's a 3/4" silk dome (not metal like I thought). If I were to put this as high as possible on the back panel, there wouldn't be much of a cavity between it and the front. I could pack that with rockwool, and maximize the cut-out size for the mid.
What are your opinions on a rear tweeter Andy? And covering the hole with grill cloth shouldn't present a problem, you think?
never used a rear tweeter, never felt it was needed. ;-))
and yeah, grill cloth shouldn't be an issue
you may actually find you need a layer of poly wadding behind anyway, let your ears tell you. !!
and yeah, grill cloth shouldn't be an issue
you may actually find you need a layer of poly wadding behind anyway, let your ears tell you. !!
Andy Graddon said:
I didn't either, but it's something I've been meaning to do, just to try. Worse comes to worst I can disconnect it if I don't like the effect. I got these tweeters for $12.00 each, so no financial strain. The low cost doesn't indicate low quality - these are nice tweeters.
Right now, my ears are telling me the midrange is good, very good, but it could be better.
I'm slightly disappointed that the wedges idea didn't work as hoped but this is how we learn, right?
Sound is a complex beast.
MJL21193 said:
Where are you currently crossing the mid, John?
I agree with Andy that it should really be as much of the rear of mid chamber as possible. I suspect that will mean from the top of the cab to the area where the bass chamber separator is. I have very little dipole experience and what I do have centers around rough work borne out through wanting to try drivers without having to build a box. But what is critical is that you give the rear of the driver almost the same respect as you would front because its going to be much more audible than before you did this. Try not to block it in and create more problems than it solves. If possible you'd get even better results from opening the sides as well, which brings me to my original question - you'll might need to consider moving the high pass on the mid up a little higher if your looking high(?) SPL.
Its tough to whole heartedly recommend this because you've built such a sturdy and good looking cabinet, those don't pop up over night. So if, and heavens forbid, it doesn't work out your looking at some heavy duty work to fix and, to be honest its going to be difficult to come back from that and you might consider a rebuild to be easier. Don't let me put you off though, no seriously! We both know decent cabs take time and effort so I'm probably just speaking what your already thinking.
Back onto and ending on a positive note; I couldn't believe the some of the quality I've heard from the dipole necessitated box construction dodging. I was literally cutting a big bit of chipboard, fixing the drivers to it and then playing music. All very ad-hoc stuff with virtually no planning. I'd hate to think how a well sorted one would sound.
Might be worthwhile taking the vifa and SS from the cabs, knocking up an OB and placing it right next to the existing cabs with woofer mounted and playing around. Far from perfect but will give you a feel for the sound.
Shin,
look at the conceptualisation behind "Blackwood".
MTM OB mids. 3" deep u-frame allows mids to roll-off around 180-200. MTM gives the extra mid headroom, and nice symmetrical mid lobing for listening.
Mids need to cross to normal size tweeter around 2200+/-, can go a bit higher with smaller faceplate tweeter. Use 1st order to give a "oneness" through the MTM.
Bass driver needs to be a real bass driver, not a sub, because it needs to get up to naturally meet the mids at 200 or so.
With the right mid choice, you end up with a real full range speaker that can be done with minimal effort and x-o design.
You should try it some time, I'm sure you would be much more precise about your methodology that I would be 😀
look at the conceptualisation behind "Blackwood".
MTM OB mids. 3" deep u-frame allows mids to roll-off around 180-200. MTM gives the extra mid headroom, and nice symmetrical mid lobing for listening.
Mids need to cross to normal size tweeter around 2200+/-, can go a bit higher with smaller faceplate tweeter. Use 1st order to give a "oneness" through the MTM.
Bass driver needs to be a real bass driver, not a sub, because it needs to get up to naturally meet the mids at 200 or so.
With the right mid choice, you end up with a real full range speaker that can be done with minimal effort and x-o design.
You should try it some time, I'm sure you would be much more precise about your methodology that I would be 😀
ShinOBIWAN said:
Hi Ant,
The mid is crossed at ~310hz. As for efficiency, I still (at my current settings) have about 30% of the active amp power for the mids in reserve. I also have the option of cutting the bass and treble to meet the mid (I have some leeway there too).
To do a fair test, I should do as you suggest. I could do one better though and roughly re-create the top of the speaker with the back cut out and also put in the rear tweeter. This would be the smart, cautious thing to do...
I"m going to throw caution to the wind though and just do it! I have a good feeling about this (like I had for the conversion to ported) and I won't be satisfied until it's done - for better or worse.
In the end, I know I have the capacity to return it to original if I want to.
First, I will use my biggest holesaw (4") to make a hole and listen to that. If there is an improvement in sound quality - I press on, feeling smug about my superior judgment. 🙂
Wish me luck!
All right, even with the 4" hole there's a definite improvement - I'm encouraged!
I'll need to make a template for the recess on the cutout and the tweeter. I'll make the cutout as big as possible - from side to side, and from the shelf up to the rear tweeter. If the rear tweeter doesn't work for me, I'll extend the opening to the top of the cab.
I'll need to make a template for the recess on the cutout and the tweeter. I'll make the cutout as big as possible - from side to side, and from the shelf up to the rear tweeter. If the rear tweeter doesn't work for me, I'll extend the opening to the top of the cab.
Attachments
I figured if I will do this, I might as well move the divider between the woofer chamber and the mid/tweeter chamber. In the beginning, I put this divider in the wrong place - too close to the midrange. It had to be gouged out for the mids magnet to clear.
I removed all of the drivers, stuffing and the Styrofoam wedges, and made a series of holes in the shelf with 2 1/2" hole saw. This made it possible to break it up and completely remove it (see picture below).
I then cut 2 pieces of 1/2" MDF, making sure they would fit in the woofer hole. Wedged the first piece in, silicone the joints, silicone on the face. Put the next piece in and silicone the joints. This makes a panel 1" thick, well glued in.
I removed all of the drivers, stuffing and the Styrofoam wedges, and made a series of holes in the shelf with 2 1/2" hole saw. This made it possible to break it up and completely remove it (see picture below).
I then cut 2 pieces of 1/2" MDF, making sure they would fit in the woofer hole. Wedged the first piece in, silicone the joints, silicone on the face. Put the next piece in and silicone the joints. This makes a panel 1" thick, well glued in.
Attachments
With the new divider glued in, I had an idea of how big the cutout could be. Make some measurements and cut out a template from 1/2" MDF that will guide the router to cut the recess for the cut out. A little tricky to clamp on, what with the rounded face, but I managed.
Made the actual cutout with the jigsaw. Laid out the tweeter recess and cut that free hand. Used the 2 1/2" hole saw to cut out for the tweeters body.
Here's how it looks. The new shelf divider can be seen in it's better position. I took the time to put some stain in the recesses - makes things look more finished.
The speaker cloth grill will probably be held in with Velcro or magnets. I'll make the from from 3/16" hardboard.
Made the actual cutout with the jigsaw. Laid out the tweeter recess and cut that free hand. Used the 2 1/2" hole saw to cut out for the tweeters body.
Here's how it looks. The new shelf divider can be seen in it's better position. I took the time to put some stain in the recesses - makes things look more finished.
The speaker cloth grill will probably be held in with Velcro or magnets. I'll make the from from 3/16" hardboard.
Attachments
Andy Graddon said:
Thanks clarifying and clearing up a couple of the points I mentioned. I have very little experience with open baffle or dipole loudspeaker design so any pointers are always gratefully received.
You work fast John. I winced a bit when I first saw the changes but it sounds like you've done the right thing.
John,you are braver man than I to have the nerve to cut such a big hole in those handsome boxes. Hopefully it gives you the desired result.
MJL21193 said:
I like the Madrigal Revel Salons very well, they have a rear firing tweeter. I liked the much better than any of the B&W speakers I listened to around the same time.
http://www.avrev.com/equip/revelsalon/
http://www.stereophile.com/floorloudspeakers/96/index.html
I think the rear firing tweeter helps compensate (partially, anyway) for something that's missing when you're not using omni speakers.
ShinOBIWAN said:
I winced a bit while doing it! 🙂
F1 FAN said:
Hi F1,
You confuse bravery with short sightedness - I knew before I started these that I preferred open midrange. As usual I thought (incorrectly) there was a better way of dealing with it.
Nothing is sacred in the name of progress (and silly obsession). 😉
I have reinstalled the drivers and reconnected everything, including the rear tweeter. I put this in parallel with the front tweeter, thereby lowering the impedance. I'm trying to listen now to see if it needs padding down. It adds a "live" quality to the sound.
Listening so far it seems total success as far as the midrange goes. My initial reactions are usually more enthusiastic, so I'll give it a day or 2 to say for sure. Vocals sound more natural.
I packed the space at the top of the chamber with rockwool and added two pieces to the sides - this made a big difference. I tried polyfill first, but it seems that that is acoustically transparent. It made no difference at all.
Attachments
Do you find any discontinuity between the differing tweeters? I assume the rear tweeter is wired out of phase?
I've read about ambience and rear firing systems on here and the general consensus was to cross relatively high on the rear tweeter to provide more space and wider radiation to the usually narrowing directivity of the upper ranges but not so low as to impact imaging.
I've read about ambience and rear firing systems on here and the general consensus was to cross relatively high on the rear tweeter to provide more space and wider radiation to the usually narrowing directivity of the upper ranges but not so low as to impact imaging.
critofur said:
It's definitely adding something. I'm not 100% sure if I like the effect. More listening required after I do the other speaker.
Andy Graddon said:
Don't worry Andy, I never blame anyone else for my mistakes. Likewise, I never give credit when I use someones good advise.
😀
ShinOBIWAN said:
It's hard to say if there is a noticeable discontinuity between the two. I assumed with the tweeter facing back, wired out of phase, the differences in response between the Pioneer and the Scanspeak wouldn't be noticeable.
The Pioneer is 1db less sensitive, same size dome, about the same dome material and higher Fs but that's no matter at the xover point of 3100hz.
I really need to do the other speaker and then have a listen. This one sounds good on it's own, but playing with the other one, there's too much of a difference now.
More listening is needed.
4fun said:
I listened to this speaker (mono) all day yesterday while I butchered my main speaker. More impressions.
Listening at a reasonable low volume, it sounds fine, with clear detail in the midrange. Maybe a little "bright".
Listening at higher volume, the bass is fine, amazing actually - you'd swear this was a much bigger speaker. The treble is very clean, crisp...BUT,
The midrange is almost unbearable. I'm not sure if I'd call it strain like 4fun suggests, but I know it doesn't sound right to me.
Much too forward, shouty. Especially bad if you leave the room and listen from an adjacent room.
I will try to find time to set up the test mic again to get some measurements here. This might give me some clue as to the source of the problem.
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