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post #541 of 2588 Old 08-18-2003, 03:02 PM
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Scott -

Drawings are not my specialty. I may have to take you up on your offer. There are a few other issues I need to resolve first, however. Arum Cantus just issued the G2si, a lower cost, lower sensitivity version of the G2. I need to evaluate it (although I don't think I'd switch to a lower performance version).

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post #542 of 2588 Old 08-18-2003, 03:11 PM
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SnowDog -

Stiffness is not the only issue here. The additional thickness on the front baffle has a damping effect. The lower the frequency, the more mass is required to damp resonances.

On small cabinets (cabinets for 5" 2-way's for example), a single 3/4" front baffle may suffice. But on those speakers, I would use 1.5" front baffles. You might go with 3/4" and prove me wrong, but the way I look at it, MDF is cheap and, if it didn't work, fixing the problem later would be a real pain.

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post #543 of 2588 Old 08-18-2003, 03:23 PM
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Quote:


Originally posted by jsalk
Back on the router bit topic, not only would a router table be advisable for round-over bits in excess of 3/4", but a variable speed router would be a good idea as well. The greater the diameter, the faster the outer edges are moving.

jmiyake got away with using his monster bit without a table (perhaps he made several passes, but his comments about the amount of dust flying made me doubt it) but personally, I would never try it...too dangerous.

- Jim

Router bits of that size are even scary to use in a router table let alone in a hand held router.
And your are absolutely 100% right about about the speed issues when you use the larger bits.
I would not even want to think about using that 1 1/2" bit spinning at 22,000 rpm!

Variable speed routers are a MUST, as far as I'm concerned.
I myself have a Bosch 1613AEVS and 1450AEVS, both are plunge routers, and I like em both. Even though they were a bit more money than some other brands.
And I also have a older Craftsman variable speed router non-plunge, that is only used in my router table. It works great for that, I just did not see a need for a real fancy or feature laden router for use in a router table setup.

At one time, about 6 or 7 years ago. I almost bought a dedicated shaper. But I liked the selection of router bits over what you could get in shaper bits. And went with the router table instead.
But if I was in the position of where I was making stuff as a business, I think I would get a shaper.
Just for the fact they are more "heavy duty" and made specifically for that task.
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post #544 of 2588 Old 08-18-2003, 03:28 PM
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Snowdog12,

If you want all four edges rounded, I would do as others have suggested, glue solid blocks of hardwood on each of the four edges of your front baffle, then when rounding over, they would show, not raw MDF.

Neither Jeff or Myself rounded all four edges.

The front panel thickness was originally specified as one inch on the Audax plans. I went with 1 1/2 since it was easy to glue two 3/4 inch pieces of MDF together. If I had easy access to 1 inch MDF, I probably would have used it. You will have to make the call.

In the grand scheme of things, it probably will not be that audible, especially if you use the dampening materials I linked to. (I did not, but others swear by their use, and they are easy to add, even after construction is complete. And no, I did not notice that one of the materials was over an inch thick on its own McMaster Carr has some reasonably priced alternatives to the Black-Hole marketed to the audiophile types.)

But, I agree with jsalk, at this point in time, to glue on a second layer of MDF and then trim it even with a flush trimming bit is easy. You know you want the speakers to sound as good as possible. Of course, if you already rounded over the edges, then you might want to go with one of the internal dampening sheets.

Matt,

If you can't bend your veneer over a 1/2 inch radius before gluing it to your cabinet, (with the grain, of course) then there is no way it will bend while gluing.

Our veneer was very thin and very flexible, and paper backed. If yours is not as flexible, then a larger radius is in order.

Of course, attempting to bend the veneer across the grain, as you would have to do if you rounded all four edges of the front baffle, is much more difficult... I would guess near impossible on even a 1 inch radius.

Oh yes... welcome to the world of time management... It took me over 9 months to complete my set. Family life comes first, making sawdust is much lower on the list. Watching a few movies in the partially completed theater with the partially completed HT speakers is somewhere in the middle.

Joe L.
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post #545 of 2588 Old 08-18-2003, 03:41 PM
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Two quick notes:

1) If you apply the hardwood and veneer over it, when you do the round-over it will look more like the entire piece is solid wood. You will avoid having a tell-tale break between the veneer and the solid wood.

2) Unless you really like frustration, I would avoid trying to apply veneer to a baffle that is rounded over on all four edges. This is serious, experienced veneer pro territory. I would not even attempt it.

If you want to round over on all four sides, use a solid wood front baffle (and you may not want to use hard glue to adhere it - the wood will expand and contract with humidity at a much greater rate than the MDF and will be prone to crack).

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post #546 of 2588 Old 08-18-2003, 03:46 PM
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Thanks all for your speedy feedback! I should have been more specific on my rounding over question. Its not a matter of asthetics to me, as I'm just using the black analine dye that JL used, and these speakers will most likely be enclosed in a wall enclosure that I'm going to build to surround my screen. Plus my MDF material is preclad in veneer, so when I roundover anything it exposes the MDF on it anyways. In other words, it ain't gonna be pretty unless I used "real" veneer like a lot of you guys, but I don't really plan on it. My question was more of an accoustical one I suppose, as in, is it ok to roundover all four sides. I suppose since no one mentioned that that it probably isn't an issue.

On the front baffle thickness issue - JSalk - I'm not sure that I really understand the term "damping" as you're using it, but since the original plans call for 1" and I'm using 3/4", we're only talking about 1/4" of difference, and I've altered the measurements to make sure the internal cabinet volume is the same (i.e. added 1/4" to it). Is that not the same thing?

- John
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post #547 of 2588 Old 08-18-2003, 04:36 PM
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Quote:


Originally posted by SnowDog12

On the front baffle thickness issue - JSalk - I'm not sure that I really understand the term "damping" as you're using it, but since the original plans call for 1" and I'm using 3/4", we're only talking about 1/4" of difference, and I've altered the measurements to make sure the internal cabinet volume is the same (i.e. added 1/4" to it). Is that not the same thing?

I may be wrong, but I 'think" a few of the main reasons you want a baffle that is thicker then the rest of the enclosure, is because the drivers themselves vibrate, as that is what makes them do what they do.
But you want to try and isolate the good vibrations of the the drivers (the sounds you want to hear) from the bad vibrations of where the drivers may interact with each other or the cabinet itself, due to the baffle vibrating or resonating in the wrong ways (the sounds you don't want to hear). And that a thicker front baffle "driver mount" over the rest of the cabinet, is needed to do that.
Plus I also "think" a front baffle being thicker than the rest of the "box" will help it all from resonating at one set point, somewhat in the same way that a brace helps in that regard. As it breaks it up from just being all the same thickness, that might tend to resonate at one certain frequency.

I may be wrong, but I "think" those are some of the main reasons why you want to go thicker with the front baffle, over what the rest of the cabinet is.
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post #548 of 2588 Old 08-18-2003, 04:50 PM
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Quote:


Originally posted by SnowDog12
Thanks all for your speedy feedback! I should have been more specific on my rounding over question. Its not a matter of asthetics to me, as I'm just using the black analine dye that JL used, and these speakers will most likely be enclosed in a wall enclosure that I'm going to build to surround my screen. Plus my MDF material is preclad in veneer, so when I roundover anything it exposes the MDF on it anyways. In other words, it ain't gonna be pretty unless I used "real" veneer like a lot of you guys, but I don't really plan on it. My question was more of an accoustical one I suppose, as in, is it ok to roundover all four sides. I suppose since no one mentioned that that it probably isn't an issue.

For that, I'd look into buying some real wood 1/4 round, that matches the veneer as close as possible to the 3/4" pre-veneered MDF you are going to use. And then use the real wood 1/4 round on the edges, instead of routing them over with a router.
That way you would not have any problems with seeing any of the MDF core of the pre-veneered MDF you are going to use.
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post #549 of 2588 Old 08-18-2003, 05:43 PM
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SnowDog -

Rounding over corners reduces baffle diffraction. Doing so on four edges may not necessarily be critical, but it is optimum. Go for it!

I guess I would describe "damping" as "soaking up" resonances created by the divers. Ideally you would like to avoid having any driver-induced resonances transfered to the cabinet. If they cause vibrations in the cabinet, the cabinet becomes an active component in the speaker.

Higher frequencies can be damped with insulation, foam, poly or other materials. They basically convert high frequency energy is into heat. But as the frequencies decrease, these materials become less effective. At lower frequencies, it takes mass to do the job. Since two layers of 3/4" MDF provide more mass than a single sheet, they are able to absorb more of this unwanted energy than a single sheet.

Again, MDF is cheap.

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post #550 of 2588 Old 08-19-2003, 04:19 AM
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Showdog12, if you go down from 1" to 3/4" you will want some extra dampening of the front baffle. Those midbass drivers are going to have some extra coloration if you don't.

Options include 1/4" solid wood (not necessarily for your project), 1/4" MDF, or other laminate on the front, or asphalt shingles, BlackHole #5, or other dampeners on the back. Nothing beats mass, though, so 1/4" more to the baffle would be my first choice.

By the way, if you went to a 1 1/2" baffle you could also get some rear loaded horn effects bouncing back through the cone unless the rear of the driver hole was rebated to open up the rear of the driver. Even on 3/4" you will have problems with some drivers, depending on how their basket is designed.
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post #551 of 2588 Old 08-19-2003, 10:58 AM
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Mass wise, I've heard of lead sheets (consider health risks first) being stapled into the enclosure, and damping wise I've heard of bitumen sheets being used.

Both these have high effects for their relative size, so don't affect the internal dimensions.

Matt
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post #552 of 2588 Old 08-19-2003, 11:28 AM
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Here is a link to Parts Express page with sound deadening sheets that come in various sizes, are easy to cut and are self-adhesive:

Sound deadening material

- Jim

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post #553 of 2588 Old 08-19-2003, 12:06 PM
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I'm sort of leaning towards the dampening stuff. I think I (somewhat) better understand damping now So, perhaps last question on this issue - does it have to be absolutely form fitting from edge to edge with cutouts around driver openings, or can it be applied with more loosely fitting pieces?

- John
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post #554 of 2588 Old 08-19-2003, 12:09 PM
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Sorry, add on to previous question - does it have to be applied to all surfaces, just the front baffle, or any internal surface? And can the accoustic foam be glued over the top of it?

- John
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post #555 of 2588 Old 08-19-2003, 12:37 PM
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As I think is stated in the product description, this material was designed to convert resonant energy into heat.

I usually apply it to all surfaces. It is easy to cut.

So, for the rear of baffles, for example, I apply it to the inside surface and then use a matt knife to remove material from the driver holes (which I previously rounded over).

I also apply it to the entire inside of the cabinet. I apply panels to all surfaces and simply cut the final panels a little larger to overlap the earlier ones. The adhesive bonds well and the material is fairly flexible so you can mold it into corners, etc. I then glue acoustic foam over it.

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post #556 of 2588 Old 08-19-2003, 09:06 PM
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Quote:


Originally posted by Teran
Showdog12, if you go down from 1" to 3/4" you will want some extra dampening of the front baffle. Those midbass drivers are going to have some extra coloration if you don't.
[snip]
By the way, if you went to a 1 1/2" baffle you could also get some rear loaded horn effects bouncing back through the cone unless the rear of the driver hole was rebated to open up the rear of the driver. Even on 3/4" you will have problems with some drivers, depending on how their basket is designed.

I went with a 1 1/2" front baffle on my speaker, so would using my roundover bit on the back of the driver hole help with the effects mentioned above?

Also,
I've been holding off on rounding the edges of my Audax Center until I could find a 3/4" roundover bit... now that I see that some of you guys have used 1/2" and 3/8" roundover bits I think I'll go ahead and use the 3/8" bit that I already have.
Would there be enough of a difference to justify spending ~$45 on a 3/4" bit? or should I save my $$ for the next speakers I make (front left/right)?

Thanks!
-aaron
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post #557 of 2588 Old 08-19-2003, 09:27 PM
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aaron -

Yes, by all means use a roundover on the inside if the front baffle.

As for the cabinet edges, the greater the roundover, the better the performance (diffraction is minimized). If you are going to be buiding speakers in the future, go ahead and get the 3/4" bit now. A smaller roundover is better than no roundover. But, IMO, it is worth the $ to improve performance. The difference is clearly measureable.

Here is a URL with graphs that show what a 3/4" roundover can do:
http://murphyblaster.com/content.php?f=cabinets.html

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post #558 of 2588 Old 08-20-2003, 05:22 AM
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Quote:


Originally posted by jsalk
aaron -

Yes, by all means use a roundover on the inside if the front baffle.

As for the cabinet edges, the greater the roundover, the better the performance (diffraction is minimized). If you are going to be buiding speakers in the future, go ahead and get the 3/4" bit now. A smaller roundover is better than no roundover. But, IMO, it is worth the $ to improve performance. The difference is clearly measureable.

Here is a URL with graphs that show what a 3/4" roundover can do:
http://murphyblaster.com/content.php?f=cabinets.html

- Jim

Why are there large differences below 100?

SM
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post #559 of 2588 Old 08-20-2003, 06:00 AM
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SM -

Ignore everything under 200Hz. You are seeing the impact of room modes at these frequencies.

I hope this answers your question.

- Jim

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post #560 of 2588 Old 08-20-2003, 06:26 AM
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Just to shed a little light on baffle diffraction and roundover size, Linkwitz has this to say:

Quote:


The benefits of edge rounding come into play only when the radius is greater than 1/8th wavelength. Thus a typical 1/2 inch radius begins to diffuse the diffracted wave at frequencies above 3.4 kHz, but will decrease in relevance at higher frequencies, when the driver illuminates less of the edge due to its increasing directivity. With most speaker cabinets the radius or chamfer is acoustically too small and is primarily cosmetic.

See additional comments here: Linkwitz Lab

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post #561 of 2588 Old 08-20-2003, 04:00 PM
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You're talking about the outer edges of the cabinet, right? I thought the only thing that rounding those edges did was make the cabinet more attractive and make it easier to wrap it with veneer. I can't imagine that my rounded edges improve the sound of the whole system. If that's the case shoudn't we round all the corners on every object in our rooms (joking). Maybe, you're talking about rounding the edges of the holes in the baffle? Even the Linkwitz article...what little I read before I got bored said there was no scientific study to support this.

I'm obviously no expert in this area, I just enjoyed building the kit. I rounded my edges because others were doing it and it looked good.


OK, I re-read the posts and figured out that you are talking about the inner baffle and not the edges of the cabinet. My attention span is fading with age.
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post #562 of 2588 Old 08-20-2003, 04:11 PM
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Quote:


Originally posted by jsalk
SM -

Ignore everything under 200Hz. You are seeing the impact of room modes at these frequencies.

I hope this answers your question.

- Jim

Ok. But if the room is different how do you know that the differences you attribute to the baffle are not caused by the room?
-sorry for such a beginners question-
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post #563 of 2588 Old 08-20-2003, 04:15 PM
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Jeff,

Rounding the edges of the cabinet looks good, and makes it sound better... A bigger radius is better (as James did on his line array) but even the smaller radius can't hurt.

Can't get much better than that.

Joe L.

Oh yes... You should only wear dark, sound (and light) absorbing clothing when watching a movie... in a room with no sharp objects... you should know that...
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post #564 of 2588 Old 08-20-2003, 07:00 PM
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Jeff and Swampfox -

A few comments:

1) We are talking about rounding the edges of the cabinets in order to minimize the effects of baffle diffraction at those edges.

2) According to studies by Linkwitz, round-overs need to be at least 1/2" in diameter to have any meaningful effect. Anything smaller is purely cosmetic. 3/4" or greater diameter round-overs will minimize effects to a greater extent.

3) How audible baffle diffraction effects are is subject to some debate (this is what the Linkwitz comment referred to). But they do produce anomolies (abnormal spikes) in the frequency response of the speaker.

4) The difference is clearly measurable (as shown by Murphy and Linkwitz). Thus, it is correct to say that baffle diffraction problems can be minimized as long as the round-over is of sufficient diameter. A 3/8" round-over will have little or no effect, 1/2" some effect and 3/4" or more, a greater effect.

5) There is little effect, if any, below about 1000Hz where the sound becomes omni-directional.

6) Measurements of speaker response under 200Hz (which are not not affected by round-overs) cannot noramlly be made in most listening environments without also recording room modes. They must be taken outside in open space or in an anechoic chamber.

7) Many people think round-overs look nice too.

In short, with a narrow front baffle, cabinet edges that are not rounded over or are rounded over less than 1/2" will produce baffle diffraction artifacts that affect the frequency response of the speaker. This effect can be measured. To minimize the effect to the extent possible, a 3/4" or greater round-over should be used on cabinet edges.

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post #565 of 2588 Old 08-20-2003, 07:16 PM
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One added thought that may help clear things up:

You often see tweeters mounted off-center in the baffle. This, too, is done to minimize baffle diffraction. When a speaker is designed, the designer takes baffle width, driver mounting locations, round-overs and other aspects into consideration to produce the flattest frequency response possible.

This is part of the design process. The crossover is developed once all of these issues are resolved.

If you depart from the design and change any of the above, the crossover will no longer be optimized for the design. The effects may or may not be audible, but they will be measurable and are not desirable.

If you would like to see just how these variables effect frequency response, Paul Verdone has created a simulator which allows you to play with the variables and see the actual effects on the speaker's frequency response in a given design even before it is built.

You can see and download his program here: http://www.pvconsultants.com/audio/d...ownloadbds.htm

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post #566 of 2588 Old 08-24-2003, 07:45 AM
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With Jim (and possibly others) around, who has build (and heard) the Criterion The opportunity for a few questions is too good to pass up. I'm looking around for a DYI design that gives me excellent music playback and works for HT use as well. The speakers need to be bookshelf size, and I plan to build a sub-woofer to take care of the low end.

The criterion seems to fit the bill for the left-right channels, and the price is right for my budget. While I'm pretty sure they'll sound great for music I have my doubts about HT use. Jim stated that the ARG2 does well in horizontal off-axis response, however, when I look at the plots provided by GR-Research the off-axis response if pretty poor. Consider the situation of someone sitting on the left side of the room vs. the right-hand speaker, 40-45 degrees is not unusual. According to the plot the high-end drops off like a stone at those angles. Now, I think I understand (somewhat) how a ribbon tweeter works and have a hard time understanding why it drops off like that. It's too high to be mid-woofer vs. tweeter interaction, so that can't be it. I'd have thought that a ribbon tweeter would disperse sound much better, working as a line-source.

If I were to build the Criterion I'd like to combine them with A/V1s for the center channel and the two back channels. Would this work from the perspective of "blending in" of the the center with the left-right? Or are these too different?

Any thoughts on this would be greatly appreciated!

-Rob-

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post #567 of 2588 Old 08-24-2003, 09:29 AM
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Rob -

I did notice off-axis response on the Criterion's drops off a little more than I expected. The funny thing is, I use the same tweeter in my Veracity design and they have an extremely wide dispersion pattern and very good off-axis response (the best of any speaker I have ever done). The G2 ribbon was actually designed to provide good off-axis response. So I assume the difference is due to the crossover.

But unless you have a very wide room, it may not be a problem.

That said, unless you went with the Criterion's all around, I would not use them. IMO, they would not match up very well with AV1's.

If you used AV1's for the center and rears, I would use AV1's all around (and have for a number of very happy customers). If I were not to use the AV1's all around, I would use an AV1+ MTM design (it may be called the AV2 now) as a center channel. At least the drivers would match.

Now, if you were concerned about music quality and still require the bookshelf format, you might consider the MBOW1 design by Dennis Murphy (http://www.murphyblaster.com). It uses essentially the same cabinet (Dennis's is a half-inch taller and deeper).

This design uses the same mid-woofer (order them from the same source as the AV1's themselves - Danny Richie at GR Research), but uses the exceptional Hiquphon OW1 tweeter, which many consider to be the best dome tweeter in the world. It also utilizes a smooth 2nd-order crossover that is among the best Dennis has ever done (and he is one of the best).

(By the way, Dennis Murphy designed the original SPCA 2-way that served as the basis for GR Research's AV1. So he has more experience with this 2-way design and variants than anyone in the world.)

The result is a more refined version of essentially the same speaker for about $100 more per pair (for the OW1's) - still far less than the Criterion's. The AV1's are good in their own right, but the Hiquphon OW1's put the MBOW1's over the top.

Five of these would make a spectacular home theater system and a great music system as well.

As a matter of fact, I am currently building two pairs of MBOW1's - one for my father and one for a major Detroit sports team. I also have cabinets cut and ready to glue up for four additional pairs. So that should tell you what I think of the MBOW1 design.

I hope this answers your questions. If not, please post again.

- Jim

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post #568 of 2588 Old 08-25-2003, 05:16 AM
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Thank you much Jim!
The MBOW1 was/is on my short list as well. Not many people out there that have had a chance to compare all of these... Good to hear you think highly of them. I noted the 'stuffing' note (or rather, not to stuff the box). Do you use BlackHole on the insides?

Before dropping this: At 10KHz the crossover of the Criterion is well above the crossover frequency. So, the mid/woofer shouldn't be playing a role any more and all that's emitting at that frequency (and above) is the G2. Wave length is around 3 cm., so even the small baffle is large compared to the wavelength. In other words, I would expect the G2 in the Criterion to have the same radiation pattern as a G2 in any other design. Just trying to understand why there's a difference.

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post #569 of 2588 Old 08-25-2003, 06:46 AM
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Rob -

In terms of BlackHole, it depends on who I'm making the speaker for and whether or not they want to spend the extra money. I have used it on a few pairs in the past, but mostly use convoluted foam together with acoustic dampening material. The result is quite similar to BlackHole.

BlackHole adds about $50 to the cost of a pair of MBOW1's or AV1's. The sound seems somewhat "tighter" with BlackHole when using it with an un-braced cabinet. It is most evident when listening to a solo piano, but is quite subtle.

As for the G2, I haven't done an analysis. Your question made me recall impressions I had when I had just completed building the design. I never saw Danny's measurements and don't know how they were made. In fact, at the time, he hadn't even posted the design on his web site yet.

I was placing a parts order for some AV1's when Danny told me about this new speaker he was working on (Criterion). I told him to send me a kit as soon as he finished the design.

I fell in love with the G2 immediately, but wondered how much better it would be coupled with a 7" Seas Excel W18, rather than the 5" Eton driver in the Criterion.

In the process, I used Paul Verdone's BDS (baffle diffraction simulator) to model numerous baffle designs. I settled on a tapered design that spread the diffraction over a wider range of frequencies. This allowed for better response in a narrow front baffle and allowed me to center the driver.

I am speculating here, but the difference in off-axis response could be related to the baffle design differences. The Criterion centers the driver on a narrow baffle without regard to baffle diffraction effects. But I have never modeled that particular baffle or run measurements on it, so I don't know if that is the answer.

The Criterion series crossover may also play a role. But this is purely speculation. I would have to research it further to see if this could contribute to the difference.

All I know is that I have no off-axis issues with the G2 in my design. To the contrary, off-axis response is about as good as it gets. So, to the extent that there is an issue with Criterion off-axis response (and I don't know if it is really significant), I doubt the G2 is responsible. Beyond that, I can't say for sure, but your question has me intrigued enough to do a little more research...

- Jim

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post #570 of 2588 Old 08-28-2003, 02:13 AM
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Guys, I found a place for some very affordable 3/4" and larger , carbide round-over router bits.
And all of them are priced at well under the $40 plus, that they are at most places.
A 3/4" is $20, a 7/8" is $26, a 1" is $28, and they even have larger bits up to 1 1/4" as well, and all for under $40.
But if you don't have or use a router table, I don't think that going larger then the 3/4" is prudent thing to do with a hand held router.
The 7/8" is a "iffy" that I myself maybe would try it, to see how it felt. But I would not recommend that others do the same.
And if ends up, that it was something I did not feel comfortable with, then I would just use it in my router table.

They say that the bits have a lifetime warranty, but I don't see how something like a router bit or a drill bit could.
Although hitting something is NOT covered, nor should it be!
So take that for what it's worth....

Anyway the place is www.woodbits.com and the round-over bits are on page 6, 26, and 32 of their on-line catalog.

Page 6 is the ones we want, as all the separate router round-over bits are on that page.
Page 26 is the shaper round-over bits, the ones we don't want.
And page 32 is a 6 piece "set" of round-over bits. Of 1/8", 3/16", 1/4", 5/16", 3/8" and 1/2" for $49, which is a good price, but the sizes are a tad small for what we want them for.
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