Importance of flush mounting drivers

[RyanC]

Hello,

I am finishing up my cabs and I was wondering about this- I was thinking about trying to flush mount my drivers in a sheet of foam- so that the foam would be flush with the 12" woofer and the 8" and tweeter would be slightly recessed-

I know that I have read that it is important to flush mount the drivers but I was wondering why? I am trying to see if I can do somthing else becuase the audax aerogel 8" would be very difficult to create a router template for-

I guess what I am really wanting to know is if there are some tricks that might be effective that would not necessarily require me to router the baffle- Fabric or foam? Is it more important (flush mounting) on tweeters and midbass- then on sub woofers?

My speakers are a 3 way with a fountek jp2 an audax 8" aerogel and a Tc2+ 12" woofer- Thanks again,

Ryan

 

[leadbelly]

I am trying to see if I can do somthing else becuase the audax aerogel 8" would be very difficult to create a router template for-

I guess what I am really wanting to know is if there are some tricks that might be effective that would not necessarily require me to router the baffle- Fabric or foam? Is it more important (flush mounting) on tweeters and midbass- then on sub woofers?

I can't be sure, but by the way you are describing the problem, it sounds like you are assuming that the flange recess must be routered AFTER the hole is cut. It does not have to be done this way, and if you router the recess first, it can be done with a simple circle cutting jig.

EDIT: I just realized you are probably talking about a non-round flange.
In that case you can avoid making a full jig by just clamping a straightedge and moving it around the cutout, but it takes patience.

 

[zobsky]

you could use leather or some such compressable covering on the front baffle, such that the driver can be impressed into the covering, ... a pseudo flush mounting

 

[RyanC]

The audax woofer is a square chassis with rounded edges- not impossible but not easy either- Here is a link-

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=296-084

thanks again,

Ryan

 

[RyanC]

So what are the negatives of not flush mounting at all? just trying to understand- thanks,

Ryan

 

[RyanC]

Ok so I think I get it- The frequencies that radiate omnidirectionally or at least beyond 180 degrees will not leave the baffle or edge of a speaker until it reaches the edge of its piece- So these are going to be the lower frequencies of a woofer (before it gets beamy) and any frequencies of a tweeter?

I have a ribbon tweeter so flush mounting would be more important on the sides than the top and bottum (not that you could actually do it that way but)??

Why is it better for the sound to reach the edge of your baffle then to project from the edge of the speaker??-

I am still going back to my first thought which was to cut a 1" thick piece of foam to flush mount and even recess mount the drivers- Then I can cover the whole peice of foam with fabric that goes into the speaker cutouts. What do you guys think about that? would it be better even then flush mounted into wood as it is sound absorbtive matierial (although not really at lower frequencies) Or will I only be minimizing the problem slightly? thanks again,

Ryan

 

[HeatMiser]

I am still going back to my first thought which was to cut a 1" thick piece of foam to flush mount and even recess mount the drivers- Then I can cover the whole peice of foam with fabric that goes into the speaker cutouts. What do you guys think about that? would it be better even then flush mounted into wood as it is sound absorbtive matierial (although not really at lower frequencies) Or will I only be minimizing the problem slightly? thanks again,

Ryan

That seems like a sound idea to me, kind of an over-engineered version of the felt or foam strips often used alongside tweeters, or the AIG Imagers (absorbtive foam circles for surrounding drivers).

Bear in mind I have no direct experience, but it seems to make sense.

 

[Vikash]

The audax woofer is a square chassis with rounded edges- not impossible but not easy either

I've attempted this by making a template for the router to follow. It worked ok, but you need patience and/or experience with router woodworking - well relative to me at least: http://www.vikash.info/audio/mtm_floorstander/build_day03.asp I would absolutely cut the recess first if I were to do it again. But next time I'll just avoid non-circular drivers

Ok so I think I get it- The frequencies that radiate omnidirectionally or at least beyond 180 degrees will not leave the baffle or edge of a speaker until it reaches the edge of its piece- So these are going to be the lower frequencies of a woofer (before it gets beamy) and any frequencies of a tweeter?

Why is it better for the sound to reach the edge of your baffle then to project from the edge of the speaker??

Well I'll have a stab at giving you an answer...
Flush mounting will reduce edge diffraction which occurs when the wave reaches sharp edges. This is more important in mid and higher frequency drivers and usually you don't need it except for looks in (large) bass drivers (ie. subwoofers). But edge diffraction will also occur when the wave reaches the end of the baffle, hence a reason for beveling the baffle edge. The width of the baffle determines the baffle step and the curvature of the edges determine to a degree how smooth the transition between radiating in half to full space is.

This is a particularly good animation to illustrate diffraction: http://www.silcom.com/~aludwig/images/difdemo.gif

 

[tiroth]

Vikash,

Excellant info! I am very new to router usage; can I ask, how did you "follow" a template that is above the work piece? All of my pilot bits have the bearing on the bottom (w.r.t. the work). Is there a kind of bit with the bearing on top?

I too have to mount some of these in the near future.

RyanC,

Can I ask, what is your mid and what are your xo points? I am very slowly working on a similar project, AC G2 and PR170M0. I am very tempted by the TC2+ but didn't want to have to run it up too high. (and box is too big with both midwoof + TC2+!
)

 

[BobEllis]

Is there a kind of bit with the bearing on top?

they are called pattern bits, available from a variety of sources. You can also use template gudes and a straight bit - in this case your template needs to be larger than the cutout. Grizzly, woodcraft and others sell them on the web. be sure to get the short ones or your templates will need to be very thick when cutting the recess.

Somewhere on the web (includung somewhere in the forum here)there is a guide to making your own templates using a 1/4" straight bit and a 3/4" - somebody who cloned JM labs stuff shows how he made a template for a Focal TLR tweeter. I used the process and ended up with a fairly good fit after a couple of tries for my T120s. Use a router with very low runout and a perfectly centered base or you'll end up with a sloppy fit. (says he knowingly) I've been able to get almost as good a fit using a straightedge and freehanding the curved parts.

 

[RyanC]

Vakish-

My XO points arn't exactly determinded yet- I have the behringer DCX a bryston 4b st for the tc2+'s and 2 EV 7100's for the audax's and the Founteks (obviosly turned way down or attenuated for the tweeters)- So it is an all active setup.

I have the behring ECM8000 test mic too so I am planning to measure the speakers in my room and tune them accordingly-

I think It will be roughly like this-

Single capacitor for 6dB oct filter on the tweeter up high like 8k or so- then I can activly boost 4k or so and achieve a slightly sharper curve as it meets the roll off of the audax- I will probably let the audax rolloff naturally at first and then put a filter up higher-
I will also include a 12 or 18dB/oct HP at maybe 1.5k just to make sure I don't damage them-

Then figure out the best way to mate the two wofers- I think the key is testing all the drivers seperatly in the inclosure this way can also hear what certain tones and pink noises sound like on each different speaker-

I'm guessing the best will either be way low like 50hz with a steep slope to avoid mid range compression at higher Spl's or softer slope like 12dB up a bit higher- I have to say that when I was breaking in the tc2+ with no baffle (just sitting on a couch) I was impressed by how good they sounded higher up (for a sub woofer at least)- I wouldn't want to go too high because you will have alot of IM in the midrange from any high excursion woofer- but it could be -12dB @150hz without too many problems. I'll post more when I know more-

Ryan

 

[Vikash]

Excellant info! I am very new to router usage; can I ask, how did you "follow" a template that is above the work piece? All of my pilot bits have the bearing on the bottom (w.r.t. the work). Is there a kind of bit with the bearing on top?

This was my first use of a router. I used a ¹/₄" flush bit with the neck against the template. The template is raised slightly to avoid cutting it when lowering and raising the bit. This worked well for the first one, then progressivley got worse for the remaining 3 driver cut-outs as the template got damaged a little each time (through my impatience and not necessarily the method I should add). I'm sure that with the right bits you can do a perfect job (I just don't know what they are).

The fourth image on that link should give you a better idea of how I attempted it.

 

[tiroth]

Thanks guys!

 

[Zaph]

Surface mounting woofers and tweeters

This is what happens to your tweeter's response when you surface mount it:

An externally hosted image should be here but it was not working when we last tested it.

Using a foam piece or felt layer usually does not help this problem and sometimes makes it worse. The only way to not have a ragged lower treble response is to countersink the tweeter.

Midwoofers however, can often get away with being surface mounted without too much effect in their usable range. If you use a foam layer on the woofer, it will be purely cosmetic and not affect the sound too much.

 

[tiroth]

Using a foam piece or felt layer usually does not help this problem and sometimes makes it worse. The only way to not have a ragged lower treble response is to countersink the tweeter.

Really? This is surprising to me. What is the mechanism by which this fails to work? I would have thought that all flush baffles would respond very similarly in terms of diffraction, regardless of what material the top layer was composed of.

 

[rolfy72]

If you surface mount your drivers does the front surface area need to cover the whole front baffle, or can it just be for a certain distance from the driver centre(up &down the baffle that is!).
Im toying on the idea of glueing thin MDF on the front of the baffle to recess the drivers and too look like "sculptured layers"(cutouts from the mdf layers) on the lower parts of the enclosure.
Im going for a painted finish with leather inserts.(I dont like veneer finishes they look fake...sorry)

 

[RyanC]

Yea thats an interesting question-

What about a piece of plexiglass or even cardboard under a layer of fabric?

Also the flange on my tweeter and the audax is about the same- the tweeter is on the side of the MW so it is like this:

T
t
t MW
t
t


W






With circles around the woofers-

The flanges are pretty much touching now so that the edge of the tweeter meets the edge of the woofer- would this cause the edge difraction do decrease as it would only really hit the audax's surround??

Im thinking if this would work on the inside then use a wedge of foam on the outside that would be pretty easy- just a thought though.


Thanks again guys-

Ryan