Hello,
I want to make a home theatre set of 5 speakers using the Fostex FE167E. The 15Lt bass reflex enclosures are my choice.
The FE167E are 85mm deep.
I want to make the thinest possible enclosures but I dont know how much space the speakers need behind them so the they function correcty.
Can I just go to minimum and make the enclosure as deep as the speakers, which would meen that the magnet would almost touch the back of the enclosure or do they need more room?
Can I place the bass reflex on top, the side or bottom?
What woud be best?
I want to make a home theatre set of 5 speakers using the Fostex FE167E. The 15Lt bass reflex enclosures are my choice.
The FE167E are 85mm deep.
I want to make the thinest possible enclosures but I dont know how much space the speakers need behind them so the they function correcty.
Can I just go to minimum and make the enclosure as deep as the speakers, which would meen that the magnet would almost touch the back of the enclosure or do they need more room?
Can I place the bass reflex on top, the side or bottom?
What woud be best?
Attempting to get the full frequency range that the 167's are capable of in that shallow an enclosure, I think you're asking for major problems with strong early reflections.
If you're aiming for minimal aesthetic intrusion into the room, and if the equipment locations will be permanent, why not consider a false wall installation?
There's another thread detailing a rather stealthy in-wall HT set-up with CSS FR125's that looks interesting:
http://www.diyaudio.com/forums/showthread.php?postid=1110803#post1110803
I agree with John that "designers" like the look of the TV above the fireplace as an artistic statement, but I doubt they spend much time actually watching such a set-up. Unless you're an NBA player, I think the neck strain will get to you real quick.
The depth required by even the shallowest of the video components, which the predominance of flat-screens these days generally means the cable box or HT receiver, would likely be more than enough to accommodate a more optimally dimensioned speaker enclosure.
In fact, I could easily envision a pair of BIBs (top vented), either built in or with a separate bridging cabinet for the electronics and TV,
If you're aiming for minimal aesthetic intrusion into the room, and if the equipment locations will be permanent, why not consider a false wall installation?
There's another thread detailing a rather stealthy in-wall HT set-up with CSS FR125's that looks interesting:
http://www.diyaudio.com/forums/showthread.php?postid=1110803#post1110803
I agree with John that "designers" like the look of the TV above the fireplace as an artistic statement, but I doubt they spend much time actually watching such a set-up. Unless you're an NBA player, I think the neck strain will get to you real quick.
The depth required by even the shallowest of the video components, which the predominance of flat-screens these days generally means the cable box or HT receiver, would likely be more than enough to accommodate a more optimally dimensioned speaker enclosure.
In fact, I could easily envision a pair of BIBs (top vented), either built in or with a separate bridging cabinet for the electronics and TV,
It is possible, but as Chris says, you are going to be fighting early reflections. Cone treatment would help there, but trying to get as much depth as possible and making the back irregular would help.
With the PAWOs (shallow FE127 cabinet), the difference adding the 3/4' suprabaffle makes is very audible.
dave
With the PAWOs (shallow FE127 cabinet), the difference adding the 3/4' suprabaffle makes is very audible.
dave
planet10 said:
what if he applied a layer of deflex or other sound absorbing or reflecting material the the back of teh cabinet? It might allow for a cabinet that might be a bit slimer than normally used. Also if the front baffle was angled it could help.
I am not advocating that the cabinet be so slim that the magnet almost touch the rear of the speaker but the object, I think, is to see how slim one can make the cabinet without hainvg serious problems.
I'll have to disagree with some on this one. the Fostex designed FE166E horn enclosure has a very close back wall, and the 168E sigma enclosure has little more room.
The magnet assembly on these speakers is large enough to prevent most direct reflections anyway. I think the basket and spider of the driver itself will show more reflections to the cone than the cabinet wall. As long as the aspect ratio (width to height) of the box isn't too high, which would effect box losses, and hence tuning frequency, I can't see the shallow box having too much of a negative impact.
I agree too a certain degree that a deeper box will breath better, but a shallow one should work.
Use a good quality fill material, preferably long fibre wool, to kill any standing waves.
Yes, you can place the port on the top, side or wherever you like, but it's a good idea not to have it too far away from the driver.
The magnet assembly on these speakers is large enough to prevent most direct reflections anyway. I think the basket and spider of the driver itself will show more reflections to the cone than the cabinet wall. As long as the aspect ratio (width to height) of the box isn't too high, which would effect box losses, and hence tuning frequency, I can't see the shallow box having too much of a negative impact.
I agree too a certain degree that a deeper box will breath better, but a shallow one should work.
Use a good quality fill material, preferably long fibre wool, to kill any standing waves.
Yes, you can place the port on the top, side or wherever you like, but it's a good idea not to have it too far away from the driver.
Well thats what I thought too.
The recommended enclosures have very little depth behind the speaker unit.
In the FE166E enclosure the speaker is only 85mm away from the back panel and the speaker is 73,2mm deep. Thats only about 1cm difference.
The FE167E is 85 mm deep because of the magnetical shielding so if the back of the enclosure is at 95mm thats even better as 85mm in the FE166E enclosure right?
Also to note that these speakers are for home theatre use so probably will be cut at 70-80 Hz anyway.
The recommended enclosures have very little depth behind the speaker unit.
In the FE166E enclosure the speaker is only 85mm away from the back panel and the speaker is 73,2mm deep. Thats only about 1cm difference.
The FE167E is 85 mm deep because of the magnetical shielding so if the back of the enclosure is at 95mm thats even better as 85mm in the FE166E enclosure right?
Also to note that these speakers are for home theatre use so probably will be cut at 70-80 Hz anyway.
Ted Jordan also advocates shallow enclosures (his VTL, for example), suggesting that the reflections will be higher in freq and easier to suppress with damping. The VTL has about a quarter inch behind the driver, the back wall lines with thick felt and a cutput for the vent in the magnet. He takes a similar approach fo the JXR6 enclosure, made up of ply frames. From the playing round I've done with tall, narrow enclosures, I definitely think it's worth going for more space around the sides of the drivers.
How are the sonics affected by the proximity of the rear wall? All I can think of is that an eigentone corresponding to this distance may be a little more noticable due to it being in the ears most sensitive frequency range.. Wouldn't some stuffing break up the reflections?
I suppose that if there was a peak in the free space response of the driver at the same frequency as the standing wave in the enclosure, it may become more of a problem, but that could happen for any dimension of the cabinet if not accounted for in the initial design.
I reckon that if there was a peak in the free space response of the driver at the same frequency as the standing wave in the enclosure, it may become more of a problem, but that could happen for any dimension of the cabinet if not accounted for in the initial design.
I think for the application promitheus has in mind, a bit of stuffing wouldn't hurt!
I suppose that if there was a peak in the free space response of the driver at the same frequency as the standing wave in the enclosure, it may become more of a problem, but that could happen for any dimension of the cabinet if not accounted for in the initial design.
Is the problem accentuated by the minimal use of damping material in most horn enclosures? I know that dynamics are addictive, so there becomes a real balancing act between the perceived speed and liveness, and a smoother response.
I reckon that if there was a peak in the free space response of the driver at the same frequency as the standing wave in the enclosure, it may become more of a problem, but that could happen for any dimension of the cabinet if not accounted for in the initial design.
I think for the application promitheus has in mind, a bit of stuffing wouldn't hurt!
As density increase the low frequency corner goes lower, but at a certain point it will start to seem solid to the higher frequencies.
In a situation like this i would use layers with decreasing density as you get further from the back wall. (in a practical ap, a thick piece of wool felt on the wall, with variably poofed poly-stuff or sheep's wool on top of that, decreasing to little or none near the driver.
dave
In a situation like this i would use layers with decreasing density as you get further from the back wall. (in a practical ap, a thick piece of wool felt on the wall, with variably poofed poly-stuff or sheep's wool on top of that, decreasing to little or none near the driver.
dave
Nothing is ever black & white... the deeper you can make the cabs the lower yoou can push the effect of the damping. Treating the driver cone also helps. Making the back wall irregular helps (but tricky with no depth).
The PAWOs are 3/5" (89mm) deep. We have/had 2 pair, one with a 3/4" thick supra-baffle, and one without. There is a midrange coloration (hollowness) we attribute to the rear wall bounce in the one without. Either the extra 3/4" made enuff difference to push the LF corner, or the MDF on the back panel of one without (vrs BB on the other) is the culprit. We'll know for sure once we have added a supraBaffle to the mules.
dave
The PAWOs are 3/5" (89mm) deep. We have/had 2 pair, one with a 3/4" thick supra-baffle, and one without. There is a midrange coloration (hollowness) we attribute to the rear wall bounce in the one without. Either the extra 3/4" made enuff difference to push the LF corner, or the MDF on the back panel of one without (vrs BB on the other) is the culprit. We'll know for sure once we have added a supraBaffle to the mules.
dave
GM said:
Yes, we used that technique there (as well as puzzlecoating the cones). I learned the trick from Bill Perkins, who was using it 30+ years ago, to try to achieve a Nautilus-like 1/2 wl line characteristic in his midrange cabs (at the time he was working on an improved design loosely based on the then popular Radford S90.
I've been playing around with it since then, and as a matter of course line critical walls with 1/4-1/2" wool or cotton felt before adding any polyfluff (if any)
dave
PS: GM is talking about a quad of ceiling speakers i made based on his bipolar 1197 centre channel ML-TL design (which works better than the MTM by a bit). BTW all 4 of these could likely be picked up for a song by anyone in LA willing to drive by and pick them up.
Attachments
The lower limit of a piece of damping material's effectiveness at killing the back wave is a function of its thickness.
And the frequency. A 90 degree reflector will return 100% of the energy minus the acoustical impedance mismatch of the two different mediums(varies with the frequency) minus the attenuation of the medium its travelling thru to return to the rear of the cone in a later time/phase of the cone position. The absorbation of the second medium is a thickenss/acoustical impedance/frequency dependant curve.
ron
And the frequency. A 90 degree reflector will return 100% of the energy minus the acoustical impedance mismatch of the two different mediums(varies with the frequency) minus the attenuation of the medium its travelling thru to return to the rear of the cone in a later time/phase of the cone position. The absorbation of the second medium is a thickenss/acoustical impedance/frequency dependant curve.
ron
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