Hi DIYaudionics.
I'm planning a single small line array PA speaker with 8 Visaton FRS 8M drivers. Its for acoustic instruments and singer, no drums and bass on own system. The long slender shape of the array suggests, that I could squeeze a few more Hz (below the Fs of 125Hz) out of it with a quarterwave-ish design, TQWT, bass reflex, TL or a combination of all (?), thus avoiding a sub-woofer, which is hardly necessary for a guitar and a female voice. The aim is not super HiFi, but something "good" sounding for small venues. I know, hard to measure.
My problem is, that when I try to use Visatons own design-program BoxSim, it is not clear to me how I combine several drivers into one vented "outer enclosure". It seems as if every driver has its own (and thus to big) enclosure. Other simulators may confuse me similarly. The exercise here is only the bass response, not the many ways of coupling the drivers and spikes and combs and whatnot. That is a different story.
When combining drivers in a common enclosure, I suppose the effective piston area is the combined cone areas when they work in phase, but what about the rest of the T/S-parameters?
I would greatly appreciate some opinions from the learned - and friendly - users of DIYaudio. I will of course document the result here with (simple, with Frequency Response Plotter 1.12a) measuments of the characteristics and the "Goodness" of the sound. How do I simulate the combined cones? Which (free-ware) program can you suggest?
Pitfalls? (yeah, lots!)
FRS 8M (11,5 Euros):
Z 8 Ohm
fs 125 Hz
Rdc 7.2 Ohm
Qms 3.24
Qes 0.58
Qts 0.49
Vas 1.1 l
Sd 29 cm²
Mms 1.8 g
L 0.3 mH
I'm planning a single small line array PA speaker with 8 Visaton FRS 8M drivers. Its for acoustic instruments and singer, no drums and bass on own system. The long slender shape of the array suggests, that I could squeeze a few more Hz (below the Fs of 125Hz) out of it with a quarterwave-ish design, TQWT, bass reflex, TL or a combination of all (?), thus avoiding a sub-woofer, which is hardly necessary for a guitar and a female voice. The aim is not super HiFi, but something "good" sounding for small venues. I know, hard to measure.
My problem is, that when I try to use Visatons own design-program BoxSim, it is not clear to me how I combine several drivers into one vented "outer enclosure". It seems as if every driver has its own (and thus to big) enclosure. Other simulators may confuse me similarly. The exercise here is only the bass response, not the many ways of coupling the drivers and spikes and combs and whatnot. That is a different story.
When combining drivers in a common enclosure, I suppose the effective piston area is the combined cone areas when they work in phase, but what about the rest of the T/S-parameters?
I would greatly appreciate some opinions from the learned - and friendly - users of DIYaudio. I will of course document the result here with (simple, with Frequency Response Plotter 1.12a) measuments of the characteristics and the "Goodness" of the sound. How do I simulate the combined cones? Which (free-ware) program can you suggest?
Pitfalls? (yeah, lots!)
FRS 8M (11,5 Euros):
Z 8 Ohm
fs 125 Hz
Rdc 7.2 Ohm
Qms 3.24
Qes 0.58
Qts 0.49
Vas 1.1 l
Sd 29 cm²
Mms 1.8 g
L 0.3 mH
For example, when you double the drivers, you double the Vas in the program. So, if you want all your 8 drivers, it will need 8x the Vas of a single driver. That will not make a slim LA.
The solution would be to have most of the drivers in sealed enclosures, and one or two drivers vented. But, For a PA line array, I wouldn’t go vented. These small drivers don’t move enough air. Keep them sealed, EQ slightly and they should play close to their Fs.
The solution would be to have most of the drivers in sealed enclosures, and one or two drivers vented. But, For a PA line array, I wouldn’t go vented. These small drivers don’t move enough air. Keep them sealed, EQ slightly and they should play close to their Fs.
Thank you, perceval, for the Vas-tip and rayma too. A cabinet of 10 by 14 by 86 cm (4 x 5.5 x 34 inches) holds the 8xVas=12 litres and can easily accomodate the 8 drivers. Interaction however could worry me, although the are fed the same signal. I guess I could build the cabinet so that walls between the drivers could be inserted afterwards if need be. It is not my impression, though, that LA-builders separate the units.
not sure what the guiding principle was but wesayso in his Two Towers thread allowed pressure between all 25 drivers in his array to be shared via ports, how that's significant i'm not sure but it may be helpful to solicit his advice.
You're not going to do anything quarter-waveish when you have drivers spread up and down the line.
Point taken, AllenB, I'll turn my head towards a vented box, although it will be a long one. Bose seems to use bass reflex in their design Panaray MA12, although you can't tell witch drivers are vented or how/if the total enclosure is parted into smaller ones.
For PA use, you want to maximise the efficiency of the vent. Narrow slots are too resistive for that.
Chris
Chris
@Chris and @Davor D: My thougths also, narrow vents must be lossy. From my first calculations it seems, that with a bass reflex enclosure I can push the -3dB point down into the top seventies Hz given all the other design constraints I am juggling. Thats not too bad for song and guitar.
Now, I may rise some eyebrows, but I plan to build a test speaker partly out of cardboard, with the drivers mounted on plywood. That gives me room for experimentation with placement and size of vents, angled (slanted?) cabinet sides and whatnot. Tested with a very low soundlevel it is my guess, that I can get reasonable measurements (of the bass response). Then start cutting, glueing, srewing, stuffing, bracing....and then measure the higher frequencies.
Now, I may rise some eyebrows, but I plan to build a test speaker partly out of cardboard, with the drivers mounted on plywood. That gives me room for experimentation with placement and size of vents, angled (slanted?) cabinet sides and whatnot. Tested with a very low soundlevel it is my guess, that I can get reasonable measurements (of the bass response). Then start cutting, glueing, srewing, stuffing, bracing....and then measure the higher frequencies.
I really appreciate your idea - you can build it like this:
- put every driver in its own enclosure - you then have less problems with standig waves in longish boxes
- put into every box a small vent tuned to approx. 100 hertz - so that it is not too long - yes for public adress systems the reflex ports should be big but it is better to have some gain of 2-4 db then nothing (when using closed box)
- do not forget damping the box with fixed foam on all internal sides of 2-4cm thickness - this is important for good sound both in the voice region and in the bass, too.
I had some very good results with four small fullrange drivers in a line array - this has really some advantages because the cylindrical wave.
Efficiency of FRS8M is 88db so
1 driver 88db
2 drivers 91 db
4 drivers 94 db
8 drivers 97 db
This is a good effiency for a public adress system!
I used four small fullrange drivers as you can see in the foto - same size like FRS8M but different ones. I really liked how they were listenable - I never built a line driver before but now I understand why it is so popular in public adress systems - often used as curved line array.
Attachments
Thanks, Freedom666, it is very encouraging to hear of good results from someone, who has been down the road of line arrays. I believe, that placing the drivers close to each other is beneficial for bringing down the comb effect of stacked drivers. That makes individual boxes hard to build. To avoid standing waves I plan to build an enclosure, that is very sligthly tapered and, unlike the commercial arrays, reaches all the way down to the floor, totalling some 180 cm/6 feet. (The commercial solutions generally have the array on a post on top of a wooferbox.) I'll move the vents around (in my test-setup) to see, if proper placing of them can counteract possible spikes in the characteristics. And as a last resort there is the peculiar damping technique of
A linear Speaker Array you can build
(scroll to below middle) using posterboard as interior oblique walls to bring down resonances.
And by the way, I'm only building one loudspeaker because stereo doesn´t make much sense in sound from a stage. Half of the audience will get mostly the sound send to the right, the other half the left, making the soundtechnician mixing the whole thing as mono. Thus: better one loudspeaker in the middle. Half the carrying around and setting up, same sound (or better, perhaps?)
I'm ordering the drivers today.
A linear Speaker Array you can build
(scroll to below middle) using posterboard as interior oblique walls to bring down resonances.
And by the way, I'm only building one loudspeaker because stereo doesn´t make much sense in sound from a stage. Half of the audience will get mostly the sound send to the right, the other half the left, making the soundtechnician mixing the whole thing as mono. Thus: better one loudspeaker in the middle. Half the carrying around and setting up, same sound (or better, perhaps?)
I'm ordering the drivers today.
Here you have simulation in boxsim, one is all 8 in one enclousor and other is each driver in 1,5liter sealed box
Thank you, pk2carlos, for the boxsim-files. You have more complete data than I have been able to find. Thats great. The simulation is interesting - the bass falling a bit to early for my taste, but as I understand, the simulation is with a common, closed 12 l box. I'll work a bit with your data to see what I can achieve with a vented somewhat larger box. And then, of course, there is what the real world will let me achieve. We'll see. Drivers are on their way from Germany.
UPDATE: How did it work out?
I build a tall (190cm, 6'4") narrow box (12 by 17 cm, app. 5" by 6" )) with the 8 drivers in the upper end, hoping to make use of the boxvolume below.
I made measurements outdoors with REW (https://www.roomeqwizard.com/) and various vents - with no success.
I came to conclude, that the long narrow box dimensions made it impossible to avoid standing waves.
I sawed the lower part of the box off and made a satellite array instead.
I have used it for one small gig so far, and everyone was satisfied with the sound.
Only the male singer used it, so it worked without a subwoofer, which I am planning to build.
It rolls of at around 190 HZ. An outdoor narrow field measurement with REW and a reasonable soundcard and mike (Focusrite Saffire6 and Audio-technica AT2020)
looks like this (SPL not calibrated):
I have no explanation for the dip at 6kHz. It doesn't seem to correlate with any of the dimensions of the box. I'm to old to care about the dip at 15 kHz ;-)
Impedance, closed box (red) and backside removed (blue):
The box is asymmetric (sides not parallel, back and front not parallel) to avoid standing waves. If it works better than parallel walls is hard for me to say, though in theory it should. But one thing I know: its a bitch to make ;-)
One final note: the Visaton FRS8m is almost impossible to fasten on plywood with screws from behind, the holes are to close to the cone and thus to the edge of the big hole in the wooden baffle. So I went with one long rod anchored in each end and applying pressure on the 8 magnets. 32 screws spared. Thanks, everyone, for all your input.
I build a tall (190cm, 6'4") narrow box (12 by 17 cm, app. 5" by 6" )) with the 8 drivers in the upper end, hoping to make use of the boxvolume below.
I made measurements outdoors with REW (https://www.roomeqwizard.com/) and various vents - with no success.
I came to conclude, that the long narrow box dimensions made it impossible to avoid standing waves.
I sawed the lower part of the box off and made a satellite array instead.
I have used it for one small gig so far, and everyone was satisfied with the sound.
Only the male singer used it, so it worked without a subwoofer, which I am planning to build.
It rolls of at around 190 HZ. An outdoor narrow field measurement with REW and a reasonable soundcard and mike (Focusrite Saffire6 and Audio-technica AT2020)
looks like this (SPL not calibrated):
I have no explanation for the dip at 6kHz. It doesn't seem to correlate with any of the dimensions of the box. I'm to old to care about the dip at 15 kHz ;-)
Impedance, closed box (red) and backside removed (blue):
The box is asymmetric (sides not parallel, back and front not parallel) to avoid standing waves. If it works better than parallel walls is hard for me to say, though in theory it should. But one thing I know: its a bitch to make ;-)
One final note: the Visaton FRS8m is almost impossible to fasten on plywood with screws from behind, the holes are to close to the cone and thus to the edge of the big hole in the wooden baffle. So I went with one long rod anchored in each end and applying pressure on the 8 magnets. 32 screws spared. Thanks, everyone, for all your input.
For the record, impedance and the wiring (counting the drivers from the top downwards) is like this:
┌──────┬──────┬───┐ ┌──────┬──────┬── +
┌┴┐ ┌┴┐ │ │ ┌┴┐ ┌┴┐ │
│8│ │8│ │ │ │1│ │6│ │
└┬┘ └┬┘ ┌┴┐ ↓ └┬┘ └┬┘ ┌┴┐
┌┴┐ ┌┴┐ │8│ ┌┴┐ ┌┴┐ │4│
│8│ │8│ └┬┘ 6.9Ω │2│ │7│ └┬┘
└┬┘ └┬┘ ┌┴┐ └┬┘ └┬┘ ┌┴┐
┌┴┐ ┌┴┐ │8│ ↑ ┌┴┐ ┌┴┐ │5│
│8│ │8│ └┬┘ │ │3│ │8│ └┬┘
└┬┘ └┬┘ │ │ └┬┘ └┬┘ │
└──────┴──────┴───┘ └──────┴──────┴── -
1 1
ΣR=──────────────── = ─────────────── = 6.9Ω
1 1 1 1 1 1
── + ── + ── ── + ── + ──
R1 R2 Rn 24Ω 24Ω 16Ω
Hi, my 2c...
I've built a few similar lines and set up tuning on a few others. I don't think there is any good reason to keep separate enclosures.
One common enclosure with a total volume and total port area of (a single driver volume and port in a single box) X number of drivers, has given results at least equal to separate enclosures.
Standing waves and drivers interfering with each other inside the box are trivial issues, if even real ime/imo. I think this is true even when some drivers are not being used full-range as when frequency shading.
The big thing with any line design, is that a good deal of EQ will be needed to shape the final response. The acoustic summations outside the box simply demand it.
So my advice.......I'd put all the drivers in the easiest to build box, with a little fiberglass insulation or whatever your fav dampening material is, and then just dial the response in with an active EQ. You can work your butt off trying further refinements, not to do much if any, better.
I've built a few similar lines and set up tuning on a few others. I don't think there is any good reason to keep separate enclosures.
One common enclosure with a total volume and total port area of (a single driver volume and port in a single box) X number of drivers, has given results at least equal to separate enclosures.
Standing waves and drivers interfering with each other inside the box are trivial issues, if even real ime/imo. I think this is true even when some drivers are not being used full-range as when frequency shading.
The big thing with any line design, is that a good deal of EQ will be needed to shape the final response. The acoustic summations outside the box simply demand it.
So my advice.......I'd put all the drivers in the easiest to build box, with a little fiberglass insulation or whatever your fav dampening material is, and then just dial the response in with an active EQ. You can work your butt off trying further refinements, not to do much if any, better.
Several enclosures are stiffer than one longish one. You can tilt the separate drivers to the left and right in order to better dispersion to the sides i.e. 45 and 60 degrees off axis. And there is a standing wave from top to bottom in a long enclosure. If you want to use bass reflex with little damping you will have undamped resonances. To prevent this you can put some damping material on the backside of each driver glued to the magnet (some foam like 15x15x5cm. This damping is in the middle of the box where standing waves are active.
For future reference, you only need to make either the top or bottom, back and one side at a > 12 deg angle to solve all the eigenmode problems.
Re stiffeners, for its tiny size a single vertical riser offset at some golden or acoustic ratio to the back plate with a few horizontal risers positioned at the pipe's odd harmonics tied to the baffle (closest you can come) makes for a very rigid, ~harmonically balanced structure, i.e. it will push the cab's Fs to well above the driver's ability to excite it.
Re stiffeners, for its tiny size a single vertical riser offset at some golden or acoustic ratio to the back plate with a few horizontal risers positioned at the pipe's odd harmonics tied to the baffle (closest you can come) makes for a very rigid, ~harmonically balanced structure, i.e. it will push the cab's Fs to well above the driver's ability to excite it.