Hi all,
Apologies if this has been discussed previously; I went looking but got lost in a myriad of info...
I'm looking at building a line array using 16 small full-range drivers; it's for a PA application, a la bose L1. The appeal is portability (relatively lightweight & wrangleable cabinets, no need to lug extra stands...). Will be augmented from about 200Hz down via a modest sub; will be used for small-med cafe/functions, so doesn't need to be a room shaker.
I'm looking to keep the drivers small (4 ") and will probably need to use some digital EQ (via a Behringer DEQ2496) to even the response out. The cabinets are some suitably shaped aluminium extrusions, but the volumes per driver may be on the low side (depends which drivers I plump for in the end, though).
I have a couple of questions that I'm hoping to get some good advice on from you very knowledgeable folk out there:
1) Small drivers tend to be on the low-side for power handling; accordingly I'm looking for hi sensitivity drivers to extract as much SPL (relatively speaking for their size, at any rate; 90dB/w/m is the best I've seen without spending big $$ per driver) out of low input power and then exploit the multiple serise/parallel driver factor to yield a 102dB/w/m figure for 8 drivers, then amp each set of 8 (2 sets for 16 in total) to get 105dB at the end.
However, hi-sensitivity seems to come with a hi-Q factor; I've seen in some cases up to 1.75 - 2 (I think they're ceiling speakers). In a small enclosure, they'll peak high as expected, but this can be flattened out using DSP-EQ. My first question is: the phase response would be less than ideal to begin with, but would flattening the repsonse improve the phase response any? Or would it stay the same (or even get worse?)
And on a vaguely related but slightly different note:
2) With a standard series/parallel drive set up of, say, 4 drivers to keep things simple, although the amp would see the equivalent impedance of a single driver, would the power handling (ie, before failure) be double that of a single driver, given that the 'weakest single link' in series is now a parallel pair?
Sorry for the long-windedness of this; any help would be much appreciated!
Thanks heaps!
Paul
Apologies if this has been discussed previously; I went looking but got lost in a myriad of info...
I'm looking at building a line array using 16 small full-range drivers; it's for a PA application, a la bose L1. The appeal is portability (relatively lightweight & wrangleable cabinets, no need to lug extra stands...). Will be augmented from about 200Hz down via a modest sub; will be used for small-med cafe/functions, so doesn't need to be a room shaker.
I'm looking to keep the drivers small (4 ") and will probably need to use some digital EQ (via a Behringer DEQ2496) to even the response out. The cabinets are some suitably shaped aluminium extrusions, but the volumes per driver may be on the low side (depends which drivers I plump for in the end, though).
I have a couple of questions that I'm hoping to get some good advice on from you very knowledgeable folk out there:
1) Small drivers tend to be on the low-side for power handling; accordingly I'm looking for hi sensitivity drivers to extract as much SPL (relatively speaking for their size, at any rate; 90dB/w/m is the best I've seen without spending big $$ per driver) out of low input power and then exploit the multiple serise/parallel driver factor to yield a 102dB/w/m figure for 8 drivers, then amp each set of 8 (2 sets for 16 in total) to get 105dB at the end.
However, hi-sensitivity seems to come with a hi-Q factor; I've seen in some cases up to 1.75 - 2 (I think they're ceiling speakers). In a small enclosure, they'll peak high as expected, but this can be flattened out using DSP-EQ. My first question is: the phase response would be less than ideal to begin with, but would flattening the repsonse improve the phase response any? Or would it stay the same (or even get worse?)
And on a vaguely related but slightly different note:
2) With a standard series/parallel drive set up of, say, 4 drivers to keep things simple, although the amp would see the equivalent impedance of a single driver, would the power handling (ie, before failure) be double that of a single driver, given that the 'weakest single link' in series is now a parallel pair?
Sorry for the long-windedness of this; any help would be much appreciated!
Thanks heaps!
Paul
Hi Paul,
I was wondering if you have got much further with this. I am working on something similar, also for a small pa. I have so far decided to go the route of using 9 full range drivers at quite low wattages on an open baffle line array and I'm trying to select the drivers whilst keeping the price down.
What did you go for in the end? - I'm just looking at visaton and tesla so far because they are easy to get hold of here in CZ.
I am not sure if the drivers require the usual robustness that pa drivers need because they won't be suffering from the same level of excursion - does anyone have an opinion on this?
Also, to deal with so many drivers and impedance, the wiring will have to be serial/parallel - does this further compound phase problems?
Anyway - I hope the project is going well for you and you are out there gigging with this thing already.
Cheers
I was wondering if you have got much further with this. I am working on something similar, also for a small pa. I have so far decided to go the route of using 9 full range drivers at quite low wattages on an open baffle line array and I'm trying to select the drivers whilst keeping the price down.
What did you go for in the end? - I'm just looking at visaton and tesla so far because they are easy to get hold of here in CZ.
I am not sure if the drivers require the usual robustness that pa drivers need because they won't be suffering from the same level of excursion - does anyone have an opinion on this?
Also, to deal with so many drivers and impedance, the wiring will have to be serial/parallel - does this further compound phase problems?
Anyway - I hope the project is going well for you and you are out there gigging with this thing already.
Cheers
There is no reason why high sensitivity speakers need to have high Qts. Ceiling speakers are designed for an infinite baffle application and are specifically designed to have high Qts.
Keep looking, you will find drivers more suited to your application.
Here is a link to a project with line arrays of inexpensive speakers equalized with the DEQ2496. I used a similar Aurasound driver for computer speakers and it sounded quite nice without equalization.
The Murphy Corner-Line-Array Home Page
The Murphy Corner-Line-Array Home Page
Well, I went ahead and made my open baffle array. I did it under my usual time constraint panic because I had a small gig coming up where I wanted to test it.
So firstly, the idea was to make a speaker that dealt with the following points:
1. Could be fairly easily transported in the small car that we use
2. Would handle nylon-acoustic guitar and vocal duties in smaller gigs where they have either no or a next to useless pa.
3. Very little bass would be needed but fairly good hi-fi production from 150hz upwards.
4. Good feedback resistance with a comfortable output to cover up to 40 (quiet) people in a cafe/gallery sized space.
5. Would cost very little in terms of money
So I cobbled this thing together with wood scraps and 8 Visaton FR10 8ohm drivers.
I did do a bit of planning for the open baffle using xbaffle and worked out the spl from having 8 drivers - after that it all became very unscientific! Still they work and for their application they do very well indeed. I felt much happier with my sound than I have in a long time, I could sit right next to it with two mics and driving it with about 50 watts rms; didn't blow mine or anyone elses ears off but could be adequately heard.
I only spent 1500kc (£40.00) in total so for a cheapo like myself it's a good thing, especially when one considers the commercial alternatives.
So firstly, the idea was to make a speaker that dealt with the following points:
1. Could be fairly easily transported in the small car that we use
2. Would handle nylon-acoustic guitar and vocal duties in smaller gigs where they have either no or a next to useless pa.
3. Very little bass would be needed but fairly good hi-fi production from 150hz upwards.
4. Good feedback resistance with a comfortable output to cover up to 40 (quiet) people in a cafe/gallery sized space.
5. Would cost very little in terms of money
So I cobbled this thing together with wood scraps and 8 Visaton FR10 8ohm drivers.
I did do a bit of planning for the open baffle using xbaffle and worked out the spl from having 8 drivers - after that it all became very unscientific! Still they work and for their application they do very well indeed. I felt much happier with my sound than I have in a long time, I could sit right next to it with two mics and driving it with about 50 watts rms; didn't blow mine or anyone elses ears off but could be adequately heard.
I only spent 1500kc (£40.00) in total so for a cheapo like myself it's a good thing, especially when one considers the commercial alternatives.
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This should be interesting reading for you.
The Murphy Corner-Line-Array Home Page
http://www.trueaudio.com/array/
-Tom-
The Murphy Corner-Line-Array Home Page
http://www.trueaudio.com/array/
-Tom-
I too am interested in this (I can't believe some other manufacturer hasn't cloned the Bose yet). The Bose is fantastic.... but (I'm a ) 2-bit musician, and really can't afford to dump $2k in a speaker column (especially in this day of nickel & dime'n the help). Since you've had time to play with this awhile... how is the dispersion (Bose claims the sound at the back of the room is equal to the sound at the front of the room)...
Any other ideas for drivers out there?
Any other ideas for drivers out there?
Well I probably can't compare my version to the Bose L1 but on first use the dispersion certainly seems better than a typical acoustic amp or PA speaker. I'll let you know more after my next gig with it - I'll be using a bigger amp/mixer this time too.
BTW - Fishman have done a small line array job called the Fishman Solo but even that retails at around £800 - £900. Definitely a good reason to build something yourself.
Tom V - I did read about your array the first time you put the link up - the whole study and the end product looks fantastic. Congrats.
BTW - Fishman have done a small line array job called the Fishman Solo but even that retails at around £800 - £900. Definitely a good reason to build something yourself.
Tom V - I did read about your array the first time you put the link up - the whole study and the end product looks fantastic. Congrats.
The line array has evolved to a CBT-design...
Hi all,
Sorry to not have monitored my thread for so long; been uber-busy. I must admit, I'd kind of given up on any responses, so wasn't actively looking either...
To sum up where things have gotten up to: The PA is still in the works. However, now I'm looking at building a straight delay-curved CBT line array (a la Keele), using 24 3.5” full-range drivers (Vifa TC9FD18-08 (apparently aka: Peerless FR35/8); sensitivity's ok-ish at 86dB, but good power handling for a small driver (50W/100W) with good wide-range performance 110Hz-15K. Qts = 0.72). CBT's look VERY cool; just Google CBT & Keele for more info, but to sum up, much better dispersion than std line-array; less vertical lobing, more consistent sound field near & far field.
It's a far more adventurous venture than the original L1-clone project, but the results should be quite exciting.
However, I have a question re acoustic outputs & driver-group sensitivities for mixed parallel/series combinations of drivers that I’m hoping someone could please help me with, but see Keele's .pdf presentation on CBT's & then read for the context first:
(Incidentally, I'll stress; all my efforts are for a PERSONAL system; in no way am I attempting to build a commercial unit. I'd also encourage all who follow to observe & respect the patents that JBL & Keele have on CBT technology). Right: now that the legal caveat is out of the way...
So far, I’ve established the appropriate delays & Legendre shading amounts of each of the drivers (like I said, see Keele's preso'!), which I’ve then grouped around -3dB increments (ie, 0dB, -3dB, -6dB etc) to simplify the amplification logistics. My shaded groups end up looking like this:
Qty . . . . . Shading (dB)
1 . . . . . -18dB
1 . . . . . -12dB
1 . . . . . -9dB
2 . . . . . -6dB
3 . . . . . -3dB
4 . . . . . 0dB (ie, no attenuation)
4 . . . . . 0dB
3 . . . . . -3dB
2 . . . . . -6dB
1 . . . . . -9dB
1 . . . . . -12dB
1 . . . . . -18dB
Those of you who understand the maths may notice that I’m actually one driver short; there should be a 9th driver at 0dB in the middle, but I’ve decided to omit it for each of amplification (8 x 8ohm drivers: yeah! But 9 x 8ohms drivers… hmmm…). I’m hoping the fact that I’m roughly approximating the curve using the 3dB increments will allow a degree of fudging.
Re the amplification: Rather than try & driver the entire lot of one amp (which I think would involve having to come up with some very strange combinations of drivers to ultimately establish a workable end impedance (ie, 16 >= Z >= 4ohms)), I’ve decided it’s probably easier to use a small number of multiple amps to drive select combinations of the groups above that naturally occur -6dB apart in relation to each other (although see the caveat below before you jump on any errors in my assumptions), ie:
Group . . . . . Qty . . . . . Shading (dB)
C2 . . . . . 1 . . . . . -18dB
C1 . . . . . 1 . . . . . -12dB
B2 . . . . . 1 . . . . . -9dB
A2 . . . . . 2 . . . . . -6dB
B1 . . . . . 3 . . . . . -3dB
A1 . . . . . 8 . . . . . 0dB (I’ve added the two 0dB groups together)
B1 . . . . . 3 . . . . . -3dB
A2 . . . . . 2 . . . . . -6dB
B2 . . . . . 1 . . . . . -9dB
C1 . . . . . 1 . . . . . -12dB
C2 . . . . . 1 . . . . . -18dB
Ignoring the symmetrical layout & combining group numbers for simplicity, this should result in the following:
Group . . . . . Qty . . . . . Shading (dB)
A1 . . . . . 8 . . . . . 0dB
B1 . . . . . 6 . . . . . -3dB
A2 . . . . . 4 . . . . . -6dB
B2 . . . . . 2 . . . . . -9dB
C1 . . . . . 2 . . . . . -12dB
C2 . . . . . 2 . . . . . -18dB
Factoring in series/parallel (S/P) combinations, I hope to achieve the following (once again, see the caveat below before you jump on any errors in my assumptions):
Group . . . . . Qty . . . . . Shading (dB) . . . . . Combo impedance (ohms)
A1 . . . . . 8 . . . . . 0dB . . . . . 4ohms (straight 1-2-4-8 parallel/series combo)
B1 . . . . . 6 . . . . . -3dB . . . . . 5.33ohms (3 paralleled sets of series-pairs)*
A2 . . . . . 4 . . . . . -6dB . . . . . 8 ohms (straight 1-2-4 parallel/series combo)
B2 . . . . . 2 . . . . . -9dB . . . . . 4ohms (parallel pair)**
C1 . . . . . 2 . . . . . -12dB . . . . . 16ohms (series pair)
C2 . . . . . 2 . . . . . -18dB . . . . . 16ohms (series pair)**
Or, when viewed in their groups:
Group . . . . . Qty . . . . . Shading (dB) . . . . . Combo impedance (ohms)
A1 . . . . . 8 . . . . . 0dB . . . . . 4ohms (straight 1-2-4-8 parallel/series combo)
A2 . . . . . 4 . . . . . -6dB . . . . . 8 ohms (straight 1-2-4 parallel/series combo)
B1 . . . . . 6 . . . . . -3dB . . . . . 5.33ohms (3 paralleled sets of series-pairs)*
B2 . . . . . 2 . . . . . -9dB . . . . . 4ohms (parallel pair)**
C1 . . . . . 2 . . . . . -12dB . . . . . 16ohms (series pair)
C2 . . . . . 2 . . . . . -18dB . . . . . 16ohms (series pair)***
* No, I’ve no idea if the B1 combo will naturally yield a group sensitivity that’s -3dB with respect to A1; that’s yet to be established & may need a little cut/boost if required. But I’m estimating that it’ll be close.
** B2 will require -3dB of extra attenuation to bring them to the -9dB target
*** C2 will require -6dB of extra attenuation to bring them to the -18dB target
I’ll add the group pairs as follows:
A1 + A1 = series (Z = 12 ohms)
B1 + B1 = series (Z = 9.33 ohms)
C1 + C1 = parallel (Z = 8 ohms) – this may require an overall C-group attenuation if the parallel-config’ raises the sensitivity, but I didn’t want to series them due to the 32ohm impedance that would result.
So, in essence, I’m hoping to achieve the shading for all six groups by running them in relative +-6dB pairs off three amplified channels, with a little extra attenuation where required.
HOWEVER, here’s the main caveat (and the point of my post’s question):
Am I correct in my assumptions about these combinations achieving a -6dB difference for each group pair? I’ve taken into account gain due to both current draw as well as driver numbers, rather than just driver numbers, so, looking at Group A for example:
Group . . . . . Qty . . . . . Shading (dB) . . . . . Combo impedance (ohms)
A1 . . . . . 8 . . . . . 0dB . . . . . 4ohms (straight 1-2-4-8 parallel/series combo)
Connected in series to:
A2 . . . . . 4 . . . . . -6dB . . . . . 8 ohms (straight 1-2-4 parallel/series combo)
Given that A1 has twice the drivers as A2, and that A1 will draw twice as much current than A1 (due to half the impedance), is it correct to say that the overall difference in sub-group sensitivities will be 6dB? Or will it only be 3dB? And does connecting them in series help/hinder this?
I hope that all makes sense; can anyone please assist me with this?
Thanks heaps!
Paul
Hi all,
Sorry to not have monitored my thread for so long; been uber-busy. I must admit, I'd kind of given up on any responses, so wasn't actively looking either...
To sum up where things have gotten up to: The PA is still in the works. However, now I'm looking at building a straight delay-curved CBT line array (a la Keele), using 24 3.5” full-range drivers (Vifa TC9FD18-08 (apparently aka: Peerless FR35/8); sensitivity's ok-ish at 86dB, but good power handling for a small driver (50W/100W) with good wide-range performance 110Hz-15K. Qts = 0.72). CBT's look VERY cool; just Google CBT & Keele for more info, but to sum up, much better dispersion than std line-array; less vertical lobing, more consistent sound field near & far field.
It's a far more adventurous venture than the original L1-clone project, but the results should be quite exciting.
However, I have a question re acoustic outputs & driver-group sensitivities for mixed parallel/series combinations of drivers that I’m hoping someone could please help me with, but see Keele's .pdf presentation on CBT's & then read for the context first:
(Incidentally, I'll stress; all my efforts are for a PERSONAL system; in no way am I attempting to build a commercial unit. I'd also encourage all who follow to observe & respect the patents that JBL & Keele have on CBT technology). Right: now that the legal caveat is out of the way...
So far, I’ve established the appropriate delays & Legendre shading amounts of each of the drivers (like I said, see Keele's preso'!), which I’ve then grouped around -3dB increments (ie, 0dB, -3dB, -6dB etc) to simplify the amplification logistics. My shaded groups end up looking like this:
Qty . . . . . Shading (dB)
1 . . . . . -18dB
1 . . . . . -12dB
1 . . . . . -9dB
2 . . . . . -6dB
3 . . . . . -3dB
4 . . . . . 0dB (ie, no attenuation)
4 . . . . . 0dB
3 . . . . . -3dB
2 . . . . . -6dB
1 . . . . . -9dB
1 . . . . . -12dB
1 . . . . . -18dB
Those of you who understand the maths may notice that I’m actually one driver short; there should be a 9th driver at 0dB in the middle, but I’ve decided to omit it for each of amplification (8 x 8ohm drivers: yeah! But 9 x 8ohms drivers… hmmm…). I’m hoping the fact that I’m roughly approximating the curve using the 3dB increments will allow a degree of fudging.
Re the amplification: Rather than try & driver the entire lot of one amp (which I think would involve having to come up with some very strange combinations of drivers to ultimately establish a workable end impedance (ie, 16 >= Z >= 4ohms)), I’ve decided it’s probably easier to use a small number of multiple amps to drive select combinations of the groups above that naturally occur -6dB apart in relation to each other (although see the caveat below before you jump on any errors in my assumptions), ie:
Group . . . . . Qty . . . . . Shading (dB)
C2 . . . . . 1 . . . . . -18dB
C1 . . . . . 1 . . . . . -12dB
B2 . . . . . 1 . . . . . -9dB
A2 . . . . . 2 . . . . . -6dB
B1 . . . . . 3 . . . . . -3dB
A1 . . . . . 8 . . . . . 0dB (I’ve added the two 0dB groups together)
B1 . . . . . 3 . . . . . -3dB
A2 . . . . . 2 . . . . . -6dB
B2 . . . . . 1 . . . . . -9dB
C1 . . . . . 1 . . . . . -12dB
C2 . . . . . 1 . . . . . -18dB
Ignoring the symmetrical layout & combining group numbers for simplicity, this should result in the following:
Group . . . . . Qty . . . . . Shading (dB)
A1 . . . . . 8 . . . . . 0dB
B1 . . . . . 6 . . . . . -3dB
A2 . . . . . 4 . . . . . -6dB
B2 . . . . . 2 . . . . . -9dB
C1 . . . . . 2 . . . . . -12dB
C2 . . . . . 2 . . . . . -18dB
Factoring in series/parallel (S/P) combinations, I hope to achieve the following (once again, see the caveat below before you jump on any errors in my assumptions):
Group . . . . . Qty . . . . . Shading (dB) . . . . . Combo impedance (ohms)
A1 . . . . . 8 . . . . . 0dB . . . . . 4ohms (straight 1-2-4-8 parallel/series combo)
B1 . . . . . 6 . . . . . -3dB . . . . . 5.33ohms (3 paralleled sets of series-pairs)*
A2 . . . . . 4 . . . . . -6dB . . . . . 8 ohms (straight 1-2-4 parallel/series combo)
B2 . . . . . 2 . . . . . -9dB . . . . . 4ohms (parallel pair)**
C1 . . . . . 2 . . . . . -12dB . . . . . 16ohms (series pair)
C2 . . . . . 2 . . . . . -18dB . . . . . 16ohms (series pair)**
Or, when viewed in their groups:
Group . . . . . Qty . . . . . Shading (dB) . . . . . Combo impedance (ohms)
A1 . . . . . 8 . . . . . 0dB . . . . . 4ohms (straight 1-2-4-8 parallel/series combo)
A2 . . . . . 4 . . . . . -6dB . . . . . 8 ohms (straight 1-2-4 parallel/series combo)
B1 . . . . . 6 . . . . . -3dB . . . . . 5.33ohms (3 paralleled sets of series-pairs)*
B2 . . . . . 2 . . . . . -9dB . . . . . 4ohms (parallel pair)**
C1 . . . . . 2 . . . . . -12dB . . . . . 16ohms (series pair)
C2 . . . . . 2 . . . . . -18dB . . . . . 16ohms (series pair)***
* No, I’ve no idea if the B1 combo will naturally yield a group sensitivity that’s -3dB with respect to A1; that’s yet to be established & may need a little cut/boost if required. But I’m estimating that it’ll be close.
** B2 will require -3dB of extra attenuation to bring them to the -9dB target
*** C2 will require -6dB of extra attenuation to bring them to the -18dB target
I’ll add the group pairs as follows:
A1 + A1 = series (Z = 12 ohms)
B1 + B1 = series (Z = 9.33 ohms)
C1 + C1 = parallel (Z = 8 ohms) – this may require an overall C-group attenuation if the parallel-config’ raises the sensitivity, but I didn’t want to series them due to the 32ohm impedance that would result.
So, in essence, I’m hoping to achieve the shading for all six groups by running them in relative +-6dB pairs off three amplified channels, with a little extra attenuation where required.
HOWEVER, here’s the main caveat (and the point of my post’s question):
Am I correct in my assumptions about these combinations achieving a -6dB difference for each group pair? I’ve taken into account gain due to both current draw as well as driver numbers, rather than just driver numbers, so, looking at Group A for example:
Group . . . . . Qty . . . . . Shading (dB) . . . . . Combo impedance (ohms)
A1 . . . . . 8 . . . . . 0dB . . . . . 4ohms (straight 1-2-4-8 parallel/series combo)
Connected in series to:
A2 . . . . . 4 . . . . . -6dB . . . . . 8 ohms (straight 1-2-4 parallel/series combo)
Given that A1 has twice the drivers as A2, and that A1 will draw twice as much current than A1 (due to half the impedance), is it correct to say that the overall difference in sub-group sensitivities will be 6dB? Or will it only be 3dB? And does connecting them in series help/hinder this?
I hope that all makes sense; can anyone please assist me with this?
Thanks heaps!
Paul
Last edited:
On reflection, this question is a bit off-topic from my original question, so I've re-posted my question here:
http://www.diyaudio.com/forums/plan...o-far-ii-question-unresolved.html#post2315737
Thanks!
http://www.diyaudio.com/forums/plan...o-far-ii-question-unresolved.html#post2315737
Thanks!
Last edited:
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