New DIY Mid High

May 8, 2011
891
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Australia
#1
Specifications (best guess)
  • 100Hz – 20KHz +/- 1.5dB approx.
    • Ignore the frequency response below about 400Hz. I don’t have a decent space to measure this speaker in. There was also a double 18 used below 100Hz
  • Weight - 32Kgs
  • Size - 930-H x430-D x 385-W mm
Low Mid
  • 100Hz – 630Hz
  • Efficiency -105 dB w/m approx.
  • Power 1300 Watts continuous – 2600 watts program
Hi
  • 630Hz – 20kHz
  • Efficiency –112 dB w/m
  • Power - 230 Watts continuous 1300 Watts peak
If anyone is interested I will post some more information when I have time.
 

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May 8, 2011
891
31
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Australia
#5
Re: New DIY Mid High

Hi Peter,
630hz seems an unusually low x-over point in a 2 way box. What are you using for the hf driver? Looks good on paper. How does it sound?
I used a BMS 4594HE with an RCF HF950 horn and 2 x RCF MB12N351s. You could use the MB12N405 for a bit more power but it makes the box a bit heavier than I wanted. The 12's are on a folded or bent and ported horn about 2ft (600mm) long.

The HF950 horn flare has a 400Hz cut off frequency and a 300 x 300mm mouth. The mid horn(s) exit above and below the HF so that the spacing will provide some directivity control just as it does with your Flex array but in the vertical plan. The dual diaphragm concentric compression driver can easily operate down to this frequency.

Think in terms of the Flex Array in point source mode with a 90 x 50 horn pattern, using a similar HF / VHF combination and crossover frequencies, and two fully horn loaded 12" drivers instead of the 10's.

"How does it sound?" - It sounds like the best studio monitor you have ever heard. The vocal are so clear and it goes loud. Everyone that has heard it comments about the clarity and that they can hear things in their favorite music they have never heard before.

Processing is Lake FIR. I don't think you need to use the lake, but it won't be able to make a square wave without it. I did the square wave just to see if I could ... and it will do a resonable square wave from 300Hz to 3kHz.

When I have a moment I will post some pictures and some hornresp sims which I have compared it to an EAW KF850 - the idea was the output of an EAW KF850 but with a speaker on a stick. It needed to be a useful size and weight and look good.

At this stage the plots are just the prototype, but I thought some people may be interested.
 
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May 8, 2011
891
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28
Australia
#7
Re: New DIY Mid High

What did you use for a crossover?
I used a Lake LM26. The system with subs was running 4 way so you need two of them.

BMS however make a nice simple passive crossover for the HF/VHF. The drivers all have excellent frequency responses and need very little DSP correction. The mid horn has a peak at around 400Hz and needs a little boost at 85Hz; provided you don't want to make square waves I think you will get away with a simple three way DSP crossover.

The BMS 4594 nd HE is probably the best compression driver money can buy. It sounds fantastic. Being able to go down as low as 600 Hz or lower solves so many design issues; it allows the 12's to operate fully in their piston range and you have a true point source above 600Hz.
 
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Apr 21, 2014
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#9
Re: New DIY Mid High

BMS coax CD is great. Does anyone know why none of "big" speaker manufacturers isn't using it in their products? The only two I know are Coda and JTR and both are relatively obscure.
 
May 8, 2011
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Australia
#10
Re: New DIY Mid High

BMS coax CD is great. Does anyone know why none of "big" speaker manufacturers isn't using it in their products? The only two I know are Coda and JTR and both are relatively obscure.
Add to the list EAW and Danley. I think Coda are using the line array version in their ViRay.

The one I'm using is the HE version with a modifed phase plug and shorting rings for reduced distortion.

Peter
 
May 8, 2011
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28
Australia
#13
Re: New DIY Mid High

Here is my best guess at modelling what’s in an EAW EAWKF850 Low (15”) and Mid-section (10”) and a Danley SM80 (bottom). The DIY double 12 is the dark trace.

They are all at their RMS continuous power level. Hornresp models things as a perfect piston so there will be a lot more HF in the real speaker. I’m sure they are not perfectly accurate but it should give some idea of what to expect from the double 12 in comparison. (all modelled in full space 4-Pi) For example if you model the 850 low with more volume behind the driver you will get more LF extension but less output around 100Hz.

There is also a picture of the prototype ... it still need quite a bit of work, a front grill and some fly track etc. etc. etc.
 

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Mar 3, 2011
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Germany
#15
Re: New DIY Mid High

Congrats on your design.

On the RCF HP I can see no fins on the 950, did you modify the horn?

And I really would like to see some off axis responses, especially vertical ( I know... :blush: )


Uwe
 
May 8, 2011
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31
28
Australia
#16
Re: New DIY Mid High

Congrats on your design.

On the RCF HP I can see no fins on the 950, did you modify the horn?

And I really would like to see some off axis responses, especially vertical ( I know... :blush: )


Uwe

Hi Uwe,

The horn is a standard HF950. RCF's picture doesn’t really show the guide veins (fins) in the throat. The HF 950 with a BMS 4594 measures very much like RCF’s spec sheet in terms of directivity.

I actually did some very rough modelling before I built the proto type. It turned out as expected; the two MF horns exits act as a dipole keeping the vertical pattern around 50 degrees at the crossover point, slowly becoming wider as the frequency decreases. There is good control down to about 300Hz. The issue is the HF horn only maintains its pattern control down to about 1.5Hkz to 2.0KHz at which point it becomes a bit wide, as you would expect having a height of 300mm.

There is no other HF horn that I could find that did any better and still be able to fit into a reasonable size box ... many actually exhibited the classic pattern flip below about 1.5 KHz.
e.g. http://www.eighteensound.it/PRODUCTS/Products/CatID/5/ProdID=180#.VH7dfWkbrq4

RCF use the HF950 in their new TT5a which is crossed at 650Hz. I would expect the HF directivity to be very much the same. The width of the box will probably mean it has similar horizontal dispersion to the TT but vertically it will be somewhat narrower below 600 Hz. I have drawn what I expected in red on the TT5a directivity plots.

My very rough measurements so far seem to confirm this.
 

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May 8, 2011
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Australia
#17
Re: New DIY Mid High

Here are some quick directivity measurements. Ignore the lumps and bumps especially in the horizontal (lower traces) frequency response. I had to put the speaker on a sub that was a bit close to the ground and there were some reflection issues.


As you can see, the directivity is more or less as I had previously indicated. The horizontal pattern is as good as it get (top traces) and vertical pattern is nominally -6dB at 50 degrees but blows out to 100 degrees or more at around 900 Hz.

At the moment the crossover slope between the Mid's and Low's is about 140 dB per Oct. I suspect if I reduce it to 24dB per octave it will improve the directivity a little between 500 and 800 Hz.
 

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Mar 3, 2011
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Germany
#18
Re: New DIY Mid High

Here are some quick directivity measurements. Ignore the lumps and bumps especially in the horizontal (lower traces) frequency response. I had to put the speaker on a sub that was a bit close to the ground and there were some reflection issues.


As you can see, the directivity is more or less as I had previously indicated. The horizontal pattern is as good as it get (top traces) and vertical pattern is nominally -6dB at 50 degrees but blows out to 100 degrees or more at around 900 Hz.

At the moment the crossover slope between the Mid's and Low's is about 140 dB per Oct. I suspect if I reduce it to 24dB per octave it will improve the directivity a little between 500 and 800 Hz.
Thanks Peter,

IMO the vertical directivity behaviour becomes more obvious when flying the speakers.
More overlap in the crossover region is one tool, but puts more stress on the BMS driver. One of my 4592 midranges was killed with 24dB HP at 1k, and my low-mid section ( 2x 15") is way less powerful ( about 100dB sensitivity ).

Did you try to build the low-mid section the other way round, so that they become one horn ?
 
May 8, 2011
891
31
28
Australia
#19
Re: New DIY Mid High

Thanks Peter,

IMO the vertical directivity behaviour becomes more obvious when flying the speakers.
More overlap in the crossover region is one tool, but puts more stress on the BMS driver. One of my 4592 midranges was killed with 24dB HP at 1k, and my low-mid section ( 2x 15") is way less powerful ( about 100dB sensitivity ).

Did you try to build the low-mid section the other way round, so that they become one horn ?
Hi Uwe,
Firstly thankyou for you input, its helping me improve this design.

I am going to have a play with the crossover frequency and try some at 48dB and 24db per octave slopes and see if I can get an improvement.

Very few speaker manufactures publish this type of information. JBL have a new Precision Directivity installation range. Below are the PD6212/95 frequency response plots …. So I don’t think I’m doing too bad :)~:)~:smile:, but hopefully with a bit of work I will be able to do better.

Did I look at building the mid-section the other way around – yes, I looked at every combination I could think of. There a couple of my idea below.
The design criterion for this box was a speaker on a stick that had almost as much output as an EAW 850. It didn’t need to go quite as low as the 850 but it needed to go down to 100Hz. The problem with every other option I considered is that the box starts to get too big and heavy.

This design has more or less no wasted space or weight. If you didn’t have the size and weight compromise it would be easy to build something like a Danley synergy horn.

 

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May 8, 2011
891
31
28
Australia
#20
Re: New DIY Mid High

Hi Uwe,

I am going to have a play with the crossover frequency and try some at 48dB and 24db per octave slopes and see if I can get an improvement.
I tried a new (rough) crossover setting use 24dB octave slope at 650 Hz to see if this idea would work ... looks quit good now :)~:)~:smile:

The plots are - 0, 10, 20, 30 & 40 degrees below the axis.
 

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