Double 10 and Horn

[Bennett Prescott]

Bennett - is there a good way to explain the model numbering system at B&C? PM or email me if you'd prefer.

Hey Max,

Sort of, but we try and avoid drawing too clear a link between a series and some intended application since we see all sorts of "unintended" applications and don't want to pigeonhole. You've got the right idea from the website. I normally suggest to OEMs that they let me know their application and I can make a suggestion using a combination of my ruthless intellect, crystal ball, and what I've seen someone else succeed with. So little about transducer behavior can be determined from T/S parameters, you can get in the ballpark but until you turn it up in your prototype box it's a crapshoot. On paper we're just another transducer supplier, eh? You're more than welcome to email me if you have some specific questions. [email protected]

 

[Carl Nygren]

Hi,
I've been reading through both of the DIY Mid High threads and got really tempted to build the 90-version. When I found the threads I couldn't stop reading, learned a lot. But as of now, I really don't need that output. I also prefer a more compact system knowing that I not always have access to suitable transport vehicle. Thats why I think I'm going to build this D10Horn with components:

BMS 4594HE
RCF HF950
B&C 10NDL64

I have a db-mark xca 48, but need new amplifiers. Thinking go passive xo for the coax to save money at first, then might buy another amp for tri amp. I've also considered using MiniDSP PWR-DSP3 to get full active box but haven't found any pro audio usage of them.

Carl

 

[Max Warasila]

Peter,

I'm about to build some of these, and was wondering what your thoughts on using the B&C 10MBX64 in this cabinet would be? I figure it might be prudent to tune it a little higher, but other than that, it would certainly be more capable of keeping up with the BMS driver than the 10NDL64.

Thanks in advance!

 

[Peter Morris]

Peter,

I'm about to build some of these, and was wondering what your thoughts on using the B&C 10MBX64 in this cabinet would be? I figure it might be prudent to tune it a little higher, but other than that, it would certainly be more capable of keeping up with the BMS driver than the 10NDL64.

Thanks in advance!

I did a quick sim on the 10MBX64 - it looked like it would work very well; and I would tuned it a little higher as you suggested.

The trick is being able to cross over to the horn at a low enough frequency so that the two 10's act as one driver.

 

[Mark Wilkinson]

The trick is being able to cross over to the horn at a low enough frequency so that the two 10's act as one driver.

Hi Peter, this (among many things is something I've yet to understand.....

I've heard 1/4 wave center-to-center spacing needs to be maintained, and I guess this makes sense looking at summation on the phase wheel.

But this seems to imply much lower x-over frequencies than seem possible.
I mean, say a pair of 10" drivers can be spaced 10" center-to-center.
10" quarter wave should = about 340Hz.
What horn can reach there?

My understanding has to be whacked....
What is a good rule of thumb here ?

thx! Mark

 

[Rob Timmerman]

Maximum driver spacing for coherent summation depends on how far off-axis you care about coherent summation. If you can tolerate some cancellation off-axis (or perhaps you'd like some LF pattern control), spacing the drivers up to a half wavelength or so apart works fine. That brings the summation point for drivers 10" apart up to ~700hz, or doable with reasonable horns.

 

[Peter Morris]

Maximum driver spacing for coherent summation depends on how far off-axis you care about coherent summation. If you can tolerate some cancellation off-axis (or perhaps you'd like some LF pattern control), spacing the drivers up to a half wavelength or so apart works fine. That brings the summation point for drivers 10" apart up to ~700hz, or doable with reasonable horns.

Exactly ... and the double 10's are crossed at 650Hz ... that gives good matching vertical directivity at the crossover point between the 10's and horn etc.

 

[Mark Wilkinson]

Ok, is it just a matter of some triangulation for the wavelength in question ? ....the path length difference to acoustic centers at whatever angle and distance to the speaker, placed on the phase wheel ?

If it is, I'm really pissed at myself for how long it's taken me to see something so simple ...lol

 

[Martin Adams]

Hi Peter,
I plan to build this one and simulated 2x 10ndl64 in a vented enclosure to get a better understanding. Why do you suggest 40l/65Hz when crossover will be around 100-120Hz? Wouldn‘t it make more sense to use say 50l/80Hz to get more out of it at 100-120Hz?

 

[Peter Morris]

Hi Peter,
I plan to build this one and simulated 2x 10ndl64 in a vented enclosure to get a better understanding. Why do you suggest 40l/65Hz when crossover will be around 100-120Hz? Wouldn‘t it make more sense to use say 50l/80Hz to get more out of it at 100-120Hz?

Hi Martin,

This is what I get when I compare the two alignments - I have set the Vc temp rise to 50 degrees C and Ql (boxes losses) to 15.

The red curve does what you said, but the peak around 90Hz is cause by resonance and the box / alignment will sound boom-y.

The yellow alignment looks good and should sound great - (at all Vc temps and box loss settings).

 

[Martin Adams]

Hi Peter,
you're right, it looks to be boomy, I've ignored temp rise and box losses and looked at it with HP set to 100Hz, so it looked quite OK

 

[Peter Morris]

Hi Peter,
you're right, it looks to be boomy, I've ignored temp rise and box losses and looked at it with HP set to 100Hz, so it looked quite OK

I'm sure you know this, but if you have an alignment that sounds boomy because of a resonance below the HP filter setting like this, you will still hear the resonance, it won't be as bad but it will still be there.

 

[Martin Adams]

Thanks Peter, got it
Do you have a polar map of one of your builds? I would like to see how smooth it is around 650Hz with the suggested low crossover frequency...

 

[Peter Morris]

Thanks Peter, got it
Do you have a polar map of one of your builds? I would like to see how smooth it is around 650Hz with the suggested low crossover frequency...

No I don't have any polar info on the double 10. To me almost all speaker + horn-at-the- top designs have issues at the crossover point. In this case being able to cross over at 650Hz minimises the problems at the crossover point and the coupling of the two 10" drivers.

Basically it a compromise between these issues and finding a practical solution to get the HF horn above the audience without having to fly the box.

I'm actually thinking about building a double 10 design based on my double 14's - their performance through the crossover region is almost perfect.

 

[Martin Adams]

A friend of mine is an experienced designer of horn systems and he explained to me that using a HF horn at frequencies that low (in relation to the horn specs) results in a bad vertical directivity in that frequency band. I've also found this behaviour in the RCF sheet for the ART745a using also the ND950 and 650Hz crossover (see http://www.rcf.it/de_DE/products/pro-speaker-systems/art-7-series/art-745-a / spec sheet / second page bottom right 700-1.200 Hz). Did you ever realize/recognize that issue (particularly indoor)? This also means that the driver needs to "throw out" a lot of acoustical power (same level on axis with broad dispersion means more energy) at that band...

 

[Peter Morris]

A friend of mine is an experienced designer of horn systems and he explained to me that using a HF horn at frequencies that low (in relation to the horn specs) results in a bad vertical directivity in that frequency band. I've also found this behaviour in the RCF sheet for the ART745a using also the ND950 and 650Hz crossover (see http://www.rcf.it/de_DE/products/pro-speaker-systems/art-7-series/art-745-a / spec sheet / second page bottom right 700-1.200 Hz). Did you ever realize/recognize that issue (particularly indoor)? This also means that the driver needs to "throw out" a lot of acoustical power (same level on axis with broad dispersion means more energy) at that band...

He is correct of course, but it’s not that simple, the trick is to match the directivity of the horn to the low frequency drivers at the crossover point. As with most things it’s a compromise.

FWIW RCF uses the same horn and crossover point in this box.
http://www.rcf.it/products/touring-and-theatre/tt5-a

If you have a look at the directivity plots of the TT5a what you will see is that the vertical control starts to collapse at around 2kHz.

If you crossed this horn over at somewhere between 1K5 and 2kHz all would be good regarding the horn directivity (in isolation) BUT the two 10” drivers would not combined very well, there will be problems associated cancelation between each of the two 10’s, and 10’s and the horn vertically. This occurs because of the different path lengths to the listener as you move up and down vertically.

If you can keep the 10” driver(s) and the horn all within ¼ of a wavelength at the crossover there would be no issue with the off axis response but in practical terms that is too low for the horn to work; if you can get close to ½ a wave length then it’s not too bad … ½ a wave length at 650Hz is 261mm, more or less the spacing of the 10’s and horn - in practice it seems to work

The cost of crossing so low is that the horn does not load the compression driver very well at the lower frequencies, so you need a large robust compression driver capable of substantial output to keep up, hence the BMS. The RCF 950 or one of the new B&C drivers with 4" diaphragm would also work.

 

[Martin Adams]

Thanks, Peter, for the quick response. As you say, it's always a compromise and listening to you and this friend of mine I get the impression that it also depends on personal experience and preferences - it's hard to decide for me what is best for my planned usage As I have 2x ND950 and HF950 (for my planned PM90) I will build two 2x10 tops and listen (and measure as much as I can with my limited equipment) to both options (crossover at 650hz and around 1.2khz)...

 

[Peter Morris]

Thanks, Peter, for the quick response. As you say, it's always a compromise and listening to you and this friend of mine I get the impression that it also depends on personal experience and preferences - it's hard to decide for me what is best for my planned usage As I have 2x ND950 and HF950 (for my planned PM90) I will build two 2x10 tops and listen (and measure as much as I can with my limited equipment) to both options (crossover at 650hz and around 1.2khz)...

Hi Martin,

The first version of the double 10 used a 1.2khz crossover with an EV HP94 horn, an RCF N850 compression driver and 2 x 10" ceramic magnet drivers. At this crossover frequency the two 10" drivers did not play that well together.

In the next version used an 18sound NSD1480, neodymium 10" drivers and crossed at 900Hz and used FIR filters. This was an improvement.
http://www.eighteensound.com/Product.../3361/nsd1480n

The current version is a big improvement, louder and clear than ever.

Also FWIW the BMS4594HE does sound better than the ND950 ... but at the price it should. I will be very interested in how you go with the ND950, as I guess I would try crossing at 700Hz - please let us know how you get on ;-)

Just to give you an idea of the pattern control achieved with the double 14" I mentioned, here is a picture on axis, 45 degrees horizontally off axis and 20 degrees vertically off axis - crossover 630Hz.

Below 200hz the ground and near by building were starting to impact the measurement

 

[Hiep Nguyen]

Peter,
What is the benefit the horn/driver on its own chamber vs share with the 2X10?

 

[Peter Morris]

Peter,
What is the benefit the horn/driver on its own chamber vs share with the 2X10?

In the case of the double 10" it was just to reduce the box volume to get the T/S alignment correct. In the case of the double 14" I mentioned, it was to stop standing waves and reflections off the back of the horn. It was also was to get the volume and tuning of the front chamber correct.

If the box volume was correct in the original double 10" I would have had the horn and the two 10's in the same chamber.