Correction!
Whole story: Speaker Off Axis: "Correct" Driver Diameters for Great Off Axis Response - Acoustic Frontiers "ka" is pi (3.141) instead of 2 in my rule of thumb.
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Great you (peljani and kipman725) have been playing with Edge and discovered the horror which is going on between 2 drivers putting out the same frequencies.
But realize that:
- This goes on with every speaker with more then 1 driver.
- These are only cancellations or dips, no peaks.
- The horror is all happening in the vertical plane (when you stack drivers vertically), going to the ground (and ceiling is there is any). This all indirect sound and the dips change rapidly with frequency.
- The more drivers you use the more peaks you see when you simulate, but overal it is getting smoother; it important to see the ongoing trend.
- A line of many small drivers does work fine: The making of: The Two Towers (a 25 driver Full Range line array)
- If you use 1 tweeter and more then 1 mid driver, the tweeter will be putting out (# number of mids) times as power as the individual mids, at the crossover 'point'. (region)
A journey to beat the cancellations: Off-Axis Response | Beat Stamm
Sorry, but this not true, but it is a good practical guide that I use myself that I found somewhere on Linkwitz Lab - Loudspeaker Design
Whole story: Speaker Off Axis: "Correct" Driver Diameters for Great Off Axis Response - Acoustic Frontiers "ka" is pi (3.141) instead of 2 in my rule of thumb.
-----------------------
Great you (peljani and kipman725) have been playing with Edge and discovered the horror which is going on between 2 drivers putting out the same frequencies.
But realize that:
- This goes on with every speaker with more then 1 driver.
- These are only cancellations or dips, no peaks.
- The horror is all happening in the vertical plane (when you stack drivers vertically), going to the ground (and ceiling is there is any). This all indirect sound and the dips change rapidly with frequency.
- The more drivers you use the more peaks you see when you simulate, but overal it is getting smoother; it important to see the ongoing trend.
- A line of many small drivers does work fine: The making of: The Two Towers (a 25 driver Full Range line array)
- If you use 1 tweeter and more then 1 mid driver, the tweeter will be putting out (# number of mids) times as power as the individual mids, at the crossover 'point'. (region)
A journey to beat the cancellations: Off-Axis Response | Beat Stamm
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Not all speakers have these behaviours. If the drivers are close enough together at the crossover and relative phase of the drivers output is correct then broad on axis axis response without dips or peaks can be mentioned in both planes. However it requires a non traditional approach like a multiple entry horn, coaxial mounting or asymetric horns that can cross low in frequency.
Got a pair of RCF LF 15X401. Optically a bit beaten, the membrane on one is repaired, but the price was really OK and both measured well on the impedance curve. The short vent version is tuned a bit higher, so I need to have a look at the longer vent version, if the speaker will fit.
By the way, 18sound ND1480A, is any good?
By the way, 18sound ND1480A, is any good?
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I use the ND1460, and it's very good.
The -A at the end of yours indicates an aluminium diaphragm, and you want to avoid those. Titanium is tolerant to some abuse (which can happen in the PA world), while aluminium is not.
Chris
You can use Hornresp to find out:
1. Set the drive voltage to the maximum linear output of the cab
2. Calculate response
3. Change to looking at the vent output rather than combined
4. Apply high pass filter that is to be used using filter wizard
5. Look at the vent output particle velocity, the velocity that is objectionable is dependent on vent cross section and flare but under 17 m/s should be fine for a large vent.
My new sub design is using 200cm^2 but only has 8mm xmax drivers so probably with the RCF you might need a bit bigger to get the most out the box. Its all a balancing act though as the port can quickly get massive.
Here are some measurements of a 15" + 1" box: http://www.prodance.cz/protokoly/taurus_152-1_uprava_ladeni_megaton.pdf
What would be your opinion about this? I see some issues there - there are two dips off axis - but the directivity does not look too bad, does it?
I am not going to build these, but I would welcome any comments to learn what to look for in a good design. Prodance does measure everything they sell and even more, so it is a nice source of information for me.
What would be your opinion about this? I see some issues there - there are two dips off axis - but the directivity does not look too bad, does it?
I am not going to build these, but I would welcome any comments to learn what to look for in a good design. Prodance does measure everything they sell and even more, so it is a nice source of information for me.
Attachments
1-2 kHz is a pretty critical range to have a massive off axis dip in. The response is tilted the wrong way so equalisation will have to be used to avoid it sounding overly bright. Only 95dB/1W. Cumulative spectral decay shows evidence of resonances. As the drivers are stacked vertically the vertical polars will be the most distorted, however I think only the horizontal is shown.
Yes, only horizontal AFAIK. If I am correct, the directivity problem can be generalized to any 15" + 1" combo crossed this high.
Now I am looking at BMS4554. They seem really nice to me - and would work for my home horn system as well. I will compare them to my JBL2445s and the ones I will like more will be at home and the others will serve in the PA tops, most probably using JBL2380 (or 2385) horn. I have no objections to use these horns and even the 2445 can be equalized "PA flat".
Now I am looking at BMS4554. They seem really nice to me - and would work for my home horn system as well. I will compare them to my JBL2445s and the ones I will like more will be at home and the others will serve in the PA tops, most probably using JBL2380 (or 2385) horn. I have no objections to use these horns and even the 2445 can be equalized "PA flat".
The 15" is crossed so high that the cone is in breakup so directivity differs a bit from a piston, this is likely to be the case for all 15" drivers around 2kHz.
The BMS4554 looks great, very high efficiency and advertised low crossover point. I use a P-Audio BM-D466 (1.8kHz recommended crossover) which has the same voice coil size and run it down to 1.5kHz at 'war' volume by using a 4th order (electrical) crossover in my tops. It may be possible to run the BMS a bit lower if you also used a 4th order crossover. Only a bit though as excursion quadruples every time you half the frequency even ignoring horn cut off related issues.
The BMS4554 looks great, very high efficiency and advertised low crossover point. I use a P-Audio BM-D466 (1.8kHz recommended crossover) which has the same voice coil size and run it down to 1.5kHz at 'war' volume by using a 4th order (electrical) crossover in my tops. It may be possible to run the BMS a bit lower if you also used a 4th order crossover. Only a bit though as excursion quadruples every time you half the frequency even ignoring horn cut off related issues.
Already explained why 15"+1" (or 1.4" or 2") is a very bad idea.
If you setup the speakers just above head height, you only need little (5-10 degrees if you tilt the speakers forward so they don't wast half the output to the ceiling or sky) vertical off axis response and that matches what CD horns or line type tweeters will give you at their highest frequencies.
(60-90 degrees) Horizontal off axis response is needed to cover all ears and to get correct indirect sound (reflections) indoors.
Harmonic distortion when the power goes up is an other problem:
http://www.bmsspeakers.com/fileadmi...te/bms_4554_2011-04_hf_compression_driver.pdf
10W output results in 10 times more 2nd HD distortion and almost 100 times more 3rd HD compared to 1W.
(if I'm looking at 10dB/division as that info is left out.....)
How would this thing sound with 80W or even 450W
And what is the obsession with big mid drivers? They are made because people buy them, not because they are the best to use.
Same with high power drivers:
4x as much power - extra power compression is a lot less then +6dB in real life.
A second acoustically coupled and powered driver gives true +6dB and no increased distortion.
Using the criteria in the linked article the RCF tops crossing to the compression driver at 650Hz close to fine
(569Hz for ka=2). In fact I would presume that frequency has been selected to match the horizontal directivity of the horn....
But technology has moved on there are multiple compression drivers that can cross low whether coaxial or just large format. The PM90 top is another example of a point source top capable of more than 130dB using a low crossed compression driver.