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Compact PA - in a car handled by a single man.
Compact PA - in a car handled by a single man.
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Old 15th October 2019, 04:00 PM   #51
pelanj is offline pelanj  Czech Republic
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Here are some measurements of a 15" + 1" box: http://www.prodance.cz/protokoly/tau...ni_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.
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Old 16th October 2019, 09:47 AM   #52
kipman725 is offline kipman725  United Kingdom
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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.
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Old 16th October 2019, 10:19 AM   #53
pelanj is offline pelanj  Czech Republic
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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".
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Old 16th October 2019, 07:28 PM   #54
kipman725 is offline kipman725  United Kingdom
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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.
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Old Today, 01:41 PM   #55
Think is offline Think  Netherlands
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Compact PA - in a car handled by a single man.
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/fileadmin...ion_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.
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Old Today, 03:03 PM   #56
kipman725 is offline kipman725  United Kingdom
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Quote:
Originally Posted by Think View Post
Already explained why 15"+1" (or 1.4" or 2") is a very bad idea.
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....
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Old Today, 05:06 PM   #57
Think is offline Think  Netherlands
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Compact PA - in a car handled by a single man.
Crossing that low might only work at low power.


If you look at the classic 15"/6"/1" 3 way full range speakers, you see that they cross to the mid around that frequency.
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Old Today, 07:25 PM   #58
kipman725 is offline kipman725  United Kingdom
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Quote:
Originally Posted by Think View Post
Crossing that low might only work at low power.


If you look at the classic 15"/6"/1" 3 way full range speakers, you see that they cross to the mid around that frequency.
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.
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Old Today, 09:36 PM   #59
Think is offline Think  Netherlands
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Compact PA - in a car handled by a single man.
and you don't need subs, according tot the specs.


Those are awesome 2 way full range speakers using a 15" and a 1.4" Titanium Compression Driver, 4.0" v.c, giving up output above 10k. These specs are no indication for real world use / output power.

PM90? Please support a link.

Last edited by Think; Today at 09:41 PM.
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Old Today, 09:47 PM   #60
David Morison is offline David Morison  Scotland
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Quote:
Originally Posted by Think View Post
PM90? Please support a link.
New DIY Mid High (90deg) | Sound Forums
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