Melded piezo array for a direct drive (non-horn)

[szantog]

Hello,

i don't have proper measurement tools here, so i'd like to order a prebuilt tweeter array from speakerhardware.com. But i don't know how many piezos do i need, please help:

- The mid speaker i plan is a Kappalite 3012HO, which plays around100-101 db in the mid range.

- I play electronic music most of the time, and for example the trance genre sound is not really good with horn mids in smaller venues. So i will drive the Kappalite in a simple bass-reflex box (and of course a separate sub). This genre also needs tweeters with "low effort", mild load on tweeters helps a lot.

- So, how much piezos do i need to reach 100-101 db sensitivity for a melded array, and handle the Kappalite's power range (3" coil, 400W RMS) with ease? Even if the DJ cranks up some stupid effect, resulting a total 400W load on the tweeters? (I know to increase SPL for piezos you need to connect them in parallel, while series connection improves power handling capability.)

I'm using piezos at least 20 years now, but never in an array, and here are my techniques to make them sound a LOT better:

- Put cotton wool behind the piezo ceramic (if the model has a small chamber behind it).
- Whip round the entire horn with some heavier cord, to reduce the plastic's resonance.

With these techniques i was able to match clarity of some average HiFi domes when played with low volume. But i also wonder if somebody knows how the SPL changes if you completely remove the horn and build the drivers directly into an L-shaped something to form a melded horn? Theoretically, removing the resonating horn and the small "phase chamber" in front of the resonator paper improves quality, no?

Thanks for any replies in advance.

Gábor

[Bruce Weldy]

- I play electronic music most of the time, and for example the trance genre sound is not really good with horn mids in smaller venues.

First of all, welcome to the forum....now on to the above issue.


Huh???

Sound is sound. What gets delivered is what's important, not how it's delivered. If a horn sounds better - it sounds better. Doesn't matter what type of music you are putting to it.

I think you are making a huge, unfounded, and uninformed assumption here. Why exactly do you think a horn is not good for your music in a small venue?

The driver you want to use would be outstanding in an OT12 or a Jack 12. Then you would know the proper number of piezos to use in the appropriate array.

[szantog]

Sound is sound. What gets delivered is what's important, not how it's delivered. If a horn sounds better - it sounds better. Doesn't matter what type of music you are putting to it.

A mid-range horn adds some color to the sound. Or at least all mid-range PA horns i listened so far in the last 20 years. For me that color is not preferred, but i really don't know how to build horns so i wonder what adds that specific sound? Too much compression or something else?

[Bruce Weldy]

Sound is sound. What gets delivered is what's important, not how it's delivered. If a horn sounds better - it sounds better. Doesn't matter what type of music you are putting to it.

A mid-range horn adds some color to the sound. Or at least all mid-range PA horns i listened so far in the last 20 years. For me that color is not preferred, but i really don't know how to build horns so i wonder what adds that specific sound? Too much compression or something else?

hmmm....I guess all enclosures add color to sound....the question is what you use for a baseline. Personally, after years of direct radiators - I love the midrange of the OT12 cabinets. Vocals are very warm and clear.

Just loaned my 4-OT12 to a band that had blown up their 15"/CD direct radiator cabinets (I went along with the deal to run sound - wasn't going to let 'em blow up my stuff) - they were very impressed with the vocals compared to their old boxes and started talking about me building 'em some.....(yeah, right)

If you'll list your location in user settings, maybe someone nearby can let you come listen to their boxes for a comparison.

[szantog]

Sure, all PA cabs are having some color, and for my genre the "direct color" is the best, with 12" mids or even smaller (not even a 15").

I understand and agree that for live music the horns are the best, but I'm going to build a small, really portable system mainly for indoors and electronic music DJ usage.

I updated my location - I don't think there are any BFM gear nearby.

[Bill Fitzmaurice]

I updated my location - I don't think there are any BFM gear nearby.

http://billfitzmaurice.info/forum/viewtopic.php?t=9828

[wallywally]

I would use the array from an OmniTop12 or Jack12 (12 or 14 piezo's if melded). Either one will keep up fine. You may want to experiment with either of those cabs loaded with the 3012ho and see if you can EQ it to your taste (they are not much more difficult to build than a bass reflex / direct radiator box).
The difference you hear is likely higher levels of harmonic distortion from the direct radiators, this distortion colors the sound. Horns filter out much of this distortion and lack that coloration.
IMHO the purpose of a PA system is to reproduce and amplify the signal without coloration. If coloration is desired it should be accomplished before the main PA.

Most people on this board have used direct radiator cabinets for years. Most that respond have also built 1 or more of Bill's designs and are "converted" to horn loaded / line array designs.

[szantog]

You guys convinced me and i'm going to build a pair of OmniTop 12. I need to solve the "sub" problem tough. A pair of Omni will take a lot room from my car, and i'm afraid a Tuba 24 will not be enough for the low end.

[szantog]

I had the opportunity to experiment a little with some piezos using a really flat response electret mic. Of course i know i'm not the first, but here are my results:

- Tested 2 different piezos with (on paper) different capabilities, identical looking to the Monacor products, but not the same factory i think. MPT 005 and MPT 165 clones.
- Frequency responses are different, but still looking identical for both models.
- The "motor" is exactly the same in them, despite of the different specs on paper. All motors produced the same curve if the horn was removed.
- If you remove the horn, the spl change is around -6 decibels.
- If you remove the "whizzer paper" from the crystal, the spl change is an additional -18 db, so totally useless.

When i removed the horn, i thought the sound quality will be better due the less chambers around the "motor". I was totally wrong, the quality is the same, but you need to use 4 times more piezos in this case.

I wonder if these results are identical to yours dear forum members?

[szantog]

I did something wrong (i was running the piezos on separate channels and the power wasn't equal), and i also listened the speakers more.

Here is the plot, red is without horn, green is with horn. They still sound quite identical, but the 5 kHz dip and the less output over 14 kHz is clearly audible for the horn. The 5k dip is also responsible why it appears to be louder.

Maybe it's safe to say that only twice as more horn-removed drivers are needed for the same spl, with better response/sound?

[spl][/spl]