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Old 1st October 2013, 10:00 PM   #1
CyrusZ is offline CyrusZ  United States
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Default QSC 151 Amp Project

Hello, My name is Cyrus i have used this forum several times reading others threads and have a project of my own i wanted to ask some of the speaker design guys about.

I am a mobile event company mainly Dj live audio, rooms with 300-1300 guests and have several components to the sound system i like to interchangeably use depending on the room and event. For tops i normally run either QSC HPR12's or the EAW MK5264 15's at larger events. I have already built a pair of the TUBA30's with a single 12" lab sub in each, and love them but they are very specific in their application, i also have a pair of the Carvin 1801 active subs, and hpr181 subs and rent larger EV 18" subs for the larger gigs.

My project is to build a pair or 4 powered subs with the QSC 151 plate amp pushing 700w @ 4ohms. I have 2 questions to bounce off of you guys both on the enclosure design as well as the drivers to use. First for the enclosure i am going with a ported cab, i wanted to do a "clam shell" design with the 2 drivers pointed approx 45deg towards etch other like some of the EAW designs, i did want to do the design with a tight mouth like the EV's have done but it became very complicated and more of a band pass design. For my purpose i would like to get a bump in output which i have heard in this design, but i also want to make the speaker more compact. Can anyone contribute to how to calculate the angle to get a gain in performance? Also for port placement any suggestions, i am leaning towards a long slot vs a round pvc port again for compact size.



I have already settled on a using pair of 8ohm drivers wired in parallel down to 4ohm, for drivers i have come down to a few options i would like to ask about I have many more choices in the 15" flavor plus the dual 15's can push much more air than a single 18 while being smaller and more nimble for a tight punchy mid bass, but my original idea was a pair of dual 18" drivers.


The only 18" drivers i found that are in spec for this amp are the Peavy Black Widow 18" 8ohm @ 350w rms, these would pair up well but have a shallow xmas of 5mm

For 15" i have the $159 Celestion FTR15-3070C with a great xmas of 10mm but wants 400w @ 8ohm, these are the drivers used in the HPR subs to begin with but i have heard they want 100% of the rms wattage and then a little more to sound great which i can not provide to them.

The other driver is $300 RCF L15P530 15" with a respectable xmas of 6.5mm asks for 350w @ 8ohm, and RCF's already have a great reputation and even with 65% of the xmas of the Celestion a pair of the RCF's would displace more than 300% of the air the BW subs would.

For the speakers besides the cost jump i have been told that even though the Celestion's are a higher rated output speaker because i am running about 80% of the rated power i will get less than 80% of that output putting them inline with the RCF's or Black Widdows for sound output. Meaning i should settle on the RCF's.

Am i going down the correct path? Any suggestions?

Thanks
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Old 1st October 2013, 10:55 PM   #2
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The enclosed space in a "V" load can also be used as part of the port, as in the EAW SB1001 cabinet.
This type of enclosure can be modeled using Hornresp.

As far as speaker choice, using a plate amp with real power like the SP1-4000 or SP1-6000 would open up real possibilities.

I can attest to the fact that the Speakerpower plate amps work great even below 2 ohms, you could power a pair of dual eight ohm speaker cabinets with one amp.

Art
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Old 1st October 2013, 11:07 PM   #3
CyrusZ is offline CyrusZ  United States
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Those are sweet, remind me of some b52 subs that you would chain up a second sub to. The benefit to the QSC is the name of course and the price below $250. I may have to get one of those amps for my next project down the road.

For the V design that is one of the cabs i really liked the design of, i thought it was a sealed unit though. From the photos one version looks like a long slot vent down the long side of the enclosure not within the V though, the other photos i can gather that the vent is in between the speakers at the point of the V looking more like this:

___ ___
| \ / |
| \ / |
| | | |
|________|

I had briefly thought about that but thought it would cause a sweet spot in the curve and cancel out on both side of that frequency. Was i wrong?

Thanks for the help.
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Old 1st October 2013, 11:37 PM   #4
sine143 is offline sine143  United States
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cyrus, the president of speakerpower was the director of engineering at QSC for 11 years.

You seem to think that you want a speaker that will *Just barely* take 700 watts (or 350 watts a piece in your box). Truthfully, there is no downside to using speakers that can handle more power than this, as long as you dont make sacrifices in other areas (cost being the big one).

I havent done the math but I dont think that 1 rcf 15" will push "300% of the air the BW subs would" seeing as they have similar xmax (5mm vs 6.5mm) and the 18" has significantly more VD. Xmax is not really the determining factor when comparing speakers of differing sizes, VD (volume displaced at xmax, SD x Xmax x 2)
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Old 2nd October 2013, 12:01 AM   #5
CyrusZ is offline CyrusZ  United States
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so the speakerpower amps are probably the same design as the HPR/RMX amps that are so reliable hunh?


I have been told over the years several theories on matching amps to speakers, i currently subscribe to the idea that an amp should never put out less power than a speaker so you don't turn it up in turn risking cliping. My reasoning for the 350w rms is because the amp is rated 700w rms i am sure the amp goes above that as the speakers can take more at "peek level" It sounds like your suggesting that the 400w or even 500w speaker would still preform to maximum specs at 350w or am i reading that wrong?

the math i was doing was (xmas*SD)2=air moved.

RCF ((6.5mm*850cm)2)2 drivers)=11,050
BW (5mm*1240cm)2)2 drivers)=24,800
Cel ((10mm*850cm)2)2 drivers)=34,000

I think i messed up when writing the first post in my head i was thinking the pair of 15" Celestion's vs a single BW would be about 3 times the air moved, but did not type it that way sorry. it has been a bunch of numbers and comparing and about 3 different plans so far. My question would be more in the lines of your first comment about if i were to use a 500w speaker with 400w power wouldn't i get 80% of the rated output?
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Old 2nd October 2013, 04:05 PM   #6
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Quote:
Originally Posted by CyrusZ View Post
so the speakerpower amps are probably the same design as the HPR/RMX amps that are so reliable hunh?
My question would be more in the lines of your first comment about if i were to use a 500w speaker with 400w power wouldn't i get 80% of the rated output?
No, the Speakerpower SP1-4000 and 6000 plate amps are a new design from the ground up specifically optimized for sub use.
I blew up one of my QSC PLX-3602 while doing comparison tests to the SP1-4000 .

As speakers reach their power rating, the voice coils heat up, their impedance rises, and the amp delivers less power to them. Power compression can be 3 dB or more.
A speaker with a higher power rating can generally handle more power before thermally compressing.

Rather than think in percentages, it is easier to think in terms of dB, as we hear in dB SPL (sound pressure level).
It takes about a 10 dB change to sound twice as loud at 1000 Hz, but only 5 dB difference at 20 Hz to sound twice as loud.
A 3 dB change is the doubling of power, 400 to 800 watts, the change from 400 to 500 watts is only 1 dB, after power compression that one dB may not be detectable, except with a thermometer .

Two other details:

Xmas is short for Christmas, Xmax is linear travel.

Most speaker power ratings are now AES, which uses a band and dynamic limited pink noise with 6 dB crest factor, an RMS figure would use a sine wave signal which has 3 dB crest factor, the AES rating is half of what RMS would be.

Art

Last edited by weltersys; 2nd October 2013 at 04:07 PM.
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Old 2nd October 2013, 05:21 PM   #7
sine143 is offline sine143  United States
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Art, DOnt you mean the RMS is Half what the AES rating is?

and yes Arts right, this is not somthing that can be thought of in percents. Most of the *magic* happens as we go from 1 to 100 watts (100X the power in equals a 20 db jump in volume). to go up another 20 db (same increase in apparent volume) we would have to jump to 10000 watts input.

The best suggestion I can think of is to grab a copy of Win ISD (or horn resp if you are okay with a slightly hirer learning curve) and start modelling SIMPLE 1 driver sealed and vented alignments (either program will do this), so you can start to identify what specs are important to loudspeaker performance and how manipulating those specs will help you achieve desired performance.
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Old 2nd October 2013, 06:12 PM   #8
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Quote:
Originally Posted by sine143 View Post
Art, DOnt you mean the RMS is Half what the AES rating is?
Yes, Dog Nabit .

1000 watts AES = 500 watts RMS.
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Old 2nd October 2013, 06:23 PM   #9
sine143 is offline sine143  United States
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hehe, no worries. almost second guessed myself though lol.
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Old 8th October 2013, 05:38 AM   #10
CyrusZ is offline CyrusZ  United States
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Thanks for the info, can i keep calling it xmas just for the fun of it?

I downloaded a couple applications and began to play with them but i am having trouble, the last time i did any speaker design was 10 years ago and with Blaubox for car audio, i thought i could jump back in but seem to have forgotten a bunch (or i never new it)

i will need to save up the cash to try one of those plate amps, they sounds impressive.

With WinISD i keep getting errors, i will input the T/S numbers i have available, it will "compute" or estimate a few others but then when i click save it kicks me back and pops an error up.

So i tried Hornresp as suggested and wow that was daunting, i am still working though the tutorial on line to try and get a design out of it.
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