Question for Art: If I were to pull the speakers out of the keystones and put them into a properly ported front loaded box how many db would I be giving up? I'm trying to understand both questions of how the keystones are so efficient and why ported boxes don't put out the same db. Hard to understand why manufacturers would take advantage of the horn loaded cabinet power. maybe cost of manufacturing is the killer. keystones aren't kid stuff to build for sure.
Yeah, different subs will have different phase responses. the SRX728s are vented subs and the Keystones are THs, which should have a phase response similar to a series-tuned 6th order BP within the passband (and very horrible phase response outside the passband - don't go there!).
According to my Hornresp sim, the phase response of the Keystone design hits 180 degrees out of phase around 70 Hz - maybe there's a connection between this and what you heard when the subs are all played together?
According to my Hornresp sim, the phase response of the Keystone design hits 180 degrees out of phase around 70 Hz - maybe there's a connection between this and what you heard when the subs are all played together?
The Keystones are a bit like series-tuned 6th order bandpass alignments. There's a bit of gain within the passband, but their usable passband is narrower, compared to a vented alignment, and the boxes are larger. As with all 6th order BP designs, the more gain you get in the passband, the narrower the usable passband. With amplifier power so cheap these days, and drivers that can take higher power being readily available (albeit for higher prices). it's tougher to beat the Plain Jane vented box, particularly if you opt for a type of "big vent reflex" alignment, giving up some passband width in exchange for less problems with vent compression at higher power levels, but then of course you'll be ending up with a bigger box too. I've recently completed such a build (an ODTL)and compared its output to a TH I built for the same driver many years ago, with a similar Fb. The new build gives up 2dB for a notceably wider usable bandwidth. Even more interesting is that if I'd made the ODTL box a bit wider, making its volume a bit closer to that of the TH, output at Fb would have been more than the TH.
The Keystone is about 6 dB more sensitive than a ported box with the same Fb.
https://www.diyaudio.com/community/threads/tapped-horn-vs-bass-reflex-case-study.184992/
I've measured the 2x18" 4 ohm JBL SRX728 as very close in sensitivity to a single Keystone loaded with a BC18SW115-4.
The phase difference between the TH and BR will only allow alignment at either the top or bottom of the sub range unless you use FIR filters, which would require more latency than would be acceptable for most live gigs.
The above phase charts are a bit off, due to the SMAART auto delay finder choosing 4.48ms different times (in retrospect should have used the same time, live and learn..) but gives an idea of the relative phase difference.
I'd suggest crossing the JBL SRX728 lower if you put them on an aux, they have less top end and more bottom end.
Your B&C 18TBW100-4 should be slightly more sensitive than the BC18SW115-4, and has more Xmax than the JBL-2268's 8mm Xmax/23mm Xlim, so will go a bit louder given similar power.
I'd suspect that much of the level difference you found is due to the Crown I-T6000 input sensitivity ranging from 1.4V to 7.75V, while the NX-6000 takes only .775V (0dBu) for full power.
Art
Just a quick question regarding the limiting on these subwoofers. I'm running 4 of these cabinets loaded with b&c tbw100@8ohm. One pair of cabinets is powered by a matrix xt7000mf, one cab pet channel. The other pair is run on an admark ad42, one cab per channel. All of this is controlled via a t. Racks 408, I've had issues in the past with the drivers getting toasty and dialed back the compressors but had problems with overall volume. Looking at my settings, I've realized I didn't know anything about the compressor and set it up totally wrong, currently the attack is set at 1ms and release at 1000ms with the voltage set to around 97v. Your first post mentions a 500ms time constant, is this in reference to the attack time? Also If so, if I set it slightly conservatively at 450ms attack and 1500ms release and 77v, would this be a safe bet and give us a little more Just a quick question regarding the limiting on these subwoofers. I'm running 4 of these cabinets loaded with b&c tbw100@8ohm. One pair of cabinets is powered by a matrix xt7000mf, one cab pet channel. The other pair is run on an admark ad42, one cab per channel. All of this is controlled via a t. Racks 408, I've had issues in the past with the drivers getting toasty and dialed back the compressors but had problems with overall volume. Looking at my settings, I've realized I didn't know anything about the compressor and set it up totally wrong, currently the attack is set at 1ms and release at 1000ms with the voltage set to around 97v. Your first post mentions a 500ms time constant, is this in reference to the attack time? Also If so, if I set it slightly conservatively at 450ms attack and 1500ms release and 77v, would this be a safe bet? Would I benefit from a longer release time?
Watafu,
The 500ms time constant mentioned in post #1 was for long term "RMS" limiting, attack or release.
450ms attack and 1500ms release at 77v should be in the ballpark for long term "RMS" limiting for a B&C TBW100@8ohm.
This PDF goes into detail as to the difference between peak and long term thermal limiting:
https://www.powersoft.com/wp-content/uploads/2019/01/powersoft_TN009_LimiterSetup_en_v1.0.pdf
The 500ms time constant mentioned in post #1 was for long term "RMS" limiting, attack or release.
450ms attack and 1500ms release at 77v should be in the ballpark for long term "RMS" limiting for a B&C TBW100@8ohm.
This PDF goes into detail as to the difference between peak and long term thermal limiting:
https://www.powersoft.com/wp-content/uploads/2019/01/powersoft_TN009_LimiterSetup_en_v1.0.pdf
Thanks for the information there, put it to good use over the weekend at 2 seperate gigs and its completely changed how the system sounds! We ran the system fairly hard the entire time and even through a couple of jungle sets, the drivers where only marginally getting warm. Compared to the previous gigs, the bass was just never there properly leading us to driving everything harder and the drivers themselves getting insanely warm! Cheers again welter!
I use a t.racks 408 to run the system, brilliant bit of kit and I can't recommend it enough! I ran a tone generator at 60hz sinewave from the laptop into the mixer, maxed out the inputs then dropped them back a touch so nothing was clipping. Depending on what country your in, you need to check what the mains actually outputs, in the UK it's 230v 60hz so that sinewave gives me the most voltage. Then measured the output with a voltmeter hooked up to an nl4 on the output side of the amplifiers. Then it's just a case of setting the attack and release settings kicking the limiter threshold down till your getting the voltage you want, then repeat for the compressor. I don't doubt I've done something wrong or I can improve the process somehow but it seems to be consistent and works well.
Usually we don't use FIR processing for subs, at least for live gigging, as the latency penalty gets excessive.
For mids and highs, or where the time penalty is not relevant such as in a home listening setup, there can be significant improvements in sound quality with a well set up FIR filter.
(For anyone not already aware, with FIR processing, the lower in frequency we operate, the more "taps" are required in the filter which means it takes longer to pass the signal through.)
For mids and highs, or where the time penalty is not relevant such as in a home listening setup, there can be significant improvements in sound quality with a well set up FIR filter.
(For anyone not already aware, with FIR processing, the lower in frequency we operate, the more "taps" are required in the filter which means it takes longer to pass the signal through.)
Concert over so I thought I would post my findings. I ended up putting the keystones center clustered laying down on the floor in front of the stage with a couple of fills on top. The JBL's were stacked like the picture with three tops on top of two subs. Of course I had to invert the phase on the keystones. We played with various crossover settings but what I found out was that I no longer heard any weird noise anomalies once I got the keystone's away from the JBL's. I ended up turning the keystone's down 9 dB to get the volumes relatively the same as the JBL's. The general consensus from the sound men that were there was that the keystone's blew away the JBL's. The amount of air that they move is incredible.
