Is there a limit to CABs per channel?

Is this amp OK?
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howiez
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Is there a limit to CABs per channel?

#1 Post by howiez » Fri Apr 29, 2022 1:55 pm

/ramble
I'm starting to source amps now for the impending debut of my pair of DR200's and pair of T48's. I may never build more. (I'm lying, i'm sure I want more...) How do you stack up all the cabs electrically to figure out when you need more amp?
I was shooting for a Crown XLS1500(or 1502) for the DR's and a 2500 (or 2502) for the Titans. Simple, one channel per cab, then I happened to stumble on a great deal for an XLS2000. More than I need for an 8ohm DR, not enough headroom for a 4ohm Titan with a 600w RMS driver. That gets me thinking, what if I still get an XLS250x and add more DR's one day. Or what if I add more Titans or (like to build a T30 or 2) something else? Do I series the T48's on a bridged amp? How do you guys tradeoff all this black electrical magic?

My question is, 8ohm DR, if I parallel a pair of them, is 4ohm. What happens when I build another pair. I'm thinking two pairs in parallel for 4ohms, no big deal. Then another pair what happens? two in parallel and one in series, 3 per amp? or two in parallel, series to another pair in parallel. Then two on a channel alone? How This is all really theoretical, I'm never doing a paid gig, this is really a hobby (addiction) to keep me off meth or whatever the cool kids are doing.

I'm thinking about this awesome 16 piezo array, all series and parallel. What happens when you do that with real impedance? There has to be some thermal or electrical limit? Yeah, i'm a mechanical guy, don't know elektracity. If I rewired my house it would be 200 or 221, whatever it takes.
/end ramble

yeah, I like to feed my brain silly things...

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Seth
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Re: Is there a limit to CABs per channel?

#2 Post by Seth » Fri Apr 29, 2022 2:28 pm

What driver are you intending to use in the T48's?
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: Is there a limit to CABs per channel?

#3 Post by howiez » Fri Apr 29, 2022 2:39 pm

Seth wrote:
Fri Apr 29, 2022 2:28 pm
What driver are you intending to use in the T48's?
*disclaimer* these are literally for my garage. I just so happened a friend is going to hook his DJ laptop to some used amps we've aquired for a family wedding in July. Just for background music. My intention is to drag them to the occasional garage/backyard party.

I have Celestion 4ohm 600w in them, Some Parts Express buyouts.
My DR200's also have NITP drivers, $22 GRS 8's, like 150w RMS at 8ohms IIRC.

DJ laptop (borrrowed)
DBX Driverack PA2 (bought from user here).
Tops amp Crown XLS2502 (used, snagged literally today)
Subs amp TBD, hopefully XLS2502, but XLS2000 for now.

I seriously just want to wrap my head around the power by voltage concept, and resistance is making me think...

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Re: Is there a limit to CABs per channel?

#4 Post by Seth » Fri Apr 29, 2022 2:52 pm

Cabs with passive crossovers can not be wired in series. For these designs, that's about the only reason to bi-amp a cab, to be able to put more cabs on a channel.

So, to put 4 DR's on one amp channel, you'd need a 2Ω stable amplifier.

And personally, for a 2 top 2 sub system, I'd just use a single amp... one channel to the tops the other to the subs. Even though your subs are 4 ohm, you'll likely (but not guaranteed to) be okay running them parallel on a 4Ω rated amplifier channel. Two things in your favor; 1) with the cabs added impedance your final load will be 3Ω (nominal)... and 2) only half the amp will be working hard, so the amp's not likely to overheat and go into a thermal protect mode. If this system was intended for regular gigging duty, I wouldn't risk it. But, for home gamer, it'll likely be just fine.

A part number or link to a data sheet for the Celestion drivers would be helpful.

Power by voltage...
Volts x Volts ÷ Ohms = Watts
Square Root of (Watts x Ohms) = Volts

Without knowing the Celestion specs, I can only assume... But, I assume they will be displacement limited around 25-28 volts (150-200 watts, using the 1st equation above, not their thermal limit of 600).

Don't worry... 150 watts is more than it seems with horns. It will be more than enough for what you're doing.
Last edited by Seth on Fri Apr 29, 2022 4:58 pm, edited 4 times in total.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: Is there a limit to CABs per channel?

#5 Post by Seth » Fri Apr 29, 2022 3:04 pm

Your XLS2502 is 2Ω stable. You can run your whole system on that one amp without any issue.

Once we figure out what driver you have, we can figure out an appropriate voltage limit.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

howiez
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Re: Is there a limit to CABs per channel?

#6 Post by howiez » Sat Apr 30, 2022 12:18 pm

Seth wrote:
Fri Apr 29, 2022 2:52 pm
A part number or link to a data sheet for the Celestion drivers would be helpful.

Power by voltage...
Volts x Volts ÷ Ohms = Watts
Square Root of (Watts x Ohms) = Volts

Without knowing the Celestion specs, I can only assume... But, I assume they will be displacement limited around 25-28 volts (150-200 watts, using the 1st equation above, not their thermal limit of 600).
Power Handling (RMS) 600 Watts
Power Handling (MAX) 1200 Watts
Impedance 4Ω
Frequency Response 40 to 3,000Hz
Sensitivity 99.72dB 2.83V/1m

Not going to win any contest with them, but for $60 they'll do the trick for me!

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Re: Is there a limit to CABs per channel?

#7 Post by Seth » Sat Apr 30, 2022 12:41 pm

howiez wrote:
Sat Apr 30, 2022 12:18 pm
Seth wrote:
Fri Apr 29, 2022 2:52 pm
A part number or link to a data sheet for the Celestion drivers would be helpful.

Power by voltage...
Volts x Volts ÷ Ohms = Watts
Square Root of (Watts x Ohms) = Volts

Without knowing the Celestion specs, I can only assume... But, I assume they will be displacement limited around 25-28 volts (150-200 watts, using the 1st equation above, not their thermal limit of 600).
Power Handling (RMS) 600 Watts
Power Handling (MAX) 1200 Watts
Impedance 4Ω
Frequency Response 40 to 3,000Hz
Sensitivity 99.72dB 2.83V/1m

Not going to win any contest with them, but for $60 they'll do the trick for me!
You may very well still win some contests.

That information doesn't really help in this particular case. We'll need the T/S parameters to determine an appropriate voltage limit. What is the model number of the driver?
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: Is there a limit to CABs per channel?

#8 Post by Bruce Weldy » Sat Apr 30, 2022 2:24 pm

Unless you have the world's biggest garage - you aren't going to need anything else. Run the subs off the XLS2500 in mono - using the parallel input mode. One per side. Run the tops off the XLS2000, one per side.....and you can add one more per side with no problem. You'll never run out of power.

But, you really need to figure out what those cheap drivers you going to use in the subs can handle as far as excursion. As Seth said - you need to get the model and T/S specs to see where you need to set the limiter.......those might not even be suitable for sub duty.....they may be for tops.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Re: Is there a limit to CABs per channel?

#9 Post by Bill Fitzmaurice » Sat Apr 30, 2022 2:47 pm

howiez wrote:
Sat Apr 30, 2022 12:18 pm
Power Handling (RMS) 600 Watts
Power Handling (MAX) 1200 Watts
Impedance 4Ω
Frequency Response 40 to 3,000Hz
Sensitivity 99.72dB 2.83V/1m
Those aren't specs. From your plans: To check pro-sound drivers for suitability the acceptable Fs is between 22 and 50 Hz, Qts from 0.25 to 0.5, xmax no less than 6 mm.

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Re: Is there a limit to CABs per channel?

#10 Post by howiez » Sun May 01, 2022 9:04 am

Seth wrote:
Sat Apr 30, 2022 12:41 pm
That information doesn't really help in this particular case. We'll need the T/S parameters to determine an appropriate voltage limit. What is the model number of the driver?
My bad I thougth you only needed wattage since that's what you asked for
SO how does T/S factor in? other than Xmax, which mine is at bottom end at 6mm

edit: I should add, while i'm using them in my Garage 365-1/4 days a year, they will power light background music for my sons upcoming wedding, and i've been asked to lend them for a birthday bash garage party. OK that one might get war volume?
In my garage the DR200's are running off a 100wpc receiver, and the T48's are running off a pair of BASH300 amps. It nicely hits 110dB, far too loud for in there. All I know is they sound crisp and clear and I had to turn them down substantially from the Bose 201's that have been hanging from the ceiling for nearly 20yrs!

Resonant Frequency (Fs) 47.7Hz
DC Resistance (Re) 3.19Ω
Voice Coil Inductance (Le) 3.06mH
Mechanical Q (Qms) 9.63
Electromagnetic Q (Qes) 0.39
Total Q (Qts) 0.37
Compliance Equivalent Volume (Vas) 3ft³
Mechanical Compliance of Suspension (Cms) 0.056mm/N
BL Product (BL) 22.16T·m
Maximum Linear Excursion (Xmax) 6mm

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Re: Is there a limit to CABs per channel?

#11 Post by Seth » Sun May 01, 2022 9:14 am

howiez wrote:
Sat Apr 30, 2022 12:18 pm
Power Handling (RMS) 600 Watts
Power Handling (MAX) 1200 Watts
Impedance 4Ω
Frequency Response 40 to 3,000Hz
Sensitivity 99.72dB 2.83V/1m
The only driver I could find on the entire internet that matches those particular stats is a Celestion product, is a 4Ω driver, is only showing up on Parts Express, and once upon a time was a "Factory Buyout" product. However, it's an 18" driver. Celestion T5867A 18-190X

I can't imagine you shoehorned (no pun intended) an 18" driver into a T48. Did you? Looking at the sketchup, you'd have to get pretty creative to make that happen.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: Is there a limit to CABs per channel?

#12 Post by Seth » Sun May 01, 2022 1:38 pm

In any case...

How many volts does it take to melt the voice coil?
How many volts does it take to make it as loud as possible without distortion (move the cone as far as possible while maintaining (mostly) linear response)?

Two different questions. Two different answers. The first is what the marketing team wants you to think matters and they make it very apparent. The second is what matters to your ears and it's not something they can advertise because a driver will behave differently in different enclosures. Each situation unique. That's where the T/S parameters come in.
howiez wrote:
Sun May 01, 2022 9:04 am
SO how does T/S factor in?
How? I'm not versed enough to speak to that with any real conviction. Here's a quick rundown on the different specs, Eminence - Understanding Loudspeaker Data

Every driver requires different enclosure designs/dimensions to maximize their response and output potential.

In this case, we need to plug the T/S values into Hornresp Horn loudspeaker modeling software. One of the many functions in the software is calculated diaphragm displacement... how much the cone moves given voltage input, which varies with frequency.


Disclaimer for the following "information": I COULD BE WRONG
I've loosely backward engineered the dimensions of the T48 from the sketchup file. I believe the dimensions are not perfectly accurate, but close enough to ballpark some of Rornresp's functions.

If the data you posted is accurate (I used an Sd of 850), it looks like a 41 volt limit, on a 40Hz, 24dB Butterworth slope high pass filter is your sweet spot... keeping everything in check.
Screenshot (177).png
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

howiez
Posts: 283
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Re: Is there a limit to CABs per channel?

#13 Post by howiez » Wed May 04, 2022 7:27 pm

Seth wrote:
Sun May 01, 2022 1:38 pm

If the data you posted is accurate (I used an Sd of 850), it looks like a 41 volt limit, on a 40Hz, 24dB Butterworth slope high pass filter is your sweet spot... keeping everything in check.
Seth that is amazing, and i'm uber confused now! Here I thought this was a simple square root of watts x impedance. I've used Hornresp to try and design a horn, or check how a driver would perform. How do you get your 41v from that screenshot?

I had planned to high pass at 35Hz with my Driverack. I dont' suppose i'll notice with recorded music.

My plan was to limit at 49v. Yes my T48 is shoehorned. I built the first like 4 or 5 years ago, I can't even remember, should be a build thread. I just nudged the first panel a hair longer. I had built it around a RS woofer from the 80s just for fun. I was so impressed with how my THT turned out, I wanted to try something with freebies. I couldn't afford at the time to buy a pair of Eminence 15's but I had a pair of 18's laying around. I really didn't care if they blew, I knew the pressure would be rough on the old cones. But then last year I came across the Celestions meant for a horn, for a song, so I upgraded. 600w instead of 200w. Anyway even the RS had impressive bass in my garage.

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Re: Is there a limit to CABs per channel?

#14 Post by Seth » Thu May 05, 2022 1:55 am

howiez wrote:
Wed May 04, 2022 7:27 pm
Seth wrote:
Sun May 01, 2022 1:38 pm

If the data you posted is accurate (I used an Sd of 850), it looks like a 41 volt limit, on a 40Hz, 24dB Butterworth slope high pass filter is your sweet spot... keeping everything in check.
Seth that is amazing, and i'm uber confused now! Here I thought this was a simple square root of watts x impedance. I've used Hornresp to try and design a horn, or check how a driver would perform. How do you get your 41v from that screenshot?

I had planned to high pass at 35Hz with my Driverack. I dont' suppose i'll notice with recorded music.

My plan was to limit at 49v. Yes my T48 is shoehorned. I built the first like 4 or 5 years ago, I can't even remember, should be a build thread. I just nudged the first panel a hair longer. I had built it around a RS woofer from the 80s just for fun. I was so impressed with how my THT turned out, I wanted to try something with freebies. I couldn't afford at the time to buy a pair of Eminence 15's but I had a pair of 18's laying around. I really didn't care if they blew, I knew the pressure would be rough on the old cones. But then last year I came across the Celestions meant for a horn, for a song, so I upgraded. 600w instead of 200w. Anyway even the RS had impressive bass in my garage.
I looked and I don't think there's a build thread on your T48's. Cool story though. I'd love to see some photos of them if you have any handy. Don't go out of your way, though.

That screenshot was of the "Filter Wizzard" screen. In Hornresp, Window 1 - input parameters... the second box (Eg) is voltage. Adjust it to a voltage you suspect should do (maybe start with a voltage equivalent to RMS Power), press calculate. "Tools" dropdown, select "filter wizzard". Open the dropdown at the bottom left of the filter wizzard screen and select "Displacement". Adjust the highpass freq and slope to values mentioned in the plans. If the indicated displacement exceeds or is below the drivers Xmax, go back to the input parameters screen and adjust the voltage and do it all again until the displacement doesn't exceed the drivers Xmax. I don't know how Bill or anyone else goes about it, but that's what I've done. It's just what made sense to me. It could be completely wrong or there may be a better way to do it.

With horn loaded subs, you typically wont hear the distortion you'd hear from a direct radiator sub that let's you know you're pushing it too far. That's why Hornresp is used to determine how many volts it will take to exceed the drivers maximum linear cone excursion. Yes, you can use Ohm's law calculations to determine how many volts equates to a wattage with a known impedance. But, just because a speaker is rated for a certain "power", that doesn't mean you need it all to get everything out of the driver. In one enclosure it may need it's full power or more and still not exceed it's Xmax and in a different enclosure it may reach it's Xmax with way less than the drivers rated power.

Exceeding Xmax isn't the end of the world. Marginally exceeding it is really not a big deal. But, pushed too far without proper filtering and limiting can quickly and easily exceed Xlim, the absolute limit to cone travel. Especially at frequencies lower than the horn is designed for, it's very easy to damage a driver. Even at less than it's rated power.

The Eminence page states it well...
Xlim is expressed by Eminence as the lowest of four potential failure condition measurements: spider crashing on top plate; Voice coil bottoming on back plate; Voice coil coming out of gap above core; or the physical limitation of cone. A transducer exceeding the Xlim is certain to fail from one of these conditions. High pass filters, limiters, and enclosure modeling software programs are valuable tools in protecting your woofers from mechanical failure
I re-ran the driver specs with a Sd of 1235cm2, a figure more akin to an 18" driver (instead of the 850 I used last time, thinking it was a 15). 24" wide cab. Here's what the diaphragm displacement looks like at 49 volts (the drivers RMS rating of 600w), highpassed at 35hz.

Actually pretty good. This looks to be the Goldilocks combination. 18dB Bessell, peaks right at Xmax.
Screenshot (179).png


24dB Linkwitz-Riley, slightly over
Screenshot (178).png


24dB Butterworth. Even at 48dB, it is still over.
Screenshot (181).png


Having run those simulations, it's worth noting that, per the plans, stacks of less than four T48 cabs should be high passed at 40Hz, 35Hz for stacks of four or more.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

howiez
Posts: 283
Joined: Sun Mar 16, 2014 5:23 pm
Location: Fox Valley, Wisconsin

Re: Is there a limit to CABs per channel?

#15 Post by howiez » Sat May 07, 2022 7:50 am

Seth wrote:
Thu May 05, 2022 1:55 am
I looked and I don't think there's a build thread on your T48's. Cool story though. I'd love to see some photos of them if you have any handy. Don't go out of your way, though.
Seth, with the math! WOW, helpful as usual.
for your viewing enjoyment, my T48 build, I had only posted on FB apparently...SORRY!
viewtopic.php?f=30&t=26255

My budget driver and it's specs since you seem to be a master at HornResp!:
https://www.parts-express.com/B-52-18-1 ... hFEALw_wcB

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