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Crossover points for TMS4 and 1850's

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Young Croc
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    Posted: 03 July 2008 at 11:00am
I'm using some 2 x TMS4 and 4 x 1850's at the weekend. I've never used 1850's with the turbo's before and was wondering what crossover points I should use.

When we run the TMS4 we generally run them 2 way set at 250hz.

Given that I'm a bit of a novice can anyone give me some advice on running three way?

Thanks
Bassmentality: Ska, reggae, funk & Hip hop every month @ The Cellar, Oxford
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Post Options Post Options   Thanks (0) Thanks(0)   Quote solution Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 11:27am
should I crossover at about 200hz as recommended by the plans?
Bassmentality: Ska, reggae, funk & Hip hop every month @ The Cellar, Oxford
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robbo Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 12:45pm
It is not so much the crossover points that you are going to have problems with, but the phasing between the 18" drivers in the TMS4 and 1850 cabinets as the two cabinets have totally different horn path lengths so you will have to have a serious play with your LMS to get them back in phase together.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Risc_Terilia Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 12:48pm
If you use 48db filters and leave a few hz between the crossover points i don't think you'll have to worry about it.  Of course it'll sound slightly better if you do get it right but there are possible work arounds.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote solution Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 1:46pm
does anyone know what the hornpath length for the 1850 is?
Bassmentality: Ska, reggae, funk & Hip hop every month @ The Cellar, Oxford
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 2:13pm
Originally posted by solution solution wrote:

does anyone know what the hornpath length for the 1850 is?


Originally posted by levyte357 levyte357 wrote:

Originally posted by Robbo Robbo wrote:

There has got to be a mistake somewhere with these horn lengths---


http://www.audioasylum.com/scripts/t.pl?f=hug&m=40882



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Re: On apparent discrepancies between mouth size and reported response of bass horns

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Hi Peter,

Well, I don’t know about the respected bit, but I’ll try and explain where I’m coming from with my horn designs.

If you look at the 1850 horn on the speakerplans site you will see that the response does drop off like a rock below its cutoff point. The horn length is 1.59 meters or 62.59 inches. This equates to a full wavelength frequency of 216.77 Hz. So divide by 4 to get the quarter wavelength figure of 54.19 Hz. Again if you look at the plot you will see it fall sharply below 54 Hz, I also quote the cutoff frequency and state that the design is good down to 54 Hz. I also assume that at least 2 horns will be used in a stack and preferably 4. So I can’t see the problem or see why you could have a problem with this. If I quote that 2 horns have a cutoff of 30 Hz then I would be lying, but I don’t do this.

Concerning the HD 15 horn, I do quote that the design will operate down to 52 Hz which for one cabinet would be impossible, but it does state that it must be used in a stack of at least 6 cabinets. When used as such the combined horn mouth and extra horn length that can be achieved by combining horns will give a new cutoff of 52 Hz. Also note that I still say you should use a reflex or bandpass type cabinet below these horns to get a fully extended bass response below 50 Hz.

The 186 horn is meant to be used singly and with higher Qts drivers than a horn normally requires. This and an over sized rear chamber can give you a shallower rolloff below cutoff. This is depicted in the response, but you will also see that the cutoff has been raised in frequency from what the horn length dictates it should be. This is again due to the rear chamber being too large, a smaller rear chamber with a lower Qts driver will have a lower cutoff (or a cutoff that behaves predictably and is true to the 4/WL rule) and an over sized rear chamber will tend to shift the cutoff up in frequency and give a shallower rolloff, especially with drivers with a higher than recommended Qts and low BL. While not ideal I do prefer listening to horns with drivers with a higher than required Qts, good for the lounge but not good if you need a quick transient response and loads of SPL like at a concert.

So I hope that has explained the figures behind the designs. I always assume that my designs will be used in multiples. This is large scale PA for big venues and no one is going to use just one small 15” horn in there PA system, well I hope not. So my mouth areas are calculated assuming that a minimum of 2 1850 horns will be used together and 6 of the HD 15 horns will be used in one stack.

After liasing with David McBean, his wonderful Horn Response program (ver 5.60 and above) now lets you calculate the response for multiple horns. While not usable for everyone it’s really helpful in the PA world where multiples are the norm.

 each.

Best wishes and happy resonating,

Rog Mogale.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote H.. Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 2:17pm

Back in the day TMS4 & FS218 would have an overlap i would guess cut the 18" of the TMS around 80Hz and run the 1850 upto 100Hz. play around on your lms, try pink noise and a RTA to get your time alignment right

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Post Options Post Options   Thanks (0) Thanks(0)   Quote solution Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 3:52pm
I'm still not getting this...sorry for being long winded and ignorant!. If anyone can help me that would be great. After speaking to Turbosound they gave me the following information for the TMS4:


Gain Polarity Delay Difference HPF LPF Limiter

dB
ms ms

dB
TMS-4






18" 0 + 0.000
15Hz * 250Hz Auto (-1dB)
10" + 1" 0 - 3.292 3.292 250Hz 22kHz Auto (-1dB)

Given the information that's been posted above about the 1850's:

The horn length of the 1850 is 62.59 inches, this equates to a full wavelength frequency of 216.77hz and the cutoff point is 54hz.

The TMS4 info if it helps is available here: ftp://ftp.turbosound.com/datasheets/legacy%20products/tms4.pdf

Can anyone help me out and give me the exact delay settings or the formula and info I need so I can work it out (which will also help me in the future!!)??

Thanks!!!




Edited by solution - 03 July 2008 at 3:53pm
Bassmentality: Ska, reggae, funk & Hip hop every month @ The Cellar, Oxford
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Post Options Post Options   Thanks (0) Thanks(0)   Quote solution Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 4:03pm
I think i may have got there but it would be good for someone to tell me if I'm right or not:

The 1850 has a hornpath of 62.59 in = 0.00 ms delay
TMS4 18" has a hornpath of 39.51 in = 5.22ms delay
TMS4 10+1" is already delayed by 3.292 ms so I need to delay by 8.52ms?

I've worked it out based on a 1ms delay per ft.

If  anyone can help that would be great.
Bassmentality: Ska, reggae, funk & Hip hop every month @ The Cellar, Oxford
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 4DPA Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2008 at 8:07pm
path length of the 1850 62.59" less the tms4 path length 39.51"  leaves a 23.1" difference to be adjusted for to get the tms4 sub in time with the 1850

delay the tms4 18" by approximately 2ms then to bring the mid/high in time with the two subs delay by 5.292ms


bs8901 compliant
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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote solution Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2008 at 9:57pm
thanks for your help 4dpa. We'll take some pics and post  them next week.
Bassmentality: Ska, reggae, funk & Hip hop every month @ The Cellar, Oxford
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