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MultiWay Conventional loudspeakers with crossovers 

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26th August 2018, 05:42 AM  #1 
diyAudio Member
Join Date: Feb 2018
Location: Brisbane

2 way TL using SB23NBACS45 and SB29RDCN
Hi all,
I have been watching and reading in this forum for quite a while and have now decided to post something of potential interest. I have a pair of SB23NBACS458 drivers that I'm not using at present, so I thought about going out on a limb and doing a 2 way TL. Crazy, maybe, but I have just measured the drivers in DATS, and they are really suited to closed box or TL use. The Qts is 0.5, Fs is 31Hz, VAS is 49.32L, Qms is 8.1, Qes is 0.54. I have modelled the data into Leonard Audio TL software and it looks good. I have my own FR data on a 30 x 60 baffle and the cone breakups are really easily tamed. Attached is my preliminary data on a 30 x 90 baffle. Woofer at pretty much the top of the baffle and tweeter directly underneath the woofer. I'm using the SB29RDCN tweeter, so the centre to centre distance between drivers is only 155mm. Crossover point is 1370Hz. Will be driven with 20W max. What does everyone think? 
26th August 2018, 10:07 AM  #2 
diyAudio Member
Join Date: Mar 2018

I tried to find data on that woofer and the stated Qts is 0.33.Which would not suit a sealed box.

26th August 2018, 02:28 PM  #3 
diyAudio Member
Join Date: Feb 2009

Don't know where you found that, but I just looked at SB's published specs for this woofer and it showed a Qts of 0.40 and an fS of 25 Hz. Those two values suggest the optimum TL tuning frequency would be equal or close to 25 Hz. The OP measured an fS of 31 Hz and a Qts of 0.5, but those two values also indicate a tuning frequency around 25 Hz would be optimum because the two ratios of fS/Qts are all but identical, 62.5 from SB's specs and 62 from the OP's measurements.
Paul SB23NBACS458 8" Black Aluminum Cone 
26th August 2018, 05:02 PM  #4 
diyAudio Member
Join Date: Nov 2009

I really like the SB29RDCN, but I'd be concerned about crossing it that low. It looks like it's about 1100  1250 Hz. You're using a 2nd order electrical, so I'd worry about distortion going that low. I have seen the full size ferrite version (SB29RDC) taken as low as 1100 Hz, but it used a 4th order electrical for a LR6 acoustical roll off. Here's the LINK. Look for the "Low Crossover LR6" design.
Last edited by ernperkins; 26th August 2018 at 05:03 PM. Reason: typo 
26th August 2018, 05:55 PM  #5 
diyAudio Member
Join Date: Feb 2009

Tapered TL model
I modeled a 10:1 tapered TL for this woofer using SB's published specs. The line length is 70" and has a net volume of ~3.3 cubic feet (starting area of 10" x 15" and ending area of 10" x 1.5"). The woofer's center is located 14" from the beginning of the line, and the first 47" of the line is filled with polyester fiber at a density of 0.75 lb/ft3. The line's tuning frequency is 2425 Hz. I modeled with 0.5 ohms added in series with the woofer to represent the resistance of a series crossover inductor. Below is the predicted anechoic system bass response (red line) for an input of 18w/1m into this nominal 6.5ohm impedance. F3 in my model is ~28 Hz, but could be lowered simply by increasing the line's volume. Using the OP's measured T/S values I'd expect very similar results, but he didn't list several parameter values needed (Re, Le, Bl and Sd), so I couldn't verify my assumption. I also agree that the proposed crossover corner is very likely too low for the tweeter.
Paul 
26th August 2018, 08:26 PM  #6 
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Join Date: Jun 2015
Location: High Wycombe, Bucks, UK.


26th August 2018, 08:35 PM  #7 
diyAudio Member
Join Date: Feb 2018
Location: Brisbane

Thanks for the comments. I have been doing some tweaking over the weekend and have come up with an approx 1500Hz crossover point. I’ll take on the task of trying an LR4 slope on the tweeter. The other woofer data is as follows: Re is 5.53 ohms, Le is 0.7mH at 1kHz, BL is 8.681, and Sd is 216cm2.
My modelled TL is 2.2 m long, 5:1 ratio with Sd1 of 500cm2 and Sd2 of 100cm2, driver at 76cm. Heavy fill of 2.5kg/m3 in the first 1.4m of the line. 
26th August 2018, 11:36 PM  #8  
diyAudio Member
Join Date: Feb 2009

I substituted your T/S measurements into my model without any other changes, resulting in the predicted anechoic system bass response (red line) attached below. The only real change is a slightly lower output SPL (0.6 dB lower) but the same f3 for the same input power I used. A shorter line with a larger taper ratio does wonders for smoothing out the ripples in the response above 200 Hz or so and allows a lighter stuffing density. Your stuffing density works out to be a bit less than 1.6 lb/ft3 and unnecessarily makes f3 higher (a stuffing density over 1 lb/ft3 usually means the basic TL design can be improved).
Paul Quote:


27th August 2018, 03:07 AM  #9 
diyAudio Member
Join Date: Jul 2014

I'm using SB23NACS458 in sealed box as woofer in 3way project. It works perfectly with very simple crossover network. I think the 10001200Hz is best working band for that driver. If you want something more using midrange is a good solution.

27th August 2018, 07:53 AM  #10 
diyAudio Member
Join Date: Feb 2018
Location: Brisbane

Ok All,
I have had a look at Zaphs pages on the crossover designs with SB29RDCN and have come up with a couple of solutions that I would like everyone to have a look at. First one is 1400Hz crossover 18db/octave and second one is 1250Hz crossover 24db/octave. 2nd pic is my current running version. Tweeter with reversed polarity. Very large suckout at crossover point when tweeter is normal polarity. I'll put the above parameters into TL software and see if I can get a better response. Cheers. 
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