MLTL design for newbies? (SB racetrack)

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CuriousAudioNoob

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Joined 2023
#1
Hello 🙂

First post here.. I am wondering if anyone can point me towards some resources for my education.

I would like to build a MLTL enclosure for the SB Acoustics SB15SFCR39-8 racetrack driver.

Initially, I was hoping to simply make a bass reflex speaker, but the dimensions I have in mind have sort of disqualified that enclosure style, if I'm not mistaken. I am aiming for a very slim tower speaker, with an external width no more than 6". Likely, I will use 1/2" thick wood for the sides of the speakers, to allow 5 inches internal width. I am less particular about the depth and height dimensions, but I have in mind something along the lines of 7 inches deep and 35 inches tall. This sort of extreme box ratio, if I understand correctly, necessitates a transmission line style design?

I like the idea of an MLTL, since it still utilizes a port like I was initially hoping.

Perusing through online resources, it looks like my best bet is to use a software called Hornresp? I am wondering if anyone can point me towards a resource that would help me get started on learning how to use this software, and hopefully specifically in the context of designing an MLTL enclosure?

Thank you in advance. I also posted the driver specifications of the SB woofer, if anyone has an opinion on the suitability of this driver for the application I have in mind. I like it because it has a good bass response, while being slim enough to fit in a tiny enclosure like I have in mind.
 

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#2
I used the racetrack for a MLTL.
It is a very good driver, and like you said, mounting it vertical makes for a nice slim tower. You can then add a little 2~3" wide range driver in a sealed cone to handle higher up. Works very well. The SBA will go down as low as 35Hz in the MLTL.

Plenty of Youtube videos and instructions on the net, a short Google search will bring out a few. HornResp will also come up with a basic design if you follow the System Design, once you selected to edit a design, and it will help you start your design.

You will need a bit more than 5" internal. Not much, but it will need a little more room to breathe
 
#3
Thank you for your reply! Indeed, it is my plan to add a midtweeter to cover the rest of the range. At what frequency did you cross over your speaker may I ask?
perceval said:
You will need a bit more than 5" internal. Not much, but it will need a little more room to breathe
Click to expand...
Also, what would the consequence be to ignoring this advice? If I was absolutely set on that width, would you say I would be better off choosing a different driver? Or would the SB still be suitable, just under less than ideal conditions?

Thank you 🙂
 
#4
CuriousAudioNoob said:
At what frequency did you cross over your speaker may I ask?
Click to expand...

I am with perceval in recommending a WAW. We often use 3” (sometimes 4”), favorites are Alpair 5.2/3, FF85wk, CHN-50 on the cheap. These, in the approproate mid enclosure are good to about 250 Hz How low you cross is a compromise between:

1/ At or below the quarter wavelength of the centre-to-centre of the drivers. The closer they are the higher the XO can be
2/ bafflestep: At a certain frequency the sound goes from 2∏ radiation to 4∏ and, if in an anechoic conditon, a 6 dB loss on axis. In a room is is a much different case, and one has to weigh falt on-axis with flat room response. If you cross somewhere between 0.707-1x the bafflestep F(-3). This is related to baffle width/shape. It will be higher with a narrower baffle. This roll off has a shape.

In a WAW you can get the XO low enuff that a pair of woofers cam be mounted push-push on the sides completely eliminating bafflestep (from the woofers), as well as creating a situation where active reaction force cancelation dramatically reduces the vibrational load on the box.

dave
 
#5
planet10 said:
In a WAW you can get the XO low enuff that a pair of woofers cam be mounted push-push on the sides completely eliminating bafflestep (from the woofers), as well as creating a situation where active reaction force cancelation dramatically reduces the vibrational load on the box.
Click to expand...
Interesting. What is the highest frequency at which you would still recommend this side mounted method? I was under the impression that anything above 100Hz or so and it would still be required for you to front mount the driver, where the sound would become noticeably directional?

I am between the Alpair 5.3 for midtweeter, and CHP 70 A with a super tweeter
 
#8
Let's see if I remember this correctly :sigh: : you can easily figure this yourself in that sound is round (spherical) and expands/contracts exponentially, i.e. if the baffle is 6" and and the driver around the corner is 3" away, then CTC spacing is 6" = ~13543/(pi*6) = ~ 718.5 Hz and since we want to overlap the baffle at least ~ a half octave = 718.5*0.707 = ~508 Hz max XO.
 
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