An EBS (Extended Bass Shelf) vented-box low-frequency alignment requires a large increase in box volume and a reduction in port tuning frequency. For the Dayton Audio SD315A-88 in a twin-woofer configuration, a reasonable-looking EBS alignment starts when we increase the box volume to Vb=340 litres (12 cubic feet) and tune the enclosure to Fb=22Hz. This alignment produces an F6 of 20.3Hz.
If we add in a 4th-order Linkwitz–Riley low-pass filter with an 80Hz cut-off frequency, the computed subwoofer response is shown below. Here we see that F3 of the subwoofer system is now a very respectable 20.6Hz.
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I've looked into this room gain effect a little further, and I can agree with you about the 6dB of gain at 20Hz, achieved by placing the woofer(s) in a corner. Allison (1990), in "Marking The Boundaries", analysed a corner placement of a low-frequency monopole loudspeaker. The results are shown below in Fig. 3 as a function of the ratio of the distance divided by the wavelength (d/λ).
For the purpose of computing the effect of corner placement on the boundary reinforcement of the SDA subwoofer's output, I've assumed that the subwoofer is located at a distance d=0.5m from a wall. If we look at where the reinforcement curves reach 1/2 their asymptotic low-frequency level, we see that d/λ is approximately equal to 0.15. With a distance of d=0.5m, this in turn corresponds to a frequency of f=343/(0.5/0.15)=103Hz.
If we ignore the cancellation dip that occurs at around d/λ=0.3 in Allison's curves, the following is a first-order approximation to the response shown above in Fig. 2. This clearly shows that at 20Hz we get a 6dB boost.
In addition, we can expect approximately 6dB of boost at frequencies below 70Hz. With an 80Hz 4th-order Linkwitz–Riley low-pass filter added to the subwoofer, it seems clear that the subwoofer's entire passband will be boosted by approximately 6dB as a result of placing it close to a wall. Another 3dB might be added in the ideal case when the subwoofer is placed in a corner (see Fig. 3 above).
Hence, the anechoic calculations completed earlier are entirely relevant. In practice, all that needs to be done is to adjust the gain of the subwoofer appropriately to get it to blend with the appropriately high-pass filtered main stereo loudspeakers. This will work when placing the subwoofer close to one (e.g., floor), two (e.g., wall), or three (e.g., corner) boundaries. This is because the boundary reinforcement will increase the subwoofer's output in a manner that is more or less uniform across the subwoofer's operating frequency range.
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I think your reference and work shows boundary gain based on Allison’s sims which would be correct…….but there’s also the room gain ………a function that’s a bit more complex and to accurately simulate would require more complex measurements. To thoroughly analyze it, you’d need to also know the construction of the enclosure walls and ceilings as well as account for any openings in the space. WinISD as Erin points out can give you a fair enough value where we would be dealing with 6 drive units which would fully couple the air in the room to the drivers as a working ‘system’…….given the size of the OPs room of course. My latest assistance in a control room build required 4 15” sealed drivers to achieve this in a 12*16 ft space with a measured in room response of 23hz. These drivers were all placed close to the floor in the corners as described above……..but the use case was different as it was better suited to have the corners volume consumed with trapping material instead to keep the 80-200hz response smooth. I wouldn’t prescribe that level of control for the OP.
Hey @witwald ! the answer to my desire for more SPL than 101dB is : No. I don't listen to my music veery loud, and in the space that I have to work with, sound compression will be totally in my favor, I believe, with 6 sub-drivers and the 15" coaxial driving top frequencies.
Sorry for responding a bit late on this question, work is holding me back from my normal vigorous researching. I am reading g and learning form you, @mayhem, and others.... If I were another poster considering DIY subs, I'd probably use these drivers if only for the excellent data you guys have freely given....just awesome!!!!
In a minute, I'm out-the-door again for work, but I'll be back to finish my read this evening. I read-through the comments and information to date, however, I need to get back to digest it. Yesterday I mention that I might just do a test build without buying the Equalizer, working @mayhem13 's plan first; prudence calling-out not buying extra hardware, as the EQ's are in the $300.ish+ range, but I think i'll just go ahead and buy them to test both of your ideas on this build.... I'll the leftovers somewhere else.
This is good stuff though! I'm already planning another build using this info, and I haven't even received the SDA's yet for this build...lol
Have a great day!
Good Morning!!
As for the 15.1" coaxial I'm using, ...they are units sold through a vender: Ladolce Audio. I understand he worked with the manufacturer Eminence to get these specific driver tailored to his design. Here's a link below to see the drivers.
https://ladolceaudio.com/product/ha15-1/
Let me know if you have any comments about the 15" drivers and any recommendations for their implementation with the respect to the subs I'm trying to build and match to them using the SDA"s.
SDA Drivers still haven't arrived yet.
Also, I looked at a few miniDSP units but I haven't decided what will best suit my application... I read your comments where I will need two mini's 1-front and 1- rear. I'm researching offerings that will possibly cover both zones in one unit.... in-for-penny, in-for-a-pound.... 🙂
Thanks again!
In the low-frequency range, the 15.1" coaxial will be acting as a dipole loudspeaker. Being an open-baffle system, it will have a typical figure-of-eight polar radiation pattern at low frequencies. On the other hand, the subwoofer drivers will be acting as monopole loudspeakers, with an omnidirectional radiation pattern at low frequencies. It will be interesting to see how the mismatch in the two quite different radiation patterns affects the sound quality. I have no idea how they will blend together.
I'm not really sure. The 15.1" coaxial driver has a Qts of around 0.60, as far as I can tell. Although it's difficult to find a concrete specification for the driver's Fs, it could be around 36Hz. All of this seems to indicate that the 15.1" woofer has some low-frequency output, and it is likely to work well if it is crossed over to the subwoofer at around 80–100Hz. The position of the subwoofers relative to the main speakers and the number of subwoofer sources seems to preclude anything else.
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I'm with you on wondering how this will sound, but for me it's not for the technical reasons you layout.
I guess I should have prefaced my ask concerning this entire thread with an example-target of where I hope to get this build as close to. Here is a link to a youtube video auditioning the system that sparked my desire to build using the 15.1 coaxial. Take a listen if you can.
Oh! the system here has moved the tweeter horn out of the coaxial position, and he has added a second tweeter into throat-path of one horn, this is odd, but it seems to work.... very interesting....
Maybe my ears are distorted via my headphones, but I think this setup sound awesome. The use the servo-subs in the video seem to play well with the open baffles.... am I missing something in the practical application? The poster called his subs "servo subs" is that something different from the subs I am planning to build?
I her others using this 15.1 driver mention it plays to 40Hz...idk if that's in-room response....I'll dig deaper as planned before I bring all together for final tuning.
Also, I found a Dayton audio offering that I think might work with your suggested application for the PEQ, it's the Dayton DSP-408. It has 4 in and 8 out.
I listened to the various music samples being played in the video. Maybe the live in-room just didn't highlight the capabilities of the loudspeaker system all that well.
With a servo subwoofer, a sensor is used to provide a signal within a feedback loop that can be used to correct nonlinearities in the subwoofer's response.
With a servo subwoofer, a sensor is used to provide a signal within a feedback loop that can be used to correct nonlinearities in the subwoofer's response.