Hi, I’m designing my first speakers. I’m a cabinet maker so the boxes should be relatively easy. I’ve had high end gear before and I would like to make some small (relatively) 3 way full range active speakers (along the lines of Seas KingR04Y but at half the cost). Here’s where I’ve got to so far:
I would be interested in feedback from those who have gone before on:
- Hypex FA253 plate amps for power and DSP
- SB Acoustics Satori 7 ½ ich coax in a 9 litre enclosure for woofer and tweeter
- DA HSS265HF 10” and DA HSS265PR 10” for sub with passive radiator
- I expect to cross over from sub to woofer around 200hz, and from woofer to tweeter around 2,000hz. Testing and the latitude of DSP will allow me to finesse these
- I want the sub and the woofer and tweeter to be in the one box. My reasoning for this is that the frequencies from around 80hz to the crossover to the woofer will be able to be localised and I want all localised frequencies to come from the same source
- Enclosure of 56 litres - Fh of 28hz (30hz @ -3db showing in transfer function magnitude)
- Enclosure of 36 litres - Fh of 32hz (33hz @ -3db showing in transfer function magnitude)
- Enclosure of 26 litres - Fh of 36hz (36hz @ -3db showing in transfer function magnitude)
I would be interested in feedback from those who have gone before on:
- Any issues with Fh of the box being so different (higher) than the Fs of the PR
- Is it reasonable to assume that DSP will manage the bump (boom?) at the lower end of the sub range arising from the use of a smaller enclosure
- I like the look of the Seas system and am tempted to make the box square rather than narrower and wider. This is just a personal preference but are there any significant problems which would follow from going wider than shallower than is customary
Working with the Dayton Audio RSS265HF-4 version, I have used VituixCAD to simulate the following low-frequency response curves when this driver is used with the Dayton Audio HSS265PR passive radiator. The curves from left to right correspond to the 56-litre, 36-litre and 26-litre enclosures.
Clearly, the 36-litre and especially the 26-litre enclosures produce a peak in the low-frequency response. The smallest enclosure without introducing a peak would be a 46-litre one.
Clearly, the 36-litre and especially the 26-litre enclosures produce a peak in the low-frequency response. The smallest enclosure without introducing a peak would be a 46-litre one.
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Thanks Witwald, I'm aware of Virtuix but I haven't used it. I modelled the 4 ohm version of the DA RSS265HF and your curves look similar to what I got in WINISD. I am willing to forgo some bottom end to achieve a smaller size (and happier wife) but I'm not sure if the DSP capabilities in the Hypex FA253 will be able to "tame" the peak of a smaller enclosure. What do you think?
Thanks and cheers
Thanks and cheers
Try a sealed slightly over-stuffed 36l box . You'll get close to 0.7 Q, easily made flat to ~30Hz with a bit of gentle low Q EQ. This woofer works very well in this mode, speaking from experience. It might also have a slight hump but slower rolloff than with PR & better phase. And yeah, DSP can eliminate that -- if you want.
You'll get less diffraction with big radius round-over edge narrow baffle but If the wider look calls to you...
You'll get less diffraction with big radius round-over edge narrow baffle but If the wider look calls to you...
Using the combination of the Dayton Audio RSS265HF-4 and HSS265PR passive radiator in a 26-litre enclosure, I have used VituixCAD to simulate the following reponse for a nominal input power of 90W re 4 ohms.
Noting that you plan on using the DSP-enabled Hypex FA253 plate amplifier, I have added a PEQ (parametric EQ) of −1.5dB at 60Hz with Q=1.0. This serves to tame the small but noticeable peak in the low-frequency response that would otherwise be present, and will help improve the transient response of the system. I also added a 2nd-order Butterworth high-pass filter set to 15Hz to suppress potential large displacements in the woofer driver when presented with music material below the system's cut-off frequency.
The low-frequency cut-off point is now 39.5Hz, which is quite reasonable for such a compact enclosure. As simulated, a 105dB SPL is reached in the passband for 90W re 4 ohms.
Noting that you plan on using the DSP-enabled Hypex FA253 plate amplifier, I have added a PEQ (parametric EQ) of −1.5dB at 60Hz with Q=1.0. This serves to tame the small but noticeable peak in the low-frequency response that would otherwise be present, and will help improve the transient response of the system. I also added a 2nd-order Butterworth high-pass filter set to 15Hz to suppress potential large displacements in the woofer driver when presented with music material below the system's cut-off frequency.
The low-frequency cut-off point is now 39.5Hz, which is quite reasonable for such a compact enclosure. As simulated, a 105dB SPL is reached in the passband for 90W re 4 ohms.
That's a good idea, and will greatly simplify the build and allow an enclosure that is much more rigid. The 36-litres is the "effective volume", which with the use of an over-stuffed enclosure probably requires a 30-litre gross volume, well withing the 26-litre design remit.
Below is the simulated response of just such a closed-box system: a 36-litre enclosure using the Dayton Audio RSS265HF-4 woofer. Here I have added a PEQ of +4.0dB at 35Hz with Q=1.0. With an input power of 60W re 4ohms, we can get around 103dB SPL in the passband witout exceeding this driver's Xmax. The F3 is a nice and low 31.3Hz, which is about 8Hz lower than the passive radiator system. Note that the nominally 2nd-order system offered by this closed-box enclosure design will have a much better transient response than the 5th-order passive radiator system.
If it is desired to go for an F3 that is extra low, then the following response could be obtained with the 36-litre closed-box enclosure. here F3 = 26.7Hz, and that's obtained using a 2nd-order high-pass peaking filter with Q=2.0 set to 27Hz, and a PEQ of −0.7dB at 60Hz with Q=0.80. The downside of this design could be that the roll-off rate is now 4th-order rather than 2nd-order. Also, the excursion demands on the woofer are much greater, so we can only run the system at an input power of 30W re 4ohms before reaching close to Xmax at 27.9Hz for the driver and an SPL of 100dB in the passband.
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Witwald and Mikessi, Thank you both for your input. The modelling is very impressive and will no doubt save me from errors or going down the wrong track. I will model the 36 litres in WINISD but I can see why VirtuixCAD is the bees knees. This will be a one off for me - well already I see a sub for LFE and surround speakers on the horizon - but definitely (hopefully) not an addictive itch which will need regular scratching
I do prefer the idea of a sealed enclosure and all that brings with it. The modelling the 36 litre box was quicker than I thought, but WINISD shows an Fsc of 42Hz @ -3dB. Does the extension to 31Hz comes from the overstuffing and the PEQ settings? Is overstuffing and PEQing likely to make that much of a difference or am I likely to have entered some incorrect parameters?
And can I please get some input on "overstuffing"? Is it as simple as more polyfilla? How do I know how much overstuffing is the correct amount? Input on reasonably priced backing and polyfilla or equivalent would also be appreciated
And can I please get some input on "overstuffing"? Is it as simple as more polyfilla? How do I know how much overstuffing is the correct amount? Input on reasonably priced backing and polyfilla or equivalent would also be appreciated
And just to confirm please - are you saying that a 30 litre overstuffed box acts like a 36 litre box - meaning I build and overstuff a 30 litre box and it is "effectively" a 36 litre box?
That's correct. Whenever we are doing the simulations in VituixCAD, we are working with an "effective" volume rather than the net volume. For a vented enclosure, we might place a thin layer of absorption material on the cabinet walls, so the effective volume and the net volume are approximately one and the same. For a closed-box enclosure, we can use a lot of filling material, and this serves to increase the effective volume of the enclosure above that of the net volume. This manifests itself as the closed-box resonance frequency not increasing as much when stuffing is added versus a stuffing-free closed-box enclosure.
According to Small: "If the filling material is chosen for low density but high specific heat, the conditions of air compression
within the enclosure are altered from adiabatic to isothermal, or partly so [1, p. 220]. This increases the effective acoustic compliance of the enclosure, which is equivalent to increasing the size of the unfilled enclosure. The maximum theoretical increase in compliance is 40%, but using practical materials the actual increase is probably never more than about 25%."
For a 30-litre enclosure, a 20% increase due to the filling material produces an effective enclosure volume that is equivalent to a 36-litre empty enclosure.
According to Small: "If the filling material is chosen for low density but high specific heat, the conditions of air compression
within the enclosure are altered from adiabatic to isothermal, or partly so [1, p. 220]. This increases the effective acoustic compliance of the enclosure, which is equivalent to increasing the size of the unfilled enclosure. The maximum theoretical increase in compliance is 40%, but using practical materials the actual increase is probably never more than about 25%."
For a 30-litre enclosure, a 20% increase due to the filling material produces an effective enclosure volume that is equivalent to a 36-litre empty enclosure.
It will enable easier integration with a subwoofer in the future too. It will also allow nearfield close-mic measurements of the low frequency response to check it.
Most of the difference is caused by the PEQ adding a significant, but not excessive, boost to the LF response. The stuffing/overstuffing just means we can work with a slightly larger effective volume to get as much LF extension as possible. It also will dampen down the rear radiation from the cone, making for a cleaner sound.
I don't think that you won't be forgoing all that much low-frequency extension by choosing the smaller enclosure size.
The FA253's DSP capabilities are quite extensive. Taming a small peak such as the one you refer to shouldn't be a problem.
When you get around to adding a subwoofer, there is a benefit to using the closed-box enclosure design. It would be possible to switch off the low-frequency PEQ, saving on applying PEQ in what is no longer a needed region. It is then possible to concentrate on choosing an appropriate 2nd-order high-pass filter to produce the required high-passed acoustic response for blending in with the subwoofer's low-pass filtered acoustic response.
A quick thought about this + bass box size.
Any box with the RSS265 woofer mounted on the front will be ~12" wide assuming 3/4" thick boards. With the mid Vb, and the need to place it & the tweeter on the front baffle, it will be bigger than the King RO4Y.
This suggests a tower config, which has the benefit of not requiring a stand. And for the shortest path from tweeter to seated ears, say ~40" is a good height.
All this to suggest that a slim tall tower 3-way with the Dayton 10" sub driver will easily accommodate 36 liters for that driver and still not look BIG, esp with roundover edges. The bigger volume is better. Imo, there is usually some advantage to avoiding digital/electrical manipulations to compensate for physical/mechanical compromises.