I am wanting to design and build my own rear and height channels for my small 5.1.2 home theater, but I am no expert in speaker design, so I’m looking to get some feedback before going straight to building.
About the current build plans:
I am using the 4” SB Acoustics SB12PFCR25-4 bass mid-woofer and the 3/4” SB Acoustics SB19ST-C000-4 dome tweeter. The drivers are mounted in a 4.8-liter ported box, tuned to 60 Hz. The expected transfer function can be seen in the pictures below, along with the 3D models.
Other than knowing that boundary gain is a thing, I don’t know how to predict or simulate it, so I don’t know how to account for it when designing the speaker. Will I get an excess amount of bass with my current design if I mount the speaker on a wall (and close to the ceiling in the case of the height channel)?
I have also read that boundary interference is a thing of concern with wall-mounted speakers. My understanding is that it’s simply one of the downsides of having a wall-mounted speaker, but is there anything you can do to mitigate the effects of it during the design process?
I am also a little unsure about the port position on the side of the speaker. It is a little unusual, but I don’t see why it should be a problem.
Other than that, if any of you have any thoughts or comments about the design, then please let me know. 🙂
About the current build plans:
I am using the 4” SB Acoustics SB12PFCR25-4 bass mid-woofer and the 3/4” SB Acoustics SB19ST-C000-4 dome tweeter. The drivers are mounted in a 4.8-liter ported box, tuned to 60 Hz. The expected transfer function can be seen in the pictures below, along with the 3D models.
Other than knowing that boundary gain is a thing, I don’t know how to predict or simulate it, so I don’t know how to account for it when designing the speaker. Will I get an excess amount of bass with my current design if I mount the speaker on a wall (and close to the ceiling in the case of the height channel)?
I have also read that boundary interference is a thing of concern with wall-mounted speakers. My understanding is that it’s simply one of the downsides of having a wall-mounted speaker, but is there anything you can do to mitigate the effects of it during the design process?
I am also a little unsure about the port position on the side of the speaker. It is a little unusual, but I don’t see why it should be a problem.
Other than that, if any of you have any thoughts or comments about the design, then please let me know. 🙂
Yes, but that's not a disadvantage, as it improves available amplifier headroom by the same amount.
Do you mean that I could EQ the bass down on my AVR and gain the extra headroom by doing so?
I've actually already bought the drivers a while back, so kinda stuck regarding that. But yes I see your point, although the HF off-axis response of the SB12PFC25-4-COAX doesn't look that good in my eyes when comparing to the standalone SB19ST-C000-4 tweeter. No?
Why not? The driver seems happy in the configuration it's in. I don't need it to play that loud, my room is quite small. Otherwise Id like to know your thoughts.
Oops, sorry. For a coax, it has very smooth treble response, and keep in mind that the off-axis is a combination of not just the tweeter but the tweeter and mid-woofer. The coax solves some problems around vertical vs. horizontal responses. Obviously do what you want to do!~ 🙂 But I'd say the off-axis response is a little worse in some ways, a little better in others.
Also, it seems these forums have given the coaxes a mixed review, so never mind!!
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Because that's what subs are for. Reducing cone displacement where possible is ALWAYS a Good Thing.
I generally find that the reason small commercial speakers sound bad is that the manufacturer has stretched the bass response as far as it will possibly go, both for initial listening impressions, and specification bragging rights. This is especially the case when the same driver is also trying to accurately reproduce the important midrange and beyond whilst failing to reproduce worthwhile bass from a tiny cone area. More is not always more...
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Yes, absolutely, the apparent increase in efficiency reduces the excursion requirements on the driver (at these boosted frequencies) thereby reducing distortion and amplifier power, but this requires downward EQ as you've correctly guessed.
It's not a good idea to use BR on the rear speakers if they are that close to the wall and ceiling or even the corner. It will sound boomy and very squishy. A sealed enclosure is the best you can do in such a situation.
Thats right, and I forgot about the comb filtering that the coax doesn't create. Maybe I should have given the coax a little more thought.
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I get your point. I can't get a smooth system response with a tuning any higher than 70 Hz. The picture below shows the driver in a smaller 3.8 liter box tuned to 70 Hz. I don't seem to gain much from doing so. It saves a little bit of driver excursion before the tuning frequency but increases after it.
Also all of the 3 design suggestions Basta provides suggests tuning frequencies below 60 Hz with ever larger box volumes. I don't know how valid the suggestions are though.
I hear many people use the word "boomy" bass. What exactly does this mean? Is it just a word for too much bass? If so, wouldn't it be more beneficial to make use of the bass extension that a bass reflex provides, now that space isn't a limiting factor, and just EQ the bass down and gain some extra headroom as @newvirus2008 pointed out?
No, that's bloated, imprecise, soft bass. It's usually too loud too but that's not the main problem.
No, because it excites the room modes most at that placement. There should not be any bass played at the rear speakers, therefore you don't need headroom in that range. And without a port no mid-garbage can come out through it. That's important because there's likely nothing at the walls that can absorb it.