After building a couple of near field speakers with small Mark Audio drivers I'm planning on building some with larger CHN 110 units.
Interested in two boxes but wondered what the difference of the port location and size will have on the two below. What would the sound difference be.
Interested in two boxes but wondered what the difference of the port location and size will have on the two below. What would the sound difference be.
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Yeah, basic max flat alignment math 'say's that Vb = Vas when Qts' = 0.403, so ideally need a Vb > Vas.
T/S max flat alignment:
Vented net volume (Vb) (L) = 20*Vas*Qts'^3.3
(Ft^3 = (Vb)/~28.31685)
Vented box tuning (Fb) (Hz) = 0.42*Fs*Qts'^-0.96
F3 (Hz) = Fs*0.28*Qts'^-1.4
(Qts'): (Qts) + any added series resistance (Rs)
T/S max flat alignment:
Vented net volume (Vb) (L) = 20*Vas*Qts'^3.3
(Ft^3 = (Vb)/~28.31685)
Vented box tuning (Fb) (Hz) = 0.42*Fs*Qts'^-0.96
F3 (Hz) = Fs*0.28*Qts'^-1.4
(Qts'): (Qts) + any added series resistance (Rs)
Yes I understand the basics but interested in why the size and position was chosen for these two plans. Does a smaller port lead to less lower bass but maybe a stronger upper bass.
Unfortunately there is quite a lot of info the charts showing frequency response but not much said about sound of an individual design which is the most important factor. I've listened to speaker with almost the same spec but very different sonic output.
Small speakers don't do bass but what they can do is speed and timing. For me I'd rather have no bass rather than bass with no control or bloated.
Unfortunately there is quite a lot of info the charts showing frequency response but not much said about sound of an individual design which is the most important factor. I've listened to speaker with almost the same spec but very different sonic output.
Small speakers don't do bass but what they can do is speed and timing. For me I'd rather have no bass rather than bass with no control or bloated.
A "shorter" port pushes the box tuning up. Here's an approximate plot showing Scott's 18L box (orange line) and an exaggerated higher 55Hz tuning (faint green line). The only difference is the port length. The port length for the 55Hz tuning is much shorter at ~71mm.
jeff
Staggering up over the parapet briefly (I'm not currently able to show up too often here for personal reasons), a few general thoughts / point[ers], for whatever they're worth (not much).
- The boxes in question aren't really akin. Pactolus is the smallest of a series of three similar vented standmounts I did for CHN-110 (Pactolus, Pelorus, Persius) which range from what I consider about the minimum practical size with a decent alignment (the alignments differ between these enclosures by intent) to a near-optimum in terms of extension, as GM indicates above
- Other than size there are other tradeoffs involved; a larger enclosure can get lower but power-handling & dynamic range are reduced -how much also varying with tuning. GD / settling time etc. also varies of course -depends what you need.
- The Fenlon boxes were largely done by Mark using an on-line calculator, and the vent size is usually chosen for convenience & small[ish] proportions. My own are generally structurally stronger as size increases, at the price of being a little more complex to build, & typically have the driver & vent positioning optimised (by certain criteria anyway) to the proportions. I also accounted for typical wire loop, connection resistances & did a more detailed damping scheme. This isn't to suggest Mark's boxes are bad: they were designed with different intentions -in his case he wanted something hyper-simple with zero frills of any kind for people new to DIY rather than a more refined / complex take on the theme.
- A rear vent position is a personal preference of mine for ducted vent boxes tuned to an acoustically low frequency for their size & driver characteristics as it usually offers less noise. It's counter-intuitive, but in practice, providing the enclosure is at least 1.5x the duct diameter away from a wall and not stuck in some cavity which may have a loading effect, it doesn't make a huge difference to the exciting of room modes with these relatively small enclosures unless you're really driving things hard in a very live environment.
- I think many might dispute the idea that a small drive unit 'won't do anything accurate below 70Hz'. That depends on the driver design (motor, suspension, cone etc.) & its resonant frequency, distortion performance, and the nature of the enclosure. Short version: they can. What they may not be able to do is to do so with as much power handling / dynamic range / SPL capacity as a larger speaker of similar type & design quality -no news here.
Thank you for a very detailed reply, a lot to take in there. I have PMC transmission line speakers in my main setup and have only just started with DIY builds last year for a second setup and near field for a computer. Just trying to make up my mind on a speaker with a larger driver like the 110 or a smaller one in a Fugal horn.