Beginners Do's and Dont's for loudspeaker building

[gem_piano]

I'd stick to a closed box design for a start. Use a speaker with a low free-air resonance as it goes up somewhat when in the box. Ported boxes (so-called bass reflex cabinets) need much more design and testing effort.
Good luck!

 

[jReave]

Is there any Thiel parameter that I might be able to consider to inform a good quality sound at low SPL?

Considerations for good performance at low volume

Bit of reading there to come up with a conclusion of high Qms and low Rms. Or in other words, a woofer with a loose suspension.

 

[DPH]

I would like to point out that in an open baffle design its the Fs ( driver free air resonance) that defines and limits the bass extension.... Not the Qts!

For example take this superb Beyma 15 inch driver: https://www.beyma.com/getpdf.php?pid=SM-115N

It has an Fs of 29Hz and a low Qts of 0.25 (and also low Qes of 0.26) with +/- 8mm Xmax ( +/- 15mm before damage) and a genuine AES power handling of 500 watts.

This driver (or even better a pair of) will produce superb bass all the way down to its Fs even in a modest size open baffle...

The shape of the fall off along the bass is going to be determined by more than simply the Fs (the driver's Qts plays a huge part), but the elephant in the room in terms of bass response is the room itself. Anyways, having that much oomph on hand certainly doesn't hurt.

But this is a side direction that will only serve to confuse the poor OP rather than help. Nor does what you say refute what I wrote, especially within the greater whole that picking out certain parameters and assuming it makes a good "this or that" style speaker is not so directly straightforward.

 

[Steve Luck]

Quite a bit of advice about tools. It's worth remembering that a lot of DIY stores and timber merchants will cut what you need to size some for nothing others for a small charge. Long term it's great to have your own tools but short term there's a lot you can still do using off the shelf timber. You can hand cut stuff to length and use a flush cut router to tidy up afterwards. Router and a Circle cutter jig for it are both very useful - worth spending a few extra bucks on a relatively good one. Cheap Ozito one I bought started disintegrating from day one. Iv'e since bought a Bosch one that's much better quality.

 

[mark100]

IMHO, the best way to get into DIY, is to figure out how to test/try things, in the easiest most economic manner.

For me, this has meant building prototype boxes where i can vary as many dimensions/aspects as easily as possible.
I decide what I'm want to let float...height, depth, width ???
How do i easily vary port size? Length?
Etc etc for what ever design you have in mind...

And the essential 2nd part is learn to measure...

Try.... measure.....
use models/formulas for starting points.
But measurements rule.

After an experienced while, measurements and ears are proven to be in sync IME.

So build in a way that you can adjust the build,
and tune/alter the build via making measurements ...

 

[oohms]

If you have limited working space and need to buy tools, to build a speaker with WAF that does well at low volumes, I think you would be much better off buying a kit with cabinets, or buying/selling second hand speakers until you find something you really like, where you can refinish the cabinet etc

Also
- Speaker building is a pain in the **** without a workshop that you can use
- Tools cost money and take up space
- Self designing speakers is really hard to do well (unless you have a full active setup, which is a whole new ballgame)
- It's a rabbit hole of collecting tools, speaker drivers, material, equipment, crossover components etc etc.

 

[Prolle]

Just for clarification, I'm not looking to self design. Plans only.

 

[chrisb]

Tons of those around, and levels of kits as well.

 

[Hydrogen Alex]

Open baffle facts

The shape of the fall off along the bass is going to be determined by more than simply the Fs (the driver's Qts plays a huge part), but the elephant in the room in terms of bass response is the room itself. Anyways, having that much oomph on hand certainly doesn't hurt.

Hi Daniel,

Sorry, but you are incorrect, and to avoid confusion here is further clarification.
Qts is not the major or even an important factor in defining bass extension in open baffle designs.
The main factors are:
(1) Driver Fs.
(2) Front baffle and side wings (if any) dimensions.
(3) DSP / Eq.
(4) Driver Xmax and power handling.
(5) Position of speaker within room ie Typically 4 to 5 feet is minimum distance required from rear of speaker to back wall.

The cardoid radiation pattern of OB reduces room interaction by 50% due to the 180 degree nulls (front / back sound wave cancellation), this is a key benefit of OB designs.

Cheers
Alex.

 

[Hydrogen Alex]

Great DIY site with budget to high end designs

Hi Prolle,

Here is a fantastic site for DIY loudspeaker design and information:
Humble Homemade Hifi - Loudspeakers

and this particular project explains a lot of OB / sealed box / ported box low frequency reproductio: design...http://www.humblehomemadehifi.com/download/Humble Homemade Hifi_Serious Sub.pdf

Cheers
Alex.

 

[DPH]

http://www.quarter-wave.com/OBs/OB_Design_Part_1.pdf

So far, the low frequency portion of the design has been optimized for the
Eminence Alpha 15A woofer. But two other woofer choices were also listed in Table 2
with lower Qts values. Figure 7 shows the low frequency responses of all three woofers
with the same baffle and crossover design. Reviewing the three plots it is seen that as
the Qts decreases the low frequency response also decreases. The only way to regain
low frequency output is to increase the baffle size which effectively shifts the dashed
blue line in Figure 6 to the left. Then to regain control of the rounded hump originally
between 100 and 200 Hz, a lower crossover frequency is required. The more expensive
woofer drivers like the Beta 15A and Gamma 15A with lower Qts values require larger
baffles, a lower crossover point, and will probably still not extend as low as the less
expensive Alpha 15A.

I'm sorry, that doesn't make mechanical sense to ignore Qts given the underlying composite of properties it embodies. The list you mention are all contributors as well, and may well dominate Qts as installed. But please read the work linked, as Martin King is nothing if not very thorough.

 

[Tweet]

Prolle,
You could go for a smaller system using a small subwoofer like this one............
8" SB23MFCL45-8 :: SB Acoustics

This driver works in a 22litre closed box, a small plate amplifer could be used to drive it, these amplifiers come with a built-in electronic crossover with variable turnover frequencies. One of these combinations would suit a stereo setup. This would take care of those lower frequencies and all that would be needed is to build a small open baffle speaker (per channel) that works in conjunction with that subwoofer. One does not need to build an overly large baffle if one has already accommodated the low frequency response with a suitable subwoofer like the above. Or, if not an O.B design then possibly some small closed box satellites would suffice. Large box sizes or O.B baffles are simply needed to provide for low frequency extension unless a specialized driver can be had.

C.M

 

[Bicicletta]

I don't see a map of the room with listening point and speakers position.

 

[Hydrogen Alex]

OB from 1919 not 2019!

http://www.quarter-wave.com/OBs/OB_Design_Part_1.pdf

I'm sorry, that doesn't make mechanical sense to ignore Qts given the underlying composite of properties it embodies. The list you mention are all contributors as well, and may well dominate Qts as installed. But please read the work linked, as Martin King is nothing if not very thorough.

Martin is a great guy, clever and experienced in the last centuries passive crossover ported box / transmission line, delayed resonance systems.... Brilliant at what he does .... A tractor engineer in a world of Formula 1 race cars!
I mean no disrespect at all, but in the 12 year old article you refer to he states he is attempting to build on the lowest possible budget, a compromised open baffle design using the cheapest drivers and passive crossovers... Literally 100 year old parts and techniques.... Nothing to do with modern OB design!

The reason "the cheaper the driver the higher the Qts" (from martins article) is high Qts drivers suffer from massive cone ringing ie their waterfall or Cumulative Spectral Decay (CSD) plots are shockingly bad.... The extra low end output is not clean bass, its simply massive unwanted resonance above, at and below Fs.
I dont want to hijack the thread and stray into another subject although I am very interested in this area and happy to discuss more in another thread?
Cheers
Alex.

 

[mikejennens]

In getting confused. My understanding up to now was high efficiency drivers are, generally, better for low SPL? Also, high QTs is also better. I understand that there are many exceptions to this, and if I am mistaken, what is

It's very easy to get confused and overwhelmed with all the knowledge shared by others on this site. I was (and still am) quite often confused by the multitude of replies, opinions, and facts shared.

I built a pair of Paul Carmody's Core 2-ways (Core 2-way - undefinition) and am very happy with everything about them. They image well, sound great at lower volumes, and are easy on the eyes. I also built a pair of his Sunflowers (Sunflower [Redux] - undefinition). I am very happy with these as well. They incorporate an open baffle for the mids and sound great. They are a little larger than you might consider due to WAF, but they are worth building if you can.

Something else I've noticed in the different speakers I've listened to; single-driver, full-range speakers typically image extremely well. Many don't need to be pushed hard to sound good either. Planet 10 offers a lot of great designs; some free, some for a fee (Frugal-phile DIY Audio Community Site). There are many nay-sayers concerning the full-range route, but to a great extent, good sound quality is in the ear of the listener. Many people augment a full-range system with a sub for the bottom end. Some people even add a super tweeter for the extra sparkle.

I've built many different speakers (other people's designs) and have usually found something I like about each pair. I don't know if there is a "perfect" speaker; there are typically compromises to made. However, each listener has something(s) he or she listens for specifically. Listening to different speakers helps a person identify what that "something" is.

Hang in there. I would suggest working with one or two of the forum members whom you've found to be understandable and seems to have a similar take on speaker building (and listening) as you do. If you try to follow too many people, it'll be extremely hard to follow and at least a little confusing and overwhelming.

Mike

 

[brig001]

Advice for beginners: Don't buy loads of tools, you don't need them to start out. Think foam board, Ikea bowls and anything else you can shove a speaker in. Play, experiment and have fun. You can get more serious if you enjoy it

Brian