The Driver/Enclosure relationship

[valvesRus]

Sometimes good things happen almost by accident.

My OB speakers started with a pair of Goodmans Magisters purchased on Ebay from a local seller for next to nothing.

The drivers were not the right ones, so the boxes were cut about to house an 18"bass unit, the back and sides cut away and a baffle added on top for new mid range and tweeter. The old bass drivers were a H & H units which I sold on.

That's where I'm at with OB, one day I'll make something better and move the 18" unit nearer the floor to improve the bass.

[valvesRus]

I don't believe that any musical device can be designed without the use of that most of important of instruments, the human ear. That was Richard's mantra and he was right.

I believe I said using the T-S parameters could get you 90% of the way. Other aspects including room acoustics ,speaker placement and personal preference sometimes are more difficult to get right.

[jimbob]

Thanks for all the input guys, much appreciated!

I’ve got a few ideas floating around and I like the idea of a 15 or 18 inch bass driver, side mounted into a slim (ish) cabinet with the mid firing upwards. No idea how it would sound! I also love the idea of an OB but would probably have to settle for a 12 or 15 inch woofer due to room constraints.

[valvesRus]

Thanks for all the input guys, much appreciated!

I’ve got a few ideas floating around and I like the idea of a 15 or 18 inch bass driver, side mounted into a slim (ish) cabinet with the mid firing upwards. No idea how it would sound! I also love the idea of an OB but would probably have to settle for a 12 or 15 inch woofer due to room constraints.

The Eminence Beta 15 is a good place to start for an OB bass unit, together with a full range unit up top, and a tweeter if you feel the need.

[NSNO2021]

Fascinating thread and enough reading to take a chunk of my lockdown time, thanks for all the links

[jimbob]

Am I right in thinking that a drivers resonant frequency is the lowest frequency that it can comfortably produce?

[valvesRus]

Am I right in thinking that a drivers resonant frequency is the lowest frequency that it can comfortably produce?

"Fs or F0 (Hertz)
This is the resonance frequency in free air. It is the frequency where the driver moves with minimal effort. If you tap a speaker (or any object for that matter), it will make a sound, which has the same frequency as its resonant frequency. When the driver reaches the resonance frequency, its response starts to roll off. Below F0, the frequency response starts to thiele small fs resonant frequency degrade and rolls off. This means that the lower the F0 , the better the bass response. Of course this is only valid for woofers. For midrange drives and tweeters, the resonance frequency will be significantly higher, and there is no better or worse values, it depends on your project."

So, yes, below that it rolls off.

[jimbob]

On the what sort of drivers are suitable for sealed boxes and which for ported, the conventional wisdom is if the Qts spec is below 0.4 it's supposed to be more of a driver for ported. Above 0.4 = sealed box. Around 0.4 give or take a bit and it's supposed to be OK for either.

But that's all general guideline stuff. And full of its and buts.
And I hate ports so much that if I were making a DIY speaker I'd start with sealed box regardless of the driver - and the frequency response and bass extension can go mate with itself.

The Eminence Beta 15 is a pleasantly affordable driver: £93 new from Thomann. I know that price often bears no resemblance to sound quality, but the 18" drivers that I've been looking out for, to try in my own DIY project cost ten times that much when new. I'm hoping to bag them used in good enough condition for under £150 each.
I did also explore getting 24" drivers, but haven't been able to find any that I fancy for reasonable money.

For sealed box enclosures it seems that the size that would look about right for the driver size gets you in the right sort of ballpark.

It also seems to make sense to make a cabinet that's a bit too big according to the online calculators, listen to it. Then add something to take up some internal space and listen to it again.

I think that there's also a lot to be said for having over-engineered cabinet sides, eg metal plated or over the top plywood walls. And for no internal wadding, or just a curtain at the halfway point to break up standing waves.

From my own personal limited anecdotal evidence, I think that the quality of the drivers is the most important factor in getting good sounding speakers. Especially in the midrange.

Edit: and something I forget to mention is that when it comes to speakers thare's more than one way to skin a cat. As in there's lots of different routes to getting good to great sounding speakers. Also with speakers there's a lot of compromises. Improve one area and you tend to get drawbacks in other areas.
I also think that there's a huge amount of value for money in DIY'd speakers. To the extent that just about anything that you make will give you better sound for the money than brand new retail off a dealers.... Although that is damning with faint praise.

[jimbob]

Lindsay, I completely agree with the importance of over engineering the cabinets. I currently have doc mod mid and bass drivers in Magnum K2 cabinets and the chipboard cabs are really letting things down. I’m also not sure that the mid is comfortable sharing the same space as the bass driver, things sound muddled when pushed.

[Latteman]

If you put a big ass bass driver in a box which is too small then you may get excited by the amount of bass. But play some electronic music with low synthetic bass and your excitement will turn to disgust as you get certain bass notes which are completely overblown and the driver seems to be out of control (like an oscillation ).

I don't agree that the driver is the most important part of a speaker. I think all aspects have equal weighting. The drivers that RD chose for the cube speakers are perfectly fine andcheap. Once doped sympathetically nobody should require anything more expensive. I bought a load of the 5.5 " drivers for less than £10 each. Maybe they become crude sounding when driven hard but if you don't ask too much from them then it's happy days.

I have found that adding more and more drivers (tweeters and mid bass) by far brings the most dramatic improvement in SQ. Ask the drivers to do less work by sharing it out and yu are rewarded with drastically reduced distortion. It is like crystal clear water from a spring compared to the water in a dirty polluted river. Add more open back drivers though and you must increase the enclosure volume. That doesn't apply to tweeters as they are usuallyclosed back. Put one on each cabinet side and be amazed.

Take it to the extreme and you end up with a floor to ceiling line array. I would love to hear one (and build one) but it is ultimately point and squirt which may or may not suit your tastes.

Cabinet material can make or break a speaker. Many like OB with no cabinet at all. I can certainly not argue with that. As far as enclosure volume goes, i prefer to err on the side of bigger is better (up to a point). An over damped Qtc of less than 0.71 sounds best to me. Take it too far though and you end up with less than convincing bass output.

Anyway, don't listen to internet experts, wannabe guru's and idiots like me. The only way to learn and find what works and what pleases you most is to experiment and try it for yourself.