Sub: 1 large or 2 small drivers ?

[planet10]

It being a sub, the woofers should be as near the floor as you can get them... and make sure you build a sub enclosure for the Bash.

F10 of ~26 Hz... that gives a good idea of its useful extension in a real room... and looks like no issues with excursion.

dave

 

[Bigun]

... and make sure you build a sub enclosure for the Bash.

dave

Thanks Dave - quick question on this one,

Do you mean a separate section outside of the sealed volume ?

 

[badman]

They are noisy & can have significant oil can rsonances.

dave

For isobaric subs, the solution is to apply a tube to the outside of the magnet, and lightly stuff it. That way it won't interfere with the venting but will introduce directionality and attenuation to any vent noise.

 

[planet10]

Thanks Dave - quick question on this one,

Do you mean a separate section outside of the sealed volume ?

I mean a completely sealed from the inside sub-enclosure.

dave

 

[Bigun]

It shouldn't be a problem sealing them I hope. Bob (Creative Sound) tells me that they are air tight and are usually installed directly into the box ?

 

[planet10]

It shouldn't be a problem sealing them I hope. Bob (Creative Sound) tells me that they are air tight and are usually installed directly into the box ?

The plate may be airtight... what you want to do is isolate the amplifier from the air in the box. The Bash needs to sealed away from the inside of the speaker box for best performance.

dave

 

[Bigun]

It being a sub, the woofers should be as near the floor as you can get them...
dave

Why is this ?

 

[planet10]

Why is this ?

Somewhere on this page i think...

http://www.nutshellhifi.com/ME2txt.html

dave

 

[Bigun]

Thanks - it's a good summary of my questions. I will have to revisit my design.

Of particular interest I noted the following:

"The alignments for best transient response (Qtc = 0.57, very large cabinet) have poor IM distortion, and the alignments for lowest IM distortion (Qtc = 1.1, small cabinet) have poor transient response."

this is something I haven't seen before and potentially changes my approach since currently I'm designing for Qtc of 0.57 yet a smaller cabinet has some claimed advantages. I don't understand the physics behind this claim though.

 

[planet10]

"The alignments for best transient response (Qtc = 0.57, very large cabinet) have poor IM distortion, and the alignments for lowest IM distortion (Qtc = 1.1, small cabinet) have poor transient response."

The IM distortion only really starts playing a role when you really start pushing the driver... and if Geddes' research holds an aweful lot of distortion can be tolerated before it becomes a problem. I'd not consider building a woof with higher then Q = 0.7, somewhere around 0.6 seems a decent compromise... as an aside i was again quite please with the bottom on Tysen (Q ~ 0.55), noting some very nice HT bottom despit having forgot to turn on the sub.

dave

 

[Bigun]

Another worry,

With one speaker pointing out the front and one out the back - am I in danger of having the back wave reflect off the wall behind and canceling out the forward wave ? In essence do I have to worry about the two drivers sound field interacting ? (such that I have to orient drivers facing side to side instead of front to back)

 

[planet10]

The wavelengths are too long... they don't exit and bounce, they ooze & flow... still i prefer to have them symetrically loaded. That is why i will orient the woofer so that it is "side" firing.

dave

 

[Bigun]

It's time for action now

I'm going to reduce the designed box volume a bit more and drop the drivers nearer the floor as suggested. Instead of a physical volume of 50L it will be built closer to 30L and then stuffed a bit to bring it to a Qtc of approx. 0.65. It seems to me that this will have a marginal impact on F3 or F10 and to my way of thinking - if I was going for the ultimate sub I wouldn't be using 8" drivers anyway.

Talking of which, the TRIO8 drivers and a 300W BASH amp are en-route from Bob (Creative Sound Solutions) and I'll pick up some Birch ply from HD tomorrow (or the day after).