best use for 8 RS225-8 's

[jmark]

I have a lot of RS225-8's and want to create a bass section for a 3 way using 4 drivers per speakers.
There are a lot of different ways to mount 4 bass drivers in a box.
All on front
2front/2back
2 on each side
2 on front/2 on bottom
a pair of isobarik drivers to save some volume

I have also thought about making a very small enclosure and then venting the enclosure to my crawl space below to make them sort of an IB tower, but not sure how loud or how low I could drive 4- 8" speakers in an IB.

These will be music only, as I will use a seperate subwoofer for my HT lfe channel



For now I will mate them to a smaller 2 way that I already have so I will use an adjustable electronic crossover to find the best xover point.


Any suggestions before I start building a half dozen versions ?

[ThomasW]

I have also thought about making a very small enclosure and then venting the enclosure to my crawl space below to make them sort of an IB tower,

You'd have 8 paperweights after the first really low bass transient...

They're woofers not subwoofers, so use them accordingly...

[Dennis H]

2front/2back

very small enclosure and then venting the enclosure to my crawl space below to make them sort of an IB tower,

I like those two ideas. They will both help you have flat response with no need for EQ. Front/back eliminates the need for BSC if you cross high. IB extends the low end response and 8 drivers should give you plenty of Vd for music.

Edit: Thomas, he said they're just bass bins for music. He has a sub for HT.

[ThomasW]

Edit: Thomas, he said they're just bass bins for music. He has a sub for HT.

IMO they should go in a smallish sealed or ported box given their 7mm Xmax

[jmark]

Venting the bass bins into my crawl space just let's me reduce my cabinet to the bare min required to phyically house the 4 - 8" woofs
I could probably get by with a 10" square x 24" tall bass box which would be nice and compact and would make a good stand for my 2 ways.
Otherwise I would need considerable volume for vented box, which I understand would be the best application for these drivers.

I it bottoms out on music, I could try this with a high pass on the bass bins maybe 30-40hz and send lowest freq's to my HT sub. Could do this with my receiver if it lets me set crossover this low, I'll have to check how low the HT receiver let's me set crossover.

Are there any 8"-10" x 4ea drivers I could use in an IB setup that would allow full low end play so I could keep the small bass box? I was hoping not to crawl under the house to build the box down below floor like typical IB
I'm afraid of spiders

[Dave Bullet]

I'm afraid of spiders

So was I, but after having handled enough drivers, I'm used to them now. :B

[mayhem13]

I like the idea of 4 per side in a 3 way tower ported of about 100L . Tuned to about 28hz shows a nice roll-off around 60hz. Thomas would know better about the sub xo point but looks pretty good to me. You would need a really efficient Mid to match-maybe the B&C 8ndl51 would be a good applicant here. Plenty of 1-1 1/8 domes could match the efficiency for the tweeter. The Vifa DX25TG seems up to the task of the low xover point the B&C mid would need. Looks like a good candidate for a waveguide retrofit experiment as well. Those would be some pretty loud and large mains! I like it !!

[ThomasW]

Why don't you slap together a quick and dirty sealed test box containing 4 drivers?

Regarding an IB with 8"-10" drivers. Run the number to calculate the Vd, then compare that to a couple of 15"s....I think you'll find the cost of admission is quite high using the smaller drivers.

If you used very high excursion smaller drivers you'd probably run into issues with the hole into the crawlspace. It needs to be no less than 50% the combined Sd of the drivers and larger is better.

People have built and installed crawlspace and attic IB subs without entering the space itself. This requires making a modular box that's inserted in sections and bolted together.

This is Chasw98's attic IB. It's location necessitated total assembly and installation from the room below.

[neuro]

I'm working on a similar project (multiple woofers per speaker). An issue I've been thinking on may apply to you, so this seems like a good place to get people's thoughts. Lets say you decide to go with the 4 woofers in a sealed box. The most obvious thing to do is to stack them 4 high. In my case though, and maybe in yours, this would result in the final speaker being too tall.
So, you could stack them 2x2. What is the highest that you would want to crossover a flat 2x2 array before directionality smearing became an issue?
Maybe 2 wide is too wide. You could mount the drivers at a 45 (or other angle) to the listener. Basically take that flat 2x2 array and give it a 45 degree bend down the vertical midline. Now you're listening to each driver 45 off-axis. Will having 4 drivers allow you to make up for the resulting amplitude degradation? You would be directly hearing a smaller portion of the total acoustic energy being pumped into the room, but in omnidirectional designs (for instance) this is a goal, so some people must like that effect. Can anything be said about off-axis frequency response of small to mid-size woofers in general? I would expect most of what could be said for this approach to vary largely depending on the crossover frequency, so is there a frequency above which this approach is a bad idea, but below which it could work. Many of the considerations here would also apply to mounting 2 woofers on each side, it's just that then you are listening 90 degrees off-axis to each woofer.
As you suggested, you could do 2 front, 2 back. As I understand it, this could be wired as either a dipole (drivers in phase) or bipole (drivers out of phase). What would be the consequences here?
Also as you suggested, you could do 2 front, 2 bottom. Then you would be listening directly to the two front woofers, and have omnidirectional input from the bottom woofers. Seems like you could get those contributions to integrate, but you might have to treat the front / bottom as two seperate components and crossover / equalize separately.
Isobarik would give you the output of two woofers in half the size needed for those two woofers. In other words, half the output of four external drivers, in a quarter the volume needed for those four external drivers. If you're really volume limited, maybe consider this, otherwise probably not.

[ThomasW]

The drivers must be wired in-phase otherwise they cancel each other.

[jmark]

Thomas,

If I make my box 10" x 10" then I could make the opening in the floor large enough based on the rule of thumb you mentioned. 12" x 12" would allow me to use up to 8 of the 8" drivers, so I could start with 4 per side and double up if necessary.

Remember my goal is to provide a small footprint and a stand for my 2 ways which I want to cross over to the bass box around 250hz and use for mostly music.

I have a seperate dedicated sub for HT but you have me thinking about building a real IB sub below the floor now.

[HareBrained]

You can send me 4 of them and that will halve your problem.

[ThomasW]

Remember my goal is to provide a small footprint and a stand for my 2 ways which I want to cross over to the bass box around 250hz and use for mostly music.

I understand that.

No way would you want to have both front and rear firing drivers with a 250Hz XO point. Build a sealed box containing 2 front firing drivers, run it to 250Hz.

Build an IB sub for everything below ~80Hz.

[JRT]

I have a lot of RS225-8's and want to create a bass section for a 3 way using 4 drivers per speakers.

Take a look at Mark Krawiec's RS-225 OB dipole, uses 4 per.

https://web.archive.org/web/20080907041801/http://audioheuristics.org/blog/?cat=3

Here is a quartering view of the back, from his website: