DIY speakers

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Great sitd BTW!! I am fairly new to diy speaker building and i had a question for you. I am attempting to design a speaker enclosure and would appreciate any help or feedback that you could give.
What I am trying to accomplish. I have 2 pair of NHT 1.5 bookshelf speakers. As with most bookshelf speakers, the bass response could be better. So i am trying to build an enclosure that will serve as a stand to make it tower-like, and also have a double array woofer design built in to help with bass frequencies. I am going to keep the same footprint as the 1.5's and will accomodate the correct volume by just increasing the length of the cabinet. I have all the driver specs and the footprint dimensions. I have calulated my volume requirements per woofer and was wondering if it would be better to have a seperate internal sealed enclosure for each woofer; and any info on how to croosover without changing the ohm load to the original speaker. any help would be greatly appreciated. if anyone has any suggestions, it would be greatly appreciated
An externally hosted image should be here but it was not working when we last tested it.
no need for separate enclosures

In all of the designs I've seen for dedicated woofers/subwoofers that have used multiple drivers, no one (that I am aware of) has ever separated the enclosure for each bass driver. As you probably know, doubling the number of drivers (2 instead of 1) means that you have to double the internal volume of the enclosure to achieve a similar response curve. You might want to add some cross bracing to the inside of the enclosure between the woofers, but I don't believe there is any audio benefit to making separate enclosures for each driver.

[Edited by Eric on 04-16-2001 at 07:43 AM]
Go Active

Hi kcalvano,
at what frequency do you plan to cross over to the main speakers?
If it's below, say, 150 Hz, a passive crossover is mighty unpractical, requiring huge inductors.
Inductors have a huge impact on bass. You will believe it once you have heard the first active speaker...
I suggest to go with a subwoofer "plate" amp which is built into the bass cabinet. This should have a variable crossover frequency between 100-50 Hertz minimum.
Probably the best result will be achieved by running this subwoofer amp in parallel to your existing amp which feeds the main speakers. (requires a pre-out or a y-cable if you have only one source)
The subwoofer amplifier will have to be 4 ohm stable because you want to parallel the woofers.
I would not incorporate a high pass for the main speakers.

I do not quite understand what you mean by "without changing the ohm load to the original speaker".

Go with the active approach... it pays!
In fact, i can't imagine to get this to sound good with a passive xo.

As to the internal dividers; well, it can't hurt and will be a welcome, stable brace. Do not underestimate how important bracing is! Tie all opposing walls together at multiple points and place the braces somewhat randomly so as to not create "free" areas of the enclosure with the same size and resonant frequency.
But Eric is right, if the drivers are matched and have the same parameters a common air volume will not hurt. To calculate two equal drivers in the same air space you just double VAS, all other parameters remain the same.

BTW, your cabinet drawings look really good.

Hi KCalvano,

Can you tell me how could I put drawings in the texts?

If you don't match the speakers, in theory will be better put each one in separate volumes, but, even not matched speakers (same model, of course and, if it's possible, manufacturing date as closer as possible) will work very well using one volume only.

If I understood correctly your question about crossovers, yes, using passive crossovers you must consider them in the overall impedance analysis. It might be better use active crossover as tim0 said, you will achieve much better results.

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