enclosure vs frequency of XO

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I am looking into getting the best sound quality I can afford and with limited knowledge of tweaking enclosure with T/S parameters. I am looking to see if anyone can help me with some basic enclosure ideas.

I would like to have two 8" woofers per speaker enclosure, each with separate chambers. I will most likely go with woofers that work best in sealed enclosures. There are enough enclosure calculators out there that I have no problem using the manufacturers recommended enclosure type and size.

Here is what I am getting at.
Bare with me, as I have no clue what I am talking about.

If the woofers are going to be crossed over to operate in the band of 100hz to 700hz, do I need to build a box that works best on a woofer that is supposed to go lower than I need it? (other than wanting full bass from speakers with NO added subs)
Can I get a better flat and transient response (control of woofer?) and better power handling by altering box capacity for above 100hz flat performance?
I can change the XO point as need be. If I go as low as 80, then I will go with normal sealed box.

I will add that I am assuming that with the roll-off of sealed enclosures, that I may not need to alter the box from normal size. Some of the 8 inch woofers I am looking at seem to start thier 3db at about 100 hz anyway.

Sorry, have not chosen a specific woofer, yet. If you have any recommendations based on the limited info I have given so far, feel free to shout it out. :D

Thanks... Todd
As I recently look at sealed enclosures with double 12" too, I can share with you that the perspective for achieving entrance into the first octave is not very good unfortunately.

I have tried with the free version of Basta and Bass box 6 pro and the returned predicted response is F3 around 50Hz for any volume under 150-200 litres...

The solution for good bass in sealed enclosure is either 1 or 2 15" long throw ultra low fs drivers in 400 + litre or low Vas low fs high qts driver with extended x-max.
Unfortunately the latter are mostly vintage drivers from 70's... I have a 10 L. Vas, 30 Hz fs 0.7 to 1 qts 8" driver with xmax around +/- 7 or more mm that can handle around 25 W RMS... And it gives very good results in 20 L sealed enclosure or a kind of TL...

The solution that I have come to is to make a port somewhere in the enclosure and thus effectively enlarge it without loosing the "sealed" sound.
Infinity for instance achieve very convincing "sealed like" bass from two "10 drivers in around 100 L with opening on the down side of the box.

For surely you'll need another component in your system - a BSC - baffle correction circuit. It fights the inevitable 6 db gain at mid to high frequencies that every enclosure has. It consists of L and R or L, R and C and you can find calculators for it on the net or use the free Tolvan Data "Edge" software that MJK recommends.

Wish You Sonic Success! :)
Regarding the enclosure - crossover relations, there is something you can do.

1. From the point of view of a diy enthusiast the enclosure does not influence the response of the system at frequencies above about 160 Hz. What does influence the response is the front baffle! - its width and shape and the driver positioning on it!

2. Every front baffle has a roll off and step up in the response.
What you can do is to design a baffle that has step beginning at the desired first crossover point and use a 6 Db lower efficiency midrange and high range drivers or pad down your mid/high to -6 db in reference to the bass driver. That way you'll avoid the use of BSC in your system.
Again for prediction of the baffle step you can use the Edge software.

3. When designing you should consider that some irregularities in the baffle step can't be overcome with BSC nor with padding and crossing below the ** beginning.
This though can be an advantage. ;) you can aim the peaks/dips at actual driver response irregularities and thus counter them...
re:'the best sound quality I can afford ' - so, what can you afford?
re:'each with separate chambers' - not necessary
re:'sealed enclosures' - ported will give better low end with minimal effort & cost
re:'700hz' - why 700Hz?
re:'100Hz' - you should be aiming for ~40Hz
re:;'do I need to build a box that works best on a woofer that is supposed to go lower than I need it?- depends on the woofer
re:' woofers I am looking at ' what are they. links?
you need to decide budget & how big your cabinets can be, and what you're using for a mid driver, before worrying about woofers. But 2x 8" is a good way to go....
*I think around 125 to 175 $USD per woofer is reasonable. (as there are 2 per cabinet) I don't like the majority of woofers offered below 100. Over 200 is a bit more than I care to spend on each woofer if there are 4 of them!

*Does a single enclosure with two woofers have the same volume as two separate enclosures summed together? And how does that effect porting (if vented at all)?

*I have always liked the sealed sound better. My preference unless the best woofer for this application (above 100hz) needs to be ported. Subwoofer is different story. All the subs I have ever owned have been sealed. BUT if I need to do ported, or any style of non sealed in order to get low, I will be more than happy to try :)

*700hz XO point, because I am using with ribbon midrange and ribbon tweeter (see ACR Isostatic rp200 or rp400). Some of those models had a 12 inch crossed over at 150 hz. But this was designed before self amplified subs and active XO's were common. I will most likely be using active crossovers and EQ. XO will allow me to filter out frequency below tuning of port, helping a bit I suppose.

*Low end will be covered by SUBWOOFER (more wattage added to system, and easier to move around) making the 7" or 8" woofers more of a midbass. If you think one high end 7 or 8 inch per cabinet will be fine, I will try. I figured 2 would be a little more efficient and handle a little more wattage.

*Cabinet size? I can't imagine it will be very big if I go with a decent 7" or even an 8" woofer. I think dual 7" may give me better midrange if I use a sub (or subs). Also, around 28 liters or less per woofer seems reasonable if sealed.

*I have been looking at madisound.com because they have a good selection. I don't have to buy from them, but US reputable distributor is needed.

*The woofers are only budget killer. :D

*I agree that the 2X 8" may be my best bet for full (non sub) speakers. Maybe even 2X 10". Something is telling me to go with 2X 7" for good midbass if used with subwoofer. (RP400 uses two 180mm woofers with two 305mm woofers cover below 150hz)

On a side note, I do have 2 very good quality Infinty Beta 8 car woofers that I am going to play with just to have fun in the mean time.
But the T/S parameters are kind of whacky. Designed for really small enclosures. I did notice that some 7 inch and 8 inch woofers are designed for very small sealed enclosures as small as 7.07 liters! These woofers are designed to be used in 7.07 liters for flat response, or 11.32 liters for enhanced bass response. Yet I think it's rediculous that the midrange would have an enclosure a bit larger than the woofer, don't you? (Fostex fs21rp uses 15l enclosure) :D
The woofer is recommended to be in sealed box, but the specs that came with the woofers state you can use a vented enclosure. Maybe I will try something new and go ported ;) I will not be stubborn and close minded, if possible :D

Infinity Beta 8 (Original car woofer, not X version)
Fs (Hz) 26.00
Vas (L) 42.00
Qms 7.69
Qes 0.26
Qts 0.25
Xmax (MM) 9.50
Re (ohms) 3.0
Diamater 8" (203.2mm)
Sensitivity (2.83 V @ 1m) 90db
Power handling 200 W rms
Frequency response 20-600 Hz

Recommended sealed
0.25 cubic feet flat response
0.40 cubic feet enhanced response

Vented enclosure flat response
0.5 cubic feet
Pl 7.10"
Pd 2.00"

Vented enclosure enhanced response
0.75 cubic feet
Pl 2.90"
Pd 2.00"

Thanks for looking over my nonsense. I appreciate it!
re:'Low end will be covered by SUBWOOFER ' - this appears to contradict your first post, if so go sealed with your mid-woofers
re:'ribbon midrange ' - what is the efficiency of these? your woofers will need to match these at least
re:'Does a single enclosure with two woofers have the same volume as two separate enclosures summed together?' - yes, a larger box tuned to the same freq will usually have a shorter port
re:'easier to move' - is there a reason you need it portable?

As most 8"ers are now buillt as bass units, not bass/mids a 2 x 8" box
can completely negate the need for subwoofers at all, see the classic
Puppy / Watt combination, for most smaller rooms its all you need.

Vented tuned low is what you want IMO.

rgds, sreten.
sreten, I think you put this in a bit better perspective for me, thanks. I am kind of referencing speaker designs that are a bit old :D I know basic driver technology has not changed much at all (piston style with cone, magnet, surround, basket etc), but materials used are varied and changing all the time.
I am better off using the mindset of designing with modern drivers.

Also, I have seen pics of that Watt Puppy around. Thanks for the heads up as I never really looked at it much. I will look into that design, more. The midrange I have is usually crossed over at 700 because it starts to drops off at 650), so not sure how this is all going to work out when comparing to other TMWW designs. The RP200 is similar in basic TMWW design, but does not have modular cabinets or the trapezoidal pyramid looking design :D

PeteMck, I think my grammar was a bit odd, so you may have misinterpreted what I meant to say.
I said, "If the woofers are going to be crossed over to operate in the band of 100hz to 700hz, do I need to build a box that works best on a woofer that is supposed to go lower than I need it? (other than wanting full bass from speakers with NO added subs)".

I meant that I plan on using the 7's or 8's as midbass that will be crossed over at 100Hz, so what's the point of making a big box for low response if I intend to have a separate box and amplifier for subwoofer? I did not contradict myself, I was just not clear :D

I do agree on the usage of sealed enclosures for woofers, if subs are being used. That was my initial intention. But your input is making me think of designing in flexibility options. If I choose woofers for above 100 HZ only, then I am stuck using a sub if I want a nice full sound. If I do a nice ported enclosure then I can have the speakers stand alone and not need to worry about subs immediately. I was only questioning clarity and transience above 100Hz when using smaller sealed enclosure. If the enclosure does not effect frequencies above 160 HZ or more as stated by T101 above, then I may be less worried about vented enclosures. Thanks.

If I remember, the efficiency of ribbon midrange is 93 db. (tweeter will have to be tested, as it is unknown model fostex supertweeter) Will that matter if I am going active crossover?

Thanks for all the responses. Helps me to narrow down options, and concentrate a bit :)

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for an insight into the Watt / Puppy see :

A Speaker project

Touch it back a notch to say 88dB and lots of great choices.

There is no point in separating the bass units volume or ports.

Dealing with BSC is the critical aspect of the above, and
why the overall design makes as much sense as it does.

rgds, sreten.

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I looked a little into BSC before and it was too much information all at once. While I am playing around with my current drivers and Audiocontrol EQX running on 12v to utilize biamping on my home theater reciever (might as well put the other channels to good use), I will start going through all those links and learn some more :D
That may shut my up for a while...

Thanks for all the links. That was more than enough help. I appreciate it!
Wow, what a lot of opinions. Here are mine (I designed speakers for a living for many years; that doesn't make me a genius but I did investigate a lot of these issues):

- Don't worry TOO much about the baffle step; depending on the size, positioning versus other boundaries can obscure that effect depending on the frequencies affected. Also, most commercial designs, including speakers that your recordings are mixed on, don't compensate for this. Honestly I haven't looked at this issue in a long time, but I wouldn't be in a big hurry to build in a 6 dB step without checking into it a lot more.

- YES, if you want to cross over at 100 Hz you would prefer response to extend lower. Unless you are trying to be tricky and make say 100 Hz with a Q of 1 and then add a -6 dB active filter for a total -18 dB Butterworth. But at those low frequencies, all the room boundaries interfere and you can't make things so theoretically perfect. Anyway, if there is more overlap between the drivers' responses, the crossover situation will be more forgiving.

- With a subwoofer, the phase and crossover situation is simpler with sealed boxes. And given your statement, you will probably like the sound more. The subwoofer probably needs to be ported just to get enough SPL to generate the very low frequencies, unless you have really big amps and lots of woofers + EQ for a sealed array.

- Ideally the subwoofer should operate primarily below 80 Hz according to research done at THX etc. If the subwoofer is near the satellite speakers, 100 Hz could be OK.

- Dr. Richard Greiner showed that the most accurate response for multiple woofers comes in a common volume. However, if one driver blows it can unload the other, so pro designs should have separated cavities if that is a concern.

- Re *Does a single enclosure with two woofers have the same volume as two separate enclosures summed together? And how does that effect porting (if vented at all)?*: what do you mean by that? Your question is not clear to me. 2 1ft3 cabinets each with an 8" is basically equivalent to 2 8" in 2ft3, if that is what you mean. If each 1ft3 cabinet had a 3" port of length L, and you built a 2ft3 cabinet with 2 ports 3" by length L, the tuning frequency should be the same theoretically. If you mean the volume, that's set by the total amount of air moved, and so doesn't matter if the drivers are in 1 or 2 cabinets.
It's been a long time since I discussed speakers with anyone, so I am re-learning how to communicate my thoughts. I have generally been around people that know less than myself in regards to basic stereo and speaker stuff. I am accustomed to using simplified and generalized terms.
This website is overwhelming, and making me realize just how little I know :D
But I love it.

I was trying to understand if combining the enclosures of two woofers had any effects on total volume and port design other than just adding the two together.

For example.
If each woofer needs 1 cubic foot sealed, then the single, combined, shared enclosure volume for two woofers would be 2 cubic feet.
It's simple math, but I was not sure if there were any strange acoustical properties involved with combining woofers and therefore changing the formula, as I have never done that before.

Same with vented, I supposed? You are saying just use same enclosure size for two woofers simply added together, with 2 ports? No strange math involved here? I like that :D

And yes, I am not worried about blowing one speaker and hurting the other one... Not at all. One big enclosure may make cabinet easier to design and build if I don't need to worry about two enclosures with evenly spaced divider walls. Less angles to cut if I have an odd shaped box :D

After scanning over some of the links posted by sreten, and going over many of the links I have found on my own, I have decided that baffle step may not be such as big of a problem in my design if I am going active crossover and EQ.

head_unit, you gave me a little more simple perspective, thanks.
I am trying to keep the design as simple as possible, yet implement as much knowledge on speaker design as I can learn and understand. I am not in any hurry, so thanks for any replies that I can research on. I have been googling and searching , but I may still miss something so all info is appreciated, even if I already came across it. :D Much of my learning curve is based on implementation and hands on experimentation.

I may consider toying with the idea of multiple subs like Geddes seems to use, so going down to 80hz may be a better choice. At this point, I am not going to worry so much about the subs. More info than I need right now :D Thanks for the info on crossover point...

Next on my agenda... Is to learn about waveguides and *possibly* attempt to make one for my rectangular ribbon midrange :D I have no measuring equipment yet, so will just learn the basics for now.

Good opinions and info offered, so thanks to all.
Happy holidays...
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Am I to understand that if higher frequencies are not as effected by the enclosure volume (not including standing waves or reflections), then I don't need an enclosure for my midrange? Do they only place midranges in seperate enclosures to reduce interaction with woofer backwave?
Yet I don't understand why my midrange is recommended to be used in a 15L enclosure.
Does the midrange still need an enclosure to get down to the lower midrange frequencies? Although most mids seem to get closer to 300Hz for crossover point, I will be using a higher 700Hz point.
I bring this up in case I build other 3-way speakers with typical drivers, not ribbons :D
And, the Watt Puppy looks to have a ported enclosure for the highs in the upper enclosure!
I meant to say, "an enclosure of specific volume" for the midrange, not "an enclosure".
If the mids don't need an enclosure, I might as well go open baffle.
If the enclosure increases the efficiency of the production of lower midrange frequencies, I will use an enclosure. I don't know how they tested the midrange on the frequency response graph I saw. I may be able to cross over lower if it is in a decent enclosure, if the enclosure helps at all.
I won't know until I test the midrange in various enclosures and baffles.
I have a tone generator. I may experiment with an spl meter to see what I can find out. May be time consuming to plot response by hand, but all I can do right now.
...I was trying to understand if combining the enclosures of two woofers had any effects on total volume and port design other than just adding the two together...

As I think you see now, not really. Nor does the placement of the port affect the total response.

Of course in real life these things all have small effects, but you need a detailed simulator like LEAP to sort them out. Failing that, you will be fine not worrying about it.

Yes, 2 subs I suppose are more flexible for playing around, that's a good viewpoint. Caveat: so long as you can get big enough ports in the smaller enclosures. You might need a shelf port.

As for the midrange, many mids are sealed back already. If you're using a loose woofer as a midrange, it can be OB (Open Baffle) but of course the sound will be very different as the rear wave propagates out the back and mixes with the front wave. If inside the box with a woofer, a non-sealed midrange must have a sub-enclosure (not a sub enclosure, ha ha) to protect it from being "pushed" by the woofer. The enclosure will affect the low frequency rolloff just like it does for a woofer. You probably need a Zobel network to notch out the midrange's impedance peak or a passive crossover won't work properly by the way.

The internal shape and stuffing of the box DOES affect the midrange. Again, not a HUGE effect, but angled surfaces and good stuffings prevent mid frequencies from the back of the woofer and midrange reflecting back through the cone. See Vance Dickason's Loudspeaker Cookbook
Thanks for the info on bass reflex ports. I had read that it's best to keep it close to woofer, but so many speakers have them on back of enclosure.

I asked about the midrange as I will be using the ribbon tweet and midrange (in specific enclosure) on my first project, but I also have a set of car components that are really good and I would like to make a nice enclosure for them. I don't need them for the car, and not ready to sell them :D It's a set of Infinty Beta car components. I have dome tweeters and 5 inch woofers with passive XO, and 8 inch woofers (Use to also have a 15 but blew that when I had an amplifier connection problem). The tweeter has a very low crossover point and comes with a very well made 24db passive XO with phase control knobs (and I think one knob is for attenuation).
You can even mod the XO by soldering in a little bulb so you have a blinking light. YAY Unfortunately, I have no T/S parameters for the 5 inch woofers. And no testing gear. I will probably just throw the 5 inch midrange in a very small enclosure and call it a day :D

Yes, I need to buy some books. Easier to sit down and read then be on the computer for so long. Also, nice to not have to keep turning computer on. I have a list of books I need to get, including the Vance Dickason one.
Most DIY speaker distributors sell books also. But if anyone has any recommendations for books that are not found in most of the popular websites, feel free to post up :D
I will hit local bookstores after the Holidays are over.

Thanks for the info.
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