enclosure vs frequency of XO

[TMHutson]

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.

Thanks... Todd

[T101]

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!

[T101]

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...

[PeteMcK]

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....

[TMHutson]

*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.

*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)
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

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!

[PeteMcK]

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?

[sreten]

Hi,

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.

[TMHutson]

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 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

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

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

Todd

[sreten]

Hi,

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.

http://sites.google.com/site/undefinition/diy
http://www.zaphaudio.com
http://www.rjbaudio.com/Audiofiles/FRDtools.html
http://www.rjbaudio.com/
http://speakerdesignworks.com/
http://www.htguide.com/forum/showthread.php4?t=28655
http://www.humblehomemadehifi.com
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm
http://www.quarter-wave.com/
http://www.frugal-horn.com/
http://www.linkwitzlab.com/
http://www.musicanddesign.com/

[TMHutson]

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
That may shut my up for a while...

Thanks for all the links. That was more than enough help. I appreciate it!