Wx System Speakers

I am going to build a pair of speakers that I intend to keep for a long time and I want to do it right. I have decided on a design I call the Wx system. This uses a two-way design with small wide-range drivers as midbasses (4") to push the crossover point up to about 10,000 Hz, out of the critical midrange area. Then to avoid extra intermodulation distortion in the midbasses, they are relieved of any bass information below 150 Hz by a stereo pair of bass modules below the speakers (similar to the Series III 6th-order Bandpass Acoustimass modules used by Bose but rather than being used as the subwoofer, it only fills in the bass range from 150Hz down to 40 Hz). I like the sound of the 6th-order bandpass enclosure.

The mains will use 4" Tangband W4-616S woofers with the paper cones and the aluminum phase plug, crossed over with a 2nd-order crossover at 10,000 Hz with a Dayton kapton-film ribbon tweeter. The Tangbands respond down to 65 Hz, but for a stereo pair which will not be used with a separate powered subwoofer for a long time, this is not suitable for me.

So I have schemed to add a pair of 6th-order bandpass bass modules with 4 Dayton 5.25" woofers each. However, I am not completely set on the 6th-order bandpass boxes yet. I like the round sound of the Bandpass box that came with the Bose Acoustimass 3 series III system but the satellites were too small and the newer Acoustimass woofers (8th-order) are too slow for my liking. I could potentially be swayed to use direct-radiating woofers if that would be the best way to make relatively high output bass modules. This is similar to the way that some speakers have optional bass modules.

So. am I out of my mind on any part of this?
 

pinkmouse

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
Hi Bam

Sorry, but IMHO bandpass boxes do not cut it for real hi-fi, they are just too slow on transient resonse, and the physics of the box causes real problems with resonance after the wave form has died away...

What attracts you to the bandpass configuration? Is it the smaller box size or the apparent need to have no crossovers?

Yes, bandpass boxes can work for HT, but that is all, and you will get a much better result using say a 12" driver with maybe a Linkwitz transorm to achieve a lot better bass with an equally small box size.

Just my ha'porth

Al
 
I agree with pinkmouse.

Lose the bandpass boxes and go for a 12" woofer crossed at 200Hz to the Tangbands. I would recommend a 4th order crossover because the Tangbands are going to be needing some thermal leeway unless you are willing to go to a MMTMM configuration. You might also consider dropping the upper crossover frequency to 4KHz to 6KHz, using a 1st order crossover and selecting one of the Tangbands which have really great high frequency performance.

May I suggest bi-amping?
 
try using fiberfill to deaden the ressonance and it will actually create a sort of crossover effect. Any sound that would be iffy as to how it would affect your other speakers in the system is almost inaudible so that the more specific midrange or tweeter could take over. Equation for faberfill is 1 lb to 1 cu. ft. This method also achieves a clearer bass sound for better imaging as long as the woofer isn't out of it's range according to the crossover. Good luck!
 
Except for the bandpass box -- works for me. Bipolar RS 40-1197 4" FRs, 1st order T at about 10k -- looks like i'll probably end up using a little cone on these (these are due to be replaced by similar bi-poles (push-push) using FE103A. 2x8" Peerless active (4th LR) below 125 Hz.

The tagbands are good. Get a pr of 8s or 10s (push-push) with extended range for the bottom. Go active -- even if it is only 1st order PLLXO to start.

Consider also going to a pr of TBs on each side -- either in 2.5 or bi-pole. This eliminates baffle-step and gives you twice the cone area to move air.

dave
 

pinkmouse

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
Yup... Definately not hi-fi!

tomasro- the whole point of hi-fi reproduction is a balanced system across all frequency bands, your system may sound good to you, but I can guess that most of what you are hearing is so called "Fast Bass" ie frequencies from about 70hz to 100Hz, and there is just a monotonal Whoomph noise below this, sounding the same whatever you play. Am I right?
 
Well, timpanies, bass drums, opera basses, bass guitars and electronicly modified noises called bass hits all sound great coming out of the speaker. The point is that the stuffing would help to eliminate all unwanted upper register sounds that might come through on an unfilterd speaker.

It also helps to reduce costs in buying speakers, and chamber resonance.

If the wood naturally vibrates at 200Hz, you are going to end up with a horribly distorted sound, dominated by the resonance of the wood itself. The only other way to eliminate this is to build to cabinet out of 1 inch thick mfd board...that is of course if you aren't going to want speakers that have a high tolerence to wattage.

Good luck!
 
Woofers

I'm using the 5.25" woofers so the woofer box can be small and compact with a 1.5-foot stand supporting the main speaker itself, and also because 4 5.25" woofers moving in unison just seems cooler. Any reason why I would be better off with a larger driver if I'm going to add an actual subwoofer later on (which will only handle mega-low stuff so there's less chance of localization? Should I try to make the main speaker bass-reflex or sealed? I think the Tangbands would be happier in bass-reflex.

There's been some experimentation on the Subwoofer DIY Page that suggests that 6th-order bandpass subwoofers may not lag all that far behind 4th-order bandpass subwoofers in terms of transient response, and since the passband will be narrow, I can get a more even frequency response with high output.

The woofers will be passively crossed-over to the mains (Which, BTW, will be MMTMM) at 150 Hz and I will expect the bandpass response of the box to F3 at around 40 Hz (The Dayton 5's have been measured down to 45 Hz) or I can use them in a direct-radiating box. I will most likely be powering these things with a stereo reciever (loudness switch is a must) and I'm just hoping to get a system that uses good drivers and good design, to be driven with a 100w RMS reciever at the most. These aren't intended to be golden-ear quality (which I cannot afford,) but I will build them out of MDF. and keep them through my college years and for years after that (all the drivers have butyl rubber surrounds.)

My attraction the the Bandpass box is its pleasantly round sound and a design that is out of the ordinary. I was having second thoughts about them, but a couple people who independently studied the waveform of a sinewave coming out of a 6th-order bandpass subwoofer posted their findings on the Subwoofer DIY forum and it was not nearly as far off as expected, suggesting apparently that a properly-constructed 6th-order bandpass woofer (when not especially designed for gain and where suggested improvements for the enclosure's alignment to lower bass boom in most rooms are implemented) are not nearly as bad as most people expect. And they couldn't be worse than the 8th-order bandpass subwoofer, which is a white elephant at best.
Another attraction to Bandpass subwoofing is that the woofer transmits the pressure to the air inside the chamber and while a tiny bit of transient response (unnoticed to my hobbyist-listener ears--I'm not exactly an audiophile, I just love listening to music and designing speakers) is sacrificed, I think that any distortion caused by cone-flex should be removed by the linear properties of air. In addition, my design for a BP subwoofer should have a high SAF for its compactness. The Dayton 5.25" woofer wil do 47 Hz in a .5-cubic foot enclosure. I really want my 5's, but this box doesn't need to shake the room with the later addition of a subwoofer. (Actually, if TC-Sound's new direct-to-the-public thing works out and lasts a long time and offers a really nice 10" woofer, I might do a LT but that's later on once I'm out of college, have a house and nice job, and (hopefully) a wife (then I'll need to worry about SAF, but again, these should be good with that, in a relatively small room.))

(I once submitted a request for information about bandpass subwoofers on this board and got a number of different responses. I took that into account here. Speaker-building is all about tradeoffs, and Bandpass boxes are a niche design, which just happens to fit my tastes.)

OK, I'm done rambling.

What do you mean by "thermal leeway"? You mean overtemperature of the midbass voice coils? These supposedly are good out to 14kHz. So I was going to use a 3rd-order crossover to the Dayton tweeter at about 10kHz because the Dayton tweeter wil take a 3rd-order crossover point of 2500Hz.
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
"I'm using the 5.25" woofers so the woofer box can be small and compact with a 1.5-foot stand supporting the main speaker itself, and also because 4 5.25" woofers moving in unison just seems cooler. Any reason why I would be better off with a larger driver if I'm going to add an actual subwoofer later on "

5.25" are not a practical choice. Use at least 8" drivers, this is a dedictated subwoofer you are discussing.

If you plan to cross at 150 hz, you need to keep the bass module within around 2 feet of the main modules.

A bigger midbass would allow more usalble low frequency output, allowing for a lower crosspoint to thw subwoofer, allowing it to be located farther away.

"The woofers will be passively crossed-over to the mains (Which, BTW, will be MMTMM) at 150 Hz and "

This will not achieve an accpetable amplitude response, when integrated with the mains. 6th order bandpass box has 3 impedance spikes, you will not be able to avoid having this impedance discontinuity within the operating range of the passive crossover. YOu must use an active crossover for good results.

"apparently that a properly-constructed 6th-order bandpass woofer (when not especially designed for gain and where suggested improvements for the enclosure's alignment to lower bass boom in most rooms are implemented) are not nearly as bad as most people expect"

Following this forumla, you have just negated the only redeeming quality of the design: efficiency(gain). If you simply want to build a bandpass to uhm...build a bandpass.....go for it. But you will achieve more linear response and far better transient decay response using a conventional 4th order vented system.

ALso, you mentioned crossing at 10khz????

IF you wish to guarantee poor power response and substandard integration with the midbass, go for it. I would find a 5.25" with at least good power response up to 3khz, and use a BG neo 3 tweeter, the planar you suggest is not nearly as good as the neo 3, and the cost difference is only about $10. If you must use 4", then you need to consider crossing around 175-200hz, and using a suitable bass section that is nor more than a foot from the mid.

-Chris
 
I don't think I'm quite following you. In the speakers, there will be 4" midbasses with a 65Hz-14,000Hz response (which are actually intended for use as full-range drivers) and a supertweeter. These are arranged in a MMTMM configuration. There is a supertweeter for more pure highs and better high end extention, and at the base of the 1-foot stand will be a woofer box using 5.25" woofers (150-50Hz), implemented in order to relieve the 4's from having to pump out lows and still put out acceptable midrange. Then there will be a separate sub-woofer added later on (50-20Hz). The main speaker used without the woofer box will handle the full range from 65 Hz to 26kHz. The woofer box just cleans things up a bit by crossing over to the box with the midbasses and tweeter at 150 Hz rather than 65Hz.

On each side, there is a 2-way MMTMM speaker sitting about 1 foot above a 6th-order bandpass subwoofer (or perhaps I will go direct-radiating if i absolutely cannot make a passive crossover work with a bandpass subwoofer. I read something about a Zobel network to tame the impedance peaks.) I did want to build a Bandpass just for the sake of building a Bandpass.
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
"there will be 4" midbasses with a 65Hz-14,000Hz response (which are actually intended for use as full-range drivers) and a supertweeter. These are arranged in a MMTMM configuration. "

14khz is a very optimistic value. However, it's not realistic on this planet. The driver will suffer severe beaming, and phase cancellation off axis at high frequences(probably starting 6-7khz) as a result of the non pistonic cone emitting mutliple maxiium phase differed wave modes, as you move off axis at high frequencies. Combine this with the onset of beaming you will get at 6-7khz, and you have a very poor contender for even power response. Now, this is bad enough, but livable when you design as a single point source, but when you add a supertweeter with very good, linear power response off axis, and it combines with the overextended mid, then this is a recipe for very poor power response. Power response refers to the total acoustical energy distributed into the room, or meaning including off axis horizontal, and vertical to an extent. This means that you will experience severly compromised soundstage, that does not image linearly through the bandwidths that are discontinous. Now, you are also doing this as a mmtmm, well...now this is taking combing effedts to the maximum. With the mulitple beaming, exponentially widening dispersion characteristics 10khz-6khz, and the combing will VERY severe along the vertical axis. Crossing at aprox. 6khz(5 even better) would be a very good compromise and reduce these effects significanlty, resulting in somethiong with a coherent soundstage.

"I read something about a Zobel network to tame the impedance peaks"

Yes, this is to stabilize rising impedance resultant of increased inductance as you rise in frequency. Hoewver, this is not what you need. YOU will have to implement a series notch filter, but this will require massive inductor and capacitor values at low frequences(ie, 150hz).

-Chris
 
Chris, you seem to be quite knowlegable when it comes to speakers.
What in your opinion is better sounding and sounstaging? MTM or TM config. I'm asking because I have really good drivers (Raven2 and Triangles) but can't decide on configuration.

Actually I have MTM built, but want to replace Raven 1 for 2 and don't know if I should do it in existing design or built knew one with TM. What you say?

Sorry to jump in but it seemed like a good opportunity.;)
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
"What in your opinion is better sounding and sounstaging? MTM or TM config"

This is dependant on many variables. Hoever, to sum, MTM is most desirable where linear amplitude response along the vertical axis is most important. The two woofers interact with each other, contributing to each other's output non linearities along the vertical axis. However, of course their are somewhat greater phase anamolies at positions, not 0 degrees on vertical axis as the woofers are still working against each other, to an extent at thier upper ranges. Hoewver, MTM is an exellent concept and alleviates the problems in many environments that invlolve variable vertical listineng positions.

MT is more coherent, in theory. However it should be pointed out that I am aware of no controlled tests evaluating true differences. Subjectively, i prefer MT. But this again, depends on the listening environment/position. Additionally, it is much easier to inset/step the baffle to align the relative acoustic centers of the dirvers, relative to the listening position.

Also, since you mention soundstage......

I feel it is important to use, at min. 2nd order acoustical slopes, preferablly 3rd/4th in order to increase linearity of vertical axis in any case. Transiet perfect responses are often referred to, but again you m ust consider the total acoustical power that will radiated into the room, and the angle of teh speaker relative to you. If the speakers at an angle to you, then the on axis time alignement is alrady compromised. So it should be noted to also 'time align' at the intended horizontal axis of listening.

Another very important issue...baffle reradiation diffraction. If it is feasible to do so, i must recommend a 3-4" radius on the edges of the front baffle. This goes beyond simple on axis linearity, resultant of high Q energy releases, at a delayed time corresponding to the baffle edge distances from the driver centers: it also considers how/where the energ distributes into the room. It is best to use the large radius to get at least some uppermidrange/ and all trebelt to reradiate linearly, and also slighlty bettering power response also into the room. This provides for superior ambient effects, read: soundstage. Of course, this again depends on your design considerations. If you are designing on axis only, and for point source optimization then you should ignore most of this paragraph.

FOr your evaluation of TM, MTM, I highly suggest you build prototype test baffles, and listen to both to evaluate. This is the only way to find what best meets your preferences. If you build one, and not the other you may always be missing what is superior. I rarely end up using the exact drivers/config i originally intended after evaluation in the 'system'. Of course, you are not considering ideal crossover voicing, etc. since this takes many months for any one design...but you can at least get a fair idea of expected results.

-Chris
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
"Thanks Chris. It reads like Vance Dickason book"

Great diyer book for many, and general reference. However, it does not elaborate on any specific data to satisfactory extent IMO. So I am not sure if that was a compliment or a diss. :)

Now, if their was a 20 volume series.....

"If you didn't have a chance to see my MTM, it's here "

Nice. I see(or appears) that you have implemented large radii already, good.

Interesting to see the large woofer up top, and bottom..kind of intimidating....like it could slap you around a bit. :)

-Chris
 
Rather than fiddle with big notch filters and stuff like that for a bandpass enclosure, I guess I'll just do my original plan, which was for a direct-radiating unit with the same 5.25" woofers and tuned nice & low with a big 3" flared port. It is much easier and the case for it is much more convincing than for the bandpass.
I stil have a question about the bandpass box, though: what effect would the impedance spikes have had on the overall sound of the speakers or the longevity of the amplifier?

Now there are a number of other questions opened up about the bass section: What if I were to fire all the 5's backwards or even downwards and have the port on the front of the box? Would it matter?

Also, I have decided to go ahead and lower the crossover point on the mains down to 5.5kHz, 3rd order. Is it okay to still use 4 midbasses in an MMTMM configuration with that crossover point?
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
"what effect would the impedance spikes have had on the overall sound of the speakers or the longevity of the amplifier?"

Dependant on the electrical slope, and distance from the impedance discontinuity, determines the severity of the problem. In your case, the 3rd spike would have been within the crossover's attenuation band. This means that as the impedance increases, the filter will attenuate less of the signal within that discontinuity, resulting in a significant peak in the slope.

"What if I were to fire all the 5's backwards or even downwards and have the port on the front of the box? Would it matter"

Well, using 2 of the 5.25" woofers for one module each, for a stereo pair..... I would use each module with the 5.25" units in teh same volume, then you can mount one of them to face into the enclosure. This will significantly reduce non-linear distortions at moderate and high excursions for those woofers. Also, doing this and making it cosmetically attractive will allow you to be a lilttle unique:) Recess the baffle into the enclosure so you can have both drivers unseen, and make a grille to cover the opening. I would use these front firing. But it depends, you want to keep the woofers and midbasses within approx. 1/2 wavelength of the crossover point(150hz, you stated). I would place the port on the rear, if you will have at least 1.5 feet available in the rear, away from a wall.

"Is it okay to still use 4 midbasses in an MMTMM configuration with that crossover point?"

Yes, you should be ok, as long as you mount the speakers as close toghether as possible.

-Chris