Does Size Matter

[sirius98]

Im currently deciding between two systems one is the audax home theater kit with 6.5" Audax drivers AP170Z0, shielded HD-A cone woofers. The other is a system with 5" HDS Peerless MidBass woofers. My question is if they both have the same lower bass limit or close, not that im sure they do but the Peerless gets down to 43 Hz or something, whats the difference in their bass performance?

I think the peerless drivers are better but im hessitant to go ahead with the project becuase i dont want to lose too much bass performance and 5" sounds small to me, though im a total novice.

Will a good 12" sub woofer make up for the lack of bottom end on these 5" drivers?

Thanks for anyones help its greatly appreciated

Pete

[BillFitzmaurice]

If the fb of both systems is the same and the total driver displacement (Sd x Xmax) is equivalent then bass will be equivalent, and the smaller driver's naturally better HF dispersion would make them a better choice. Beyond that, since you plan on having a sub, which will cover up to 80 Hz anyway, what the satellites are capable of below 80 Hz is rather moot in any event.

If I may be so bold check out my AutoTuba; it delivers better performance than any 12" IB or VB sub and is not a terribly difficult build.

[jackinnj]

Originally posted by BillFitzmaurice
If the fb of both systems is the same and the total driver displacement (Sd x Xmax) is equivalent then bass will be equivalent, and the smaller driver's naturally better HF dispersion would make them a better choice. Beyond that, since you plan on having a sub, which will cover up to 80 Hz anyway, what the satellites are capable of below 80 Hz is rather moot in any event.

If I may be so bold check out my AutoTuba; it delivers better performance than any 12" IB or VB sub and is not a terribly difficult build.

Now I made the connection -- having gone to your website -- I really enjoy the series of articles in AudioXpress !

[tiroth]

Bill,

Those horns seem pretty impressive sensitivity-wise. Do you have an Autotuba graph in in half or quarter space, as opposed to the one with cabin gain? And how much power can the autotuba or the Tuba 30 take at 20, 30, 40Hz?

[tiroth]

Perhaps I should restrict my question to Autotuba/Tuba 18. Didn't see the latter at first since it isn't on the site yet.

Link to Tuba 18 graphs
http://www.audioroundtable.com/HighE...sages/875.html

87dB efficiency (quarter space) at 30Hz is impressive for an 8", but will this really beat a sealed Shiva for HT? It seems like this sub really gets going around 40Hz, which is the end of the passband for a true sub....most full size mains will get somewhere south of 50Hz.

[sirius98]

Hi Bill thanks for your reply,

I couldnt find fb but i found fs and i assumed that was the same thing the fs for the Audax driver is 49 Hz and for the Peerless its 59.9 Hz.

I again assumed that there was no point in making the calculation you sugested as it violated the assumption of equal fs's.

So whats going to be the difference in bottom end performance of these drivers? Will a good sub make this difference inconsequential?

Thanks

[Drew Eckhardt]

I don't think 5" drivers are suitable for home theater use with the standard 80Hz XO because even a pair can't produce enough clean midbass in a sealed configuration. I don't understand ported speakers well enough but haven't been impressed with the small driver designs I've heard at reasonable volumes.

Other questions are :

1. What's the maximum output at useful frequencies?

Each 6dB doubles your displacement requirements.

2. What's the distortion?

Distortion comes from excursion. Displacement = area * excursion. All else equal smaller speakers mean more excursion and distortion. IM distortion mucks up the midrange. But - all else won't be equal.

3. What's the off-axis response?

Larger drivers are more directional at higher frequencies. A phase plug helps. A lower tweeter cross-over can offset thisbut may require a more expensive tweeter.

4. How do they integrate with the sub. I think the two best solutions are sealed speakers with Qts = .7 Fb = 80Hz + a second order butterworth electrical highpass OR ported designs with F3 approaching 40Hz, LR4 electrical highpass at 80Hz.

[John Sheerin]

>Larger drivers are more directional at higher frequencies. A phase plug helps. A lower tweeter cross-over can offset thisbut may require a more expensive tweeter.

Um, why is more directivity a bad thing? Use an appropriate tweeter, and you can actually get some directivity control and keep the sound from bouncing all over the room. Admittedly, it's not a lot of directivity, but some is better than none.

[BillFitzmaurice]

I'm personally using TL/Line arrays using eight 4" midbasses per side (Parts Express $0.87 cheapies) crossed over at 80 Hz to a Tuba 18 sub; the line array runs at 96dB/watt and integration is seamless. A pair of good fives is adequate to 80 Hz unless you like it really loud, and will sound better in the midrange than 6 1/2s, all other things being equal. The extra cone area of a 6-1/2 is only worth 3dB over a five. If you've modeled the drivers out and you get an f3 no higher than 80 Hz then I'd go the smaller drivers,especially with Peerless reputation.

AutoTuba corner-loaded runs about 6dB less from 20 to 40 Hz than in a car, so about 89-90dB/watt, tapering to the same SPL at 120 Hz. Still plenty for HT, a few dB stronger than Tuba 18, which I find quite adequate for HT.

Tuba 18 beat a Shiva at 30 Hz? Don't know, but bass power requirements are not linear, on average 50 Hz runs with at least 15dB more program capability required than 30 Hz, and at 50 the Tuba 18 gives 108dB/watt corner loaded. That I'm sure the Shiva or for that matter any direct radiator sub can't touch by a wide margin.

[sirius98]

Hey Bill whats an F3 and how do i work it out? Im building these speakers from plans, I thought that would be wise for my first project.